Geothermal Air Conditioning: Closed Loop or Open Loop?

 

Jay Egg, CMC, CEO,  Author of Geothermal HVAC, Green heating and Cooling, McGraw-Hill Professional Books

Geothermal Air Conditioning: Closed Loop or Open Loop? 

The purpose of the study is to determine the placement of Open Loop GHP or Closed Loop GHP systems.

 

Egg Geothermal has monitored installation of GHP (geothermal heat pump) systems for the past twenty years in many climates, but especially in Hot and Humid Climates. Our findings are the result of considerable design, fabrication, research and interviews during that time.  We are currently involved in a research project with the US Department of Energy through Florida International University.

Among the earth coupled loop systems observed by Egg Geothermal in Hot and Humid climates, we find with few exceptions that the following is true:  They perform well the first year.  The second year, they begin to experience thermal retention with higher-than-normal return temperatures.  By the third year, thermal retention of the soil reaches a point greater than the capability of the GHP equipment operational range, requiring additional external thermal capacitance, such as leaching or open loop exchange.

Situations involving thermal retention have occurred numerous times in projects with high cooling loads in all climates.  With the revitalization of renewable technologies, GHP’s in Hot and Humid climates are once again failing to be engineered properly by a new generation of contractors.   

Egg Geothermal finds that while closed-loop systems have many good applications, it is not uncommon that an open-loop pump and injection well installation would be a more energy efficient opportunity, especially in commercial and cooling-dominant situations.  The variables are extraordinary, and each system must be engineered for proper heat transfer and fluid flow so that maximum efficiency is attained.  Lack of proper engineering can cost thousands and even millions of dollars over the life of a system.