Case Study on Wood Heating at Coillte HQ

As the state forestry company and the country’s largest land-owner Coillte recently decided to re-locate its corporate headquaters outside Dublin to an already existing eight – year old timber building in Newtownmountkennedy. The building was designed by the Architects ‘Stewart & Sinnott and was constructed by Griffner Coillte. A new joint venture company, Griffner Coillte is jointly owned by Coillte and the Austrian timber frame company ‘Griffner Haus’ and has its new manufacturing facilities at Mullingar, Co Westmeath. Griffner had already established its reputation for building ecologically sound buildings for private housing. This proved an opportunity for them to become involved with the commercial end of the market. The property is Coillte’s show case building displaying best practice in the use of Renewable Energy technologies. It was important then that both wood and solar energy be used to heat and power the new building. The site which houses 100 employees has evolved into a low energy building with very effective wood heat generation combined with solar power.

The new two -storey building is approx 16,800 sq ft (including a basement of 4,500 sq ft) and is linked to the current timber frame building which was built in 1996. While the existing building was ahead of its time in terms of demonstrating best practice in timber building technology, the new one seeks to build on this experience and to demonstrate best practice in all around sustainable design with the primary building material being timber from sustainable sources and insulation using recycled paper product to levels better than current building regulations.

The building is designed with a narrow plan to encourage natural cross ventilation via opening windows. The windows are designed to have different opening positions to provide trickle / background ventilation in Winter, minimal ventilation in Spring and Autumn and large full opening areas for Summer ventilation. High level windows are motorised and can provide secure night time cooling in Summer as required. A generous brise soleil (overhang) has been provided at roof level to minimise high angle summer solar gains whilst allowing the gains from low angle sun to help heat the building in Winter. High level windows in the sloping roof also have inbuilt retractable external blinds to reduce solar gains in Summer but without daylight or heat penalty in Winter.

The demand for mechanical cooling is therefore removed and in addition the high insulation levels ensure very low heat demands in Winter.

The primary heat source are from two arrays of solar thermal panels – a flat plate array and an evacuated heat tube array. The heat is stored in a large buffer vessel that is topped up as necessary from a wood burning boiler which was supplied by the Austrian company KWB. The heated water is stored in a 1500 litre buffer tank situated inside the energy centre. However the system's buffer capacity is 2250 litres because the large, highly insulated pipe which connects the energy centre with the main building (they are 100m apart) also acts as a buffer vessel. "Using the underground pipes as extra buffer capacity saved money and space," says Rob Ruttledge, of Buro Happold, who designed the system.

The water heated in the energy centre flows directly to a manifold in the main building. From there it is pumped to different parts of the building and back to the energy centre for reheating. The system is programmed to heat the water to 55 degrees Centigrade.

The level of insulation in the 1500m² headquarters means that heating requirements are lower than a building which only reaches minimum building standards. Nevertheless the volume of radiators and baseboards is slightly greater than normal.

One challenge posed by programming the system at 55 degrees was how to bring hot water to the canteen and bathroom taps. An initial suggestion was to use individual electric heaters under each sink to boost the water temperature. However this would have required extra energy input.

The solution was to install heat exchangers in each toilet area and in the canteen. These extract heat from the closed heating circuit and use it to heat fresh water for the sinks.

The aim of the system, other than simply heating the building, says Ruttledge, is to demonstrate that integrating solar thermal panels and a biomass boiler is a viable option. The main benefit is that the solar thermal panels, which are carbon neutral, will cover the vast majority of the heating load other than during three or four months of the year.

According to Billy White, Head of Group Compliance and Facilities with Coilte; "It's a renewable resource and there's no doubt as we go into the future and as oil becomes dearer this is going to become more and more cost effective,"

In terms of cost the wood boiler was 24,000 euro, with an extra 3,500 euro for installation.

Given that the system has only recently been commissioned it is too early to say what lessons have been learnt. However Ruttledge says it is important to put a lot of research into how best to integrate a system. But there is "absolutely" no reason why it couldn't be replicated elsewhere, at either a smaller or larger scale, he says. Wood heating in large buildings is an important potential market in Ireland as more than half of building’s energy goes on heating alone. Potential customers in the large buildings sectors (schools, hotels and hospitals) can now opt for high quality, automatic wood heating.

The boiler (which has been sized to allow the current building of 10,000 sq ft to be linked to the system) is of 100kW capacity and will be capable of utilising either wood pellets or wood chips. Currently Coillte imports the wood pellets however this will change once Balcas open Ireland’s first wood pellet production plant at the end of the year. Balcas is one of Ireland’s largest wood products suppliers and their extensive product portfolio includes construction timber, fencing products, internal mouldings and pallet and packaging products.

All of these systems are located in a purpose made energy centre which will contain full monitoring and feed back facilities and be open to the public for education and demonstration purposes. The storage area beside the boiler room stores twenty cubic metres of pellets and needs to be filled twice a year. Ash is removed once a month. Natural Power Supply is responsible for maintenance of the boiler.

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