Life in an eco-house
We built a new house six years ago and it would have been hypocritical to do anything other than go down the eco route. So here's a brief account plus more detail at the end for those who want specifics.
How it started
We had been living in a house we converted from a cowshed back in 1980 and we had about a hectare of land including a small wood we had planted. We were able to get planning permission to adapt and extend an outbuilding to create a single-storey two-bedroom house with a footprint of 100 sq.m. The build took just over six months from bringing in the digger to shifting our belongings in September 2015. We sold our old house with most of the land, keeping the woodland and felling a few trees to create a garden area.
The house is approximately 40% conversion of the original brick outbuildings and 60% new build exension using timber frame, insulated to well above minimum Building Regulation requirements and designed from the start to be energy efficient and 'eco'.
The systems include underfloor heating powered by an air source heat pump, thermal and photovoltaic solar panels and mechanical ventilation with heat recovery, all in addition to the usual mains drainage, water and electricity supplies. There are no special water recycling measures but water butts collect water for the garden and the overflow keeps two ponds topped up.
Having our own supply of firewood and having been reliant on a wood-burning stove to keep us warm in previous winters, we included a small wood burner in the living area, and aside from the energy systems we included a central vacuum system and a boiling water tap to make life more convenient.
How it's going
We had to make a mental adjustment at first, coming from a rather draughty older house with an oil-fired boiler and hot-water radiators. We soon learned that heat pumps and under-floor heating work better with a hands-off approach. Basically the system is on from 6am to 10pm seven days a week all year round. Once we had calibrated the thermostats we could basically forget it. The controls switch the heat pump and heating loops on and off as needed completely automatically, keeping the house at a comfortable temperature day in and day out. The MVHR runs constantly 24/7 ensuring a supply of fresh air pre-conditioned using heat recovered from the extract air. We did turn the heating off the first time we went away in the heating season, programming it to come back on the day before we returned. Never again! It took two or three days to warm the house up again.
Over the first year we used about as much electricity as we had in our old house, but this was our total energy expenditure whereas the year before we had been spending more than £1000/year on heating oil and still struggled to keep warm in the winter.
After a hiccup at the start, when the engineers had to be called to fix a delivery fault with the heat pump it has run reliably for over six years with only minimal attention. We did get it checked after three years and it was running 'just like new'. Similarly, the MVHR is pretty much 'fit and forget' - we just need to clean the filters once a year or so. The ASHP hums away outside the bathroom when it's running but is barely audible from inside, and the house has to be very quiet indeed to be able to hear the MVHR, unless it's turned up to 'party' mode.
Back in 2015, the idea of controlling and monitoring house systems from a smartphone was pretty new. We had apps for the MVHR and the heating and I can check and adjust the ventilation system from my phone but never really need to. I could adjust the six thermostats from an app for a while - until it stopped working - but not the heat pump side of the system. The PV inverter will log data to a USB stick but doesn't have an app as I believe is the norm today.
The only system that has given any trouble is the thermal solar panels which have needed attention several times over the first six years. First, their output wasn't appearing on the controller display, then a failed air-release valve leaked fluid in the plant room, and most recently a leaking connection caused a loss of pressure shutting the system down. The heating engineer tells me they rarely fit these panels now, opting instead for a simpler approach which uses surplus power from the PV panels to heat hot water. The thermal panels are very effective when they work, but the electrical approach would be more reliable and makes sense since the house normally uses very little electricity when the sun is strong.
We light the wood burner maybe four times a year, mainly for the glow of the fire, but after an hour or two it gets too warm.
I had hoped the central vacuum would be much quieter than our old Henry, being housed in a cupboard in the car port, but it turns out most of the noise is the air being sucked up. It is, though, much less hassle and only needs emptying about once a year!
The boiling water tap is so much more convenient than a kettle and doesn't seem to use any more juice, but I did have to replace the boiler/reservoir earlier this year - more expensive than a new kettle.
I have kept a log, since moving in, of energy use and system performance and so can draw some conclusions about how the house is performing. There are some figures in the next section.
In conclusion, I can say the combination of super-insulation, orientation and design for passive heating, heat pump, solar panels, heat recovery ventilation and automatic controls works even better than we could have hoped. I'm biased of course, but I think all new houses should be built this way.
Numbers
When we designed the house the SAP (standard assessment procedure) calculation estimated the maximum monthly heating requirement to be around 1680kWh plus 190kWh for hot water and the heating engineer specified a 5kW heat pump, the smallest in the manufacturer's range and capable of producing 3600kWh over thirty days.
Over the last twelve months the heat pump has used 4292kWh of electricity to produce 7513kWh of heat - mainly for space heating but a fair proportion for domestic hot water. Averaged over the year this is 20.6kWh heat using 11.8kWh electricity per day - an average heat output of 860W and electrical consumption of 490W. At 15p/kWh the cost of heating and hot water for the year was £644.
The maximum monthly heat requirement was in January - not quite the highest ever but quite close. Over the month the heat pump used 710kWh of electricity to output 1057kWh of heat - a daily average of 34.1kWh heat from 22.9kWh electricity or 1.42kW output from 950W input.
The thermal solar panels heat the domestic hot water when the sun shines but were out of action due to faults for several weeks and produce very little heat when skies are overcast. When they were working, they produced 1070kWh of heat over the year - a little less than half the estimated requirement - with the heat pump supplying the rest.
Over the same twelve months, the PV solar panels produced 1666kWh of 'green' electricity, an average of 4.56kWh/day. Taking the average time the sun is above the horizon as twelve hours per day, this is an average of 380W. It was not the sunniest summer and the peak monthly output was 261kWh in April. The panels are partially shaded by trees (especially summer mornings) and the neighbours' house (in the winter months) so the output is less than it could be, but the theoretical 3kW output is clearly not a good guide to real-world performance.
On the whole, solar panels produce the most electricity when you are least in need of it. Excess is fed into the grid and so helps reduce overall emissions, but we now have an electric car and try to charge it when the sun shines, to make the most of the free electricity. I am also looking into the viability of a solar battery. Using surplus PV output to heat the hot water, as an alternative to thermal solar, is another way of storing energy.
Manufacturers claim that heat recovery ventilation can save 90% of ventilation heat losses. I have no data for the performance of our system but looking at the app right now I can see that the outside air is at 11C, the air being extracted from the kitchen and bathrooms is at 23C (the sun is shining, supplying passive solar gain) and the fresh air is being warmed to 21.6C before being distributed to the living room and bedrooms. So I think the 90% claim is probably justified and the heat saved is certainly far more than the energy needed to run the fans.
The capital costs in 2015 were... air-source heat pump: £6837; thermal solar panels: £2980; heat recovery ventilation: £4593; PV solar panels: £7340; and associated electrical work: £1700; total: £23450. This was less than 12% of the total build cost.
Nitty gritty
The conversion part of the house has new floors and windows and is completely dry-lined and insulated using mineral wool and PIR board insulation, breather membranes and foil vapour barriers, The new-build part uses Kingspan Tek SIPs (structural insulated panels) for the walls and roof. No steel is used but there are glulam beams supporting the roofs. The Tek panels comprise sheets of OSB (oriented strand board) bonded each side of expanded polyurethene insulation, lined with foil-faced PIR and plasterboard internally and clad with Siberian larch to the walls and concrete tiles on the roof, over a breather membrane. The site sloped so floors are mainly solid concrete with a suspended 'beam-and-block' floor over about one third of the new build. Over these is 150mm PIR insulation and a screed incorporating underfloor heating pipes.
Doors and windows are all triple-glazed Velfac - wood inner frames with the glazing in powder-coated aluminium sashes - plus one triple-glazed Velux roof window. The house was designed to make the most of passive solar energy. Most of the glazing is south-facing with two windows on the east side to take advantage of the best views and the morning sun, a little facing west for the evening sun, and the bare minimum on the north side. Building on the edge of the wood gives some shade from the heat of the summer sun while, once the leaves have fallen, winter sunshine provides warmth via the south-facing windows. This sun falls mainly on the concrete floors which help store the heat. Half the south side of the house has roof overhangs to shelter the patio doors and give some shade from midday summer sun, reducing overheating, while the winter sun is lower in the sky and so can shine right in to warm the house.
The conversion has tube-type thermal solar panels on the south slope of the roof which provide plentiful hot water when the sun shines and the system is working (see below) while there are twelve 250W photovoltaic solar panels on the new-build roof, providing a theoretical 3kW of free energy.
A 5kW air-source heat pump (ASHP) provides the heat for the underfloor heating and heated towel rails, and for domestic hot water when the sun isn't shining. Each space has its own thermostat - there are six 'stats controlling seven heating loops - so we can set different temperatures and programmes for each space. We have the thermostats set to 21C in the living/dining/kitchen areas and bathrooms and 20C in the bedrooms, and a minimum of 18C during the night.
The house is very leak-proof (thought we have opening windows for mainly summer use) and ventilation is provided by a whole-house mechanical ventilation unit with heat recovery (MVHR) via a heat exchanger. This sits in a plant room in the roof space along with the hot water storage cylinder, the solar inverter, expansion vessels, pumps, and assorted ducts and pipes. The mechanical ventilation means windows don't need trickle vents, the kitchen and bathrooms don't need extract fans, and we have filtered fresh air even when the windows are all tightly shut.
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