It was interesting to hear that the UK government is going to push heat pumps in order to help decarbonise the UK. This is planned to be achieved by the offer of a grant to replace gas boilers. Gas boilers are planned to be eventually phased out and replaced by this technological advancement. I am sure that heat pumps are not a particularly well known technology for most, so I thought in this post it might be interesting to take a look at them.
Method of operation
A heat pump can operate in one of two ways either using the ground or the air. In a simple way it takes heat from the air or land surrounding a building and magnifies it so that it is at a usable temperature. A common analogy is that it is like a reverse fridge. Air source heat pumps look almost identical to air conditioning units.
Now for the technical bit…
Initially the outside air is blown by a fan over a heat exchange area that forms the external part of the heat pump. The heat, even though it is not necessarily all that hot, causes a liquid refrigerant to evaporate. The next phase involves compressing the gas to such an extent that it causes a significant rise in temperature. The heat magnified gas will next travel over an internal heat exchange area where it can be blown into a building or used to heat water that can be pumped through a central heating system. Once the heat has been transferred to a building the refrigerant gas will drop significantly in temperature and return to being a liquid. At this point the gas will have cooled significantly (as the heat has been removed). It is then returned to the outside heat exchange area where the process occurs again.
Are these things a good idea?
Well good question! Currently most homes and commercial buildings are heated by gas boilers. The carbon from gas makes up a significant concentration of carbon emissions as it is used for heating and hot water (around a fifth of the UK’s carbon emissions for example). By eliminating the need for gas the carbon footprint of a heat pump is much less of that for an equivalent size gas boiler. Heat pumps also work well in cold to moderate climates. It can even provide heating at temperatures of -20 degrees Celsius.
Heat pumps have been developed to keep a building at steady temperature rather than through an initial blast of heat as occurs when a gas boiler operates. For this reason, they tend to work best when heat saving measures have been installed in a building such as cavity wall insulation, triple glazing or loft insulation. They sort of provide an increased ambient temperature that is evenly spread throughout a property rather than a direct instant form of heat as occurs from gas produced heat.
Are there any alternatives?
A heat pump may not be for everybody. Hydrogen is a potential future fuel source that could replace gas. Hydrogen can be generated in such a way that it has a relatively low environmental impact. Another option is to provide localised heating whereby domestic and commercial properties can be heated from a specified source such as the ground (geothermal) or an incinerator. For example, it is planned that a heat network will be developed in the Borough of Bexley in south east London which will warm 21,000 homes from an incinerator. This is surely a good use of this heat and certainly better than letting it escape. However, there are certainly better ways to manage waste than incineration.
I think heat pumps will have a significant role in decarbonising countries around the world. Heating is a significant source of greenhouse gas emissions, although it is often a source that is not thought about. Heat pumps won’t be for everyone, but their alternatives that exist such as green hydrogen and area heating.
John Binns BSc (Hons), MSc, MIEMA
With over 19 years’ experience working in environment management, John Binns BSc (Hons) MSc MIEMA is an experienced environmental tutor and consultant with knowledge of health and safety management.