DESIGN MASTERCLASS 9 SUSTAINABILITY Daily Maximum Demand
By my estimate of future supply and demand, 22,000,000 homes with an average of 4 kWp PV would generate more electricity than the UK can possibly consume, negating any carbon offset potential, whilst the increase in winter demand for electric heat pumps in just two-thirds of these homes would result in a 50% increase in peak demand
140000
Current Demand Future Prediction
120000 100000 8000 6000 4000 2000 0
energy efficiency. Unlike major generators, the grid operators cannot ask millions of householders to temporarily disconnect their photovoltaics in order to balance the demand. This would create a massive,
unmanageable surplus of electricity; we cannot store electricity on that scale, so, to achieve the fossil fuel offset needed to justify zero carbon, we would have to export to countries without renewable generation. This would require 15 to 20 times the undersea cable capacity that we presently have connecting us to the European mainland. Even then, if the whole of Europe is working to similar carbon reduction goals, there may be no demand for our surplus and therefore no offset available. In winter, of course, it will still be
necessary to power the heat pumps. It is almost inevitable that, in the short term at least, this huge demand will be met almost entirely from gas-fired power stations. All renewable generation suffers problems of intermittency and requires the quick backup provided by gas, whilst it is projected to take until around 2040 simply to replace our present, obsolete nuclear capacity. Clean coal technologies are as yet unproven and almost as expensive as nuclear power. Then we need to consider the actual
performance of heat pumps in practice. Typically the quoted coefficient of performance of 3 to 5 will be measured at an outside air temperature of 5C to 7C. With well-designed new and refurbished housing there should be little demand for
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any space heating at these temperatures. The heat pumps will be required to work most at outdoor temperatures below 0C, when the performance rapidly approaches that of a direct electric heater. In fact, in many instances you may be better off, in carbon terms, with a good-old condensing gas boiler. It is conceivable, therefore, that the
current policies on zero carbon homes could actually lead to higher carbon emissions overall. This is, of course, an extreme example, but it does serve to highlight that the approaches we take in order to meet policy goals in the short term may not in fact be the most sustainable approach in the long term. We need to be aware that the directions we are taking now, through expedience, may not lead us directly to our destination, and that we may have to change direction before we can reach our ultimate goal. If we want to deliver a sustainable, low
carbon society, we simply cannot continue to act individually. We must consider all the implications to society of the decisions we make about individual buildings. We need to radically reappraise the approach that we take to design, and learn to think across a much wider range of disciplines than we are used to. Only then will we stop being mere building services engineers and become sustainable low carbon engineers. © Doug King
l Doug King is principal of consulting engineers King Shaw Associates and visiting professor of building physics at Bath University.
If we want to deliver a sustainable, low carbon society, we must consider all the implications to society of the decisions we make about individual buildings
MEMBER BOOK OFFER
CIBSE is pleased to be able to offer its members a discount during October on publications relevant to this Masterclass.
TM25 - Understanding Building Integrated Photovoltaics and KS15 - Capturing Solar Energy, can be purchased as a pair for £24, a discount of £16.
KS10 - Biomass Heating is £10, a saving of £12.
The price for non-members remains unchanged. See
www.cibse.org/bookshop for further details.
October 2011 CIBSE Journal 61
01/01/2010 15/01/2010 29/01/2010 12/02/2010 26/02/2010 13/03/2010 26/03/2010 09/04/2010 23/04/2010 07/05/2010 21/05/2010 04/06/2010 18/06/2010 02/07/2010 16/07/2010 30/07/2010 13/08/2010 27/08/2010 10/09/2010 24/09/2010 08/10/2010 22/10/2010 05/11/2010 19/11/2010 03/12/2010 17/12/2010 31/12/2010
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