HVAC SYSTEMS ACOUSTICAL, COST & ENERGY STUDY

Transcription

1 HVAC SYSTEMS ACOUSTICAL, COST & ENERGY STUDY Prepared for the Los Angeles Unified School District Facilities Services Division June 6, 2005 By Maroko & Shwe, Inc., Professional Engineers With Schaffer Acoustics Inc

2 Table of Contents Executive Summary Introduction & Methodology Conclusions for Basic Systems Conclusions for Other Systems Other Factors New Developments Recommendations School HVAC Systems Comparison (Basic Systems) School HVAC Systems Comparison (Other Systems) PAGE i i ii iii iii iv vii viii HVAC Systems Acoustical Cost & Energy Study Introduction 1 Basic Systems Description 1 Standard Design Measures for HVAC Sound Attenuation 2 Air Inlet / Outlet Connection Details Figure Acoustical Improvement Measures 4 Basic Systems 6 System 1 : Rooftop Packaged Air Conditioning with Gas Heating 7 System 2 : Split System Heat Pumps 14 System 3 : Four Pipe Fan Coil Units with Remote Central Plant 21 System 4 : Central Air Handling Units with Remote Central Plant 27 System 5 : Radiant Panels with Remote Central Plant 32

3 PAGE Other Systems 36 System A : Water Source Heat Pump 37 System B : Wall-Mounted Packaged Heat Pumps with Ducted Supply 42 System C : Duct Free Systems 45 Acoustical Requirements of LAUSD Design Guidelines 51 Acoustical Measures in the Guide Specifications 52 Acoustical Measures in the School Design Guide 62 Different Perspectives 67 Acoustical Engineer s Report & Calculations 70 Report of Schaffer Acoustics Inc Calculations made by Schaffer Acoustics Inc

4 EXECUTIVE SUMMARY

5 EXECUTIVE SUMMARY Introduction and Methodology This study was initiated to explore the costs and benefits of five basic classroom air conditioning systems for new schools, specifically relative to the background sound levels generated by each system, their relative capital cost, and energy usage. The methodology used was to: (1) Define clearly each HVAC system, so that costs, energy use, and acoustic performance could be calculated; (2) Define noise-reduction options for each system; (3) Calculate the energy use for each system using the Trane Company s TRACE 700 simulation program; (4) Calculate the acoustical performance and classroom sound levels for each system and its options, using the Trane Acoustical Program (TAP); (5) Summarize the findings and make recommendations for LAUSD design standards to improve energy and acoustical performance with minimal increase in capital cost. To amplify and verify the mechanical engineering acoustical simulations, the services of Mark Schaffer, P.E., were engaged. He is one of the nation s leading authorities on the sound and vibration effects of air conditioning equipment, and was chair of the ASHRAE committee on HVAC sound and vibration. His findings are an integral part of the conclusions of this report. Five Basic Systems are described in the report. The first two are unitary systems which are in common use in Southern California. The next three all involve a central energy plant. Two of these are currently in use in some LAUSD schools. The last system, Ceiling Radiant Heating and Cooling Panels, is relatively new and not currently in common use in California. In addition, a brief analysis of several other systems was included in the study. Conclusions for Basic Systems The comparative results of the study of the five systems are summarized in the table, School HVAC Systems Comparison (Basic Systems), on page vii. The general conclusion of the five system study is that improvement in the background sound levels in the classroom can be achieved with more centralized HVAC systems in lieu of unitary systems, but at considerable increase in capital and operating costs. In addition, the following conclusions could also be made: Systems with remote central-station air handling units (AHU) and central energy plants (Systems 4 and 5) will yield the quietest classroom sound levels, falling in the range of i

6 35 to 37 dba thus meeting the ANSI Standard criteria. They also have a higher capital cost of about two times (or more) that of the unitary systems. The added cost for central AHU s does not include the cost for building equipment rooms, if they are not located on the roof. A key finding of the study was that the acoustical performance was controlled by excessive duct breakout sound at the lowest octave bands, and that increasing the duct wall thickness from the usual 26 gage to 18 gage reduced the classroom sound levels by 4 to 5 dba. This finding is theoretical only and has not yet been verified by field tests. Rooftop (System 1) or split unitary systems (System 2), designed in accordance with current LAUSD practice can achieve a background sound level of approximately 45 dba. If the thicker duct gage is incorporated, a level approaching 40 dba can theoretically be achieved. The additional capital cost for increasing the duct gage is approximately $1,900 per classroom above that of the District s current practice. The cost of the central energy plant for the four-pipe fan-coil unit in the classroom (System 3) is not justified by sound-level improvement or energy savings. It might only be useful in multi-story buildings not practical for split-system unitary equipment. Fan-coil units located above the classroom ceiling will always generate fan noise that reduces the ability to lower background sound levels. If fan-coil units can be located outside the classroom area for example, above an adjoining work-room ceiling sound levels can be improved, but with some additional cost. Conclusions for Other Systems In addition to the five Basic Systems for new schools, several other systems currently used in existing schools were analyzed and evaluated as a supplement to the major study. The comparative results of the study of the three additional systems are summarized in the table School HVAC Systems Comparison (Other Systems) on page viii. Because the fans and air openings, and often the compressors, are within the classroom space, the noise generated is sufficiently loud that none meet the District s standard for New Schools of 45 dba background sound level as recommended by the Collaborative for High Performing Schools (CHPS). Within ten feet of the unit, these systems produce at best a sound level of 50 dba, and closer to the unit the levels reach 55 and 60 dba in most cases. As an adjunct to this study, a completed classroom installation was investigated that has been measured and reported to have achieved a background sound level of 37 dba or less with unitary rooftop equipment. It is characterized by an existing one-story wood-frame building, with a rooftop unit and all the distribution ducts for four diffusers and two return grills supported above the roof levels. Thus, the duct breakout noise does not reach the classroom. This is an appropriate installation for the DHH classroom it serves. However, exposing all the ducts on the roof is not a practical solution for all classrooms in a school. Multiple roof penetrations increase the chances of leakage. Re-roofing is complicated. It is ii

7 unsightly. And it works only for the top-floor classroom. Also, it is significantly more costly to construct. (A separate report will be prepared on this installation.) Other Factors Apart from basic system selection and design, HVAC systems sometimes produce excessive classroom noise levels because of oversights or errors in design or construction. Some of these are: Over estimating in design the duct static pressures (SP). Because the fan noise is proportional to the static pressure, if the fan SP is higher than needed, the installer is likely to choke the system by closing the manual volume dampers (and sometimes the opposed blade dampers at the diffusers and registers) rather than the longer and correct process of adjusting the fan speed by replacing the fan drive sheaves. The result: significantly increased noise. Improper air balance can also cause the situation described above, even when the system is properly designed. High air-flow velocities in the ducts and through the diffusers and grills a definite noise increase. It is often caused by reducing duct sizes to fit into space that is inadequate. Insufficient duct length between the diffusers and grills that is, they are located too close to the fan, not permitting some attenuation of the fan noise. Locating the manual volume dampers and control dampers too close to the diffuser and grill outlets. Insufficient sound insulation for equipment rooms or between the rooftop units and the ceiling space below. Insufficient vibration isolation of major equipment. Structures that are not strong and stiff enough to absorb or dampen the equipment vibrations, even when vibration isolators are provided. Locating large equipment too close to classrooms. These have been addressed in the District s design guidelines, as well as being part of sound engineering practice. New Developments Even as this study has progressed, manufacturers have introduced new and improved units. Both Carrier and Trane now have new packaged rooftop HVAC units with substantial improvements in both acoustical performance and energy efficiency. iii

8 The new Carrier Centurion unit may be able to reduce classroom background sound levels from 46 dba to 38 dba although this has not been verified. A comparable unit, the Trane XL1600, seems to have similar capability. Full acoustical data on these units, though, has so far not been available. They also appear to have a significant cost increase. One of these was used in the special classroom described above. Recommendations Follow Standard Design Measures The following Standard Design Measures for HVAC Sound Attenuation should be incorporated in all new systems designs: 1. Size diffusers and registers for NC 25 or less. 2. Provide proper duct connections at diffusers and registers as indicated in Figure 0.1 of this report. 3. Provide a minimum 5-0 of flexible duct at all air inlets and outlets. 4. Provide an adequate number of manual volume dampers. Locate the dampers a minimum 3 duct diameters up stream or downstream of air inlets and outlets. Maximize the distance between dampers and take-offs and elbows. 5. Size ducts per velocities recommended by project acoustical consultants, but not to exceed in Systems 1, 2 and 3, 850 feet per minute for main ducts and 450 feet per minute for branch ducts. 6. Provide turning vanes at all rectangular elbows. 7. Provide ducted returns with the air inlet registers at a minimum 15-0 from the main duct risers in Systems 1, 2 and 3 and as recommended by project acoustical consultants in Systems 4 and Provide vibration isolators for all rotating or reciprocating HVAC equipment including packaged units, fans and compressors. 9. Provide sound barriers and acoustic sealant at the inside of the curb and duct roof penetrations, and beneath the unit (similar to in Figure 1.2). iv

9 10. Provide duct lining and duct silencers (as required by the project acoustical consultant) for the larger fans, air handling units and larger packaged units (generally larger than 6 Tons) serving areas such as multi-purpose rooms and gymnasiums. 11. Do not locate duct sound attenuators inside the building above (the ceiling of) occupied spaces where the breakout noise will increase indoor sound levels above acceptable limits. 12. Do not provide duct lining for the classroom packaged units and fan coil units of less than 5 Tons capacity unless directed by the project acoustical consultant for unique conditions. 13. Do not over estimate the fan static pressures or system capacities. 14. Specify the allowable sound levels for all HVAC equipment. Select fans for optimum sound levels. The specified sound levels shall be rated in accordance with the current industry standards. (Standards by ARI - Air Conditioning and Refrigeration Institute; AMCA Air Movement and Control Association, etc.) as published in the Codes and Standards Chapter of the current ASHRAE (American Society of Heating Refrigerating and Air Conditioning Engineers) Handbook on HVAC Systems and Equipment. 15. Provide flexible connectors for ducts at fan connections and pipes at all pumps and air handling equipment connections. 16. Ensure that the systems are balanced properly. 17. Carefully consider the location of HVAC equipment. 18. Ensure that the Architects provide sufficient space for the proper installation, performance and service of ductwork and equipment. Detailed requirements that include the above measures are already part of the LAUSD design guidelines and guide specifications. These guidelines and guide specifications related to HVAC Acoustics are included in the later part of this report as reference. The designers should make themselves familiar with the latest LAUSD design guidelines and specifications before starting a new project. Field Test the Effectiveness of the Increase in Duct Wall Thickness Find two existing classroom locations, the first with an existing curb mounted, down shot, rooftop gas/ electric packaged unit and the second with a split system fan coil unit above the ceiling. Measure the sound levels as installed. Replace all the ducts. Replace the main v

10 supply and return air ducts from the unit to the first branch take off with 18 gage sheet metal ducts. Reconfigure the duct system layout to comply with the standard system design measures in the preceding paragraph. Measure the sound levels again and compare with the previous measurements. Adopt the increase in duct wall thickness to 18 gage as a standard if it is found to be effective. vi

11 vii

12 viii

13 HVAC SYSTEMS ACOUSTICAL, COST & ENERGY STUDY Introduction For this study and evaluation, five basic systems for air conditioning school classrooms were selected. Four of these systems are currently used extensively throughout California. The last system, ceiling radiant heating and cooling panels, is relatively new and is not commonly used in California. The acoustical performance relative to classroom background noise of each system was evaluated, in conjunction with different optional attenuation measures. Also evaluated were capital cost and energy efficiency. Basic Systems Description Following is a brief description of each of the five basic systems. These are described in much greater detail in the drawings and narrative for each system in the following pages. 1. Unitary Rooftop Packaged Air Conditioning System Roof-mounted units installed directly above a classroom and serving one classroom each, with gas heating and electric direct-expansion cooling. Ducted to four supply-air diffusers and two return-air registers. Non-recirculated air is relieved to the outside thru a register ducted to a dampered opening in the exterior wall. 2. Unitary Heat-Pump Split-System Condenser unit is installed on the roof directly above a classroom (or in some other remote location) and serving one classroom each. Fan-coil unit is located above the ceiling in the classroom, mounted on vibration isolator hangers. Ducts are the same as System 1, except there is also an outside-air opening in the wall and duct to the unit. 3. Four Pipe Fan Coil Unit System Fan-coil unit, serving one classroom, provided with hot and chilled water from a remote central plant with air- or water-cooled chillers and gas-fired hot water boilers. Fan-coil unit is located above the ceiling in the classroom, mounted on vibration isolator hangers. Ducts are the same as System 2. (There is no local condenser unit, and noise from the piped water system is negligible.) 1

14 4. Remote Air Handling Unit (AHU) System Remote air-handling unit (rooftop or equipment room), serving several classrooms and provided with hot and chilled water from a remote central plant with air- or water-cooled chillers and gas-fired hot water boilers. Each classroom is provided with a variable-air-volume zone control terminal. AHU has built-in sound attenuators for both supply and return fans. The fans are mounted on vibration isolators internal to the unit, and are also optimized for both energy efficiency and sound. If not installed in an equipment room, the unit is typically installed above a corridor adjacent to student toilets so that the roof penetrations for the supply and return air ducts are separated from the classroom with significant lengths of ductwork. The variable air volume terminal is located above the classroom ceiling and serves four diffusers. The return air is ducted through two registers. 5. Ceiling Radiant Heating and Cooling Panel System Ceiling -mounted panels are provided with hot and chilled water from a remote central plant with air- or water-cooled chillers and gas-fired hot water boilers. Classrooms have a dedicated outdoor-air ventilation system with pre-treated air, cooled and dehumidified or heated as demand requires, provided from a remotely located air-handling unit with built-in sound attenuators. The fan is mounted on vibration isolators internal to the unit, and is also optimized for both energy efficiency and sound. The AHU is installed similarly to System 4. The supply air is distributed through only two ceiling diffusers, due to the lower volume of air for ventilation only. Standard Design Measures for HVAC Sound Attenuation The following conditions and sound attenuation measures have been assumed for the analyses of this report, and apply to all five basic systems. 1. Diffusers and registers sized for NC 25 or less. 2. Proper duct connections at diffusers and registers as indicated in Figure Minimum 5-0 of flexible duct at all air inlets and outlets. 4. Proper placement of manual volume dampers. Minimum 3 duct diameters up stream or downstream of air inlets and outlets. Maximize the distance between dampers and take-offs and elbows. 5. Ducts sized per velocities recommended by project acoustical consultants, but not to exceed in Systems 1, 2 and 3, 850 feet per minute for main ducts and 450 feet per minute for branch ducts. 2

15 6. Turning vanes at all rectangular elbows. 7. Ducted returns with the air inlet registers at a minimum 15-0 from the main duct risers in Systems 1, 2 and 3 and as recommended by project acoustical consultants in Systems 4 and Vibration isolators for mounting units. 9. Sound barrier and acoustic sealant at the inside of the curb and duct roof penetrations, and beneath the unit (similar to Figure 1.2). 10. The effects of items 8 and 9 above cannot be calculated with the TAP program, but in previous projects, a difference of about 3 dba was measured between rooftop units mounted on curbs without vibration isolators with unsealed roof penetrations and rooftop units mounted on isolator curbs with sealed penetrations. The above attenuation measures and some others are indicated in Figures 0.1 and 1.2 following in the report. 3

16 Air Inlet / Outlet Connection Details - Figure 0.1 Acoustical Improvement Measures The following measures to improve acoustical performance and to reduce background sound levels were investigated: Step-1: Step-2: Add duct lining (1-inch and 2-inch were investigated). Add duct silencers at supply and return ducts above the ceiling for the rooftop unitary packaged unit only. Step-3: Increase duct thickness (investigated in steps from 26, 24, 22, and 18 gage). 4

17 Step-4: Add gypsum-board duct enclosures from the roof penetrations of supply and return ducts extending to enclose the first duct elbow (to reduce fan or air sound leakage or breakout noise into the ceiling cavity). The significant effects of each of the above measures on sound levels, energy use, and other building components were simulated using the TAP Acoustical Analysis and Trace 700 Energy Analysis Program. Findings from the analysis include: Of these, it was found through the TAP acoustical analysis of Systems 1, 2 and 3 that the acoustical improvement measures of Step 1 duct lining, and Step 2 duct silencers, offered insignificant improvements in the background sound levels. This is due to the fact that Systems 1, 2 and 3 have individual supply fans that discharge directly into main ducts located above the classroom ceiling and the breakout portion of the fan noise through the duct walls dominates over the airborne noise. For larger packaged units, (6 Tons and above) installed with the main ducts outside of the building, duct lining and duct silencers are still effective. Duct silencers and internal lining are proven to be effective in Systems 4 and 5. The air handling units used in the analysis for Systems 4 and 5 are provided with integral duct silencers and 2 acoustical lining constrained with perforated steel sheets at the fan sections. In Step 3 increasing duct thickness, only the increase in duct-wall thickness to 18 gage offered significant sound-level improvement for Systems 1 and 3 and insignificant improvement for System 2. This is discussed with numerical results later in the report. This finding has not been substantiated through actual installation and measurement. The enclosure of Step 4 is not subject to the TAP analysis, but has been measured to demonstrate improved acoustical performance for System 1. The provision of vibration isolators for the rooftop unit and a sound barrier between the unit and the ceiling space for System 1 also offer significant improvements, but cannot be analyzed with the TAP program. Comparative field measurements in other buildings indicate that these can reduce the background sound level by approximately 3 dba. After preliminary calculations and analysis, the five Basic Systems were analyzed further by the acoustical consultant Mark Schaffer, using the sound-attenuation measures described for System 1 for ducts, diffusers, dampers, air velocity, and structural attenuation. 5

18 BASIC SYSTEMS 6

19 SYSTEM 1: Roof Top Packaged Air Conditioning with Gas Heating Typical Roof Top Unit Air Distribution System Figure-1.1 This system is preferred by most districts and is LAUSD s system of choice for smaller schools with multiple single or two story buildings that are less than 50,000 square feet each. A dedicated HVAC unit is provided for each classroom. The HVAC unit is typically installed directly on top of the classroom it serves, to avoid combination smoke / fire damper in the ducts. For two story buildings, two units are typically installed on the roof of the second floor classroom. The ducts for the first floor classroom are routed above the 7

20 ceiling of the second floor classroom from the HVAC unit to a shaft that goes into the space above the first floor ceiling. The majority of the units are 4 Tons capacity. The supply airflow rate is 1,600 CFM of which 1,000 CFM is returned and 600 CFM is relieved to outdoors through gravity relief openings. The typical basic design of this system for LAUSD consists of a rooftop packaged air conditioning unit mounted on a factory curb with vibration isolators and minimal ductwork serving two to four supply diffusers and one to two return registers. The measured background sound levels for installed systems of this type typically range between 42 and 49 dba, depending on attenuation methods adopted, the type of construction of the building, and the quality of the design and installation. Measurements for a Type V, wood-frame building is usually higher than for a steel and concrete building. The lowest sound levels for this system were measured at a new high school building with steel frames where some sound attenuation measures were incorporated into the design and the quality of the construction and air balance was more controlled. These measures have already been adopted into the LAUSD design guidelines. The standard sound attenuation measures for this system are indicated in Figure

21 Typical Section of Down Discharge Rooftop A/C Unit Figure-1.2 The Trane Acoustical Program (TAP) Version-2 is used to estimate the classroom sound levels of each system type using sound data from two different manufacturers and the standard design measures for sound attenuation. The cost of each system with the standard design measures for sound attenuation is estimated using the Means Cost Estimating program with manufacturer provided equipment cost. Additional attenuation measures are then added to the standard system singly and in combinations to evaluate the attenuation of each arrangement. 9

22 The following measures are found to have little or no effect on improving the acoustical performance of Roof Top Packaged Units of the 3, 4 and 5 Ton sizes that are typically used for classrooms (in the down discharge configuration). 1. Duct lining 1-inch thick 2. Duct lining 2-inch 3. Duct enclosures near the duct roof penetrations installed in conjunction with 1 lining 4. Installing duct silencers on both the supply and return near the duct roof penetrations at the cost of $ 1, for each classroom (i.e. about a 12% increase in overall HVAC cost). Also, duct silencers are effective only when the selfgenerated noise could be minimized by using silencers with thick (20 gage minimum) sheet steel casings or providing enclosures around the silencers that will add more cost. According to the TAP analysis, the most effective measure for improving acoustical performance is to use 18-gage ductwork for the rectangular main ducts. The overall increase in cost is about 20%. The theoretical attenuation is significant, but it has not been verified through field tests. The results are tabulated for easy comparison on the next page. 10

23 Cost Benefit Analysis of Roof Top Gas/Electric Unit System Attenuation Cost Vs Sound Level Equipment Carrier 48HJ rooftop unit Trane Precedent rooftop unit 26 gauge Ducts Throughout 18 gauge Rect. Main Ducts & 26 gauge Round Branches NC dba System Cost NC dba System Cost $9, $11, $9, $11,

24 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Annual Energy Usage 900 Square feet area classroom Rooftop Air Conditioning Unit with Gas Heating Manufacturer Trane Carrier Model Precedent HJ Cooling Eff. 1 SEER AFUE 2 % Energy Use Cooling Heating Cooling Heating kwh $/kwh Total $ Therms $/Therm Total kwh $/kwh Total $ Therms $/Therm Total $ $ 4, , Seasonal Energy Efficiency Ratio 2. Annual Fuel Utilization Efficiency Indoor Air Quality Air Filters: Indoor air circulation rate: 2 thick air filters of MERV 8 (30%) efficiency 10 air changes per hour 100% outdoor air economizers: Provided Indoor air circulation rate: 10 air changes per hour Maintenance Cost: Level of Difficulty: $ per classroom per year Low Reliability Very reliable. Also, the breakdown of one unit will not affect the entire school. 12

25 After-hours operation Easy to operate after hours and also very energy efficient as individual units can be started from the thermostat through a preprogrammed by-pass timer and the activation of a central plant is not necessary. Interface with operable windows Individual units can be stopped through a special preprogrammed switch provided on the thermostat. The thermostats for unitary equipment in the current LAUSD guide specifications is provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. Environmental impact Cooling: The current refrigerant, R 22 will be phased out in Units with environmentally friendly (non-cfc/hcfc) refrigerants are available from a few manufacturers but they are not recommended as yet because the refrigerants are reported to be unstable mixtures and the required lubricants are so extremely hygroscopic that extra drying of the entire system is required before charging. We should wait until industry standards are more stable. Heating: Low NO x burners are provided with units sold in California. 13

26 SYSTEM 2: Split System Heat Pumps Typical Split System Heat Pump Unit Air Distribution System Figure-2.1 This system is used for the lower floors of a classroom building of three stories or more and for modernization projects. A dedicated system is provided for each classroom. The majority of the units are 4 Tons capacity. The supply airflow rate is 1,600 CFM of which 1,000 CFM is returned and 600 CFM is relieved to outdoors through gravity relief openings or an exhaust system. The typical basic design of this system consists of an outdoor section that consists of a scroll compressor, an air cooled condenser and a condenser fan and an indoor section that 14

27 is a fan coil unit with a DX coil. Minimal ductwork serving four supply diffusers and two return registers is provided. Outdoor air is typically obtained through wall louvers or a dedicated outdoor air system. The outdoor section of the system is typically installed on the roof on a vibration isolator frame in new construction as indicated in Figure 2.2. On grade installation is preferred for modernization of single story to save the expense of the vibration isolators and roof structural upgrades. The indoor section is typically suspended above the ceiling of the classroom from hangers provided with vibration isolators as indicated in Figure 2.3. Typical Vibration Isolator Rail for Outdoor Unit Figure

28 Typical Suspended Fan Coil Mounting Above Ceiling Figure-2.3 Sound attenuation measures similar to the rooftop unit in the preceding section were taken as a standard for LAUSD in designing the ductwork. The measured background sound level for this system with 1 of duct lining throughout in a Type 1 steel frame building is about 43 dba. The sound level estimates with TAP for various additional sound attenuation measures and their associated costs are tabulated on the next page. 16

29 Cost Benefit Analysis of Split System Heat Pump Unit Attenuation Cost Vs Sound Level Equipment Carrier FB4B split system Trane Odyssey split system 26 gauge Duct Throughout 18 gauge Rect. Main Ducts & 26 gauge Round Branches NC dba System Cost NC dba System Cost $8, $8, $10, $10,

30 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Annual Energy Usage 900 Square feet area classroom Split System Heat Pump Unit Manufacturer Trane Carrier Model TWE FB4B Cooling Eff. 1 SEER HSPF Energy Use Cooling Heating Cooling Heating kwh $/kwh Total $ kwh $/kwh Total Total kwh $/kwh Total $ kwh $/kwh $ $ 3, , Seasonal Energy Efficiency Ratio 2. Heating Seasonal Performance Factor Indoor Air Quality Air Filters: Indoor air circulation rate: 2 thick air filters of MERV 8 (30%) efficiency is typically provided when outdoor air is obtained directly by the indoor section through wall louvers or roof vents. Higher efficiency filters can be provided when a dedicated outdoor air system is provided. 10 air changes per hour 100% outdoor air economizers: Can be provided for individual systems but usually are omitted due to space limitations and higher cost. 100% outdoor air economizer systems cannot be provided with dedicated outdoor air systems. 18

31 Maintenance Cost: Level of Difficulty: Reliability $ per classroom per year Low but not as convenient as the rooftop units as the service person has to enter the classroom and lift up the ceiling tiles to service the indoor unit. Secondary drain pans, evaporator freeze stats and high condensate level shut-off switches are necessary to prevent ceiling damage from condensate overflow. This system is quite reliable. The breakdown of one unit will not affect the entire school but the refrigerant lines are usually hidden in permanent construction and are difficult to access. When they leak, it is as difficult as repairing a water pipe leak between building studs. When a dedicated outdoor air or a common exhaust system is provided the breakdown of these added system components could affect an entire building and renders the systems less reliable After-hours Operation If a dedicated outdoor air or a common exhaust system is not provided, this system is easy to operate after hours and also energy efficient as individual units can be started from a programmable thermostat through a preprogrammed by-pass timer and the activation of a central plant is not necessary. An energy management system is not required. Additional controls are necessary when a dedicated outdoor air or a common exhaust system is provided. Also, air moving energy is wasted if only a few fan coils units among the many served by the system are necessary to operate. Interface with Operable Windows Individual units can be stopped through a special preprogrammed switch provided on the thermostat. The thermostats for unitary equipment in the current LAUSD guide specifications are provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. Some energy waste occurs when a dedicated outdoor air or a common exhaust system is provided. 19

32 Environmental Impact Cooling: The current refrigerant, R-22 will be phased out in Units with environmentally friendly (non-cfc/hcfc) refrigerants are available at present from a few manufacturers but they are not recommended as yet because the refrigerants are reported to be unstable mixtures and the required lubricants are so extremely hygroscopic that extra drying of the entire system is required before charging. We should wait until industry standards are more stable. Heating: Heat pumps produce no combustion products at the site. 20

33 SYSTEM 3: Four Pipe Fan Coil Units with Remote Central Plant Typical Four Pipe Fan Coil Unit with Remote Central Plant Air Distribution System Figure-3.1 This is an older system that preceded reliable packaged equipment, and is still used extensively for larger buildings. A fan coil is provided for each classroom and is typically suspended above the ceiling of the classroom from hangers provided with vibration isolators as indicated in Figure 2.3. Minimal ductwork serving four supply diffusers and two return registers is provided. Outdoor air is typically obtained through wall louvers or a dedicated outdoor air system. Each fan coil unit is provided with a chilled water coil for cooling and a hot water coil for heating. Chilled water and hot water is pumped to the fan coil from a remote central plant that is provided with air or water cooled chillers and gas fired hot water boilers. 21

34 The majority of the classroom fan coil units are about 4 Tons capacity. The supply airflow rate is 1,600 CFM of which 1,000 CFM is returned and 600 CFM is relieved to outdoors through gravity relief openings or through an exhaust system. Sound attenuation measures similar to the rooftop unit in the preceding section were taken as a standard for LAUSD in designing the ductwork. The measured background sound level for this system in a Type 1 steel frame building is about 46 dba. The sound level estimates with TAP for various additional sound attenuation measures and their associated costs are tabulated on the next page. 22

35 Cost Benefit Analysis of 4 Pipe Fan Coil Unit System Attenuation Cost Vs Sound Level Equipment NC 26 gauge Ducts Throughout dba Carrier 42BH 4-pipe fan coil unit Trane BCHC 4-pipe fan coil unit System Cost (per classroom) $21, $20, gauge Rect. Main Ducts & 26 gauge Round Branches NC dba System Cost (per classroom) $23, $22,

36 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Annual Energy Usage 900 Square feet area classroom Four Pipe Fan Coil Unit Manufacturer Trane Carrier Model BCHC 42BH Energy Use Cooling Heating Cooling Heating kwh $/kwh Total $ Therm $/Therm Total Total kwh $/kwh Total $ Therms $/Therm $ $ 1 5, , With 30% Filters. Indoor Air Quality Air Filters: Indoor air circulation rate: 2 thick air filters of MERV 8 (30%) efficiency is typically provided when outdoor air is obtained directly through wall louvers or roof vents. Higher efficiency filters can be provided when a dedicated outdoor air system is provided. 10 air changes per hour 100% outdoor air economizers: Can be provided for individual systems but usually are omitted due to space limitations and higher cost. 100% outdoor air economizer systems cannot be provided with dedicated outdoor air systems. 24

37 Maintenance Cost: Level of Difficulty: Reliability $ per classroom per year Higher as the service person has to enter the classroom and lift up the ceiling tiles to service the fan coil unit. Secondary drain pans and high condensate level shut-off switches are necessary to prevent ceiling damage from condensate overflow. The central plant requires a higher level of expertise and effort to service. The breakdown of one chiller or boiler can affect the entire school especially in smaller schools where there is no redundancy and only one chiller or boiler is provided. When a dedicated outdoor air or a common exhaust system is provided the breakdown of these system components could affect an entire building and renders the systems less reliable. After-hours Operation An energy management system or the assistance of a plant operator is required. Additional controls are necessary when a dedicated outdoor air or a common exhaust system is provided. Also, considerable energy is wasted if only a few fan coils units among the many served by the system are necessary to operate as the dedicated outdoor air fan, Central exhaust fan a chiller or boiler and related circulating pumps are necessary to be in operation, especially in smaller schools where a small dedicated chiller for after hours operation is not provided. Interface with Operable Windows Individual units can be stopped through a special preprogrammed switch provided on the thermostat. The thermostats for unitary equipment in the current LAUSD guide specifications are provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. Some energy waste occurs when a dedicated outdoor air or a common exhaust system is provided. 25

38 Environmental Impact Cooling: Heating: Chillers with environmentally friendly (non-cfc/hcfc) refrigerants are available at present from all manufacturers. Boilers are required by code to be provided with best available technology to comply with the Air Quality Management District Low Pollutant Emission Standards. 26

39 SYSTEM 4: Central Air Handling Units with Remote Central Plant Typical Central Air Handling Unit with Remote Central Plant Air Distribution System Figure

40 This is an older system that preceded reliable packaged equipment, and is still used extensively for larger buildings. A central air handling unit is provided on the roof or inside an air handling unit room preferably one unit for each floor of the building. A variable air volume (VAV) terminal is provided for each classroom and is typically suspended above the ceiling of the classroom. Minimal ductwork serving four supply diffusers is provided downstream of the VAV terminal. The space above the ceiling is traditionally used as a return air plenum but due to CHPS indoor air quality requirements and the need to prevent high space air pressure fluctuations to maintain ADA door closer forces, ducted return air systems are used for current LAUSD projects. Each air handling unit is provided with a chilled water coil for cooling and a hot water coil for heating. Chilled water and hot water is pumped to the fan coil from a remote central plant that is provided with air or water cooled chillers and gas fired hot water boilers. The majority of the classroom VAV terminals are about 4 Tons capacity. The supply airflow rate is 1,600 CFM of which 1,000 CFM is returned and 600 CFM is relieved to outdoors through the return or relief fans at the air handling unit. This system is not as effective in controlling space humidity as systems with individual cooling coils. Also, the outdoor air to each room will also be reduced with VAV modulation unless special controls are provided to maintain a constant outdoor air flow rate at the cost of $ 3, for the smallest system. Sound attenuation measures similar to the rooftop unit in the preceding section were taken as a standard for LAUSD in designing the ductwork. The air handling units are provided with computer selected fans optimized for sound and internal vibration isolators. Duct silencers are provided on the roof or in the air handling unit room at both supply and return air main ducts. Custom air handling units with quieter fans, cabinets with higher sound absorption and built-in duct silencers are also available at substantial additional cost. The calculated background sound level for this system with a custom rooftop air handler with 5 feet long duct silencers in the supply and 3 feet long duct silencers in a Type 1 steel frame building is about 44dBA with the VAV terminal inside the classroom at the classroom closest to the air handler which is located on the roof above the corridor. The sound level is reduced to 37 dba for the classroom farthest from the air handler with the VAV terminal located in the corridor. The sound level estimates with TAP for various additional sound attenuation measures and their associated costs are tabulated on the next page. 28

41 Central Air Handling Unit System Cost and Acoustical Performance Equipment Corridor Classroom NC dba NC dba System Cost (per classroom) Temtrol ITF-RDHRE43 AHU $19, Energy Labs AHU $20,

42 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Unit Manufacturer Unit Model Annual Energy Usage 900 Square feet area classroom Central air handling units with VAV System Temtrol ITF-RDHRE43 Energy Use Cooling Heating kwh $/kwh Total $ Therms $/Therm Total $ 1 4, Minimal _ Minimal 1. Two Stages of Air Filtration with 30% Pre Filters and 95% Final Filters. Indoor Air Quality Air Filters: Indoor air circulation rate: Higher efficiency filters can be provided without any limitations. 10 air changes per hour or more at full load if duct space is available. A classroom with a VAV system will receive only about 4 or 5 air changes of re-circulated air during part load and heating. The outdoor air to each room will also be reduced unless special controls are provided to maintain a constant outdoor air flow rate. Air filter manufacturers recommend higher air changes to limit indoor particle counts. The coil leaving temperature could be reset higher to satisfy the zone with the highest cooling demand at the sacrifice of air moving energy savings from VAV and also reheat for humidity controls during periods of high humidity. 100% outdoor air economizers: Provided. 30

43 Maintenance Cost: Level of Difficulty: $ per classroom per year Higher. The central plant requires a higher level of expertise and effort to service. Reliability The breakdown of one chiller or boiler can affect the entire school especially in smaller schools where there is no redundancy and only one chiller or boiler is provided. The breakdown of one air handler could affect an entire floor or building. After-hours Operation An energy management system or the assistance of a plant operator is required. Considerable energy is wasted if only a few rooms among the many served by the system are necessary to operate as the central air handler, exhaust fan, a chiller or boiler and related circulating pumps are necessary to be in operation. Interface with Operable Windows Individual VAV terminals can be closed from a programmable thermostat through a preprogrammed switch. The thermostats for unitary equipment in the current LAUSD guide specifications are provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. A similar method could be applied to a VAV system through the Energy Management System. Interface with an energy management system through proximity switches at the windows is not absolutely necessary. Environmental Impact Cooling: Heating: Chillers with environmentally friendly (non-cfc/hcfc) refrigerants are available at present from all manufacturers. Boilers are required by code to be provided with best available technology to comply with the Air Quality Management District Low Pollutant Emission Standards. 31

44 SYSTEM 5: Radiant Panels with Remote Central Plant Typical Radiant Panels with Remote Central Plant Air Distribution System Figure

45 This system is a relatively new type of system in the United States though it has been extensively used in Europe and Canada. This system is very quiet and energy efficient due to drastically reduced air movement since air moving energy is the major component of HVAC energy use. However, the design and installation of this system, requires a much higher level of expertise and cost. A central air handling unit is provided on the roof or inside an air handling unit room preferably one unit for each floor of the building to provide de-humidified outdoor air to each classroom. Radiant panels integrated with the ceiling are provided for each classroom to provide heating and cooling. Minimal ductwork for two outdoor air diffusers is provided for each classroom. All the supply air to the room is relieved through gravity to outdoors or is exhausted through a central exhaust fan system. The space above the ceiling can be used as a relief or exhaust air plenum but the need to prevent high space air pressure fluctuations to maintain ADA door closer forces may necessitate ducted exhaust air systems for larger buildings with fan assisted relief. Each dedicated outdoor air unit is provided with a chilled water coil for cooling and a hot water coil for heating. Chilled water and hot water is pumped to the air handling unit from a remote central plant that is provided with air or water cooled chillers and gas fired hot water boilers. The radiant panels are also provided with chilled water and hot water from a remote central plant. Sound attenuation measures similar to the rooftop unit in the preceding section were taken as a standard for LAUSD in designing the ductwork. Duct silencers are provided on the roof or in the air handling unit rooms at both supply and return air main ducts. The air handling units are provided with computer selected fans optimized for sound and internal vibration isolators. Duct silencers are provided on the roof or in the air handling unit room at both supply and return air main ducts. Custom air handling units with quieter fans, cabinets with higher sound absorption and built-in duct silencers are also available at substantial additional cost. The background sound level for this system with a custom rooftop air handler with 5 feet long duct silencers in the supply and 3 feet long duct silencers in the return in a Type 1 steel frame building is expected to be about 37dBA at the classroom closest to the air handler which is located on the roof above the corridor. 33

46 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Manufacturer Model Annual Energy Usage 900 Square feet area classroom Radiant Heating and Cooling Panels with Dedicated Outside Air System Temtrol DOA Air Handler with TWA Radiant Panels ITF-RDH17 Energy Use Cooling Heating kwh $/kwh Total $ Therms $/Therm Total $ 1 6, , Two Stage Filtration with 30% Pre Filters and 95% Final Filters. Indoor Air Quality Air Filters: Indoor air circulation rate: Higher efficiency filters can be provided without any limitations. 100% outdoor air (No return) but 3 to 4 air changes per hour only. Air filter manufacturers recommend higher air changes to limit indoor particle counts. Interior zones of office buildings with VAV systems normally receive less than 4 air changes of re-circulated air. A classroom with a VAV system will receive only about 4 or 5 air changes of re-circulated air during part load and heating. 4 air changes of 100% outdoor air should be sufficient. Maintenance Cost: Level of Difficulty: $ per classroom per year Higher. The central plant requires a higher level of expertise and effort to service. 34

47 Reliability The breakdown of one chiller or boiler can affect the entire school especially in smaller schools where there is no redundancy and only one chiller or boiler is provided. The breakdown of one dedicated outdoor air handler or central exhaust fan could affect an entire floor or building. Condensation problems could occur with control system failure or operator error. After-hours Operation An energy management system or the assistance of a plant operator is required. Considerable energy is wasted if only a few rooms among the many served by the system are necessary to operate as the central dedicated outdoor air handler, central exhaust fan, a chiller or boiler and related circulating pumps are necessary to be in operation. Interface with Operable Windows Individual zone heating and cooling valves to the room radiant panels can be closed from a programmable thermostat through a preprogrammed switch. The thermostats for unitary equipment in the current LAUSD guide specifications are provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. A similar method could be applied to a VAV system through the Energy Management System. When outdoor humidity is high, condensation problems could occur with control system failure or operator error. Environmental Impact Cooling: Heating: Chillers with environmentally friendly (non-cfc/hcfc) refrigerants are available at present from all manufacturers. Boilers are required by code to be provided with best available technology to comply with the Air Quality Management District Low Pollutant Emission Standards. 35

48 OTHER SYSTEMS 36

49 SYSTEM A: Water Source Heat Pumps Typical Water Source Heat Pump Unit System Figure-6.1 Water source heat pump systems are considered hybrid systems, where a common water loop for condensing or heat exchange is provided from a central source for a building or a campus, while primary cold or heat generators may be distributed. A water source heat pump is provided for each classroom and is typically suspended above the ceiling of the classroom from hangers provided with vibration isolators as indicated in Figure 6.1. Minimal ductwork serving four supply diffusers and two return registers is provided. Outdoor air is typically obtained through wall louvers or a dedicated outdoor air system. The water source heat pumps are provided with a common water loop for condensing or heat exchange pumped from a campus wide central condenser water system. A minimum of two independent cooling towers, two boilers, and associated 37

50 accessories must be provided for a campus wide central condenser water system for redundancy. Positive means for fresh air make-up and sufficient means of relief to maintain door opening and closing pressures that comply with California Building Code accessibility requirements must be provided for classroom units. The majority of the classroom units are about 4 Tons capacity. The supply airflow rate is 1,600 CFM of which 1,000 CFM is returned and 600 CFM is relieved to outdoors through gravity relief openings or through an exhaust system. Sound attenuation measures similar to the rooftop unit in the preceding section were taken as a standard for LAUSD in designing the ductwork. The measured background sound level for this system exceeds 50 dba for most installations when measured per current ANSI standard methods. 38

51 OTHER CONSIDERATIONS Energy Efficiency We estimated the following annual energy usage for a typical 960 square foot classroom with Trace 700 using typical school operating schedules: Manufacturer Model Annual Energy Usage 900 Square feet area classroom Water Source Heat Pumps Carrier 50 R Series Cooling Eff. EER Heating Eff. COP Energy Use Cooling Heating kwh $/kwh Total $ kwh $/kwh Total $ 1. Energy Efficiency Ratio 2. Coefficient of Performance Indoor Air Quality 6, , Air Filters: Indoor air circulation rate: 2 thick air filters of MERV 8 (30%) efficiency is typically provided when outdoor air is obtained directly through wall louvers or roof vents. Higher efficiency filters can be provided when a dedicated outdoor air system is provided. 10 air changes per hour 100% outdoor air economizers: Can be provided for individual systems but usually are omitted due to space limitations and higher cost. 100% outdoor air economizer systems cannot be provided with dedicated outdoor air systems. Maintenance Cost: $ per classroom per year 39

52 Level of Difficulty: Higher as the service person has to enter the classroom and lift up the ceiling tiles to service the unit. Secondary drain pans, and high condensate level shut-off switches are necessary to prevent ceiling damage from condensate overflow. The central cooling tower and boiler plant requires a higher level of expertise and effort to service. Reliability The breakdown of one cooling tower or boiler can affect the entire school especially in smaller schools where there is no redundancy and only one tower or boiler is provided. When a dedicated outdoor air or a common exhaust system is provided the breakdown of these system components could affect an entire building and renders the systems less reliable. After-hours Operation An energy management system or the assistance of a plant operator is required. Additional controls are necessary when a dedicated outdoor air or a common exhaust system is provided. Also, considerable energy is wasted if only a few fan coils units among the many served by the system are necessary to operate as the dedicated outdoor air fan, central exhaust fan, a tower or boiler and related circulating pumps are necessary to be in operation. 40

53 Interface with Operable Windows Individual units can be stopped through a special preprogrammed switch provided on the thermostat. The thermostats for unitary equipment in the current LAUSD guide specifications are provided with a 0-6 hours after hours override button. Holding down the override button for 5 seconds will deactivate the unit. This feature is included to avoid costly and unreliable proximity switches that will automatically deactivate the unit when the windows are opened. Some energy waste occurs when a dedicated outdoor air or a common exhaust system is provided. Environmental Impact Cooling: The current refrigerant, R-22 will be phased out in Heating: Boilers are required by code to be provided with best available technology to comply with the Air Quality Management District Low Pollutant Emission Standards. 41

54 SYSTEM: B Wall-Mounted Packaged Heat Pumps with Ducted Supply Typical Wall Mounted Heat Pump Unit System Fig

55 Section for Typical Wall Mounted Heat Pump Unit Fig

56 Wall mounted packaged heat pumps are the lowest cost and least invasive (least disruptive to existing Architecture to install) for modernization projects. They are also very inexpensive to operate. These advantages are offset by the significantly higher sound levels. Within ten feet of the unit, these systems produce at best a sound level of 50 dba, and closer to the unit the levels reach 55 and 60 dba in most cases. Because there is usually no ductwork exterior to the units (though the above drawings indicate a ducted supply air installation with no ductwork on the return), no opportunity to attenuate the units externally exists. The only option is to improve the design of these units to make them quieter. The following items should be considered for unit improvement: 1. Make indoor air supply fans quieter by using bigger fans operating at a lower speed. 2. Make condenser fans quieter by using centrifugal fans or specially designed quieter propeller fans in lieu of the noisy propeller fans that are currently used. 3. Make compressors quieter by using scroll compressors in thicker gauge housings, provide higher density insulation for the housings or provide external lagging. 4. Provide vibration isolators at fans and compressors. 5. Provide flexible connectors for pipes at compressors. 6. Provide flexible connectors at fan outlets. 7. Make the unit cabinet quieter by using a double wall cabinet of thicker gauge sheet metal with gaskets at all joints and thicker insulation. The locations of these units also have a substantial impact on the classroom sound level. The typical location on a classroom wall in a modernization project is at a window that is adjacent to or between existing windows that are usually of 1/8 glass as indicated in Figure 7.1. These windows offer very little sound attenuation and the radiated noise from the unit entering through the windows, contributes significantly to the classroom sound level. The manufacturer s recommended installation as indicated in Figure 7.2 suggests that these units are intended for installation against a solid wall. 44

57 SYSTEM C: Duct Free Systems Typical Hi Wall System Fig

58 Typical Ceiling Suspended System Fig

59 Typical Console Unit System Fig

60 Typical in Ceiling Cassette System Fig

61 The above systems are variations of split-system heat pumps that were studied as System 2 in an earlier section, with ductless indoor units. They are less invasive (least disruptive to existing Architecture to install) than rooftops or conventional split systems for modernization projects. They are also relatively less expensive as installation of ductwork is not required. They are also quite energy efficient and match those of the split system heat pumps. They are available in three typical configurations: High Wall as indicated in figure 8.1. The indoor sound pressure level measured 1 meter away from the indoor unit of this system is about 48.3 dba at low speed for a 2 ton Unit. Indoor sections of high wall systems are only available up to 2 Tons capacity. Two indoor units will be required for a typical LAUSD classroom thus increasing the indoor sound level to about 51 dba. Ceiling suspended (valance) as indicated in figure 8.2. The indoor sound pressure level measured 1 meter away from the indoor unit of this system is about 58.0 dba at medium speed for a 4 ton Unit. This unit is not available in low speed. Console as indicated in figure 8.3. The indoor sound pressure level measured 1 meter away from the indoor unit of this system is about 40.0 dba at low speed for a 2 1/2 ton Unit. Indoor sections of console systems are only available up to 2 ½ Tons capacity. Two indoor units will be required for a typical LAUSD classroom thus increasing the indoor sound level to about 43 dba. A Ceiling Cassette System is shown in figure 8.4. The indoor sound pressure level measured 1 meter away from the indoor unit of this system is about 45.6 dba at medium speed for a 4 ton Unit. This unit is not available in low speed. Some severe limitations exist with these systems. Indoor sections of high wall systems are only available up to 2 Tons capacity and console systems up to 2 ½ Tons capacity. Therefore, two indoor units would be required for a typical LAUSD classroom. These systems are also only available with low-efficiency; cleanable air filters (filters that are required to be periodically cleaned). The current LAUSD standard is minimum 30% efficiency, low-pressure drop, pleated, disposable air filters, which are more effective and less costly to maintain. Outdoor air ventilation is not readily available through the unit with high wall, console and ceiling suspended systems. Classrooms are required by code to be provided with 20 cubic feet per minute of outdoor air per student. This limitation alone precludes three configurations of this type of system from classroom applications in new construction. For modernization projects, these units may be used in conjunction with a dedicated outdoor-air ventilation system after careful analysis. However, the cost and invasiveness of the dedicated outside air system may render the systems impractical. 49

62 These systems cannot provide a 100% outdoor-air economizer cycle. The maintenance cost is higher and the level of difficulty to service is also considerably higher. The indoor sections have to be practically totally dissembled for service. After-hour operation and interface with operable windows is relatively easy and is similar to split-system heat pumps. Environmental impact is similar to split-system heat pumps. 50

63 ACOUSTICAL REQUIREMENTS OF LAUSD DESIGN GUIDELINES 51

64 ACOUSTICAL REQUIREMENTS of LAUSD DESIGN GUIDELINES General Requirements in the LAUSD Design Guidelines that relate to the acoustic and noise aspects of HVAC systems are contained in the Guide Specifications that specify equipment, installation measures and testing methods, and in the School Design Guide that present design criteria for the AE firms. Following are excerpts from those documents illustrating the measures related to HVAC acoustics that the District requires. These include all of the noise mitigation measures included in this study and report, with the exception of the increase in duct wall thickness to 18 gage. Actual field testing of this measure is recommended prior to its adoption as a standard. Acoustical Measures in the Guide Specifications Section Test and Balance, Article 3.02 E and F: E. Verification: The Test and Balance Agency shall recheck ten percent (minimum ten) of the measurements listed in the report. The locations shall be selected by the IOR/OAR. The recheck will be witnessed by the IOR/OAR. If twenty percent of the measurements that are retested differ from the report and are also out of the specified range, an additional ten percent will be tested. If twenty percent fall outside the specified range, the report will be considered invalid and all test and balance work shall be repeated. F. Due to more stringent acoustical requirements in the educational environment, the Test and Balance Agency shall recheck the air systems where the sound level is higher than the design intent or district standard and demonstrate compliance with the methodology specified in this document with emphasis on fan speed adjustment and balancing for optimum acoustical performance. The recheck will be witnessed by the IOR/OAR. When there are multiple air systems, a system selected by the IOR/OAR shall be rechecked. If this system is found to be not in compliance, a second system shall be checked. If the second system if also found to be not in compliance, the report will be considered invalid and all test and balance work shall be repeated. 52

65 Section Test and Balance, Article 3.06 Q and R: Q. The following sound test data is required: 1. Area or location 2. Sound level in db(a) as specified in Section Sound level at the center band frequencies of eight non-weighted octaves with equipment on and off for 5 rooms selected by the OAR/IOR. 4. Plot corrected sound-level reading on Noise Criteria (NC) curve for the measurements in Q 3 above. R. The following vibration test data is required: 1. Equipment identification number 2. Vibration levels at all accessible bearings, motors, fans, pumps, casings, and isolators 3. Measurements in mils defection and velocity in inches per second as specified per section XIV of this document 4. Each measurement taken in horizontal, vertical, and axial planes as accessible. Section Test and Balance, Article 3.09 (k 1 5): k. Fan speed adjustments and balancing for optimum acoustical performance: 1) As the very first step, the speed of all fans (supply, return, exhaust, inside packaged equipment or air handling units) shall be adjusted to deliver the required fan total air quantity with all volume dampers and other flow rate control devices fully open. Adjustments shall be made with the outdoor air intake dampers, return air dampers and relief air dampers in the minimum outdoor air position. The adjustments shall be made again in the100% outdoor air position in systems with 100% outdoor air economizers. 2) The above adjustment shall be done with wet cooling coils where cooling coils are provided. 53

66 3) The airflow rates at each branch duct shall be adjusted as the second step with air with all volume dampers and other flow rate control devices fully open. 4) The airflow rates at each air inlet and outlet shall be adjusted as the final step. The volume damper in the branch duct shall be used for balancing. Opposed blade dampers at air inlets and outlets where provided shall only be used for fine adjustments and shall not be closed beyond 60% open or when the dampers start to generate audible noise. 5) Contractor shall provide the labor and materials for all dampers, pulleys and belt changes required for balancing. The design documents indicate the worstcase scenario with safety factors in fan static pressures for contingency. Properly coordinated and installed air systems may require a lower static pressure and a reduction in fan speed. Section Test and Balance, Article 3.18, 3.19: VIBRATION TESTING A. Furnish instruments and perform vibration measurements if specified in Division 15. Provide measurements for all rotating HVAC equipment half horsepower and larger, including reciprocating/centrifugal/screw/scroll compressors, pumps, fans and motors. B. Record initial and final measurements for each unit of equipment on test forms. Where vibration readings exceed allowable tolerance and efforts to make corrections have proved unsuccessful, forward a separate report to Architect SOUND TESTING A. Perform and record sound measurements as specified in this section and if specified in Section 15240: Sound Vibration and Seismic Control. Take additional readings if required by Architect. B. Take measurements with a calibrated Type 1 sound level meter and octave band analyzer. 54

67 C. Sound reference levels, formulae and coefficients shall be according to ASHRAE handbook, Current Systems Volume; Chapter: Sound and Vibration Control. D. Determine compliance with the Contract Documents as follows: 1. Where sound pressure levels are specified as noise criteria or room criteria in Section 15070: Sound, Vibration and Seismic Control. a. Reduce background noise as much as possible by shutting off unrelated audible equipment. b. Measure octave band sound pressure levels with specified equipment "off". c. Measure octave band sound pressure levels with specified equipment "on". d. Use difference in corresponding readings to determine sound pressure due to equipment. DIFF.: or More FACTOR: Sound pressure level, due to equipment, equals sound pressure level with equipment "on" minus factor. e. Plot octave bands of sound pressure level due to equipment for typical rooms, on a graph, which also shows, noise criteria (NC) curves. 2. When sound power levels are specified: a. Perform steps in Section 3.20, D, 1.a. through 1.d. b. For indoor equipment: Determine room attenuating effect; i.e., difference between sound power level and sound pressure level. Determine sound power level will be sum of sound pressure level due to equipment, plus room attenuating effect. c. For outdoor equipment: Use directivity factor and distance from noise source to determine distance factor, i.e., difference between sound power level and sound pressure level. Measured sound power level will be sum of sound pressure level due to equipment, plus distance factor. 3. Where sound pressure levels are specified in terms of dba, measure sound levels using the "A" scale of meter. Single value readings will be used instead of octave band analysis. 55

68 E. Where measured sound levels exceed specified level, Contractor shall take all remedial action and necessary sound tests shall be repeated. F. Measure and record sound levels in decibels at each diffuser, grille or register in occupied areas. Sound levels shall be measured approximately 5'-0" above floor on a line approximately 45 degrees to center of opening, on the "A" and "C" scales of a General Radio Company sound level meter, or similar instrument. E. G. Report shall also include ambient sound levels of rooms in which above openings are located, taken without air-handling equipment operating. A report shall also be made of any noise caused by mechanical vibration. Section Basic Mechanical Requirements, Article 1.01 M: M. Noise and Vibration Reduction 1. Correct noise or vibration problems caused by failure to install work in accordance with Contract Documents. Include all labor and materials required as a result of such failure. Pay for re-testing of corrected noise or vibration problems by the project acoustical consultant including travel, lodging, test equipment expenses, etc. Section Mechanical Sound, Vibration, and Seismic Control: Entire Section Section Heating, Ventilating and Air Conditioning Equipment, Article 2.02 A (1. c and d): 2.02 AIR CONDITIONING UNITS A. AC-1a (2.5 Tons-20 Tons): (Specify when higher energy efficiency, higher air filtration efficiency or lower sound levels are required) Furnish packaged air conditioning unit with gas heating for roof top installation. Unit shall be self-contained, completely factory assembled, with complete internal wiring and controls. Unit shall also be provided with a fully piped refrigerant circuit, fully charged with an environmentally friendly refrigerant that is not scheduled for phase out. Unit shall be field configurable for down-flow or horizontal discharge. Cooling and heating capacities, electrical characteristics, indoor sound levels, outdoor sound levels and operating conditions shall be as indicated on Drawings. 56

69 1. Quality Assurance: c. Unit outdoor sound levels shall also be rated in accordance with ARI sound standards 270 and 370. d. Unit indoor sound levels shall also be rated in accordance with ARI sound standards 260. Section Air Distribution, Article 1.03 : 1.03 QUALITY ASSURANCE A. Installer's and Manufacturer's Qualifications: Comply with provisions stated under Section 15010: Basic Mechanical Requirements. B. All sound power level measurements and Manufacturers' NC value calculations shall be conducted in complete accordance with the latest version of ASHRAE Standard 70 and ADC Standard 1062: GRD-84. Equivalent test and calculation procedures may be substituted for the above procedures if approved in advance by the Architect. Section Air Distribution, Article 2.01 E and H 4 and 5: E. Galvanized steel ducts gage thickness and permissible joints and seams of concealed ductwork shall conform to requirements in HVAC Duct Construction Standards of Sheet Metal and Air Conditioning Contractor s National Association (SMACNA) and the California Mechanical Code (CMC) unless noted otherwise on the drawings. The more stringent requirements shall prevail. Galvanized steel ducts gage thickness and permissible joints and seams of exposed ductwork shall conform to requirements in Table 2, Minimum Metal Gages, of this section. When more stringent requirements are noted on the drawings the most stringent requirement shall prevail. H. Round and Oval Galvanized Steel and Aluminum Ducts: 4. Minimum duct wall thickness for concealed flat oval duct construction shall conform to requirements in HVAC Duct Construction Standards of Sheet Metal and Air Conditioning Contractor s National Association (SMACNA) and the California Mechanical Code (CMC). The more stringent requirements shall prevail. Gage thickness and permissible joints and seams of exposed ductwork shall conform to requirements in Table 1, of this section. 57

70 5. Flexible duct shall be non-metallic, insulated for conditioned air supply and return. The flexible ducts shall be factory fabricated with exterior reinforced laminated vapor barrier, 1-1/2 inch thick fiber glass insulation 75 degrees F.), encapsulated zinc-coated spring steel wire helix and impervious, smooth, non-perforated interior vinyl liner and factory fabricated steel connection collars. For the composite assembly, including insulation and vapor barrier, comply with NFPA Standard 90 A or 90 B and tested in accordance with UL Standard, UL-181. Noninsulated metallic ducts shall be provided for exhaust only. Section Air Distribution, Article 2.03 A, 2.05 A (1 3), 2.06 : 2.03 ACOUSTICAL DUCT AND PLENUM LINERS A. Duct liners shall conform to requirements of Section 15080: Mechanical Insulation AIR DISTRIBUTION DEVICES A. General: 1. Grilles, registers, diffusers and appurtenances shall conform to requirements specified herein and shall be of type and sizes as specified and indicated on Drawings. Performance shall be in accordance with Air Diffusion Council Test Code 1602R2 including airflow velocity, pressure, temperature, and sound measurements. 2. Sponge neoprene, rubber, vinyl or felt border gaskets shall be provided for surface-mounted registers, grilles or diffusers. 3. The noise generating characteristics of all specified grilles, registers, and diffusers shall be tested to, and comply with, all requirements of this specification. Representative samples shall be subjected to tests in accordance with applicable standards and procedures in order to demonstrate such compliance. A special test for this project is not required if the manufacturer has previous certified test results that can be made applicable to this project. Maximum Sound Levels of diffusers, grilles and registers shall be as follows: 58

71 Administrative office area: NC 30 Classrooms: NC 20 Libraries and other noise sensitive areas: NC 25 Gymnasiums, cafeterias, lockers areas: NC SOUND ATTENUATING EQUIPMENT - DUCT SILENCERS A. Provide factory fabricated duct silencers of tubular or rectangular type, for high or low velocity service, with arrangements, sizes and capacities as indicated on Drawings. Construct silencers of galvanized steel with casing seams sealed or welded to be airtight at a pressure differential of 8 inches water gauge between inside and outside of unit, and stiffen or brace as required to prevent structural failure or deformation at same condition, or audible vibration during normal operation. Filler material shall comply with the following: Fire Safety Standards: NFPA 90A & B Temperature: ASTM C 411 Air velocity: ASTM C 1071, UL 181 Fire Hazard Classification: ASTM E 84, UL 723-Class 1, NFPA 255 Corrosion Resistance: ASTM C 739, C 665 Fungi Resistance: ASTM G21 Bacteria Resistance: ASTM G22 Water Vapor Sorption: ASTM C 1104, less than 1% by weight Formaldehyde, Phenoloc Resins or other Volatile Organic compounds: 0% B. Select and provide silencers from acoustical and aerodynamic rating tables based on actual test readings or interpolated values of such readings obtained from tests made by recognized independent laboratories. Tests shall be in accordance with ASTM E 477. C. Select and provide silencers for air pressure drops not exceeding those indicated on Drawings, and of types, sizes and models for which noise reduction values, dynamic insertion loss, in decibels reference watts, are not less than indicated on Drawings. Section Air Distribution, Article 3.02 F: F. Construct and install ducts to be completely free from vibration under operating conditions. Section Air Distribution, Article 3.10 A: 59

72 3.10 FLEXIBLE CONNECTIONS A. At points where sheet metal connections are installed to fans or air handling units, or where ducts of dissimilar metals are connected, a flexible connection of commercial grade, Duralon by Duro-Dyne Corporation, or equal, noncombustible material shall be installed and securely fastened by zinc-coated steel clinch-type bands or a flange type connection. Inlet and outlet openings shall be axially in-line, maximum deviation of centerline shall be less than 5 percent of diameter or shortest dimension of a rectangular inlet of fan or air handling unit, with system at rest. Duct end of connection shall be seismically restrained if more than 4 feet from last support. Section Air Distribution, Article 3.12 A: 3.12 DAMPERS A. Manually operated dampers, gravity dampers, fire dampers, and motor operated dampers shall be furnished and installed as specified and indicated. Upon completion of installation, dampers shall be checked, lubricated, and adjusted so that they operate freely, without binding. Dampers shall be of standard commercial manufacture, complete with damper frame. Where painting is required, they shall be shop finished unless otherwise noted. 1. Provide and install manual volume dampers per current SMACNA standards to allow balancing per current AABC, NEBB or TABB Procedures and Standards whether indicated on the drawings or not. 2. Balancing dampers shall be installed in main supply ducts from fan discharge plenums, where 2 or more ducts are connected to each plenum, although such balancing dampers may not be indicated. Each zone shall be provided with a manual volume damper. Sheet metal screws shall be installed through handles and into ducts to lock damper in place after test and balance. 3. Each Supply, return, and exhaust branch shall be provided with manual volume dampers. 4. Do not provide opposed blade dampers at air inlets and outlets. 5. Each supply, return, and exhaust inlet or outlet shall be provided with a manual volume damper. This damper shall be a minimum of 5 feet upstream of the air outlet/inlets. An acoustic flexible duct should be provided between the outlet/inlet and the damper for concealed ducts. 60

73 6. Dampers installed in accessible locations shall be provided with locking and indicating quadrants. Ventlock, Duro-Dyne, or equal. 7. Dampers installed in ductwork in furred ceiling spaces or in roof spaces with less than 30 inches of clearance below beams, joists, or other construction, and where access panels are not provided shall be furnished with damper rods extended below ceiling and terminated with a concealed damper regulation. Ventlock, Young, or equal. 8. Dampers not identified as splitter, extractor, or butterfly dampers shall be of multi-louver type arranged for opposed blade operation. Damper shall be same dimension as adjoining duct and be tight closing. Blades shall not be greater than 9 inches. Dampers shall be not less than 18 gage steel. 9. Motor operated dampers shall be furnished by temperature control manufacturer as part of temperature control equipment and shall conform to requirements of Section 15900: HVAC Instrumentation and Controls. 10. Dampers shall be provided with accessible operating mechanisms. Where operators are exposed in finished portions of building, operators shall be chromium-plated with exposed edges rounded. Splitter dampers are not permitted unless specified and reviewed by the Architect. 11. Dampers shall not be installed in combustion air ducts. 12. Access panels shall be installed for access at each damper s operating mechanism. 61

74 Acoustical Measures in the School Design Guide Book 3 Technical Criteria, Section 3.6 HVAC SYSTEMS, Article C, HVAC System Selection, 1. Criteria 14, page 5: 1. Criteria 14. Acoustically compatible with occupied spaces Book 3 Technical Criteria, Section 3.6 HVAC SYSTEMS, Article E, Air Distribution, page 11-12: E Air Distribution Ventilation and Outside Air Ducts: a. Provide outside air to each room through the HVAC system in compliance with current CEC Standards and ASHRAE recommendations.. b. Clearly indicate outside-air provisions and flow rates for each HVAC unit, and relief provisions to balance the fresh outside air make-up and to relieve exhaust air in all operating cycles. c. Fresh Air Intakes: 1. Locate fresh air intakes to prevent contamination from kitchen exhaust, garage exhaust, or any process exhaust by locating the intakes on the upstream (prevailing wind) side of exhaust openings, as distant as possible. 2. Limit intake velocity to 750 FPM through net free louver area at 100 percent fresh air quantities to keep noise, pressure drop and rain carryover to a minimum. a. Comply with current code and SMACNA Guidelines for duct construction. Thicker metal gages for ducts and hanger straps, as specified in the Guide Specifications, must be used for exposed ductwork and other special considerations. b. Size ductwork for conditioned air on equal-friction method based on 0.08" WC per 100 feet with a high velocity limit of 1,000 FPM above occupied areas and 1,500 FPM inside shafts, or as directed otherwise by the Project Acoustical Consultant. Changes in sizes at every 62

75 Fans branch or every interval are not warranted economically unless branch represents a substantial percentage. c. Size return-air and exhaust air ducts on equal-friction method based on 0.08" WC per 100 feet with a high velocity limit of 1,000 FPM above occupied areas and 1,500 FPM inside shafts or as directed otherwise by the Project Acoustical Consultant.. d. Allowable air velocities for ducts above acoustically sensitive areas shall be determined by an Acoustical Engineer. e. Duct the return air. Ceiling plenum return is not allowed as a means to improve indoor air quality. f. Sound attenuators or lined ducts should be installed on inlet and outlet side of fans, and between fans and ducts, to prevent fan noise entering rooms through the duct system. Do not locate duct sound attenuators inside the building above (the ceiling of) occupied spaces where the breakout noise will increase indoor sound levels above acceptable limits. 1. Select fans to minimize noise and to meet noise level criteria in occupied spaces. 2. Commissioning Measures 1. Air Balance: Systems must be balanced for both the regular and economizer modes. Most unitary systems are specified with a safety factor in the static pressure. The Contractor must be required by the specifications to replace the drive sheaves and slow the fan down to achieve the required air balance and prevent energy waste and noise. If this is not done, the air flow is left higher creating higher static pressure and noise levels. Cooling Towers: a. Size cooling towers for 120% to 150% of required capacity, to guarantee full capacity from chiller at any wet bulb conditions and to allow for fouling of tower. b. Provide a bleed-off system and a chemical feeder to prevent mineral build-up and to maintain water quality. c. Provide for make-up water to replace evaporation and bleed. Locate cooling towers to avoid unsightly conditions and so that noise generated by fan will not be objectionable in adjoining buildings. Provide louvered screens, masonry walls, or planting for concealment. 63

76 Book 3 Technical Criteria, Section 3.6 HVAC SYSTEMS, Article I, Sound and Vibration Control, page 22: B SOUND AND VIBRATION CONTROL: 1. Criteria: a. Because mechanical systems and equipment are a major source of disturbing noise within buildings, sound and vibration control measures must be incorporated to the maximum extent economically practical. In general, refer to current ASHRAE guidelines, District Guide Specifications, chapter 2.4 Environment and Sustainability of this Guide, and the following recommendations. b. Since the District desires to achieve noise levels from HVAC systems better than 45 dba, especially in instructional spaces, plan and describe in the Basis of Design narrative how this improved acoustical quality will be achieved together with the associated cost impacts. 2. Equipment Sound Levels: Schedule the sound level of the design base HVAC equipment on the drawings. These sound levels must be at the design conditions and tested per applicable current standards such as ARI Standards 260, 270, 370 and AMCA 300. Duct and Fan Noise: a. Ductwork: 1. Use ducts of thicker sheet metal gage and sound attenuators to reduce fan and equipment noise. Lined ductwork may be used when recommended by the Project Acoustical Engineer. Duct lining, acoustical panels in ductwork and sound attenuator media when used shall be of the type that inhibits the growth of mold, mildew and fungi, contain harmful VOC s or contain glass fiber. 2. Provide flexible connectors for ducts at fan connections 3. Do not locate sound attenuators above spaces where the self generated noise of the attenuator will increase the space sound level above requirements. 64

77 b. Fans: 1. Fan-noise in occupied spaces is typically caused by poorly constructed roof fans, roof fans operating at too great a tip speed, fan noise traveling through air intake louvers and then into adjoining spaces, and fan noise traveling to occupied spaces through inadequately treated return systems. Fan noise also comes from rooms without sound-attenuating walls or from roof-top units with inadequate sealing of roof openings and duct chases. 2. Locate fan and equipment rooms away from classrooms and other noise-sensitive spaces. 3. Make fan and equipment room walls of dense material, poured concrete or concrete block with all voids filled where feasible or sound-attenuating walls of studs and gypsum board. 4. Provide details to assure adequate sealing of duct penetrations through roof or mechanical equipment room walls. 5. At roof fans exhausting from ceiling plenums over occupied areas, provide a sound attenuator installed at fan inlet. Equipment Mounting and Isolation: a. For roof-top HVAC units, no roof penetrations are allowed except the minimum necessary for ducts and electrical conduit. All such openings shall be sealed with acoustical sealant. In addition, beneath the units provide a sound-isolation barrier of a close-fitting layer of ¾ waterproof plywood or cement board, sealed with acoustical tape to the curb. b. For fans over 24" provide inertia type concrete bases with spring isolators. For smaller fans provide spring-type vibration isolator rails under fan and motor. c. Floor-mounted pumps shall be bolted directly to concrete bases and shall have flexible pipe connections, except when located over or under an occupied area where noise could be transmitted by piping or building structure to occupied space. In this case, they shall be mounted on inertia type concrete bases with spring-type vibration isolators and shall have flexible connections rigidly anchored and braced to prevent elongation of the flexible connections. d. Air compressors shall be mounted on spring-type vibration isolators, except larger sizes shall also have concrete inertia bases and flexible pipe connections. 65

78 Pipe, Conduit and Duct Connections to HVAC Equipment a. Pipe, duct and electrical conduit connections to HVAC equipment with rotating or reciprocating components shall be provided with flexible connectors. b. Provide spring, neoprene or rubber in shear type hangers as required for pipes and ducts near connections to HVAC equipment that are located near or serve acoustically sensitive spaces as directed by an acoustical engineer. Classroom HVAC Sound Control: a. To meet District standards, HVAC systems must be designed so that noise from the system does not cause the ambient noise in a classroom to exceed the level of 45 dba as measured in accordance with ANSI Standard Make design recommendations to the District to achieve a lower sound level, within reasonable economic limits b. ASHRAE recommended design criteria for classroom HVAC sound control is Noise Criteria (NC) Curve NC-35. An HVAC system will probably meet the District 45 dba criteria when no portion of octaveband spectrum of noise lies above NC-35 curve. (This is approximately equivalent to a sound level of 45 dba from a standard sound level meter reading,) c. Refer also to the Environment and Sustainability chapter of this Design Guide for additional standards and reference to CHPS Best Practices. 66

79 Different Perspectives Two articles published in 2004 HVAC trade magazines stating two very different points of view are also attached. An acoustical engineer thinks that the ANSI S12.6 is impractical but a duct lining manufacturer strongly supports the standard. 67

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82 ACOUSTICAL ENGINEER S REPORT & CALCULATIONS 70

83 Schaffer Acoustics Inc 869 Via de La Paz, Suite A Pacific Palisades, CA tel fax [email protected] Mr. James Shwe Maroko & Shwe Sepulveda Blvd., #380 Mission Hills, CA January 31, 2005 Subject: LAUSD HVAC Cost, Energy and Acoustical Study James: At your request, and with your assistance, Schaffer Acoustics Inc performed acoustical calculations for several classroom HVAC system alternatives. This report summarizes the calculation results for the following HVAC system designs: System 1A System 1B Carrier 48HJ rooftop package unit Trane Precedent rooftop package unit System 2A Carrier FB4B DX split system fan coil unit in classroom ceiling plenum System 2B System 3A System 3B Trane Odyssey DX split system fan coil unit in classroom ceiling plenum Carrier 42BH 4-pipe fan coil unit in the classroom ceiling plenum Trane BCHC 4-pipe fan coil unit in the classroom ceiling plenum System 4A Remote central station air handling unit (Energy Labs custom unit) with a 1600 CFM VAV terminal unit in the classroom ceiling plenum System 4B Remote central station air handling unit (Temtrol ITF- RDHRE43) with a 1600 CFM VAV terminal unit in the classroom ceiling plenum System 5 Remote central station air handling unit (Temtrol ITF-RDH17) constant air volume system (720 CFM per classroom) with radiant cooling panels in the classroom this system was not analyzed but is discussed in this report All calculations assumed a 960 sq. ft. classroom with an acoustical tile ceiling at 9 feet above the floor. CRITERIA

84 LAUSD HVAC Acoustical Study January 31, 2005 Page 2 of 6 Schaffer Acoustics Inc Consulting, Testing & Design The new ANSI Classroom Acoustics Standard S recommends maximum A- weighted and C-weighted classroom sound levels of 35 dba and 55 dbc, respectively. The LAUSD currently uses a maximum sound level limit of 45 dba for classrooms that are served by ducted HVAC systems. The sound levels in many LAUSD classrooms are less than the 45 dba limit. This report analyzes the 5 basic systems to determine their classroom sound levels, and to determine the most cost-effective sound attenuation measures for reducing the classroom levels. Comparing various systems A-weighted sound levels work best where the systems sound energy is mostly above 250 hertz. However, since the highest sound levels from most HVAC systems are usually at frequencies of 250 hertz or less, a rating system that considers the octave bands with center frequencies from 63 to 4000 hertz is more useful for estimating the acceptability of HVAC system designs. The 1957 Noise Criteria (NC) rating system was the first popular system that looked at octave band sound levels, and it is still the most popular among acoustical professionals; and we recommend using it for assessing classroom system designs. Newer rating systems are being tested, and will be recommended in the future if they prove to be more reliable than the NC system. For now, we recommend that the classroom NC ratings not exceed the NC-35 curve, which is equivalent to about 44 dba, only 1 dba less than LAUSD s current 45 dba sound level limit. We will notify the district in the future when cost-effective attenuation measures are available. As you will see from the calculation results summarized herein, there is not a direct correlation between a sound spectrum s dba and NC values. In most cases the dba value is higher, but a spectrum that has a low frequency octave band that is especially out of balance with the other octave bands can create the rare situation in which the NC value is higher. One feature of a well-balanced spectrum is that its dba value is 5 to 9 points higher than its NC rating. CALCULATION RESULTS SUMMARY All of the calculations were done using Version 2.3 of the Trane Acoustics Program, which is based on the algorithms published in the 1991 ASHRAE special publication titled Algorithms for HVAC Acoustics. In some cases we used our field experience to modify a calculation parameter to obtain a more reliable calculation result. We assumed the following for all calculations: 1. The supply and return air sheet metal duct gauges were assumed to be the lowest cost alternative per the SMACNA Duct Design Guide 26 gauge for Systems 1, 2 & 3; 24 gauge for the trunk ducts in Systems 4 & The systems delivered 1600 CFM to the classroom, except for the System 5, which used radiant ceiling panels. This system needed only about 640 CFM per classroom. 3. The systems had ducted return air.

85 LAUSD HVAC Acoustical Study January 31, 2005 Page 3 of 6 Schaffer Acoustics Inc Consulting, Testing & Design 4. All connections to ceiling grilles and diffusers were made with a 5 length of Casco Silent-Flex II acoustical flex duct. Several other flex duct manufacturers make a similar product that uses a spunbond nylon inner liner. 5. All grilles and diffusers are selected for a catalog Noise Criteria rating of NC-25 or less. 6. All system components that are remote from the classroom (e.g., central plant for the 4-pipe systems and condensing units for the split systems) are installed and treated so that they create insignificant sound exposures in the classrooms. 7. All equipment was mounted on the proper vibration isolators so that structure-borne sound due transmission was not significant. The attached Figures 1 through 8 compare the calculated classroom octave band sound level spectra for each system alternative with the NC-35 octave band Noise Criteria curve, which has an equivalent A-weighted sound level of 44 dba. Systems 1, 2 & 3 are similar in that each system s prime air mover is very close to the classroom being served and their ductwork layouts are similar. We have, therefore, summarized the calculation results for these systems in Table 1 below. The table refers to the attached Figures 1 through 6, which show the octave band spectra associated with each calculation. TABLE 1 Summary of Classroom NC and dba ratings for Systems 1, 2 & 3 Figure System 26 gauge ducts 18 gauge ducts Equipment # # NC dba NC dba 1 1A Carrier 48HJ rooftop unit B Trane Precedent rooftop unit A Carrier FB4B split system B Trane Odyssey split system A Carrier 42BH 4-pipe fan coil unit B Trane BCHC 4-pipe fan coil unit Table 1 includes NC and dba results for both 26 and 18 gauge ductwork. We included both duct gauges because our initial calculations using 26 gauge sheet metal ductwork showed that the acoustical ratings were controlled by excessive breakout sound at the lowest

86 LAUSD HVAC Acoustical Study January 31, 2005 Page 4 of 6 Schaffer Acoustics Inc Consulting, Testing & Design octave bands, and our experience has shown that increasing a duct s thickness (decreasing its gauge number) is the most economical way to reduce breakout noise. The table above shows that the school district s 45 dba limit is exceeded for all of the tabulated systems, except the Carrier FB4B split system, if 26 gauge ducts are used. The table also shows that increasing the ductwall thickness to 18 gauge brings all of the systems into compliance with the 45 dba limit. More noteworthy is the fact that none of the calculation results, except for the Carrier FB4B split system, complies with our suggested NC-35 limit; a close review of Figures 1 through 6 shows that the excesses are comprised of residual 63 and 125 hertz band noise, even with the 18 gauge ductwork. Controlling this residual low frequency noise will require one or more of the following mitigation alternatives: 1. Require that the equipment sound power level (L W ) values not exceed certain values (each type of equipment would have its own set of L W value limits). 2. Move the equipment so that it is not directly over a classroom. 3. Insert duct silencers in the supply and return air ductwork. Re the rooftop units (System Type #1) - We considered rooftop equipment from manufacturers other than Carrier and Trane, but we did not carry out a complete system analysis with them because the alternative manufacturers provided estimated acoustical performance rather than measured performance. All of the calculation results in this report are based on measured equipment performance in accordance with ARI Standard , which is the only test standard that is accepted for determining the acoustical performance of air handling units, fan coil units and other ducted air-moving equipment. Figures 7 & 8 show the octave band sound spectra for central station variable air volume systems that use Energy Labs and Temtrol air handling units, respectively. The solid curve in each figure shows the acoustical spectrum in the corridor directly beneath the AHU s large trunk ducts; the acoustical phenomenon here is called duct breakout noise. The dotdashed curve in each figure is the classroom spectrum due to the in-duct noise that is generated by the AHU, the terminal unit and the diffusers & grilles. Table 2 below summarizes the NC and dba results for these units. TABLE 2 Summary of NC and dba Values for Systems 4A & 4B Figure # System # Equipment Corridor Classroom NC dba NC dba 7 4A Energy Labs AHU

87 LAUSD HVAC Acoustical Study January 31, 2005 Page 5 of 6 Schaffer Acoustics Inc Consulting, Testing & Design 8 4B Temtrol ITF-RDHRE43 AHU The calculation results in Table 2 show that the classroom sound level with either system will be much lower than the LAUSD 45 dba limit, and will even approach the ANSI S12.60 limit of 35 dba. The classroom noise exposures for both systems are identical because the classroom sound levels are controlled not by the AHU, but by the low pressure air distribution system that serves the room, and this part of the system is identical for the two AHU alternatives that were analyzed. The corridor sound exposures for the Temtrol AHU are higher than those for the Energy Labs AHU because the Energy Labs unit had internal sound traps, which were not included in the Temtrol unit. However, the NC-46 and 44 dba noise exposures are not considered excessive for a corridor, so thickened duct gauges are not needed for the supply and return air trunk ducts above the corridor. System 5, which uses reduced airflow to each classroom along with radiant cooling panels, will have classroom noise exposures that are very close to the NC-31 and 37 dba values for the 2 central station systems in Table 2 above if the relevant system design assumptions are followed; that is, the diffusers and grilles are selected for a maximum catalog noise rating of NC-25 and are connected to their ducts with 5 long sections of a flexible duct that uses a spunbond nylon inner liner. The corridor noise ratings will fall midway between the ratings for the 2 units tabulated in Table 2, even without the internal sound traps, so further mitigation of this noise is not needed for the example of the Temtrol ITF-RDH17 air handling unit. General Comments The calculation results in this report suggest that the systems with remote central station air handling units will yield the quietest classroom sound levels. This is confirmed by our field experience, as well. The results in Table 1 indicate that all of the systems that use a single fan-based unit for each classroom will meet the school district s 45 dba sound level limit if 18 gauge supply and return trunk ducts are used. Re our comment on measured versus estimated factory noise data all of the major equipment manufacturers are continually improving their product lines, so the school district can expect to see quieter equipment in the near future. We ve also just learned that York has recently begun running acoustical tests on their Sunline rooftop product and will be submitting measured sound power level data for consideration by the district in the very near future. Summary No matter what type of system is used to condition classroom air, the following design steps are important for controlling the classroom noise exposure: 1. Install 4-pipe and DX fan coil units in the ceiling plenums over corridors, work areas, or other non-sensitive rooms. Do not install them over classrooms.

88 LAUSD HVAC Acoustical Study January 31, 2005 Page 6 of 6 Schaffer Acoustics Inc Consulting, Testing & Design 2. Select the air-moving equipment for the lowest possible set of discharge and inlet sound power levels, as measured per the latest revisions of ARI Standard 260. Do not accept sound data obtained from any other test standard or estimation method. It is beyond the scope of this report to present specific sound power level limits because they will be different for each type of unit selection and installation, but a general rule of thumb is that larger fans at lower RPM rates are quieter than smaller fans at higher rotation speeds. Also, a unit whose fan is mounted on spring isolators inside of the cabinet will produce less noise than a unit whose fan is either directly bolted to the cabinet or installed with neoprene grommets or bushings. 3. Use 18 gauge sheet metal for all rectangular ducts that run directly over classrooms. A thinner duct gauge is OK for circular ducts. 4. Select classroom diffusers and grilles for a catalog sound rating of NC-25 or less. 5. Use a 5-foot long section of Casco SilentFlex II or Toro-Aire Toroflex flex ductwork to connect each diffuser and grille to its sheet metal ductwork. 6. Install all diffuser and grille balancing dampers at the metal/flex interface, not at the connection of the flex duct to the diffuser or grille collar. At your request we will provide the summary and detailed calculations sheets that we used to develop the octave band spectra that are shown in Figures 1 through 8. Please call if you have any questions. Yours truly, Schaffer Acoustics Inc Mark E. Schaffer, P. E. President MES:bh Encl.

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