Energy Use

At last after eighteen months I have managed to get a handle on my heating energy use. For a whole caleadar year which includes both of the two recent winter cold snaps my total use has been 1786kWh costing less than £200. This equates to just 7.4kWh/m2/y which is very low. April 2011

Having lived in our new house for just over a year now I thought that I would briefly report back. The house is nice, warm in the winter; cool in the summer, quiet mainly due to the triple glazing and air sealing, fresh feeling due to the MHRV, tidy due to the lifestyle of the inhabitants. The energy use is 45kWh/m2/y and for heating approximately 7kWh/m2/y but I am still having difficulty separating heating and hot water energy use so the heating could well be lower as when the sun does not shine the house is cooler and uses more back up hot water. I have relatively high base load energy consumption due to the computer control systems, security and monitoring systems etc.

The solar systems have performed extremely well producing an excess of hot water as was anticipated during the summer, this surplus heat was stored under the basement in my interseasonal thermal store. It was disappointing that August didnt happen this year and I even heard of people running their heating during that month as it got so cold! This meant that my target for the ground warming was missed but next year I am dreaming of getting it to 19C down under the house and not the 17.9C peak achieved this year at the end of July.

I added a glass porch and have done a couple of talks about the house now and am very much enjoying living in it especially the lack of heating bills! I try to keep the website updated regularly and have lots of extremely nice comments from far and wide. I also get asked technical questions from time to time and have consulted on some similar projects.

The first winter was a little disappointing with energy use higher than I had hoped but none the less it is still very low. The house has been lovely to live in, everything clean, new and warm.

I have been monitoring total energy use since before I moved in and am gradually getting better at recording it. I am now monitoring the MHRV and some appliances separately too.

I can project the total energy use for the first year with some degree of certainty as 10,000 to 10,500 kWh. This equates to 42 to 44 kWh/m2/y.

I have analysed and been able to project the total energy use for heating and hot water for the first year in occupation as between 11 and 12 kWh/m2/y. I cant as yet separate out the hot water element.

Total energy use spreadsheet
Energy use spreadsheet - updated occasionally

MHRV energy use spreadsheet
MHRV use spreadsheet

Several people have asked me if my house will stay cool in the summer. I tell them that the high levels of insulation that I have will help to keep the heat out.

I can open my window shutters during the night in the summer which we usually keep closed overnight in the winter. This maximises the heat loss during the hours of darkness and although a small effect helps keep us cooler. I can run the MHVR system with a higher flow rate at night again maximising the heat loss from there. I can also use nighttime cooling. In winter it runs slower at night. The house has very high thermal mass and so the temperature changes very slowly and so we are somewhat isolated from sudden changes in outdoor temperatures.

The biggest and best way to keep the house cool is to close the external window shutters while the sun is shining on them and cut out the solar gain completely. This works brilliantly well, much better than I had expected and I hope to write some computer control software to manage this process. I did have to fit low energy bulbs in the lounge main light in May as it had has some incandescent bulbs in for the winter months, naughty I know but as we have no formal heating maybe I could be forgiven.

This is despite the fact that the base load is relatively high as a result of several computer control systems and a security system. In the first year we used 10,800kWk for our 240m^2 = 45kWh/m^2/y.This includes a home office, office equipment and all the data collection and monitoring equipment. For heating the figure is 7 kWh/m2/y this is included in the figure above.

Someone asked how much energy my MHRV used last winter (2010/11) --- I have all the information but when did winter start? for me it was 2/10 and ended certainly by 18/3, and on that basis if I subtract the summer cost of MHRV then it used 895kWh for the winter, the total it actually used was 1156.In addition I did have a small heater drawing a couple of hundred Watts when the outdoor temperature went below -3c which it did a lot which I didnt design for adding 250kWh? I am 240m^2 there have been 7 of us here for the last month and if they had been here in the winter I wouldnt have needed any additional heating. I worked out energy use was 39kWh/m^2/y plus 7 more for heating, it should get lesss as my store warms up.

Indeed it is 33 now (May 2012) and my energy cost has fallen to below zero as my FIT income exceeds my electricity bill and that includes the power used to charge my electric car.