Experimental research and performance study of a coaxial hybrid-power gas engine heat pump system based on LiFePO4 battery

• A novel coaxial LiFePO4 battery hybrid-power gas engine heat pump system is proposed.
• Logic threshold control strategy is established.
• Experimental research on dynamic efficiency and economical performance are operated.
• Results are compared with lead-acid battery HPGHP and conventional GHP.
• LiFePO4 battery HPGHP can achieve an obvious energy saving effect.

Power batteries of hybrid-power gas engine heat pump (HPGHP) often encounter instantaneous power demand. Due to working modes switching caused by the frequent variation of external load, the batteries tend to perform frequent charge and discharge operations, which has an adverse effect on energy conversion efficiency of system. In order to improve the dynamic efficiency and economical performance of HPGHP, this paper raises a novel HPGHP system, which takes the LiFePO4 battery as the auxiliary power source to drive the compressor. Logic threshold control strategy is put forward to distribute power between the gas engine and battery pack. Test research on COP, heating capacity, engine thermal efficiency, fuel-consumed rate, energy conversion efficiency and reclaimed heat have been operated to verify the advantageous performance of LiFePO4 battery HPGHP. The results show that LiFePO4 battery HPGHP can achieve an obvious energy saving effect, especially in low-load condition and high-load condition. When compressor speed increases from700 rpm to 2500 rpm, COP decreases from 4.76 to 3.25, heating capacity increases from 14.52 to 33.13 kW. Compared with lead-acid battery HPGHP under the same load, LiFePO4 battery HPGHP shows better performance. Engine thermal efficiency and energy conversion efficiency of LiFePO4 battery HPGHP are higher than those of lead-acid battery HPGHP, and fuel-consumed rate is lower. The maximum differences of engine thermal efficiency, energy conversion efficiency, fuel-consumed rate are 13.2%, 10.2% and 11.28%, respectively. In addition, reclaimed heat is also tested and the result shows that LiFePO4 battery HPGHP is 11.82% lower than conventional GHP.