The performance of heat pumps in service—A simulation study

A computer model is developed to simulate the performance of air-to-water heat pumps heating a house via a radiator system. The performance characteristics of the heat pumps are derived from laboratory measurements. Hourly weather observations are used to calculate the heat demand of the house and the performance of the heat pump. The effects of changes in heat pump characteristics, changes of radiator size, and changes in heat demand of the house due to insulation, are compared in terms of their effects on annual energy consumption.     

The energy saving obtainable with solar heating and heat pumps in a northern climate

The energy saving obtainable with active solar heating and heat pumps has been studied for several years in the Northern climate of Finland. The studies deal mainly with small houses. A computer program is developed which calculates hour by hour the annual energy balance of different heating systems. The performance, of the heating systems are also measured in inhabited houses. The calculations show that the useful solar energy obtainable from the collector is 50–400 kWh/m² annually depending on the system and the collector size. A heat pump in the system is very advantageous, because it keeps the heat losses low and the collector efficiency high. It approximately doubles the energy obtainable. The measurement results have not been as good as expected. The solar energy obtained from the collector has been 120–160 kWh/m² annually. The main reasons for the low solar energy are design and equipment faults and the shading effects. The best energy saving device is the earth heat pump. It is also therefore very advantageous that the peak power demand decreases markedly. When the area of the earth pipes is large enough, energy may be extracted from earth through the whole year. The annual coefficient of performance is 2–3. Also a heat pump which extracts heat from exhaust air in dwelling houses has been very promising.     

Investigation of thermal performance of a ground coupled heat pump system with a cylindrical energy storage tank

An analytical and computational model for a solar assisted heat pump heating system with an underground seasonal cylindrical storage tank is developed. The heating system consists of flat plate solar collectors, an underground cylindrical storage tank, a heat pump and a house to be heated during winter season. Analytical solution of transient field problem outside the storage tank is obtained by the application of complex finite Fourier transform and finite integral transform techniques. Three expressions for the heat pump, space heat requirement during the winter season and available solar energy are coupled with the solution of the transient temperature field problem. The analytical solution presented can be utilized to determine the annual variation of water temperature in the cylindrical store, transient earth temperature field surrounding the store and annual periodic performance of the heating system. A computer simulation program is developed to evaluate the annual periodic water and earth temperatures and system performance parameters based on the analytical solution. Copyright © 2003 John Wiley & Sons, Ltd.     

Application of a heat pump system using untreated urban sewage as a heat source

Untreated urban sewage contains large amounts of thermal energy; and its temperature is suitable as a heat source in heat pumps for the heating and cooling of buildings. However, it is not widely used in heat pump systems due to the problem of filth. This paper presents an untreated sewage source heat pump (USSHP) system in which auto-avoiding-clogging equipment is used to continuously capture suspended solids in the sewage. Thus, the block problems caused by filtration and fouling in the heat exchanger tubes can be efficiently resolved in this system. In an actual engineering application, the characteristic parameters of USSHP system are tested under typical operating conditions for heating status. Based on the test results, the performances of the USSHP system are examined. The results indicate that the thermal resistance of the convective heat transfer and fouling on the sewage side in the sewage exchanger is 80% of its total thermal resistance. The COP of the heat pump unit and the COP of the USSHP system are 4.3 and 3.6, respectively.     

Performance of a low energy house in a mild cooling season. Part 2: Thermal performance of the heat pump

A low-energy house located in Halifax, Canada was monitored for a year using a computerized data acquisition system. Data on indoor and outdoor temperatures, relative humidities, and power consumption were collected for a whole year. The results of the analysis of the cooling season data from the heat pump system are presented in this paper. The analysis of the data indicated that a large part of the latent cooling done by the heat pump was subsequently converted to sensible cooling as a result of the evaporation of the condensate from the indoor coil. It was found that 25% of the total sensible cooling supplied to the house during the cooling season was as a result of the conversion of latent cooling to sensible cooling. This phenomenon has important implications in design, operation, and modelling of heat pumps and cooling systems with direct expansion coils. The seasonal EER of cooling was 1.95, and the total power consumption was 1194 kWh with a corresponding cost of Can $84. It was also found that temperature set-up during unoccupied periods did not result in any savings in the daily power consumption.     

The performance of an open-loop lake water heat pump system in south China

A district heating and cooling (DHC) system that utilizes lake water as heat source–sink of heat pumps has been constructed in Xiangtan, a city in Hunan province in south China. An initial analytical study had been carried out before the construction. In this paper, a simplified two-dimensional model is developed to simulate the steady lake water temperature (LWT) distribution during continuous operation. The simulation results indicate that the impacts of the discharge on entering water temperatures (EWT) and the ecological environment of lake are acceptable. Field test results showed that the COP values of the system were, respectively, 0.7–0.85 higher in cooling season and about 0.46 higher in heating season than those of the air-source heat pump (ASHP) units at the same sink and source temperatures. An acceptable payback period of 5.6 years was found through an economic analysis based on the comparison between the initial and operating costs of the system and those of the distributed ASHP units that would have been installed according to initial scheme.     

Short-term thermal energy storage as a means of reducing the heat pump capacity required for domestic central heating systems

The effects upon the economics, size and performances of domestic central heating heat pumps by the incorporation of some thermal energy storage between the heat pump and the heat distribution system are studied with the aid of computer simulation programs. It is demonstrated that significant reductions in the capacity of the heat pump and system annual running costs can be made by using moderate quantities of heat storage without causing any detriment to the overall performance of the heating system. The results are being validated in the laboratory, where a phase-change material thermal energy store is linked to a heat pump and heat distribution system, and the performance of this system is being monitored.     

Modeling and optimization of a solar assisted heat pump using ice slurry as a latent storage material

This paper presents the modeling and optimization of a solar assisted heat pump using ice slurry. Solar collectors are used as the primary source of thermal energy, with two distinct loops allowing the collectors to operate in series with an ice tank, or a warm water tank. Thermal energy stored in the ice tank is transferred to a warm water distribution tank via a heat pump. First, a new mathematical model of an ice slurry storage tank is presented. Validation of the model with experimental data confirms its ability to predict the ice mass and tank fluid temperatures during the charging and discharging modes of operation. The developed ice tank model is combined with the TRNSYS energy simulation program to formulate a complete model of the proposed heat pump system. This computer model then serves as a base for a mathematical optimization with the objective to minimize the energy use for heating and DHW over a single heating season. Simulated results demonstrate the potential of the optimized system in reducing the heating operating energy use of a high performance home in Montreal, QC.     

Experimental investigation of a vapor compression heat pump used for cooling and heating applications

The present work aims at evaluating the performance characteristics of a vapor compression heat pump (VCHP) for simultaneous space cooling (summer air conditioning) and hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of evaporator water inlet temperature (14:26 °C) and condenser water inlet temperature (22:34 °C). R134a was used as a primary working fluid whereas water was adopted as a secondary heat transfer fluid at both heat source (evaporator) and heat sink (condenser) of the heat pump. Performance characteristics of the considered heat pump were characterized by outlet water temperatures, water side capacities and coefficient of performance (COP) for various operating modes namely: cooling, heating and simultaneous cooling and heating. Results showed that COP increases with the evaporator water inlet temperature while decreases as the condenser water inlet temperature increases. However, the evaporator water inlet temperature has more effect on the performance characteristics of the heat pump than that of condenser water inlet temperature. Actual COP of cooling mode between 1.9 to 3.1 and that of heating mode from 2.9 to 3.3 were obtained. Actual simultaneous COP between 3.7 and 4.9 was achieved.     

Assessment of an integrated active solar and air-source heat pump water heating system operated within a passive house in a cold climate zone

In the pursuit of energy savings and emission reductions, solar energy heating systems have been promoted in China. However, there still exist many barriers to the operation of solar heating systems, in combination with other systems, under realistic conditions. In order to investigate this further, an integrated space heating system including passive sunspace, active solar water heating, and air-source heat pump (ASHP) was built. The detailed running performance of each subsystem was comparatively analyzed in a full-scale test house in a cold climate zone. This integrated system showed many encouraging results in terms of the maintenance of a stable and comfortable indoor thermal environment during the winter season. The study building consumed electricity as convectional energy, which only accounted for about one-third of the total energy supplied for heating. However, our study also found some shortcomings in the system design. Feasible suggestions regarding the running procedures aimed at a more optimal and effective design were proposed. The systems proposed in this study could be used as a promising future technology for energy savings and emission reductions in rural buildings. The study could also help achieve targets for energy savings and renewable energy utilization in China and other countries.     

First and second law analysis of a solar assisted heat pump based heating system

We propose a model for the heating system of an ecological building whose main energy source is solar radiation. The most important component of the heating system is a vapour compression heat pump. Both the first law and the second law were used to analyse the heat pump operation. The state parameters and the process quantities were evaluated by using, as input, the building thermal load. The second law analysis emphasised that most of the exergy losses occur during compression and condensation. Preliminary results show that the photovoltaic array can provide all the energy required to drive the heat pump compressor, if an appropriate electrical energy storage system is provided.     

A review of heat pump systems for heating and cooling of buildings in China in the last decade

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.     

Energy analysis of a low‐temperature heat pump heating system in a single‐family house

Energy costs and environmental concerns have made energy optimisation a viable option for buildings. Energy‐efficient heating systems together with an effective use of buildings thermal mass and tightness have a significant impact on the energy requirement and on the possibility for sizeable running cost savings. In this study we use the simulation tool TRNSYS‐EES to model and analyse the performance of a residential house and the low‐temperature heating system that serves its thermal needs. The building is a single‐family house with controlled ventilation and the chosen heating system is a hydronic floor heating system connected to an exhaust air heat pump. The aim of the simulation is to study the performance of the building, the heating system and the controls in an integrated manner. Overall, the results indicate that the energy efficiency issue implicates system design and system thinking concerns as well as techno‐economic difficulties. The controls and the choice of the operation mode are of a great importance. Copyright © 2004 John Wiley & Sons, Ltd.     

Heat transfer in a twin-screw multiphase pump: Thermal modeling and one application in the petroleum industry

This paper presents a model of the heat transfer processes in the casing and rotors of a twin-screw multiphase pump. The model was developed to study the influence of temperature rise in the subsea multiphase pumping system-500 (SMPS), being developed by Petrobras, that operates with a twin-screw multiphase pump. The model is divided in three parts: heat transfer in the casing, in the rotor and energy balance of fluid. For the rotor, a helicoidal coordinate system is used to calculate the heat transfer. Axial symmetry is considered so it is possible to construct a two-dimensional model. The casing is modeled using an eccentric cylindrical coordinate system. In this case, the temperature gradient in axial direction is neglected and a two-dimensional calculation is carried out. The finite volume method is used to solve the transformed partial differential equations. With the two heat transfer models implemented, the fluid temperature is calculated using a simple energy balance that takes into account electric power, transferred heat and fluid internal energy. The implemented model was used to simulate thermal behavior of casing and rotors during loss of prime events faced by SMPS-500. Experimental data collected in pump trials are used as initial input parameters and the model calculates temperature evolution during the loss of prime events.     

柴油机热泵供暖系统

本文从热力学分析出发，提出了一种由柴油机驱动热泵的供暖装置。该装置可将柴油机中部分排气热损失及冷却系统热损失加以回收利用，具有较高的供热效率和很好的开发前景。     

A study on the design and analysis of a heat pump heating system using wastewater as a heat source

In this study, the compression heat pump system using wastewater, as a heat source, from hotel with sauna was designed and analyzed. This study was performed to investigate the feasibility of the wastewater use for heat pump as a heat source and to obtain engineering data for system design. This heat pump system uses off-peak electricity that is a cheap energy compared to fossil fuel in Korea. For this, the charging process of heat into the hot water storage tank is achieved only at night time (22:00–08:00). TRNSYS was used for the system simulation with some new components like the heat pump, which we create ourselves.As a result, it was forecasted that the yearly mean COP of heat pump is about 4.8 and heat pump can supply 100% of hot water load except weekend of winter season. The important thing that should be considered for the system design is to decrease the temperature difference between condenser and evaporator working fluids during the heat charging process by the heat pump. This heat pump system using wastewater from sauna, public bath, building, etc. can therefore be effectively applied not only for water heating but also space heating and cooling in regions like as Korea.     

Optimizing a heat pump for heating purposes

A computer simulation routine is used to analyse the economic effects of varying the heat exchangers and fans of a 3 hp commercial (base-line) air-air heat pump, on the assumption that it is used only for heating purposes. Both long-term (life-cycle costing) and short-term (pay-back time) economic measures are considered. the results indicate that there is economic justification for substantial increases in the capacity of the heat exchangers of the base-line unit. Such an optimized heating-only heat pump has technical and energetic advantages over the base-line unit.     

Numerical simulation and experimental validation of indirect expansion solar-assisted multi-functional heat pump

A novel indirect expansion solar-assisted multi-functional heat pump (IX-SAMHP) system which composes of the multi-functional heat pump system and solar thermal collecting system is proposed and studied in this paper. This system can fulfill space heating, space cooling and water heating with high energy efficiency by utilizing solar energy. For solar water heating mode and solar space heating mode, a dynamic model is presented and validated with the experimental results. The simulation results show good consistency with the experimental data, and the established model is able to predict the system performance at a reasonable accuracy (with the root mean square deviations less than 5%). On this basis, the performances of the IX-SAMHP system are investigated under different parametric conditions. For solar water heating mode, simultaneously operating the solar thermal collecting system and multi-functional heat pump system can be an energy efficiency method. With the solar irradiation rising from 0W/m² to 800W/m², the COP increases from 2.35 to 2.57. In solar space heating mode, the effect of the mass flow rate of water in evaporator is investigated. To balance the heating capacity and COP, the mass flow rate of water should be adjusted according to different temperature demands and heat load.     

Energy analysis and modeling of a solar assisted house heating system with a heat pump and an underground energy storage tank

An analytical model is presented and analyzed to predict the long term performance of a solar assisted house heating system with a heat pump and an underground spherical thermal energy storage tank. The system under investigation consists of a house, a heat pump, solar collectors and a storage tank. The present analytical model is based on a proper coupling of the individual energy models for the house, the heat pump, useful solar energy gain, and the transient heat transfer problem for the thermal energy storage tank. The transient heat transfer problem outside the energy storage tank is solved using a similarity transformation and Duhamel’s superposition principle. A computer code based on the present model is used to compute the performance parameters for the system under investigation. Results from the present study indicate that an operational time span of 5–7 years will be necessary before the system under investigation can attain an annually periodic operating condition. Results also indicate a decrease in the annually minimum value of the storage tank temperature with a decrease in the energy storage tank size and/or solar collector area.     

Experimental study of an air-source heat pump for simultaneous heating and cooling – Part 1: Basic concepts and performance verification

This article presents the concepts of an air-source heat pump for simultaneous heating and cooling (HPS) designed for hotels and smaller residential, commercial and office buildings in which simultaneous needs in heating and cooling are frequent. The main advantage of the HPS is to carry out simultaneously space heating and space cooling with the same energy input. Ambient air is used as a balancing source to run a heating or a cooling mode. The second advantage is that, during winter, energy recovered by the subcooling of the refrigerant is stored at first in a water tank and used subsequently as a cold source at the water evaporator to improve the average performance and to carry out defrosting of the air evaporator using a two-phase thermosiphon. Unlike conventional air-source heat pumps, defrosting is carried out without stopping the heat production. A R407C HPS prototype was built and tested. Its performance on defined operating conditions corresponds to the data given by the selection software of the compressor manufacturer. The operation of the high pressure control system, the transitions between heating, cooling and simultaneous modes and the defrosting sequence were validated experimentally and are presented in the second part of this article [1].