Jiang Yiqiang

A field study of a wastewater source heat pump for domestic hot water heating

An experimental heat pump utilizing wastewater discharged from the common bathroom in a SPA center as a heat source was built. In this article, the field measured operating performance of the wastewater source heat pump is reported. An analysis based on the collected field data under various operating conditions is included. It was shown that the temperature of wastewater greatly affected the evaporating temperature and the coefficient of performance of the wastewater source heat pump. Circulating wastewater from the bottom to the top of the wastewater storage tank could weaken even out the vertical wastewater temperature distribution inside the wastewater storage tank and improve the coefficient of performance and compressor suction pressure of the wastewater source heat pump accordingly. The daily averaged coefficient of performance of the wastewater source heat pump was monitored for over an entire month. It was shown that the measured coefficient of performance gradually reduced, suggesting the need for regular cleaning of the heat exchangers used in a wastewater source heat pump system. In addition, the recorded maximum transporting capacity of the wastewater pipe reduced by 16.9% over the 1 month operation and by 20.1% after ∼5 months due to the bio-fouling build-up. Finally, an analysis comparing the economics of operating a wastewater source heat pump system with that of operating conventional water heating systems is presented. Practical application: The use of heat pump to recover heat from wastewater is significant to energy conservation and environmental protection. A number of researches and projects on wastewater source heat pumps using urban sewage or treated sewage as a heat source have been carried out. However, field measured results on a heat pump, which recovered heat from waste bath water, was not previously reported. As the quality of waste bath water was different from that of sewage in terms of temperature, amount, and the degree of cleanliness, the experiences on designing and operating urban sewage source heat pumps previously obtained could not be used as a full reference for designing a waste bath water source heat pump. In this article, field experiment work of designing and operating a heat pump which used waste bath water as a heat source for hot water heating is presented, and the results can be used as a key reference for designing and operating waste bath water source heat pump systems in the future.

Improving reverse cycle defrosting performance of air source heat pumps using thermal storage based refrigerant sub-cooling energy

When an air source heat pump (ASHP) unit is used for space heating at a low ambient temperature in winter, frost may be formed on its outdoor coil surface. Over time, frost accumulation on coil surface may become sufficient to restrict air passage through the coil and increase the heat transfer resistance between ambient air and coil surface, leading to performance degradation for the outdoor coil, or even the shutdown of the ASHP unit. Therefore, periodic defrosting is necessary. Currently, the most widely used standard defrosting method for an ASHP unit is reverse cycle defrosting. During a standard reverse cycle defrosting (SRCD) operation, the indoor coil in an ASHP unit actually acts as an evaporator. Because the indoor fan is usually turned off during defrosting, there is an insignificant amount of energy from indoor coil, leading to a number of associated operational problems such as a longer defrosting duration and the risk of having a lower air temperature inside a heated space during defrosting, etc. To solve the fundamental problem of insufficient heat available during defrosting while ensuring the efficient and safe system operation, a novel reverse cycle defrosting (NRCD) method which is thermal energy storage-based using sub-cooling energy of refrigerant for ASHPs has been developed. Comparative experiments using both the SRCD method and the NRCD method were carried out on an experimental ASHP unit with a nominal 2.5 kW heating capacity. Experimental results clearly suggested that when using the NRCD method, the discharge and suction pressures were increased by 0.56 and 0.12 MPa, respectively. Furthermore, the defrosting duration and heating-resumption duration were shortened by 30.8% and 25.0%, respectively, and the defrosting energy consumption was reduced by 13.9%, compared to those when using the SRCD method. Practical application: ASHPs have been widely used worldwide due to their significant energy-saving potentials. However, frost can be formed on the outdoor coil surface when an ASHP unit operates for space heating. Frost accumulation on coil surface reduces the coil’s efficiency, or causes even the shutdown of the ASHP unit. Reverse cycle defrosting is the most widely used standard defrosting method. This paper presents the reverse cycle defrosting performance for an ASHP unit with a PCM-HE acting as both a sub-cooler during heating operation and a heat source during defrosting operation, which could help to ensure the safe operation and achieve a higher defrosting efficiency of the ASHP unit.

Thermal accumulation effect of ground-coupled heat pump system

A software TRNSYS is used to simulate operation characteristics of ground-coupled heat pump for an office building. It analysis the soil temperature changes and groundsource heat pump system efficiency last several years in different climates conditions. The results show that the greater the difference between cooling load and heat load, the greater the annual average temperature of soil increases, the system efficiency down faster. The soil average temperature raises 6.5 degree after the system running five years. The temperature decreases 2.4 degree in Qiqihar. To ensure long-term stable operation of the system, proposing solution to thermal accumulation problem of geothermal ground source heat pump system.

An Experimental Study on Thermal Energy Storage Based Reverse Cycle Defrosting Method Using Sub-cooling Energy of Refrigerant for Air Source Heat Pump: Characteristics of Thermal Energy Storage Operation

the introduction of the system of thermal energy storage (TES) based reverse cycle defrosting method using sub-cooling energy of refrigerant for air Source heat pump(ASHP) is given firstly. And then the characteristic of TES using sub-cooling energy of refrigerant in heating is experimentally researched. The results show that storing sub-cooling energy of refrigerant in the PCM can not only improve the system COP in heating, but also provide energy for defrosting. Two modes of TES are inferred and it proves that improved system performances and indoor thermal comfort can be resulted in mode of starting TES process when heating for one hour.