Ground Source Heat Pump Comparisons

Trying to find the best heating system for your property? Thanks to the efficiency of ground source heat pumps, running costs can be reduced by as much as 30 – 50% compared to fossil fuels. See how they compare to other heating systems:

•  Air source vs. ground source heat pumps

•  Oil & LPG boilers vs. ground source

•  Geothermal heating vs. ground source

•  Biomass vs. ground source

Kensa Ground Source Heat Pumps Diagram for Self Builds and Renovations with Renewable Heat Incentive

What is the best heating system?

Ground source heating

A ground source heat pump delivers the best low-carbon heating. It’s an affordable and eco-friendly alternative to fossil fuels such as gas, oil and LPG, which typically contribute to carbon emissions, air pollution and ultimately, play a part in climate change and global warming.

Achieving a net-zero carbon future

Heating and hot water make up 25% of total energy use in British homes, equating to 15% of our greenhouse gas emissions.¹ To reduce the UK’s carbon emissions, the best heating systems are being encouraged by the government.

This starts with the proposed ban of fossil-fuel heating in domestic new-build properties from 2025 – forming a part of the government’s plans to achieve net-zero by 2050. Gas and oil boilers are some of the fossil fuel systems that the government hopes to ban from 2025.

What is a heat pump?

In brief, a ground source heat pump will:

See how a heat pump works

What are the advantages of ground source heat pumps?

The advantages of ground source heat pumps vs. other heating systems include:

  • No planning permission required
  • Quiet operation
  • Safe and easy to operate
  • Simple to install
  • No risk of vandalism or theft
  • No noxious gasses or risk of combustion
  • No point-of-use emissions such as Nitrogen Oxide (NOx), Sulphur Oxide (SOx) or Carbon Dioxide (CO²)
  • Can be used to provide passive and active cooling.

Having a ground source heat pump means the property is much more energy efficient and less reliant on fossil fuels.

Alistair Mackintosh, Selfbuilder

Air source heat pumps vs. ground source heat pumps

Although both air source and ground source heat pumps are renewable alternatives to fossil fuels, they hugely differ in efficiency, running costs, carbon savings and durability.

Unlike air source heat pumps, the inherent efficiency of ground source heat pumps means they can deliver the lowest running costs of any type of heating system and the best return from the RHI – giving you payback on your investment typically in 5 or 6 years.

Main disadvantages of air source heat pumps

 

  • Winter and night-time efficiency affected by colder air temperatures, increasing running costs
  • Planning permission required due to outside installation and noise
  • Exposure to the outside elements can lead to regular maintenance and reduced lifetime
  • Realistic outputs limited to ~11kW, which restricts potential to smaller homes.
air source heat pumps issues compared to ground source heat pumps

Efficiency of air source vs. ground source

Air source

Air source heat pumps use heat energy from the air to compress or ‘pump’ higher temperature heat into a building. The efficiency of an air source heat pump varies across the seasons. They can be problematic in winter because when you need heating the most, the air – its source of energy – is at its coldest.

Going by generous and often unrealistic testing conditions, the efficiency of air source heat pumps can be deceptive. Their performance is based on an inlet temperature of 7°C, which could be very different from reality if the air temperature fluctuates. On the other hand, ground source heat pumps are tested by their performance when collecting an inlet temperature of 0°C – representing true climate conditions.

While air source temperatures can fluctuate considerably, the ground can maintain temperatures of 8-12°C all year. This suggests that figures show an unfair representation of true performance, with air source possibly requiring more electricity to produce heat due to inefficiency.

Ground source

The average ground temperature in winter will always be significantly warmer than the average air temperature. This means the ground source heat pump does not have to work as hard to upgrade the source’s energy into usable heat for space heating and hot water – making ground source more efficient for heating and hot water systems.

Unlike air source, a ground source heat pump also offers efficiency in terms of operational times. Using smart controls and dynamic tariffs, a ground source heat pump can participate in load shifting, where times of electricity consumption can be shifted to low-cost or low-carbon hours.

Upfront cost of air source vs. ground source

Air source heat pumps are typically cheaper than ground source heating systems, as you only have to pay for the unit itself. A ground source unit, however, comes with the additional cost of groundwork and ground arrays.

The cheaper upfront cost of air source heat pumps seems appealing in the short term. Unfortunately, any savings could be quickly negated by higher running costs due to lower efficiencies, half the lifetime vs. ground source, and a lower income from the RHI.

Both forms of heat pumps share the same costs when it comes to the internal heating distribution system, such as radiators or underfloor heating.

Running costs of air source vs. ground source

Ground source

Ground source heat pumps offer the lowest running costs compared to any type of heating system, producing up to four times the energy they absorb.

To minimise running costs even further, ground source owners can take advantage of time-of-use tariffs. The heat pump can shift its electricity consumption to times when the demand and cost of electricity are at their lowest, such as overnight. An owner could actually recharge the hot water cylinder through the night – ready to use the next day for a cheaper price.

Air source

Due to the lower efficiency of air source heat pumps, the same amount of energy you’d get from a ground source system could end up costing more.

Another disadvantage is that air source heat pumps are ineffective with time-of-use tariffs. The air temperature is usually significantly cooler at 2 am – when the tariff is likely to be cheaper – than 2 pm, meaning an air source unit will operate at its lowest efficiency through the night.

Meanwhile, the prevailing air temperature does not impact the performance of a ground source heat pump, as the ground arrays are buried at sufficient depth and insulated from such fluctuations.

RHI Income for air source vs. ground source

Ground source heat pumps have the highest RHI tarrif compared to any other renewable heating system.

Compared to air source heat pumps, the superior efficiency of ground source maximises returns from the RHI. With quarterly payments that typically pay back your investment in five or six years, ground source heat pumps also qualify for a higher RHI tariff than air source heat pumps.

See how much you could earn

Installation of air source vs. ground source

Air source

A heating-only air source heat pump is simple to fit outside of the property. Unlike a ground source heat pump, there is no need for ground arrays such as trenches or boreholes. It even has the benefit of coming ‘in a box’ like any other heating appliance and therefore needs no ground installation expertise.

However, when you factor in planning permission, installing an air source heat pump can be a long-winded process. The majority of air source heat pumps require planning permission because they’re particularly noisy and must be fitted outside of the property. It doesn’t help that they have to run throughout the night to maintain adequate temperatures, meaning the noise will occur when the household and neighbours are trying to sleep.

Ground source

The groundwork for a ground source installation is completed outside the property by specialist subcontractors, with minimal disruption and a flexible schedule to suit residents. Once the groundwork has been completed, installing the ground source heat pump is no different to fitting a traditional boiler in an airing cupboard or cabinet.

Designed to be installed inside, most ground source heat pumps run quietly and discreetly. In fact, our Kensa Evo heat pump is one of the quietest on the market – equating to the sound of a dishwasher.

The unobtrusive nature of a ground source installation is an attractive feature for many properties. A ground source heat pump generally doesn’t require planning permission, avoids visual pollution and runs durably from the comfort of the building.

Ground source slinky trenches

Find a ground source heat pump installer

Carbon emissions of air source vs. ground source

Due to its inherent efficiencies, a ground source heat pump is the lowest carbon heating system. Under the Standard Assessment Procedure (SAP), a rating of a property’s energy efficiency from 1 – 100, the default value of ground source efficiency is 320%, while air source is 250%.

This shows that the more efficient a system is – through crucial elements such as design and installation – the lower its carbon intensity can be. The choice of variables such as the heat distribution system and the heat source can make a significant difference.

Lifetime of air source vs. ground source

An air source heat pump tends to last about 10 years due to its exposure to external elements.

Doubling the lifetime of an air source heat pump, a ground source unit is a closed system that is installed inside the property. The unit itself has a design life of 20 years, while the ground array it’s connected to can last over 100 years.

See lifetime savings on our pricing page

Oil & LPG boilers vs. ground source heat pumps

Oil and liquefied petroleum gas (LPG) is traditionally the go-to alternative fuel for buildings that are not connected to mains gas. However, prices of oil continue to fluctuate against a backdrop of growing global concerns – particularly energy security.

Meanwhile, heat pump technology has evolved, along with guaranteed RHI income and affordable running costs. Ground source heat pumps have therefore become a more viable and preferred option for off-gas areas.

Add to this the pressure of government plans to ban fossil-fuel heating systems in new builds from 2025, and it looks like oil and LPG boilers could be phased out entirely by 2050.

Disadvantages of oil & LPG boilers

  • Vulnerable to energy price hikes and fluctuations
  • Bulky and unsightly fuel storage tank
  • Highly flammable
  • Reliance on fuel deliveries
  • Possibility of fuel theft
  • Pay for the energy upfront all in one go
  • Complicated installation
  • Contributes to air pollution through the emission of particulates, Nitrogen Oxide (NOx) & Sulphur Oxide (SOx)
  • High carbon content.

Unsightly tank

Running costs of oil boilers vs. ground source

Oil boilers

There are a number of factors that make oil prices volatile. The price of crude oil is particularly sensitive to the laws of supply and demand, which can vary worldwide with fluctuations in the economy, political unrest and extreme weather events.

Supply can be influenced by the Organisation of Petroleum Exporting Countries (OPEC), who will cut output in order to strengthen prices by reducing supply.

Ground source

Ground source heat pumps can save occupants around 30 – 50% in running costs compared to oil boilers. Electricity prices, as used to drive a ground source heat pump, do not suffer from the same volatile prices.

Aside from a ground source heat pump’s inherent efficiency, delivering typically 3 to 4kW of free heat energy for 1kW of electrical energy and making the use of off-peak tariffs in well-insulated buildings, the running costs of ground source heat pumps are significantly lower than oil boilers.

That, plus an income from the RHI, is a benefit you wouldn’t see from oil.

Combating fuel poverty & oil in off-gas areas

The savings on our energy bills compared with oil is fantastic and our house value has increased as a result of the installation - we’re over the moon!

Stephen Chidgey, Homeowner

Maintenance of oil boilers vs. ground source

Oil boilers

Oil boilers use combustion in the heating process, so they must be serviced and maintained correctly. Failure to do this can lead to major health risks, such as the production of poisonous gases like carbon monoxide.

Ground source

As ground source heat pumps do not use combustion, there is no risk of poisonous gases being emitted.

Moving parts are kept to a minimum and are non-serviceable, so maintenance is minimal. This makes ground source heat pumps significantly cheaper to maintain, saving occupants or ground source owners money by eliminating the need for annual servicing.

Lifetime of oil boilers vs. ground source

Oil boilers

These days most oil boilers are condensing boilers, as they provide a much higher efficiency than non-condensing boilers. Oil-fired condensing boilers typically have a shorter life (7 to 10 years) than traditional non-condensing boilers, as the heat exchangers can rot out quickly due to the acidic condensate.

Ground source

Ground source heat pumps generally have a design life of approximately 20 years due to their lack of moving parts and secure installation inside the home.

Storage of oil vs. ground source

Oil

Oil supply for oil boilers must be stored on site. It’s generally stored in a bunded oil tank, which is basically a small tank within a large tank. The larger tank is able to hold 110% of the capacity of the smaller tank. This is used to protect the surroundings of the tank from any oil spills of leakages. When storing oil, there needs to be sufficient space and access to the tank.

With OFTEC health and safety regulations stating that it must be located within 1.8m of the building, the unsightly oil tank can take away from the aesthetics of a property. As well as that, security measures against theft need to be considered if large volumes of oil are being stored on site.

Ground source

As ground source heat pumps run on electricity, no fuel storage or deliveries are required on site – allowing for additional space, peace of mind, and preventing the need for storage that many people feel is an eye sore.

Carbon emissions of oil boilers vs. ground source

Using the carbon intensity factors proposed for SAP 10, an oil boiler emits almost five times as much carbon as a ground source heat pump.

In terms of carbon emissions, there is no justification for the use of oil or LPG boilers when far more appealing and renewable heating options are available. This is why the government is phasing out oil boilers in favour of lower carbon renewable heating systems such as ground source heat pumps.

Can a heat pump replace an oil boiler?

Yes. For older properties that are not especially well insulated, Kensa will help you to establish whether the existing heating system and existing insulation levels will be compatible with a ground source heat pump, or if your heating distribution system and energy efficiency measures require any upgrades.

If you are undecided on whether you should upgrade your radiators or insulation levels, you can run a trial over a heating season. To do this, we recommend you turn down the flow temperature of your existing boiler to 50°C and run the system through the winter heating season to mimic the output of a ground source heat pump system.

If you find you can maintain your required comfort conditions at this lower flow temperature, then you have proved that your existing heating distribution system and the current heat loss of your property is compatible with a ground source heat pump installation – without any upgrades required. If you were not satisfied with the comfort levels then we advise you to upgrade your radiators, and improve the insulation levels in the property prior to installing a ground source heat pump.

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Geothermal heating vs. ground source heat pumps

What is the difference between ground source heat pumps & geothermal heating?

There is often much confusion when it comes to comparing ground source heat pumps to geothermal heating. Some people use the terms interchangeably, but there are key differences:

  • Geothermal heating uses heat directly from the earth’s core, such as hot springs, geysers and volcanic hot spots.
  • Ground source heat pumps absorb the sun’s energy stored in relatively shallow ground and upgrade this for use in domestic and commercial applications.

Ground source heat pumps, like those manufactured by Kensa Heat Pumps, generally take heat from 1.2m – 200m depths. In this zone, there is a large amount of low-grade energy available, which needs a heat pump to upgrade this to more useful temperatures.

The reason geothermal heating is often confused with ground source heating is that both ultimately harness heat energy from the ground to provide heating and hot water to buildings.

However, the main differences are where the heat originates and the application the heat will be used for.

What is geothermal heating & how does it work?

Geothermal heat comes from the earth’s core; ‘geothermal’ literally means ‘earth’s heat’. It uses heat directly from drilling deep or shallow sources emanating from the earth’s core, such as hot springs, geysers and volcanic hot spots.

Borehole drilling for geothermal heating can often be drilled to depths many kilometers below the ground. In the UK, you have to go down 500m – 2500m before there is any appreciable input from the earth’s core. Geothermal typically needs to be deployed at large scales to make it financially viable.

Geothermal systems operate at temperatures of 120°C – 300°C and therefore do not necessarily need a heat pump to upgrade the heat, nor a ground loop system.

Large-scale plants and communities tend to use geothermal energy over ground source heat pumps.

Ground source heat pumps vs geothermal heating - A geothermal power plant

Why does the difference between geothermal & ground source matter?

The supply of geothermal energy is virtually infinite, while the solar energy used for ground source heat pumps is finite and very measurable. This means that geothermal systems do not require the high degree of design accuracy that is required of ground source heat pumps.

Ground collectors for ground source heat pumps must be accurately sized to ensure the system is not taking more heat from the ground than can be naturally replenished by heat energy from the sun or rain. The ground arrays are sized to meet the heat needs of the building; geology and the ground condition’s thermal conductivity are taken into account when sizing the ground collector.

What are the other common names for ground source heat pumps?

The following terms are sometimes used when referring to ground source heat pump installations, and can be misleading and technically inaccurate due to their ‘geothermal’ references:

  • Geothermal heat pumps
  • GeoExchange heat pumps
  • Earth-coupled heat pumps.

Other less commonly used terms for geothermal heating include:

  • Deep geothermal
  • Enhanced geothermal systems
  • Geothermal, direct use
  • Hydrothermal
  • Hot rocks
  • Hot dry rocks
  • Geothermal power.

Biomass vs. ground source heat pumps

Disadvantages of biomass heating compared to ground source heat pumps:

  • Space required for fuel storage
  • Reliance on regular fuel deliveries
  • High maintenance compared to ground source heat pumps
  • Planning permission required due to emissions
  • Contributes to air pollution through the emission of particulates, Nitrogen Oxide (NOx) & Sulphur Oxide (SOx).

References

  1. UK housing: Fit for the future? Committee on Climate Change, 2019