Geothermal Heat Pumps: Advantages and Drawbacks
Ground source heat pumps are a type of renewable energy system that uses the Earth’s temperature to produce hot water or space heating. They can also be used for cooling and they are efficient, quiet, and long-lasting.
An increasingly popular option for homeowners worried about their energy costs and environmental impact, maasoojuspumbad (geothermal heat pump) transfer heat between your home and the ground around it by circulating a water/anti-freeze solution through buried polyethylene tubing, also known as a “loop field” or “ground array.” Even though this technology has only been around for 50 years, the idea actually dates back much further.
They work by using two different sources of power – electricity from the grid (or generator) and the earth’s thermal gradient. There are three main types of ground source heat pump systems:
- Electric Geothermal Heat Pump (EGHP)
- Direct Use Geothermal Energy System (DUGES)
- Vertical GeoStream™ Solar Water Heater / Geothermal System (VHGSS)
- We will discuss each in more detail below.
Electric Geothermal Heat Pump (EGHP)
An electric geothermal heat pump is one where the heat pump uses the natural thermal gradient between the surface and deeper levels of the earth as its primary resource. This allows it to be used in colder areas than traditional ground source heat pumps, such as areas with less than 15 degrees Celsius per hour average temperatures. The electric geothermal heat pump has a compressor that moves refrigerant through a closed loop system to extract and absorb heat from the earth and then return the heated fluid back into the earth’s core. The heat pump itself is powered by either an electrical connection to the power grid or solar panels connected to the heat pump via a battery backup system.
The Electric Geothermal Heat Pump is very similar to the other two types of ground source heat pump except that the compressor is powered by the grid rather than by the thermal gradient of the earth’s core.
Because this type of heat pump can operate at low ambient temperatures it is more efficient than other types of heat pumps. Efficiency rates can reach up to 90% on average.
Since the electricity powering the electric geothermal heat pump comes from the grid, there is no need for any additional noise making equipment like fan coils.
These heat pumps have no moving parts so they do not wear out quickly or require regular maintenance. They last much longer than conventional ground source heat pumps.
An electric geothermal heat pump costs around $1000-$2000 more than a direct use geothermal system.
- Solar Powered
Since these units are powered by the grid, you cannot choose your own source of power and must depend upon the availability of the grid. You may also need to install solar panels which can add another $1000 to the cost.
DIRECT USE GEOSTREAM SYSTEM (DUGES)
A direct use geothermal heat pump uses the same principles as the electric geothermal heat pump but instead of using electricity from the grid, it uses the thermal gradient of the earth’s core to provide the power source. Instead of the compressor being powered by the grid, the DUGES unit uses a separate set of motors that move the refrigerant to absorb heat. Because the heat pump uses less electricity than an electric geothermal heat pump, it is less expensive and easier to install. However, because it does not use the grid, it needs to be equipped with batteries just in case the power goes out during installation. It is recommended that two sets of batteries be installed at 10 feet apart to ensure that the unit will still function if the power fails.
- Low initial operating cost
The direct use geothermal heat pump is less costly than other types of geothermal heat pumps because it doesn’t need to purchase a grid connection.
- Easy installation
Direct use geothermal heat pumps only need to be installed underground and do not require drilling to install the piping.
- No additional noise
Unlike a typical geothermal heat pump, there is no fan coil to make noise.
- Less expensive
A direct use geothermal heat pump costs about half the price of an electric geothermal heat pump.
- Requires batteries
In addition to needing the extra set of batteries mentioned above, a direct use geothermal heat pump requires a battery charger. This adds another $100-$200 to the cost of a new system.
- Lack of control over the power source
The batteries will run down eventually and will need to be replaced periodically. Since the batteries are constantly losing their charge, it is important to replace them before they completely die. If the batteries run down too far, they won’t be able to start the unit and it will need to be reinstalled. This could be an expensive proposition.
- VERY LITTLE CONTROL OVER THE HEAT EXCHANGE
While this system provides much lower initial operational cost, it does not offer the ability to control the amount of heat that is extracted from the earth’s core and returned to the earth’s surface. Thus, while it is cheaper to install initially, it is difficult to predict how much heat will be produced over time and there is little control over the amount of heat that is actually being transferred into the environment.
VERTICAL GEOSTREAM SOLAR WATER HEATER AND GEOSTREAM SYSTEM (VHGSS)
A vertical geo stream solar water heater and geothermal system works similarly to a direct use geothermal heat pump but instead of using electricity from the grid, it uses the thermal gradient of the earth’s core to provide the power source.
The VHGSS combines the functionality of both a solar water heater and a geothermal heat pump. The water flowing through the solar water heater heats up the earth’s core which produces heat throughout the entire house. Thus, the VHGSS is ideal for homes with multiple rooms to heat or cool. The VHGSS is also useful for houses with large amounts of glass windows since the sun directly warms the exterior surfaces without having to pass through the interior walls.
- Control over the power source
The VHGSS provides more control over the amount of heat being transferred into the environment. By turning off the solar water heater when the house isn’t occupied and installing a programmable thermostat, the homeowner can control the amount of heat being generated.
- High efficiency
The VHGSS is highly efficient since it utilizes the sun’s heat to generate heat throughout the entire home.
The VHGSS is currently priced at around $10,000-$15,000
- Not suitable for all regions
The VHGSS is only designed to work in areas where the earth’s temperature is conducive to providing enough heat to meet the needs of a home with two or more bedrooms and no air conditioning.
All three of the ground source heat pump systems discussed here are effective methods of generating heat for residential purposes. The decision regarding which system to implement should take into account several factors including cost, available area, and heat requirements. For instance, the electric geothermal heat pump is a good option for homes with a limited living area and a high demand for space heating.
The DUGES and VHGSS systems are excellent options for homes that require more than one bedroom and have a relatively small footprint. The VHGSS is particularly well suited for homes with large amounts of glass windows and doors.