Split System Heat Pump

How a Heat Pump Works


A heat pump is also known as a ‘split system’ or a reverse cycle air-conditioner. The description ‘split system’ refers to a unit which is made up of two separate units that work together. A split system heat pump is a unit that has one part affixed inside the home and the other outdoors. The description ‘reverse cycle’ comes about as a heat pump can be used for both heating and cooling.

So, in short, a heat pump is an air-conditioner that also has a heating mode with both an indoor and outdoor unit.

How Does It Work?

Okay, let’s get into the details. There is a compressor/motor which pumps refrigerant gas down to smaller volumes under pressure to collect heat. Then there are two car radiator like sections called evaporators with fans behind them, one on the indoor unit and one on the outdoor unit. One steals heat and the other dispenses heat, reversing roles to suit both heating and cooling.

But how does it create heat from refrigerant gas? This gas is cold. Well, that is when it gets a little scientific…

Because refrigerant gas is not very dense like water for instance, it also does not freeze at 0ºC like water. It actually ‘boils’ off at just below -40ºC. Also, you may have thought that if it was sitting at 0ºC, this would mean there is no more heat? Well in actual fact there is, because absolute zero heat is at Kelvin* Zero or (minus) -273.16ºC.

So the heat pump works by collecting this heat from air, even at well below zero.

Collecting Heat Using Refrigerant Gas

In the outdoor unit we have our refrigerant gas in a cylinder at high pressure. Once we let the gas out into a bigger area it expands. As it expands, it drops in temperature. Exactly like a BBQ gas bottle, the gas feels cold right? So because we are in heating mode, we need to bring this temperature up.

To do this we control the gas release and it expands into a vacuum of copper pipes in a car radiator looking part of the outdoor unit called a evaporator. To then warm up this gas quickly we use a fan to pass the outside air over the evaporator. This is the secret, the gas then rises in temperature as it steals heat from the outside air, even from air down to -25ºC. Thus we have gathered heat from outside air in the process of equalising temperatures as nature does.

That is the first part of the heating process. The second part is where we make that little bit of heat into a lot of heat. So we have our spread out refrigerant gas with more energy in it than we started with. Now we simply compress it back down to its small original volume. And guess what, as we squeeze it down it heats up and we get more units of energy in the original small space.

How is this? Its a bit of science and maths… “It takes one unit of energy to raise the temperature of water one degree centigrade is out metric”. If we squeeze 10 cubic centimeters of water into 1 cubic centimeter, we get 10ºC. But actually water does not compress, so this is why we use “very squeezable” refrigerant gas which we can squeeze down so much that we get some 50ºC plus from the process.

From there you simply run the now hot refrigerant gas into the indoor units evaporator section and use its fan to blow the room air through it to heat your home. This is controlled very precisely to deliver controlled heat to the room space. Then we simply work the whole system in reverse for cooling, stealing the heat from a room and dumping it away outside while using the cold refrigerant gas to cool.

This process is all run by computer chips, sensors and the like to warm and cool the air to the desired temperature very accurately and cheaply. Up to 7 times more cheaply than direct electric element heating methods and cheaper than any other home heating method.

Energy Efficient Heating System

Effectively the system uses very little power to steal the free heat from even very cold air, which is why is it much cheaper to run than other heating alternatives. Old type heat pumps used around 1kw of power to steal and deliver some 2.65kw of heat from the outside air. This is known as EER (Energy Efficiency Ratio) or COP (Co-efficientcy of Performance) Dakin now have a world leading EER of 7 in their product line up. Meaning, 1kw of power is used to produce 7kw’s of heat!

Want to know how you can heat your space with an energy efficient heat pump? Request a free evaluation to get a tailored recommendation and quote.

You may still have some questions about heat pumps. If you still have any pressing questions that we haven’t answered, please do not hesitate to contact us on 1300 552 785 immediately and we will help.

John Thirgood
Managing Director,  Jessups Solar Squad


*The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the Celsius degree, which has the same magnitude. Subtracting 273.16 K from the temperature of the triple point of water (0.01 °C) makes absolute zero (0 K) equivalent to −273.15 °C (−459.67 °F).

More from our blog: