Powering extractor fans

[Sigurd]

We are installing two extractor fans in a church hall which is used fro meetings, lectures, etc. Also occasionally for Lent lunches and coffee mornings. As you can guess, finance is an issue.

Is it safe and legal to power these from standard 13 amp sockets (which are fed from professionally installed RCD consumer units. Our intention is to plug the extractor fan into a count down type time which is in turn plugged into a 13 amp socket, so that at the end of a meeting or whatever, it can be switched on from the timer, and it will automatically switch off after a set time - usually 2 hours.

We haven't decided on a fan as yet but it needs a to be in the 9"/10"" size to fit the pane of glass.

Many thanks for any help offered.

 

[Marvo]

Yeah, to achieve 1800 litres/sec you're in the realms of a boxed and ducted mixed flow fan. The 2 window fans you're looking might give 500 l/min in free air together which means you'll realistically get 300-400 l/min with normal real-life static pressure across them.

How do you intend to accomodate the entry of 'make-up' air into the hall where the fans are extracting? You're going to need to install some passive vents unless the building leaks air like a seive.

The fans you mentioned can be both started by a single timer or occupancy sensor and they don't need any additional protection other than the FCU.

 

[Sigurd]

Thanks Marvo
Entry of make up air is not an issue. The building is nearly 200 years old. Air entry is not a problem; well it is, but not from the point of view of lack of!
I realise we are well down on recommended air extraction rates, but the suggested fans will be adequate for our needs.
I am grateful that you have more or less confirmed that what I propose is safe and legal.

 

[Midwest]

Its not clear, well to me, what the intended use of the fans are for. Extraction obviously, for removal of damp or stale air, but IMO never works for temperature control, if that's the intended use?

 

[Sigurd]

After use the atmosphere in the hall is rather humid from 30 or so people breathing. Occasionally a bit smelly, for example once a month there is a "Men's breakfast". Spiritually healthy but physically not - too much fry up! I can't stop people breathing or eating fry ups, so the fans are intended to run for a couple of hours or so after the event. The hall does not have any opening windows as the Victorians who built it didn't seem to believe in them, and planning authorities are fussy about allowing changes to Listed buildings.

I know what we plan is not ideal. But I am up against planners and limited finance.

 

[Midwest]

Before you spend your money, it may worth consulting a professional ventilation 'expert', bearing in mind the size of the room, design & your intended use. Your plans may not achieve what you are seeking.

 

[Sigurd]

Thank you all for your helpful comments. I am now in a better position to move forward.

 

[johnduffell]

That target extraction rate seems a bit high, 1800l would be over 100 air changes an hour, in normal circumstances (at least for domestic) even purge ventilation is only several air changes. And back ground would be 0.5 or less.
With 300+ people in the room, i could just about understand 1800l though. But I'm guessing not so many.

 

[Marvo]

555 litres per second would give around 10 air changes per hour. Sensibly I'd be aiming around that figure.

 

[Sigurd]

The capacity of the hall is 50 but in practice rarely more than around 30. Part of our problem has been humidity due to people breathing and heating by IR heaters - quick rise in temp, fast fall, cold walls, = condensation. The biggest part of the refurbishment, apart for sorting out roof and pointing problems, is the installation of gas fired central heating. That will provide a background temp of around 8 degrees boosting when hall is in use. That was and is done in the church which had similar condensation problems (Grade I Listed, built in 1120) That has made a big difference in there.

 

[Deleted account]

Hi Sigurd,
Once you've completed your install could you come back and let us know what you did?
Quite often we never hear from people again once advice is given. I would like to know how you resolved it.

Cheers peter

 

[Sigurd]

Will certainly do so. My simple (I thought) question seems to have stimulated quite a discussion so I will make sure I bring it to a conclusion!

 

[Marvo]

Simple questions are rarely simple and discussion is a good thing, hopefully you've got enough info to prevent money being spent on something that's not going to fulfil the brief.

If you find your extract rates are a bit shy you can set a longer overrun time on the system if you use an occupancy sensor.

Good luck.

 

[johnduffell]

The volume of the hall is around 200 c.m.

555 litres per second would give around 10 air changes per hour

good point, slight calculation, I should have said 1800 would give nearly 40 ACH.

Thanks for the correction!