Installing geothermal or ground source heat pump systems to heat and cool homes and businesses is nothing new and has been around for many years. What is new is the amount of interest that geothermal has been receiving during the last couple of years.
This increased interest can be attributed to incentives from municipalities, state governments and the federal government and increased awareness and interest in “green” energy.
The following is a very basic description of the typical components of a ground source heat pump system:
- Basic components inside the building:
- A heat pump/exchanger that forces the transfer of heat.
- Blower fan and duct work for air distribution.
- Basic components outside of the building:
- Loop field.
- Header pipes that tie the loop field and heat pump(s) together.
- An environmentally friendly anti freeze fluid that is circulated through the loop field.
The ground source heat pump system works as follows:
- During cool months, the earth’s heat is transferred into the loop pipes. The fluid in the loop pipes carry the heat into the building. From there, the heat pump/exchanger concentrates the heat and releases it inside the building at a higher temperature through the duct work inside the building.
- During warm months, the heat pump/exchanger and loop pipes draw heat from the building and allow it to be absorbed into the earth. This system cools the building in the same way that a refrigerator keeps food cool: by drawing heat from the interior of the building, not by blowing in cold air.
There are several methods for installing the underground loop field:
- This type of installation is done with vertical drill rigs and vary in depth (up to 200 ft for typical residential systems and up to 500 ft for typical commercial systems).
- An advantage of vertical installations is you do not need as large of a lot to install the loop field because you are drilling straight down. This is usually advantageous on residential projects in which the lot size limits the amount of area you have to drill in.
- A disadvantage of vertical is you typically will be drilling into tougher formations due to the depths of the holes.
- This type of installation can either be done with a horizontal directional drill or by open cutting a ditch with a trencher or backhoe.
- An advantage of horizontal installations is that you typically drill in more consistent formations than when drilling vertically.
- A disadvantage of horizontal installations could be the amount of area that is required to install the loop field.
- Diagonal or steep angle:
- This type of installation is done with a drill.
- An advantage of diagonal installations could be the ability to get a longer borehole, when compared to a vertical hole, before you would encounter a rock layer. This would then allow more loop pipe installed per hole.
It is important to understand what your state’s or area’s drill operator licensing requirements are before you begin bidding work.
The hole diameter is similar for any of the above installation methods but obviously varies with the loop size being installed. Typical loop pipe sizes are ¾ in. for residential and 1 to1 ¼-in. for commercial. Common hole diameters are 5 to 6 in.
Once the borehole is complete, the loop pipe is installed. On vertical installations, the loop pipe can be installed manually by hand or with an insertion tool attached to the drillstem, where the drill would then push the loop pipe into the borehole. On diagonal installations, the loop can be installed with an insertion tool attached to the drillstem. When installing the loop pipe in a horizontal borehole, you can use different tools attached to the drillstem and pull the loop pipe in with the drill.
Finally, be sure to understand the grouting requirements for the project you will be working on. Check for any state requirements on grouting boreholes. The soil that you are boring in and the conductivity of that soil will also help you determine proper grouting specifications. On larger projects, a civil engineer will typically set specific grouting requirements.
The ground source heat pump market is exciting and growing. Just be sure to do your homework before bidding on your first project.
Ed Savage is trenchless segment manager at Vermeer Corp. and a member of the Drillmasters Advisory Board. All Drillmaster Reports are reviewed by the Drillmasters Advisory Board: Savage; Frank Canon, Baroid Industrial Drilling Products; Ronald Lowe, Myers-Aplex, a Pentair Pump Co.; Richard Levings, Ditch Witch; and Trevor Young, Tulsa Rig Iron.