help with gas question

[malone]

Hi I'm currently study for my level 3 in plumbing and I have come across this question: open flued appliances with an input rate between 7kw and 70kw gross need how much ventilation??Now I know how to get net and the rest of the equation. But not how get to get the 7kw/70kw into a single figure!!Any help would be much appreciated!!As my mind has gone blank.apparently for this it's meant to be 21??? but don't know how the get to that figure?????Hope this makes sense as I have been studying since 8 this morning and getting a bit frustrated now!! thanks

 

[PETE 123]

70-7 (adventitious air)

 

[heliotrope]

The question you are being asked is how many square centimetres of free air per kilowatt input is required
for combustion air to an open flued appliance of between 7 and 70 kilowatts.

 

[kirkgas]

It's asking you if you know the calculation of appliance(s) between 7-70
First thing is do you understand adventitious will look after the first 7, and 70 is the max a domestic gas can work on. It also mentions gross HI so you need to convert to nett by dividing by 1.1
So using above what free air is required for
A) 65kw OF boiler in a room
B) 35kw net OF boiler in a room

for A as it doesn't say nett you know it's gross ( old appliances don't say gross, but new ones say nett so we know what's happening) so 65/1.1-7x5

For B it's 35-7x5

You can do the maths,

Once you are sure you understand what I've written, we will move onto appliances in compartments

 

[malone]

Thanks for taken time to reply.

Just to try and clear it up a bit: I know how to get net from gross I need to divide it by 1.11 = net.
Then -7 for adventitious ventilation and times it by 5 = ? cm2.

The bit I don't understand is if the open flued appliances in question has input rate between say 18kw and 22kw, how do I put this into figure to divide it by 1.11??

(The question was for a open flued appliance 7kw and 70kw input Gross, they managed to get a figure of 21!! but they dont show me how they got this? and I can work it out!!)

Hope this makes senses, and thanks again for the help

 

[kirkgas]

It's asking you if you know the calculation of appliance(s) between 7-70
First thing is do you understand adventitious will look after the first 7, and 70 is the max a domestic gas can work on. It also mentions gross HI so you need to convert to nett by dividing by 1.1
So using above what free air is required for
A) 65kw OF boiler in a room
B) 35kw net OF boiler in a room

for A as it doesn't say nett you know it's gross ( old appliances don't say gross, but new ones say nett so we know what's happening) so 65/1.1-7x5

For B it's 35-7x5

You can do the maths,

Once you are sure you understand what I've written, we will move onto appliances in compartments

Haha he's not been back is his brain fried??????????

For anyone else

OF boiler 42kw nett, in compartment vented to outside
OF boiler 37kw in compartment vented internally,

List all ventilation requirements

 

[heliotrope]

No one willing to stick their neck out on this one eh!

Here goes then,

In the absence of MIs.

A. 42kw = 210 cm2 high level 420 cm2 low level (42x5 =210. 42x10 = 420)

B. 37kw = 370 cm2 high level 740 cm2 low level (37x10 = 370 37x20 = 740)

 

[Reg Man]

ACS mode? Up to 70kW net BS5440 parts 1 and 2, over 70kW to 1.8mW BS6644. First 7kW advantageous air, except that DFE gas fires don't allow for this. Put that one in, as thread did not specify boilers, although a 70kW DFE would be obscene.LOL

 

[Killy Bing]

ACS mode? Up to 70kW net BS5440 parts 1 and 2, over 70kW to 2mW BS6440. First 7kW advantageous air, except that DFE gas fires don't allow for this. Put that one in, as thread did not specify boilers, although a 70kW DFE would be obscene.LOL

saw a very old dfe in a pub.
the early type that were basicly made in a shed
back rail was just inch and a quarter with slits cut in it.
no fsd, just a fan valve to turn it on or off

Thank god it had been fed with 8mm.
I brought it up and they complained it had been cut off

i wonder why?
i could only imagene what would have happened if they had fed it with a bigger pipe.

 

[Kev the gas]

I was an apprentice, back in 1988.
The gas engineer I was with did a smoke test on an old dfe fire in a pub, open 2 sides.

The pub clients evacuated in seconds , fecking smoke everywhere due to the extractors.

 

[Reg Man]

I was an apprentice, back in 1988.
The gas engineer I was with did a smoke test on an old dfe fire in a pub, open 2 sides.

The pub clients evacuated in seconds , fecking smoke everywhere due to the extractors.

Sounds about normal. Pub trade are a nightmare with DFE's and size of builders openings and extraction from the kitchens. Fortunately the air changes per hour help and the problem is ignored. I have a classic one close to me. Have highlighted it to the management who have ignored me, Obviously thinking I am an anal regular customer. Most of the products of combustion on this two sided opening chimney are sucked up across he bar, through the open kitchen extraction system canopy.

 

[johnnyplumb]

No one willing to stick their neck out on this one eh!

Here goes then,

In the absence of MIs.

A. 42kw = 210 cm2 high level 420 cm2 low level (42x5 =210. 42x10 = 420)

B. 37kw = 370 cm2 high level 740 cm2 low level (37x10 = 370 37x20 = 740)

only 1 out of 3 i'm afraid, not good enough
return your gas safe card immediately, you can no longer work on gas ,
your a danger to yourself and more importantly to the public :grin:

 

[kirkgas]

Thanks for taken time to reply.

Just to try and clear it up a bit: I know how to get net from gross I need to divide it by 1.11 = net.
Then -7 for adventitious ventilation and times it by 5 = ? cm2.

The bit I don't understand is if the open flued appliances in question has input rate between say 18kw and 22kw, how do I put this into figure to divide it by 1.11??

(The question was for a open flued appliance 7kw and 70kw input Gross, they managed to get a figure of 21!! but they dont show me how they got this? and I can work it out!!)

Hope this makes senses, and thanks again for the help

An appliance vent is based on its MAXIMUM HI, so on an 18-22 range rated appliance you base it on 22kw

 

[kirkgas]

No one willing to stick their neck out on this one eh!

Here goes then,

In the absence of MIs.

A. 42kw = 210 cm2 high level 420 cm2 low level (42x5 =210. 42x10 = 420)

B. 37kw = 370 cm2 high level 740 cm2 low level (37x10 = 370 37x20 = 740)

B isn't right, please read the question carefully HAHAHA

 

[heliotrope]

Duh!:furious3:

My own fault replying at a late hour with belly full of red stuff.

Okay, try again.

B. 37kw gross = 37/1.11 = 33.3kw nett.

33.3kw = 333cm2 high level 666cm2 low level (33.3x10 = 333 37x20=666)

:smug2: No red tonight Plenty gin and orange though:29:

 

[kirkgas]

Duh!:furious3:

My own fault replying at a late hour with belly full of red stuff.

Okay, try again.

B. 37kw gross = 37/1.11 = 33.3kw nett.

33.3kw = 333cm2 high level 666cm2 low level (33.3x10 = 333 37x20=666)

:smug2: No red tonight Plenty gin and orange though:29:

NO NO NO NO NO
haha I said READ THE QUESTION

I asked for the the full ventilation requirement,
A) is vented to outside so it's ok
But
B) is vented internally, your calculations are correct this time, HOWEVER, what's the point in fitting properly sized compartment vents if you aren't going to provide a properly sized combustion vent to outside, and it would be sized at NETT HI -7 x 5

 

[kirkgas]

I'm going to have some fun when we move onto multi appliances in the same room ;-)

 

[tamz]

I'm going to have some fun when we move onto multi appliances in the same room ;-)

And a coal fire in the corner just to add to the confusion :smile:

 

[dancinplumba]

And it used to be two rooms

 

[kirkgas]

"You not want this lot ripped out and storage heaters fitted?"

 

[Reg Man]

With a flueless heater in there as well

 

[kirkgas]

Have some replies went AWOL from this thread?

 

[village idiot]

Have some replies went AWOL from this thread?

no, they are still coming

 

[kirkgas]

Next one
make all HI nett, to save one calculation
There is a
RS boiler 42kw
OF fire 6.5kw
Gas cooker 22kw
OF water heater 23kw
It's a kitchen 6m x 4m x 2.4m
Again list the full ventilation requirements

 

[Reg Man]

What? all that lot in a kitchen, what on earth do you get up to in Coatbridge.