By Rory Macnamara – technical input by Derick Gomez of MD Water

The Heat Pump – How does it work?Simply put, a heat pump is a device that uses a small amount of energy to move heat from one location to another. Heat pumps are typically used to pull heat out of the air or ground to heat a home or office building, but they can be reversed to cool a building. A heat pump offers one a way to use electricity to heat water efficiently. Where a geyser uses three units of electrical energy to produce three units of heat energy, a heat pump converts just one unit of electrical energy into four units of heat energy.

Typical installation of heat pump to geyser (seen in the Plumblink Durban DC Technical and Demo Centre).

Typical installation of heat pump to geyser (seen in the Plumblink Durban DC Technical and Demo Centre). Image credit: Plumblink Durban DC Technical and Demo Centre

One of the big advantages over solar is that one does not need sun as these systems run day or night, rain or shine to deliver hot water at a fraction of the cost. Bear in mind that like solar, the investment in a heat pump has a medium-term ROI and it is important to get the installation done by an accredited specialist to ensure that all components of the system are high quality and are properly matched to your client’s requirements.

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Many heat pumps are imported and the plumber or air-conditioning contractor, in promoting the use of heat pumps to a client, needs to consider import versus local. As always, the unit must suit the application and full appreciation of the actual ambient temperature at the site where the unit is to be installed. Failure to do this will result in the heat pump not performing correctly.

Hot water storage heaters, commonly referred to as geysers, can be supported by a heat pump and correctly installed can reduce electricity costs. A South African company has a local patent to retrofit existing geysers with a copper element that retains the heat consistently without heat loss. SANS 151 calls for minimum heat loss as well as geysers achieving a B energy rating, and the heat pump can contribute to reducing further energy consumption.

There are basically four types of hot water heaters:

  • Conventional storage water heaters store and heat in a tank, making use of electricity or gas.
  • Tankless or demand type water heaters which heat water directly on its way through the pipes to the outlet. Correct pipe sizing is critical.
  • Solar Water Heaters use the sun to warm up water and save on energy. Takes longer time to warm the water and runs out quicker on average. This type of heater must be correctly positioned to gain the optimum benefit.
  • Heat Pump water heaters work off ambient warmth from the air and compress it to heat up the water i.e., they convert one kW to four kW, making them highly efficient and cost saving.

Whether a straightforward installation or part of a rational design, the application is critical and can only be done by a qualified engineer or installer/contractor.
The general components of a heat pump are:

  • Tank which is larger than a standard tank.
  • Compressor which pressurises the refrigerant inside the evaporator and condenser coils causing it to expand and heat up. It also helps move through the system.
  • Evaporator which collects warm air pulled in via the fan. The refrigerant, which runs inside, warms up, is compressed, and evaporates creating high pressure and high heat.
  • Condenser is located outside or in the tank and the coils are where the refrigerant loses pressure, cools, and condenses back to liquid thus releasing the hot temperature to the water inside the tank.
  • Fan is located at the top or side and is responsible for pulling in the ambient warm air from the point it is positioned.
  • Thermostats consist of two – one to measure the water temperature at the bottom of the tank and another to measure temperature at the top. The thermostats control the system to either heat or cool the water depending on the requirement and settings.
  • Cold water inlet drawing cold water from the main line.
  • Hot water outlet where the now heated water leaves the water heater to go to the outlet i.e., tap, shower, basin, sink, etc.
    Drain which is there should one ever have to release water from the tank.
How the heat pump works.

How the heat pump works. Image supplied.


A much-used word these days for very good reason. The causes of an energy crisis are:
An increasing population.

  • Excessive use of non-renewable sources of energy.
  • Use of less fuel-efficient machines.
  • The affluent lifestyle of people.

Whichever one chooses to accept or ignore, they all play a part in the guidance professionals and contractors give customers. These are facts that cause an energy crisis, excluding the political aspect.

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