Heat pump outside residence

By Sarah MacNamara, Assistant Editor, Pump Industry Magazine

In the face of a potential climate crisis and the stride to net zero, individuals and companies alike are looking to implement sustainable practices wherever possible. In the world of HVAC, heat pumps are an increasingly popular choice due to their energy efficiency.

Heat pump technologies are many and varied and each has its own benefits. All heat pumps, however, work on the same basic principle of pumping heat from one location to another with this
process utilised to offer both heating and cooling.

To warm an area, heat pumps gather heat from outside and warm it to a higher temperature before pumping the heat inside. To cool an area, this process is reversed – the heat pump extracts heat from inside and pumps it outside to lower the temperature indoors.

Heat pumps are a sustainable option because they work by transferring heat from the ambient air, as opposed to traditional heating and cooling systems that rely on the generation of heat, often by burning fossil fuels.

In addition, because they are able to provide both heating and cooling with minimal energy consumption, heat pumps are a more energy efficient solution to alternative methods that rely
on combustion or resistance.

The main types of heat pump technologies in Australia include air-source, geothermal, absorption and desiccant heat pumps and the differences in each lie in where they source their heat from.

Refrigerants: the heart of the heat pump

Refrigerants are essential to heat pump systems because they enable heat to be transported from one component to the next.

Though they have been widely used since the 1920s, refrigerants have been subject to a range of changes and upgrades over the last 40 years to bring them in line with modern sustainability expectations.

Chlorofluorocarbons (CFCs) were the first refrigerants to hit the market, however were eventually phased out in the 1970s due to their high chlorine content and the consequences this had on the earth’s ozone layer.

In the 1990s, hydrofluorocarbons (HFCs) were developed as an alternative to CFCs because they had a lesser impact on the ozone layer. Despite this, it was later discovered that the global warming potential of HFCs was 1,430, which means that they have the potential to trap as much as 1,430 times the amount of heat in the atmosphere as carbon dioxide. As such, HFCs are also being phased out.

Since then, CO₂ and HFO are among the new wave of refrigerants that have been introduced that are far more environmentally friendly than their predecessors, paving the way for the continued uptake in heat pumps as an energy efficient method of heating and cooling.

Air-source heat pumps

Air-source heat pumps are the most common type of heat pump and utilise solar heat that is stored in the air outside in the form of thermal energy that is stored in the air outside. They use this air as either the heat source or the heat sink depending on whether they are being used to heat or cool an area.

Air-source heat pumps absorb ambient air into a refrigerant and then compress it to increase its temperature, before the hot refrigerant is passed through a coil that transfers the heat into the heating system.

There are two configurations of air-source heat pumps: integrated and split systems. In an integrated system, all of the components used for heat generation are located inside the heat pump, whereas a split system separates the tank and the compressor.

Geothermal heat pumps

Geothermal heat pumps utilise the heat from the ground or a water source to provide heating and cooling and work well in climates with extreme conditions. This is because solar heat is absorbed by the surface of the earth through the ground, which maintains a relatively constant temperature throughout the different seasons.

Ground source heat pumps

Ground-source heat pumps extract the heat from the ground and use it as either a heat source or heat sink to regulate the temperature indoors.

They absorb heat from the ground and then transfer it indoors by using a loop of underground piping filled with a refrigerant. The refrigerant’s temperature is increased as it moves through a compressor before it’s eventually transferred into the indoor heating system.

Water-source heat pumps

Water-source heat pumps are very similar to ground-source heat pumps, however, they use a body of water as the heat source or sink.

Water-source heat pumps can use either a closed-loop or an open-loop system to heat and cool an area.

Closed-loop systems pump a mix of water and antifreeze through a closed system that circulates the fluid through the pipes, with the same fluid travelling through the pipes over and over again.

In comparison, open-loop systems pump water to the heat exchanger, circulating directly through the heat pump, before being directed elsewhere to drain.

Absorption heat pumps

Rather than using air or water to generate heat, absorption heat pumps use heat – or thermal energy – as their energy source.

They can be driven with a variety of heat sources, but are most commonly powered by natural gas, propane or solar energy to drive a chemical process that extracts heat from the air or water.

Once they have extracted the heat, absorption heat pumps work by absorbing the heat into a refrigerant which then moves through a compressor to increase its temperature before transferring the heat inside.

Desiccant heat pumps

Desiccant heat pumps use a desiccant material such as activated charcoal, silica gel or calcium chloride to absorb moisture from the air, with calcium chloride most commonly used.

By their very nature, desiccant materials absorb water and promote dryness and as such, desiccant heaters are primarily used in humid climates due to their ability to effectively dehumidify
indoor air.

A heat source such as electricity is used to heat the desiccant material to release the absorbed moisture before the heat is pumped indoors.

Other heat pumps can also utilise this process to improve the overall efficiency of the system.

Round up: heat pump pros and cons

Each kind of heat pump has its own individual advantages and disadvantages. For example:

  • Air-source heat pumps have lower installation costs than ground-source heat pumps, however they are less efficient in colder temperatures
  • Ground-source heat pumps offer higher efficiency in cold temperatures but have higher installation costs
  • Water-source heat pumps present an alternative to air-source and ground-source heat pumps, however they rely on the availability of a nearby water source
  • Absorption heat pumps provide higher efficiency than traditional heat pumps but are more expensive to install and maintain
  • Desiccant heat pumps allow temperature control in humid environments however they also have higher installation and maintenance costs

Energy efficiency

One of the major benefits of modern heat pump technology is the energy efficiency they provide. Heat pumps require significantly less energy than traditional heating technologies because they transfer heat instead of generating it.

The performance of a heat pump is represented by its coefficient of performance (COP), which is the ratio of energy input it requires versus the useful energy output it provides. Modern
heat pumps often have a COP of around three, which means for every one unit of energy consumed, they produce three units of heating or cooling.

To further increase energy efficiency, heat pumps can be integrated with renewable energy sources such as solar panels.

As individuals and businesses across Australia continue to look towards integrating sustainable practices, heat pumps can offer an economical and energy-efficient solution to both heating and cooling

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