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Community heating – the green options

The UKs ‘zero carbon’ house programme, should see a mix of electricity and heat supplying on-house technologies including photovoltaic (PV) panels, solar heat collectors, biomass-fired CHP units and heat pumps. In addition we now have a Renewable Heat Incentive, which from Oct next year, should also see the wider adoption solar collectors, biomass , heat pumps and so on.

While it is sensible to try to get house energy efficiency up to the maximum possible and to use local energy sources wherever available to meet the needs of individual houses, there are other more collective approaches, supplying groups of houses, whole communities or even cities. The RHI can be used for some community scale projects, so they may prosper, and we might see some innovative ideas.

As I discussed in an earlier Blog, elsewhere in Europe district heating networks are common and some make us of solar and other green energy inputs- and they include systems with inter-seasonal heat stores. http://environmentalresearchweb.org/blog/2011/01/green-heat—-district-heating.html

That idea is now being taken up in the UK, for example, for large school premises. ICAX have developed an Inter-seasonal Heat Transfer system, which includes a ‘Thermal Bank’, used to store heat in a very large volume of earth for a period of months, as distinct from a standard heat store, which can hold a high temperature for a short time in an insulated tank.

The ICAX system involves capturing heat energy from the sun via a collection pipe network just beneath the surface of black tarmac roads , or car parks or school playgrounds, and then storing it in the ground under the foundation of buildings. It is then released to heat the buildings in winter via heat pumps linked to underfloor heating.

ICAX say ‘unlike a normal ground source heat pump which typically starts with an autumn ground temperature of 10°C, the heat pump in an Inter-seasonal Heat Transfer system starts with a temperature of over 25°C from the Thermal Bank. This doubles the Coefficient of Performance of the heat pump and allows a 50% saving of carbon emissions compared to providing heat from a gas boiler’. They add ‘Where it is not practical to create a horizontal Thermal Bank to store energy, ICAX uses a borehole field to perform the same function.’ www.icax.co.uk/interseasonalheattransfer.html

Interestingly, summertime solar heat storage has also been put forward as a way to heat parts of the tarmac at Heathrow airport in winter- to reduce icing up of the aircraft stands. That, you may recall, was a major issue last winter.

However if the UK summer is not seen as reliable enough for winter heating of buildings or whatever, then how about wind-powered district heating? The Danish District Heating Association says that more than 20 partly wind powered heating element systems, with a total capacity of more than 200 MW, will have been installed in district heating plants by the end of this year. They can be powered using surplus electricity from Danish wind turbines- the energy thus being stored as hot district heating water. Heating elements work like giant immersion heaters, which can automatically heat water when there is surplus power. The system regulates itself based on electricity prices. When wind power is available, the heating elements are switched on, the district heating plant’s own electricity-generating plants are switched off, thus saving on fossil fuel use.

This may be an advanced idea, but District Heating networks in the EU are increasingly supplied using green sources. For example 62% of Danish households are linked to district heating, supplied from gas-fired CHP plants, but also from surplus heat from industrial production, solar heating and waste combustion. And there are plans to increase to solar share to 40% by 2050. www.solar-district-heating.eu

It’s the same in the Sweden. The district heating sector there achieved a market share of 60% during 2008 in the heat market for buildings in the residential and service sector, using a mixture of waste incineration, industrial surplus heat, biomass, with only limited fossil CHP. And in recent years, this fossil CHP has been replaced by biomass CHP. Overall carbon dioxide emissions are now claimed to be more than 80% lower than in other European cities and towns using natural gas and fuel oil to heat buildings. It now supplies over 50TWh p.a. The majority of the plants feeding the DH systems use wood and peat (30TWh p.a). 94% of multi-family houses are connected and 78% of public and commercial premise.

District Heating is cost effective. For example, a paper in Applied Energy 88 (2011) 568-576 puts the marginal capital cost of DH distribution at only 2.1 €/GJ, which means energy at around 4.8p/kWh. And in the Netherlands, CHP/DH was found to be one of the least cost carbon abatement options at 25 EUR per tonne CO2, lower than building insulation, condensing boilers and wind power. www.ecn.nl/docs/library/report/2004/c04040.pdf

We may yet see it in the UK- the Renewable Heat Incentive does support district and community renewable heating, and the UK Energy Technologies Institute is looking at inter-seasonal heating storage systems, as I noted in an earlier Blog: http://environmentalresearchweb.org/blog/2011/01/green-heat—-district-heating.html

There are some examples already. The University of Warwick has a 4.7 MWe 14MWTh Combined Heat and Power (CHP) system, linked to an extensive district heating network around the campus, which supplies 50% of campus power and reduces overall energy use by up to 34%, compared to separate electrical and heat generation. It also uses thermal energy storage (in a water tank) to meet peak heat demand and also allow for power generation when demand is low, without any heat dumping. http://www2.warwick.ac.uk/about/environment/energy/chp

Finally, ‘DH’ may not be the most riveting of subjects graphically, but it’s brought to life in a fun, if simple, Danish animated video: www.youtube.com/watch?v=IysslE4OvKI

Posted by Dave Elliott on July 2, 2011 12:27 PM | Permalink