Open Loop Ground Source Heat Pumps

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What an Open Loop Ground Source Heat Pump Is

Heat pumps are devices designed to transfer thermal energy from a cold source to a hot space, that is, in opposite direction to the natural heat flow. The criteria for the broader classification of heat pumps is based on the heat source. In that sense, heat pumps are divided into air and ground types. If you're interested in receiving quotes and offers regarding heat pumps, GreenMatch provides you with an easy to use, free and without obligations service that, based on your preferences, will give you quotes from up to four different heat pump suppliers. The only thing you have to do is filling in the form on the right. It'll take only a few minutes!

Air Source Heat Pumps

Air source heat pumps take heat from external air. That heat can be transferred to the inside air of a house by ductwork or to water that will run through radiators, for space heating purposes. So air source heat pumps can be classified into:

  • air-to-air heat pumps
  • air-to-water heat pumps

Ground Source Heat Pumps

Ground source type includes water source (that could be ponds, lakes, aquifers,etc.). Among ground source heat pumps, the more general classification considers the nature of the circuit that carries the fluid responsible for exchanging heat with the ground (or water). Closed-loop and open-loop are then the types of ground source heat pump systems.

  • Closed-loop heat pump: a mixture of water and anti-freezing flows through a closed net of pipes (known as the ground loop). In one part of the circuit it exchanges heat with (in heating mode - the standard mode that it’s being used as reference in this post-, collects heat from) the ground (or with a pond or lake or aquifer). In the other part, it exchanges that heat with (releases it to) the evaporator of the heat pump.There’s no contact between the working fluid and the ground and between the working fluid and the fluid of the heat pump at any moment.

Open Loop Diagram

  • Open-loop heat pump: groundwater is pumped from an aquifer or alike and carried to the heat pump, where, by means of the evaporator, transfers its heat. After that, that water is either re-injected in the ground or discharged at the surface. Thus, the heat source is the same as the fluid that runs through the circuit. And it has to be constantly replaced, since it’s not re-circulated.

Advantages and Drawbacks of Open Loop Ground Source Heat Pumps

Closed-loop are by far the most commonly used type of heat pumps. That doesn't mean open-loop heat pumps don’t have some advantages over closed-loop. Let’s have a look at them, as well as at the disadvantages.

Advantages

Advantages of open-loop over closed-loop:

  • Lower installation costs. The installation of an open-loop ground source heat pump is generally cheaper than that of a closed-loop. As long as the necessary conditions for the installation of an open-loop heat pump to be viable are met, its simpler design and implementation make it usually less expensive than that of a closed-loop in the same conditions. This shouldn't, however, be regarded as a universal rule; each case has to be studied individually to determine whether an open-loop heat pump is truly cheaper to install than a closed-loop according to the specific conditions of the case.
  • Less area needed. The fact that open-loop ground source heat pumps only demands a borehole to pump water from an aquifer, in contrast to the grid of pipes typical of closed-loop systems, make them more suitable for situations where space is a major limitation. This difference can be explained by pointing out that the ground (water) heat is directly extracted in an open-loop system, whereas it’s transferred to a working fluid in a closed-loop system, reducing the efficiency and increasing the area and complexity of the ground heat exchanger in the latter.

SavannahDisadvantages

Disadvantages of open-loop when compared to closed-loop:

  • Dependence on groundwater availability. Open-loop systems rely on the presence of an aquifer or other source of groundwater beneath the property where the ground source heat pump is planned to be installed. Than constitutes a very limiting condition for their usage. In addition to that, factors such as the depth of the aquifer and its extraction/ replacement rate need to be taken into account. By contrast, a closed-loop ground source heat pump doesn't demand any particular condition, since it’s a self-contained system and the temperature of the Earth’s crust are constant everywhere all year round. It can be installed anywhere.
  • Regulation. Closed-loop systems are not regulated by environmental agencies; open-loop systems are. The reason for this different treatment of the two types of ground source heat pumps is that open-loop systems alter their energy source by the extraction of water from the aquifer, that could in turn affect the characteristics of the ground and, eventually, result in the desiccation of the aquifer, while closed-loop systems are limited to exchanging heat with the ground (or groundwater), thus not modifying the environment.

Aquifer

  • More maintenance required. Once a closed-loop ground source heat pump has been installed, it’s not necessary to check or maintain the ground loop. Being a closed, self-contained system, the quantity and quality of the working fluid won’t vary. Subsequently, there’ll be no need of periodical maintenance. On the other hand, the continuous extraction and release of water that takes place in an open-loop ground source heat pump cannot guarantee optimal water conditions are met at any moment. That could affect, for example, the performance of the heat exchange at the evaporator and could even damage the pump responsible for the circulation of the groundwater.