Heat pumps offer a ton of advantages to their owners, despite some common misconceptions. The fact that a heat pump system can offer an energy efficiency of above 400%, or even 600% surprises many people and raises the question: what’s so magical about heat pumps, and how do they work?
A heat pump is a device that moves heat from one source of heat to another, using very little electricity. It can extract warmth from the cold outside environment, turn it into heat and move it into a building. A heat pump can also operate in reverse for cooling by extracting the heat from a building and releasing it outside.
What makes heat pumps so special? Unbeatable efficiency. Heat pumps are by far the most energy efficient way of heating and cooling. This efficiency makes them a great investment since they reduce bills significantly and last for many years.
What can a heat pump do?
Besides heating and cooling, heat pumps can heat domestic hot water (DHW), or even swimming pools. Additionally, heat pumps may also offer a level of ventilation and humidity control. In commercial applications, a heat pump can also capture and recycle energy from industrial processes such as a server room or a production line.
Heat pumps are extremely flexible heating and cooling systems. They can be used for a multitude of home, business or industrial applications. Essentially, heat pump systems can be used to do a combination of tasks:
1) Sanitary hot water can be produced for domestic use (showers, faucets, etc.) at extremely high efficiencies either with an autonomous DHW heat pump, or a heat pump with a HydroTank (or domestic hot water tank).
2) Air heating, cooling and dehumidification, if an indoor air handler or fan coils are used.
3) Radiator heating. If your home already has radiators installed, a heat pump can be connected to them to provide heating without the need for replacing them.
4) Underfloor heating. Compared to radiator heating, underfloor systems are more efficient and don’t require such high temperatures to heat a space. That’s why heat pumps can reach even higher efficiencies when used with underfloor heating.
5) Swimming pool heating. Heat pumps are incredibly efficient at heating water, which makes them the ideal solution for heating swimming pools.
6) Energy storage and self-sufficient carbon-neutral heating. Combined with solar photovoltaics (PV) the financial gains of both systems improve and energy can also be stored in thermal form. Energy storage can also be used for complete self-sufficiency.
7) Thermal energy recycling. Heat from industrial applications (i.e. waste incineration, chemical processing, steel production, food pasteurization, etc.) can be captured and recycled for other applications. A heat pump system can also produce cold air (as a byproduct) when heating and hot air when cooling. This cold air can be used to cool wine cellars or server rooms while heating other spaces. When cooling a space in summer, the heat can be used to heat up a swimming pool or DHW.
8) Refrigeration. Heat pumps are used in certain commercial refrigeration systems.
The heat source and distribution system
When a heat pump is in heating mode it transfers heat from outside the building (the heat source) to the interior of the building (the heat distribution system).
The heat pump heat source
A heat pump will take warmth from a source and convert it into heat through compression. It can also remove heat to result in cooling. Either way, the heat pump needs to use a source from which it can extract and multiply heat.
The heat source can be the air (air-source heat pumps) or geothermal, which could be either ground-source or water-source. In an installation, the outdoor units and / or source apparatus (collectors, submersible pumps, etc.) deal with the heat source.
Heat sources include the air, the ground and water. Heat can also be recycled from other processes in any of these forms as well.
The heat pump distribution or storage system
Once the heat pump has produced heat or cold, it needs to distribute it efficiently through space or store it for later use. Distribution can happen in many ways, but the most typical output forms are air and water.
If the building has fan coils, underfloor heating or radiators, the distribution output system would be water. If the building uses ventilation ducts or other indoor air units, the distribution output system would be air.
Typically, indoor units deal with heat distribution, storage or other such functions. Domestic Hot Water heat pumps for example prepare and store hot water.
Distribution systems include radiators and underfloor heating units, different types of fan coil units (wall units, duct and ceiling units, freestanding units, cassettes etc.) and even swimming pools. In addition, Domestic Hot Water (DHW) used for showers, faucets, dishwashing etc. also forms part of the distribution system.
There are many different types of heat pumps. Although they operate on the same principles of heat transfer, they work in slightly different ways. Let’s take a quick look at the main types of heat pumps and how they differ.
What are the different types of heat pumps?
Heat pumps are extremely flexible. There are many variants, each suited to a specific type of situation. We split them between air-source heat pumps, where the heat source is air outside the building, and geothermal heat pumps where the heat source can be the ground or water.
Air-source heat pumps
Air-to-air heat pumps
Air to air heat pumps (split systems) consist of an external heat source unit and an internal distribution unit which provides heating or cooling of the air – just like an air conditioning system.
Air-to-water heat pumps
Air to water units use an external air source unit which works with an indoor unit (TermoPlus Hydrobox) and radiators or underfloor heating to provide heating. These often incorporate domestic hot water production – as in the case of the TermoPlus Hydrotank series).
Domestic hot water (DHW) heat pumps
Domestic hot water heat pumps produce hot water for use in faucets or showers. Some traditional models consist of two units (one indoor and one outdoor, using the outside air as a heat source). Autonomous DHW heat pumps, on the other hand, consist of a single indoor DHW unit that uses the indoor air as a heat source. DHW heat pumps systems can also cool the cellar where they are usually installed.
Hybrid heat pumps
Hybrid heat pumps use two heat sources or distribution systems. Some indoor units utilize refrigerant and water. The system efficiently heats and cools each building zone using the best manner. Hybrid heat pump systems enhance energy efficiency based on demands and conditions by combining heat sources and distribution techniques.
Geothermal heat pumps
Ground-source heat pumps
Ground-source heat pumps use the earth as a source of heat. The temperature below the ground is warmer than the outside air during the winter and more stable throughout the year. They can use a vertical (borehole) or a horizontal collector.
Water-source heat pumps
Water-source heat pumps use water as a source of heat. This could be located deep underground or in open bodies such as lakes or streams. Their collectors could be closed loop (sealed) or open loop (using the actual source’s water). They offer the highest coefficient of performance of all heat pumps.
How a heat pump works – the components of a heat pump system
It’s important to note that heat pumps do not generate heat using a source of fuel. They don’t create heat as an electric resistance heater, an oil furnace or a gas furnace would. An air source heat pump takes heat energy from the air outside and moves heat from one place to another. Similarly, a ground-source heat pump pulls heat from the ground and a water-source heat pump extracts it from the water.
Heat pumps don’t use fuel to create heat, but they do use a small amount of electricity to move heat energy from the outside indoors.
To understand how a heat pump works we need to take a look at the heating / cooling cycle and each heat pump component. Let’s take a look at how this works when using an air source heat pump to heat your home during the winter.
1) The evaporator
The evaporator is located in the heat pump’s outdoor unit and extracts the heat energy from the outdoor air heat source and transfers it to the fluid refrigerant. As the fluid refrigerant absorbs heat from the air, it evaporates into a gas state.
Essentially, the vaporized refrigerant in the heat source captures the ambient warmth from the environment and then moves towards the compressor.
2) The compressor
The compressor is also located in the outdoor unit.
At this point, the heat extracted from the cold outdoor air is stored in the refrigerant. This heated refrigerant reaches the compressor in the form of a low-pressure gas.
When the gas refrigerant reaches the compressor, it is then compressed, which increases its temperature even further.
Finally, the compressed heated refrigerant is transferred to the heating system of the building where it can be used to warm up indoor spaces.
3) The condenser
Now that we have transferred heat from one place to another, we need to distribute the heat inside your home. The role of the condenser is to turn the hot vapors into fluid, which can then heat the building’s heating system (radiators, underfloor units, fan coils etc.). Yes, heat pumps work well with radiators too. Typically, a heat exchanger is used to transfer the heat from the refrigerant to the water circulated in the radiators or underfloor heating. Once the heated refrigerant fluid has circulated through the heat exchanger, it moves on to the expansion valve.
4) The expansion valve
The expansion valve decompresses the fluid refrigerant, allowing it to vaporize in the evaporator. This allows the vaporized refrigerant to absorb further heat in the evaporator. And that is how the cycle starts again.
This whole process is called the “Refrigeration Cycle”.
How does a reversible air source heat pump work when cooling?
Many heat pumps also have the ability to provide cooling inside your home during the summer – just like an air conditioner. These are called reversible heat pumps because they can reverse the flow of the refrigerant in order to cool your home by extracting heat from inside the home. Reversible heat pumps can be water, air or ground source and can be an incredibly efficient way to heat and cool your home. Let’s look at how a reversible air-source heat pump works.
When the heat pump is in cooling mode, the internal unit switches to evaporating mode to capture the heat from inside the house while the external unit switches to condensing mode to release the heat into the outside air.
When using a heat pump system for cooling we need a way to bring cool air inside a home. This is achieved with fan coils or an air handler. The heat is removed from the air and the cool air is returned indoors by the air handler or the fan coils.
In cooling, the terms evaporator and condenser are often referred to in reverse, as in the case of air-conditioners which work in the same way as a heat pump cooling a home.
What is the electric heat function? Why is a heaterless heat pump better?
Traditional heat pumps use an electric resistance heater as backup. This auxiliary heating feature uses electricity to directly provide heating and is typically activated when the heat pump can’t cope during a very cold day. This heating element (as all other resistance heaters) has a heating efficiency of 100%, which is much lower than the 400% of a typical air-source unit.
A heaterless heat pump is powerful enough to solely use the heat pump’s compression / evaporation cycle to provide heating and can operate reliably in extremely cold temperatures as low as -15°C or even -30°C.
All TermoPlus heat pumps are heaterless by design and can constantly produce hot water up to 60˚C or even 70˚C in some models. We achieve this by using larger evaporators, optimized defrost cycles, and, in some units, flash injection technology. This results in greater efficiency and long-term savings.
So, what is an inverter then? Is it the same as in air conditioners?
You have probably heard of air conditioners and heat pumps with inverters. An inverter is a part of the heat pump that regulates the compressor motor’s speed. This allows the heat pump’s compressor to run at various speeds as opposed to just being switched on or off.
You see, traditional heat pump compressors could be either switched on or off. This didn’t allow the system to run at lower speeds, which are more efficient.
This way, a heat pump with an inverter-driven compressor can meet heating requirements with more precision and efficiency. A side effect of lower compressor speeds is the extension of the compressor’s lifespan due to reduced wear and tear. Inverter-equipped heat pumps offer a more efficient way to heat a home while at the same time increasing the level of comfort.
The best inverter-driven compressors for air-source heat pumps have been developed by Mitsubishi and are exclusively used in TermoPlus air-source heat pump systems.
How do Domestic Hot Water (DHW) heat pumps work?
Autonomous DHW heat pumps are air-source heat pumps that work independently of the building’s heating system. They use indoor warmth as a form of heat source. The DHW heat pump moves heat from the indoor air to the refrigerant, which is compressed to heat the water through a heat exchanger and then vaporized through an expansion valve to capture more heat again.
Our TermoPlus DHW heat pump units use thermostatic expansion valves (or electronic in some cases) with an internal equalizer instead, which is much more efficient than industry standard capillary tubes. Insulating the tank properly reduces heat losses and reduces the energy consumption further. That’s why we also use high-quality Polyurethane (PU) insulation.
As a byproduct of the refrigeration cycle, the DHW tank produces cold air that can either be expelled from the building or used to cool a small space (such as a small home-server rack or wine cellar).
When do heat pumps work best?
An air source heat pump system relies on the outdoor air as a source of heat. Since heat is transferred from that source, there are certain temperature conditions that need to be met. Whereas most heat pumps can operate in conditions as low as -15°C, a cold climate heat pump absorbs heat from as low as -30°C.
Ground source heat pumps don’t need to abide by the temperature restrictions of air to water heat pumps. Heat is extracted from the ground or water bodies with a much more stable temperature that is almost always warmer than the air outside.
Heat pumps use electricity, as do oil furnaces, electric resistance heaters, gas furnaces, and even many wood stoves. Even if electricity is expensive, they are extremely efficient. Combining a solar PV power plant with a heat pump makes for an even more fruitful investment. Adding storage to a PV system can also contribute to the self-sufficiency of a heat pump system.
Find out more about heat pumps by downloading our free Quick Guide to Heat Pumps, or get in touch with us for a free quote.
