Monday, March 7, 2011

Retrofit with GSHP

EcoBuild note: DNC writes: There were some good lectures and seminars, including Retrofit topics. One that I liked was one from Robin Curtis of Earth Energy with advice on retrofitting with ground source heat pumps. I have always thought this would be too difficult, due to the need for a borehole and the need for underfloor heating, and the bulkiness of the GSHP - difficult to fit to an existing house. But it is not as tough as I thought, and the Penwith Housing association (HA) has done it on a huge scale in Devon and Cornwall, with social housing. (This talk is due to be on the EcoBuild site as a PDF and I will download it when possible).

Borehole or horizontal?: Certainly, ground based horizontals are difficult to fit because it is unusual to have enough space in the garden to bring in a JCB and churn it up to the required depth. A vertical borehole is a very quick and tidy solution, and yes it is expensive - a bit like root canal therapy in dentistry, painful, but once it's done it's done. And then provides several hundred years of free heat.... If there is no access to the rear of the house, it can be done in the front driveway! I have never regretted getting the borehole at the Peveril Solar house. It has been instrumental to making my Solar Charging project work.

Underfloor or Radiators?: Underfloor has always been more efficient at distributing heat from a Heat pump because they work more efficiently if they don't have to heat above 35-40 degrees. But for those contemplating retrofit, there is an answer, and it doesn't have to be gigantic wide aluminium radiators as is often thought.
   If you are replacing night storage heaters, you already have electric points but need to add water pipes. If replacing water radiators, you already have the pipes and the circulating pump, but need to add nearby electric points.
  The space may be limited to the size of the previous radiator. With the circulating temperature at only 35-40 degs, you can put in a fan assisted radiator of nearly the same size as your existing high temperature one. The huge annual savings in overall energy cost justifies the consumption fan assisted radiator, one of the same width and height as the previous, but with a very quiet low wattage fan which comes on when the thermostat deems it necessary.
[postscript: Jaga and Dimplex make these type of radiator.]

Space for the GSHP?: We are familiar with Air source heat pumps being placed externally, but GSHPs need better protection, so usually go indoors. If they will not fit indoors, the Penwith HA have retrofitted many houses with GSHPs using a small lockable prefab garden store from B and Q, just large enough to hold the pump, and this can be close to the external wall in a suitable place. It can be insulated to reduce heat loss from the connecting pipes etc. 

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