Air Versus Ground Source Heat Pumps, Energy Efficient Air or Water Heating and Cooling

Air source heat pumps (ASHP) and ground source heat pumps (GSHP) are exactly the same, they are very energy efficient in providing cooling and heating, use refrigerant to transfer energy from inside a building to the outside and they are either air to air or air to water cooling & heating. The difference between an ASHP and a GSHP, is that the heat pump's either get their outside energy (heat) from the ambient air temperature or the ground ambient temperature.

In the UK, air temperature ranges average from -0簞c to 30簞c, the ground is around 10簞c to 16簞c at 3m depth and can be 20簞c at depths of 50m. As you can see, the air has a larger variable than the ground, which allows the manufacturers to get very high efficiency ratios in the GSHP as compared to the ASHP, as the smaller temperature variable allows the system to be fine tuned within the 10簞c variable for GSHP, than the 30簞c variable for the ASHP.

ENERGY EFFICIENCY

So, the GSHP is the best, right!? Well, let's look at the efficiency ratios, they are defined for heating as Co-efficiency of Performance or CoP and for cooling is Energy Efficiency Ratio or EER. CoP and EER are basically the amount of kW cooling or heating provided per kW of electricity consumed.

ASHP:

Heating at -5簞c outdoor ambient provides a 2.5 EER.

Heating at 7簞c outdoor ambient provides a 4 EER.

Cooling at 23簞c outdoor ambient provides a 4 CoP.

Cooling at 35簞c outdoor ambient provides a 2.5 CoP.

GSHP:

Cooling or Heating at 15簞c ground ambient provides a 4 CoP & 4.5 EER

It's long been thought that ASHP systems are not capable of working at low temperatures, this was actually the case up until recently, as the EER dropped considerably at -5簞c, as the capacity of the unit's were designed to a maximum of -5簞c for heating. Now, manufacturers have changed the design and the new lower operating design temperatures are to 15簞c and even 20簞c depending on the manufacturer.

COST

Well, this is hard to detail as each system is bespoke and engineered to each required solution, but I will try to make it simple by detailing estimated prices for an average 3 bedroom home in the UK.

Air to air ASHP @ 瞿12,000 + vat

Air to water ASHP @ 瞿15,000 + vat

GSHP with slinky @ 瞿15,000 + vat

GSHP with bore holes @ 瞿20,000 + vat

It will probably best to now look at the pro's and con's for the ASHP and GSHP, so you can understand the cost benefits or losses.

ASHP PRO'S:

• Equipment is cheaper.


• Cheaper to install, less labour time.


• Existing tried and tested technology.


• New higher energy efficiency levels.


• New lower ambient operating temperatures to -15簞c.


• Compact & low noise systems

ASHP CON'S:

• Larger variable operating temperatures


• Lower CoP's and EER's in extreme lower and higher temperatures

GSHP PRO'S:

• Constant year round and smaller variable temperature of 10簞c to 16簞c


• High CoP's and EER's

GSHP CON'S:

• Expensive equipment.


• New technology not so tried and tested.


• Large quantity of land needed for slinky or bore holes.


• Expensive to dig slinky or drill bore holes, large excavation or drilling machines.


• When drilling bore holes, it is unsure of how many drill heads will be used and they're chargeable per drill head.


• If the slinky or bore hole leaks, extremely expensive to fix considering it is buried.

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GOVERNMENT FINANCIAL ASSISTANCE

The government have introduced the Renewable Heat Incentive (RHI) to assist in the carbon reduction 2020 targets which is basically a payback scheme for buying a renewable and sustainable heating system for your home or business. The RHI only applies to air to water systems, otherwise known as ASHP or GSHP boilers.

For the home or for systems below 45kW of heating, the incentive will pay you 7.5p per kW of heat you generate in a year,

IDEAL SOLUTIONS

ASHP air to air work well in the following environments:

Domestic:

• Conservatories for energy efficient & stand alone cooling and heating.


• Bedrooms for cooling, town house top floor or master bedrooms which have high insulation and retain heat, making night times to uncomfortable to sleep.


• Home office, for the study or home worker.


• Commercial:


• Offices, retail shops etc.

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ASHP air to water work well in the following environments:

Domestic:

• Boiler replacement for existing properties, heating and hot water.


• New build installations, heating, hot water and cooling.

Commercial:

• Smaller Offices, boiler replacement, heating, hot water and cooling.


• Offices, boiler replacement for sanitary hot water.

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GSHP air to water work well in the following environments:

Domestic:

Large New build installations with acres of land, heating, hot water and cooling.

Commercial:

New build offices with acres of land, boiler replacement, heating, hot water and cooling.