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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, which is close to two stage compressor. But the power consumption increases because of the huge back-pressure volume which related to the area and location of the injection port. The influence of the parameters of the injection port on the compressor is researched based on a numerical model verified by experimental results. The results show that the smaller injection port can decrease the power consumption obviously and increase COP. The heating capacity doesn’t change significantly when the injection area is over 20.1mm2 in this compressor but decreases if the injection area is too small. So the injection port scenario should consider heating capacity and COP synthetically.

Refrigerant mixtures are commonly regarded as a potential substitute because rare pure refrigerants can totally meet all the requirements of environmental, thermodynamic and safe properties. Meanwhile as an effective means, vapour injection is widely applied to improve the system performance of heat pump under large pressure ratio. However, the difference of using pure refrigerant and refrigerant mixtures, which configuration of vapour injection is more suitable for refrigerant mixtures are still unclear. In this paper, R32/R1234ze(E) mixtures are chosen as refrigerant pairs for its great potential in the future, and the scroll compressor is chosen as well to carry out the research for its wide application in vapour injected system. The thermodynamic model with different suction and injected concentration is derived, on the basis of this model, a detailed compressor and system performance comparison of different vapour injected configurations with R32/R1234ze(E) mixtures are investigated. The results indicate that the lower concentration of R32 in flash tank (FT) system will result in higher power consumption compared with intermediate heat exchanger (IHX) system. For the system performance, the heating capacity of FT system is 5%~9.1% higher than IHX system, while the COP of latter system is usually higher, the largest improvement is 2.7% when charged with R32/R1234ze(E) (40/60) mixtures.

Recently, R32 has been considered as an important alternative in application of small to middle capacity air conditioner by many countries due to its advantages such as low global warming potential (GWP), favorable thermal properties, less refrigerant charge and low cost. However, the much increased discharge temperature of R32 compressor, as compared with the R22, becomes the main barrier affecting the wide and quick alternation. Refrigerant injection has proven to be effective in decreasing discharge temperature. In this work, three kinds of refrigerant injection technology used to decrease the discharge temperature of R32 scroll compressor are discussed, namely, two-phase suction, liquid injection and two-phase/gas injection. The detailed scroll compressor model proposed in previous work is modified and validated by experimental data of R32 scroll compressor. The potentials in decreasing discharge temperature of the three methods are investigated. The detailed performance comparisons are presented. The results indicate that the two-phase/gas injection achieves the best performance with the enhancement of cooling capacity by 14.2% and increase in COP by 8.1%.

The room air conditioner is widely used in residential and office buildings for both cooling and heating. However, the operation condition of the room air conditioner changes largely due to the variations of the cooling/heating load of the room, the indoor temperature and the outdoor one, which always decreases the efficiency of the compressor and eventually the seasonal energy efficiency of the air conditioner. The refrigerant release technology relieves even eliminates the over-compression loss of scroll compressor by bypassing the refrigerant in the compression chamber to the suction pipe under small system pressure ratio conditions, By using it, the efficiency of the air conditioner can be increased. The effect of refrigerant-releasing on the annual energy performance of the room air conditioner is analyzed and the applicability is evaluated in this paper. The typical residential and office building models are built in a building load simulation software, DeST. The annual cooling and heating loads of these buildings located in different climate zones are calculated. The numerical models of the fixed speed and inverter room air conditioners with and without refrigerant-releasing function are built and verified. For the air conditioner with refrigerant-releasing, a control strategy to activate the refrigerant release is determined to keep the efficiency as well as satisfy the indoor load. Based on the calculated cooling/heating load and the models of the air conditioners, the energy consumptions of all four kinds of air conditioner during each hour can be calculated. Finally, the performance of variable and fixed speed air conditioner with and without refrigerant release in the cooling period and heating period is obtained and the contribution of refrigerant-releasing is evaluated. The results show that the variable speed air conditioner with refrigerant-releasing saves 24.2~25.5% and 18.9~25.3% energy compared to the one without refrigerant release for the office and residential buildings, respectively. For the fixed speed air conditioner, the refrigerant-releasing technology decreases 20.2~23.0% and 17.1~23.6% energy consumption for residential and office building, respectively. Variable speed air conditioner with refrigerant release saves more energy than fixed speed one. The refrigerant-releasing technology has good applicability for the room air conditioner and should be considered as an effective method to enhance the seasonal performance for it.

Two-phase thermosyphon loops (TPTLs) are highly effective devices for spontaneously transferring heat through a relatively long distance. Therefore, TPTLs are extensively used in various fields, such as cooling of electronic components, light water reactors, etc. Recently, the TPTL has also been found to be an effective way to recover or transfer heat in air-conditioning systems for energy saving. A typical TPTL consists of an evaporator, a riser (gas tube), a condenser, and a downcomer (liquid tube), and the condenser is higher than the evaporator by a certain vertical distance. The TPTL is powered by the natural force --- gravity, which means the pressure drop in the cycle always equals to the liquid head caused by the density difference of the liquid in the downcomer and the vapor or vapor/liquid mixture in the riser. Therefore, the liquid head is a key factor affecting the circulation flow rate and energy performance of TPTLs. In the traditional applications, the liquid head is considered to be proportional to the height difference between the condenser and the evaporator based on the underlying assumption: the downcomer is fully liquid filled. According to that, the TPTL will perform better with a larger height difference. The conclusion may be correct in the cases with large temperature difference and heat flux, such as in the field of cooling of electronic and light water reactors. However, when the TPTL is used in air-conditioning system, which has quite small temperature difference and small heat flux, some special phenomena were observed: the liquid heat is lower than the height difference and the downcomer is partially liquid filled. That is largely different from the thermosyphons in traditional applications. What’s the thermodynamic mechanism of partially liquid filled in the downcomer? How to determine the liquid head and the height difference? These are the fundamental questions that required answers before using two-phase thermosyphon in air conditioner field. In this study, the thermodynamic mechanism of partially liquid filled in the downcomer is researched and the effect of height difference on the performance of TPTL is investigated theoretically and experimentally. Firstly, a visual experimental setup is established, and the performance of a water-water TPTL is measured when the height difference ranges from 0 m to 2.4 m. Based on it, the basic phenomena are observed and the thermodynamic mechanism is investigated. Secondly, a generalized distributed-parameter model is developed based on the conservations of momentum, energy, and mass, which can determine liquid head and overall performance simultaneously according to external conditions. The model is verified by experiments. Then the model is used to analyze the variation of liquid head, circulation flow rate, heat transfer rate, system pressure under different height differences. The results show that with the increase of the height difference, the liquid head rises continuously until remain stable. Therefore, the liquid head is less than the height difference in some cases. Consequently, with the increase of height difference, the circulation flow rate and thermal performance firstly increases then remains constant.