Ventilation commissioning and the requirements.................

[CVA]

Firstly Please accept my appologies but I am a pen pusher in the office and not an electrician but I have picked up few things over the years on various site days with the lads and seminars so would like to think I had some sort clue but please accept any sign of ignorance on my part.

PLEASE NOTE : This is a New Build site we are working on and that the NHBC requires the ventilation commissioning certificate !!!!!!!

Well I am at a loss here,

First we are told that all ventilation is to require commissioning and therefore we are required to get the Anemometer and cowl and that sets us back about £ 400 which we have spent this week and then we are told by the manufacturers of the fans that we want to commission that not only is it not possible to commission that particular fan as they are bigger than the cowl itself but also that the jury is actually still out as to whether the readings that we obtain from fans that will actually fit in the cowls will be correct anyway.

They have now told me that the cowl will have an air resistance (that apparently is not calculated in the details on the side of the cowl) and that any reading taken will actually be false and therefore rendered useless ........ We are to refer to the manufacturers data sheets and advise the NHBC or the Building Reg's to accept these results as to the values they require..........

So are we then now required to commission or not commission any fans then ??????

I am at a loss as to what some people really want us to do ......

What do you more experianced guys with far more experiance think on this subject and what are your findings from what you have done.

 

[Engineer54]

If you want to clear this up quickly, get in touch with CIBSE (Chartered Institute of Building Services Engineers) and see what they have to say!! Generally they are very helpful i've found, unlike our own ITE, who are quite happy giving you the run around!!


EDIT... I should have read the OP more closely, i was under the impression we were talking about bigger fans than those you'll usually find in a domestic setting!! ...lol!!

 

[JulianC]

Domestic ventilation systems with adjustable fan speeds do indeed need to be commissioned, with the aid of an anemometer. Design values for the various types of system and different extract areas are provided in part F. The results are notifiable to building control (This may only apply to new build installations, I can't remember and haven't got part F to hand). Since it is unlikely you'd be fitting extract or supply terminals larger than 6" in a domestic situation (more usually 4") I am left wondering why your cowl won't fit. What type of system are you talking about and have you or your guys done the BPEC course?

 

[CVA]

Thanks Engineer 54 (will look at getting in touch with them) and also thanks to Julian for the reply,

We have been asked in the spec to use the Nuaire Genie X Fans and the distance between the front of the fan and the wall is around 173mm, I have taken a picture but I need to have a few more tpics posted to get a pic on here to show you all. The lads we have here have all been on the Bepec course and they are prepared for the commissioning of standard fans or the MVHR systems that we often get called to fit fit as they all fit the cowl ...

But with this actual fan not fitting the cowl (it may fit if we part sink it but the clients do not want that due to the changes they have to make with the carpenters on the site) what am I supposed to do and also with the fact that the manufacturers are now saying the cowl distorts the readings anyway I am at a loss.......

 

[JulianC]

Aah, I see what you mean. I'd be tempted to get the chippy to knock you up a wooden frame, the same footprint as your cowl, to stand it off from the wall (effectively simulating the fan being sunk into the wall), then take a reading from that. We use the rectangular Airflow cowl and it's big enough to cover a Genie apart from the depth away from the wall if it's not sunk in.

Bit of a loss as to why Nuaire say the cowl distorts the readings though - we enter a correction factor into our anemometer based on the cowl we use, regardless of the shape or size of fan or duct we cover. As far as I am aware there is no other way to measure air flow during system commissioning.

 

[CVA]

That may be our only option to be honest and may ask our lads to get the on site chippy to knock one up as soon as possible so that we can at least get the NHBC off our backs. My only concern then would be would it not throw the correction factor of the cowl off if we do this ?
May Have to cover the base with some form of rubber to avoid air comming in from the base of the base board as I guess as this will then form a bit of a seal then do you think ?

 

[JulianC]

Definitely seal the frame against the wall with something. Perhaps steal some pipe insulation off the plumber - should seal OK when pressed against the wall. As I see it, providing any framework etc. doesn't intrude inside the cowl, or block any of it off, the correction factor shouldn't be affected. Will have to investigate exactly what the correction factor is now as it's got me wondering. I know it's an 'area' that roughly equates to a 45mm radius circle for our unit but what that relates to has got me puzzled! If it is the effective free area of the anemometer head (ie. hole size, less a bit for the impeller) then in theory, the size and shape of the cowl is irrelevant. I shall see what I can find out.