The natural flow of heat is from hot places to cold places. However, with the use of a heat pump, an equipment usually driven by an electric motor, heat can be pushed to the other direction, from cold to hot. In the same principle, air conditioners transport heat from a cool place to the hot outdoors, so generally speaking they are in essence heat pumps. But in the building business, the term heat pump usually refers to a special kind of air conditioner that can reverse direction, moving heat from the cold outdoors to the warm indoors. These types of equipment can be used for both cooling and heating.
The efficiency of heat pumps to operate decreases as the temperature difference between indoors and outdoors increases. This is the main reason why heat pumps are not very effective in very cold climates and usually include electric heating elements whenever the time arises that it isn’t able to accommodate the load.
The second most common problem with heat pumps is that, it gets cold on its outside coils when heating, to the point where sometimes ice actually forms there. Because of this, heat pumps generally provide defrost cycles, switching into a cooling mode that warms the outside coils and melts the ice. And of course, this in turn decreases the heating efficiency, although these are minor difficulties. Heat pumps are still considered more efficient compared to electric heating.
There are some heat pump designs that address the problems mentioned above. These designs are called “ground-coupled”. They work by exchanging heat with the ground instead of the outside air.
During cold days, the ground is generally much warmer then the air, and on hot days the ground is generally cooler than the air. Because of this, ground-coupled heat pumps should be on average operating more efficiently than air coupled ones.
Other terms for ground-coupled heat pumps are ground-source heat pumps, earth-coupled heat pumps, and geothermal heat pumps although they do not really make use of geothermal heat in a strict sense. Instead of their coils exchanging heat with air, they exchange heat with either a body of water like rivers or lakes, which is called water-source heat pump. They also exchange heat with the earth through a bored straight hole or a horizontal trenching within the ground.
A heat pump usually uses below half the energy needed by an electric resistance furnace, so it doesn’t just save money but also decreases emissions from fossil fuel power plants.
Its performance can also beat the performance of directly burning natural gas in terms of emissions and fossil fuel consumption.
Ground coupling also adds another level of efficiency when compared to standard air source heat pumps. In fact, manufacturers of ground source heat pumps claim that there is a yearly heating cost reduction of up to 50% and a yearly air conditioning cost reduction of up to 25%. The total amount actually saved depends on several factors like locate climate and particular installation.
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