Xiaowei Fan

Modeling and simulation of a transcritical R744 heat pump system

To analyze the performance of a carbon dioxide heat pump system, a steady state simulation model has been developed. The effects for different operating parameters such as compressor speed and water inlet temperature of the gas cooler were studied. It was shown that there was an optimum compressor speed for a certain system, and the maximum COP decreased and the optimum discharge pressure increased with the increasement of water inlet temperature of the gas cooler. The maximum COP and optimum pressure were correlated as functions of water inlet temperature of the gas cooler, and it is expected to offer useful guidelines for CO2 heat pump design and development.

Survey and analysis of urban residential building energy consumption in Shangqiu city

To understand the characteristics of building energy consumption in underdeveloped small and medium-sized cities, a questionnaire of residential building energy consumption in Shangqiu city is implemented, which consists of basic conditions of residents, power consumption, fuel consumption and indoor thermal environment, etc. Then index of building energy consumption and information of possession and usage of household appliances are obtained, and the present condition of indoor thermal environment in the region is analyzed.

Experimental study of optimum heat rejection pressure for a CO 2 heat pump water heater

As an environmentally friendly refrigerant, CO2 is seen as one of the best fluids for a heat pump water heater application system. To investigate the relationships between optimum heat rejection pressure and other related operating parameters, an experimental research has been conducted for a transcritical CO2 heat pump water heater with two throttling valves. It proved that it is relatively reliable to control the heat rejection pressure of the CO2 system with two throttling valves; there exists an optimal heat rejection pressure, under which the system can reach the maximum heating coefficient of performance. Meanwhile, the research also reveals that the optimal heat rejection pressure chiefly depends on the outlet refrigerant temperature of the gas cooler, and in the next place, the evaporating temperature; on the other hand, the superheat degree of CO2 at the inlet of the compressor was found to have little to do with the optimum heat rejection pressure.

An investigation of a heat pump system using CO2/propane mixture as a working fluid

ABSTRACT In order to decrease the heat rejection pressure of heat pump using pure working fluid, CO2 or R744, other natural component including hydrocarbons (R290, R600a, R600, R1270, R170, R601) and dimethyl ether (RE170) is added to CO2, respectively, and then six binary mixtures are achieved. By environmental and thermodynamic comparisons, R290 is selected to be the most appropriate component candidate to mix with CO2, and meanwhile to weaken the flammability and explosivity for pure R290. Then, the system performances of heat pump using mixture of CO2 and R290 were experimentally studied when R290 is added to CO2 with a small fraction, and compared with that of the pure CO2. The experimental test rig is designed and set up for the transcritical heat pump system. When the refrigerant charge is variable, the heating coefficient performance, optimum heat rejection pressure, compressor power, mass flow rate of refrigerant, and total heat coefficient of gas cooler were researched. The variation ratios of heating coefficient performance and heating capacity with deviation from the optimum refrigerant charge were also investigated. The optimum refrigerant charge of CO2/R290 is obtained and the research results show that the addition of R290 to CO2 can efficiently reduce the heat rejection pressure and improve the system performance. The results in the present work could provide useful guidelines for the design and operation of heat pump system using CO2-based mixture.

A Ventilation Cooling Solution to Improve Thermal Environment of High Energy Density Li-Ion Battery Packs

This paper focuses on the cooling solution to a high energy density and large capacity Li-ion battery system which consist of four packs of 26650 cells. The cooling measure is a critical technology for many Li-ion battery systems especially that designed for hybrid electric vehicles, in which, high energy density within a limited space is very common in these systems. Both the safety and efficiency of Li-ion battery cells rely on the temperature which is under control of the battery thermal management system. In this study, temperature fields within battery boxes are simulated with the computational fluid dynamic (CFD) method. With the help of an airconditioner, a cooling solution is proposed for a relatively large dimensional, high energy density Li-ion battery cells array using by vehicles. Through the proposed solution, the maximum single-cell temperature is restricted to a reasonable level, and the maximum temperature difference throughout the battery system is also improved.Copyright

Theoretical Study of Heat Pump System Using R744/R1234yf as Refrigerant

In this paper, the eco-friendly zeotropic mixture, R744/R1234yf was chosen as the alternative refrigerant in the instant heat pump water heater system. The cycle performance of heat pump was analyzed theoretically under the nominal working condition of heat pump system. The prediction results show that the new mixture has significant advantages for the instant heat pump with a large heat-sink temperature lift, and there exists an optimal mass fraction of R744/R1234yf, at which the maximum COPh should be obtained. The optimal mass fraction of R744/R1234yf is 17/83 and the system COPh should be attained to 4.29.Copyright

Research on Condensation Pressure and Temperature of Heat Pumps Using Blends of CO2 with Butane and Isobutane

Based on the Thermodynamic theorem of corresponding states, the relationship between condensation pressure and temperature of subcritical heat pump systems using CO2/R600 or CO2/R600a as the working fluid is proposed. With the proposed correlation, the effective mass fraction range of component R600 or R600a can be readily determined according to the designed condensation pressure. Or if the condensation temperature is given, it is convenient to get the effective mass fraction scope of R600 or R600a. Within the condensation pressure range of 4.00–7.38 MPa, 36 points are calculated by the fitting formula and then checked by REFPROP8.0. The mean deviation between the fitting relationship and REFPROP8.0, below 1 %, shows that the proposed relationship can be used with satisfactory certainty under the given conditions. The research results may provide a beneficial basic data to promote the application of medium temperature heat pumps using blends of CO2 with butane and isobutane.

Performance Assessment of Blends of CO2 With Eco-Friendly Working Fluids for Heat Pump Applications

Since pure CO2 as refrigerant has some disadvantages failing to meet requirements, binary blends of CO2 (or R744) with other eco-friendly working fluids, R290, R1270, R170, RE170 and HFC134a are proposed in this paper to be used for medium temperature heat pump systems. The eco-friendly refrigerant mixtures can reduce the heat rejection pressure as that for pure CO2, and meanwhile suppress the flammability, explosivity as that for pure HCs or RE170. Based on the pinch point of heat transfer, the numerical models of heat pump cycle using CO2-based mixture are developed. With a comprehensive consideration of heating coefficient of performance (COPh), optimum heat rejection pressure, volumetric heating capacity, discharge temperature, the binary mixture CO2/R290 is determined as the most suitable working fluid for the given heat pump application. Compared to pure CO2, the optimum heat rejection pressure of mixture for 95/5, 90/10, 85/15 and 80/20 is decreased by 0.82, 0.94, 1.06 and 1.86MPa respectively for heat sink outlet temperature of 65°C. The experimental testrig is designed and set up for the transcritical heat pump system. The experimental study with different CO2 mass fraction has been carried out, which conducts a study on the variations of heat pump performance, component’s mass fraction and working fluid charge. The experimental results validated the CO2/R290 natural mixture proposed in theory. The experimental results provide useful references on the optimization and improvement of CO2/R290 heat pump testrig.Copyright

Study on model predictive control of VAV air supply system under summer condition

In this paper, a model of VAV air supply system is established based on ventilation network, by which the model predictive control is used to control the VAV air supply system. Simulation tests of VAV air supply system under summer condition show that the structure of VAV air system, which is controlled by this control strategy is very stable and flexible, the control system has good performance. The model predictive control based on ventilation network make the air supply system of VAV more accurate and reliable.