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This paper proposes a fresh air-handling unit, comprising an earth-air heat exchanger (EAHE) and a heat recovery unit, to solve the problem of insufficient fresh air and save primary energy use in severe cold regions. A new construction of double-layer buried pipes was adopted to enhance heat transfer and save land use. Annual performance of system from January to December 2017 was evaluated by analyzing inlet/outlet air parameters, thermal capacity, and power consumption variation. Different operation modes were adopted to simulate use patterns of various building styles. Results show that during heating operation, the maximum temperature produced by EAHE was 22.2 °C and its maximum heating capacity was 7718 W. The average temperature drop during the cooling operation was 13.6 °C. The system can provide fresh air with sufficient temperature independently. Both heat and mass transfer exist inside the buried pipes when operated under the cooling mode. Latent cooling capacity occupied 32.1% of total cooling capacity averagely, which reveals the importance of mass transfer. From the correlation analysis, it is clear that the heating capacity and sensible cooling capacity have the strongest correlation with inlet air temperature and the latent cooling capacity reacts to the moisture content. The average annual C O P ¯ of the system is 8.5. Compared to an air-source heat pump handling unit, the dynamic payback period is only 2.38 years and proposed system can further provide an 82.5% reduction in greenhouse gas emissions. • A fresh air-handling unit based on Earth-Air Heat Exchanger was proposed and verified. • Experiments were conducted during whole year to evaluate the annual performance. • Correlation between thermal capacity of EAHE and inlet air conditions was strong. • The proposed system can bring free cooling load to indoor environment under cooling operation. • The economic and ecology analysis showed the sustainability of system. [ABSTRACT FROM AUTHOR]

In the recent decade, with solar energy assisted heat pump systems have increasingly developed. In the previous studies, a hybrid air source heat pump (ASHP) system was proposed, which coupled with latent heat thermal energy storage (LHTES) and solar thermal collector, for operating in various types of configurations. This paper describes the approach and principle for organizing the hybrid system in detail. Thereafter, a phase change material (PCM) based solar–air source heat pump (PCM-SAHP) prototype was set-up and implemented under variant testing conditions. Experimental results demonstrate that the PCM-SAHP system presented remarkable advantages on correcting the mismatch between supply and demand of thermal energy and electricity. Further, when the ambient temperature was higher than 38 °C, cooling COP of the hybrid system enhanced by 17%, compared with that of ASHP system under same surroundings. During the days that outdoor air temperature was below −10 °C, heating COP of the PCM-SAHP system rose by 65% comparing with that of ASHP system. In additional, switching operating strategies during system running will scarcely result in the violent or continuous fluctuations on the operating parameters. Therefore, the efficiency of the PCM-SAHP systems can be improved with capacity lapse avoiding, and exhaust controlling as well. [ABSTRACT FROM AUTHOR]

Heat pump technology fully shows the principle of energy recycling in terms of Heating, Ventilating and Air Conditioning (HVAC). It avoids unipolarity of energy using in the conventional HVAC system. Heat pumps use high-grade energy as a driving energy, recovering and upgrading low-grade energy for avail, like a pump. Because heat source used in HVAC usually is low temperature heat, heat pump systems adopted in HVAC will help improve heating performance coefficient. Therefore, HVAC is one of ideal users of heat pump applications, and thus high-grade energy used in HVAC can be replaced with a large number of low-temperature renewable energy. Through the heat pump technology, natural low-grade energy stored in the soil, water, air or waste heat from variant industries and daily lives, is supplied for building cooling/heating and hot water serving. Therefore, vast applications and developments of heat pump technology are presented in HVAC in China, and some progresses are achieved in the system innovation, experimental research, product development and engineering application, etc. This paper reviews the progress of researches, applications and development in the field of heat pumps for building cooling/heating in China since the 21st century. [ABSTRACT FROM AUTHOR]

During experiments on investigating the application feasibility of variable-frequency air source heat pump with vapor injection (ASHPVI) in severe cold region, it was found its frosting performance varied significantly from that in former investigations, e.g. in a severe frosting condition (0 °C, 80%), the experimental unit was frost-free. To investigate the frosting characteristics of variable-frequency ASHPVI for space heating in severe cold region, a test rig was built and used to supply heating for a lab in two heating seasons. A new frosting map was developed through summarizing its running performance under frosting condition. Results showed the frosting map of variable-frequency ASHPVI was affected by heating load. Owing to the consideration of heating load, the critical relative humidity decreased from 80.60% to 62.75% when outdoor temperature (OT) dropped from 1.0 °C to −26.5 °C, opposite to the change trend in former investigations. Besides, compared with values obtained in cold region, the upper and lower limits of OT of frosting region in severe cold region were both lower, and its critical relative humidity was higher. Moreover, the highest frosting speed appeared at OT of approximately −10 °C in severe cold region, but not at 0 °C as previously thought. • A new frosting map considering the variation of heating load was developed. • The change trend of critical relative humidity was opposite to the former ones'. • The critical relative humidity at 0 °C reached up to 79.25% in severe cold region. • The fastest frosting speed in severe cold region appeared at about −10 °C. • Heating load had significant influence on frosting performance. [ABSTRACT FROM AUTHOR]

A temperature and hydraulic-balance control strategy has previously been proven effective for improving the operational performance and achieving significant energy-savings in air source heat pump (ASHP) heating systems. In this study, a frequency-conversion technique was added to the control strategy for the pump operation, evolving into an updated control strategy. To investigate the performance and evaluate the energy-saving benefits when using the updated strategy, a field experiment was conducted in two almost identical ASHP heating systems in a teaching building, one with the updated strategy (system A) and the other without (system B). Results showed that the updated strategy can ensure an appropriate indoor temperature without overheating. The working number and hours of ASHP compressors in system A were lower than those in system B. Moreover, the savings of heat and electricity of system A were 46.6% and 43.0%, respectively. Electricity-saving of the pump using frequency-conversion technique reached 20.2%, and the effect is more remarkable in the high-frequency range. The percentage of pump's electricity consumption of system A was only 16.4%, which was significantly lower than the previous experiment. Additionally, the COP of ASHP units of system A was 3.23 and was not affected by the introduction of frequency-conversion technique. • A temperature and hydraulic-balance control strategy was used in an ASHP heating system. • A frequency-conversion technique was added to update the control strategy. • The updated strategy achieved significant energy-saving benefits in the operation of ASHP units and pumps. • Energy-saving effect of frequency-conversion is obvious in high-frequency range. [ABSTRACT FROM AUTHOR]

Owing to the government's policy of clean-energy heating reform, air-source heat pump (ASHP) heating projects are growing rapidly in number in China, and an efficient operation mode for this type of heating system has become an issue for researchers. In this study, a new temperature and hydraulic-balance control strategy is proposed for ASHP heating systems. This strategy utilizes the cooperation of three different devices: room thermostats, pressure independent balancing and control valves, and a differential pressure relief controller. Two almost identical ASHP heating systems in areas A and B of a teaching building, one with the new control strategy (system A), were field tested. The operation mode was divided into two periods of school terms with a return water temperature of 35 °C for heating and winter vacation with a temperature of 20 °C for frost protection. Through a 67-day monitoring of operating performance, the results showed that system A could not only realize a more suitable indoor temperature, but also provided on-demand heating with the setting of thermostats. This new control strategy will not affect the COP of ASHP. Compared with system B , a significant energy conservation achievement of 38.6% heat savings and 31.5% electricity savings was achieved for system A during the school term. Moreover, the static payback period for the devices of the new control strategy is only 1.46 years. System A can realize a further positive environmental benefit with a 37.2% reduction in emissions. • A new temperature and hydraulic balance control strategy was proposed for ASHP heating system. • 38.6% heat savings and 31.5% ASHP units' electricity savings was achieved. • The COP of ASHP unit was 3.56 and was not affected by the new control strategy. • The economic benefits of the new control strategy are remarkable. • The environmental benefits of the new control strategy were demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Due to high power consumption and air pollution situation in China, insufficient indoor fresh air during heating season can be a noteworthy problem. Unlike previous researches, which mainly focused on cooling capacity of Earth-air Heat Exchanger (EAHE), feasibility of EAHE combined with Heat Recovery Unit (HRU) as an independent heat source to heat cold air in severe cold regions was firstly verified. U-shaped buried pipes were proposed to enhance heat transfer as well as save land-use. Thorough measurements of air and soil parameters and power consumption were conducted under several operation modes, performance indexes like heating capacity, heat transfer efficiency and COP were analyzed. Results showed average temperature rise of 14.0 °C provided by EAHE and further 12.1 °C promotion brought by HRU helped outdoor air reach to an acceptable level without auxiliary heating equipment. Heating capacity of EAHE increased with decreasing inlet temperature, when inlet temperature changed from −0.4 to −24.4 °C, heating capacity increased from 709 W (19.7 W/m) to 7718 W (214.4 W/m). Performance of HRU rarely reacted to climatic conditions because of the stable outlet temperature of EAHE. Maximum comprehensive COP was 16.3, which indicated the high efficiency of system. Results showed EAHE can be expanded to severe cold regions and achieve good efficiency. Highlights • Feasibility of applying Earth-air Heat Exchanger in severe cold regions was firstly investigated. • Experiments were conducted during heating season to evaluate the performance of system. • Correlation between heating capacity of EAHE and inlet air temperature was strong. • The proposed system can effectively heat fresh air without auxiliary heating equipment. • The influence to indoor environment brought by proposed system can be ignorable. [ABSTRACT FROM AUTHOR]