GSHP: How much space is needed for a GSHP installation?
Ground source heat pumps have both outdoor and indoor components. If your home or business lacks the space for either of these, you may be better served by another heating and cooling technology—like an air source heat pump, which has lower space requirements.
As suggested by its name, you will need space outdoors to install a GSHP in the ground. While GSHPs don’t have above-ground components that will take up space outdoors, wells and loops will need to be installed underground—under a yard, a parking lot, or other landscaped area. This also means that whatever area you choose to install your GSHP’s wells in will need to be dug up during installation. The amount of space needed will depend on the amount of space available and will affect the cost and performance of the system.
Vertical wells are typically used for systems where less ground area is available or the ground is not suitable for horizontal trenches. Multiple four to six inch boreholes are drilled into the earth approximately 10-20 feet apart to depths of 50 to 400 feet. Piping (also known as “loops”) is then installed into the boreholes, which are then often filled with a solid medium (“grout”) to facilitate heat exchange and seal the hole from groundwater.
Vertical wells are usually more efficient, as the heat exchanging piping is buried deeper in the earth where the ground temperature is more constant year round. Installation will also result in fewer disruptions to existing landscaping. However, vertical wells are more expensive than the horizontal wells, as the drilling process will require experienced, qualified contractors to complete. Costs may further increase based on the drilling conditions of the site.
In some cases, vertical wells may be the only option available. For example, if there is insufficient ground area, the soil is too shallow, or there is extensive hard rock in the installation area, a vertical system may be necessary. Commercial GSHP systems will often use vertical wells as space is typically at a premium, while homeowners typically opt for horizontal wells to keep costs down.
Horizontal wells use a larger amount of ground area than vertical wells. Multiple trenches up to six feet deep and two feet wide are dug into the earth for the pipes, which are laid across the bottom of the trench. A typical system will require 300 feet of trenches for every two tons of heating load. The amount of space needed can be significantly decreased by looping the piping and placing it at the bottom of the trench (in a “slinky configuration”), though more piping will be required.
The largest primary advantage of horizontal wells is cost: shallow trench digging is usually cheaper than drilling boreholes several hundred feet in the ground. However, more space will be needed for the trenches, and landscaping will need to be dug up in order to install the loop field. Efficiencies are also expected to be lower, as the ground temperature in the trenches will change more with the seasons than the ground temperature in boreholes. More total piping area will need to be installed to account for the larger changes in temperature.
Pounds and Lakes
If your home or business happens to have a pond nearby, you can also coil the piping and anchor it at least eight feet under water near the bottom of the pond. In this case, the pond water will serve as the heat reservoir, as the water near the bottom of the pond will stay well above freezing even when the pond appears frozen over (around 39°F) and will stay cool in the summer.
If you have an existing pond on your property, this is the cheapest GSHP installation option available. While more piping will be required for underwater installations compared to underground installations, no excavation will be required.
The system types listed above are all referred to as “closed loop” systems, because the heat exchange fluid in the pipes stays there at all times and is not exchanged with the environment. An open loop system will use surface or ground water as the heat exchange fluid, drawing and discharging water from underground aquifers or ponds. While open loop systems are cheaper than closed loop systems in the right conditions, they also involve discharging water into the environment. As a result, you will likely need to get a permit for ground or surface water discharge, depending on the local codes and regulations.
Open loop systems usually draw from ground water like a well—drawing from surface water can be difficult in freezing conditions, and unclean or hard water could clog up the heat exchanger. After being piped through the heat exchanger, the water can be discharged into a nearby pond or river (the easiest and cheapest solution) but may need to be pumped back into an underground aquifer (which is more expensive, but will protect the groundwater resource needed over the life of your heat pump system). Open loop systems the draw from and discharge into aquifers will take up a similar amount of space as a vertical well (though you will obviously need to have an aquifer on your property in the first place!).
The indoor component of your ground source heat pump system will not take up any more room than a traditional boiler or furnace. This heat pump unit can then link up with most existing ductwork or hot water distribution systems. It can also be linked up with your water heating system. In some cases, your heat distribution systems may need modifications or reconfiguration in order to work with your ground source heat pump.