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When it comes to reducing a school’s carbon footprint, one of the first places to look is at the heat sources for hot water and heating, says Ian Dagley of Hoval
 In the last couple of years there has been a marked change in the way people talk about energy consumption. The amount of energy consumed is still important, of course, but it’s also important to consider the source of that energy. And ‘green’ is the order of the day.
When it comes to using ‘green’ energy in schools, it makes sense to pay particular attention to ‘energy-guzzling’ services such as heating - and wood burning biomass boilers are proving particularly suitable for many projects.
Wood pellet boilers
A case in point is Pontllanfraith secondary school, where Caerphilly Council has replaced four old coal-fired boilers with three 350kW STU wood pellet boilers, manufactured by Hoval in the UK. A major benefit of using wood pellets, rather than wood chips, is that the pellets are a consistent size and easier to feed to boilers using automatic stokers and feeders in response to heating demands. The boilers at Pontllanfraith are linked to a control system which brings them on in sequence as and when required.
Crucially, in terms of minimising the carbon footprint, the wood pellets are derived from sustainable sources and are classified as ‘carbon-neutral’. This is because the carbon dioxide they produce during combustion is equivalent to that consumed by the trees during growth.
A further benefit to Caerphilly Council is an increase in energy efficiency. “Although wood has a slightly lower calorific value than coal, the new Hoval boilers are more than 90 per cent efficient, compared to the 68 per cent efficiency of the coal-fired boilers, so we are achieving significant improvements in efficiency,” commented John Davies of Caerphilly Council’s Property Service’s department.
Becoming carbon neutral
In some situations it may also be possible to combine biomass boilers with other renewable energy sources, such as solar heating, along with other sustainability features. A new building for Bowbridge Primary School in Newark, for example, comes very close to being carbon-neutral by using a range of techniques. These include a Hoval biomass boiler, solar water heating, rainwater toilet flushing and a sedum roof. The building has also been designed to make full use of natural daylight and non-mechanical ventilation. Sourcing products locally was also important, so the fact that Hoval’s biomass boilers are manufactured in Newark was a definite bonus.
“We evaluated fuel costs and found that as gas prices continue to rise, the wood pellets are on a par with gas and are set to become cheaper,” head teacher David Dixon explained. “The boiler is also very easy to use as it has automatic fuel feed and ash removal. The wood pellets will be stored in a specially-constructed transparent pellet hopper so that people can see how it works,”.
Solar heated hot water
When solar heating is used for hot water it will, on sunny days, heat all of the water to the required temperature. When less solar energy is available it may be used to pre-heat mains cold water before it is brought up to temperature by another heat source, such as a biomass boiler.
In these circumstances it is beneficial to store the solar energy in a thermal storage vessel and pre-heat the cold feed water through a suitable heat exchanger. Hoval’s recently launched Combisol thermal storage vessel, for example, allows various renewable and conventional heat sources to be easily combined – and controlled effectively - in a single system for space heating and hot water. Suitable heat sources include solar panels, heat pumps, biomass and gas or oil boilers (condensing or conventional). An immersion heater can also be installed for hot water, if required.
Solar heating is also good for swimming pools because the pool acts as a large heat sink, so there is no need for thermal storage vessels, and the relatively low operating temperatures (typically 26-30°C) are easily achieved.
Where there are high demands for hot water, the most efficient solution could be to combine these renewables with conventional condensing boilers. The solar heating and biomass boilers can be used for hot water while the condensing boilers supply the space heating and take full advantage of the low water return temperatures to achieve maximum efficiency.
Technology working in harmony
Undoubtedly, the specifics will vary from project to project, but the challenge will always be to ensure that these different technologies work in harmony to give the best results and the lowest carbon footprint. Thanks to sophisticated control systems designed for that purpose, such as Hoval’s TopTronic controllers, this is now readily achievable; so that the most appropriate technologies can be deployed for each project.
For more information
www.hoval.co.uk
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