Sunday, 20 September 2015

Modern air tight homes need modern ventilation

We are used to living in homes that are so leaky that ventilation is not an issue. However modern standards of air tightness require modern standards of ventilation control. Too little ventilation can trigger health problems such as asthma, as reported in the Guardian today, and there is some evidence for this: see Do energy efficient homes damage your health. However, air tightness does not have to mean insufficient ventilation. For example mechanical ventilation with heat recovery (MVHR) is an effective solution. We find it comfortable, reliable and you don't have to think about it. Also, the home I visited yesterday through Open Eco Homes (the Lingrey Court one) is a new build with  MVHR  and the residents love it because it gives them good quality air and gets rid of smells quickly. You can read what they think in the Be-zero blog).


Some people don't like MVHR because it uses power for the fans and/or because there is some noise (and sometimes a lot more than there should be - see What can go wrong with MVHR). You can ventilate effectively with natural ventilation, but you will waste heat unless it is limited according to need. This is also possible - such as the humidity triggered system from Aereco that I wrote about a couple of years ago. (How much ventilation do you need?). However, it is nice to be able to have more ventilation than absolutely necessary without wasting heat which is where heat recovery comes in. So can you have heat recovery without mechanical ventilation? Apparently so, at least according to Ventive. They call it PVHR  - passive ventilation with heat recovery.  I expect to learn more about this on Tue. 13th October at the Open Eco Homes follow up event on Air Tightness and Ventilation  In the meantime I am visiting another two homes with MVHR next weekend one of which is a retrofit, though not quite like ours I think.

My only gripe about MVHR is how expensive it is to change the filters. In our house I do this every 6 months but I don't put new ones in every time. The inlet filter is always the worst  in our house, because of traffic outside and I usually throw that one out. The outlet filter, which cleans the air going out of the house, is not so bad so I get the worst off with the vacuum cleaner, then swap that into the inlet and put a clean one in the outlet. That means I need just one new set each year. The residents at Lingley Court clean theirs by washing it under the tap once a month. If you have an MVHR system I would be interested to hear what you do.

Incidentally, the main reason for  the MVHR filters is to keep the heat exchange surfaces clean. However, the fact that they also improve our air quality is a big plus. You can find out more about what it is like to live with an MVHR system here.





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