Gas rating!!!!

[Hobo128]

Im confused, when gas rating what should I be comparing my answers to in the technical data, should I be comparing it to the Kw of the boiler or should it be compared to the Gas flow rate, I think the gas flow rate.

 

[Killy Bing]

Gas rating is just that.
how many m3 per hour or ft3 per hour is burnt

working out the heat input you do it in kw.

 

[TBServices]

Doesn't matter, equates to same thing.

 

[Hobo128]

The technical data I have in front of me is for a 32kw worcester. Max rated heat input is 32.65.
The gas flow rate in the tech data is 3.5m3/hr . If you work this out 32.65 x 0.095 = 3.1. this doesn't equal to 3.5 m3/hr. So when I gas rate this boiler ft3 meter and get 33 second for one revolution 1x3600x1040 / 33 /3.412 = 33.25 kw 33.25 x 0.096 = 3.1m3/hr Seems better to compare to kw and not gas flow rate?????

 

[TBServices]

The stated heat input is nett, not gross

 

[sheff paul]

Im confused, when gas rating what should I be comparing my answers to in the technical data, should I be comparing it to the Kw of the boiler or should it be compared to the Gas flow rate, I think the gas flow rate.

Calm down mate,in the mid 90's had a corgi inspection I was fluffing about with pen and paper showing I could work out the maths and that ,the inspector pulled out some kind of early personal organiser bit like a mini pc ,and said ''bugger the maths' get one of thease.Down load an app on your phone it works it out bang on .Look in the MI's they normally state a tolerance + - 5 %,for example,check the MIs for this tolerance as they differ.You never get it bang on ,Gas apps show both Gross and net,KW BTU,cubic m,and cubic feet ,all the info for the benchmark you need for gas rating

 

[AlexGas]

So when I gas rate this boiler ft3 meter and get 33 seconds...

Could it be 32 sec, not 33!?

 

[Hobo128]

ok, when I gas rate is the answer in gross or net?

 

[lame plumber]

the meter reading gives you the gross amount of gas used and your calculation will net or gross it depending on the formula used!

 

[Hobo128]

Only reason i ask is that i had a inspection today and the guy who came out gas rated the boiler and im 99% sure he did it 93x3600x10.76 / 120 = 30.02kw and that was it !!!!!????

 

[lame plumber]

m3/hr*10.775

 

[Hobo128]

m3/hr*10.775

??????

 

[tamz]

There are a dozen ways to work it out. They are all approximate as you need the calorific value and correction factor to work it out exactly.
Just use whatever way sticks in your head.

 

[lame plumber]

??????

do the calculations

 

[Hobo128]

Ok, I no how to do the calculations, I think people are missing the point.
When I gas rate a boiler is the answer i get from it in gross or net. Example: .500 first index .593 second index- So 0.093 x 3600 x 10.76 divided by 120 = 30.02 kw Gross or net ????????????????

 

[heliotrope]

Gross when rating direct from the meter. Divide by 1.11 to get net.

 

[smileyplumber]

Ok, I no how to do the calculations, I think people are missing the point.
When I gas rate a boiler is the answer i get from it in gross or net. Example: .500 first index .593 second index- So 0.093 x 3600 x 10.76 divided by 120 = 30.02 kw Gross or net ????????????????

the 120 makes it gross but I could be wrong if I was good at Maths I'd be a banker or better off
I do 3600x.093x10.76div by 120 = 30.02
as said before lots of way use the one that sticks in your head

 

[Killy Bing]

Did you get the indexs from two minutes apart?
on a metric meter?

if so just do the amount passed in two minutes times 30 to get m3/hr

0.093 x 30 = 2.79 m3/hr

Then times by 10.775 to get kw gross

2.79 x 10.775 = 30.06 kw gross

then divide by 1.11 to get kw nett

30.06 divide by 1.11 = 27.08 kw nett

 

[glenno1]

Get the gas rate app or the slide rule from corgi or flea bay it makes life a lot easier

 

[kirkgas]

Take the gas used over 2 mins and multiply by 321 I will do that quicker than you will use the slide rule

 

[lame plumber]

Did you get the indexs from two minutes apart?
on a metric meter?

if so just do the amount passed in two minutes times 30 to get m3/hr

0.093 x 30 = 2.79 m3/hr

Then times by 10.775 to get kw gross

2.79 x 10.775 = 30.06 kw gross

then divide by 1.11 to get kw nett

30.06 divide by 1.11 = 27.08 kw nett

took me less writing to say most of that but all I got was ?????????

 

[Hobo128]

Cheers everyone, I have sorted it now. Alot of the time when gas rating boilers the gas flow rate in the technical data will be miles out because it will have been checked under different conditions when manufactures test it BUT saying that, the answer you get when gas rating is in KW and will be within the tolerances. I hope everyone knows what I mean, this came from the guy who came to inspect my work. It was confusing the sh*t out of me and I thought I wasn't getting correct gas rates from most of the boilers I had put in. I thought I had under sized pipe work or something. Thanks anyway for all the help