Increase In COP Research Articles

과부하 및 착.제상 조건에서 히트펌프 칠러의 난방성능에 관한 실험 연구

In the present study, the performance characteristics of the heat pump chiller under heating conditions were experimentally investigated. Capacity, input power and COP under overload, frost and defrost conditions were obtained. The experimental data for the heat pump chiller were measured using the air-enthalpy calorimeter and the constant temperature water bath. At overload condition, the heating capacity and COP increase about 25.7% and 19.1%, respectively. The variations of the evaporator, the compressor outlet and the condenser temperature were obtained under frost and defrost conditions. The frost and defrost period of the heat exchanger decreases about 36.0~56.1%.

공기열원 히트펌프의 난방 성능특성에 관한 실험적 연구

ABSTRACT:This paper presents the heating performance characteristics of the air source heat pump with air to water type. The heating capacity, COP, P-h diagram were measured at various operating conditions, air-side temperatures, relative humidities, and inlet/outlet water temperature under the standard heating condition of KS B 6275. The experimental data for the heat pump were measured using the air-enthalpy calorimeter and the constant temperature water bath. As the air-side temperature increases, the heating capacity and COP increase. The effect of the air-side relative humidities on the heat pump performance is insignificant. The heat pump performance on inlet and outlet water temperatures and air-side temperatures(-7, -11, -15℃) were studied. Heating capacity and COP increased about 27～39% with the air-side temperature increasing. Enthalpy between the front and the rear of condenser decreased about 6% by increasing of the inlet water temperature. These results can be utilized in the design of the air source heat pump system with air to water type.Keywords:Air to water(공기-물), COP(성능계수), Heating capacity(난방능력), Heat pump(히트펌프), Performance(성능)

Study on the performance of a solar assisted air source heat pump system for building heating

This paper proposed a new solar assisted air source heat pump system with flexible operational modes to improve the performance of the heating system. A mathematical model was established on the solar assisted air source heat pump system for building heating with a heating capacity of 10 kW, and an air source heat pump unit was developed to validate the model. The effect of the solar collector area on the performance of the system running in Nanjing was studied. The results showed that the COP of the heat pump unit was enhanced with the increase of the solar radiation density during the typical sunny day in the heating season. In addition, the COP also increased in proportion to the solar collector area. Compared with the case when the solar collector area was 0 m 2, the COP increase of the heat pump and the energy-saving rate were 11.22% and 24% respectively when the solar collector area was 40 m 2. Meanwhile, the solar equivalent generation power efficiency could reach 11.8%.

Theoretic Study on a Direct-Expanded Ground-Source Heat Pump

A distributed parameter method has been established for a ground-source heat pump in this paper, with this model, the working process of this heat pump system was simulated. The results agree well with experimental data and show that heat-capacity and COP increase when the cooling water flow rate in the tube-in-tube heat exchanger increases; heat-capacity decreases when the temperature of inlet water of the tube-in-tube heat exchanger rises; COP, between 3.8 and 4.5, is higher than that of conventional air-source heat pumps.

A Forecast of Effective Global Warming Countermeasures for the Residential Sector in China for the year 2050

Energy consumption in the Chinese residential sector is increasing quickly. In this study, we developed a Micro-model to forecast residential CO2 emissions. The model outputs support decision making for appropriate CO2 emission reduction goals. First, for Chinese urban residential buildings, we developed a CO2 emissions forecast model for 2050 taking into account lifestyle changes and Global Warming countermeasures. Second, we used the model to estimate the CO2 reduction potential of both residential and electrical countermeasures. Compared to the business as usual (BaU) scenario, implementation of residential countermeasures achieved 38%, 24% and 23% emissions reductions for Beijing, Shanghai and Hong Kong respectively. After combining them with the implementation of electrical countermeasures the reduction rates rose to 60%. We also compared the countermeasures to see which could bring the greatest emissions reduction. For Beijing, improvement of insulation was most efficient. For Shanghai and Hong Kong, COP increase of hot water supply appears to be the most efficient countermeasure. Through this study we were able to model global warming countermeasures for the Chinese residential sector, and found that reducing CO2 emissions by 60% from BaU is an achievable goal.

A method of improving the effectiveness of a mechanical vapour compression process and of its applications in refrigeration

The work proposes a thermodynamic method for increasing the effectiveness of the polytropic and adiabatic compression processes. The method is further used for improving the COP of the compression refrigeration cycles. The method theory is considered. A theorem proved here shows that ideal method application leads to the isothermal compression operation. The method application is illustrated by schemes running with single, two-stage and multi-stage compression, for the air conditioning, normal and industrial refrigeration. According to the proposal, the compression refrigeration should stimulate the compressor operation with high temperature discharge gas and the conversion of its heat into work, rather than using an additional compression work for limiting the discharge gas temperature, as it is happening today in the two-and multi-stage refrigeration. The schemes’ operation has been modelled. The model results emphasize a reasonable feasibility of the single-stage, but the three-stage and especially the two-stage compression are the most feasible, enjoying a great potential in the refrigeration COP increase, and therefore in the primary energy savings and carbon footprint reduction (∼50–100% and more).

Simulation Of A Air Liquid Combined Heat Exchanger

Air liquid composite heat exchanger can implement refrigerant combined heat exchange synchronization with liquid and air heat source. This article has established steady state mathematical model of the heat exchanger, and simulation the solar air double heat sources combined heat pump performance with the air liquid combined heat exchanger. Results show that the performance of the solar-air double heat sources composite heat pump is improved significantly by single air source heat pump in heating under various conditions. When the outdoor air temperature is about 1.5°C, the dual heat-source heat pump heating capacity and COP can reach single air-source heat pump. When the outdoor temperature is -15°C, dual heat-source heat pump heating capacity and COP are further increases, heating capacity increase nearly 40%, COP increase nearly 30%.

Simulation of an ammonia–water compression–absorption refrigeration system for water chilling application

A detailed simulation of a 400 kW ammonia–water compression–absorption refrigeration system has been carried out for water chilling application for summer air conditioning. Simulation has been performed for three different configurations of system having 17%, 23%, and 30% relative solution heat exchanger areas. The effect of relative solution heat exchanger area and mass flow rate of weak solution on the COP, cooling capacity and absorber heat load has been studied. The results show that the COP of the system can be increased by maintaining low mass flow rate of weak solution and large relative solution heat exchanger area. Increase in the relative solution heat exchanger area from 10 to 30% resulted in an increase in COP by about 16%. Further increase in relative SHX area revealed that there exists an optimum area at which COP becomes maximum. The performance of this system has been compared with that of a conventional R 22 vapor compression type chiller.

Theoretical study of a transcritical ejector refrigeration cycle with refrigerant R143a

In this paper, a transcritical ejector refrigeration cycle (TERC) using refrigerant R143a as working fluid is proposed to improve the performance of the ejector refrigeration systems driven by low-grade thermal energy. This method adopts an adequate combination of thermal and mechanical energy through the operation of the transcritical process for generator to enhance the performance of the conventional ejector refrigeration cycle (ERC) at the cost of additional driving mechanical energy. The performance characteristics of the TERC are investigated based on theoretical simulations. The TERC is also compared with the conventional ERC using refrigerant R134a. The study shows that when utilizing the low-grade thermal energy, the TERC yields significant increase in COP by adding auxiliary mechanical energy of the cycle pump and has a higher potential in making effective use of the low-grade thermal energy with gradient temperature, such as solar energy gained by a flat plate or evacuated tube solar collector. This also indicates that the TERC is an attractive alternative to the ejector refrigeration systems driven by low-grade thermal energy. Further experimental work for the TERC may be launched in the near future to verify practical applications.

Increase of COP for an experimental heat transformer using a water purification system

The experimental results of a water purification system of single effect evaporation integrated into a heat transformer of 700W are presented, using lithium bromide water as solution. It is demonstrated that it is possible to increase efficiency of energy use with heat recycling of a water purification system. The typical coefficients of performance values were increased from 24.7% to 30.3%, obtaining a maximum of 684 mL/h of distilled water. The behavior of the coefficient of performance in function of the absorber temperatures before and after the purification process is showed. Experimental and simulated data with the water purification system integrated into a heat transformer are analyzed.

핀-관, 평행류 열교환기를 적용한 공조기의 냉방성능 실험연구

본 연구에서는 핀-관 열교환기와 평행류(PF) 열교환기를 실외 열교환기로 적용한 공조기의 실내외 온도/습도와 같은 환경변화에 대한 냉방성능을 비교 조사하고자 하였다. KS C 9306의 냉방표준 온도조건을 기준으로 핀-관, 2종류의 PF 열교환기를 적용한 공조기 성능변화를 이해하기 위하여 냉방능력과 COP를 획득하였다. 실험을 위해 공기엔탈피 방식의 칼로리미터를 사용하였다. PF 열교환기는 핀-관 열교환기보다 우수한 열전달 능력을 보였다. 그리고 사각형 핀을 적용한 PF형 공조기의 성능이 삼각형 핀의 경우보다 우수하였다. 실내 토출공기의 유속, 실내온도 그리고 실내상대습도가 높아질수록 냉방능력과 COP는 증가를, 실외온도가 높아질수록 냉방능력과 COP는 감소를, 그러나 실외 상대습도 증가에 따른 성능변화는 미미하였다. In the present study, the cooling performance characteristics on environment changes of A/C applied fin-tube and PF heat exchangers were experimentally investigated. Capacity and COP on an air velocity, an indoor/outdoor temperature and an indoor/outdoor relative humidity were obtained. Fin types of PF heat exchanger were a triangler and squarer form. The experimental data for the three kinds of heat exchangers were measured using the air-enthalpy calorimeter. Performance of PF A/C was more excellent than that of a fin-tube A/C. Also, the performance of PF-2 A/C with the squarer fin was more excellent than that of PF-1 A/C with the triangler fin. As the air velocity, the indoor temperature and the indoor relative humidity increase, capacity and COP increase. And as outdoor temperature increases, capacity and COP decrease. But, the performance change on the outdoor relative humidity was insignificant.

Experimental Investigation of The Performance of Hybrid Desiccant Air Conditioning Systems(Dept.M)

In this study, an experimental evaluation of a hybrid desiccant air conditioning in post and pre-cooling arrangements is studied and compared versus the traditional vapor compression system (VCS). The system is mainly consisted of a rotary dehumidification unit integrated with a VCS. The dehumidification unit comprises a rotating liquid desiccant wheel. Lithium chloride is used as the working desiccant material in this investigation. The effect of regeneration air velocity. temperature and rotational speed of the wheel an the performance of the system is studied. The post cooling hybrid system is found to be an energy efficient system, it saves nearly 23% of cooling coil capacity compared to VCS. The COP. of the post cooling arrangement is nearly twice that of VCS with reheat. The pre cooling arrangement ensures low dew point temperature with an increase of COP of about 70% compared to VCS with reheat. A rotational speed of 1 rph is recommended for optimum performance. The results of the numerical model of another work is used for comparison with the experimental results of this study.

Analysis of a novel refrigeration Carnot-type cycle based on isothermal vapour compression

A novel Carnot-type cycle is proposed to reach high performances for sub-critical and trans-critical applications. Two natural fluids, ammonia and carbon dioxide each one corresponding to one of the application, were chosen. Compared to conventional cycles, the Carnot-type cycle leads to COP increase by 4–70% depending on the application. For the most suitable case (CO 2), a simpler design resulting from a trade-off between complexity and performances still exhibits high performances (92.5% of COP Carnot vs. 95.4% for Carnot-type cycle). Compared to conventional one, this simpler design appears to be more sensitive to the expander efficiency but still achieves higher performances: 80% vs. 50% of COP Carnot. The impact of the compression cooling efficiency was explored too. With a temperature pinch equal to 20 K, the performances are still better than those of the conventional one (+21% of COP) despite a decrease by 24% of the COP.

Influence of absorber mass transfer effectiveness on performance of R 134a-DMAC based single, double and half-effect absorption cooling systems

A thermodynamic analysis was performed on half-effect, single-effect and double-effect VARS with R-134a-DMAC as working fluid to study the influence of absorber mass transfer effectiveness (Ea) at various generator and evaporator temperatures on performance parameters namely circulation ratio, Coefficient of performance (Cop) and second law efficiency. The variations in heat quantities of absorber and generator were also studied, using a computer simulation which revealed that the single, double and half effect system can efficiently be applied, where the heat source is available at 80, 130 and 55°C, respectively. Double-effect system yielded maximum percentage increase in Cop, when Ea varied from 0.5 to 1. The thermo-dynamic penalty of half-effect system is its high rate heat rejection at the absorbers.

Numerical modeling of a zeolite/water adsorption cooling system with non-constant condensing pressure

A new transient two-dimensional model with non-constant condensing pressure for a zeolite/water adsorption cooling cycle is proposed in this paper. This numerical model focuses on the heat and mass transfer behaviors in the adsorber and is solved by the control volume method. Due to the heat transfer limitation in the condenser, the simulated pressure during the isobaric generation phase of the cycle is not constant and will decrease with time. Compared with the model for constant condensing pressure, the cycle duration and cycled adsorbate for the base case are increased. Furthermore, the effect of mass flow rate of condenser cooling water on system performance is also investigated. It is found that both COP and SCP increase with an increase in the mass flow rate of cooling water in the condenser.

Performance characteristics and energy–exergy analysis of solar-assisted heat pump system

In this study solar-assisted heat pump (SAHP) system with flat plate collectors was investigated experimentally and tested for domestic space heating. SAHP system was located in a test room with 60 m 2 floor area in Firat University, Elazig (38,41°N, 39,14°E) Turkey. The experiments were performed in heating season of January 2003. The coefficient of performance of the SAHP system was calculated. The system COP of the SAHP was obtained as 3.08 while the exergy loss of the solar collector was found to be 1.92 kW. The second law efficiency of the compressor, condenser, evaporator and solar heat exchanger in SAHP system were evaluated 42.1%, 83.7%, 43.2% and 9.4%, respectively. The first law efficiency and exergetic efficiency of the whole system are found to be 65.6%, 30.8%, respectively. Consequently the energy and exergy loss analysis results show that the COP increase when the exergy loss of evaporator decrease.

Numerical model of sprayed air cooled condenser coupled to refrigerating system

Because of technological, economic and environmental constraints, many refrigeration and air conditioning units are equipped with a simple air cooled condenser. Spraying the condenser seems to be an original solution to improve the energetic performances of such systems. To characterise this energetic benefit, a semi-local mathematical model was developed and applied to a refrigerating machine with and without spraying its air cooled condenser. It is found that, compared to a dry air cooled condenser, both the calorific capacity and machine COP increase by 13% and 55%, respectively. Furthermore, the model shows that a spray flow rate threshold occurs. It should not be exceeded to assure an effective and rational spray use.

Increase of COP for heat transformer in water purification systems. Part II – Without increasing heat source temperature

The integration of a water purification system allows a heat transformer to increase the actual coefficient of performance, by the reduction of the amount of heat supplied by unit of heat. A new defined COP called COP WP is proposed for the present system, which considers the fraction of heat recycled. Simulation with proven software compares the performance of the modeling of an absorption heat transformer for water purification (AHTWP) operating with water/lithium bromide, as working fluid–absorbent pair. Plots of enthalpy-based coefficients of performance (COP ET) and water purification coefficient of performance (COP WP) are shown against absorber temperature for several thermodynamic operating conditions. The results showed that the proposed (AHTWP) system is capable of increasing the original value of COP ET up to 1.6 times its original value by recycling energy from a water purification system. The proposed COP WP allows increments for COP values from any experimental data for water purification or for any other distillation system integrated to a heat transformer, regardless of actual COP A value or working fluid–absorbent pair.

Studies on a two-stage transcritical carbon dioxide heat pump cycle with flash intercooling

Simulation studies on a two-stage flash intercooling transcritical carbon dioxide heat pump cycle are presented. Sub-critical and super-critical thermodynamic and transport properties of carbon dioxide are calculated employing an exclusive precision property code based on recently published correlations. Results exhibit that flash intercooling technique is not economical with CO 2 refrigerant unlike NH 3 as the refrigerant. COP is considerably lower than that of the single cycle for a given gas cooler and evaporator temperature. There is no optimum inter-stage pressure as well. However, a marginal increase in COP occurs as inter-stage pressure decreases from the classical estimate of geometric mean of gas cooler and evaporator pressure. It is observed that incorporation of desuperheating of vapour in the intercooler almost doubles the mass flow rate in the second stage which can be attributed to the large flashing that occurs in the intercooler; this increase depends on the discharge temperature from the first stage and mass flow rate of refrigerant flow in the evaporator. Compressor isentropic efficiency shows marginal influence on system performance.

Constraints of using thermostatic expansion valves to operate air-cooled chillers at lower condensing temperatures

Thermostatic expansion valves (TXVs) have long been used in air-cooled chillers to implement head pressure control under which the condensing temperature is kept high at around 50 °C by staging condenser fans as few as possible. This paper considers how TXVs prevent the chillers from operating with an increased COP at lower condensing temperatures when the chiller load or outdoor temperature drops. An analysis on an existing air-cooled reciprocating chiller showed that the range of differential pressures across TXVs restricts the maximum heat rejection airflow required to increase the chiller COP, though the set point of condensing temperature is reduced to 22 °C from a high level of 45 °C. It is possible to use electronic expansion valves to meet the differential pressure requirements for maximum chiller COP. There is a maximum of 28.7% increase in the chiller COP when the heat rejection airflow is able to be maximized in various operating conditions. The results of this paper emphasize criteria for lowering the condensing temperature to enhance the performance of air-cooled chillers.