Development of Solar Assisted Heat Pump Water Heating Systems

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The environmental impact and availability of standard energy sources has become increasingly important. It is also recognized that while the development of new energy sources is necessary, so too is a conscious effort towards conservation and smarter use of energy. Buildings have long been considered a primary focus for energy efficiency, with the most ambitious efforts aimed at net-zero energy targets. New and more efficient water heating strategies are critical to meeting this goal, as water heating is the second largest energy consumer in Canadian residences at approximately 18% of total energy consumption (19 GJ of energy per household). Solar Domestic Water Heating (SDHW) systems have proven to be a cost effective and reliable method of water heating that reduces primary energy consumption in residential buildings. In northern climates, however, SDHW systems require a back-up heat source to provide additional thermal energy during period of insufficient solar input. One could use an electrical resistance heater to provide this back-up heating, where the ratio of heat input to electrical input is 1:1. Alternatively, one could use a heat pump, where the ratio of heat input to electrical input could be in the range of 3:1 or 10:1, depending on the operating conditions. From a thermodynamic perspective, using this electricity to run a heat pump is a far more efficient use of energy. The synergistic combination of heat pump and SDHW technologies to provide hot water or air for domestic purposes is called a Solar Assisted Heat Pump (SAHP). In addition to being a better use of electricity, the inclusion of a heat pump will pre-cool the fluid going to the solar absorber. Colder fluid supply temperatures will reduce thermal losses from the absorber, thereby improving system efficiency and increasing system run-time in colder weather. More importantly, if the SAHP is capable of reverting to a standard SDHW system when the heat pump is not needed, there is potential that the system could meet the year round demands of an energy efficient building. Removing the need for back-up heat sources would have the added benefit of reducing the capital cost of the system. To get to that point, however, the systems need further development. In particular, component sizing and reliability, smart control strategies, and system interaction with building and occupant requirements need to be assessed in order for the SAHP to reach its maximum potential. The proposed research will address some critical limitations of current SAHP technologies. The overarching goal is to develop robust, reliable, and economically viable SAHP systems, to develop design tools that will allow builders and homeowners to make informed choices about the technology, and to train HQP in fields related to solar energy and building sciences. Ultimately, this will benefit Canada by helping reduce the energy demands of buildings. Over the course of the next five years, the proposed program will address several shorter term objectives. Initially, several novel solar-only SAHP system configurations will be investigated both analytically and experimentally, resulting in accurate models of the systems. These models will be used to develop innovative control strategies which will allow the SAHP to operate at peak efficiency. Next, the compatibility of the systems with other novel energy efficient technologies, such as heat recovery and photovoltaic/solar thermal hybrids, will be assessed. Finally, the systems will be built and operated to assess system robustness in a real world setting. As with any building technology, the key to efficient operation is to understand and develop the system in the context of its location and usage characteristics.