The UK Government recently set out its 10-point plan for a 'green industrial revolution' to accelerate the UK towards its ambitious goal of becoming net-zero carbon by 2050. The plan committed considerable investment for the increased deployment of heat pump technology, aiming to have 600 000 heat pumps installed every year by 2028.
Which variant - ground source heat pumps or air source heat pumps – is best suited to the task? UK ground source heat pump manufacturer, Kensa Heat Pumps, argues that ground source will be the lowest cost heat decarbonisation strategy, and the optimal heat pump solution for the householder, the community, and the environment.
Several degrees of difference
In principle, a ground source heat pump (GSHP) and an air source heat pump (ASHP) are similar appliances. As a consequence, many people consider that the efficiencies and capabilities are the same, but there are significant differences between the two technologies, that become especially clear when evaluated against the scale of mass deployment needed to meet the Government’s targets.
First and foremost, any mass heat pump rollout programme featuring large numbers of ASHPs will require far more back up generating and storage capacity. This is because the efficiency of air source heat pumps is hugely compromised in cold weather when the air temperature drops, which unfortunately coincides with when heat demand is at its peak.
Sub-surface ground (and water) temperatures remain fairly stable night or day, all year round. As a result, the source temperature for a GSHP on the coldest day can be up to 15°C warmer than the cold air coming into an ASHP. A higher source temperature means the GSHP has to do less ‘work’ to produce temperatures useful for home heating; this means less electricity is consumed, which results in higher efficiency.
Kensa smart controls with GSHPs.
Fit for purpose for mass deployment
It is a fact that the more thermally efficient a property is, the easier it will be to heat effectively with any type of heating system, but is a myth that ground source heat pumps are only suitable for the best-insulated buildings. Ground source heat pumps can bring running cost savings to a wide range of buildings from every era through their superior efficiency.
GSHP and ASHP appliances are a similar price, but a GSHP system has always been more expensive because it requires a ground array. For reference, a ground array is typically either pipe buried in shallow horizontal trenches, or a probe installed within a deep vertical borehole.
There is a common misconception that many properties will not have space for a ground array. However, even in Victorian terraced properties - the densest low-rise housing in the UK - there would still be space for deeper boreholes, which could be run down the centre-line of the street.
ASHPs would be questionable for these types of properties, because of their potential to cause noise nuisance – planning conditions prevent their installation in high-density housing.
Rather than being viewed as a cost burden, Kensa views ground arrays as an asset that can unlock all the advantages of GSHPs. Ground arrays last over 100 years; they are buried, making them entirely unobtrusive and unable to be stolen, unlike air source units. And they allow for a unique system architecture for effective, sustainable renewable heat extraction, that is scalable and perfectly suited to large scale domestic developments.
Shared ground loop arrays, passive cooling, and waste heat recapture
Since 2012, Kensa has pioneered the installation of small GSHPs within individual dwellings linked to a shared ground array. This system architecture allows multiple properties to benefit from the same underground infrastructure and for ground array installation costs to be reduced significantly through economies of scale.
Kensa believes that shared ground arrays should be regarded as the 21st century equivalent to the gas network, with a renewable heat infrastructure that effectively mimics the existing mains gas model and allows the householder to have a ‘white box GSHP’ inside the property that mimics a boiler.
Individual Kensa heat pumps installed every property.
GSHPs on shared ground arrays with ambient temperature pipework are extremely versatile, as they can deliver cooling, as well as heating, reducing room temperatures by several degrees without the use of any air conditioner. The ability to provide cooling in summer will become increasingly attractive as temperatures continue to rise, and with a ground source heat pump, that cooling is provided at zero cost and will reduce annual carbon emissions.
Further cost savings are available if waste heat is utilised. Excess heat from a property can be absorbed by the ground array fluid returning to the ground, helping to re-charge the ground’s temperature and improving winter heating efficiency. The benefits of this waste heat recapture increase as the size and number of properties on the shared ground loop array are scaled up.
Smart controls and load-shifting
The mass deployment of GSHPs will help reduce the additional generating capacity required to support any electrification of heat strategy. This is because GSHPs can run at times when electricity demand is lowest and prices are therefore cheapest, and also when there is more power available from renewable electricity generation sources, such as wind and solar, meaning the electricity supplied is lowest in carbon.
GSHPs are better suited to this type of load-shifting, than ASHPs, as they are quiet and unlikely to disturb anyone, and also the temperatures below ground remain constant no matter the time of day, (or indeed season). A homeowner could recharge their hot water cylinder through the night when demand and price are lowest – ready to use the next day.
GSHPs can integrate with smart controls that cleverly learn a household’s unique heating schedule, and synchronise this with flexible time-of-use tariffs that vary the cost of electricity throughout the day depending on demand. Other emerging smart technology, such as thermal storage batteries and phase change materials, allow households to store the heat energy generated during those low-cost and low-carbon hours for later use.
A Kensa shoebox installation.
Laying the grounds for a low carbon future
All the evidence shows that shared ground arrays are the lowest cost way of delivering GSHPs and a street-by-street approach, beginning with the areas with the most suitable geology, surface features, or sources of waste heat, is the sensible place to start, as these are most conducive to lower-cost installations.
The industry is calling on the government to recognise that the ground source heat pumps are the best low carbon heating solution available, and by providing the right support they can unlock the potential of shared ground array infrastructure, allowing the industry to rapidly and effectively scale up to reach the volumes needed to deliver 600 000 heat pump installations a year.
Read the article online at: https://www.energyglobal.com/special-reports/06012021/a-heat-pump-by-any-other-name/