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Ground Source Vs. Air Source Heat Pump: Which One to Choose?

Anamika Kumari
Here is a resolution to all your queries on heat pumps. Nature lays out a ground source vs. heat source comparison chart enlisting their pros and cons for you to opt for the best among the two.

Go Green, Save More Bucks!

The American Recovery and Reinvestment Act (ARRA) revised Residential Energy Property Credit (Section 1121) and Residential Energy Efficient Property Credit (Section 1122), which raised the energy tax credit rate by up to 30% of the total cost of equipment and improvisations to them apart from the existent energy incentives.
A deserving reward to homeowners to invest in heat pumps for their homes without having to worry about the installation expenses.
The energy consumption pattern has shown a considerable rise all across the globe over the past two decades. The increased usage of conventional energy resources and the hike in oil and gas prices has compelled us to look for sources of renewable energy.
The renewable energy heat pumps have gradually gained popularity, with the heat energy from ground or air sources being used for heating, ventilating, and air conditioning (HVAC) systems. It is essential to familiarize oneself with all the factors associated with the ground source heat pump (GSHP) and air source heat pump (ASHP) to enable us to choose a suitable option.
These heating systems are designed to encourage the idea of a greener Earth, and are non-toxic and cut down on carbon emissions to a great extent. However, the operation of the heat pumps is dependent on the refrigerant (fluids) that are essential for their working. Till recent times, chlorodifluoromethane (R-22 ) was being used as a working fluid, which is an ozone depleting gas. EcoCute, an ASHP, makes use of superficial carbon dioxide instead of the R-22.
Now let us take a closer look at the working of these heat pumps.

Installation Requirements

  • Check for availability of space and its conformity to IgCC regulations.
  • Ensure adequate insulation of the structure where the heat pump is to be used.

Ground Source Heat Pump

  • The ground or Earth is the ultimate receiver of solar heat. Irrespective of climatic variations across the globe, the Earth surface or ground remains at a relatively constant temperature.
  • Heat exchangers are placed horizontally or vertically at a depth of about 3-20 feet below the surface of the ground. These heat exchangers may be 'open loop' or 'closed-loop' ducts.
  • The open loop duct is completed at water reservoirs present nearby or underground, while the closed-loop duct circulates anti-freeze solution or water within the ducts.
  • This fluid absorbs heat from the ground, which is further compressed by a pump to raise the temperature.
  • Part of the heat generated is sent to underground heating systems or to radiators, and waste heat is used to heat water stored in tanks.
  • The GSHP functions in reverse when the building gets too warm, heat from the building is absorbed and sent to the ground, maintaining a cool temperature inside the building.
  • The GSHP functions in reverse when the building gets too warm, heat from the building is absorbed and sent to the ground, maintaining a cool temperature inside the building.

Air Source Heat Pump

  • Air, at any temperature, can be used as a source of heat energy.
  • The heat exchanger of an ASHP functions as a transferring medium of heat between two spaces divided by an interface. 
  • The outdoor coil pumps the compressed ambient air at a higher temperature into the indoor ducts. This heat is passed on to underground heating systems, radiators, and water tanks.
  • The operation is reversed when the indoors require cooling. Interestingly, ASHP can work with ambient air as low as -30°F; however, the coefficient of performance drops below 1.
The replacement of oil and gas boilers by renewable source heat pumps has resulted in the cut down of almost 5 tons of carbon emission. The difference is minimal when natural gas is used as an alternative. 
Governments across the globe are promoting the usage of ground or air source heat pumps especially where natural gas is scarce or expensive. Both GSHP and ASHP use electric pumps, with electricity as the common source. Users aiming towards zero carbon footprint can use solar panels to run these pumps.

Ground Source vs. Air Source

Ground Source Air Source ~ Required Space
The GSHP requires a large ground space for the installation of ground heat exchangers. If the area is not large enough, the service providers dig deep trenches for placing the exchange loops. Great care is taken when backfilling the trenches, ensuring sharp rocks or debris do not damage the pipes.
The external unit of an ASHP needs a properly ventilated space not more than 0.6 cubic meters. The internal unit takes up a floor space lesser than a refrigerator. 

Installation Cost
The initial cost varies from country to country and may be as high as USD 20,000 Its cost may range between USD 9,000 to 17,000.
Installation Time
It requires the heat exchangers to be placed underground, which can be tedious. The installation time is longer. Its installation takes less time, and heat generation is comparatively quicker. If ventilating ducts are not present in the house, then ductless units called mini split heat pumps may be used.
Maintenance Cost
The absence of exposed or moving parts protects it from vandalism and any mechanical wear and tear. Hence, maintenance is minimal. The external unit of the ASHP is prone to get affected by dust, frost, and sometimes, mishaps. The maintenance, in this case, is moderate
Its efficiency is approximately 60% more than that of any conventional fuel source. The overall efficiency of a fuel source heat pump increases by 40% when replaced by air source.
Coefficient of Performance (COP)
For every unit of electrical energy consumed, a GSHP produces 4-5 units of heat energy. The COP for an ASHP is about 3-3.5 units.
Returns on Investment
The net investment may be recovered within 3-5 years. It depends on the kind of fuel source that was replaced. The rate of ROI for an ASHP is slow, and the recovery may take more than 5 years.
Noise Level
Its operation is noise-free. The fans and moving parts of the ASHP mechanism may generate some noise, with the noise level well below 42dB.

The lifespan of a GSHP is more than 50 years with minimal maintenance. With proper maintenance, an ASHP is expected to have a lifespan up to 20 years or more.
Remember! Go green and breathe clean. Hope this story's comparison chart helps you make the right choice between an GSHP and ASHP for your homes.