heat extraction from a school kitchen

[studentspark]

Kitchen in a nursery is very hot.

Only has a large domestic style hob extractor 120mm duct

Would increasing the hob extraction to a commercial type, make a BIG difference in bringing the room temperature down.

Cooker is a six plate electric hob and oven

It must remove some heat, any ideas on how this could be calculated

 

[333rocky333]

Im no expert but i think too much extraction can cause other problems, ie with gas, large kitchens tend to have supply fans as well as extraction

 

[studentspark]

Yes I don't know much about this, and its not a job I will be undertaking.

They have had some big quotes to do the work.

I do some electrical work in the building and the owner asked me what I thought. Said I wasn't sure, but will do some research...hence asking here

 

[Lectrician]

With larger extraction, you either need decent passive intake, or mechanical intake fans. Best to let a proper canopy company do the calcs and fit the kit. You can just wire it

 

[thetman]

HOw many fridges / freezers are there ?

That is usually the source of any high temps

 

[ban-all-sheds]

Best to let a proper canopy company do the calcs and fit the kit. You can just wire it

Actually, best to let a proper HVAC engineer do it, as it would be a shame to just throw all of that heat away.

 

[flyingsparks]

I fit a lot of commercial canopies in kitchens for my dad's business. They manufacture them. My dad could work out the size of fan required to get the required number of air changes per hour in the room. There are a lot of variables such as the length and size of the ducting.
Input fans are often required to replace the air taken out as you can't have a pressure difference between out side and inside.
With gas hobs there is requirements the canooy must meet to do with overhang of the hob and height above it. There is also a requirement for a gas interlock panel and solenoid valve to switch off gas supply if the fans stop.

A big fan (typically we may fit a 450mm diameter fan In a kitchen canopy.) will definitely cool the room down. We recently fitted an 880mm fan (looks like a jet engine with the silencers on it!) in a factory to remove fumes Fromm soldering stations. There was also a similar sized fan to bring fresh air in, we tried to warn the management that in the winter the staff WILL complain about being cold! Not surprisingly 6 weeks after fitting it all we were back to fit heaters on the intake fan duct work!

Picture below!

Untitled

• flyingsparks
• 21 Oct 2014
• 1

 

[cam1989]

How big is the room? You mention in your original post that it's only a 6 plate electric hob and oven.

Has overheating always been a problem or has it only recently become apparent? If it's the latter it may just be that the filters in the hood need replacing.

Either way I do not think that a commercial style extract system is necessary for a single oven/hob setup. As it's a nursery I doubt you're looking at heavy loads for long periods. Nu-Aire suggest 15-30 air changes per hour for a commercial kitchen.

Could do with knowing the room size, current extract rates etc.

 

[ban-all-sheds]

There was also a similar sized fan to bring fresh air in, we tried to warn the management that in the winter the staff WILL complain about being cold! Not surprisingly 6 weeks after fitting it all we were back to fit heaters on the intake fan duct work!

Why?

What were you doing with the heat in the air which you were removing from the room?

 

[ericmark]

As already said two ways to remove the heat from the room. One reduce the heat in the room and the other increase general ventilation or of course a air conditioner.

As BAS says what will you do with the heat? A heat recovery unit could be used to return heat to other parts of the nursery.

Again fridges and freezers do pump out heat. I remember in a caravan during the summer it was really hot so I installed a fan behind the fridge so the heat never got into the van and this really cooled the van down.

You say electric already so swapping to induction hobs will help.

Even with my domestic cooker there are cooling fans to keep the casing cool clearly if this air is ducted outside then it will really cool down the kitchen.

 

[studentspark]

Thanks for the replies

Its a new build so the insulation levels through out the building are high and the general temperature is too high throughout the building.
Underfloor heating is used throughout (Not in kitchen)
I looks like lots of thought was put into keeping the place warm, but little thought put in to keeping it at a pleasant temperature, especially during the warmer months.

The kitchen a thin long room about 3m 10m

Appliances that produce heat

Big two door fridge and two door freezer
Electric oven and electric 6 plate hob
Tumble dryer !
Several toasters
Two staff


Current ventilation
Hob extractor about 120 watts I think
300mm (ish) extractor fan.

A HVAC company will be doing the work, but I am unsure how cooling is 'Guaranteed' for want of a better word.
Do they take an average temperature of the kitchen say 28oC, and say with the measures they put in place, they can get it down to 20oC.

I take the point about heat recovery as well

 

[Steve]

Appliances that produce heat

Big two door fridge and two door freezer

If these are big "foster" type units like:

then these do produce a LOT of heat, and if this heat is not given any means of escape it will just build up in the room. Your chimney fan will only be running when the cooker runs and is primarily for the removal of grease and moisture.

You need some "trickle" ventilation, ideally on a thermostat, so that the fans run when the temperature rises above, say, 23 degrees and cuts out at 21. Two fans, one either end of the room, one sucking, one blowing (on the same stat so they run together).

As others have said, I dont think the place really needs a massive extraction system as seen in commercial kitchens as there isn't actually much cooking area. A domestic fan suits a domestic cooker! Your issue is background heat.