Facts and Trivias!

Summary: Heat pumps are very popular units. A heat pump is one of the most complex units in a typical residential home. A special thermostat is required for the proper operation between heat pump operation and the auxiliary electric resistance heating. Here are some simple facts about the heat pump mechanics.




Q. How does it work?

A. The vast majority of Heat Pumps work on the same principle as the domestic refrigerator utilising a vapour compression cycle but for heating the Heat Pump utilises the ‘hot end’ of the process. The vapour compression process utilises low grade heat that is normally too cool for human or process requirements and lifts the same quantity of energy to a higher temperature that is suitable for human comfort.

Heat Pump Illustrations and Facts
Heat pumps are very popular machines. They appeal to many land developers and builders because they are relatively easy to install. Since electricity is already being extended into the subdivision and your home, there is no real extra utility costs. Installing natural gas lines and service is an extra step for a developer and a builder. Heat pumps don't require masonry chimneys for that matter. 

Q. Why is this remarkable?

A. The thermodynamic cycle occurs at constant energy content throughout even though the temperature has been increased from say 5ºC to say 35ºC. A refrigerant is utilised in the cycle to act as the transfer medium and the only prime energy required is the energy to circulate the refrigerant.

The Heat Pump Coil
Standard air conditioners have two coils. One distributes cooling and the other one disposes of collected heat. One of these coils is hidden inside your home in the furnace or air handler unit where the fan is located. The other coil is outdoors in the big metal contraption. Heat pump coils need to be designed a little differently because they have to serve both purposes. In other words, when the pump switches from heating to cooling, the tasks of the coils switch as well.

Q. What sort of efficiencies can be produced?

A. Depending on the application and type of Heat Pump utilised efficiencies of 300% to 500% are normal. When dealing with Heat Pumps efficiency is known as Coefficient of Performance (COP), so the COPs for the above example would be 3 to 1 and 5 to 1.

High Efficiency
How do heat pumps become more energy efficient? There are several primary ways. One of the most practical things to do is to increase the size or surface area of the indoor and outdoor coils. This will definitely help move heat one direction or another faster.Heat pump manufactures are also re-introducing the expansion valve. This used to be standard equipment on air conditioners and heat pumps years ago. An expansion valve meters the flow of refrigerant. Because the internal pressure of the refrigerant in the system changed with a rise or fall in outdoor air temperature, metering the flow of Freon delivers just the right amount of heating or cooling to the living space. Prior to the re-introduction of expansion valves, a fixed orifice in the refrigerant system was used to regulate the flow of refrigerant.

Q. So they save energy but what about CO2 emissions?

A. Heat Pumps emit considerably less CO2 to the atmosphere than gas or oil fired heating systems so they are environment friendly and the low grade heat source utilised is considered to be a renewable energy source (CO2 reduction is generally proportional to the COP for each application).

The Defrost Mode
When the air temperature drops below 32 degrees outside and the outside air is fairly saturated with humidity, frost can form on the outdoor unit coils. This is perfectly natural. The frost can turn to a thin layer of ice rather quickly during periods of operation. The most efficient heat pumps have sensors that tell the heat pump that ice is forming. When the sense ice, they actually send heat back outdoors to melt the ice. Less efficient heat pump models do this on a time and temperature basis and may send heat to the outdoor coil when it isn't necessary to do so. If this happens, you have to pay more to heat the house back up! Ask about this feature when you shop for a heat pump.

Q. Can money be saved as well?

A. Yes of course. Due to the dynamic nature of Heat Pumps their capital cost is higher than conventional heating systems, however, the savings delivered in energy efficiency allows for very low operating costs. When utilised in commercial buildings that also require cooling additional cost benefits occur as there is no need to expend further capital on a second system.