Thursday, 27 January 2011
Ground Source Heat Pump @ One New Change
'One New Change', the shopping mall located adjacent to St Paul's Cathedral, opened its doors in October. Yesterday the Energy and Climate Change minister Greg Barker 'flipped the switch' to activate Europe's biggest ground source heat pump, expected to deliver between 15 and 20% of the sites energy demand. Designers had been set the task of delivering at least 10% of energy from 'renewable or low carbon' sources, so this, they claim, more than satisfies that figure. The system comprises over 60km of pipes over 150m deep into the ground.
All this sounds good right? Ground source heat pumps, Europe's biggest, must be clean as a whistle. Well hold on a second - ground source heat pumps are neither 'renewable' or 'low carbon'.
Ground source heat pumps work by pumping a refrigerant around pipework in the ground, collecting the heat from the ground (which, at just a few metres below ground level, is a constant temperature of around 12 degrees). This is then compressed, heating up the refrigerant, and passes the heat to water for useful space heating. The refrigerant is then expanded, and sent through the loop again.
'Pumping', 'compressing' and 'expanding' are not processes that occur without energy input. And in the case of GSHPs, this energy is sourced from that big dirty rock, coal. The coefficient of performance (COP) of a typical GSHP is around 3-4, meaning that for every 1 unit of electricity used, 3-4 units is obtained. Free energy no?!
No. If instead of installing this pink elephant, natural gas had been used to provide this 15-20% of demand, then there would have been very little difference in carbon emissions. This is because the process of burning coal is around 3-4 times 'dirtier' than burning gas. Heat pumps are best used in places off the grid, such as in rural areas. The only way this technology would reduce carbon emissions is if the electricity used for all this pumping, compressing and expanding was sourced from renewables - maybe used in conjunction with roof mounted PV panels (although we haven't studied the feasbility).
In our view, it is disappointing that this 'flagship scheme' should be allowed to shirk its environmental responsibilities in this manner. Once again, used in conjunction with a decarbonised grid, the system would be fantastic, multiplying renewable energy by 3 or 4 times - however, quietly using coal to power this beast and passing it off as low-carbon is an embarrassment to the sustainability credentials of our world city.