APPLICATION AND DESIGN OF AIR-TO-AIR VARIABLE REFRIGERANT FLOW SYSTEMS by PAUL WICOFF B.S., Kansas State University, 2010 A REPORT submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Architectural Engineering and Construction Science College of Engineering KANSAS STATE UNIVERSITY Manhattan, Kansas 2010 Approved by: Major Professor Julia Keen Abstract This report addresses the operation, use, and design of air-to-air variable refrigerant flow systems, also known as VRF. Relatively new to the United States, these HVAC systems have potential to reduce energy consumption and utility costs in the correct applications. Although useful in many applications, the best building types for VRF are those requiring a large number of zones and with low ventilation air requirements. The report explains design and system selection considerations and accordingly presents two flowcharts to help designers implement this system. To show how the system compares to traditional technologies in terms of efficiency and cost, the report presents results from several studies comparing VRF to other systems. In addition, an energy modeling study is conducted to clarify the effect of climate on the system; this study established air-to-air VRF as having highest energy consumption in dry, southern climates, based on energy use and operating costs. With this report, HVAC designers can learn when air-to-air VRF is an acceptable method for providing heating and cooling in a building. Table of Contents List of Figures ................................................................................................................................. v  List of Tables ................................................................................................................................ vii  Acknowledgements ...................................................................................................................... viii  Chapter 1 - Introduction .................................................................................................................. 1  1.1 What is Variable Refrigerant Flow ....................................................................................... 1  1.2 Reasons for Slow Adoption in the United States .................................................................. 4  1.3 Advantages ............................................................................................................................ 6  1.4 Disadvantages ....................................................................................................................... 9  1.5 Useful VRF Applications .................................................................................................... 11  Chapter 2 - Operation.................................................................................................................... 13  2.1 Major Equipment and Components ................................................................................... 15  2.1.1 Outdoor Components .................................................................................................. 15  2.1.2 Indoor Components ..................................................................................................... 18  Chapter 3 - Design ........................................................................................................................ 24  3.1 Heat Pump or Heat Recovery System ................................................................................ 24  3.2 Sustainability ..................................................................................................................... 25  3.3 Code Compliance ............................................................................................................... 28  3.4 Latent Heat ......................................................................................................................... 30  3.5 Building Load Profile and Unit Selection .......................................................................... 31  3.6 Piping ................................................................................................................................. 32  3.7 Power and Maintenance Accessibility ............................................................................... 33  3.8 Controls .............................................................................................................................. 33  3.9 Specifications ..................................................................................................................... 34  3.10 System Completion and Commissioning ......................................................................... 35  Chapter 4 - System Selection ........................................................................................................ 37  4.1 Zoning ................................................................................................................................ 37  4.2 Refrigerant ......................................................................................................................... 38  4.3 Climate ............................................................................................................................... 38  iii 4.4 Ventilation ......................................................................................................................... 39  4.5 Costs ................................................................................................................................... 42  4.6 Building Space Allocation ................................................................................................. 43  Chapter 5 - Comparison of VRF to Conventional Systems .......................................................... 45  5.1 VRF vs. Chiller/Boiler Hydronic Systems ........................................................................ 45  5.2 VRF vs. Conventional DX Systems .................................................................................. 46  5.3 VRF vs. Heat Pump Systems ............................................................................................. 48  5.4 VRF vs. VAV Systems ...................................................................................................... 49  Chapter 6 - Climate Study............................................................................................................. 51  Chapter 7 - Recommendations and Conclusion ............................................................................ 58  Bibliography ................................................................................................................................. 61  Appendix A - Design Flowchart ................................................................................................... 64  Appendix B - Latent Heat ............................................................................................................. 66  Appendix C - Example Specification ........................................................................................... 69  Appendix D - System Selection Flowchart ................................................................................... 87  Appendix E - Climate Study Building Floorplans ........................................................................ 89  Appendix F - Climate Study TRACE 700 Values ........................................................................ 93  Appendix G - Releases ................................................................................................................ 114  iv List of Figures Figure 1.1 VRF Systems ................................................................................................................ 2  Figure 1.2 Self-balancing Heat Recovery System. ........................................................................ 4  Figure 2.1 The Refrigeration Cycle. ............................................................................................ 14  Figure 2.2 The Heat Pump Cycle. ................................................................................................ 15  Figure 2.3 Outdoor Units. ............................................................................................................ 16  Figure 2.4 Indoor Units. ............................................................................................................... 19  Figure 2.5 Three-pipe Heat Recovery System. ............................................................................ 22  Figure 2.6 BC Controller. ............................................................................................................ 22  Figure 4.1 100% Outdoor Air Unit Independent of VRF Fan Coils ............................................ 41  Figure 4.2 100% Outdoor Air Unit Connected to VRF Fan Coils. .............................................. 41  Figure 6.1 Building Floorplan...................................................................................................... 52  Figure 6.2 Building Peak Cooling and Heating Loads. ............................................................... 54  Figure 6.3 Total Yearly Building Electric Consumption. ............................................................ 54  Figure 6.4 Total Cooling Equipment Electric Consumption. ...................................................... 55  Figure 6.5 Total Heating Equipment Electric Consumption. ...................................................... 55  Figure 6.6 Total Yearly Operating Costs. .................................................................................... 56 Figure A.1 Design Flowchart ....................................................................................................... 65  Figure B.1 The Cooling Curve..................................................................................................... 67  Figure B.2 The Supercooling and Reheat Process. ...................................................................... 68  Figure D.1 System Selection Flowchart. ..................................................................................... 88  Figure E.1 First Floor Plan ........................................................................................................... 91  Figure E.2 Second Floor Plan ...................................................................................................... 92 Figure F.1 Floor Construction...................................................................................................... 95 Figure F.2 Partition Construction ................................................................................................ 96 Figure F.3 Roof Construction ...................................................................................................... 97 Figure F.4 Wall Construction and Glass Type ............................................................................. 98 Figure F.5 Lights, Miscellaneous Loads, People, and Ventilation .............................................. 99 Figure F.6 Occupancy Schedule ................................................................................................ 100 v Figure F.7 Miscellaneous Load Schedule .................................................................................. 101 Figure F.8 Lighting Schedule .................................................................................................... 102 Figure F.9 Availability Schedule ............................................................................................... 103 Figure F.10 Lighting and Utility Rate Schedule ........................................................................ 104 Figure F.11 Cooling and Heating Equipment ............................................................................ 105 Figure F.12 Heat Rejection ........................................................................................................ 106 Figure F.13 Plant Values............................................................................................................ 107 Figure F.14 System Checksums ................................................................................................. 109 Figure F.15 Monthly Utility Costs ............................................................................................. 110 Figure F.16 Energy Consumption Summary ............................................................................. 111 Figure F.17 Equipment Energy Consumption ........................................................................... 112 Figure F.18 Monthly Energy Consumption ............................................................................... 113 vi List of Tables Table 1.1 VRF Advantages and Disadvantages. .......................................................................... 11 Table 3.1 VRF Minimum Efficiency Requirements. ................................................................... 27  Table 6.1 Climates and Corresponding Locations ....................................................................... 51  Table 6.2 Design Temperatures for Studied Locations ............................................................... 52  Table 6.3 Electricity Rates per Location. ..................................................................................... 53  vii Acknowledgements The author wishes to express sincere appreciation to Dr. Keen for her assistance in the preparation of this manuscript. In addition, the author would like to thank Professors Hasler and Kramer for their comments and insight on ideas in this paper. viii Chapter 1 - Introduction As of 2008, the commercial building sector was responsible for 19% of energy consumption in the United States; of which 32% is dedicated to space heating, space cooling, and ventilation loads (Center for Sustainable Systems, 2009). As reducing energy consumption becomes a higher priority, heating, ventilation, and air conditioning (HVAC) designers in the United States’ building and construction industry are specifying systems in which sustainable design lowers energy use in commercial buildings. Variable refrigerant flow systems (VRF) are HVAC systems that have great potential to reduce energy consumption when applied correctly. This research addresses the most common type of this technology, air-to-air VRF. Water-to-air VRF systems exist, but little published research exists on them, making accurate discussion about the use and efficiencies beyond the scope of this report. However, research has shown that these systems can expand the use of VRF into areas where air-to-air systems are generally less efficient than water-to-air systems, particularly dry, southern climates. This report defines air-to- air VRF, describes how it works, details how to properly design and select the system, compares the system to more traditional systems, and investigates the effect of climate on the overall performance and operating costs of the system. 1.1 What is Variable Refrigerant Flow The term VRF stems from ability of the system to modulate the amount of refrigerant flowing to each indoor unit, called a fan coil unit. The system runs constantly at loads between 10% and 100%, but cycles on and off only at loads below 10% (Nye, 2002). To provide heating and cooling, this HVAC system utilizes refrigerant piped via one set of pipes from a single outdoor condensing unit, referred to simply as an outdoor unit, to terminal fan coil units indoors; these will be referred to as fan coil units throughout this report and should not to be confused with traditional fan coil units commonly used in hydronic systems. Instead of using hot water for heating and chilled water for cooling, these fan coils utilize refrigerant delivered via a single pipe for either heating or cooling; in some climates, electric backup heat is required in addition to the basic VRF system. Regardless, each VRF fan coil unit receives only the volume of refrigerant needed to condition the space so that each unit meets the specific needs of each zone 1 when individual temperature controls are provided (Goetzler, 2007). One outdoor unit can accommodate up to 60 indoor units and loads up to 25 tons, rendering the system useful in almost any size structure and extremely versatile in the commercial building industry (Amarnath & Blatt, 2008). Figure 1.1 illustrates how these fan coil units are connected to the outdoor unit. Figure 1.1 VRF Systems. (Modified with permission by Ammi Amarnath and the Electric Power Research Institute) This system can be utilized in a wide variety of commercial buildings, including offices, hotels, historical renovations, additions, hospitals, and schools (Roth, Westphalen, Dickmann, Hamilton, & Goetzler, 2002). In the past, such buildings have been conditioned primarily by conventional HVAC systems, including hydronic systems, variable air volume systems, conventional direct expansion split systems, and heat pump systems. However, designed and implemented properly, VRF can match the zoning and flexibility of these systems much more efficiently and comfortably, making VRF a viable option for an HVAC system. Two types of VRF systems exist: heat pump systems and heat recovery systems. Heat pump systems require a refrigerant liquid line and suction line be connected to the outdoor unit. This type of system provides either all heating or all cooling because it cannot perform both 2