Geothermal heat pump systems are invented to improve the efficiency of the air-to-air heat pump system. The air-to-air heat pump operates well when the outside ambient temperature is above 0°C. Below this freezing point, the system's efficiency drops rapidly. In order to cater for this drop in efficiency, peripheral components such as auxiliary heater is installed indoor to boost the heating capacity of the unit.
This auxiliary heater is turned on whenever the capacity to heat up the room drops due to the freezing of outdoor coil when outdoor temperature goes below 0°C.
The study by experts show that our earth is a huge mass with stable temperature. The temperature of the earth is about 50°F or 10°C at about 4-6 feet below the ground. Coils that carry the liquid refrigerant are buried underneath the earth below the frost line which is usually about 4-6 feet deep.
The coils can be buried vertically or horizontally underneath your property and are connected to the heat pump systems in the house. This ground coil may also be placed in the bottom of a lake or a pond. The coil or also known as the loop is usually made of highly durable high-density polyethylene plastic material. The coil can also be made using copper piping.
In places where the temperature drops below freezing point, anti-freeze solution is added to the liquid refrigerant to prevent it from freezing and thus breaks the coils. The anti-freeze solution can be glycols or alcohol which are relatively safe and non-corrosive.
Heating Mode
During winter, the system runs heating cycle where the liquid refrigerant flows in the coil which is buried underneath the ground. It starts to boil and absorbs heat from the ground that surrounds the coil. The vaporized refrigerant is then channeled to the compressor where it is compressed and discharged into the indoor coil (which now acts as a condenser).
The condenser changes the vaporized refrigerant to liquid form and provide heat to the air in the room. This liquid refrigerant then returns to the ground coil and the cycle is repeated.
Cooling Mode
During summer, the system runs cooling cycle which is done by the use of a 4-way valve. The 4-way valve causes the refrigerant to flow in the reverse direction causing the indoor coil to become an evaporator and the ground coil a condenser. The direction of the flow to the compressor remains the same.
The ground absorbs the heat from the vaporized refrigerant and the evaporator provides cooling to the room.
Advantages of Geothermal Heat Pump System
Although the initial setup cost of this system is more costly compared to conventional heat pump, some of the advantages that can be derived include:
● Life Expectancy of the system can easily go up to 25-30 years. Many manufacturers of ground coils provide warranty up to 50 years that use high-density polyethylene material.
● Lower Cost in operation and maintenance is another plus factor. No maintenance is required for the coil that is buried underground. Utility bill can do down by 30%-40% compared to the conventional systems.
● Noise from the outdoor is eliminated. The air-to-air heat pump system uses a propeller fan to cool the outdoor unit thus creating noisy environment in the neighbourhood.
● Efficiency of a geothermal heat pump is better compared to the conventional system. In heating mode, the savings in electricity can go up to 70% compared to conventional heating system. Savings of up to 60% have been recorded for cooling mode.
● Clean Energy is another aspect of this system in which there is no combustion of natural gas or coal in the system. Hence this is the direction that all who are into the protection of our environment should pursue. Hot water can also be produced for domestic use besides heating or cooling the space of the building.
Heat Pump Principles
There are two types of heat pumps that are commonly used today. They are known as air-to-air HP and geothermal HP. The former uses the outdoor air whereas the latter uses the underground (water or earth) temperature as its source of heating or cooling.
Using water as the source or sink gives better performance characteristics compared to the air.
Nevertheless, the air-to-air type is more economical and is popular in residential and commercial buildings applications.
These equipment work on the principle that heat will move from higher temperature to lower temperature. Therefore, a heat transfer coil that is kept a low temperature compared to its surrounding will take away the heat from the surrounding, hence cooling the space.
In order to transfer heat to the surrounding, the heat transfer device is heated up to a higher temperature than the surrounding.
This system is designed to be used for cooling the space during summer and heating during winter. The coils at the indoor and outdoor become evaporator or condenser depending on the mode of operation. If it is operating in cooling mode, the indoor coil behaves as evaporator and outdoor as condenser.
In heating mode, the indoor coil becomes a condenser and the outdoor coil evaporator. This is accomplished without moving the coils around by using a reversing valve known as four-way valve which reverses the flow of the refrigerant.
HP Operation
The HP that is commonly used is known as vapor compression refrigeration machine. An absorption machine can also be used but is not as common. The vapor compression cycle is used in our refrigerators and large industrial refrigeration systems. The diagram below shows the basic schematic of operation of a typical HP in cooling mode during summer.
In cooling mode, the direction of the refrigerant flow is counter clockwise and the room coil is acting as an evaporator coil where the space is cooled by blowing a fan across the coil. Cool air will be generated here. The heat from the room is sink into the air, water or the ground.
During winter, heating mode is activated and the direction of the refrigerant is reversed after leaving the compressor. Take note that the flow of the refrigerant in the compressor remains the same. This reversal of flow is achieved by using a reversing valve. The air, water or ground is the source of heating.
The change of flow causes the room coil to become a condenser and the outdoor coil an evaporator. The fan that blows the room air across the condenser coil causes heat to be released into the room. The heating cycle is illustrated in the figure below.
A reversing valve has four ports, two of which are opened at any one time to allow the refrigerant flow in the direction chosen.
In winter condition where temperature drops below -7°C, the heat pump heating cycle becomes less efficient as the outdoor ambient temperaure drops below freezing point. When the outdoor coil freezes with a layer of ice, the unit will have to run cooling mode to defrost the ice that accumulate on the coil.
During this time, the unit will be extracting heat from the room to the outdoor. Most controllers will stop the indoor fan from blowing the cold air into the space. This is one of the main disadvantage of this type of system when used in extreme winter condition.
Heat Pump Maintenance
Some of the actions that you can do to maintain you HP to ensure it continuous operations are listed below.
● Clean the filters, fans, indoor coils once a month or when necessary according to the recommendation of the manufacturer. Dirty filters or coils will cause the reduction of airflow in the system. The reduction of airflow will make the compressor work harder and hence more electricity is consumed.
● Clean the outdoor coils whenever they are stuck with leaves or other materials. Ensure that there is nothing near by that prevent the heat transfer to the surroundings. Do not put block the fan. Straighten fins that have been bent to ensure that the surface contact with the surrounding is good.
● Check the proper operation of the thermostat which controls the compressor, reversing valve, fans and other electronic functions.
Related Links
This system is a special application for heat pump and is used in places where temperature dips below freezing point.
Find out more on the defrost function in a split or window HP unit.
A more detailed thermostat operation covered here.
Consider installing Water Source Heat Pump as this is one of the most efficient system available today. Simultaneous cooling and heating can operate on the same system.
Post a Comment