Lower Energy Costs with Rooftop Air-Conditioning Package Units

Transcription

1 Lower Energy Costs with Rooftop Air-Conditioning Package Units Sponsored by Mike West, PhD, PE Advantek Consulting, Inc

2 Package Unit Efficiency Factors Sensible and latent performance ratings Unit efficiency ratings (IPLV, SEER, or EER) Fan motor drive and efficiency rating Fan is 10 to 20% of unit power draw [kw] Fan is 20% to 50% of unit energy usage [kwh] Number of stages / capacity control Geographical location / climate Likelihood of maintenance Total life-cycle installed and operating costs including options

3 EER Rating Specification

4 Efficiency Ratings EER Energy Efficiency Ratio MBH per kw SEER Seasonal EER MBTU per kwh IPLV Integrated Part-load Value MBH per kw Energy Star light commercial HVAC equipment uses 7 10% less energy than standard equipment. Energy Star package units can save $3 to $4 per square foot over the life of the equipment. For example, a 12,000 square foot building using an ENERGY STAR qualified HVAC product, could save $36,000 to $48,000 over 15 years, more than enough to justify the upgrade cost.

5 Energy Star efficiency rating Units rated at 65,000 to 135,000 Btuh 11.0 EER or higher -and IPLV or higher Units rated at 135,000 to 250,000 Btuh 10.8 EER or higher -and IPLV or higher Three-phase equipment rated below 65,000 Btuh SEER 13.0 or higher Air conditioner EER ratings are measured at outdoor temperature of 95 F, indoor 80ºF db 67ºF WB or 50% Relative Humidity. IPLV takes into account the higher efficiency of air conditioning units at part load. IPLV is measured using ARI Standard weightings and provides more of an apples to apples comparison than EER alone. SEER was intended to rate efficiency over an entire cooling season, not a single outdoor temperature. In theory, SEER is calculated by total amount of cooling (Btu) over the entire season divided by the total Watt-hours it will consume. SEER is used only for units 5-tons and less.

6 SEER ratings In some cases manufacturer s simply rate SEER as x EER at 82 F outdoor (instead of ARI 95 F) The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82 F outdoor temperature, 80 F db and 67 F wb indoor entering air temperature by the Part Load Factor (PLF) of the system. (The PLF is supplied by the government.) The PLF is a measure of the cyclic performance (CD) of a system and is calculated as follows, where CD is Cyclical Data: PLF = (CD x 0.5) "The cyclic performance (CD) value in the above equation has been determined by the government to be 0.25." The government contends that the PLF should equal: (.25 x.5) = 0.875, which yields: PLF of 0.875

7 Rating Specifications

8 Savings Estimates / Quick Need estimated annual operating hours, cost of electricity. MBH unit size = Tons x 12 EER 1 = rating of standard efficiency unit EER 2 = rating of high efficiency Energy Star unit Hours = annual operating hours ~ 1.3 x CDD Rate = $ cost of electricity, demand and tax per kwh MBH EER 1 MBH EER 2 Savings = ( - ) x Hours x Rate

9 Capacity selection Avoid Oversizing Performance Ratings are at steady-state Larger units costs more & use more power Example: compare power of 2 units at full load 15 ton: 15.7 kw 17½ ton: 18.9 kw added cost of $1500 Added electric demand of 3.2 kw ~ $400 per year Documented sizing calculations should be performed using accepted ACCA or ASHRAE procedures. ACCA methods have sufficient built-in safety factors. Use ASHRAE design conditions. Don t exaggerate outdoor design temperatures by using the AHR 95 F test point, or an unrealistically low indoor space condition such as 70 or 72 F.

10 Load-calc Lessons Learned Perform an accurate hourly load calculation Use the correct project location weather data 1. Peak Sensible Load 2. Maximum Latent Load 3. Lowest SHR Reasonably estimate infiltration airflow ACH Or, if an hourly load calc is not feasible, calculate the cooling load at three design conditions: ASHRAE Fundamentals 2003 Chapter 27, Miami 0.4% F.2005 Chapter 28 data available on CD-ROM 1. Cooling: 91db / 78wb / 125 grains 2. Dehumidification: 83db / 79 wb / 145 grains 3. Latent-Part-Load: 75db / 72 wb / 116 grains

11 Equipment Specification Tips Use manufacturer s performance software or tables to determine actual unit capacity (don t use nominal) Select the model closest in capacity to the load Specify that TAB shall include supply air CFM, fan RPM, External SP, and EAT LAT OA CFM must meet ASHRAE 62, provide exhaust makeup, and pressurize the building 0.02 to 0.04 in.wg [5 to 10 Pa] Request prices - be able to support and defend your equipment specification with hard economics.

12 The importance of carefully selecting the design airflow The SHR of a DX package unit will try to follow it s capacity curve to match the SHR of the space load. Load SHR drops as the space humidity drops, yet equipment SHR increases as entering wet bulb drops. If airflow is too low, temperature may rise and energy is wasted. If airflow is too high, humidity may be excessive at times. Higher airflow increases fan kw, but cooling capacity also increases, so EER usually goes up at the higher fan speeds. However, too high a fan speed means the latent load will not be met at times and fan energy use will be excessive.

13 Air Delivery Considerations Air leakage and heat gain from ducts significantly reduce air-conditioning system efficiency. The insulation level of traditional ducting is typically only R-4 to R-6 (1.5 to 2.2 inches). Specify R-8 (2¾ to 3 inches) Larger ducts typically mean lower static pressure, less leakage and higher system efficiency, if well insulated. With no attention, duct leakage rates can be 10% to 15% of total system airflow, sometimes higher. Specify ASHRAE Leakage Class-3 on the design drawings Test and Balance the Unit and Duct System

14 Test and Balance Package Units are not Plug-and-Play Engineering observation of startup is a must. Set fan speed and airflow according to design engineers specifications. Verify rotation direction of fan. Check and adjust refrigerant charge according to manufacturer s procedure. Adjust and calibrate fresh air damper and linkage to obtain design amounts of fresh air. Properly install high-efficiency filters.

15 Commissioning Example: Motorized Fresh-air damper with Economizer

16 Commissioning Some problems can be identified in the design phase: sizing, supply and outside airflows, controls Most problems can be identified at the project site: 1. Leak-test curb and ducts under pressure 2. Calibrate thermostats and sensors 3. Check ceiling diffusers for short-circuits 4. Functional performance test in all modes 5. Operations and maintenance training 6. Checkup visits at 30 and 90 days

17 Equipment Selection Factory Equipment Options Select evaporative condenser option wherever available Motorized fresh-air damper with Economizer Dehumidification enhancements needed below SHR ~ 0.65 Face and bypass damper, heat pipes, liquid reheat, hot gas reheat Filter pressure drop sensor so filter losses remain low BACNET Communications interface Avoid High Static Drive Use static regain duct design, and VFD or staged air-volume with SP or LAT control DCV - Demand Controlled Ventilation based on return air CO 2 Field Installed LPA liquid pressure amplification for low ambient conditions EER-Plus desuperheater / subcooler for the adventurous Auxiliary Condenser - increased heat rejection is a plus

18 Stages and Capacity Control This unit has 1- compressor, thus 1 refrigerant circuit Single scroll compressor Digital Scroll TM provides variable capacity control

19 Stages and Capacity Control This unit has 2 compressors, but only 1 refrigerant circuit 1 2

20 Stages and Capacity Control This unit has 4 compressors and 4 refrigerant circuits, but only 2 control stages. Modification to 4 stages is simple

21 Model Selection This unit has a Thermostatic Expansion Valve (TXV) Evaporator coil TXV

22 Evaporative Condenser Wet condenser coil uses evaporative cooling like a cooling tower, except refrigerant flows inside copper tubes. Less condenser fan HP Energy savings are typically 20% - 30%, up to 40% in dry climates Highly climate dependent Near-peak versus off-peak operating hours and MC wet-bulb temperatures wb 10 to 30 degrees cooler than db Integrated water treatment system, chemical and/or ozone Stainless steel, copper, PVC, FRP Desuperheater coils not wetted

23 Evaporative Condenser - AAON

24 Savings Estimates / Calculator

25 Savings Estimates / Calculator Range is still 8.9 to 13.5 Estimate based on location and type Billed rate including kw demand and tax

26 Savings Estimates / Calculator Annual Hours of Operation to 900 hours to 1400 hours to 2000 hours to 2800 hours to 4000 hours

27 Savings Estimates / Calculator Hours of Operation = 1.3 x CDD

28 Savings Estimates / Calculator $ $3200 = $994 savings per year Cost of 10-ton high efficiency (EER 13.5) unit: $7,000 Cost of a standard (EER 10.3) typical unit: $5,000 Upgrade cost for a high-efficiency unit: $7,000 - $5,000 = $2,000 Payback period = $2,000 / $994 = 2 years to recover higher price Return on investment = $994 / $2000 = 49% every year for life of equipment

29 Savings Estimates / Calculator Lifetime savings for 5 units: $82,370 in today s dollars (15 years) assuming a 4.1% annual increase in electricity Cost of 5 units: 5 x $7,000 = $35,000 Benefit / Cost Ratio = 83,370 / 35,000 = 2.4

30 Market Availability ENERGY STAR Partner List Results Look for Product Manufacturers in a different Country and State: New Search Refine Search Results 1-7 of 7 All Countries All States All # A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Name Product Type Location Award Category (Year) Carrier Central ACs and Air-Source Heat Connecticut Corporation Pumps, Furnaces, Geothermal Heat Pumps, Light Commercial HVAC, Programmable Thermostats, Room Air Conditioners Daikin U.S. Light Commercial HVAC New York Corporation Goodman Manufacturing Company, L.P. Lennox Industries Incorporated Rheem-Ruud Manufacturing Central ACs and Air-Source Heat Pumps, Furnaces, Light Commercial HVAC, Room Air Conditioners Central ACs and Air-Source Heat Pumps, Furnaces, Light Commercial HVAC, Programmable Thermostats Central ACs and Air-Source Heat Pumps, Furnaces, Light Commercial HVAC, Programmable Thermostats Texas Texas Arkansas Trane Company Light Commercial HVAC Tennessee York International Central ACs and Air-Source Heat Oklahoma Corp. UPG Pumps, Furnaces, Light Commercial HVAC Go Excellence in Efficient Products(2003,2004,2005,2007) 1. Carrier 2. Daikin 3. Goodman 4. Lennox 5. Rheem-Ruud 6. Trane 7. York

31 Market Availability Carrier Centurion EER , SEER , to 5-tons Centurion EER , IPLV , 6 to 25-tons WeatherMaster EER 11.8 to 25-tons Goodman SEER 13 to 5-tons EER 11.5 to 7.5-tons Lennox Strategos EER , IPLV , to 20-tons L-Series EER 12.2 to 30-tons T-Class EER 11.0 to 25-tons S-Class EER 10.8 to 50-tons Trane Precedent SEER 15 to 5-tons, EER 11.5 to 10-tons Voyager Hi-E EER to 25-tons York Affinity SEER to 5-tons Predator EER 11.5 to 12½-tons

32 Savings Example / Quick MBH unit size = 20-Tons x 12 = 240 MBH EER 1 = rating of Lennox T-Class = 10.8 EER 2 = rating of Lennox Strategos = 12.6 Hours = annual operating hours ~ 1.3 x CDD = 3000 Rate = cost of electricity = $0.12 per kwh billed MBH EER 1 MBH EER 2 Savings = ( - ) x Hours x Rate Savings = ( - ) x 3000 x 0.12 $1,143 per year savings

33 Design-in Maintainability Numerous energy surveys clearly show that lack of preventative maintenance is by far the major cause of air conditioning performance degradation. Common and costly problems include: clogged, corroded cooling and condenser coils sizeable duct leaks and cabinet air leaks low refrigerant, even in brand-new units maladjusted or stuck air dampers un-calibrated or nonfunctioning controls or sensors Design for Easy Access Provide Manuals and Training

34 Model Selection Likelihood of maintenance is important. VS.

35 Model Selection filter compartment access door Ease of Maintenance Fiberglass pre-filters MERV-11 final filters Filter rack was specified to fit 2-inch pre-filters and 2-inch final filters. Angled position of top filters improves flow.

36 Refrigerant Charge Both Over- and Under-charging are common Even a 5% adjustment is worthwhile the air conditioning system can be performing below its capacity because of poor maintenance and maintain comfort while energy use increases. I don t see anyone really checking charge right, most technicians only do a touch method. I have even found 8 ounces overcharge on brand new units. [total charge is 5 to 8 pounds]

37 Preventative maintenance program critical to realizing rated performance for the life of the unit.

38 Lower Energy Costs with Rooftop Air-Conditioning Package Units Thank you! Mike West, PhD, PE Advantek Consulting Engineering, Inc.