Friday, June 22, 2012

Types of Geothermal Heat Pump Systems

There are four basic types of ground loop systems. Three of these—horizontal, vertical, and pond/lake—are closed-loop systems. The fourth type of system is the open-loop option. Which one of these is best depends on the climate, soil conditions, available land, and local installation costs at the site. All of these approaches can be used for residential and commercial building applications.

Closed-Loop Systems

Most closed-loop geothermal heat pumps circulate an antifreeze solution through a closed loop—usually made of plastic tubing—that is buried in the ground or submerged in water. A heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze solution in the closed loop. The loop can be in a horizontal, vertical, or pond/lake configuration.
One variant of this approach, called direct exchange, does not use a heat exchanger and instead pumps the refrigerant through copper tubing that is buried in the ground in a horizontal or vertical configuration. Direct exchange systems require a larger compressor and work best in moist soils (sometimes requiring additional irrigation to keep the soil moist), but you should avoid installing in soils corrosive to the copper tubing. Because these systems circulate refrigerant through the ground, local environmental regulations may prohibit their use in some locations.


This type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. It requires trenches at least four feet deep. The most common layouts either 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 allows more pipe in a shorter trench, which cuts down on installation costs and makes horizontal installation possible in areas it would not be with conventional horizontal applications.
Illustration of a horizontal closed loop system shows the tubing leaving the house and entering the ground, then branching into three rows in the ground, with each row consisting of six overlapping vertical loops of tubing. At the end of the rows, the tubes are routed back to the start of the rows and combined into one tube that runs back to the house.


Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, and they minimize the disturbance to existing landscaping. For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100–400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building.
Illustration of a vertical closed loop system shows the tubing leaving a building and entering the ground, then branching off into four rows in the ground. In each row, the tubing stays horizontal except for departing on three deep vertical loops. At the end of the row, the tubing loops back to the start of the row and combines into one tube that runs back to the building.


If the site has an adequate water body, this may be the lowest cost option. A supply line pipe is run underground from the building to the water and coiled into circles at least eight feet under the surface to prevent freezing. The coils should only be placed in a water source that meets minimum volume, depth, and quality criteria.
Illustration of a pond or lake closed loop system shows the tubing leaving the house and entering the ground, then extending to a pond or lake. The tubing drops deep into the pond or lake and then loops horizontally in seven large overlapping loops, then returns to the water's edge, extends up near the surface, and returns back to the house.

Open-Loop System

This type of system uses well or surface body water as the heat exchange fluid that circulates directly 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 obviously practical only where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.
Illustration of an open loop system shows a tube carrying water out of the house, into the ground, and over to a well, where it discharges into the groundwater. A separate tube in a well some distance away draws water from the well and returns it to the house.

Hybrid Systems

Hybrid systems using several different geothermal resources, or a combination of a geothermal resource with outdoor air (i.e., a cooling tower), are another technology option. Hybrid approaches are particularly effective where cooling needs are significantly larger than heating needs. Where local geology permits, the "standing column well" is another option. In this variation of an open-loop system, one or more deep vertical wells is drilled. Water is drawn from the bottom of a standing column and returned to the top. During periods of peak heating and cooling, the system can bleed a portion of the return water rather than reinjecting it all, causing water inflow to the column from the surrounding aquifer. The bleed cycle cools the column during heat rejection, heats it during heat extraction, and reduces the required bore depth.


Mijal said...

Interesting information on the various types of Geothermal Pump Systems. I think Hybrid system should be more suitable for Malaysian users since it focused more on cooling needs such as air-conditioners rather than heating needs.

Mijal said...

Any alternative energy production methods should be considered so that we can have more options in hand.

Anonymous said...

It will be better if the alternative energy production is affordable.

Hinamori said...

This design takes advantage of the moderate temperatures in the ground to boost efficiency and reduce the operational costs of heating and cooling systems, and may be combined with solar heating to form a geosolar system with even greater efficiency.

Hinamori said...

Geothermal heat pumps are durable and require little maintenance. They have fewer mechanical components than other systems, and most of those components are underground, sheltered from the weather.

Pool heat pumps said...

Geothermal, or ground source heat pumps, take advantage of the constant ground or groundwater temperatures to heat and cool your home at a cost of 25-50% less than traditional electric, gas or oil fired heating and cooling systems.

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