HPH062 : Does a Passivhaus Need a Heating System? – with Alan Clarke
Building services engineer Alan Clarke explains what factors should be considered when choosing a heating system for a low energy home.
Interview with Alan Clarke
Alan Clarke has been involved in energy and buildings his whole career. He's worked on a variety of projects, from schools to housing developments and individual self-builds.
N.B. In this episode we are talking about heating systems relevant to the central European climate. In hotter climates you will be focused on cooling rather than heating!
A Passivhaus is Likely to Have Fewer Radiators than a Traditionally-Built House
When it comes to looking at heating systems for a Passivhaus there are a couple of key differences to consider.
Compared to a traditionally-built house it is not necessary to heat every little corner (as the heat loss from each room is a lot less).
There are also no cold surfaces. So, in a Passivhaus (where thermal bridges have been eliminated, etc.) it will not be necessary to put radiators under the windows.
The Amount of Heat a Building Needs Comes Down to the Heat Loss!
In simple terms, the heating requirement of a house will be determined by the heat loss of all the elements of the fabric and the ventilation.
The total heat load will clearly be affected by the size of the building, but then it comes down to the insulation value of the wall, the windows, the ventilation system and so on.
Even in a Passivhaus You Can't Dispense Completely with Heating
Working with Passivhaus specifications and including heat recovery ventilation very low levels of heat might be needed but there's no expectation that we can do without heat completely.
The Snag with Solar Gains and Internal Gains is How Variable They Are
Alan gives an example of why it's a good idea not to do away with a heating system.
He says: “You could have a sunny day when it's -5ºC and with the right house no heating is needed. It's great. Then a week later it could be raining, it could be 3ºC, completely overcast and actually it would get a bit cold.”
Good Temperature Control is Essential
In a Passivhaus it's no longer simply a case of it's winter we need heat: some days you need a lot and some days you might not need any.
So good temperature control based on the temperature inside the house is important.
Generally, if you're using gas heating you're trying to throttle down a boiler which is really too big for the job. So controls that are able to lower the temperature that it runs at are a good option. They effectively reduce the power of the radiators by reducing the temperature at which they run, as well as increasing the boiler efficiency.
Reducing Energy Demand is Always the First Step
Alan does not advocate moving away from gas as a fuel in situations where there is already a connection to the gas main.
The reason for this is that the emphasis of a Passivhaus building is always to think about energy first and reducing the energy demand. So to some extent it is less important where that energy comes from afterwards because one source of energy is often convertible to another. The key point is to use less.
Find Out More
Download a transcript of the interview with Alan Clarke.
Join the AECB
For building professionals in the UK, the AECB is a fantastic organisation that shares knowledge and aims to promote sustainable construction.
Their yearly conference is also an opportunity to be invigorated by like-minded individuals.
They have just hosted their 2014 conference in Bristol but this video from 2013 sums up what people get out of it.
Video produced by Regen Media