Annual Coefficient Of Performance Research Articles

New multi-energy sources coupling a low-temperature sustainable central heating system with a multifunctional relay energy station

Due to short cost-effective heat transportation distance, the existing geothermal heating technologies cannot be used to develop the deep hydrothermal type geothermal fields situated far away from urban area. To solve the problem, a new multi-energy source coupling a low-temperature sustainable central heating system with a multifunctional relay energy station is put forward. As for the proposed central heating system, a compression heat pump integrated with a heat exchanger in the heating substation and a gas-fired water/lithium bromide single-effect absorption heat pump in the multifunctional relay energy station are used to lower return temperature of the primary network step by step. The proposed central heating system is analyzed by using thermodynamics and economics, and matching relationships between design temperature of return water and main line length of the primary network are discussed. The studied results indicate that, as for the proposed central heating system, the cost-effective main line length of the primary network can approach 33.8 km, and the optimal design return temperature of the primary network is 23 ℃. Besides, annual coefficient of performance and annual exergy efficiency of the proposed central heating system are about 3.01 and 42.7%, respectively.

Investigation on the two-phase loop cooling system composed of maglev compressor and liquid pump for data centers

• The cooling system composed of maglev compressor and liquid pump is proposed. • The two-phase loop cooling system is oil free and structurally reliable. • As pressure ratio varies from 2.64 to 1.13, system COP increases from 3.85 to 8.16. • The outdoor unit COP is 31∼40 and the system COP is above 12 in pump-driven mode. • The annual GCOP is above 6.5 and PUE is 1.2 or less in most climate zones of China. The increasing demand for data processing, storage and distribution is escalating the energy usage of data centers, in which cooling system energy consumption could take up 30%∼50% of the total energy consumption. In this regard, improving cooling system efficiency will contribute to the optimization of energy utilization. In this paper, a two-phase loop cooling system driven by maglev compressor and liquid pump, which is oil free and structurally reliable, is proposed and investigated experimentally. The system performance under three different operating modes is explored experimentally. The application effects of proposed system in typical climate zones of China are analyzed. The results show that the coefficient of performance (COP) of the system is about 12 and the COP of the outdoor unit is as high as 31∼40 in pump-driven mode. In integrated mode and vapor compression mode, the COP of system increases from 3.85 to 8.16 while pressure ratio varies from 2.64 to 1.13, which means that the maglev compressor and the liquid pump can cooperate well to achieve an expected performance. The annual COP of the integrated system applied in China is above 6.5 in most climate zones. The power usage effectiveness of data center can be as low as 1.2, under the assumption that the energy consumption of auxiliary system except the cooling system accounts for 5% of the information technology equipment energy consumption.

Analysis of the operation performance of a hybrid solar ground-source heat pump system

The operational performance of a hybrid solar ground source heat pump (HSGSHP) system built at the Hebei University of Technology and composed of a ground source heat pump (GSHP) system and a solar-assisted ground source heat pump (SAGSHP) system is investigated in this work. For the GSHP system, the coefficient of performance (COP) of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively, in the cooling seasons from 2012 to 2016. During the heating season, the COP of heat pump unit and system of the GSHP system varies from 4.59 to 5.07 and 3.87 to 4.28, respectively. The annual COP of heat pump unit and system of the GSHP system increases from 3.19 to 4.18 and 3.03 to 3.63, respectively. For the SAGSHP system, solar space heating can improve performance by nearly 79.0%. For the HSGSHP system, increasing the proportion of the heat supply of the SAGSHP system within a certain range can effectively improve the COP of the HSGSHP system in the heating season. The results show that solar space heating can improve the performance of the HSGSHP system by nearly 25.8%.

New medium-low temperature hydrothermal geothermal district heating system based on distributed electric compression heat pumps and a centralized absorption heat transformer

Development of geothermal heat for district heating has attracted considerable attention in China. However, transporting geothermal heat for long distance has become the bottleneck for developing large-scale medium-low temperature hydrothermal geothermal fields that located far away from heat load areas. To solve this problem, a new medium-low temperature hydrothermal geothermal district heating system based on distributed electric compression heat pumps and a centralized absorption heat transformer is proposed and evaluated both from the aspects of thermodynamic performance and economic benefit. Analysis of the results may lead to following main conclusions: (i) for the proposed system, its cost-effective main line length of the primary heating network is about 10 km. (ii) The annual coefficient of performance, annual product exergy efficiency, and heating cost of the proposed system are found to be 24.5, 61.4% and 55.62 ¥/GJ, respectively. The centralized absorption heat transformer can reduce irreversible loss of the heating station and improve performance of distributed electric compression heat pumps. (ⅲ) Unlike the conventional medium-low temperature hydrothermal geothermal district heating system with longer distance of transporting geothermal heat, the annual coefficient of performance and annual product exergy efficiency of the proposed one can be improved by about 4.34 and 7.4%, respectively.

New Low-Temperature Central Heating System Integrated with Industrial Exhausted Heat Using Distributed Electric Compression Heat Pumps for Higher Energy Efficiency

Industrial exhausted heat can be used as the heat source of central heating for higher energy efficiency. To recover more industrial exhausted heat, a new low-temperature central heating system integrated with industrial exhausted heat using distributed electric compression heat pumps is put forward and analyzed from the aspect of thermodynamics and economics. The roles played by the distributed electric compression heat pumps in improving both thermal performance and financial benefit of the central heating system integrated with industrial exhausted heat are greater than those by the centralized electric compression heat pumps. The proposed low-temperature central heating system has higher energy efficiency, better financial benefit, and longer economical distance of transmitting exhausted heat, and thus, its configuration is optimal. For the proposed low-temperature central heating system, the annual coefficient of performance, annual product exergy efficiency, heating cost, and payback period are about 22.2, 59.4%, 42.83 ¥/GJ, and 6.2 years, respectively, when the distance of transmitting exhausted heat and the price of exhausted heat are 15 km and 15 ¥/GJ, respectively. The economical distance of transmitting exhausted heat of the proposed low-temperature central heating system could approach 25.1 km.

Technico-economic modelling of ground and air source heat pumps in a hot and dry climate

In a hot and dry country such as Saudi Arabia, air-conditioning systems consume seventy per cent of the electrical energy. In order to reduce this demand, conventional air -conditioning technology should be replaced by more efficient renewable energy systems. These should be compared to the current standard systems which use air source heat pumps (ASHPs). These have a poor performance when the air temperature is high. In Saudi Arabia, this can be as much as 50 °C. The purpose of this work, therefore, is to simulate and evaluate the performance of ground source heat pumps (GSHPs) compared with systems employing (ASHPs). For the first time, both systems were comprehensively modelled and simulated using the Transient System Simulation (TRNSYS). In addition, the Ground Loop Design (GLD) software was used to design the length of the ground loop heat exchanger. In order to assess this configuration, an evaluation of a model of a single story office building, based on the climatic conditions and geological characteristics that occur in the city of Riyadh in Saudi Arabia was investigated. The period of evaluation was twenty years in order to determine the Coefficient of Performance (COP), Energy Efficiency Ratio (EER) and power consumption. The simulation results show that the GSHP system has a high performance when compared to ASHP. The average annual COP and EER were 4.1 and 15.5 for the GSHP compared to 3.8 and 11 for the ASHP respectively, and the GSHP is a feasible alternative to ASHP with an 11 years payback period with an 18% total cost saving over the simulation period and 36% lower annual energy consumption. The TRNSYS model shows that despite the positive results of the modeling, the high rate of the underground thermal imbalance (88%) could lead to a system failure in the long term

Comparison between experiment and simulation for the development of a Tri-generation system using photovoltaic-thermal and ground source heat pump

In order to develop a more accurate photovoltaic–thermal collector and ground source heat pump integrated simulation model, it is necessary to consider the operation condition assumed in real situations, such as partial load of system, energy use situation, or energy production condition. Furthermore, the integrated simulation model should be verified by measurement data based on real-scale experiment. Therefore, in this study, we constructed a demonstration plant considering the real application for a residential house, and installed a monitoring system that could measure detailed operation situations, such as weather conditions, heat source temperatures, and individual system performance. The integrated simulation model was composed of a Photovoltaic–thermal collector model, a ground heat exchanger model, a heat pump model, a building load model, and a controller model. The error rate between the monitoring result and the integrated simulation model was determined. This was used to verify the prediction accuracy of the integrated simulation model. The coefficient of variation of root mean square error (CV(RMSE)) for the heat pump coefficient of performance (COP) and system coefficient of performance were calculated as 19.2% and 14.8%, respectively. In addition, the error rates of the PVT collector and the heat pump relative to the daily heat exchange rate (HER) were calculated to be less than 30%, respectively, while the error rate of the integrated simulation model satisfied ASHRAE Guideline 14-2014. Moreover, the long-term performance of the system was analyzed through the integrated simulation model considering the weather condition of Seoul. The annual COP of the system was calculated to be 4.03.

A novel ground thermal recovery system for horizontal ground heat exchangers in a hot climate

Ground Source Heat Pumps (GSHP), as a renewable source heating, ventilating, and air conditioning (HVAC) technology, has the highest energy efficiency among different heat pump types. One of the major drawbacks of GSHPs is the long-term ground temperature variations as a result of heat accumulation or depletion in the ground. This contribution puts forward a novel ground thermal recovery system for horizontal ground heat exchangers in a hot climate. The proposed recovery system consists of open-loop horizontal Ground-Air Heat Exchangers (GAHEs) that are buried between the horizontal Ground-Water Heat Exchangers (GWHEs). A fan supplies ambient air to the GAHE pipes when the soil around GWHE pipes is warmer than the ambient air, to remove the accumulatedheatfrom the ground. A three-dimensional quasi-steady Computational Fluid Dynamics (CFD) model of the system is developed. This model is then used to evaluate the five years performance of the GSHP system with the proposed thermal recovery system for space cooling of a residential house in a hot desert climate. Moreover, the effect of various geometrical parameters, i.e., GWHE length, GWHE pipe spacing, GWHE buried depth, and GAHE pipe diameter on the system performance, are investigated. It is demonstrated that, by deploying the proposed recovery system, the five-year average annual Coefficient of Performance (COP) of the system can be increased by up to 20.2%. Moreover, applying the proposed recovery system not only enhances the ground thermal recovery but also improves the maximum cooling load that can be supplied to the building per unit land area. Furthermore, it is demonstrated that by applying the proposed recovery system, the average annual COP of the system gradually increases; however, it decreases for the GSHP without a recovery system.

Increased efficiency of combined heat and power plants by utilizing waste heat for resorption chillers and their combination with hydrocarbon chillers

The use of waste heat has long been a topic to increase the efficiency of large-scale industrial processes, but it is becoming as well important in the commercial sector and in small and medium-sized industrial plants. For a sustainable and decentralized energy supply it is necessary to utilize all exergy flows much more than before. Particularly in decentralized combined heat and power (CHP) plants, the annual coefficient of performance is low due to seasonal temperature fluctuations, as the generated heat cannot be used or can only be used partly during the summer and transitional months. Interface technologies such as sorption technology can be used to further increase the utilization rate of such CHP plants and provide cooling capacity at the same time. This concept allows the utilization of previously unused waste heat to generate cooling in the temperature range from -6°C to 15°C, without the necessity of significant amounts of electric energy for the operation of additional compression refrigeration systems. In a pilot project funded by the German Federal Ministry of Economic Affairs and Energy, a thermally driven refrigeration plant with a small cooling capacity of maximum 25 kW using the resorption principle was evolved under these aspects and installed in a supermarket. Special focus is given to the flexibility of the plant technology as well as to the potentials of combinations of thermally and electrically driven chillers with natural refrigerants such as hydrocarbons and ammonia and the integration of thermal storage for temporal decoupling or discontinuous availability of heat and cooling load.

Seasonal performance evaluation of CO2 open refrigerated display cabinets

An increasing number of supermarkets and convenience stores has led to a proportionally higher demand for open refrigerated display cabinets (ORDCs). Ease of access to refrigerated products is the main advantage of ORDCs; however, they also exhibit high cumulative energy consumption as well as direct and indirect CO2 emissions. This work aims to formulate, establish, and apply a seasonal performance evaluation method for ORDCs and “walk-in” type refrigerated device driven by CO2 chillers. First, a thermodynamic modeling approach is used and fitted to experimental data. The relative error between the predicted and actual heat load is within ±10%, whereas it is within ±20% for the normalized compressor electric input. Then, an evaluation tool is constructed using the seasonal energy consumption of ORDCs commonly used in Japan and driven by a transcritical CO2-compression chiller within Japanese climatic conditions. This tool can be used to predict the annual energy demand for given ambient conditions as well as the reduced environmental impact of multiple combinations of refrigerated display cabinets compared to conventional HFC/HCFC-based systems. According to the annual temperature distribution in chosen regions, the annual thermal load, annual electricity consumption, and annual coefficient of performance are calculated and analyzed. Simulation results quantitatively evaluate the beneficial effect of Te as being translated to a better COP, and lower energy consumption and CO2 emissions. Considering the geographic location of the store, the quantitative results show how a hotter climatic condition leads to higher energy consumption and CO2 emissions, and lower COP. The proposed evaluation method is generally applicable to any regional setting and any chiller-ORDC combination.

Study on the influence of the design method of the ground source heat pump system with considering groundwater seepage

The identification model of the thermal response test (TRT) equates the actual complex stratified soil with seepage to a homogeneous soil without seepage. In this paper, a three-dimensional dynamic simulation experiment platform for the ground source heat pump system (GSHPS) was established where the equivalence of the TRT and its influence on the long-term performance of the GSHPS with different thermal loads were analyzed. The results showed that there was a big difference of the soil thermal properties between under the actual and equivalent conditions. Under the conditions in this paper, the soil thermal diffusivity under the equivalent condition was 151.16% higher than that under the actual condition, but the difference of short-term heat transfer performance between them was only 2.65%. Under the Harbin, Shenyang and Beijing thermal load, the annual COP in the tenth year in the actual condition decreased by 0.82%, 0.61% and 0.12%, respectively; these in the equivalent condition decreased by 5.31%, 3.95% and 0.33%, respectively, compared with the first year. Under the A1 condition, the annual coefficient of performance (COP) of the system in Beijing thermal load in the 10th year was 62.67% and 38.59% larger than that in Harbin and Shenyang thermal load, respectively.

Performance evaluation of heating tower heat pump systems over the world

Heating tower heat pumps (HTHPs) are proposed as an alternative to the conventional heat pumps. However, lacking performance evaluation of the HTHPs in different regions limits their applications worldwide. To address this issue, this paper carries out a large-scale comprehensive performance evaluation of the HTHPs in 869 typical locations. These locations are in the warm, mixed, and cool climate zones, where buildings need both cooling and heating supply. Seven performance indices are adopted, including the annual coefficient of performance (COP), COP in cooling season, COP in heating season, regeneration ratio, number of unsatisfactory hours, matching degree of heat pump, and matching degree of heating tower. The performance evaluation of the HTHPs is conducted by the processes of location selection, building load calculation, system sizing, simulation, and evaluation. The results show that the HTHPs have excellent performance in the warm and mixed climate zones, where the average annual COPs are 4.67 and 3.68, respectively. The HTHPs are also applicable in the cool climate zone with an average annual COP of 3.11. The distributions of all the performance indices are presented through color maps, and the results are analyzed considering the air temperature and relative humidity data of the locations.

Different Operational Alternatives of Aquifer Thermal Energy Storage System for Cooling and Heating of a Residential Complex under Various Climatic Conditions of Iran

In this research, a confined aquifer with low groundwater flow was considered to meet the cooling and heating requirement of residential complexes. The complexes were located in the cities of Ahvaz, Ardabil, Bandar Abbas, Esfahan, Kerman, Rasht, Tehran and Zahedan. The complex in Ardabil required mostly heating, the ones in Ahvaz and Bandar Abbas required mostly cooling, whereas the complex in other cities required both heating and cooling. Four different alternatives of aquifer thermal energy storage (ATES) were analyzed in this study. These alternatives were:1) using ATES alone for cooling 2) for cooling coupled with a conventional refrigeration system or a chiller 3) for heating by employing flat plate solar collectors and 4) for heating by employing flat plate solar collectors and a heat pump. Thermal energy recovery factor and the annual coefficient of performance (COP) of the alternatives were determined. The results showed that, for buildings located in cities with mild climatic conditions(such as Esfahan), where the annual heating and cooling energy requirements are early equal, the use of ATES is highly recommended when employing any of the alternatives considered in this investigation.

Energy efficiency in a building complex through seasonal storage of thermal energy in a confined aquifer

Confined aquifers are formations surrounded by impermeable layers called cap rocks and bed rocks. These aquifers are suitable for the seasonal storage of thermal energy. A confined aquifer was designed to meet the cooling and heating energy needs of a residential building complex located in Tehran, Iran. The annual cooling and heating energy needs of the buildings were estimated to be 8.7 TJ and 1.9 TJ, respectively. Two different alternatives were analyzed for an aquifer thermal energy storage (ATES) system. These alternatives were: 1) using ATES for cooling alone, and 2) coupling ATES with a heat pump for both cooling and heating. The thermal annual energy recovery factor and the annual coefficient of performance (COP) of the system were determined. A COP of 10 was obtained when ATES was employed for cooling alone. When ATES was employed for cooling and heating (using a heat pump), a COP of 17 was obtained for the cooling mode, and 5 for the heating mode.

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.

Protein-losing gastroenteropathy

Heating tower heat pumps (HTHPs) are proposed as an alternative to the conventional heat pumps. However, lacking performance evaluation of the HTHPs in different regions limits their applications worldwide. To address this issue, this paper carries out a large-scale comprehensive performance evaluation of the HTHPs in 869 typical locations. These locations are in the warm, mixed, and cool climate zones, where buildings need both cooling and heating supply. Seven performance indices are adopted, including the annual coefficient of performance (COP), COP in cooling season, COP in heating season, regeneration ratio, number of unsatisfactory hours, matching degree of heat pump, and matching degree of heating tower. The performance evaluation of the HTHPs is conducted by the processes of location selection, building load calculation, system sizing, simulation, and evaluation. The results show that the HTHPs have excellent performance in the warm and mixed climate zones, where the average annual COPs are 4.67 and 3.68, respectively. The HTHPs are also applicable in the cool climate zone with an average annual COP of 3.11. The distributions of all the performance indices are presented through color maps, and the results are analyzed considering the air temperature and relative humidity data of the locations.

Significance of heat pump coefficient of performance

This paper deals with the load aspects and economic aspects of three types of residential heat pump systems which employ supplementary heat sources. It contains illustrations of their load characteristics over a wide range of annual COP (coefficient of performance), depicts relationships of the relative costs to serve these loads from long-range and short-range considerations, and provides, as a reference, load characteristics and economic data for three comparable types of resistance heating systems with their complementary electrical cooling loads, and a band of competitive operating costs to customers using gas for heating and cooling.