How
Geothermal
Heating Works
Geothermal systems are electrically-powered systems that take advantage of the earth's relatively constant ground temperature to provide heating, cooling, and hot water for residential & commercial buildings.
Rather than creating heat like a fossil fuel system, geothermal moves heat that already exists in the ground into your home in winter and reverses this cycle in summer. In the winter, the ground heat exchanger collects heat from the ground and delivers it to the Air or Hydronic delivery system in the home. In the summer, this cycle reverses and sends the heat from the home to the earth. Geothermal systems consist of piping in which liquid such as water or antifreeze is the medium. There are four types of ground loop systems to choose from: Horizontal, Vertical, Lake, and Open. The same loop works for both heating and cooling.
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Horizontal, Vertical and Lake systems are all closed-loop systems. The heat pump and loop form a sealed pressurized system through which the liquid medium is circulated. Open loop systems, however, are not sealed and are open on either end to obtain the liquid medium (water) from an existing well, and to discharge it when it gets too cold or warm.
Horizontal and Vertical closed-loop systems are laid horizontally in trenches or vertically in wells. Both are placed in an area adjacent to the buildings they serve. These systems can go in yards, under parking lots, or under playing fields. Pond or lake loops require a nearby body of water with adequate depth in which to put the loops. Open loops require adequate water for the needs of the system
Geothermal systems transfer heat from the earth into your home or business in the winter and transfer it back in the summer to keep you at a comfortable temperature year round. Geothermal offers heating, cooling, and hot water in a system that is cost saving, reliable, energy efficient, and environmentally sound. Geothermal can be used in residential and commercial applications, in new construction as well as in existing homes or businesses. Geothermal systems are highly efficient technology that is fast becoming the most reliable and competitive heating & cooling systems available.
There are three major components to a geothermal system. A geo-exchange well, ground source heat pump, and a distribution system. Often times consumers have a hard time understanding which of the multiple options is best for them. Therefore, we will talk a little about all of these in detail so that you will better understand what options may make the most sense for you.
Geo-Exchange Wells
There are different types of geo-exchange wells to consider.
Closed Loop
A closed-loop system is simply a borehole in which two high-density polyethyelene pipes with a U-bend at the bottom are installed with a thermally enhanced grout the length of the borehole. This design typically consists of multiple 200' to 400' wells. With this type of geo-exchange well we are strictly reliant on conductive heat transfer which is the natural flow of heat energy from the earth through the thermally enhanced grout, high density polyethelene tubing and into a glycol/water solution. This is the most common type of geo-exchange well across the United States. However, this is purely in relation to geology. In Maine, New Hampshire, Vermont, and much of New England closed loop is not as economical as some other options.
Advantages of Closed Loop Wells
- There is no issue with water quality
- Sediment will not be a problem with this system
Standing Column Well
A standing column well is constructed in the same manner as conventional drilled water well with a submersible pump system. This type of geo exchange well also has conductive heat transfer characteristics. Heat energy transfers from the bedrock directly into the column of water. Then the column of water is circulated into the home through the heat pump in which it extracts heat energy, and then returns this colder water back to the earth where it is reheated by the earth's crust. This type of heat transfer is more efficient than the closed loop for the heat does not have to go through resistant materials such as the grout, HDPE pipe and into the glycol/water solution.
In addition to this conductive heat transfer, we can in most cases incorporate a bleed into the system. This gives us what is called an advective heat source. This is simply an act of discharging some of the cold water out of the well to allow the well to recover with warmer water. This can reduce the drilling to 55'-85' per ton, and add efficiency to the system by keeping the well temperature higher. This will save $ on up front cost and add efficiency at the same time! A 150' per ton borhole is needed with a no bleed scenario. Though this is still less than the 175' per ton for the closed loop, and again more efficient because of a better heat transfer. We want to use bleed whenever we can responsibly discharge of the water.
Advantages of Standing Column Well
- Can use same well for drinking water as for the geothermal system (saves on up front cost!!)
- Heat pumps can be sized smaller because of warmer incoming water temperature (about 20% smaller)
- Boreholes can be drilled shallower which saves on upfront costs
Open Loop Well
An open loop well is very much the same as a standing column. The only difference is that the open loop can be used in more applications, though most common with the standing column.
With an open loop well, we could pump water from one well and return it to another, otherwise known as an open to recycle, this being a total advective heat source. For example you may drill a well 150' deep and come in to a vast amount of water. If this were to happen you could drill a second well in hopes to encounter the same aquifer. In which case you do a pump and dump. Thus the water goes into the home through the heat pump and then returns to a second well. If you do not return any cool water to the well you are pulling from then the well stays at a constant warm temperature. Thus being the most efficient of the options.
Another example of an open loop would be to discharge the water to some other sort of dry well. You would want to make sure this is in an area that will accept the amount of water you wish to discharge. Would not recommend this design if there is a chance of contaminating another water source or discharging of water into any lakes, streams, ponds etc without MDEP's approval.