backblog #2: mvhr system commissioned

 Paul Novus300 Commissioning in progress

The heat recovery ventilation system has been running for some three months now. The system is a Paul Novus 300 unit, which has a heat recovery efficiency of up to 94%. The system commissioning included balancing the supply and extract air flows and setting the fan speeds for each setting. This all went well and the system balanced well (which isn’t always the case). The photo above left shows the ventilation unit set within a cupboard within my new office. With all the attenuators on the ductwork (see earlier post), and the sound insulation around the cupboard, the system is almost silent: audible only in boost mode.

The photo above right shows the commissioning taking place. The total air flow was measured and adjusted through the intake and exhaust terminals (outside) to ensure total design air flow was achieved. The internal terminals within each rooms are then measured, adjusted and-re-measured to ensure each room receives the right air flow.

More performance data will follow on future blog postings. Keep checking back.

2 thoughts on “backblog #2: mvhr system commissioned

  1. I am renovating a 1925’s house in North Dorset and was very interested in your blog and the site. The topics covered (air tightness, cold bridging, EWI etc) will be items I will be encountering in the build. I will installing an MVHR eventually – one question if I may in the ventilation which you seem to have professional knowledge on is the use of metal spiral ducting. Most of the MVHR supply companies only have rigid plastic which is exceedlingly expensive per metre compared with metal. One site only gives the reason that the use of metal is a major loss of heat even if well insulated and reduces the overall efficiency and is only suitable in a commercial situation. Grateful if you had a view on the use of metal versus plastic pipe. Thank you.

    • Joe, Sorry for late reply. Metal has some benefits over plastic, and plastic has some benefits over metal. In summary these are:
      In favour of plastic: cheaper to supply and install (so confused why you are saying the opposite); it is easier to install (a bit more flexible); attenuates sound transmission better than metal.
      In favour of metal: Installed properly, it is the most mechanically robust solution; also tends to be the most airtight (depends upon seals).
      The main things to consider, whether plastic, or metal, is to minimise resistance of the air flow, as this will affect performance and create noise. So, ensure the ducting layout is correctly designed and co-ordinated (not viable with ‘free’ design service available from manufacturers); it is correctly sized – as a guide, start at 160dia if possible until first branch (if unit only allows 125dia max, then keep to this size until you branch off to individual rooms); ensure ducting is smooth inside – avoid flexible ducting (even short spigot connections) completely.

      Regarding thermal bridging: this is only possible to occur if the ducting is running between heated and unheated spaces, i.e. intake and exhaust. This is why those ducts need to be well insulated: min 25, preferably 50mm if position of fan unit spigots allow. Done properly, there will be minimal thermal bridging. Whether plastic or metal, intake and exhausts will need insulation. Remember, for intake and exhaust duct, you will need to use vapour resistant insulant. For supply and extract, these will only usually need insulation if run in a cold space, such as loft. I’m sure you have seen my loft insulation posting which shows the best way of dealing with this. Insulated correctly, metal is no more of a heat loss risk potential than plastic.

      Hope this helps.

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