Groundwater Temperature Map for Potential Heat Pump in Mueang Chiang Mai District, Chiang Mai Province

Abstract

This study focuses on groundwater temperature distribution and groundwater quality of 45 shallow wells at depth less than 10 meters, in Mueang Chiang Mai district. Groundwater temperature and groundwater quality are essential parameters in evaluating the suitability of heat pump installation application. In a heat pump system, groundwater is used as a heat carrier or heat sink to provide space cooling during hot season as air conditioning. Groundwater temperature must be constant and lower than atmospheric temperature. Groundwater quality is assessed using the values of hardness, alkalinity, total dissolved solid and pH to calculate the Langelier Saturation Index (LSI) and the Ryznar Stability Index (RSI) to make a qualitative determination of installing heat pump.

The temperature measurements of 45 shallow wells illustrated range values of 26 - 28°C. The plots of temperature and depth as temperature-depth profiles, showed constant temperature at depth of more than 2 to 10 meters below ground surface. The analytical results of groundwater quality indicated soft water to very hard water. Based on the mean value of chemical parameters, the cations in the order of abundance were Ca2+ > Na+ > K+ > Mg2+ > Mn2+ > Fe, while the anions revealed order of abundance as HCO3- > Cl- > SO42-. The LSI and the RSI ranged from -3.23 to 0.37 and 6.85 to 12.46 which indicated groundwater of slightly scale forming to corrosion. This study identified shallow groundwater map for potential heat pump installation. The central toward western area were moderate potential for heat pump installation with a treatment of corrosive groundwater quality while eastern part was high potential for heat pump installation. Economic evaluation was calculated with sets of data, 25 degree Celsius room temperature and 28.8-36 degree Celsius outside air temperature. The groundwater heat pump system was approximately 11 - 28%, reducing energy power and electric energy cost.