Dragon Renewables were asked to provide an automated system that was as green as possible for a new-build Passive House near Ipswich. The only available fuel was electricity. We suggested an Õkofen pellet boiler connected to a Pellaqua Thermal store for hot water and heating. The Õkofen pellet boiler is self lighting and self filling and ash only needs to be removed once a month (or less frequently in the Summer).
Due to the very low heat demand in the proposed building we specified an 8kW boiler, this meant that the recovery time for the hot water would be lengthy however so a thermal store is an ideal choice to ensure plenty of mains hot water is available night and day. The advantage of the Pellaqua system is that the pump stations come pre-plumbed on the tank - this saves us installation time and the client money. The boiler computer system controls the pump stations on the store and also controls the solar thermal pump station. There is an external temperature sensor which the boiler computer uses to obtain the ideal start time so the home is always at the correct temperature in relation to the outside temperature. Having the pumps attached to the Pellaqua meant a saving of space and kept the plumbing simple. The boiler house was built as part of the home but outside the airtight layer this got round the problem of combustion air for the boiler. If the boiler was within the airtight layer it would not be possible to comply with Building Regulation requirements as having a large hole through a wall to allow combustion air into the boiler house would negate the benefits of the air tightness and result in uncontrolled heat loss.
The majority of the heat output of boiler is used for domestic hot water production however the remainder is used in two forms of heating. The first is underfloor heating which was cast into the 200mm slab allowing full use of the thermal mass of the excellently insulated concrete foundation. This is used to provide a steady background heat and to maximise thermal comfort (it is more comfortable to walk around on a floor that is at room temperature and as a result of this the air temperature can be lower). The second is the Mechanical Heat and ventilation recovery scheme (MHVR) which has a heater battery heated by hot water from the lower section of the thermal store. The MHVR extracts stale air from the 'wet' areas of the home and uses the heat in this used air to warm the incoming fresh air. When the outside temperature is very low the heater battery comes on and raises the temperature of the fresh air and stops the MHVR system from cooling the house.
The client did not want to burn pellets over the summer months so we designed and installed four Gasokol on roof solar thermal panels which are mounted on a single ply waterproof membrane. The pipes from the solar system run through the ceilings to the boiler house at the rear of the property. The solar pump station is controlled by the boiler's computer and the Pellatronic controller allows the user to interface with the heating system to see what the boiler is doing when it comes on and off and to allow us as installers to set and check all the system parameters including the solar hot water. The controller switches on the solar pump station when the solar panels are hotter than the bottom of the thermal store and switched off when it is heated up. We chose four panels on the basis of four people occupying the premises and this gave us a store size of 480 litres however the optimum size for this small boiler was 600 litres. It is always better to have a larger rather than a smaller store as the larger store will prevent the solar system from going into stasis in periods of high insolation.
Biomass Boiler and Thermal Store
Dragon Renewables installed an 8kW Õkofen auger fed pellet boiler into a new build Passive house near Ipswich. The boiler heats an Õkofen Pellaqua Thermal store to provide comfort heating and hot water.
We calculated it would need approx 4000kWhs per year of fuel. However owing to the way SAP software works the EPC calculates at 13561kWhs pa
RHI income: £1654.44 pa
Total income (over 7 years) = £11,581.00
Solar Thermal 'On Roof' Hot Water Panels
Dragon Renewables installed 4x Gasokol on-roof Solar Thermal hot water panels:
Fuel Saving: 1207kWhs
Income: 2055kWh x 0.192p/kWh = £ 394.56 pa
Total income (over 7 years) = £ 2761.92
RHI: Calculated at 19.2p/kWh
I would just like to express my satisfaction with the installation of Õkofen wood pellet boiler, thermal store and solar tubes by Dragon Contracts, initially I was very cautious with this type of installation as building my very first Eco efficient house to live in was a minefield with all the types of products on the market.
Jonathan from Dragon is very straight talking and knew what he was talking about and not just out to make a quick buck, I listened to his advice I also visited his very own eco property and now that I have had Dragon install the above I am just amazed how efficient the system is. I use between ½ - 1 bag of wood chip pellets a day only when the weather is very poor so estimated cost for biofuel equates to around £375.00 per year based on 5 months usage as for the remainder the natural sunlight provides the energy to heat my water etc even on a partially cloudy day.
Yes the initial outlay is more expensive but with rising fuel bills this is by far the best way to go. You even get grants back from the government which all helps.
For more information, or to arrange a free telephone interview about your requirements, please contact Jonathan Cooke today
Saffron Walden (01799) 598 086