Commissioning MVHR

[Greengauge]

Hello

What is the current thinking or consensus on techniques for commissioning MVHR? I seem to recall there was some doubt cast on the reliability of measurements taken using an anemometer with a hood. Does this just relate to the external intake/outlet where the volume is higher and therefore more likely to be influenced by the constriction of the throat of the hood, or does the issue affect the individual room supply/extract grilles also? Has anyone tried measuring the effect, e.g. by looking at the change in flow rate at the intake while a hood is placed/removed on a supply valve, and vice versa?

It seems to me a simple way to mitigate this is to place an open-ended cardboard box over each vent and use an anemometer with a time-averaging mode, and sweep across the open face of the box and multiply by the area of the open face. (Similar technique used by acousticians to calculate average sound level in a room, colloquially know as the tai-chi technique!). Thinking of getting an anemometer of some sort so it would be useful to know what best practice is considered to be!

[Paul Mallion]

Recent Kent group event on this subject suggests that what really matters is that the same device is used for measuring every inlet and outlet. Results will then be consistent and repeatable. Richard Porteous of Built Environment Tech in Kent was our speaker, very helpful: Richard Porteous

[Jon Hand]

Hello, I have been giving workshops which discuss the acoustic requirements of the mechanical ventilation and I realise that there might be an issue when the general environment of the building is noisy.  I was about to do a quick test of a grill in our office when I noticed that the room had a background ~42-48 db.

Short of arriving back at 2AM I suspect that it will never be anything close to whisper quiet in that building.  I don’t do formal testing for acoustics so how would ‘official’ testing staff handle such a situation? Is there special kit they use to isolate the grill from the room for an acoustic test? -Jon Hand

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