Desiccant HVAC system driven by a micro-CHP: Experimental analysis

In the Mediterranean area, there is increase in demand for summer cooling satisfied by electrically driven units in domestic and small commercial sectors; this involves electric peak loads and black-outs. Consequently, there is an increasing interest in small scale polygeneration systems fuelled by natural gas.In this paper, attention is paid to a test facility, located in Southern Italy, to carry out experimental analysis on a small scale polygeneration system based on a natural gas-fired Micro-CHP and a desiccant HVAC system. The MCHP provides thermal power, recovered from engine cooling and exhaust gas, for the regeneration of the desiccant wheel and electric power for the chiller, the auxiliaries and the external units (computers, lights, etc.). The HVAC system can also operate in traditional way, by interacting with electric grid and gas-fired boiler. An overview of the main experimental results is shown, considering both the desiccant wheel and the global polygeneration system.The experimental results confirm that the performances of the desiccant wheel are strongly influenced by outdoor thermal-hygrometric air properties and regeneration temperature. The polygeneration system guarantees primary energy savings up to 21.2% and greenhouse-gas emissions reductions up to 38.6% with respect to conventional HVAC systems based on separate energy “production”.     

Study on a novel thermally driven air conditioning system with desiccant dehumidification and regenerative evaporative cooling

Existing desiccant cooling systems reduce the temperature of process air either by adopting evaporative coolers or incorporating vapor compression systems. While the former is restricted by inaccurate control, the latter still consumes certain quantity of electric power. To solve this problem, a thermally driven air conditioning system, which combines the technologies of rotary desiccant dehumidification and regenerative evaporative cooling, has been proposed and investigated. In addition to dehumidification, the system is capable of producing chilled water, thereby realizing separate temperature and humidity control without increasing electrical load. To find out the characteristics of produced chilled water and evaluate the feasibility and energy saving potential of this novel system, a mathematical model has been developed. Case studies have been conducted under Air conditioning and Refrigeration Institute (ARI) summer, ARI humid and Shanghai summer conditions. It is found that the system can achieve a thermal COP higher than 1.0 and an electric COP about 8.0. The temperature of chilled water produced by the system is around 14–20 °C. This chilled water can be used with capillary tube mats for radiant cooling. It is suggested that the system can also be designed as a standalone chilled water plant. As a desiccant dehumidification-based chilled water producing technology, this would expand desiccant cooling to a boarder niche application. The effects of chilled water flow rate, air distribution ratio, inlet air conditions and regeneration temperature have been analyzed in detail. Reachable handling regions, which will be helpful to system design and optimization, have been obtained.     

Simulation and experimental analysis of a fresh air-handling unit with liquid desiccant sensible and latent heat recovery

This article introduces a liquid desiccant fresh air processor. Its driving force is low-grade heat (heat obtained from 65 – 75°C hot water). Inside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air. A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COP _f was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COP _sys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor. The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions.     

新型排风能量回收装置的分析与研究

作者从全铝制板翅式换热器与凝结水间接蒸发冷却联合应用的试验获得的结果出发，对该换热器应用于集中空调系统的能量回收做出了计算，并且进行较为详尽的分析，计算结果表明全新风空调系统使用该能量回收装置后，可以节省机组装机容量50％，节省运行费用一半；这对需要大量新风的厂房，医院的特殊病区等有很好的节能效果；而普通的舒适性空调系统，应用该能量回收装置后也可以节省装机容量20％；这表明在集中空调系统中应用全铝制板翅式换热器既能改善室内空气品质又能回收排风能量，是集中空调系统节能和人性化行之有效的措施：     

燃气在空调制冷中的应用前景

介绍了燃气吸收式冷温水机组、燃气机驱动的冷水机组和除湿冷却式空调机的优点。它们是可以用天然气驱动的空调机。小型的燃气吸收式冷不机且在住宅建筑领域有很大的潜在市场。     

Effects of utilizing seawater as a cooling source system in a commercial complex

This paper treats energy and cost performance of a cooling source system with indirect seawater utilization for air conditioning in a commercial complex. Seawater utilization has merits as a cooling source, because seawater temperature is lower than outdoor air in summer and it is cost effective because there is no water monetary cost. Actual operating data has been measured for about 2 years and the chiller and system co-efficient of performance (COP) have indicated about 4.77 and 2.93, respectively, even in summer season and the mean efficiency of the thermal storage system was about 89.9% taking into account heat loss of pumps. In addition, we have constructed simulation models for cooling tower systems, air cooling chiller systems and direct seawater utilization systems then compared them to this system. The electric power consumption of the indirect seawater utilization system was almost the same as the other systems except the air cooling chiller system, because using lower seawater temperature made the chiller efficiency higher. In conclusion, our results showed the indirect seawater utilization system was able to improve the system COP compared to air cooling chiller system, and cancel water consumption compared with the cooling tower system, and cut down an initial and maintenance costs compared with the direct seawater utilization system.     

A simulation appraisal of performance of different HVAC systems in an office building

The article reports on a simulation appraisal of energy consumption, energy costs and environment impact of three systems used for space heating, and space cooling of an office building in Kragujevac, Serbia. Three investigated systems are (1) a system with a natural gas boiler and convective baseboard heaters for water space heating and window air conditioners for air space cooling; (2) a system with a natural gas boiler and individual air reheaters for air space heating and a chiller plant for air space cooling; and (3) an air-to-air heat pump for air space heating, and cooling. The systems are modeled and simulated by using EnergyPlus software. After simulations, it is found that the first investigated system has the highest energy efficiency, the best economy, and the lowest environmental impact. That is because of the fact that the first system has water as a heating medium and uses predominantly natural gas as fuel. However, in future, when for generation the grid electrical energy requires less primary energy, and becomes decarbonized, the third system would be best to conserve energy resources and environment.     

Energy savings potential of a desiccant assisted hybrid air source heat pump system for residential building in hot summer and cold winter zone in China

In hot summer and cold winter zone in China, air conditioning system has four running modes yearly including cooling with dehumidification, cooling, dehumidification and heating in residential buildings. The conventional air source heat pump (ASHP) system is not designed to independently control temperature and humidity, and is not very suitable for the dehumidification mode in the view of building energy consumption. A novel ASHP system combining radiant cooling/heating for residential buildings was presented. The main feature of this hybrid ASHP system is that desiccant wheel and cooling coil accomplish dehumidification process together, and the regenerative heat needed by the desiccant wheel is supplied by the condenser dissipated heat. Based on simulation studies and performance analysis, this paper predicts the primary energy consumption of the hybrid ASHP system in comparison with the conventional ASHP system during the cooling and heating seasons. It was found that primary energy requirement can be reduced by more than 8% in cooling with dehumidification mode, by 50% in dehumidification mode, and by more than 14% in heating mode. The study results prove that the hybrid ASHP system can keep great energy saving and running cost saving yearly, especially in the dehumidification process.     

酒店建筑空调和生活热水方案优化设计

本文利用负荷全年逐时计算数据,引入全寿命周期费效比方法,对北京一家酒店的冷源设计方案的初投资和运行费用比较分析,综合考虑初投资、控制策略、维保难度、运行费用等多方面因素,该项目最终推荐选用水冷冷水机组机＋电热水器的方案。     

Exergetic modeling and experimental performance assessment of a novel desiccant cooling system

New approaches to space conditioning of buildings are required to resolve economic, environmental, and regulatory issues. One of the alternative systems that is brought to agenda is the desiccant cooling systems, which may provide important advantages in solving air conditioning problems. This study deals with the performance analysis and evaluation of a novel desiccant cooling system using exergy analysis method. The system was designed, constructed and tested in Cukurova University, Adana, Turkey and has been successfully operated since 2008. This system consists of a desiccant wheel, heat exchangers, fans, evaporative cooler, electric heater unit and refrigeration unit. The exergy transports between the components and the destructions in each of the components of the desiccant cooling system are determined for the average measured parameters obtained from the experimental results. Exergy efficiencies of the system components are determined in an attempt to assess their individual performances and the potential for improvements is also presented. The exergetic efficiency values for the whole system on the exergetic product/fuel basis are calculated to range from round 32% to 10% at the varying dead (reference) state temperatures of 0-30 °C.     

Proposal for a new hybrid control strategy of a solar desiccant evaporative cooling air handling unit

Correctly controlled solar desiccant evaporative cooling is an interesting option for achieving savings in building air-conditioning consumption. The operation of this system (open loop cooling cycle) is strongly influenced by indoor and outdoor air conditions. This influence is characterized using numerical simulations. First the air conditioned room and the cooling system are simulated using a validated model of the desiccant wheel. Then the influence of each parameter of the desiccant air handling unit is evaluated. The third step is to assess the system cooling power for each operating mode with fluctuating outdoor and indoor air conditions. This allows for making relevant choices for a new control strategy taking into account both indoor and outdoor air conditions. This control strategy is tested for a whole cooling season and compared to a reference compression system with promising results, allowing for energy savings of about 40% for French climate.     

北京某商业建筑温湿度独立控制空调系统的全年能耗分析

以北京某一商业建筑为模拟对象,对其空调冷负荷进行模拟,并在此基础上计算普通空调系统和温湿度独立控制空调系统的能耗.经过对能耗的比较和分析表明,温湿度独立控制空调系统的能耗比普通空调系统的能耗降低了16.4%,冷水机组全年平均性能系数提高了13%.结果表明温湿度独立控制空调系统具有很好的应用前景.     

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.     

冰蓄冷辐射供冷系统的综合评价

日本办公建筑的空调耗电占其总耗电的50％以上，尤其在夏季是加剧电力需求高峰的主要因素。为了平衡负荷，电力生产部门和政府都在致力提倡蓄热空调系统。介绍了东京一座典型办公楼的与冰蓄冷系统结合的辐射供冷系统，包括其均衡负荷的作用，节能的潜力，施工及运行费用的估算等。     

空气源热泵加冷水机组耦合水蓄能系统在某工程中的应用

针对青岛市信息与金融产业示范区一项目,结合当地能源情况和建筑使用功能,经过技术经济比较,空调系统冷热源采用空气源热泵加电制冷冷水机组耦合水蓄能系统.介绍了冷热源的系统设计、运行时间和控制策略,认为所采用的冷热源方案初投资和运行费用均较低.     

基于DPSSHP的分布式供能系统在赣南地区的研究

赣南地区城市污水排放量较大,工业废水富含大量余热。发展基于直接式原生污水源热泵(Direct Primary Sewage Source Heat Pump,简称DPSSHP)的分布式供能系统,向建筑供冷供热,将大大降低建筑空调采暖能耗。根据赣南地区实际情况,提出了DPSSHP系统针对不同类型建筑的应用规划。选取了地下水源热泵,大型螺杆式冷水机组+燃煤锅炉,风冷式空气源热泵、DPSSHP,从系统初投资、运行费用、单位面积运行成本等方面进行经济性比较,得出DPSSHP较为经济。     

热电联供系统复合除湿空调系统动态仿真

将燃气内燃机热电联供系统(CHP)与热湿独立处理空调系统(采用固体除湿转轮)组成复合空调系统.供冷期,利用燃气内燃机余热再生除湿转轮.供暖期,利用燃气内燃机余热加热新风与供暖.针对上海某超市建筑,使用动态仿真方法对常规分供系统(采用热湿联合处理,配置电制冷机、燃气锅炉)、复合空调系统的一次能源利用率、静态投资回收期、二...     

空调内区余热问题解决方法探讨

建筑物内区余热已成为空调设计中不容忽视的问题。提出了内区分路设置冷冻机、内区分路设置板式换热器利用冷却塔供冷、利用新风机组送冷风以及利用设双风机的全空气系统解决内区余热问题的几种方法。     

溶液调湿技术在既有建筑空调系统改造中的应用

针对既有建筑空调系统改造中存在的问题,提出采用溶液调湿空调系统的改造方案,以达到降低改造难度,保证改造后空调系统节能、舒适的目的.以某大型三甲医院综合服务楼为例,对其空调效果不佳的现象进行了测试分析,对溶液调湿空调改造方案和传统改造方案进行了分析比较,指出了溶液调湿空调在既有建筑改造中应用的可行性和优势.     

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.