Thermal Storage Technology Assessment An introductory assessment of thermal storage in residential cold climate construction February 2013 by Vanessa Stevens Colin Craven Bruno Grunau With funding from the Alaska Housing Finance Cor- poration & the Alaska Department of Commerce, Community, and Economic Development Acknowledgements The authors would like to acknowledge the many people who participated in interviews for this report, sharing their knowledge and expertise on the topic of thermal storage. Several of the systems built by these individuals appear in Appendix B. Also, thanks to the Alaska Department of Commerce, Community, and Economic Development and the Alaska Housing Finance Corporation for providing funding for this project. 3 Thermal Storage Technolog y Assessment www.cchrc.org Contents Acronyms ............................................................................................................................................................ 5 Introduction ........................................................................................................................................................ 6 1. Thermal Storage Fundamentals........................................................................................................................ 7 1.1 Definition ................................................................................................................................................... 7 1.2 Uses of thermal storage ............................................................................................................................. 7 1.3 Basic types of storage............................................................................................................................... 10 1.3.1 Sensible heat storage ........................................................................................................................ 10 1.3.2 Latent heat storage (phase change materials) ................................................................................... 11 1.4 Active vs. passive thermal storage ............................................................................................................ 15 2. Design Considerations.................................................................................................................................... 16 2.1 Method of charging thermal storage ........................................................................................................ 16 2.2 Storage material....................................................................................................................................... 17 2.3 Time frame .............................................................................................................................................. 18 2.4 Temperature range .................................................................................................................................. 18 2.5 Size .......................................................................................................................................................... 19 2.6 Efficiency ................................................................................................................................................. 20 2.7 Retrofit and new construction considerations .......................................................................................... 21 2.8 Commercialization of thermal storage...................................................................................................... 21 3. Thermal Storage Examples ............................................................................................................................. 23 3.1 Electrical thermal storage (ETS) ................................................................................................................ 23 3.2 Biomass technologies ............................................................................................................................... 23 3.3 Solar thermal systems .............................................................................................................................. 24 Synthesis of Findings.......................................................................................................................................... 27 Research Recommendations .............................................................................................................................. 29 Works Cited ....................................................................................................................................................... 30 Appendix A: Literature Resources ...................................................................................................................... 32 Appendix B: Thermal Storage Systems in Cold Climates ..................................................................................... 38 Wood boiler thermal storage for daily cycling ................................................................................................ 38 Seasonal storage of solar and wood energy in Fairbanks ................................................................................ 40 Seasonal storage of solar and wood energy in Homer .................................................................................... 42 Off-peak power use of a ground source heat pump........................................................................................ 43 Electric grid stabilization through the use of thermal storage ......................................................................... 44 Solar thermal storage with water tank and soil .............................................................................................. 45 District solar thermal heating system ............................................................................................................. 46 Seasonal storage of solar energy in Edmonton ............................................................................................... 48 Wood boiler thermal storage for multi-day heating ....................................................................................... 49 Appendix C: Sample Thermal Storage Calculations ............................................................................................. 50 4 Thermal Storage Technolog y Assessment www.cchrc.org Acronyms AFUE Annual Fuel Utilization Efficiency ASHRAE American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. BTU British Thermal Unit C Celsius CCHRC Cold Climate Housing Research Center COP Coefficient of Performance DOE Department of Energy EPS Expanded Polystyrene ETS Electrical Thermal Storage F Fahrenheit PCM Phase Change Material PHPP Passive House Planning Package 5 Thermal Storage Technolog y Assessment www.cchrc.org Introduction Space heating accounts for 74% of energy consumption in single-family residences in Alaska (ARIS, 2012), while domestic hot water heating accounts for 15 – 25% of home energy use in America (U.S. Department of Energy, 2011). As such, researchers and residents of Alaska and other heating-dominated climates are continually searching for methods to raise efficiencies and reduce costs. One such method that has recently attracted attention in Alaska is thermal storage, which is currently being used in Alaska and other cold climates in conjunction with heating systems. For instance, a thermal net-zero home was recently built in Fairbanks. The heating system uses solar thermal panels and a masonry heater to charge a 5,000-gallon thermal storage tank that provides heat to a radiant floor for space heating. The thermal storage tank also provides heat for the domestic hot water system. The potential of thermal storage to enhance the use of renewable heating systems in cold climates, increase the efficiency of heating systems, and reduce emissions has raised interest in its use. In spite of its potential, there are few informational resources on the successful application of thermal storage in cold climates. Currently, there are limited educational materials and literary articles on thermal storage systems in cold climates, and on how thermal storage can be best integrated into a heating system. This report aims to provide an informative, though introductory, assessment of the current status of thermal storage in residential construction in cold climates. The authors’ primary motivation is to provide building researchers and building owners living in cold climates with a document outlining the applications and potential of thermal storage in heating systems. It is hoped that this document can also be used to inform and define future research on thermal storage in cold climates. This report consists of three main sections, which are a compilation of preliminary findings from literature research and interviews with homeowners in cold climates on the topic of thermal storage for use with residential space heating and domestic hot water systems. First, readers will find Thermal Storage Fundamentals, with general definitions and information on the different types and uses of thermal storage. The second section, Design Considerations, includes information on characteristics of thermal storage, its efficiency, and construction considerations. Lastly, Thermal Storage Examples contains more details about three commonly used methods of charging thermal storage systems. The report concludes with