Heat Pumps (Geothermal)
We currently offer ClimateMaster geothermal heat pumps for ducted systems that provide heating and cooling in conjunction with a geothermal field. In our experience, the ClimateMaster brand is robust in terms of dealing with Vineyard voltage issues while providing flexibility and efficiency in heating and cooling your home. It is important to determine what your summer and winter comfort goals are – the size of the geothermal field depends on the planned use of the house. Because the winter heat loss is greater on Martha’s Vineyard than the summer heat gain, we usually size the geothermal heat pump system based on the cooling load and use electric strip heat to assist the geothermal heat pump on the coldest days of the year. This works out to be a good mix of efficiency and reduced first cost.
The inside heat pump needs to be connected via black plastic piping to the geothermal field outside – this field can either be horizontal (buried 4 to 6 feet below grade) or vertical (in vertical boreholes typically 250 feet deep). Site conditions usually dictate which type of field is the best fit for your project. For more information visit:
How they work:
Geothermal heat pumps use the solar energy that heats up the Earth to provide heating inside your home.
In the winter, the geothermal heat pump is able to extract this energy via the horizontal or vertical buried plastic piping and use it to heat refrigerant up to 180 F. The heat pump uses this heated refrigerant to heat up air – the inside unit has a fan or blower in it which uses the heated refrigerant to heat the air in the room.
In the summer, the refrigerant flow is reversed and the heat from the room is absorbed by the refrigerant and sent outside via the black plastic pipes.
Because these units use the free solar energy as their source of heat, they are much more efficient than fossil fuel heating equipment. Because they use a buried geothermal field, there is no equipment outside to be affected by coastal salt air or snow. This is important if it is critical to have the heat working at all times – an important consideration for seasonal homes. This also means that there is no need for a defrost cycle because there is no heat pump unit outside. Additionally, geothermal heat pumps do not lose heating capacity when the outside air gets colder. This means that sizing of the geothermal heat pump for the heating load on the coldest day of the year is much easier than for air source heat pumps.
These heat pumps are an excellent match with solar electric PV panels – they are an essential part of reducing the carbon footprint of your home towards net-zero.
Because these units are connected to a geothermal field outside, they are more expensive to install than air source heat pumps. Because of dramatic advances in air source heat pumps, there is now a very small efficiency difference between geothermal and air heat pumps. This means that it will usually take 20 years to recoup the difference in installed cost between the two types.
Geothermal Field and Heat Pump Types – More Detail:
Geothermal systems use several approaches to connect to the stored solar energy in the Earth – via copper refrigerant lines (direct exchange) or plastic pipe (water source or ground source) in the ground or via plate heat exchangers in the ocean or a pond.
DIRECT EXCHANGE GEOTHERMAL:
We are dealers for Earthlinked Technologies, the world leader in direct exchange geothermal systems. These systems use copper refrigerant lines to couple to the earth and extract or dispose of heat (depending on heating or cooling mode). Many of our customers are curious about the durability of the copper underground. The Copper Council of America has deemed that these lines should last virtually indefinitely in non-aggressive soil. For problem areas, anode protection (similar to a zinc bar on a boat hull) systems ensure that the copper experiences no corrosion. The refrigerant in the lines in non toxic and will not hurt the aquifer or the ozone.
With Direct Exchange, there are three ways that we can couple to the earth – horizontally, vertically, or diagonally. In all installations, the copper lines are installed into manifolds that must be six feet below finish grade. These manifolds are then connected to two main refrigerant lines that extend into the building and are connected to an EarthLinked heat pump. This heat pump is then connected to a new or existing heating, cooling, or hot water system.
WATER OR GROUND SOURCE:
This geothermal approach uses water to convey the stored heat in the Earth or pond or ocean to the heat pump. This may done is a wide variety of ways:
Closed Loop Horizontal:
There are many arrangements for the installation of closed loop horizontal installations. However, they all consist of HDPE pipe and they are all installed below six feet. They can be installed in trenches or fields. The most common type of installation is the “Slinky” patter. Coils of HDPE pipe are arranged in a “Slinky” pattern and are buried six feet down. This creates the ground couple heat exchanger that is then connected to the heat pump. We can assume approximately 2 -4 square feet of yard to one square foot of conditioned space. If the closed loop geothermal field is too small then the geothermal heat pump will not work well. Learn more about a recent project to correct this issue:
Closed Loop Vertical:
This installation uses large diameter bore holes (about 6 – 10 inches) cored into the earth. We can assume approximately 250 to 400 feet per ton (12,000 BTUs). An HDPE loop is installed into each hole, and then the hole is filled with a bentonite grout as required by the MA Ground Water Association and the DEP. These lines are then connected together into a manifold and the manifold is then connected to the heat pump. The heat pump is then connected to your heating, cooling, or domestic hot water systems.
Water source open loop systems remove or extract heat from the earth by drawing water out of the local aquifer, running this water through a heat pump, and delivering it back to the aquifer. This is usually the least expensive of the geothermal approaches but the most risky as the aquifier water quality can change or the water level can drop. We had to perform a geothermal rescue on an open loop geothermal system and convert it to a closed loop approach using a special heat exchanger. Learn more about this project:
Ocean Front and Lake Front Geothermal:
Plate type heat exchangers can be installed in fresh water ponds, brackish water ways, or in the ocean. Plate type heat exchangers eliminate the ground coupling installations described with horizontal and bore hole type systems. This is a very cost effective way to install a geothermal plant. Instead of hundreds of feet of refrigerant or HDPE lines connected to the earth, plate type systems use the solar energy stored in a waterway. The plate is installed in the water with two lines connected the plate with the heat pump. This system is filled with a food grade propylene glycol that is completely non toxic.
Our goal is to be Martha’s Vineyard’s premier plumbing and HVAC shop – we appreciate the opportunity to service, install, and rescue your geothermal heat pump system!