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Introduction

Pilot Project for Development of 70kW Solar Assisted Ground Source Heat pump System for Heating and Cooling



Huge energy consumption and greenhouse gas emissions due to rapid consumption of the conventional resources are getting the world on verge of environmental destruction. Developed countries are utilizing every means necessary to help prevent the dreadful future of earth. However, developing countries are still entwined in their political instability, poor economic structure, and limited resources of generation and shifting to green resources. Pakistan Government is determined to survive in this energy dilemma by adopting modern renewable resources technology and to play its part in national sustainability. Statistics show that about 80% consumption load is due to the cooling and heating load in summer and winter season respectively. Common and intelligent approach to effectively harmonize the load over our generation capacity is to cut down our cooling/heating load.

Geothermal systems are being widely deployed for extracting ground heat to provide heating for large spaces and similarly cooling in summer season for very long time. Categorization of geothermal resources is described as high enthalpy, medium enthalpy and low enthalpy [1]. High enthalpy resources with temperatures ranging above 100?C are working fuel for electricity production. Whereas low enthalpy ground surface (not very depth) can be considered as constant temperature medium which can store seasonal heat underground. Hence, this low depth reservoir is perfect source for large space heating/cooling systems using heat pump system.

Technology of heat pump is consisting of a heating source, heat pump and a system for distribution within the premises of the destination building. Ground source heat pump (GSHP) extracts heat from underground during winter as ground temperature is up than the surroundings and circulates through heat distribution system of the building/any space. Same system installation can be used for delivering cooling load by reversing the cycle of heat pump. In this case, inner temperature of destination space will be cooled down by extracting heat from backgrounds and giving it off to the ground. GSHP systems can be divided as: closed loop called ground coupled heat pump (GCHP) and open loop called ground water heat pump (GWHP). Piping loops can be described as either vertical loop or horizontal loop [2]. Depending upon the installation space limitations, any looping configuration can be adopted. Mostly, u-shaped vertical loops are installed.

To completely reduce the dependence on electrical input, solar system can be source of power to heat pumps. Refrigeration components consist of compressor, condenser, evaporator; evaporator delivers low pressure vapors to compressor. Compressor outputs high pressure and high temperature refrigerant vapors which are pushed towards condenser to cool them down to low temperature and low pressure refrigerant liquid by disposing of heat to the ground during refrigeration cycle; this same heat can be delivered for space heating. After passing through expansion valve, refrigerant is converted to low pressure and cycle starts again in evaporator when low pressure refrigerant vapors are produced. Ground coupled heat pump (GCHP) cycle is shown below [3]:

Inline image 2 Figure 1: GCHP working [3] Same heat pump system works for heating as well as cooling delivery by using reverse valve. This reverse valve has function to interchange the working of condenser and evaporator. Its working is explained in fig 2. below [3]: Inline image 3 Figure 2: cooling/heating modes of heat pump [3] We will implement geothermal cooling and heating systems using heat pumps. Our main idea is to reduce the electricity input and provide comfort conditions to occupants at the same time. Our team has already deployed 35.1KW solar system to provide for the crucial needs and same type of 10kW system will continue to input for heat pump system too. Our next proposition is to convert compressor; that is the major load of any air conditioning device, into DC compressor with soft starter. DC compressors will then be operated on by DC sources (solar etc.) and major consumption will be minimized. So, Our project is to develop a geothermal based cooling and heating system and design DC compressor for various applications. Geothermal design of system must be accomplished with large enough piping to maximize the heat exchange for efficient operation of whole system