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.     

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.     

Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to evaluate the exergetic performance of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis is carried out to calculate the thermal and electrical parameters, exergy components and exergy efficiency of a typical PV/T air collector. Some corrections are done on related heat loss coefficients. An improved electrical model is used to estimate the electrical parameters of a PV/T air collector. Further, a modified equation for the exergy efficiency of a PV/T air collector is derived in terms of design and climatic parameters. A computer simulation program is also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. It is observed that the modified exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency, overall energy efficiency and exergy efficiency of PV/T air collector is about 17.18%, 10.01%, 45% and 10.75% respectively for a sample climatic, operating and design parameters.     

潜热、显热分级处理的复合空调系统性能研究

在实验数据的基础上,针对分别采用两种干燥剂(硅胶、氯化锂)的复合空调系统和压缩式空调系统进行了性能比较分析,发现复合空调系统比压缩式空调系统不仅节电25.6%～35.4%,而且由于转轮处理了潜热负荷可使蒸气压缩制冷系统蒸发器面积减少11.1%～15.6%,冷凝器面积减少15.4%～21.4%。     

溶液除湿空调在高温高湿地区的应用研究

设计了一种新型的溶液除湿装置。综合利用太阳能、天然水源、热回收和溶液除湿技术,对新风进行分阶段除湿,同时,利用太阳能和室内排风对溶液进行再生,克服了传统溶液除湿空调技术在高温高湿地区应用过程中的局限性。结果表明,与传统溶液除湿方案相比,该系统的溶液循环量减小,运行能耗降低,对太阳能的依赖程度降低,溶液的吸湿效率和再生效率提高。     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

转轮除湿与冷却除湿相结合的复合式除湿工艺空调系统

介绍一个转轮除湿与冷却除湿相结合的复合式除湿工艺空调系统，分析比较氯化钙、乙二醇冷冻水载冷剂在同一温度之间及同一载冷剂在不同温度下的换热系数差异，分析该工艺空调系统不能正常运行的原因，并提出改进措施。     

Performance analysis on a hybrid air-conditioning system of a green building

This paper presents the performance analysis on a hybrid air-conditioning system according to the hybrid building energy system of the green building demonstration project in Shanghai, in which a 150 m² solar collector is used to power two 10 kW adsorption chillers, a vapor compression heat pump is used to cool air in the evaporating end while the condensing heating at about 80 °C is fully used to regenerate a liquid desiccant dehumidification system. In the hybrid system, the sensible cooling to the air is treated mainly by solar adsorption cooling and vapor compression cooling, whereas the latent heat is treated by the liquid desiccant dehumidification system with regeneration from the condensing heat of the heat pump. The results show that the performance of this system is 44.5% higher than conventional vapor compression system at a latent load of 30% and this improving can be achieved by 73.8% at a 42% latent load. The optimal ratio of adsorption refrigerating power to total cooling load for this kind of hybrid systems is also studied in this paper.     

Comparative study on internally heated and adiabatic regenerators in liquid desiccant air conditioning system

Liquid desiccant regeneration has important effect on performance of a liquid desiccant air conditioning system. Compared with conventional packed regenerator, internally heated regenerator is proposed to achieve better regeneration performance. This study emphasized on both regeneration rate and regeneration thermal efficiency to evaluate the performance of both regenerators. A validated heat and mass transfer model was used to analyse and compare the performance of internally heated and adiabatic regenerators. The results indicated that internally heated regenerator not only could increase the regenerate rate, but also could exhibit higher energy utilization efficiency. Different from adiabatic regenerator, internally heated regenerator can provide comparable regeneration efficiency and regeneration rate at low desiccant flow rate, so it should be a good alternative to avoid carryover of desiccant droplets. Higher air flow rate would result in a deduction of regeneration thermal efficiency although achieving higher regeneration rate. Suitable flow rate of the air should be considered carefully in liquid desiccant regeneration. The internally regenerator could have considerable prospect in liquid desiccant air conditioning application.     

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.     

Application of desiccant systems for improving the performance of an evaporative cooling-assisted 100% outdoor air system in hot and humid climates

The purpose of this study was to enhance the energy-saving potential of an indirect and direct evaporative cooling-assisted 100% outdoor air system (IDECOAS) by integrating it with either a solid or liquid desiccant system. The desiccant system can be installed either at the scavenger air side of the indirect evaporative cooler (IEC) to enhance its effectiveness or at the primary air side of the IEC to reduce the latent load of outdoor air. The operating energy consumption affected by the location and type of the desiccant unit integrated with IDECOAS was simulated under three different hot and humid climates using TRNSYS 17 integrated with commercial equation solver programme. And then, the most energy-conservative configuration was selected for each climate zone as the proposed system. The simulation results showed that configurations with the desiccant dehumidification unit located upstream of the IDECOAS consume 76–85% less cooling coil energy than those with the desiccant unit located downstream of the IDECOAS. It was also found that the liquid desiccant system saves 21–50% more primary energy than the solid one, when it is integrated with IDECOAS.     

Experiences with a gas driven,desiccant assisted air conditioning system with geothermal energy for an office building

Thermal driven desiccant assisted air conditioning systems make use of waste heat to dehumidify humid outside air in a desiccant wheel. Within the scope of a research project, an investigation of a desiccant assisted air conditioning system was carried out, and a demonstration plant was built in an office building in Hamburg, Germany. The HVAC system consists of a small CHP-plant, a desiccant assisted ventilation system and an earth energy system (borehole heat exchangers) for cooling instead of an electric driven compression chiller. The radiant floor heating system of the building is used for cooling. In this paper, measurement results and investigations of performance, energy demand and operating costs will be presented. It was found that considerable primary energy savings can be achieved (70%) using desiccant air conditioning with borehole heat exchangers. But even if electric chiller is used, savings of 30% in primary energy can be accomplished. Starting costs for the demonstration plant were not higher than for a conventional system, but running costs could be reduced drastically.     

A heat pipe photovoltaic/thermal (PV/T) hybrid system and its performance evaluation

Building-integrated photovoltaic/thermal (BIPV/T) system has been considered as an attractive technology for building integration. The main part of a BIPV/T system is PV/T collector. In order to solve the non-uniform cooling of solar PV cells and control the operating temperature of solar PV cells conveniently, a heat pipe photovoltaic/thermal (PV/T) hybrid system (collector) has been proposed and described by selecting a wick heat pipe to absorb isothermally the excessive heat from solar PV cells. A theoretical model in terms of heat transfer process analysis in PV module panel and introducing the effectiveness-number of transfer unit (?-NTU) method in heat exchanger design was developed to predict the overall thermal-electrical conversion performances of the heat pipe PV/T system. A detailed parametric investigation by varying relevant parameters, i.e., inlet water temperature, water mass flow rate, packing factor of solar cell and heat loss coefficient has been carried out on the basis of the first and second laws of thermodynamics. Results show that the overall thermal, electrical and exergy efficiencies of the heat pipe PV/T hybrid system corresponding to 63.65%, 8.45% and 10.26%, respectively can be achieved under the operating conditions presented in this paper. The varying range of operating temperature for solar cell on the absorber plate is less than 2.5 °C. The heat pipe PV/T hybrid system is viable and exhibits the potential and competitiveness over the other conventional BIPV/T systems.     

Experimental investigation and theoretical analysis of solar heating and humidification system with desiccant rotor

In this paper, a solar heating system, which combines the technologies of evacuated tube solar air collector and rotary desiccant humidification together, has been configured, tested and modeled. The system mainly includes 15 m² solar air collectors and a desiccant air-conditioning unit. Two operation modes are designed, namely, direct solar heating mode and solar heating with desiccant humidification mode. Performance model of the system has been created in TRNSYS. The objective of this paper is to check the applicability of solar heating and evaluate the feasibility and potential of desiccant humidification for improving indoor thermal comfort. Experimental results show that the solar heating system can convert about 50% of the received solar radiation for space heating on a sunny day in winter and increases indoor temperature by about 10 °C. Compared with direct solar heating mode, solar heating with desiccant humidification can increase the fraction of the time within comfort region from about 10% to 20% for standalone solar heating and from about 30% to 60% for solar heating with auxiliary heater according to seasonal analysis. It is confirmed that solar heating with desiccant humidification is promising and worthwhile being applied to improving indoor thermal comfort in heating season.     

TRNSYS simulation for solar-assisted liquid desiccant evaporative cooling

ABSTRACT

Recently, desiccant cooling systems are well thought of as a competent method for controlling the water content in the air. A solar flat-plate collector has been used as it decreases the dependency on non-renewable resources. Solar-aided liquid desiccant systems have been used to reduce the dependency of air-conditioning systems on non-renewable sources of energy. Manipal’s humid and searing climate provides certain benefits in setting up such a system. The suggested system has reliability and equipment life and also takes complete advantage of the available solar energy for the renewal of the liquid desiccant. TRNSYS simulation is used to predict the efficiency and feasibility of the system. The temperature and energy-load variations were successfully obtained. An effective simulation was developed whereby the solar air conditioning of a room was indicated.     

Evaporative air cooler coupled with variable frequency drive for dehumidification of indoor air

This study deals about the investigation of a solar-powered desiccant dehumidification system coupled with variable frequency drive (VFD). The proposed design of the system consists of two evaporative air coolers. One cooler performs as an absorber and the other one as desiccant regenerator coupled with a solar water heater. The VFD is connected with the first evaporative air cooler. In this work, using solar energy, a zeolite is regenerated as part of the investigation. Regeneration cycle for hot water absorption is explained and analysed. A simple expression for the cycle is proposed. System efficiency is derived with consideration of flow of work and heat to and from the system. The operating concentration of desiccant used greatly affected regeneration temperature limits and mass of strong solution for unit mass of vapour produced.     

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.     

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.     

液体除湿空调系统国内外研究进展

对液体除湿空调系统、除湿剂、除湿系统中热质交换数学模型的国内外研究进展进行了阐述.     

民用空调吸附材料的除湿性能研究

选取民用空调常用的两种吸附材料-硅胶和4A分子筛,在实验的基础上,对比分析了硅胶和4A分子筛两种吸附材料的除湿量、吸附能效以及脱附能效,结果表明：4A分子筛在整个吸附阶段都能保持较高的单位除湿量,比较适于二次除湿或深度除湿工作。而硅胶在很快时间内达到吸附平缓值,较适用于表面除湿及一次除湿工作。在相同的吸附和再生条件下,硅胶较4A分子筛有着更高的吸附和脱附能效,因此将硅胶作为民用空调系统的除湿材料较4A分子筛节能效果更佳。