Geological Survey Program
Wellhead Protection Section Heat Pumps
Ground source heat pump systems are designed to heat or cool a house or structure by using the earth’s constant ground temperature. During winter the outside air temperature averages about 20 degrees Fahrenheit; however, groundwater stays an average of 55 degrees Fahrenheit. The idea of a ground source heat pump system is to pump groundwater or other fluid through a buried loop to a heat exchange unit. The heat exchange unit will transfer the temperature of the fluid to warm up your home in the winter or cool your home in the summer.
There are three main types of ground source systems installed: the horizontal closed loop system, the vertical closed loop system and the open loop system. The closed loop system uses a loop of heat fused polyethylene or polybutylene pipe. The pipe is laid in trenches (horizontal system) or put down boreholes (vertical system), connected to the heat exchange unit and filled with an approved heat exchange fluid. Approved fluids include pure glycerine solution, food grade propylene glycol, dipotassium phosphate, sodium chloride, potassium acetates, methanol, water, or ethanol.
Horizontal systems are only regulated if the horizontal system is constructed at or over 10 feet deep. A vertical closed loop system has a borehole depth limitation of 200 feet. If there is a situation where a system needs to be installed to a depth greater than 200 feet contact the Wellhead Protection Section at 573-368-2165.
Open loop systems use a domestic water well to supply groundwater to the heat exchange unit. The water is either pumped back into the ground through a second well or to a surface lake or pond. Keep in mind that if you are disposing of this water to the surface it must remain on the landowner’s property. It may not be run to drainage that leaves the property unless applicable permits are obtained through the Water Pollution Control Branch, within the Department of Natural Resources.
A system that is not used often in Missouri is the Direct Exchange System. These closed loop systems use a network of copper tubing or other material also placed in a pit, trench or borehole. The refrigerant is circulated through the tubing allowing the heat transfer to take place. In January 2010, the HVAC industry completed a transition to non-ozone depleting refrigerants agreed to by countries around the world as part of the Montreal Protocol. In the United States and Canada, R410A is the primary replacement for the chlorine-containing refrigerants such as R-22 that have been in use for many years. This type of heat pump system using refrigerants in their closed loops may be placed into vertical wells only if written approval is received in advance from the department.