机械泵驱动分离式热管应用于空调冷量回收

为了探究机械泵驱动分离式热管对空调系统冷量回收和除湿能力的影响,搭建了四组该热管系统进行实验,其循环工质为R134a。在入口空气干球温度28.5℃、相对湿度60%的条件下,当运行热管由0增加到4组时,系统的机器露点由11.7℃降到8.2℃,供风温度由11.7℃升到24.1℃,系统的除湿能力增加了29.5%。指数δ(热管系统回收的冷量与制冷机蒸发器的制冷量之比)达到66.0%。研究结果表明,机械泵驱动分离式热管可以显著提高空调系统除湿能力,降低系统能耗。     

采用替代工质的空气源热泵性能试验研究

测试了热泵系统在典型空调工况下采用R22的替代工质R134a,R404A,R407C时的制热量、功耗和COP。结果表明R407C的性能与R22比较接近,是R22比较理想的替代工质。     

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation Solver) environment and validated by published experimental data. Correlation between the cooling (wet-bulb) effectiveness, system COP and a number of air flow/exchanger parameters was developed. It is found that lower channel air velocity, lower inlet air relative humidity, and higher working-to-product air ratio yielded higher cooling effectiveness. The recommended average air velocities in dry and wet channels should not be greater than 1.77 m/s and 0.7 m/s, respectively. The optimum flow ratio of working-to-product air for this cooler is 50%. The channel geometric sizes, i.e. channel length and height, also impose significant impact to system performance. Longer channel length and smaller channel height contribute to increase of the system cooling effectiveness but lead to reduced system COP. The recommend channel height is 4 mm and the dimensionless channel length, i.e., ratio of the channel length to height, should be in the range 100 to 300. Numerical study results indicated that this new type of M-cycle heat and mass exchanger can achieve 16.7% higher cooling effectiveness compared with the conventional cross-flow heat and mass exchanger for the indirect evaporative cooler. The model of this kind is new and not yet reported in literatures. The results of the study help with design and performance analyses of such a new type of indirect evaporative air cooler, and in further, help increasing market rating of the technology within building air conditioning sector, which is currently dominated by the conventional compression refrigeration technology.     

Assessment of the thermal environment effects on human comfort and health for the development of novel air conditioning system in tropical regions

This research shows the result of a brainstorming by medical experts in the first ranking university medical school and hospital of Thailand. It was based on Delphi technique. The objective of this research was to study both direct and indirect effects of humidity and temperature on human health in air-conditioned buildings in Thailand. Afterwards, the result was used to design and develop split type air conditioner (conventional air conditioner) which could control relative humidity and temperature with precision air conditioning system to comply with the climate and the suitability of the people living in Thailand building. The result of operation with precision inverter air conditioning system showed that the temperature inside the room changed from the default value around ±0.2 °C (Case 1) and around ±0.35 °C (Case 2) and it could control relative humidity as a desired condition between 50-60% (both cases) which was the appropriate range for Thai climate. Moreover, energy consumption of precision inverter air conditioning system was still less than conventional air conditioning system for about 7.5%. This research could provide people living in Thailand air conditioned building with human thermal comfort and health.     

Experimental study of performance of digital variable multiple air conditioning system under part load conditions

An experimental study on performance of digital variable multiple air conditioning system under part load conditions in hot summer and cold winter zone was conducted in this paper. The effects of outdoor air temperature and on-unit ratio on total power consumption in 1 h, hourly heating performance factor or hourly energy efficiency ratio were analyzed by experiments. The variations of hourly heating performance factor (or hourly energy efficiency ratio) and total power consumption in 1 h with part load value under different outdoor air temperature were obtained. The results indicate that digital variable multiple air conditioning system can keep economical and reliable operation under part load conditions. And it is necessary to study the index which may reflect the seasonal energy consumption of digital variable multiple air conditioning system.     

Boiling heat transfer enhancement with carbon nanotubes for refrigerants used in building air-conditioning

In this study, the effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer is investigated. Two halocarbon refrigerants of R123 and R134a for building chillers were used as working fluids and 1.0 vol.% of CNTs was added to them to examine the heat transfer enhancement with CNTs. The experimental apparatus was composed of a stainless steel vessel and a 152.0 mm long plain horizontal tube of 19.0 mm outside diameter heated by a cartridge heater. All data were obtained at the pool temperature of 7 °C in the heat flux range of 10–80 kW m⁻². Test results showed that CNTs increase nucleate boiling heat transfer coefficients for these refrigerants. Especially, large enhancement up to 36.6% was observed at low heat fluxes of less than 30 kW m⁻². With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the heat transfer surface was not observed during the course of this study. Optimum dispersion of CNTs should be examined for their commercial application to enhance nucleate boiling heat transfer in building air-conditioning applications.     

Experimental study on dehumidifier and regenerator of liquid desiccant cooling air conditioning system

A new type of air conditioning system, the liquid desiccant evaporation cooling air conditioning system (LDCS) is introduced in this paper. Desiccant evaporation cooling technology is environmental friendly and can be used to condition the indoor environment of buildings. Unlike conventional air conditioning systems, the system can be driven by low-grade heat sources such as solar energy and industrial waste heat with temperatures between 60 and 80 °C. In this paper, a LDCS, as well as a packed tower for the regenerator and dehumidifier is described. The effects of heating source temperature, air temperature and humidity, desiccant solution temperature and desiccant solution concentration on the rates of dehumidification and regeneration are discussed. Based on the experimental results, mass transfer coefficients of the regeneration process were experimentally obtained. The results showed that the mean mass transfer coefficient of the packing regenerator was 4 g/(m² s). In the experiments of dehumidification, it was found that there was maximal tower efficiency with the suitable inlet humidity of the indoor air. The effective curves of heating temperature on the outlet parameters of the regenerator were obtained. The relationships of regeneration mass transfer coefficient as a function of heating temperature and desiccant concentration are introduced.     

Experimental studies on the indoor electrical floor heating system with carbon black mortar slabs

A room using carbon black mortar slabs (CBMS) as the electrical floor heating element has been built in our lab. Studies showed that an electrical power of about 123.8 W/m² resulted in the indoor temperature rise of 10 °C within 330 min. Temperature distribution along the height of the room was uniform. Temperature rise was slightly higher if floor tiles rather than the wood flooring was used. In the process of heating, self-heating of CBMS has consumed more than 30% of the generated heat by Joule effect, which was advantageous for the stability of the thermal state. The indoor air absorbed over 50% of the generated heat. Results derived from repeated tests show that the electrical power of the CBMS system was stable during several cycles of heating. Further, the procedure and power consumption for the system to maintain a certain indoor temperature were studied. Continuous tests for 72 h has shown that the higher the indoor controlled temperature was, the longer the working time and the shorter the rest time in every cycle of heating were required. Accordingly, the power consumption to maintain the heat state increased with the controlled temperature increasing.     

Modeling solar-driven ejector refrigeration system offering air conditioning for office buildings

A lumped method combined with dynamic model is proposed for use in investigating the performance and solar fraction of a solar-driven ejector refrigeration system (SERS) using R134a, for office air conditioning application for buildings in Shanghai, China. Classical hourly outdoor temperature and solar radiation model were used to provide basic data for accurate analysis of the system performance. Results indicate that during the office working-time, i.e., from 9:00 to 17:00, the average COP and the average solar fraction of the system were 0.48 and 0.82 respectively when the operating conditions were: generator temperature (85 °C), evaporator temperature (8 °C) and condenser temperature varying with ambient temperature. Compared with traditional compressor based air conditioner, the system can save upto 80% electric energy when providing the same cooling capacity for office buildings. Hence, the system offers a good energy conservation method for office buildings.     

Thermal behavior of a novel type see-through glazing system with integrated PV cells

Steady natural convective airflow in a novel type glazing system with integrated semi-transparent photovoltaic (PV) cells has been analyzed numerically using a stream function vorticity formulation. Based on the resulting numerical predictions, the effects of Rayleigh numbers on airflow patterns and local heat transfer coefficients on vertical glazing surfaces were investigated for Rayleigh numbers in the range of 10³ ≤ Ra ≤ 2 × 10⁵. Significant agreement for the Nusselt numbers was observed between numerical simulation results in this study and those of earlier experimental and theoretical results available from the literature. In addition, the effect of air gap thickness in the cavity on the heat transfer through the cavity is evaluated. The optimum thickness of the air layer in this research is found to be in the range of 60–80 mm. This novel glazing system type could not only generate electricity but also achieve potential energy savings by reducing the air conditioning cooling load when applied in subtropical climatic conditions and simultaneously provide visual comfort in the indoor environment.     

Field performance of an energy pile system for space heating

This paper describes the field performance of air conditioning with an energy pile system, which was applied to the pile foundations of an actual building for the purpose of reducing the cost of the underground heat exchanger. First, the building for both office and residential use, for which a space heating and cooling system using friction piles was installed, was built in Sapporo in December 2000. Second, three tests were carried out to specify the design of a heat exchanger inside the pile, and a U-tube type underground heat exchanger was adopted from the viewpoint of energy efficiency and installation costs. Long-term space heating operation measurements indicated that the seasonal average temperatures of brine returning from the underground and pile surfaces were 2.4 and 6.7 °C, respectively. The average coefficient of performance for space heating was quite high at 3.9, and the seasonal primary energy reduction rate compared with a typical air conditioning system reached 23.2%.     

Feasibility study of a novel dew point air conditioning system for China building application

The paper investigated the feasibility of a novel dew point evaporative cooling for air conditioning of buildings in China regions. The issues involved include analyses of China weather conditions, investigation of availability of water for dew point cooling, and assessment of cooling capacity of the system within various regions of China. It is concluded that the dew point system is suitable for most regions of China, particularly northern and west regions of China where the climate is hot and dry during the summer season. It is less suitable for Guangzhou and Shanghai where climates are hot and humid. However, an air pre-treatment process involving a silica-gel dehumidification will enable the technology to be used for these humid areas. Lower humidity results in a higher difference between the dry bulb and dew point of the air, which benefits the system in terms of enhancing its cooling performance. Tap water has adequate temperature to feed the system for cooling and its consumption rate is in the range 2.6–3 litres per kWh cooling output. The cooling output of the system ranges from 1.1 to 4.3 W per m³/h air flow rate in China, depending on the region where the system applies. For a unit with 2 kW of cooling output, the required air volume flow rate varies with its application location and is in the range 570–1800 m³/h. For a 50 m² building with 60 W/m² cooling load, if the system operates at working hours, i.e., 09:00 to 17:00 h, its daily water consumption would be in the range of 60–70 litres. Compared with mild or humid climates, the dry and hot climates need less air volume flow rate and less water.     

The feedback of heat rejection to air conditioning load during the nighttime in subtropical climate

Taipei City, located in the subtropical zone, has a basin landform. The summer is always hot and humid and the air temperature right after sunset is typically higher than 30 °C. Heat rejection from residential buildings in urban area, equipped with lots of the window type air conditioners, not only increases the air temperature outside, but also burdens the cooling load. Based on the time schedule of air conditioner use of Taipei citizens, the heat rejection/building energy use and the air temperature distribution were evaluated, and finally the additional electric consumption of air conditioners was predicted. Two software, EnergyPlus (building energy program) and Windperfect (CFD, computational fluid dynamics software) were employed in this study. In the CFD simulation, the geometry of buildings that covers 700 m in diameter was created with GIS (geographical information system) and the total mesh number was more than 3 millions. Three specified temperatures (T_am, T_bu and T_ac) were used to describe the temperature distribution within the urban canopy by hourly time variation and spatial distribution with height and horizontal profile. The results revealed that the temperature gradually increased with height and the temperature next to the buildings was always higher than the ambient air. The feedback (penalty) of heat rejection to cooling load was found 10.7% during 19:01 to 02:00 h on the following day.     

Condenser heat recovery with a PV/T air heating collector to regenerate desiccant for reducing energy use of an air conditioning room

This paper presents an experimental test along with procedures to investigate the validity of a developed simulation model in predicting the dynamic performance of a condenser heat recovery with a photovoltaic/thermal (PV/T) air heating collector to regenerate desiccant for reducing energy use of an air conditioning room under the prevailing meteorological conditions in tropical climates. The system consists of five main parts; namely, living space, desiccant dehumidification and regeneration unit, air conditioning system, PV/T collector, and air mixing unit. The comparisons between the experimental results and the simulated results using the same meteorological data of the experiment show that the prediction results simulated by the model agree satisfactorily with those observed from the experiments. The thermal energy generated by the system can produce warm dry air as high as 53 °C and 23% relative humidity. Additionally, electricity of about 6% of the daily total solar radiation can be obtained from the PV/T collector in the system. Moreover, the use of a hybrid PV/T air heater, incorporated with the heat recovered from the condenser to regenerate the desiccant for dehumidification, can save the energy use of the air conditioning system by approximately 18%.     

空调用环形热管换热器的实验研究

以R22为工质,对环形热管换热器在不同充液率和风量下的换热性能进行了实验研究,研究结果表明环形热管换热器在实验条件下的最佳充液率在70％左右,当充液率一定时,环形热管换热器的换热量随着风量的增加而增加,但换热量增加的效果随着风量的增加而逐渐减小。     

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 m², 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 m². Meanwhile, the solar equivalent generation power efficiency could reach 11.8%.     

Theoretical performance assessment of an integrated photovoltaic and earth air heat exchanger greenhouse using energy and exergy analysis methods

In this paper, a simplified mathematical model develops to study round the year effectiveness of photovoltaic/thermal (PV/T) and earth air heat exchanger (EAHE) integrated with a greenhouse, located at IIT Delhi, India. The solar energy application through photovoltaic system and earth air heat exchanger (EAHE) for heating and cooling of a greenhouse is studied with the help of this simplified mathematical model. Calculations are done for four types of weather conditions (a, b, c and d types) in New Delhi, India. The paper compares greenhouse air temperatures when it is operated with photovoltaic/thermal (PV/T) during daytime coupled with earth air heat exchanger (EAHE) at night, with air temperatures when it is operated exclusively with photovoltaic/thermal system (PV/T) and earth air heat exchanger (EAHE), for 24 h. The results reveal that air temperature inside the greenhouse can be increased by around 7-8 °C during winter season, when the system is operated with photovoltaic (PV/T), coupled with earth air heat exchanger (EAHE) at night. From the results, it is seen that the hourly useful thermal energy generated, during daytime and night, when the system is operated with photovoltaic (PV/T) coupled with earth air heat exchanger (EAHE), is 33 MJ and 24.5 MJ, respectively. The yearly thermal energy generated by the system has been calculated to be 24728.8 kWh, while the net electrical energy savings for the year is 805.9 kWh and the annual thermal exergy energy generated is 1006.2 kWh.     

夏热冬暖地区太阳能溶液除湿空调的应用分析

本文介绍了太阳能溶液除湿空调系统的形式及其工作原理,并将该系统运用到广州某一小型办公楼上,利用DesT软件,进行了逐时模拟计算。计算结果表明：在不考虑传统空调的再热量,忽略其他传热损失下,溶液除湿空调系统用电量仅为传统空调系统的40％;由于通过溶液的蓄能来充分利用太阳能,使得燃气加热器的供热量仅为再生热负荷的13．4％;在广州地区的电、燃气价格下,太阳能溶液除湿空调系统的运行费用仅为传统空调系统的49．03％。     

Performance analysis of earth-pipe-air heat exchanger for summer cooling

Earth-pipe-air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth-air-pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth-air-pipe heat exchanger systems are studied. The 23.42 m long EPAHE system discussed in this paper gives cooling in the range of 8.0-12.7 °C for the flow velocities 2-5 m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0 m/s.     

The development of a finned phase change material (PCM) storage system to take advantage of off-peak electricity tariff for improvement in cost of heat pump operation

An experimental system consisting a longitudinally finned RT58 phase change material (PCM) in a horizontal cylinder has been conducted to evaluate the heat transfer characteristics of RT58. The investigation forms part of a wider study to investigate a suitable PCM to take advantage of off-peak electricity tariff. The system consisted of a 1.2 m long copper cylinder filled with 93 kg of RT58 with an embedded finned tube at the centre to serve as a heat transfer tube. The experimental data has been reported using hourly temperature profiles, isotherm plots, overall heat transfer coefficients and energy stored. The results show a quadratic relationship between heat transfer coefficient and the inlet HTF temperature within temperature range (62-77 °C) investigated. Increasing charge inlet heat transfer fluid temperature by 21.9% increased heat transfer coefficient by 45.3% during charging and 16.6% during discharge. The potential implication of integrating PCM storage system to an air source heat pump to meet 100% residential heating energy load for common buildings in UK has demonstrated that with an improvement in heat transfer, store size can be reduced by up to 30%.