Geothermal – heating from the earth

How it works

What better way to be warm in your off-grid haven then to let the Earth�s own temperature do the work for you? Around 40,000 geothermal heat pumps are installed in the United States each year, and although they do need electricity to suck the heat out of the ground they give back four times what you put in.
Geothermal, GeoExchange, earth-coupled, ground-source, or water-source heat pumps all use the constant temperature of the earth as the exchange medium instead of the outside air temperature. They can also be used to cool your space on days when the temperature of the air is greater than the constant temperature 12 feet below ground.


While many areas of the US experience seasonal temperature extremes, from scorching heat in summer to sub-zero in winter, a few feet below the ground the temperature remains relatively constant, ranging from 45�F to 75�F (7�C to 21�C) depending on the latitude. These systems take advantage of that when they exchange heat with the earth through their ground heat exchanger.


Geothermal and water-source heat pumps are able to cool, heat, and supply the home with hot water (if equipped). Models available of geothermal systems can include a two-speed compressors and variable fans to increase comfort and energy efficiency. Another plus is that compared to air-source heat pumps they last longer, need less maintenance, are quieter, and outside air temperature has no effect

The cost of a geothermal system is several times that of the air-forced system with the same capacity. This additional cost is recouped in your energy savings over the first 5-10 years. Since the internal components have a life is estimate of 25 years, with the ground loop at 50+ years, you will be reaping those energy savings for a long time to come. There are four distinct types of geothermal systems, three of those are closed-looped and 0ne is open looped.

The horizontal closed-loop type of installation is generally most cost-effective for residential uses, especially in new construction where land is available. It requires trenches to be at least four feet deep. The most common layouts are either to use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench. The Slinky� method of looping pipe gives more pipe in a shorter trench, which cuts on the cost of installation and makes horizontal installation possible in areas where conventional horizontal applications would not fit.

For schools and large commercial buildings vertical systems ar e often used because the land area required for horizontal loops would be a problem. Vertical loops are also used where shallow trenching isn�t possible or a disturbance to existing landscaping is called for. For a this system, holes (about 4? in diameter) are drilled about 20 feet apart and 100�400 feet deep. Two pipes that are connected at the bottom with a U-bend to form a loop are inserted into each hole. These vertical loops are then connected with horizontal pipe and placed in trenches, which are connected to the heat pump for building.

The closed loop sytem needs an adequate water body, though this may be the lowest cost option. A supply line pipe is run underground from the building to at least 8 feet under the water and then coiled into circles to prevent freezing. This can only bee done if the water source that meets minimum volume, depth, and quality criteria.

The last geothermal system is an open loop system which uses well or surface body water as the heat exchange medium that directly circulates through the GHP system. Once it has circulated through the system, the water returns to the ground through the well, a recharge well, or surface discharge. This option is only usable where there is an enough of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.

The dual-source heat pump uses both geothermal and air-source heat pumps. By combining both systems you get a higher efficiency, though not as efficient as the true geothermal unit. The lower cost of the dual-source system and ability to work almost as well is a strong plus for this system.

2 Responses

  1. I’m looking for a mention of the feasibility of geothermal heating and cooling for fully off-grid systems. In other words, would it be possible to generate/store enough electricity to operate a geothermal system through a cloudy week of winter living off-grid in the northeast US? What sort of battery storage would be necessary? For a small home (under 1000 feet) or a larger one?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.


Join the global off-grid community

Register for a better experiencE on this site!