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:
All “designed” ventilation (the openings in the building fabric that are designed to be there, e.g. windows, doors, extract fans, etc) is sealed;
A fan in an air tight lining is fitted into the main doorway of the property;
The fan is powered up until it maintains a constant excess pressure of 50 Pascals;
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.
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!
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Saving energy in the home is a book written by Nick White in association with HHP. Nick has been a member of HHP since the start of the construction of the homes in 1996. He contributed to the self-build and has led the development and marketing of the Project’s on site ‘eco-business’ since 1998. Now with this book, Nick offers you straightforward and achievable strategies for reducing your energy bills and living a more environmentally aware life. With lots of useful tools to assess your energy and carbon use, Saving energy in the home gives practical advice on everything from heating homes to managing those teenage consumers.
In February, Laurence Llewelyn Bowen visited the Hockerton Housing Project to find out more about Eco homes and sustainable living. This was for a current series called Laurence Llewelyn Bowen’s History of Home , charting the changing relationship and attitudes towards our homes. The 9th out of 10 programmes, The Eco House , uses Hockerton Housing Project (HHP) as a case study. This will be broadcast on Thursday 3 April 2008 15:45-16:00 (Radio 4 FM).
Laurence interviewed both Nick White and Simon Tilley, both residents of HHP, to try and find out more about the emergence of eco housing, discover some of the misconceptions, and try to understand where it maybe leading to, for instance zero carbon homes. In Laurence’s typical flamboyant style, the interviews were very spontaneous, tangential and with distinct velvety undertones!
HHP opened the doors of its new ‘Sustainable Resource Centre’ (SRC) for visitors at the beginning of 2005, after 18 months of construction and kitting out. The building was designed, work supervised and most of the labour contributed by project members themselves. The new building is in stark contrast to the infamous ‘shed’ used for visitors over the last 7 years for slide presentations, offering comparatively luxurious facilities including a dedicated audio-visual room, seminar facilities and permanent exhibitions.
The new facilities will allow HHP to demonstrate more effectively the key sustainability principles of the project. The ‘eco-community building’ is low profile situated near and complimenting the houses, including an earth covered roof. This building has been designed to meet the same high standards as the homes, ‘Zero CO2’, ‘Zero heated’, and ‘Autonomous’ standards’.