空调用蒸发式冷凝器能耗实验研究

当室外气温较高时,风冷热泵系统冷凝器存在换热效果下降的问题,而蒸发式冷凝器可以改善此问题,蒸发式冷凝器因此逐步得到广泛重视。为研究采用蒸发式冷凝器制冷系统的能耗情况,通过正交实验的方法,对比研究了蒸发式冷凝器与风冷式冷凝器在相同工况下压缩机能耗情况,并对影响其性能的因素进行了分析。研究表明,各因素对压缩机耗功量的影响能力依次为:冷凝器进口空气温度、速度及冷凝器喷水量。压缩机耗功量随进口空气温度的升高、进风空气速度降低而增大,随喷水量增加存在先减小后保持不变的现象。     

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%.     

Hydronic radiant cooling — preliminary assessment

A significant amount of the electrical energy used to cool non-residential buildings equipped with all-air systems is drawn by the fans that transport the cool air through the thermal distribution system. Hydronic systems reduce the amount of air transported through the building by separating the tasks of ventilation and thermal conditioning. Due to the physical properties of water, hydronic systems can transport a given amount of thermal energy and use less than 5% of the otherwise necessary fan energy. This improvement alone significantly reduces the energy consumption and peak-power requirement of the air conditioning system. Radiant cooling has never penetrated the US markets significantly. The scope of this survey is to show the advantages of radiant cooling in combination with hydronic thermal distribution systems, as compared to the commonly-used all-air systems. The report describes the development, thermal comfort issues, and cooling performance of the hydronic systems. The peak-power requirement is also compared for hydronic systems and conventional all-air systems.     

Modelling and performance prediction of an integrated central cooling plant for HVAC energy efficiency improvement

The aim of this paper is to explore methods to reduce the energy consumption of a central cooling plant. To achieve this, we have developed a new design for heating, ventilating and air conditioning (HVAC) efficiency improvement. A storage tank together with an immersed heat exchanger is installed in the discharge line between the compressor and condenser. The heat exchanger uses the make-up water of the cooling tower to reduce the refrigerant temperature entering the condenser. To investigate the potential of energy savings, we used a real-world commercial building with a central cooling plant, located in a hot and dry climate, for our case study. The energy consumption and relevant data of the existing central cooling plant were acquired over the course of a typical week in summer. The integrated system has been modeled and analyzed to achieve energy conservation. The performance of the proposed cooling system was simulated using a transient simulation software package. Comparison of the proposed system with existing cooling plant is included in this paper to demonstrate the advantages of our new configuration. Results show that up to 18% power saving can be obtained by using our design.     

浅析相变材料储能在空调中的应用前景

概述了相变材料储能在空调系统中的应用前景，分述了相变材料蓄冷装置在空调蒸发器侧，冷凝器侧，空气处理机内以及其它方面的应用状况。阐述了相变材料储能装置的优点，分析了相变储能方式与冰蓄冷，水蓄冷，蓄热方式的不同之处，并指出大规模使用这种储能装置，会带来可观的节能效益和环境效益。     

Combined space cooling and water heating system for Hong Kong residences

The combined space cooling and hot water preheating system that utilizes the rejected condenser heat is considered one of the most cost effective energy conservation measures. However, simultaneous consumption characteristics are absent in public domain. Questionnaire surveys have been conducted to obtain the relevant information from 126 households residing in high-rise public rental residential buildings in Hong Kong, achieving a confidence level of 95%. The candidate households were selected by a convenience sampling approach, and the questionnaire was constructed using either forced-choice format or in numeric response format. The data obtained were verified by correlation analysis. Data collected includes the occupancy pattern, the installed air-conditioner and water heater characteristics, and the utilization pattern of air-conditioning and hot water. Based upon the collected data and site measurements, hourly, daily and monthly heat recovery and hot water heating demand profiles were established, as well as the correlation between tap water and outdoor air temperatures. The combined profiles enable the evaluation of the feasible use of the combined system, and for future sizing of hot water storage tanks. The potential energy and fuel cost saving associated with the use of the proposed combined system for typical public rental housing in Hong Kong was estimated to be 50%.     

Comparison of underfloor and overhead air distribution systems in an office environment

This study compares thermal environment of two air distribution systems in an office setting. Airflow, heat and mass (water vapor and contaminant gas) transfer in steady-state condition are modeled for an underfloor air distribution system and an overhead air distribution system. The models include a typical cubicle in a large office floor with a chair, a desk with a personal computer on top, and heat sources such as seated person, desktop computer, and lights. For underfloor air distribution system, cool air enters the occupied zone through an inlet located at the floor level supplying a vertical upward inflow. Three different locations of the inlet diffuser are considered. For overhead air distribution, the inlet is located on the ceiling with slower and cooler inflow. Three inlet angles are considered. For both systems, the air return location is on the ceiling at the same place. Distributions of velocity, temperature, relative humidity, and contaminant concentration in various cases for both systems are computed. Thermal comfort factors are assessed for the two systems. The results are compared among cases of each system, as well as between two typical cases of the two systems and to experimental data for an actual office building given in literature. The results provide a detailed understanding of air transport and its consequence on thermal comfort and indoor air quality that are useful for office building air conditioner design. It is found that underfloor system gives better performance than overhead system in contaminant removal and significantly in energy saving while maintaining the same thermal comfort condition.     

Saving energy in the make-up air unit (MAU) for semiconductor clean rooms in subtropical areas

The energy requirements to cool, dehumidify, preheat and/or humidify outdoor air are significant in the make-up air unit (MAU) of clean room air-conditioning systems, and can represent 30% to 65% of the total thermal energy required to maintain a clean room environment. Because of these high-energy requirements, cost-effective means to reduce energy costs can influence unit production costs. Reducing or displacing mechanical cooling or electrical heating requirements can achieve the greatest opportunity for significant energy savings. This paper, therefore, aims to improve the energy performance of the MAU system by properly arranging compositions of components of a typical MAU applied in a semiconductor clean room. Explicitly, we investigated the influence of various factors including the fan location (draft-through type vs. push-through type), chilled water system (single-chilled water temperature system vs. two chilled water temperature system) and reheating scheme (electrical heating vs. hot water provided by heat recovery chiller). The result shows that the draw-through type accompanied by two chilled water temperature system with heat recovery function exhibits the lowest electrical power consumption.     

Computer modelling and thermodynamic assessment of an aqua-ammonia absorption cycle solar heat pump

An assessment based on steady state thermodynamic analysis of an aqua-ammonia absorption cycle solar heat pump for space heating is presented. The system consists of a solar heated generator, rectifier, condenser, evaporator, absorber liquid heat exchanger and a subcooler. During heat pump operation, the evaporator absorbs heat at low temperature from the outside atmospheric air, while the heat rejected by the absorber, condenser and rectifier is used to warm the interior air of the space to be heated. A numerical computer modelling based on the solution of simultaneous heat and mass balance equations for various components of the system has been carried out. The influences of component temperatures and heat exchanger effectiveness on the heating coefficients of performance and heat transfer rates have been investigated to obtain optimum operating conditions for the proposed heat pump system. Further, the absorption cycles are compared with an ideal reversible cycle operating over the same range of temperatures. It has been found that the performance of the absorption cycle does not continue to improve as the input temperature increases and that additional components will be required to allow the machine to take advantage of the higher temperatures available from modern collectors.     

Effects of outdoor air conditions on hybrid air conditioning based on task/ambient strategy with natural and mechanical ventilation in office buildings

This research aims to clarify the effects and indoor environmental characteristics of natural and mechanical hybrid air-conditioning systems in office buildings during intermediate seasons and to obtain design data. Natural and mechanical hybrid air conditioning is an air-conditioning system that utilizes natural ventilation and mechanical air-conditioning systems to improve the quality of the indoor thermal and air environment, and to reduce energy consumption. This report first categorizes the available natural ventilation conditions and estimates the amount of natural ventilation available in a model building. Furthermore, based on the concept of task-ambient air conditioning, after controlling the average temperature in the task zone to a target air conditioning temperature (26°C), changes in the outdoor temperature/humidity and the inflow rate, and the indoor environment and amount of cool heat input were studied with changes in the size of the natural vent using three-dimensional Computational Fluid Dynamics (CFD) analysis. The results of these studies indicated that natural ventilation at temperatures lower than the indoor temperature effectively covered the lower indoor task zone through negative buoyancy, which enabled energy-saving air conditioning in the task zone.     

Saving energy in the heat-pump air conditioning system driven by gas engine

The main functions of the heat-pump air conditioning system driven by gas engine (GEHPAC) are to maintain the room temperature and control the humidity of the room. In summertime, the air can be reheated by the waste heat water from the gas engine, while the air can be reheated and humidified by the waste heat water in winter. Reducing or displacing electrical heating requirements can achieve the greatest opportunity for significant energy savings. This paper, therefore, aims to improve the energy performance of the AC system by using the waste heat from the gas engine. The mathematical model for the second heat exchanger, the sprayed room, the mixed air, was used to research the GEHPAC. Explicitly, we investigated the influence of various factors including the outdoor air temperature and humidity in summer and winter. Results from the analysis show that the GEHPAC can save more energy than the electricity engine heat pump. The GEHPAC runs beautifully in part load mode. PERx is higher in winter than in summer. The maximum PERx is over 1.6 in summer, while over 1.9 in winter. The GEHP which can control the room humidity can be used in more areas than the common GEHP.     

Experience on the application of a ground source heat pump system in an archives building

A ground source heat pump (GSHP) system was designed and constructed in Minhang archives of Shanghai. As a demonstration project, it is the first archives to use a GSHP system in China. The system consists of two heat pumps with the rated cooling capacity of 500 kW for each and 280 boreholes with 80 m in depth. In the cooling mode, the heat extraction from the condenser of the heat pump was divided: part of it was rejected to the soil while the rest was used to reheat the air in air handling units. The GSHP system has continuously run for nearly two years. It was shown that the indoor thermal environment met the “Archives Design Code” issued by China national archives. Compared with an air source heat pump system which is widely used in archives buildings, the operating cost of the GSHP system is reduced by 55.8% and the payback time is about two years. Owing to its great potential in energy conservation, such kind of GSHP system is testified to be applicable to the air-conditioning systems of the archives buildings. Besides, the applications of GSHP systems corresponding to different climatic zones of China were analyzed.     

Analysis of indoor environmental conditions and heat pump energy supply systems in indoor swimming pools

For indoor swimming pools, a lot of energy is needed to control the indoor temperature, relative humidity and pool water temperature. Meanwhile, the indoor air contains a high specific enthalpy due to water evaporation. A new heat pump dehumidifier is studied to reduce energy consumption. The most significant feature of this system is that it can not only recover the latent heat from indoor moist air, but also absorb heat from outdoor air to heat the indoor air and pool water. First, indoor environmental conditions, including space parameters and pool temperature, are analyzed based on human thermal comfort and energy saving. Subsequently, the models of heat and moisture gain are built. After that, the construction and operating modes of the heat pump dehumidifier are described, and the system model is established based on polynomial equations model. In a case study, an indoor swimming pool with a heat pump dehumidifier in Shanghai is studied. When outdoor air specific enthalpy is higher than 18.6 kJ/kg, the requirement of pool water heating can be met only by the heat pump dehumidifier, thus, auxiliary pool heater will not to be put into use. At last, economic analysis between the heat pump dehumidifier and conventional dehumidifier is conducted.     

天然气CHP、CCHP系统在工业企业的应用

介绍了天然气热电联供（CHP）系统、天然气冷热电联供（CCHP）系统在我国的发展现状,提出在工业企业应用天然气CHP、CCHP系统,改变采用一次能源直接供应热风、热水的现状,实现能源的梯级利用,提高能源利用效率。     

Optimal control development for chilled water plants using a quadratic representation

Optimal supervisory control strategy for the set points of controlled variables in the cooling plants has been studied by computer simulation. A quadratic linear regression equation for predicting the total cooling system power in terms of the controlled and uncontrolled variables was developed using simulated data collected under different values of controlled and uncontrolled variables. The optimal set temperatures such as supply air temperature, chilled water temperature, and condenser water temperature, are determined such that energy consumption is minimized as uncontrolled variables, load, ambient wet bulb temperature, and sensible heat ratio are changed. The chilled water loop pump and cooling tower fan speeds are controlled by the PID controller such that the supply air and condenser water set temperatures reach the set points designated by the optimal supervisory controller.The influences of the controlled variables on the total system and component power consumption were determined. The predicted power obtained from the quadratic regression equation was found to be a good fit to the simulated one. Because the Hermitian matrix of the system quadratic cost function was positive, the optimal control variables for the minimum power consumption were able to be obtained. There are relatively high effects of the load and sensible heat ratio on the optimal supply air and chilled water set temperatures, while the effect of ambient wet bulb temperature is less. In contrast to that result, the ambient wet bulb temperature has a much larger effect on the optimal condenser water set temperature, while the load has less, and the sensible heat ratio has no influence on it. The trade-off among the components of power consumption results in that the total system power use in both simulated and predicted systems are minimized at lower supply, higher chilled water, and lower condenser water set temperature conditions.     

空调系统中热湿处理过程的(火用)评价方法及应用

提出对热、湿处理过程进行单独(火用)评价的概念,并构建了相应评价指标.以某一次回风空调系统的典型夏季空气处理过程为例,在热力学极限意义上阐明了对热、湿处理进行单独(火用)评价的实施过程,计算结果表明该空气处理过程的显热(火用)效明显高于潜热(火用)效,潜热(火用)效低下的原因主要在于再热显热(火用)损和冷凝水(火用)损...     

Experimental investigation of a low energy consumption air conditioning system based on conventional central heating installation

This paper deals with the development of a low cost and low energy consumption air conditioning system based on the conventional central heating installations. It is aimed to convert, with minimal cost and work intervention in the interior of the buildings, the classic central heating systems into a new type system which can cool during summer and heat during winter period. In general, the above mentioned heating–cooling system constitutes an integrated new technology in building air conditioning, with good prospects in replacing eventually the conventional air conditioning systems.The experimental installation is described in detail and the experimental results are presented and analysed. The achieved energy saving is also calculated. The advantages and disadvantages of the proposed system are discussed and useful conclusions are drawn.     

城市原生污水作为热泵空调系统冷热源的应用探讨

利用热泵技术回收城市污水中的热能为建筑物供暖、空调具有较大的现实意义.本文介绍了国内外利用城市污水作为热泵空调系统冷热源的工程实例,并结合我国相关工程应用现状,分析了几种应用形式的优缺点.     

Choosing heat sinks for cooling in tropical climates

Efforts to limit CO₂emissions from buildings in the tropics either focus on reducing energy demand, i.e., air-conditioning, or on replacing fossil with renewable sources. The link between energy demand and supply is often overlooked, especially the effect of the temperature lift of air-conditioning systems on energy consumption. But while heat and humidity gains define energy demand, operating temperatures of the system define the necessary energy input. We aim to transfer our experience of using the LowEx paradigm for heat pump systems in moderate climates to the tropical climate of Singapore. In this paper, we took a systematic overview of a range of heat sinks, to which we refer to as anergy sinks. We analysed their thermal properties and their effect on the performance of air-conditioning systems, expressed as COP. The predominantly used dry air-cooled condenser units performed worst, especially when subject to a stack effect in (semi-)confined spaces. The performance is highest for cooling towers using the wet bulb temperature followed by water body based anergy sinks and the soil. The wide spread of results confirms that the heat rejection temperature is a decisive factor for the performance of the overall cooling system and the input of primary energy.     

Performance of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been proposed for use in hot and humid climates. The system aims to dehumidify the ventilation air which is the major source of latent load. A heat exchanger is used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The simulation procedure for the proposed system has been presented. By inputting the climatic data and the physical parameters of all equipments, the operating parameters at each equipment and the performance parameters of the system can be evaluated. The simulation procedure is demonstrated by showing the daily profiles of the operating and performance parameters on a typical day as well as investigating the influence of the selected operating parameters on the system performance. The results suggest that the most influential parameters are solar radiation, ventilation rate, and desiccant solution concentration. The balance between the water removed at the dehumidifier and that evaporated at the regenerator needs to be considered to maintain uniform performance during continuous operation.