Sizing a Geothermal Heat Pump
Geothermal heat pumps vary in size from home to home. There are a number of factors that determine how big of a pump. Since sizing a geothermal heat pump is a intricate process you'll need to contact a qualified geothermal heat pump installer. An installer will start with an analysis of the heating and cooling demands of your home. From there he'll be able to calculate the right size system. The size of the system will dictate the size of the loop field.
It is very important to contact an experienced geothermal professional before choosing a heat pump size because there
can be problems with undersized and over-sized systems. A quality contractor will design the system accurately which ensures a long lifespan and low operating costs.
Undersized Systems - Never Choose on Cost Alone
A geothermal heat pump has the potential to save you as much as 70% on your heating and cooling bills but with an undersized system you may find yourself paying for it in both comfort and savings. Systems are generally sized in tons, an average home might be 3 tons, while a larger home might be 6 tons. Larger systems are more expensive because of the increased size of the loop field and larger geothermal unit.
If an undersized system is installed it will strain to reach your desired heating and cooling needs. This could result in high utility bills as the heat pump tries to make up for its size by using more electricity. An undersized system will prevent a homeowner from reaping the greatest benefits of geothermal: reduced utility bills.
Never choose your contractor based on price alone. An inexperienced contractor can under-size your system, thus the installation cost will be less expensive but the results will be poor. A good contractor will do their homework and correctly size the system. You should never have an option of different size systems, there is only once correct answer! Ask your contractor how they came up with the system size, it should not have anything to do with what size system you had prior.
Bigger is Not Always Better
Some people may believe that installing an over-sized system to err on the side of caution is a safe choice, but
this is a misguided assumption as an over-sized system comes with problems of its own. An
over-sized system can produce too much airflow at a given time resulting in extremely short run
times. Short run times cause the system to cycle on and off very frequently once again reducing
its efficiency. A geothermal heat pump is expected to be 300%-400% efficient, but too large of a
unit causes significant decreases in this efficiency. And once again, decreased efficiency results
in higher electric bills.
An over-sized unit will also have a negative effect on the comfort level of the occupants. During the hot and humid summers a short run time will cool a room but fail to remove the air’s humidity. While your home may be cooler it will still be clammy and sticky. Also, some pieces of equipment operate for a fixed period of time and if the equipment is over-sized it can overshoot the thermostat setting causing a home to overheat in the winter and become an icebox in the summer.
Loop Size Requirements
While the geothermal heat pump equipment size is based on the heat gained and lost, the loop field depends on the size of equipment, soil type and climate conditions. To clarify, the loop field is the series of piping that is placed underground. As would be expected, the larger the geothermal system’s equipment, the larger the loop field must be. A larger loop field may mean the drill has to go deeper, the field has to be longer, or the pipes must be installed farther apart loops in order to move more heat to and from the ground.
Soil type affects the necessary loop field size because different types of soil have different abilities to absorb energy. Extremely dense soils, such as rock and clay, have the ability to hold a great deal of heat and can therefore transfer more heat. Sandy soils absorb far less heat and therefore require a larger loop field. As a general rule of thumb, the drier the ground the larger the loop field required.
Sizing a geothermal heat pump is a complex process and therefore it is important to contact a qualified geothermal contractor before making any decisions.