ENERGY IMPACT OF COMMON RETRO- COMMISSIONING FINDINGS FOR COMMERCIAL BUILDINGS

Transcription

1 FINAL REPORT NCEMBT ENERGY IMPACT OF COMMON RETRO- COMMISSIONING FINDINGS FOR COMMERCIAL BUILDINGS SEPTEMBER 2009 Michael Chimack, Principal Investigator Noel Corral, Research Engineer University of Illinois at Chicago Davor Novosel National Center for Energy Management and Building Technologies

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3 FINAL REPORT NCEMBT NATIONAL CENTER FOR ENERGY MANAGEMENT AND BUILDING TECHNOLOGIES TASK 05-06: ENERGY IMPACT OF COMMON RETRO- COMMISSIONING FINDINGS FOR COMMERCIAL BUILDINGS SEPTEMBER 2009 Prepared By: Michael Chimack, Principal Investigator Noel Corral, Research Engineer University of Illinois at Chicago Davor Novosel National Center for Energy Management and Building Technologies Prepared For: U.S. Department of Energy William Haslebacher Project Officer / Manager This report was prepared for the U.S. Department of Energy Under Cooperative Agreement DE-FC26-03GO13072

4 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. NATIONAL CENTER FOR ENERGY MANAGEMENT AND BUILDING TECHNOLOGIES CONTACT Davor Novosel Chief Technology Officer National Center for Energy Management and Building Technologies 601 North Fairfax Street, Suite 250 Alexandria VA ii NCEMBT

5 TABLE OF CONTENTS EXECUTIVE SUMMARY PROJECT OBJECTIVE BACKGROUND Brief History of Commissioning Benefits of Commissioning Drivers for Commissioning Market Potential of Commissioning Adding to the Knowledge Base METHODOLOGY Literature Review Goals of Literature Survey Survey Process Building Modeling Simulation Software Building Types Building Models Building Loads Building Schedules Baseline HVAC Systems Baseline Economizer High-Limit Shutoff Baseline Ventilation Rates Building Summary Retro-commissioning Findings Weather Data Energy Analysis Economic Analysis Schedule HVAC Equipment Repair the Economizer (Minimum & Maximum Position) Implement a Zone Temperature Setpoint Setback Schedule Reset the VAV Minimum Flow to the Optimal Setpoint Implement a Supply Air Temperature Reset Implement a Condenser Water Temperature Reset Retrofit Supply Fan with a VFD All Measures Implemented iii

6 4. RESULTS Baseline Systems HVAC Operates during Unoccupied Hours Economizer Failed in Minimum Position Economizer Failed in Maximum Position Zone Temperature Setpoint Setback during Unoccupied Hours VAV Box Minimum Flow Setpoint Higher than Necessary Supply Air Temperature Reset is not Implemented Condenser Water Temperature Reset is not Implemented VAV System is Equipped with Inlet Vane Dampers All Findings Present DISCUSSION Literature Review Definitions of Types of Commissioning Commissioning Process and Participants Building Types and Climatic Issues Commissioning Tools Building Simulation in the Commissioning Process Literature Survey Conclusions Building Simulation Baseline Systems HVAC Operates During Unoccupied Hours Economizer Failed in Minimum Position Economizer Failed in Maximum Position Zone Temperatures are not Setback during Unoccupied Hours VAV Box Minimum Flow Setpoint Higher than Necessary Supply Air Temperature Reset is not Implemented Condenser Water Temperature Reset is not Implemented VAV System is Equipped with Inlet Vane Dampers Interactive Effects Summation of the Individual RCx Findings All Findings Present (AFP) Model Interactive Effects EnergyPlus Problems and Limitations Applicability of Simulation Results to General Building Population CONCLUSION iv NCEMBT

7 7. REFERENCES APPENDIX A EXPANDED SIMULATION RESULTS A1. Building Type: Office A1.1 RCx Finding: Baseline A1.2. RCx Finding: HVAC System Operates during Unoccupied Hours A1.3. RCx Finding: Economizer Failed in Minimum Position A1.4 RCx Finding: Economizer Failed in Maximum Position A1.5 RCx Finding: Zone Temperature Setback Not Implemented A1.6 RCx Finding: VAV Box Minimum Flow Setpoint Set Higher than Necessary A1.7 RCx Finding: Supply Air Temperature Reset Not Implemented A1.8 RCx Finding: VAV System Equipped with Inlet Vane Dampers A1. 9 RCx Finding: All Findings Present A2. Building Type: School A2.1 RCx Finding: Baseline A2.2 RCx Finding: HVAC System Operates during Unoccupied Hours A2.3 RCx Finding: Economizer Failed in Minimum Position A2.4 RCx Finding: Economizer Failed in Maximum Position A2.5 RCx Finding: Zone Temperature Setback Not Implemented A2.6 RCx Finding: All Findings Present A3. Building Type: Hospital A3.1 RCx Finding: Baseline A3.2 RCx Finding: HVAC System Operates during Unoccupied Hours A3.3 RCx Finding: Economizer Failed in Minimum Position A3.4 RCx Finding: Economizer Failed in Maximum Position A3.5 RCx Finding: Zone Temperature Setback Not Implemented A3.6 RCx Finding: VAV Box Minimum Flow Setpoint Set Higher Than Necessary A3.7 RCx Finding: Supply Air Temperature Reset Not Implemented A3.8 RCx Finding: Condenser Water Temperature Reset Not Implemented A3.9 RCx Finding: VAV System Equipped with Inlet Vane Dampers A3.10 RCx Finding: All Findings Present APPENDIX B BUILDING SIMULATION SCHEDULES v

8 LIST OF FIGURES Figure 1. Hospital Model Layout Figure 2. School Model Layout Figure 3. Hotel Model Layout Figure 4. Office Model Layout Figure 5. Baseline Hospital HVAC System Figure 6. Office Building HVAC System Figure 7. School HVAC System Figure 8. Baseline Hotel HVAC System Figure 9. RCx Finding Selection Process Figure 10. Chicago Temperature Joint Frequency Figure 11. Denver Temperature Joint Frequency Figure 12. Houston Temperature Joint Frequency Figure 13. Los Angeles Temperature Joint Frequency Figure 14. Phoenix Temperature Joint Frequency Figure 15. Baseline Energy Usage Figure 16. HVAC Operates during Unoccupied Hours Energy Impact Figure 17. HVAC Equipment Scheduling Energy Cost Savings Figure 18. Economizer Failed in a Minimum Position Energy Impact Figure 19. Economizer Repair Energy Cost Savings (Minimum Position) Figure 20. Economizer Failed in Maximum Position Energy Impact Figure 21. Economizer Repair Energy Cost Savings (Maximum Position) Figure 22. Zone Temperature Setback Not Implemented Energy Impact Figure 23. Zone Temperature Setpoint Setback Energy Cost Savings Figure 24. VAV Box Minimum Flow Setpoint Higher than Necessary Energy Impact Figure 25. VAV Box Adjustment Energy Cost Savings Figure 26. Supply Air Temperature Reset is not Implemented Energy Impact Figure 27. Supply Air Temperature Reset Energy Cost Savings Figure 28. Condenser Water Reset Not Implemented Energy Impact Figure 29. Condenser Water Temperature Reset Energy Cost Savings Figure 30. Inlet Vane Dampers Energy Impact Figure 31. Supply Fan VFD Retrofit Energy Cost Savings Figure 32. All Findings Present Energy Impact Figure 33. All Measures Implemented Energy Cost Savings Figure 34. Summation of RCx Findings vi NCEMBT

9 Figure 35. All Faults Model Results Figure 36. Interactive Effects vii

10 LIST OF TABLES Table 1. Floor Space Analysis of CBECS Data... 9 Table 2. Building Model Information Table 3. Design Building Loads Table 4. Hospital HVAC Configuration Table 5. Hospital Central Plant Controls Table 6. Hospital HVAC Controls (Patient and Procedure Zones) Table 7. Hospital HVAC Controls (Operating Zone) Table 8. Hospital HVAC Controls (Office Zones) Table 9. Office HVAC Configuration Table 10. Office HVAC Controls Table 11. School HVAC Configuration Table 12. School HVAC Controls Table 13. Hotel HVAC Configuration Table 14. Hotel HVAC Controls Table 15. Zone Ventilation Requirements Table 16. Hospital and Office Zone Ventilation Requirements Table 17. Hospital Building Summary Table 18. Office Building Summary Table 19. School Building Summary Table 20. Hotel Building Summary Table 21. Retrocommissioning Findings and Associated Measures Table 22. Testing Matrix Table 23. Climate Data for the Cities Selected Table 24. HVAC Equipment Scheduling Cost Estimates Table 25. Economizer Repair Cost Estimates Table 26. Zone Temperature Setpoint Scheduling Cost Estimates Table 27. VAV Box Minimum Flow Setpoint Adjustment Cost Estimates Table 28. Supply Air Temperature Reset Cost Estimates Table 29. Condenser Water Temperature Reset Table 30. VFD Retrofit Cost Estimates Table 31. Total Implementation Cost Table 32. Baseline Energy Usage Table 33. HVAC Operates during Unoccupied Hours Energy Impact Table 34. HVAC Equipment Scheduling Economic Analysis viii NCEMBT

11 Table 35. Economizer Failed in a Minimum Position Energy Impact Table 36. Economizer Repair Economic Analysis (Minimum Position) Table 37. Economizer Failed in Maximum Position Energy Impact Table 38. Economizer Repair Economic Analysis (Maximum Position) Table 39. Zone Temperature Setback Not Implemented Energy Impact Table 40. Zone Temperature Setpoint Setback Economic Analysis Table 41. VAV Box Minimum Flow Setpoint Higher than Necessary Energy Impact Table 42. VAV Box Adjustment Economic Analysis Table 43. Supply Air Temperature Reset is not Implemented Energy Impact Table 44. Supply Air Temperature Reset Economic Analysis Table 45. Condenser Water Temperature Reset Not Implemented Energy Impact Table 46. Condenser Water Temperature Reset Economic Analysis Table 47. Inlet Vane Dampers Energy Impact Table 48. Supply Fan VFD Retrofit Economic Analysis Table 49. All Findings Present Energy Impact Table 50. All Measures Implemented Economic Analysis Table 51. Hospital Energy Intensity Table 52. Office Energy Intensity Table 53. School Energy Intensity Table 54. Hotel Energy Intensity Table 55. Annual Hours of Economizer Availability Table 56. RCx Findings Modeled Simultaneously (AFP Model) ix

12 GLOSSARY AABC Associated Air Balance Council AFP All Findings Present ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers BAS Building Automation System BCA Building Commissioning Association C Celsius CBECS Commercial Buildings Energy Consumption Survey CCx Continuous Commissioning CFM Cubic Feet per Minute ChW Chilled Water CV Constant Volume Cx Commissioning DOE US Department of Energy DX Direct Expansion EIA Energy Information Administration F Fahrenheit HVAC Heating, Ventilating and Air Conditioning HW Hot Water LBNL Lawrence Berkeley National Laboratory LEED Leadership in Energy and Environmental Design NEBB National Environmental Balancing Bureau OA Outside Air PECI Portland Energy Conservation, Inc. PTAC Packaged Terminal Air Conditioner Rx Re-commissioning RCx Retrocommissioning VAV Variable Air Volume VFD Variable Frequency Drive x NCEMBT

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15 EXECUTIVE SUMMARY The incorporation of commissioning in a new building construction or retro-commissioning in existing buildings has the potential to not only result in significant energy savings, but also extend building equipment life and improve occupant comfort by ensuring that building systems operate the way they were designed or intended. The objective of this project is to affect market transformation with respect to commissioning and retro-commissioning by improving access to the existing knowledge base regarding these activities and by adding to the knowledge base with quantitative estimates of their energy savings potential. The course towards market transformation as it pertains to commissioning utilized a three-stage approach. First, a literature survey was conducted that identified current practices and quantified potential costs and savings associated with commissioning and retro-commissioning in the commercial sector. Second, simulation software was used to quantify the potential energy impact resulting from common retro-commissioning findings and to determine the economic benefit of resolving these building faults. Finally, training materials were developed with the purpose to be used in educating key decision makers such as building owners and operators, engineering and design firms, and government officials, including code officials, in the benefits and economic feasibility of commissioning and retrocommissioning commercial buildings. The major findings of this project were: Literature Review: A total of 104 research and technical studies concerning commissioning was collected and summarized. The literature survey identified the primary types of commissioning, followed by the multi-phase process and participants in the process. RCx Findings Modeling: Eight RCx findings were simulated using EnergyPlus simulation software. The RCx findings were simulated in four different building types (hospital, office, school and hotel) across five different climates (Chicago, Denver, Houston, Phoenix and Los Angeles). The impact of the RCx findings on energy consumption was reported on a per square foot basis (energy intensity). When compared to baseline buildings, the change in energy intensity due to the RCx findings was found to have a widely varied impact on energy consumption. The change in energy intensity ranged from Btu/ft2 to Btu/ft2. Energy cost savings ranged from -$0.04/ft2 to $0.89/ft2. 1

16 1. PROJECT OBJECTIVE 1. PROJECT OBJECTIVE The objective of this project is to affect market transformation with respect to commissioning and retrocommissioning by improving access to the existing knowledge base regarding these activities and by adding to the knowledge base with quantitative estimates of their energy savings potential. The lack of understanding of the benefits of commissioning and the cost of commissioning contribute to the barriers affecting the market penetration of commissioning. Of concern to building owners and developers is primarily the cost associated with the commissioning process and the benefits, both measured and perceived. The ability for those benefits to continue after the commissioning process is also of concern to building owners, operators, maintenance personnel and occupants. Furthermore, there is limited information on quantifying the energy-related benefits of commissioning broader terms of climate or building type, either from case studies or estimated. To accomplish the project objective, a two-step process was completed: 1. Literature Review Available literature, research papers and technical studies, concerning the subject of commissioning were collected as part of the literature review. The literature search included defining the types of commissioning activities that are currently in use, outlining the commissioning process, identifying building types and climates analysis methods, and compiling commissioning tools that are available. 2. Benefits Quantification through Building Modeling The benefits of the RCx findings were quantitatively evaluated through building simulation. The technologies were simulated across a wide range of climate types, building types, and occupancy densities. An analysis of energy intensity change and associated energy cost savings (when compared to baseline systems) demonstrated the quantifiable benefits of the RCx activities and identified where and in what type of buildings the activities have the greatest potential benefit. 2 NCEMBT

17 2. BACKGROUND 2. BACKGROUND Commissioning (Cx) a building or systems within a building (e.g. decentralized heating, ventilating and air conditioning systems) is a method of reducing risk by ensuring that proper systems operation is achieved for the building owner. In essence, the building owner gets what he paid for in the design intent documentation. This is ensured through verifying that the design intent is satisfied before and during the construction process. Functional performance testing of buildings systems serves as the validating step prior to owner occupancy. It confirms that the building is operating as it was designed, which minimizes building operational costs, while maintaining a healthy indoor environment. Retro-commissioning (RCx) occurs after construction and occupancy, as an independent process. The focus of RCx projects is typically high energy-using systems such as mechanical equipment, with the goal of: Minimizing operational costs by returning equipment to design intent specifications Maximizing operational benefits and equipment longevity by implementing a proper operations and maintenance program 2.1 BRIEF HISTORY OF COMMISSIONING Building commissioning has been a standard in Europe for many years, and has been employed with other management practices in North America since the early to mid-1970s (NEMI 2002). The energy crisis of the 1970s served as a catalyst for the development of new methods and practices that increased energy efficiency. The initial version of commissioning introduced during this decade was a fragment of the comprehensive process used today. The process tended to focus on specific building systems, generally mechanical, and lacked a holistic approach. The enactment of the U.S. Energy Policy Act of 1992 required each new Federal building to meet or exceed the energy building standards established by the U.S. Department of Energy (USDOE). This affected the development of commissioning by transforming it from a component based process to a whole building process, thus the term whole building commissioning. The systems generally commissioned as part of the whole building commissioning process include: Mechanical Heating, Ventilation and Air-Conditioning (HVAC) Building envelope Electrical Fire suppression Plumbing Irrigation Laboratory fume hoods, gas control Other factors contributed to the adoption of whole building commissioning. Increasingly complex systems that required careful coordination to install and operate emerged. Also, poor design and construction management practices that resulted in high change order costs, overrun schedules and substandard performing buildings, increased the application of commissioning. Although whole building commissioning has gained support in recent years, it has yet to become a common building practice. 3

18 2. BACKGROUND Currently less than 5 percent of new construction is commissioned and less than 0.03 percent of existing buildings are commissioned annually. However, up to 58 percent of the existing building stock is considered to be commissionable (NEMI 2001). 2.2 BENEFITS OF COMMISSIONING The benefits from incorporating commissioning into new construction and retro-commissioning existing buildings have been documented throughout the literature, through modeling, market analyses, and case studies. Commissioning benefits the building owner, operator, occupants, architect and construction project manager as follows: Improved occupant comfort Increased energy efficiency Reduced operation and maintenance costs Longer equipment life expectancy Reduced energy consumption Reduced energy costs Additional construction management oversight Fewer change orders Commissioning is generally provided by an independent third-party engineering company. The commissioning provider serves the owner s representative to ensure that the installed systems meet the owner s requirements. The commissioning provider is typically hired by the owner. However, it is not uncommon for the architect or general contractor to do the hiring. 2.3 DRIVERS FOR COMMISSIONING There are several factors driving the market to adopt commissioning as a standard building practice. On the national and regional level, higher energy costs, energy efficiency mandates and building energy codes have aided in driving the market towards commissioning. Initiatives to encourage commissioning, such as making commissioning a requirement to obtain a Leadership in Energy and Environmental Design (LEED) certification (Green Building Rating System, developed by the U.S. Green Building Council) work to drive the market towards commissioning. In addition, organization and associations work to promote commissioning to the market. These organizations include (but not limited to): American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Building Commissioning Association (BCA) Associated Air Balance Council (AABC) National Environmental Balancing Bureau (NEBB) Portland Energy Conservation, Inc. (PECI) At the building level, the drivers for commissioning are less market related and tend to be more consumer specific. In addition, the reasons for commissioning differ for new construction and existing buildings. A recent study conducted by Mills et al. (2004) that 4 NCEMBT

19 2. BACKGROUND analyzed 224 buildings that had undergone commissioning revealed the top three drivers for new construction buildings to be (based on 30 projects): Ensure system performance (energy and non-energy related systems) Ensure or improve thermal comfort Ensure adequate indoor air quality According to the same study, the top drivers for existing building commissioning included (based on 85 projects): Obtain energy savings Ensure system performance Improve thermal comfort 2.4 MARKET POTENTIAL OF COMMISSIONING Estimations have been made to the market potential for commissioning and the resulting energy savings for both new and existing construction. The energy savings for commissioning even 1 percent annually of existing commercial buildings (greater than 25,000 square feet) is estimated to be 3,730 billion Btu annually for 285 million square feet, at a cost of $0.17 per square foot (PECI 2004). For new construction, the costs are slightly higher at $0.42 per square foot, but commissioning 7 percent of all new buildings would result in 341 billion Btu of annual energy savings (PECI 2004). However, there are issues that prohibit the adoption of commissioning in each process, commissioning and retrocommissioning: cost to commission and cost/benefit data to validate the use of commissioning. 2.5 ADDING TO THE KNOWLEDGE BASE The objective of this project is to affect market transformation with respect to commissioning and retrocommissioning by improving access to the existing knowledge base regarding these activities and by adding to the knowledge base with quantitative estimates of their energy savings potential. The literature survey was part one in a three-stage approach to identifying and addressing market transformation issues with respect to commissioning and retro-commissioning. A survey of current literature available on the topic was completed that identified current practices and attempted to quantify potential costs and savings associated with commissioning and retro-commissioning in the commercial sector. The benefits of adopting commissioning practices into both new construction and existing buildings is addressed, along with current tools that are available to assist in the commissioning process. A significant knowledge gap identified by the literature review was that there is limited information on quantifying the energy-related benefits of commissioning in broader terms of climate or building type, either from case studies or estimated. The focus of the second phase of the three-stage market transformation approach was to address this specific knowledge gap. The second stage of the approach concentrated on utilizing simulation software to quantify the energy impact of common RCx findings (building faults/deficiencies) and determining the economic benefits of retro-commissioning measures used to resolve the findings by system and as a building as a whole. The RCx findings selected to be modeled include: HVAC Operates during unoccupied hours It is not unusual for commercial buildings to operate around the clock 24 hours a day 7 days a week due to continuous occupancy. 5

20 2. BACKGROUND However, in the majority of cases, these buildings are occupied only for a portion of the day and are unoccupied for the rest, typically after business hours. To conserve energy, the HVAC system is typically turned off when people are not present in the building. This typically occurs during nights and weekends. The HVAC system is one of the most energy intensive building systems to operate. Therefore, the operation of the HVAC system is limited to the period of time when occupants are present. Failure to do so typically results in wasted energy and increased energy costs. Economizer failure (open/closed) Air side economizers save energy in buildings by using outdoor air to cool the indoor space. Savings occur when the building s zones call for cooling and the outdoor air is sufficiently cool enough to supplement or replace mechanical cooling. The economizer utilizes a damper mechanism to control the flow of the outside air into the system. Several causes can result in the failure of the damper systems including: broken damper linkages, corrosion, and control and sensor failure. The increase in energy consumption resulting from economizer failure depends on the type of failure. A failure in the closed position will limit the amount of cooling the economizer can provide, increasing mechanical cooling costs. A failure in the open position will allow an excess amount of outside air to enter the system increasing the need for mechanical cooling and also negatively affecting the system s ability to deliver conditioning. Zone temperature setpoint are not setback during unoccupied hours The majority of commercial buildings are not occupied continuously, meaning 24 hours a day 7 days a week. When the building is occupied, the HVAC system must condition the air supplied to the zones to meet a specified temperature setpoint. When the building/zone is unoccupied, the temperature setpoint can be setback to a lower temperature (heating setpoint) or a higher temperature (cooling setpoint), depending on the requirements of the zone. Setting the temperature required by the zone to a less demanding temperature setpoint reduces the conditioning load of the HVAC system. Conversely, failure to do so typically results in increased energy usage. VAV box minimum flow setpoint is higher than necessary A Variable-Air Volume (VAV) box varies the amount of conditioned air supplied by the HVAC system to the zone depending on the demands of the space. A VAV box that is supplying too much air to a zone will end up overcooling the zone. This then results in wasted energy on the heating side, because the heating coil would be energized to compensate for the overcooling. In addition, the excess air will increase the fan power consumption. Setting the VAV box to its optimum minimum flow setpoint reduces simultaneous heating and cooling and fan energy consumption. Hot water supply temperature supply reset is not implemented A hot water supply temperature reset is an energy-saving feature for hot water boilers. The hot water reset control measures the outdoor air temperature and modulates the temperature (up or down) of the hot water supplied to the heating coils. Failure to implement a hot water temperature reset holds the hot water supply temperature to a fixed setpoint. As a result, the boiler maintains a temperature setpoint that is higher than what the heating load demands, resulting in increased energy consumption. Chilled water supply temperature reset is not implemented A chilled water supply temperature reset is an energy-saving feature for chilled water systems, specifically chillers. The chilled water reset control measures the outdoor temperature and modulates the temperature (up or down) of the chilled water supplied to the cooling coils. Failure to implement a chilled water temperature reset holds the chilled water supply temperature to a 6 NCEMBT

21 2. BACKGROUND fixed setpoint. As a result, the chiller maintains a temperature setpoint that is lower than what the cooling load demands, resulting in increased energy consumption. Supply air temperature reset is not implemented A supply air temperature reset is an energy-saving strategy for HVAC systems. The supply air temperature reset control raises the supply air temperature at part-load conditions to save compressor and/or reheat energy. Failure to implement a supply air temperature reset holds the supply air temperature to a fixed setpoint. As a result, the supply air temperature setpoint is lower than what the cooling load demands, resulting in increased energy consumption. Condenser water temperature reset is not implemented A condenser water temperature reset is an energy-savings strategy for cooling plants. The cooling tower is set to follow the outdoor wetbulb temperature within a given approach, usually 5-7 F. As the outdoor wetbulb temperature decreases, so to does the cooling water supplied to the chiller from the cooling tower, increasing the efficiency of the chiller. This comes at a cost of increased energy usage by the cooling tower fans. Because the cooling tower is required to meet a lower condenser water setpoint, the fans are required to meet a greater cooling load. However, the energy savings associated with the increased efficiency of the chiller generally outweighs the energy increase of the cooling tower fans. Failure to implement a condenser water temperature reset holds the cooling water temperature to a fixed setpoint. As a result, the chiller efficiency decreases resulting in increased energy consumption. VAV system is equipped with inlet vane dampers VAV systems equipped with constant speed fans utilize inlet vane dampers to modulate the flow through the HVAC system. To control the flow through the system, the inlet vane damper opens and closes to regulate the amount of air moving through the system, while the speed of the fan remains unchanged. To increase the system efficiency, the combination of constant speed fans and inlet vane dampers is often replaced with a fan driven with a variable frequency drive (VFD). The VFD allows the speed of the fan to vary depending on the volume of air that is required by the system. The ability to modulate the speed of the fan results in energy savings when compared to the operation of a constant speed fan, especially during part-load operation. The third and final stage involved developing training and outreach materials to be used in educating building owners and operators, engineering and design firms, and government officials, including code officials, in the benefits and economic feasibility of commissioning and retro-commissioning commercial buildings. Through demonstration of the range of benefits that can be achieved through the commissioning and retro-commissioning of buildings, quantifying the benefits by climate region and commercial building type, key decision makers will be informed and educated, leading to market transformation. 7

22 3. METHODOLOGY 3. METHODOLOGY 3.1 LITERATURE REVIEW Goals of Literature Survey The benefits from incorporating commissioning into new construction and retro-commissioning existing buildings have been documented throughout the literature, through modeling, market analyses, and case studies. However, building owners, developers, and operators are not as aware or convinced of the benefits that commissioning and retro-commissioning can offer, are concerned with first costs and the added cost of commissioning or retro-commissioning buildings, and have not been convinced of the cost/benefit of commissioning. This literature survey examined not only the processes for each type of commissioning identified (commissioning, retro-commissioning, and continuous commissioning) but also includes market analyses, tools that are used in determining savings (both energy and non-energy), and the value of persistence in the commissioning process. By examining current practices and the existing knowledge base in the field of commissioning, the areas that need further evaluation or research can be identified. This evaluation of the resources and information available will help in the overall goal of market transformation in the inclusion of commissioning as part of the standard building process for all buildings Survey Process The literature survey was performed to determine the current practices in the field of building commissioning, as well as the developing tools and methods to encourage the use of commissioning in the existing building stock. The focus was on buildings and practices in the United States, current market trends and predicted market potential. First the types of commissioning had to be identified, followed by the multi-phase process and participants in the process. The types of buildings considered to be candidates for commissioning and potential climate types that may need to be addressed were also included in the survey. Existing and developing tools and methods for evaluation of energy and cost related benefits of commissioning were identified. Finally the benefits of commissioning on the commercial (including institutional) building sector are presented along with the documented costs associated with implementing commissioning. Throughout the literature survey, the major gaps in the current published literature were identified as a means to determine where additional research and education may be of benefit. 8 NCEMBT

23 3. METHODOLOGY 3.2 BUILDING MODELING Simulation Software Several building energy simulation software systems were evaluated to determine which was most appropriate for simulating the RCx findings. EnergyPlus was chosen as the most appropriate simulation software for several reasons: 1. System Configuration Flexibility Because building components are created individually and can arranged as needed, EnergyPlus is more flexible than the simulation programs it was designed to replace (BLAST, DOE-2.1E, and equest). Furthermore, component control can better be specified in EnergyPlus. 2. Reporting Capabilities EnergyPlus can be configured to report on a wide range of simulation variables and can output a wide range of report formats. 3. Available at no Cost The fact that EnergyPlus can be downloaded free from the Department of Energy means that models developed for this report can be distributed and utilized without the need for expensive software Building Types An analysis of the 2003 data showed nine building use categories that individually accounted for at least five percent of the total floor space of the commercial building population. Building categories and their corresponding floor space usage are shown in Table 1. Building Type Total Estimated Floor Space (sq. ft.) Table 1. Floor Space Analysis of CBECS Data Percentage of Total Floor Space Office 12,208,003,656 19% Warehouse 10,077,856,132 16% Includes Non-Refrigerated & Refrigerated Education 9,873,750,179 15% Retail 4,316,826,746 7% Health Care 4,145,713,757 6% Includes Outpatient, Inpatient & Nursing Lodging 4,113,125,465 6% Service 4,050,413,295 6% Public Assembly 3,939,151,925 6% Religious Worship 3,754,342,877 6% Notes Food 2,908,661,935 4% Includes Service & Sales Vacant 2,567,160,329 4% Public Order & Safety 1,089,881,723 2% Other 1,084,535,860 2% Laboratory 653,707,418 1% Totals 64,783,131, % 9

24 3. METHODOLOGY Of the building use categories that accounted for at least five percent of the total population floor space, four were selected as candidates for modeling: office, education, health care and lodging. The four building types selected for modeling represent 47 percent of the total floor space within the U.S. commercial building stock, according to CBECS data. Five categories were eliminated from consideration for the following reasons: Warehouse Eliminated due to the fact that non-refrigerated warehouses have rudimentary HVAC systems and minimal internal loads (with the possible exception of lighting). Because non-refrigerated warehouses have rudimentary HVAC systems, a less complex retrocommissioning process would be considered instead of the typical version. Refrigerated warehouses have special internal temperature requirements that are unique to each warehouse, making a generalized model difficult to construct. Retail Eliminated due to the wide variety of retail building types, loads and schedules. The wide variety demonstrated by this building category made constructing a generalized building model impossible. Service The EIA includes any building where a service is provided (other than food or retail services) in this category. Some examples of buildings in this category include: vehicle repair, dry cleaning, gas station and copy center. These internal loads in these buildings vary widely making a generalized model impossible. Public Assembly The EIA includes any building where public assemblies take place. Some examples of buildings in this category include: community centers, sports arenas, libraries and transportation terminals. These internal loads, HVAC system types and building construction types in these buildings vary widely making a generalized model impossible. Furthermore, schedules vary widely from building to building. Religious Worship These buildings tend to be used for relatively limited time periods. Lighting, plug loads and HVAC systems may or may not operate during periods when the buildings are unoccupied, making an accurate estimation of building loads impossible for simulation purposes. 10 NCEMBT

25 3. METHODOLOGY Building Models Four main commercial building types were simulated. Table 2 shows building types and general information about the models. Building Type Healthcare Education Lodging Office Building Description The hospital is representative of a large modern research hospital This is representative of a common elementary school This is representative of a modern 80 room hotel This building is representative of a small to medium office building Building Area (ft 2 ) Table 2. Building Model Information Floors Number of Zones Zone Types Area (ft 2 ) % Area by Zone 199, Patient Rooms 87,382 44% Procedure/Recovery 44,966 23% Office/Administration 44,966 23% Operating Rooms 22,478 11% 22, Classrooms 13,482 59% Gymnasium 4,885 21% Library/Media Center 2,195 10% Offices 2,195 10% 23, Hotel Rooms 21,542 93% Office/Reception 1,592 7% 50, Exterior Offices 20,619 41% Interior Open Offices 22,596 45% Conference Rooms 7,424 15% 11

26 3. METHODOLOGY Information for all building types was collected from a number of sources: Energy Information Administration (EIA) Commercial Buildings Energy Consumption Survey (CBECS) Database The database was used as a source of the bulk of building model data including, but not limited to building area, number of floors, zone type area breakdown, exterior glazing type and glazing area. Building prototypes developed by Huang et al. (1991) at the Building Technologies Division of Lawrence Berkeley National Laboratory (LBNL) in the early 1990s. Because the models were developed for DOE2, they were not immediately applicable for use in EnergyPlus. Furthermore, due to the age of the models, they do not accurately reflect modern building practices. LBNL is in the process of updating and translating these models to a format compatible with EnergyPlus, however, the updated models are not currently ready for release. Whitestone Building Maintenance and Repair Cost Reference This source was used as a check on much of the information collected from the CBECS database (Lufkin et al. 2004). It also served as a source for determining appropriate building materials and constructions. All buildings comply with code requirements defined in ASHRAE Standard and ASHRAE Standard Code compliance includes, but is not limited to the following building aspects: Building envelope insulation values Fan power limitations Water heating performance Lighting power density Minimum ventilation rates for all zone types Diagrams of the basic layout of each building type are shown in Figure 1 through Figure 4. North is indicated in each figure by the directional arrow. Figure 1. Hospital Model Layout 12 NCEMBT

27 3. METHODOLOGY Figure 2. School Model Layout Figure 3. Hotel Model Layout 13

28 3. METHODOLOGY Figure 4. Office Model Layout The layouts of each model were created with directional neutrality in mind, i.e. each building was created so that its energy consumption would be independent of the orientation of the building with respect to the cardinal directions. The hospital and office models are direction neutral, the school and hotel buildings are not completely neutral, but are as close as possible considering the realities of building zones (all hotel rooms need exterior exposure & all classrooms need exterior exposure). In all cases, the number of zones in each building was minimized as much as possible while still maintaining acceptable building modeling practices (separating interior and exterior zones, separating zones exposed to different cardinal directions, etc). Similarly, the types of spaces incorporated into the models were minimized as much as is practicable. For each building type, the most important zone types and those with the largest usage by area were identified and included in the models. Therefore, specialty zone types such as bathrooms, mechanical spaces, server rooms, etc. were not included in the models. Furthermore, in practice, these specialty type zones are likely to have special HVAC systems installed that are separate from general HVAC systems due to their unique ventilation requirements and loads. Building simulations were further simplified by assuming that that all interior dividers between zones are adiabatic. This is a reasonable assumption to make, as all zones within all buildings will be conditioned to similar temperature set points. Therefore, heat transfer between zones can be considered to have a negligible affect on energy balances within the building. To simplify model generation and ensure that comparisons between results from different climate zones can be compared accurately, building models are similar from climate zone to climate zone. Special construction practices that may exist in each climate zone were not incorporated into the models. Building construction for all models consists of a standard brick wall with air space, insulation and interior cinder block wall system for all buildings. This system is common in all climate zones and is standard for commercial buildings. The main difference in construction for this type of wall system across climate zones is the presence and thickness of rigid insulation adjacent to the airspace. For the purposes of this project, the thickness of the insulation layer was specified so that the buildings meet minimum building envelope requirements (ASHRAE ) for each climate zone simulated. 14 NCEMBT

29 3. METHODOLOGY Building Loads Design occupancy levels for all simulated zones were determined utilizing Default Occupancy Density and Estimated Maximum Occupancy rates found in Table 6-1 and Table E-1, respectively, in ASHRAE Design lighting load densities were determined using the Space-by-Space Method in ASHRAE The Space-by-Space Method specifies allowable lighting power densities for spaces in all building types, according to how a space will be used. Equipment power densities were drawn largely from building models developed by Joe Huang at LBNL (Huang et al. 1991). Table 3 details all design loads for all buildings. Table 3. Design Building Loads Building Type Zone Type Equipment (W/ft 2 ) Lights (W/ ft 2 ) Max Occupancy (people/thousand ft 2 ) Hospital Patient Rooms Procedure/Recovery Office/Administration Operating Rooms School Classrooms Gymnasium Library/Media Center Offices Hotel Hotel Rooms Office/Reception Office Exterior Offices Interior Open Offices Conference Rooms Building Schedules Design occupancy levels, lighting and equipment power loads are modified during the simulation by associated schedules. The schedules for the office, school and hotel were largely drawn from previous simulation work completed by the University of Colorado (Brandemuehl et al. 2001). Schedules for several zones were developed specifically for this study. These zones include: Hospital all zones Office conference room School gym and library Hotel office/lobby All schedules for the school were subject to the constraint that the school was assumed to be unoccupied between June 15th and August 31st (summertime). Zone equipment, lighting and HVAC systems were not operated during this time. 15

30 3. METHODOLOGY All schedules for the hotel were subject to the constraint that room vacancies were assumed to take place on a rotating basis. When a room was considered vacant for the simulation, the following constraints applied to affected zones: Occupancy in the zone was set to zero. All zone equipment loads were turned off. Lighting loads were turned off. Room air conditioners, Packaged Terminal Air Conditioner (PTACs), were turned off. Ventilation air supply from the central HVAC system was not turned off. Room vacancies were simulated by rotating periods where the rooms were unoccupied. Rooms on the first floor were simulated as vacant Sundays and Mondays of every week. Second floor rooms were simulated as vacant Tuesdays and Wednesdays of every week. Third floor rooms were simulated as vacant Thursdays and Fridays of every week. All floors and rooms were assumed to be occupied (not vacant ) during Saturdays. Schedules for occupancy, lighting and equipment loads are shown Appendix B Baseline HVAC Systems The baseline HVAC systems represent the end result of the retro-commissioning process, meaning that they are free of faults and the energy conservation measures have been implemented. The retrocommissioning findings (deficiencies) were simulated as modifications to the baseline HVAC systems. The initial approach of this project was to equip the baseline models with a built-up single duct Variable Air Volume (VAV) HVAC system type, however, this proved to be an inadequate approach in practice. The analysis of the CBECS database generated office, hotel and school building profiles that were smaller than would normally be installed with both a central chilled and hot water system. Furthermore, modern hotels are equipped with built-up single duct Constant Volume (CV) systems. As a result of these issues, the baseline HVAC system in each building type differs. Hospital Building The hospital building was simulated with a built-up single duct VAV system as a baseline system. The zones in the building are grouped according to zone type (patient zones, operating zone, procedure/recovery zones and office zones). One air handling system serves each group of zone types. This system configuration required a minimum number of separate systems (thereby reducing simulation complexity) while still enabling economizer/outside Air (OA) controls to adequately meet the varied ventilation requirements of each type of zone. Table 4 shows the configuration of each zone and corresponding HVAC system. 16 NCEMBT

31 3. METHODOLOGY Table 4. Hospital HVAC Configuration Zone Name Zone Type Connected HVAC System 1E Patient Rooms Patient Zones VAV System 1S Patient Rooms 1W Patient Rooms 1N Patient Rooms 2E Patient Rooms 2S Patient Rooms 2W Patient Rooms 2N Patient Rooms 3E Patient Rooms 3S Patient Rooms 3W Patient Rooms 3N Patient Rooms 4E Patient Rooms 4S Patient Rooms 4W Patient Rooms 4N Patient Rooms 5E Patient Rooms 5S Patient Rooms 5W Patient Rooms 5N Patient Rooms 1C Operating Rooms Operating Zone VAV System 2C Procedure Rooms Procedure Zones VAV System 3C Procedure Rooms 4C Offices Office Zones VAV System 5C Offices Figure 5 shows the basic baseline VAV system for the hospital including a single air handler and the central boiler and chilled water plants, which are common to all four air handlers. The hospital is the only building type equipped with humidifiers as it is the most likely to have humidity control in actual systems. The hospital building type was also the only building equipped with an OA preheating coil. The large OA fraction required for the hospital necessitated the preheating coil to provide cooling coil freeze protection. To simplify simulations, baseboard radiation was not used in this model. 17