Things don’t always go to plan; to misquote  Michael Caine in the Italian Job, “You weren’t supposed to blow the bl*!%y doors off!”

[youtube=http://www.youtube.com/watch?v=x1_KNgnvBjo]

With apologies to Simon Feeley, the BSRIA test engineer.

After reducing the energy demand of the houses significantly through insulation and the harvesting of passive solar energy, one option to offset the remaining energy consumption was to introduce on-site generation.  We’re taking a different approach however, and investing in off-site generation.

Each house will have £1,500 of shares in a local community wind turbine project (in reality the house doesn’t have the shares, but the social landlord, Newark and Sherwood Homes (NSH) does).  This investment is predicted to generate about 2,500kWh of electricity per year, effectively offsetting the equivalent consumption in the homes.  NSH get an annual return on that investment, and no maintenance headaches of on-site renewables; and the tenant doesn’t get technology that they don’t understand and/or cannot operate.

And financially it stacks up too.  Consider if we’d put solar panels on the roof (if we’d had the luxury of a south-facing roof).  A 1kWp array (occupying around 10sqm of roof space) would have set us back about £6,000 and generated around 800kWh per year.  Yet for a quarter of that cost we get in excess of 3 times the output, and none of the hassle of maintaining/operating it.

Today was the official opening (by Alan Simpson MP) of the community wind turbine at the nearby village of Hockerton.  The houses couldn’t be there, but we went along for them and recorded the video below.

[youtube=http://www.youtube.com/watch?v=-Wn4ipKChgI]

Thermal imaging of a property enables you to see where heat is escaping through the fabric of the building.

All properties involved in the Retrofit for the Future competition are having thermal imaging carried out before and after the retrofit by an independent testing organisation, BSRIA.  By comparing before and after images we will then be able to see how successful our retrofit has been in insulating the properties.

The “before” thermal imaging of our properties was carried out today, and the video below summarises the day’s events.

[youtube=http://www.youtube.com/watch?v=awBxmZewdbk]

An air pressure test on a building is a way to measure the air permeability of the building, or put simply, the rate at which it leaks air, and therefore heat.  The less heat a building loses, the less energy is required to heat it.

To perform an air pressure test, the following steps are carried out:

1. All “designed” ventilation (the openings in the building fabric that are designed to be there, e.g. windows, doors, extract fans, etc) is sealed;
2. A fan in an air tight lining is fitted into the main doorway of the property;
3. The fan is powered up until it maintains a constant excess pressure of 50 Pascals;
4. The rate at which the fan is then working defines the air permeability of the building, which is measured in cubic metres per hour.  A minimum score of 10 (the lower the air permeability the better) is required under current building regulations for new build houses.

All properties being retrofitted are having air pressure tests carried out before the retrofit work commences, and then again afterwards to see what improvement has been made.

Our properties were air pressure tested today and actually scored well for 1940’s houses; one achieved a score of 9.36 (slightly better than current new build standards) and the other 10.6.

Below is a video of the air tightness testing on one of the houses.

[youtube=http://www.youtube.com/watch?v=9y_uZnamrfM]

Our target for the retrofit is to get those scores down to at least 5.  Our homes at HHP scored an average of 1 when tested just after they were built.  With air permeability rates this low, you need to mechanically ventilate the building, but this can be combined with a heat exchange unit so that much of the heat in the stale air you are extracting can be used to pre-heat the cooler fresh air you are bringing in.  We plan to incorporate a mechanical ventilation with heat recovery unit in the houses as a part of the retrofit, but more on that another day …

For the thermal imaging tomorrow, the internal temperature of the properties needs to be at least 10 degrees celsius greater than the external temperature.  Given that the vacant property has been unoccupied for at least two weeks and therefore unheated, this poses a bit of a problem, as it is currently colder inside than outside – when we went in there today it was 10 degrees inside, and about 13 outside!

This problem was further exacerbated by the fact that the gas supply has been disconnected – not a long-term problem as we’re removing the gas central heating system as a part of the retrofit – but it would have been nice to be able to whack on the gas boiler overnight in such a thermally poor property.

So we had to resort to electricity.  A minor problem was that there was a £50 debt on the keycard meter, so we had to pop down to the local Post Office to clear that and add some credit to cover our heating need.  It was then time for an electric heater amnesty at Hockerton (OK, the secret’s out; even we heat our houses occasionally.  But with the sun being strong for at least the last week our houses are now back up to 20+ degrees internally, and the heaters are well and truly back in storage for at least another 8 months).

So having rounded up about 20kW capacity of heaters, our next problem was that the house only has two ring mains (the kitchen and the rest of the house), each with a capacity of 8kW, so we couldn’t even deploy them all!

Anyway, we got about 12kW of heat output running at about 2pm, so hopefully by 10am in the morning the temperature inside the house will be 10+ degrees above that outside; I’ll be there early to check though …

Here’s a quick video of the heaters in action; apologies for the poor video quality – a new camera and a new operative – but I promise the video quality will improve!

[youtube=http://www.youtube.com/watch?v=R15PXY2mw6E]