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• A segmented control strategy for ultra-low temperature running was proposed. • Experiments lasted a whole heating season was conducted using the control strategy. • Discharge temperature was well controlled with the highest value of 118.82 °C. • Low temperature frosting was a main challenge for QTASHP in severe cold region. • Energy saving property and environmental benefit of QTASHP were remarkable. The quasi-two stage compression air source heat pump (QTASHP) is still restricted in use in severe cold region due to the excessive discharge temperature caused by ultra-low ambient temperature. To promote the application of QTASHP in severe cold region, a novel control strategy was proposed, and it was used in a test rig in Harbin. The test rig adopted a scroll compressor with vapor injection, and its technical feasibility was investigated through supplying heating for a lab in the whole heating season. Then based on experimental results, its economic and environmental benefits were analyzed. Results showed that QTASHP could run smoothly in the whole heating season, and its highest discharge temperature was 118.82 °C at the highest compression ratio of 12.13. This indicated the proposed control strategy could solve the excessive discharge temperature problem effectively. Apart from ultra-low temperature, low temperature frosting was also a main challenge for QTASHP in severe cold region. Besides, comparing with central heating and electric boiler, its primary energy efficiency increased by 18.67% and 140.54%, while pollutants/CO 2 emission decreased by 15.41% and 58.27%. However, its economic benefit was worse than central heating due to high initial investment, while far better than electric boiler. [ABSTRACT FROM AUTHOR]

Variable refrigerant flow heat pump system is still restricted in use in severe cold region due to ultra-low outdoor temperature there. With the development of vapor injection technique, applying this technique to it is an effective method to promote its heating performance at low outdoor temperature. To promote the application of variable refrigerant flow heat pump system with vapor injection in severe cold region, a test rig was built in Harbin and used to supply heating for a lab. To prevent excessive discharge temperature at ultra-low outdoor temperature, a novel control strategy was proposed and used in the test rig. The application characteristics of the experimental unit were introduced firstly. Then its application potential was analyzed through comparing with quasi-two stage compression air-water heat pump. Results showed the experimental unit run smoothly in the whole test period, even when outdoor temperature dropped to −28.7 °C. Its heating effect was good at outdoor temperature of −22.5 to 7.5 °C. Besides, mal-defrost had more serious influence on heating capacity shortage than ultra-low outdoor temperature in severe cold region. In addition, comparing with quasi-two stage compression air-water heat pump, the experimental unit had advantage on heating capacity and discharge temperature. [ABSTRACT FROM AUTHOR]

• A thermo-hydraulic coupling model for residential building heating system was proposed. • Thermal zones divide detailed and each user could regulate his heat in the simulation model. • Infiltration rates and increased thermal resistance of buried pipes are considered in the model. • The calibrated model could respond to heating and hydraulic conditions based on users' regulation. Demand-side regulation is a practical method to decrease the overheating loss and improve comfort level of users. The existing simulation model methods are difficult to evaluate the interaction of user regulation. And there is still no reasonable model method to prove the feasibility of demand-side regulation. To solve this problem, a residential building heating system model considering the thermo-hydraulic coupling and demand-side regulation was built on TRNSYS 18. It was calibrated by a residential building in Harbin. Results showed that using infiltration rates recommended by ASHARE as stochastic calibration parameters, the users that met the validation criteria would increase by 7%. The increased thermal resistance caused by internal surface fouling in the buried pipe should also regarded as a stochastic parameter in the calibration process. After calibrated these two stochastic parameters, the model achieved satisfactory accuracy and all the 144 users met the validation criteria. The calibrated model could provide the ability to simulate the various regulation behaviors of each user, and truly response to heating and hydraulic conditions based on users' regulation. The validated simulation model can be leveraged as a rigorously validated benchmark residential heating system based on demand-side regulation. [ABSTRACT FROM AUTHOR]