Thermodynamics Analysis And Heat Transfer Research Of Direct Radiant Floor Heating System With ASHP

A new kind of direct radiant floor heating system with air source heat pump (ASHP) using refrigerant flow as heating medium was studied in this paper. The performance of ASHP and indoor thermal environment of two rooms installed embedded-piping radiant floor heating with pipe interval of 150mm(1st room) and 100mm(2nd room) were investigated by experiments under the weather condition of Zhengzhou during the winter, respectively. The energy and exergy of direct heating system with ASHP was also analyzed by theory and simulation based on experiments, as well as the heat transfer performance of floor structure. The results could be used as design and operation reference of direct radiant floor heating system with ASHP. The following introductions are the main research results.1. A new kind of direct radiant floor heating system with ASHP using refrigerant flow as heating medium was designed and constructed. The experimental results confirmed that this direct heating system provide comfortable indoor thermal environment in accordance with standard of JGJ142-2004, while the indoor air and floor slab temperature could be maintained at 21.8℃and 26.5℃, respectively, with ASHP worked at capacity output of 30% load.2. This direct floor heating system show well performance of preheating and heat storage. The preheating time of this direct heating system with ASHP was shortly at 80min for the indoor air temperature and floor slab temperature reached to 19.7℃and 25℃from 15℃, respectively. And after 3 hours since the ASHP taken off, the indoor air and floor slab temperature decreased only 1.0℃and 3℃, respectively.3. This direct floor heating system show comfortable indoor thermal performance. The floor slab temperature and indoor air temperature of 2nd room (100mm) varied among 26.5～27.2℃and 22.6～23.1℃, underwent a 0.7℃and 0.5℃variation, which of 1st room (150mm) varied among 24.1-25.1℃and 20.0-21.1℃, with 1℃and 1.1℃variation.4. The hourly energy efficiency ratio(HEER) of ASHP was 2.76 during continuous heating experiment with ambient temperature of 2℃and humidity of 20.5%, while HEER was 3.42 with ambient temperature of 7.8℃and humidity of 13.5%. Besides, the HEER was also larger than 2.4 running in defrosting mode, which shows excellent energy performance.5. The exergy efficiency, of this system was larger than 30%, and the highest exergy loss occurs in the compressor, followed by the floor coil condenser and outdoor evaporator, the smallest was expansion valve, which was about 24%,13%,11%,5%, respectively. It also can be seen that the exergy loss of transport pipeline was larger than 12%.6. The pipe interval, cover thickness, floor materials and compressor capacity output were important influencing factors of direct radiant floor heating system. A steady-state, two-dimensional heat transfer mathematical model was established, in which refers to the refrigerant condensing heat transfer coefficient calculation method and composite-fin mode for radiant floor heating developed by Kilkis. The numerical calculation software ANSYS was used to simulate the effects of each factor, and the error was less than 10% between numerical simulation and experimental results.