Heat Pump Coefficient Of Performance Research Articles

Development and application of a domestic heat pump model for estimating CO2 emissions reductions from domestic space heating, hot water and potential cooling demand in the future

This paper outlines the development and application of a domestic heat pump model for space heating and cooling energy. The model is intended to bridge the gap between the single coefficient of performance parameter currently used in the UK procedures for the assessment of the energy efficiency of dwellings and the dynamic simulation models frequently developed for the academic estimation of heat pump energy use. It is responsive to variations in source and sink temperatures whilst being simple enough to be embedded in a spreadsheet model.The model was developed by: building a regression model, using heat pump performance test results, relating heat pump coefficient of performance to the differential between source and sink temperatures – “lift”; deriving estimating rules for monthly supply temperature estimates for commonly-used heat pump sources and for demand temperatures for normal wet central heating sinks to give a monthly estimate for the source/sink differential; embedding the regression model in the UK standard model for domestic energy estimation, with additional routines to estimate energy consumption for additional heat and for space cooling.The model developed was validated by comparison with the existing BREDEM model. Compared with the standard BREDEM estimates, the resulting model showed correct response to changes in ambient temperatures, allowing correct estimating of consumption for additional heat under conditions of climate change. It showed variation of heat pump coefficient of performance across the year, allowing better estimation of winter peak load.

Fundamental optimal relation of a generalised irreversible quantum Carnot heat pump with harmonic oscillators

An irreversible quantum Carnot heat pump model working with many non-interacting harmonic oscillator systems is established in this paper. The quantum heat pump cycle is composed of two isothermal processes and two irreversible adiabatic processes. The irreversibilities of heat resistance, internal friction and bypass heat leakage are considered in the model. Based on the quantum master equation, semi-group approach and finite time thermodynamics (FTT), the cycle period, heating load and coefficient of performance (COP) of the quantum Carnot heat pump are derived, and detailed numerical examples are provided. At high temperature limit, the fundamental optimal relations between the heating load and COP of the quantum heat pump are deduced and analysed by using numerical examples. The effects of internal friction and bypass heat leakage on the optimal performance of the quantum heat pump are discussed in detail. The endoreversible, frictionless and without bypass heat leakage cases are discussed. The obtained results are general to the performance optimisation of quantum Carnot heat pumps and can provide some guidelines for optimal design of real quantum heat pumps.

Two-parameter Rankine Heat Pumps’ COP Equations

Equations for ideal vapour compression heat pump coefficient of performance (COPR) which contain two fit-parameters are reported in this work. These equations contain either temperature term alone or temperature and pressure terms as the only thermodynamic variable(s). The best equation gave error ≥5% over wide range of temperature-lift and for different working fluid types that include fluorocarbons, hydrocarbons and inorganic fluids. In these respects the equation performs better than the one-parameter models reported earlier.

Simulation of a high efficiency multi-bed adsorption heat pump

Attaining high energy efficiency with adsorption heat pumps is challenging due to thermodynamic losses that occur when the sorbent beds are thermally cycled without effective heat recuperation. The multi-bed concept described here enables high efficiency by effectively transferring heat from beds being cooled to beds being heated. A simplified lumped-parameter model and detailed finite element analysis are used to simulate a sorption compressor, which is used to project the overall heat pump coefficient of performance. Results are presented for ammonia refrigerant and a nano-structured monolithic carbon sorbent specifically modified for the application. The effects of bed geometry and number of beds on system performance are explored, and the majority of the performance benefit is obtained with four beds. Results indicate that a COP of 1.24 based on heat input is feasible at AHRI standard test conditions for residential HVAC equipment. When compared on a basis of primary energy input, performance equivalent to SEER 13 or 14 are theoretically attainable with this system. ► A multi-bed concept for adsorption heat pumps is capable of high efficiency. ► Modeling is used to simulate sorption compressor and overall heat pump performance. ► Results are presented for ammonia refrigerant and a nano-structured monolithic carbon sorbent. ► The majority of the efficiency benefit is obtained with four beds. ► Predicted COP as high as 1.24 for cooling is comparable to SEER 13 or 14 for electric heat pumps.

Study of the optimal control problem formulation for modulating air-to-water heat pumps connected to a residential floor heating system

For implementation in controllers with limited computational power, simplified optimal control formulations are desirable. For the case of a modulating heat pump system, the optimization problem is nonlinear due to the supply water temperature and load dependency of the heat pump coefficient of performance (COP). By neglecting these nonlinearities, e.g., by assuming a constant COP, the optimization problem becomes convex and fast convergence to the global minimum is ensured. This study quantifies the impact of these simplifications for the case of a modulating air-to-water heat pump connected to a residential floor heating system. A first comparison suggests a significant deterioration of the control performance. While the nonlinear formulations result in continuous operation at part load, the convex approximations give rise to large power fluctuations, increasing the energy cost with 7% to 16%. However, by penalizing power peaks in the cost function, the achieved control performances are almost identical. This reveals that the cost function is flat near the optimum. Compared to a conventional heating curve control strategy, the energy cost savings amount to 5% for optimization-based control strategies (in the case of a day/night tariff structure). Although less than expected, this improvement is still significant given the wide spread presence of the application.

Energy analysis of a solar-ground source heat pump system with vertical closed-loop for heating applications

A heat pump system is the ideal way to extend the heat supply of existing oil or gas fired heating system. Consumption costs are lowered through the use of free energy from the environment, and the dependence on fossils fuels simultaneously reduces. In order to investigate the performance of the solar-ground source heat pump system in the province of Erzurum having cold climate, an experimental set-up was constructed. The experimental apparatus consisted of solar collectors, a ground heat exchanger (GHE), a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. In this study, the performance of the system was experimentally investigated. The experimental results were obtained from October to May of 2008–2009. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP) and the system performance (COPS). The coefficient of performance of the heat pump and system were found to be in the range of 3.0–3.4 and 2.7–3.0, respectively. This study also shows that this system could be used for residential heating in the province of Erzurum being a cold climate region of Turkey.

Uncertainties in heat-pump coefficient of performance (COP) and exergy efficiency based on standardized testing

The uncertainties allowed in testing following international (ISO) and European (CEN) standards for testing of residential heat pumps (HPs) were investigated and quantified. For air/air HPs, the relative uncertainties of COP and exergy efficiency allowed by the CEN standard were found to be from 7% to 9%. For the ISO standard the figures were from 5% to 10%. For air/water HPs, the CEN standard allowed up to 9% relative uncertainty in the COP and 7% in the exergy efficiency. In addition to the uncertainties described in the standards, it was also shown how to estimate the uncertainty of COP due to uncertainties in the levels of temperature where the heat transfer occurs. For air/air HPs at standard rating conditions, this contributed 3% to the relative uncertainty of the COP and the exergy efficiency. Exemplary calculations based on published test data showed that very few HPs had performance clearly above or below those with the median results. The exergy efficiency of the air/air HPs, with some exceptions, showed a decrease with increasing outdoor temperature. A similar, but weaker tendency was observed for air/water HPs. The exergy efficiencies for air/water HPs were typically found in the range from 0.3 to 0.4.

Experimental thermal performance of a solar source heat-pump system for residential heating in cold climate region

Abstract Solar source heat pump systems present tremendous environmental benefits when compared to the conventional systems for residential applications. In addition to not exhausting natural resources, their main advantage is, in most cases, total absence of almost any air emissions or waste products. In order to investigate the performance of a solar source and energy stored heat-pump system in the province of Erzurum, an experimental set-up was constructed, which consisted of twelve flat-plate solar collector, a sensible heat energy storage tank, a water-to-water plate heat exchanger, a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. The experiments were carried out from January to June of 2004 and, the collector efficiency ( η c ), the heat pump coefficient of performance (COP) and the system performance (COPS) were calculated. In these months performed of the experiments, the outdoor temperature range varies from −10.8 °C to 14.6 °C. This study shows that the system could be used for residential heating in the province of Erzurum having the coldest climate of Turkey.

Experimental study of vertical ground-source heat pump performance evaluation for cold climate in Turkey

Heat pump systems are recognized to be outstanding heating, cooling and water heating systems. They provide high levels of comfort as well as offering significant reductions in electrical energy use. In addition, they have very low levels of maintenance requirements and are environmentally attractive. The purpose of this study is to evaluate the experimentally performance and energy analysis of vertical ground-source heat pump (GSHP) for winter climatic condition of Erzurum, Turkey. For this aim, an experimental analysis was performed on GSHP system made up in the Energy Laboratory in the campus of Ataturk University. The experimental apparatus consisted of a ground heat exchanger, the depth of which was 53 m, a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement and control equipments. Tests were performed under laboratory conditions for space heating, in which experimental results were obtained during January–May within the heating season of 2007. The experimentally obtained results were used to calculate the heat pump coefficient of performance (COP) and the system performance (COPs). The COP and COPs were found to be in the range of 2.43–3.55 and 2.07–3.04, respectively. This study also shows that the system proposed could be used for residential heating in the province of Erzurum which is one of the coldest climate region of Turkey.

Performance enhancement of a heat pump system with ice storage subcooler

This article experimentally investigates the thermal performance of a heat pump system with an ice storage subcooler. The system supplies heating and cooling demands to two greenhouses with temperature ranging 308∼323 K and 273∼291 K respectively and utilizes an ice storage tank to subcool the condensed refrigerant, which can enhance the system coefficient of performance (COP). The ice storage tank charges for storing ice, when the cooling load is less than the nominal cooling capacity. While the cooling load is larger than the nominal cooling capacity, the ice storage tank discharges for subcooling. The results show that in the charge mode the heat pump COP of ice storage system is 12% higher than that without ice storage tank. Under the discharge mode, the ice storage system provides the refrigerator COP 15% higher than that without ice storage tank.

Predicting the fluid temperature at the exit of the vertical ground heat exchangers

The energy analysis of ground source heat pump systems is based on the instantaneous fluid temperature at the ground heat exchanger outlet. This temperature defines the ground source heat pump coefficient of performance (COP) and hence the electricity consumption required in order to fulfill the energy demands of the building. The aim of this work is to present a model able to predict the fluid temperature at the ground heat exchanger outlet, taking into account the heat transfer phenomena in the soil and the temporal variation of the thermal load of the ground heat exchanger. The model developed was verified using experimental data, expanding over a three years period, of a vertical ground heat exchanger. It is proved that the model is able to satisfactorily predict the recorded temperature values throughout the verification period. The differences between measured and estimated outlet water temperatures impose a deviation between the estimated and the actually recorded electricity consumption of less than 4%.

Defrost improvement by heat pump refrigerant charge compensating

During winters, the air-source heat pump often operates with substantial frost formation on the outdoor heat exchanger, and the frost layer has to be melted away periodically to keep a high heat pump coefficient of performance (COP). Otherwise, the unmelted frost layer and water will become high density frost or ice layer in heating mode. However, it is difficult to melt the frost layer in the defrosting cycle, where the effective defrosting time plays an important role in improving the defrosting ability. Generally, the defrosting time can be decreased by the following ways: increasing the refrigerant flow rate effectively, and rapidly establishing the suction pressure, discharge pressure, and the compressor power. A new heat pump defrost system with a refrigerant charge compensator, instead of the accumulator which is a key component for the frosting cycle performance, is developed in this paper. Furthermore, test results showed that the improved frost system with the compensator worked as expected, and its suction and discharge pressures and the power of the compressor during the defrosting were much larger than before.

Performance of the photovoltaic solar-assisted heat pump system with and without glass cover in winter: A comparative analysis

An application of photovoltaic/thermal (PV/T) technology in heat pump, known as the PV solar-assisted heat pump (PV-SAHP) system, is presented. Comparative performance tests were conducted through an experimental rig under two different working conditions of the PV/T collectors: with and without glass cover. The energy performance in terms of PV/photothermic conversions and refrigeration cycle was compared in typical winter days of the temperate climate zone in China. It was found that with a single glass cover, the exergy efficiencies of PV/photothermic conversions and overall PV/T conversion were, respectively, 12.83, 5.26, and 18.09 per cent, and the heat pump coefficient of performance (COP) was 4.85. Without the glass cover, the exergy efficiencies and COP were 13.36, 3.04, and 16.40 per cent, and 3.41, respectively. The results imply that although the presence of the glass cover leads to a small reduction in the PV exergy efficiency, it is able to improve considerably the photothermic exergy efficiency, the overall PV/T exergy efficiency, and the COP of the PV-SAHP system in winter.

Heat transfer effect on optimal performance of two-stage thermoelectric heat pumps

A model of two-stage semiconductor thermoelectric heat pumps with external heat transfer and internal irreversibility is built. Performance of the heat pump with Newton's heat transfer law is analysed and optimized using the combination of finite-time thermodynamics and non-equilibrium thermodynamics. The analytical formula about heating load versus working electrical current, and the coefficient of performance (COP) versus working electrical current are derived. For the fixed total number of thermoelectric elements, the ratio of number of thermo-electric elements of top stage to the total number of thermoelectric elements is also optimized for maximizing the heating load and the COP of the thermoelectric heat pump. The effects of design factors on the performance are analysed.

Performance optimization for a two-stage thermoelectric heat-pump with internal and external irreversibilities

A model of the behaviour of a two-stage semiconductor thermoelectric heat-pump with external heat transfer is devised. Performance of the heat-pump, assuming Newton’s heat-transfer law, is analyzed using the combination of finite-time thermodynamics and non-equilibrium thermodynamics. The analytical formula describing the heating load versus working electric-current, and the coefficient of performance (COP) versus working electric-current are derived. For the fixed total number of thermoelectric elements, the ratio of number of thermoelectric elements of the top stage to the total number of thermoelectric elements is also optimized for maximizing the heating load and the COP of the thermoelectric heat-pump. The effects of design factors on the performance are analyzed.

ENERGY EFFICIENCY OF A NEW HEAT PUMP SYSTEM FOR DRYING GRAIN

An experimental closed-loop heat pump grain drying system was designed and evaluated for energy performance while drying shelled corn and grain sorghum. The system was designed based on an estimated heat pump coefficient of performance (COP) of 4.0, an air-to-air exchanger efficiency of 80%, and a fan efficiency of 50%. The objective of this research was to develop and evaluate a closed-loop heat-pump system for drying grain that is more efficient than conventional gas-fired dryers. Four drying tests using three corn lots with initial moisture contents of 25%, 20%, and 18% w.b. and one grain sorghum lot with initial moisture content of 25% w.b. were conducted during the 1998 fall harvest season. Temperature of the heated air was controlled in the range of 43 to 48°C with airflow rates of 0.26 and 0.25 m 3 /h per dry mass of grain for corn and grain sorghum, respectively. The average amount of input energy (all electric) required to remove 1 kg of water from the corn lots was 1186 kJ based on grain lot weight differences before and after drying. The best drying performance observed in a 4-6 h period was 942 kJ/kg of water removed. The average drying capacity was 230 kg/h based on an equivalent moisture reduction from 25% to 15.5% w.b. The drying performance for drying grain sorghum was lower (1516 kJ/kg of water) than that for drying corn. The average thermal energy transfer rate of the air-to-air heat exchanger was 11.47 kW, which represented about 28% of the total (source-sink) thermal energy transfer rate of 39.38 kW. The average efficiency of the air-to-air heat exchanger was about 34%. The average COP for the heat pump was 6.4 including the air-to-air thermal transfer and 4.7 excluding the air-to-air thermal transfer.

PRODUCTION OF VOLATILE FATTY ACIDS AND ALCOHOLS FROM DAIRY WASTEWATER UNDER THERMOPHILIC CONDITIONS

An experimental closed–loop heat pump grain drying system was designed and evaluated for energy performance while drying shelled corn and grain sorghum. The system was designed based on an estimated heat pump coefficient of performance (COP) of 4.0, an air–to–air exchanger efficiency of 80%, and a fan efficiency of 50%. The objective of this research was to develop and evaluate a closed–loop heat–pump system for drying grain that is more efficient than conventional gas–fired dryers. Four drying tests using three corn lots with initial moisture contents of 25%, 20%, and 18% w.b. and one grain sorghum lot with initial moisture content of 25% w.b. were conducted during the 1998 fall harvest season. Temperature of the heated air was controlled in the range of 43 to 48
C with airflow rates of 0.26 and 0.25 m 3 /h per dry mass of grain for corn and grain sorghum, respectively. The average amount of input energy (all electric) required to remove 1 kg of water from the corn lots was 1186 kJ based on grain lot weight differences before and after drying. The best drying performance observed in a 4–6 h period was 942 kJ/kg of water removed. The average drying capacity was 230 kg/h based on an equivalent moisture reduction from 25% to 15.5% w.b. The drying performance for drying grain sorghum was lower (1516 kJ/kg of water) than that for drying corn. The average thermal energy transfer rate of the air–to–air heat exchanger was 11.47 kW, which represented about 28% of the total (source–sink) thermal energy transfer rate of 39.38 kW. The average efficiency of the air–to–air heat exchanger was about 34%. The average COP for the heat pump was 6.4 including the air–to–air thermal transfer and 4.7 excluding the air–to–air thermal transfer

Experimental and theoretical investigation of a solar heating system with heat pump

In this study, the performance of a solar heating system with a heat pump was investigated both experimentally and theoretically. The experimental results were obtained from November to April during the heating season. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load met by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. The average seasonal heating performance values are 4.0 and 3.0 for series and parallel heat pump systems, respectively. A mathematical model was also developed for the analysis of the solar heating system. The model consists of dynamic and heat transfer relations concerning the fundamental components in the system such as solar collector, latent heat thermal energy storage tank, compressor, condenser, evaporator and meteorological data. Some model parameters of the system such as COP, theoretical collector numbers ( N c), collector efficiency, heating capacity, compressor power, and temperatures ( T 1, T 2, T 3, T T) in the storage tank were calculated by using the experimental results. It is concluded that the theoretical model agreed well with the experimental results.

Energy Performance Analysis of Isobutene/Water/ tert-Butanol Chemical Heat Pump

A chemical heat pump cycle for upgrading waste heat from ≈ 70°C to ≈ 110°C has been proposed, which utilizes the reaction of isobutene/water/tert-butanol. The thermal performance was analysed by process simulation, based on experimental data. A flow cycle of the heat pump is proposed. The reaction conditions for the model were optimized. The performance of the proposed heat pump was evaluated in order to compare its coefficient of performance (COP) with that of the conventional compression heat pump. The proposed heat pump system has a COP of 6.4 when operating between 70 and 110 °C, which is higher than the COP of the conventional compression heat pump of 4.0 under the same conditions. In addition, the proposed heat pump has a higher exergy efficiency than the conventional compression heat pump.

Investigation of a combined solar-heat pump system for residential heating. Part 1: experimental results

In order to investigate the performance of the combined solar–heat pump system with energy storage in encapsulated phase change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set-up was constructed. The experimental results were obtained from November to May during the heating season for two heating systems. These systems are a series of heat pump system, and a parallel heat pump system. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. Copyright © 1999 John Wiley & Sons, Ltd.