Cooling potential of ventilated PV façade and solar air heaters combined with a desiccant cooling machine

Thermal energy collected from a PV-solar air heating system is being used to provide cooling for the Mataro Library, near Barcelona. The system is designed to utilise surplus heat available from the ventilated PV facade and PV shed elements during the summer season to provide building cooling. A desiccant cooling machine was installed on the library roof with an additional solar air collector and connected to the existing ventilated PV façade and PV sheds. The desiccant cooling cycle is a novel open heat driven system that can be used to condition the air supplied to the building interior. Cooling power is supplied to the room space within the building by evaporative cooling of the fresh air supply, and the solar heat from the PV-solar air heating system provides the necessary regeneration air temperature for the desiccant machine. This paper describes the system and gives the main technical details. The cooling performance of the solar powered desiccant cooling system is evaluated by the detailed modelling of the complete cooling process. It is shown that air temperature level of the PV-solar air heating system of 70 °C or more can be efficiently used to regenerate the sorption wheel in the desiccant cooling machine. A solar fraction of 75% can be achieved by such an innovative system and the average COP of the cooling machine over the summer season is approximate 0.518.     

Preliminary performance of CSU Solar House I heating and cooling system

The NSF/CSU Solar House I solar heating and cooling system became operational on 1 July 1974. During the first months of operation the emphasis was placed on adjustment, “tuning”, and fault correction in the solar collection and the solar/fuel/cooling subsystems. Following this initial check out period, analysis and testing of the system utilizing a full year of data was begun. This paper discusses the preliminary performance of the heating and cooling system.

During the period 1 August 1974–31 January 1975, approximately 40 per cent of the cooling load was provided by solar energy. Solar heating over the same period of time provided 86 per cent of the space heating load and 68 per cent of the domestic hot water heating load. These percentages represent a total solar contribution of 33,996 MJ delivered to load (8061 MJ to the cooling unit; 20,687 MJ to heating; 5248 MJ to hot water). Natural gas accounted for 22,442 MJ, total. In addition, preliminary analysis has provided several significant results associated with the operating characteristics of the solar system and the individual components.     

Development and construction of the novel solar thermal desiccant cooling system incorporating hot water production

This paper reports the development and construction of the novel solar cooling and heating system. The system consists of the thermal energy subsystem and the desiccant cooling subsystem. The system utilizes both the cheaper nighttime electric energy and the free daytime solar energy. The system is conceptualized to produce both cooling during summer daytime and hot water production during winter. Testing and evaluation of the system had been done to determine its operational procedure and performance. Based on the results, the thermal energy subsystem functioned to its expected performance in solar energy collection and thermal storage. The desiccant cooling subsystem reduced both the temperature and the humidity content of the air using solar energy with a minimal amount of back-up electric energy. The system however, needs further investigation under real conditions.     

Design of a solar heating and cooling system for CSU solar house II

This paper describes the design of a solar air heating and night/day exchange cooling system with emphasis on the operational modes. In this type of system the collector absorbs solar energy and converts it to heat for space heating and domestic water heating. Cooling is accomplished by using the cool night air available in dry climates) to cool a pebble-bed storage unit and subsequently using the cool pebbles to lower the air temperature in the building during the day. Circulation is from the solar system to the building in the same manner as most modern heating and air conditioning units but uses air as the medium for heat transfer. The air system is particularly suited for climatic regions where heating loads are high and cooling requirements are moderate. The system utilized in Solar House II operates in either the heating or cooling mode as selected through a seasonable change-over switch. Solar preheated hot water is furnished for domestic use in either mode.     

Identifying key design parameters of the integrated energy system for a residential Zero Emission Building in Norway

This study examined an integrated solution of the building energy supply system consisting of flat plate solar thermal collectors in combination with a ground-source heat pump and an exhaust air heat pump for the heating and cooling, and production of domestic hot water. The supply energy system was proposed to a 202 m² single-family demo dwelling (SFD), which is defined by the Norwegian Zero Emission Building standard. The main design parameters were analyzed in order to find the most essential parameters, which could significantly influenced the total energy use. This study found that 85% of the total heating demand of the SFD was covered by renewable energy. The results showed that the solar energy generated by the system could cover 85–92% and 12–70% of the domestic hot water demand in summer and winter respectively. In addition, the solar energy may cover 2.5–100% of the space heating demand. The results showed that the supply air volume, supply air and zone set point temperatures, auxiliary electrical volume, volume of the DHW tank, orientation and tilt angle and the collector area could influenced mostly the total energy use.     

Experimental investigation of a liquid desiccant system for solar cooling and dehumidification

Growing demand for air conditioning in recent years has caused a significant increase in demand for primary energy resources. Solar-powered cooling is one of the environmentally-friendly techniques which may help alleviate the problem. A promising solar cooling method is through the use of a liquid desiccant system, where humidity is absorbed directly from the process air by direct contact with the desiccant. The desiccant is then regenerated, again in direct contact with an external air stream, by solar heat at relatively low temperatures. The liquid desiccant system has many potential advantages over other solar air conditioning systems and can provide a promising alternative to absorption or to solid desiccant systems.Earlier work by the authors included theoretical simulations and preliminary experiments on the key components of the liquid desiccant system. The objective of the present study has been to construct a prototype system based on the knowledge gained, to monitor its performance, identify problems and carry out preliminary design optimization. A 16 kWt system was installed at the Energy Engineering Center at the Technion, in the Mediterranean city of Haifa. The system comprises a dehumidifier and a regenerator with their associated components operating together to dehumidify the fresh (ambient) air supply to a group of offices on the top floor of the building. LiCl-water is employed as the working fluid. The system is coupled to a solar collector field and employs two methods of storage – hot water and desiccant solution in the regenerated state. The performance of the system was monitored for five summer months under varying operating conditions. The paper describes the operation of the experimental system and presents the measured data and the calculated performance parameters.     

Solar hybrid air-conditioning system for high temperature cooling in subtropical city

Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5–7 °C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15–18 °C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city.     

Monitoring and operational results of a hybrid solar-biomass heating system

Solar thermal systems, that provide auxiliary energy for space heating, represent a growing opportunity in European countries like Austria and Germany. However, such systems are as yet not widely known in the rest of Europe, unlike thermosyphon water heating systems. In addition, the need for energy conservation and reduction of CO₂ emissions, to combat climate change, demands the use and advance of renewable energy sources in new sectors than for common domestic water heating.The purpose of this research work is to present a full cycle of operational results of a hybrid solar thermal-biomass space heating system in Greece.The hybrid heating system was installed at the Centre for Renewable Energy Sources (CRES), Pikermi, central Greece in September 2005 with the intension to provide all the heat requirements for a specific office block of 60 m² area. The system was analyzed and optimized over a period of 6 months. The solar contribution during the actual measurement period (60% of the operating period) covered 52.9% of the total heating demand.The operational results of this unit from November 2005 till April of 2006 are presented and analyzed. The main parameters presented here include the operation of the system, the results, the coverage fraction (f%) of the solar and the biomass subsystems, the actions taken to increase its efficiency and the technical problems faced along with possible solutions to overcome them.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.     

Analysis of solar desiccant cooling system for an institutional building in subtropical Queensland,Australia

Institutional buildings contain different types of functional spaces which require different types of heating, ventilating and air conditioning (HVAC) systems. In addition, institutional buildings should be designed to maintain an optimal indoor comfort condition with minimal energy consumption and minimal negative environmental impact. Recently there has been a significant interest in implementing desiccant cooling technologies within institutional buildings. Solar desiccant cooling systems are reliable in performance, environmentally friendly and capable of improving indoor air quality at a lower cost. In this study, a solar desiccant cooling system for an institutional building in subtropical Queensland (Australia) is assessed using TRNSYS 16 software. This system has been designed and installed at the Rockhampton campus of Central Queensland University. The system's technical performance, economic analysis, energy savings, and avoided gas emission are quantified in reference to a conventional HVAC system under the influence of Rockhampton's typical meteorological year. The technical and economic parameters that are used to assess the system's viability are: coefficient of performance (COP), solar fraction, life cycle analysis, payback period, present worth factor and the avoided gas emission. Results showed that, the installed cooling system at Central Queensland University which consists of 10 m² of solar collectors and a 0.400 m³ of hot water storage tank, achieved a 0.7 COP and 22% of solar fraction during the cooling season. These values can be boosted to 1.2 COP and 69% respectively if 20 m² of evacuated tube collector's area and 1.5 m³ of solar hot water storage volume are installed.     

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.     

An experimental study of a solar-regenerated liquid desiccant ventilation pre-conditioning system

A solar-regenerated liquid desiccant ventilation pre-conditioning system has been installed and experiments were carried out for a period of nine months covering rainy, cold, and hot seasons in a hot and humid climate (Thailand). A heat exchanger was 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 evaporation rate at the regeneration process was always greater than the moisture removal rate at the dehumidification process indicating that the concentration of the desiccant in the system would not decrease and so the performance would not drop during continuous operation. The system could reduce the temperature of the delivered air by about 1.2 °C while the humidity ratio was reduced by 0.0042 kg_w/kg_da equivalent to 11.1% relative humidity reduction. The experimental results were also compared with models in literature.     

太阳能吸收式空调系统的经济性分析

针对一个特定的对象,进行了太阳能吸收式空调系统寿命周期内的模拟计算及影响因素的分析,结果表明：（1）单纯太阳能空调（无采暖与热水供应）的经济性很差,太阳能空调与供热的复合系统的经济性要优于单纯的太阳能空调系统;（2）太阳能采暖与空调的复合系统,采暖与供冷的负荷比对系统的经济性有很大影响,即使在最佳的负荷比时仍无法和常规的系统竞争;（3）太阳能与生活热水系统的负荷系统中,热水负荷所占比重越大,经济性越好,当太阳能空调使用生活热水系统夏季多余的热量时,太阳能空调系统经济上可以和天然气锅炉＋电动制冷机竞争,并具有很好的节能性和环境效益。     

Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney

Buildings represent nearly 40 percent of total energy use in the U.S. and about 50 percent of this energy is used for heating, ventilating, and cooling the space. Conventional heating and cooling systems are having a great impact on security of energy supply and greenhouse gas emissions. Unlike conventional approach, this paper investigates an innovative passive air conditioning system coupling earth-to-air heat exchangers (EAHEs) with solar collector enhanced solar chimneys. By simultaneously utilizing geothermal and solar energy, the system can achieve great energy savings within the building sector and reduce the peak electrical demand in the summer. Experiments were conducted in a test facility in summer to evaluate the performance of such a system. During the test period, the solar chimney drove up to 0.28 m³/s (1000 m³/h) outdoor air into the space. The EAHE provided a maximum 3308 W total cooling capacity during the day time. As a 100 percent outdoor air system, the coupled system maximum cooling capacity was 2582 W that almost covered the building design cooling load. The cooling capacities reached their peak during the day time when the solar radiation intensity was strong. The results show that the coupled system can maintain the indoor thermal environmental comfort conditions at a favorable range that complies with ASHRAE standard for thermal comfort. The findings in this research provide the foundation for design and application of the coupled system.     

Case study and theoretical analysis of a solar driven two-stage rotary desiccant cooling system assisted by vapor compression air-conditioning

In this paper, a solar hybrid desiccant air conditioning system, which combines the technologies of two-stage desiccant cooling (TSDC) and air-source vapor compression air-conditioning (VAC) together, has been configured, experimentally investigated and theoretically analyzed. The system mainly includes a TSDC unit with design cooling capacity for 10 kW, an air-source VAC unit with 20 kW in nominal cooling capacity, a flat plate solar collector array for 90 m², a hot water storage tank and a cooling tower. Performance model of the system has been created in TRNSYS simulation studio. The objective of this paper is to report the test result of the solar hybrid air conditioning system and evaluate the energy saving potential, thereby providing useful data for practical application. Experimental results show that, under typical weather condition, the solar driven desiccant cooling unit can achieve an average cooling capacity of 10.9 kW, which contributes 35.7% of the cooling capacity provided by the hybrid system. Corresponding average thermal COP is over 1.0, electric COP is up to 11.48. Under Beijing (temperate), Shanghai (humid) and Hong Kong (extreme humid) weather conditions, the solar TSDC unit can remove about 57%, 69% and 55% of the seasonal moisture load, thereby reducing electric power consumption by about 31%, 34% and 22%, respectively. These suggest that the solar hybrid system is feasible for a wide range of operating conditions.     

Parametric Analysis of Solar Heating and Cooling Systems for Residential Applications

Abstract

In this paper, a parametric analysis of two solar heating and cooling systems, one using an absorption heat pump and the other one using an adsorption heat pump, was performed. The systems under investigation were designed to satisfy the energy requirements of a residential building for space heating/cooling purposes and domestic hot water production. The system with the absorption heat pump was analyzed upon varying (i) the solar collectors’ area, (ii) the volume of the hot water storage, (iii) the volume of the cold water tank, and (iv) the climatic conditions. The system with the adsorption heat pump was evaluated upon varying (i) the inlet temperature of hot water supplied to the adsorption heat pump, (ii) the volume of the hot water storage, (iii) the volume of the cold water tank, and (iv) the climatic conditions. The analyses were performed using the dynamic simulation software TRNSYS in terms of primary energy consumption, global carbon dioxide equivalent emissions, and operating costs. The performance of the solar heating and cooling systems was compared with those associated with a conventional system from energy, environmental and economic points of views in order to evaluate the potential benefits.     

Performance characterization of gas engine generator integrated with a liquid desiccant dehumidification system

Combined heat and power (CHP) involves on-site or near-site generation of electricity along with utilization of thermal energy available from the power generation process. CHP has the potential of providing a 30% improvement over conventional power plant efficiency and a CO₂ emissions reduction of 45% or more as compared to the US national average. In addition, an overall total system efficiency of 80% can be achieved because of the utilization of thermal energy that would be wasted if only the electric power were utilized, and because of the reduction of transmission, distribution, and energy conversion losses. The current research is being carried out in a four-story educational office building. This research focuses on the design, installation, and analysis of a modular CHP system consisting of a natural gas fired reciprocating engine generator with a liquid desiccant dehumidification system. The engine generator provides 75 kW of electric power to the building load bus while the combined waste heat from the exhaust gases and jacket water are used to regenerate the liquid desiccant. The liquid desiccant unit dehumidifies and cools the ventilation air to the building and supplies it to the mixed air section of the roof top unit. This paper discusses the various aspects involved in the design and installation of the system such as the heat recovery loop design and the electrical interconnection with the building load bus. Test results are also presented and the performance is compared to a traditional power plant with a conventional heating, ventilating, and air-conditioning system.     

Experimental study of the burning-cave hot water soil heating system in solar greenhouse

In the northern China areas, the traditional heating methods are widely used in solar greenhouse, for example: electric heating, hot air heating, hot water heating, burning-cave heating etc. If copying the assuring building indoor environment of constant heating ways into solar greenhouse, it will further increase building energy consumption, thus improving the efficiency of energy utilization, establishing appropriate growing environment, and realizing the agricultural waste recycling are important ways of consistent with the Chinese conditions, construction of sustainable development, improving the efficiency of the greenhouse production. To solve the problem of traditional heating method for high heating energy consumption, the inharmonious between greenhouse air temperature and soil temperature, uneven soil temperature, the research build the burning cave hot water soil heating system of solar greenhouse experimental platform in accordance with principle of energy cascade utilization. This experiment platform will transfer burning cave internal heat into soil heating system. The soil is evenly heated by system. Through testing the actual operation effect of the burning cave hot water soil heating system of new solar greenhouse, electric heating system, no taking any heating measures system, burning cave hot water soil heating system of solar greenhouse can improve the soil average temperature 5 ∼ 6 °C. This research provides experimental basis for practical applications and promotion.     

Experimental study with operational solar‐sorption cooling

Building integrated solar systems have been considered as a reasonable system for building heating, cooling and hot water supply. Various types of solar collectors, such as plate type, evacuated tube type and solar air collector, have been used as the heat source, whereas adsorption chillers, absorption chillers and desiccant dehumidification systems have been considered to match the above solar heat sources. Now, such sorption chillers are more matured, but their coupling with suitable solar heat source is not well researched. Experimental study has been done in this paper to analyse four kinds of typical solar air‐conditioning system with different sorption chillers and solar collectors. Copyright © 2012 John Wiley & Sons, Ltd.     

A review for absorbtion and adsorbtion solar cooling systems in China

In the past decades, solar water collectors were installed for the main purpose of preheating domestic hot water or to cover a fraction of the space heating demand in China. However, solar cooling systems were constructed just for demonstration purposes. Since the building of the first solar-powered absorption cooling system in Shenzhen in 1987, there have been over 10 additional solar cooling demonstration projects constructed. In this paper, the most representative five projects including both absorption and adsorption cooling systems are introduced and summarized. From the demonstrations, solar absorption cooling systems have been shown to be more suitable for large building air-conditioning systems. Comparatively, solar adsorption cooling systems are more promising for small size air-conditioning systems. In order to attain high utilization ratio, it is highly recommended to design solar-powered integrated energy systems in public buildings. In addition, highly efficient heat pumps are considered as the most appropriate auxiliary heat sources for solar cooling systems, for the purpose of all-weather operation. In the 11th Five year research project (duration 2006–2010), solar cooling technologies will be further investigated to achieve a breaking through in the integration of solar cooling systems with buildings.