Baolong Wang

Performance improvement of ammonia/absorbent air source absorption heat pump in cold regions

Air source absorption heat pump is promising in energy saving and emission reduction of heating and domestic hot water, but performs badly or even cannot work in cold climate. The ammonia/absorbent air source absorption heat pump with low-pressure boosting is proposed to solve the problem. The hybrid air source absorption heat pump + compressor system is modeled and the compression ratio is optimized to obtain maximum primary energy efficiency. The integrated system is simulated with air temperature ranging from −30℃ to 10℃ and hot water temperature from 30℃ to 60℃. Comparative simulations on three working fluids reveal that NH3–LiNO3 system has the lowest compression ratio and the highest primary energy efficiency value. By pressure boosting, the air source absorption heat pump can operate under air temperatures as low as −30℃. Primary energy efficiency of the hybrid system is about 15–50% higher than that of coal boiler, showing great potential for heat supply in cold regions. Practical application: Heating and domestic hot water consumes a large amount of energy every year. Air source absorption heat pump can be a potential alternative to the traditional boiler systems in the point view of primary energy efficiency. However, air source absorption heat pump performs badly or cannot work when the air temperature is low. This paper presents a hybrid air source absorption heat pump with pressure boosting to improve the performance of the air source absorption heat pump heating system, making it operate under lower outdoor air temperatures with higher primary energy efficiency. The novel heat supply system is expected to make contributions to building energy saving as well as pollution reduction.

Crystallization Analysis and Control of Ammonia-Based Air Source Absorption Heat Pump in Cold Regions:

Energy consumption of heating and domestic hot water is very high and will keep increasing. Air source absorption heat pump (ASAHP) was proposed to overcome the problems of low energy efficiency and high air pollution existing in boiler systems, as well as the problem of bad performance under low ambient temperatures for electrical heat pumps. In order to investigate the crystallization possibility of ammonia-salt ASAHP, crystallization margin (evaluated by solution mass concentration) at generating temperature ranging from 100 to 150°C, evaporating temperature from −30 to 10°C, and condensing temperature from 30 to 65°C are analyzed. To prevent the NH3–NaSCN solution from crystallizing, ASAHP integrated with pressure booster located between the evaporator and absorber is simulated. Analysis and comparisons show that NH3–NaSCN is easy to crystallize at relatively high generating temperature, low evaporating temperature, and low condensing temperature. But crystallization margin of NH3–LiNO3 can always stay above 5% for most conditions, keeping away from crystallization. Pressure booster can effectively avoid the crystallization problem that will take place in the NH3–NaSCN ASAHP system.

Dynamic Soil Temperature of Ground-Coupled Heat Pump System in Cold Region

Ground-coupled heat pump (GCHP) has been widely used as an energy-saving and environment-friendly heating and cooling system. But for the buildings in cold regions, because the heat extracted from ground is much larger than the heat rejected into it, the ground cannot keep thermal balance and consequently the soil temperature will decrease year by year. With the decrease of the soil temperature, the ground-coupled heat pump system declines in performance or even stops running after a longtime operation. This paper aims at specifically revealing the phenomenon of soil temperature decrease in cold regions by an integrated dynamic simulation. 10 year’s dynamic soil temperatures of GCHP used for just heating and for both heating and cooling in four typical cities are simulated and compared. The results show that the office building using GCHP just for heating has a severer soil temperature decrease: the temperature drop is respectively 11.7 °C in Harbin, 9.6 °C in Shenyang, 9.0 °C in Beijing, 5.8 °C in Zhengzhou. For the system with both heating and cooling, the soil temperature drop is 8.2 °C and 3.4 °C in Harbin and Shenyang, while the soil temperature rise is 0.02 °C and 5.5 °C in Beijing and Zhengzhou. The results of simulation are valuable for the design and operation of GCHP system applied in cold region.

Experimental Investigation of Discharge Performance and Temperature Distribution of an External Melt Ice-on-Coil Ice Storage Tank

A 633 MJ (50 ton-h) ice storage tank was built to study the discharge characteristics of an external melt ice-on-coil ice storage tank. Temperature distributions in the tank were measured to analyze the performance of the ice storage tank. Several control parameters, including the entering mode, water flow rate, inlet temperature, load power, initial ice storage quantity, and ice bridging were considered to determine the outlet temperature, discharge rate, and cumulative heat transfer, etc. The results showed that (1) the tank using bottom-in mode could more easily acquire stratified temperature distribution in the ice tank and a lower output temperature than in top-in mode; (2) the increase of water flow rate led to an even temperature distribution and a slightly higher outlet temperature; (3) the increase of inlet temperature led to the decrease of thermocline thickness and slightly increased the outlet temperature; (4) initial ice storage quantity and load power had little effect on the discharge performance; (5) ice bridging could badly deteriorate discharge.

Experimental research on vapor-injected rotary compressor through end-plate injection structure with check valve

The refrigerant injection technology can improve the performance of heat pump in low ambient temperature. Traditional end-plate injection of rotary compressor controls the injection by the rotation of the piston, which leads to some drawbacks, such as small injection area and bad adaptability to variable working condition. By adopting a check valve system, a novel end-plate gas injection structure for rotary compressor had been put forward to increase injection port area and enhance the adaptability to variable working condition in previous research. In this paper, a vapor-injected rotary compressor prototype is manufactured and tested compared to single-stage and two-stage rotary compressor. The experimental results indicate that the vapor-injected compressor can enhance the heating capacity by 23.8~42.3% and COP by 4.0~11.8% compared to single-stage compressor. Furthermore, the influence of the parameters of the injection port are researched based on a numerical model verified by experimental results. The results show that the smaller injection port may decrease the power consumption obviously and increase COP, but has little effect on the heating capacity. So, there is an optimal injection port for the end-plate injection with check valve.

Energy-Efficient Heating and Domestic Hot Water Systems Suitable for Different Regions

Heating and domestic hot water consume a large amount of energy. The heat supply systems based on fossil fuel burning are of low energy efficiency as well as high air pollution. Air source electricity heat pump (ASAHP) was analyzed to be energy-saving for heating in cold regions. In order to select suitable system for different areas, the primary energy efficiency of electricity heating, coal boiler, gas boiler, electrical heat pump, and ASAHP-driven by various heat sources are compared. Combing the weather characteristics in different areas, the applicability of different systems in China are investigated in the energy efficiency point of view. Results show that the primary energy efficiency of ASAHP is generally higher than that of ASEHP except when the air temperature is very high. Both ASEHP and ASAHP are efficient in the hot summer and warm winter area for domestic hot water. And direct gas-fired ASAHP is the best choice in hot summer and cold winter area, temperate area, cold area as well as severe cold area. Additionally, hot water-driven ASAHP using gas boiler is the second choice for heating in hot summer/cold winter area and temperate area, and for both heating and domestic hot water in cold and severe cold areas. This work is to explore the most suitable heat supply systems for different regions, and is expected to make contributions to building energy saving and emission reduction.