Economic comparison of solar absorption and photovoltaic-assisted vapour compression cooling systems

The intermittent nature of solar energy is a dominant factor in exploring well-designed thermal energy storages for consistent operation of solar thermal-powered vapor absorption systems. Thermal energy storage acts as a buffer and moderator between solar thermal collectors and generators of absorption chillers and significantly improves the system performance. Vapor absorption chillers are available in half, single, double, and triple-effect modes of operation and operate at temperatures ranging from 75 to 220 °C to produce a cooling effect with COPs ranging from 0.3 to 1.8. Thus, the selection of appropriate solar collectors and thermal energy storages are two significant decisions affecting the consistency of output of a vapor absorption refrigeration system. The present review of state of the art is focused on the appropriate selection, from among different types of solar collectors available to meet the demand of capacity and degree of thermal energy required in operating absorption chillers at optimum performance. Characteristics of various thermal energy storage systems and their integration with solar thermal collectors and absorption chillers are also investigated to meet the demand for heat during non-sunshine hours or periods of low solar intensity. In the latter section, economic feasibility is explored so that a sustainable solar cooling system can be proposed which can work consistently with the best performance throughout its entire life.

A state of the art on solar-powered vapor absorption cooling systems integrated with thermal energy storage

............................................................................................................................ 7 Declaration ........................................................................................................................ 8 Copyright Statement .......................................................................................................... 9 Acknowledgement........................................................................................................... 10 List of Publications ......................................................................................................... 11 List of Tables .................................................................................................................. 12 List of Figures ................................................................................................................. 13 Abbreviations and Symbols ............................................................................................. 17 Chapter 1: Introduction ................................................................................................... 22 1.1 Background ........................................................................................................... 22 1.2 Energy .................................................................................................................. 22 1.3 World Energy ....................................................................................................... 23 1.4 Pakistan and Energy .............................................................................................. 25 1.4.1 Electricity Generation History ....................................................................... 27 1.4.2 Current Status and Future Plans .................................................................... 28 1.5 Impact of the Energy Crisis ................................................................................... 30 1.6 Conclusion ............................................................................................................ 32 1.7 Aims and Objective ............................................................................................... 33 1.8 Structure of the Thesis .......................................................................................... 34 Chapter 2: Renewable Energy Resources in Pakistan ...................................................... 36 2.

Simulation of solar powered absorption cooling system for buildings in Pakistan

Recently, researchers have started serious discussions of using adsorptive processes for refrigeration and heat pumps. There is some success for the >100 ton adsorption systems but none exists in the <10 ton size range required for residential air conditioning. There are myriad reasons for the lack of small-scale systems such as low Coefficient of Performance (COP), high capital cost, scalability, and limited performance data. A numerical model to simulate an adsorption system was developed and its performance was compared with similar thermal-powered systems. Results showed that both the adsorption and absorption systems provide equal cooling capacity for a driving temperature range of 70-120 oC, but the adsorption system is the only system to deliver cooling at temperatures below 65 oC. Additionally, the absorption and desiccant systems provide better COP at low temperatures, but the COP’s of the three systems converge at higher regeneration temperatures. To further investigate the viability of solar-powered heat pump systems, an hourly building load simulation was developed for a single-family house in the Phoenix metropolitan area. Thermal as well as economic performance comparison was conducted for adsorption, absorption, and solar photovoltaic (PV) powered vapor compression systems for a range of solar collector area and storage capacity. The results showed that for a small collector area, solar PV is more cost-effective whereas adsorption is better than absorption for larger collector area. The optimum solar collector area and the storage size were determined for each type of solar system. As part of this dissertation work, a smallscale proof-of-concept prototype of the adsorption system was assembled using some novel heat transfer enhancement strategies. Activated carbon and butane was chosen as the adsorbent-refrigerant pair. It was found that a COP of 0.12 and a cooling capacity of 89.6 W can be achieved. Mechanical Engineering Doctoral Defense Research and Development of a Small Scale Adsorption Cooling System

Research and Development of a Small-Scale Adsorption Cooling System

Solar Energy can be used for producing cold either for cooling of buildings (generally known as air-conditioning) or for refrigeration required for preserving food. Solar cooling appears to be an attractive proposition due to the fact that when the cooling demand is more the sunshine is strongest. This, alongwith the necessity for providing thermal comfort for people in hot areas of the world, and for providing food preservation, may be the motivating factors in continuing research and development in the field of solar cooling systems. Although considerable work on solar cooling system has been done for the last three decades, due to its complexity, both in concept and in construction, the utilization and commercialisation of solar cooling is not as widespread as other solar energy applications like solar water heating and solar space heating. However, if solar cooling of buildings is combined with the solar heating then the combined solar cooling and heating systems can become economical.

S. Ayyash

Papers

An assessment of the feasibility of solar absorption and vapor compression cooling systems

On the parasitic power of solar absorption cooling systems and criteria for operational control