Perthshire Self Builder Low Energy Home
Having previously self built four properties, the owners of this pioneering low energy home were keen to build their final house to meet their current, and more importantly, their future needs.
After much searching, the owners found a half acre site in Perthshire. To take advantage of the views afforded by the site, and to ensure they ended up with a house specifically designed for their needs, the owners bypassed the usual architect, completing all design and planning work themselves. Specifying a super insulated / air tight building system (timber frame injection filled with polyurethane insulation) as a way of exceeding building regulations and lowering running / heating costs, the owners contracted out the building work to a local firm they had used previously.
With mains gas unavailable, the owners looked to new technology to provide their hot water, heating and ventilation. After much consideration, the owners specified a NIBE F470 Exhaust Air Heat Pump, as an all in one, fully programmable and automated heating, hot water and ventilation system. Paired with a small wood-burning stove, the owners were confident that they were prepared for the worst a Scottish winter could throw at them. They were soon put the test with one of the coldest winters on record following completion of the build in November 2010! Their super insulated home quickly proved itself over that winter, with heating costs being a quarter of those previously experienced by the owners in other houses they had lived in. A constant 19 degree internal temperature has been maintained by the NIBE F470 since the house was completed. Additional heat is provided by the wood-burning stove. When lit, the wood-burning stove quickly lifts the internal temperature to 21 degrees or above and reduces the energy used by the NIBE F470. The mechanical ventilation with heat recovery (MVHR) delivered by the NIBE F470 ensures that moisture is extracted from the house and provides a very pleasant and healthy indoor climate.
A 3.6kW solar PV array generates an estimated 3400kWh /year which means that income from the Feed-in Tariff nearly covers the cost of the family's energy bills.
Solar PV is an excellent combination with heat pumps which use the electricity generated through the day to produce heat. The more electricity generated from the Solar PV used by the household, rather than being exported, the greater the savings since this is electricity that would have had to be bought from the grid.
Summary of Energy Use over 2 Years
Logs for Wood-burning Stove - space heating
2010/2011 2.25 m3 used
2011/2012 0.75 m3 used
NIBE F470 - space heating, domestic hot water, ventilation
2010 / 2011:* Compressor heating 4520 hrs, DHW 2845 hrs, Immersion 622.5 hrs
2011 / 2012:** Compressor heating 4526 hrs, DHW 3031 hrs, Immersion 582.2 hrs
Average: Compressor heating 4523 hrs, DHW 2938 hrs, Immersion 602.3 hrs
*2010/2011, wood burner on every day during the cold snap so timber use (% of heating provided) probably higher than 10% of heating demand. Probably balances out over the two years.
**2011/2012, included some experimentation (programming higher water temp for off peak electricity, increasing ventilation rates etc) and minimal use of the wood burner.
The average cost for delivering heating, hot water and ventilation to the house has been £585 / year.