Heat Pump Subsystem Research Articles

Solar-Driven LiBr/H20 Air Conditioning System With a R-123 Heat Pump Assist

This paper presents an energy system that utilizes solar energy to produce air conditioning with an absorption refrigeration system. Since there is often a temporal variance between the availability of the required solar energy and the demand for commercial building air conditioning, a liquid natural gas (LNG) subsystem is often used to supplement the solar-thermal array system. Because of operating cost consideration, this paper proposes the use of a R-123 heat pump to supply the required additional heat and temperature needed to effectively operate the absorption air conditioning system. Waste heat from the absorption system water condenser is used by the R-123 heat pump subsystem evaporator to supply the additional required heat at the appropriate temperature to the absorption system generator using the R-123 heat pump subsystem condenser. Under conditions when the pricing ratio of electric power and LNG is at certain level or when LNG is not available, the proposed R-123 heat pump subsystem offers a cost effective option. The solar-thermal collector array and R-123 heat pump are in a series just before the generator of the absorption system. The temperature differential between the absorption system water condenser temperature and the required absorption system generator temperature is relatively moderate, so that the coefficient of performance of the R-123 heat pump subsystem is sufficiently high to be a competitive alternative when compared to a LNG assist subsystem. Because of this moderate temperature difference, the proposed R-123 heat pump assist subsystem appears to be a better choice under certain conditions, than the use of LNG to raise the solar-thermal array transport fluid temperature to the required generator temperature when the solar-thermal array system fails to do so.

Performance analysis of a rooftop wind solar hybrid heat pump system for buildings

Utilization of wind and solar energies coupled with heat pumps is a promising technology for energy conservation and emission reduction. This paper describes a rooftop wind solar hybrid heat pump system for building hot water, heating and cooling loads and presents energy and exergy analyses as well as an environmental benefit assessment. The system consists of a shrouded wind-lens turbine subsystem, a flat-plate solar thermal subsystem and a water/air source heat pump subsystem, where the wind and solar subsystems are compactly installed on the rooftop. The solar collector heats water for supplying domestic hot water and increasing the heat pump evaporation temperature for room heating. Heat pumps are used for room heating and cooling and auxiliary heating domestic hot water. Wind power contributes to satisfying the heat pump power demand. Energy and exergy analyses show that the solar thermal subsystem is exergetically inefficient and thus a better design of the solar collector can improve the system exergy efficiency. Wind power can provide 7.6% of the yearly heat pump power demand to satisfy the thermal loads of a 198m2 residential building in Beijing. The system can yearly reduce 31.3% carbon dioxide emission compared with conventional energy systems.

Fluids and parameters optimization for a novel cogeneration system driven by low-temperature geothermal sources

A novel cogeneration system was proposed and techno-economically investigated, consisting of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger subsystem and a heat pump subsystem. The main purpose is to identify suitable working fluids (among 27 fluids with boiling point temperature ranging from −47.69 to 47.59 °C) and optimized cycle parameters for the ORC-based power generation subsystem. The screening criteria include net power output per unit mass flow rate of hot source ( P net), the ratio of total heat transfer area to net power output ( A/ W net), and electricity production cost (epc). Results show that there exists optimum evaporating temperatures maximizing the P net value and minimizing the A/ P net and epc values. The optimum temperatures vary with different screening criteria and fluids. Optimized fluids based on each screening criteria are not the same. E170, R600 and R141b show the lowest A/ W net and epc values with averagely 3.78% lower P net value than R236ea which presents the largest P net value.

Selection of working fluids for a novel low-temperature geothermally-powered ORC based cogeneration system

A novel cogeneration system driven by low-temperature geothermal sources was investigated in this study. This system consists of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The main purpose is to identify appropriate fluids which may yield high PPR (the ratio of power produced by the power generation subsystem to power consumed by the heat pump subsystem) value and QQR (the ratio of heat supplied to the user to heat produced by the geothermal source) value. Performances of the novel cogeneration system under disturbance conditions have also been studied. Results indicate that fluids group presenting higher normal boiling point values shows averagely 7.7% higher PPR values and R236ea and R245ca outstand among the group. Δ T P (pinch temperature difference in heat exchangers) and η t (turbine efficiency) values play more important roles on the variation of PPR values. QQR values change slightly with various Δ T P , η t and η rp (refrigerant pump efficiency) values while the variation range is larger under various geothermal source and heating supply parameters. Smaller Δ T P value, higher η t value, higher geothermal source parameters and lower heating supply parameters lead to higher PPR values but lower QQR values.

Working fluids of a low-temperature geothermally-powered Rankine cycle for combined power and heat generation system

A novel combined power and heat generation system was investigated in this study. This system consists of a low-temperature geothermally-powered organic Rankine cycle (ORC) subsystem, an intermediate heat exchanger and a commercial R134a-based heat pump subsystem. The advantages of the novel combined power and heat generation system are free of using additional cooling water circling system for the power generation subsystem as well as maximizing the use of thermal energy in the low-temperature geothermal source. The main purpose is to identify suitable working fluids (wet, isentropic and dry fluids) which may yield high PPR (the ratio of power produced by the power generation subsystem to power consumed by the heat pump subsystem) value and QQR (the ratio of heat supplied to the user to heat produced by the geothermal source) value. Parameters under investigation were evaporating temperature, PPR value and QQR value. Results indicate that there exits an optimum evaporating temperature to maximize the PPR value and minimize the QQR value at the same time for individual fluid. And dry fluids show higher PPR values but lower QQR values. NH3 and R152a outstand among wet fluids. R134a outstands among isentropic fluids. R236ea, R245ca, R245fa, R600 and R600a outstand among dry fluids. R236ea shows the highest PPR value among the recommended fluids.

Optimum design of multi-stage cascaded refrigeration-heat pump system

A multi-stage cascaded refrigeration-heat pump system which employs two-stage compression on high temperature (HT) side and single-stage compression on low temperature (LT) side is numerically optimized for preliminary design of the system. System cycle considered is very close to realistic one. Design quantities pertaining to the optimum performance and minimum running cost of the system, e.g. inter-stage and condensing temperatures, economic water rates, power requirements etc. are presented for unit tonnage capacity in the form of graphs and tables. Qualitative effects of the operating variables are also displayed. Most widely used and comparatively cheaper refrigerant R-22 is selected for heat pump subsystem and R-13 for refrigeration sybsystem. The evaporator and ambient temperatures' ranges are −60 to −30°C and 10 to 60°C, respectively. Overall coefficients of performance of the system are found to be 2.8 to 7.4, if the system operates within the considered ranges of the operating variables/parameters.