DEVELOPMENT OF DISTRIBUTED MULTIPLE SOURCE AND MULTIPLE USE HEAT PUMP SYSTEM USING RENEWABLE ENERGY

Outline of the test building and experimental evaluation of cooling and heating performance

Abstract

 The energy input for building operations is mainly composed of fossil fuel-based energy carriers, and therefore accounts for a large proportion of global greenhouse gas emissions. Thus, significant effort such as application of heat pumps has been focused on boosting renewable energies in building to decrease the energy demand and its related emissions. However, the conventional heat pump systems proposed such as air source heat pump or ground source heat pump systems commonly employ only one renewable energy sources to meet the cooling and heating demands. Each renewable energy source has its own advantages and disadvantages: solar radiation is a type of flow energy and is quantitatively limitless, but its availability is intermittent; geothermal energy is a stable stocked energy source but is quantitatively finite. Therefore, the combination of various energy sources has been proposed and practiced to account for their shortcomings.

 In this study, we developed a multiple source and multiple use heat pump (MMHP) system which use renewable thermal energy sources around building. In the MMHP system, multiple heat sources such as solar heat, geothermal heat and air source are utilized and multiple thermal uses such as cooling, heating and domestic how water supply are used in light of heat source temperature. We developed a unique sky heat source heat pump that can use solar heat and air heat. A double-helix underground heat exchanger that can be used in conjunction with a heat pump is proposed to achieve a daily cycle operation of MMHP system. In addition, we developed water source heat pumps for domestic how water supply, floor heating and air conditioning based on commercial products. The MMHP system is expected to achieve a higher efficiency than conventional heat pump systems. Since the MMHP system is a network with distributed machines, it is easy to cope with the different scale and application and can extended according to the size and application of various buildings. To evaluate the performance and applicability of MMHP system, an experimental house called RE house was constructed in Chiba, Japan. Several self-developed water heat pumps and ground heat exchanger were used to build the MMHP system.

 We conducted summer and winter field experiments to investigate the performance of each heat pump and the whole system. From the results, we can draw the following conclusions: 1) adoption of PVC pipe and decentralized pumping system helped heat transfer power and water piping cost. 2) the sky source heat pump achieved a heat collecting operation with a COP of 23.2 on a sunny day and 7.4 on a cloudy day, the COP of heat dissipation operation at night was 4.5; 3) the stable and efficient long-term operation can be expected by the daily cycle operation method combining a ground heat exchanger and a sky heat source heat pump; 4) the floor heating heat pump achieved a stable operation with a COP of 11.5 based on a 1 month experiment in Chiba, Japan; 5) a water source heat pump for hot water supply was developed. It is necessary to adjust the operation method and equipment since the performance was lower than expected; 6) based on the results of long-term operation and representative day in Chiba, Japan, the system realized a heating operation with COP of 8.4 and a cooling operation with COP of 5.3.