Heat Pumps

Heat pumps work like fridges in reverse. Powered by electricity, they concentrate heat from the air or the ground to heat your house and your hot water.  And if you switch to a green electricity tariff, you will be heating your home without carbon emissions.

Air Source Heat Pumps

Air source heat pumps are units that sit outside your house extracting heat energy from the air.  They can do this even when it’s below zero outside.  Key points:

  • They are less efficient than ground source, but much cheaper to install.
  • RHI grants will repay you quarterly amounts for 7 years.  Exact amounts depend on the system design, but find out roughly how much grant you get here.
  • The pumps that extract heat from outside are powered by electricity.  This means that if you choose a green tariff, buying electricity from wind farms etc, your heating will be zero carbon.
  • The running costs (in electricity) are said to be roughly the same as using gas.
  • They are now very quiet, so unlikely to be a noise issue for you or the neighbours.
  • Most heat pumps produce relatively low temperature water – around 40 to 50 degrees.  This works best with underfloor heating.  If you don’t or can’t have underfloor heating, your radiators will need replacing with thicker, larger radiators.  This can be quite expensive, and compromise your room layouts.
  • There are now high temperature air source heat pumps available, producing water up to 75 degrees, avoiding any changes to your radiators.  Until now, these have been less efficient, and more costly to install.  But there’s a new generation coming out in 2020 that are claimed to be much more efficient.  Awaiting costs.  This looks like a very interesting development.  Running costs could start beating gas.  Info here.
  • Heat pumps generally require the heating to be on for longer, because the temperatures are lower than from oil or gas.  If you have smart controls on your radiators which automatically heat up only the rooms you need to heat, a high temperature air heat pump is probably better, as high temp heat pumps operate at similar temperatures to traditional boilers.
  • In freezing conditions, the outside unit detects any build up of ice on the blades, and will momentarily run in reverse to clear it.

Ground Source Heat Pumps

Ground source heat pumps use an extensive network of pipes buried in your garden or a field to extract heat energy from the ground.  The pipes are generally laid around 60cm deep.  Alternatively you can install the pipes vertically in a series of boreholes (very expensive).  They work even when it’s below zero outside.  Key points:

  • More efficient than air source as the ground temperature is more stable through the winter.
  • The heat you extract is solar energy, not geothermal.
  • The pumps that extract heat from outside are powered by electricity.  This means that if you choose a green tariff, buying electricity from wind farms etc, your heating will be zero carbon.
  • Significantly costlier to install, including significant groundworks with a digger to install the pipes.  But probably cheaper over the long term due to lower running costs and higher grants.
  • If you’re already digging up the ground, it won’t cost much more to lay the pipes.  Really worth considering ground source for new houses or with significant extensions.
  • Running costs are lower than air source, so lower than gas or oil.  Which means savings to offset the higher outlay.
  • RHI grants will repay you quarterly amounts for 7 years.  Exact amounts depend on the system design, but find out roughly how much grant you get here.  The grants for ground source are around 50% higher than air source – to compensate for the higher outlay, and to reflect the higher efficiencies.
  • The heat pump along with associated equipment will be sited probably where your oil or gas boiler current is.
  • I’m not aware of any high temperature ground source heat pumps.  So to install, you ideally need underfloor heating (which operates at lower temperatures), or you will need to replace your radiators with bigger ones.
  • Life spans are longer than air source – fewer moving parts.
  • You’ll need to dig up a fair size area of ground for the pipes.

 

More detailed info at Greenmatch.co.uk

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