Thursday, May 20, 2010

Heatloss estimation and approx COP

19 May: I did a bit more calculation, to find out what is required to heat this house.
    This isn't as detailed as a SAP (Standard Assessment Procedure), but SAP is difficult to use when the scenario is made complex with a heatpump and underfloor heating, integrated water tank and sunboxes.
    This is using more old fashioned methods of just adding everything up, and multiplying out! - ignoring, of course, the PV roof and the effect of Sunboxes.... treating the house as just a house, not a weird research rig full of pipes and sensors!

Having worked out the heatloss, I then compared it with the electrical consumption for the previous 2 years, and came up with a very approximate COP over 2 full years from Aug 07 to Aug 09 = simply a ratio of the heat it is required to produce, compared with the electricity it actually consumed while doing it.
    This algorithm is now added to the Peveril Metering spreadsheet in case I want to elaborate it.

Future electricity calculations will be more complex, as the daily meter readings since Sept 2009 will be muddied by the fact that power is generated from the roof in daytime, and for certain periods in daytime, the meter stands still, even when appliance and the heatpump are on. We will have to apply the Feed in Tariff rule of approximately 50-50 ratio of power used in house and power sold to Grid.

Once you have insulated a house well, I now see how strong is the argument for MVHR (Heat Reclaim unit) to recycle the air. In this calculation, 4295 is through fabric losses, and 7345 through air replacement. I wish we had installed this during construction, as it so much more difficult to do later.

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