Real world vs theoretical hot water temperatures

[Dan Robinson]

For an engineer you're none too bright.

A formula is used. This formula has 2 variables and a constant. No use giving 1 variable in order to get answer unless you want to fart about putting random numbers in.

Give a gas rate and get an answer simples.

For an RGI you don't seem to know the basics

I know a hell of a lot more than you all the same .

 

[jakeycrx85]

Well I say random numbers, most of us know roughly what it could be, but like I said... this is quite funny. Certainly beats pricing an UFH job anyway.

You can work it out accurately like i have though. It's not difficult.

 

[Dan Robinson]

48.5

Well, do enlighten us, what is the delta at 7/lmin?

 

[jakeycrx85]

To work out the 35 degree rise or any rise you use the following formula:

KW rating of boiler ÷ 35 degrees (or which ever temp rise you want to work out) ÷ specific heat capacity of water = flow in kg/s

You then multiply kg/s by 60 to give l/min

Just to prove the point I'll work it out for 4 different boilers and compare it to Vaillants specified flow rates.

For my boiler it is: 23 ÷ 35 ÷ 4.18 x 60 = 9.43 l/min (Rounds down to 9.4)

Ecotec 831: 31 ÷ 35 ÷ 4.18 x 60 = 12.71 l/min (Rounds down to 12.7)

Ecotec 837: 37 ÷ 35 ÷ 4.18 x 60 = 15.17 l/min (Rounds up to 15.2)

Pro 28: 28 ÷ 35 ÷ 4.18 x 60 = 11.48 l/min (Rounds up to 11.5)

If you look at the Vaillant manual it all correlates with their given flow rates:

If you want to work out what the temperature rise is for a given flow rate you just simply rearrange the formula to:

KW rating of boiler ÷ specific heat capacity of water ÷ flow rate in kg/s = Temperature rise

To convert from l/min to kg/s you need to divide by 60 so 8 ÷ 60 = 0.1333

So for my boiler at 8 l/min it is: 23 ÷ 4.18 ÷ 0.1333 = 41.28 degrees

7 l/min is 47.19 degrees

Like I said you don't need to know the gas rate.

 

[AGAS]

WE ARE TALKING ABOUT YOUR BOILER PERFORMANCE. taking info from the manus is the performance when leaving the factory ( we hope )

 

[jakeycrx85]

WE ARE TALKING ABOUT YOUR BOILER PERFORMANCE. taking info from the manus is the performance when leaving the factory ( we hope )

I'm talking about calculating temperature rises

 

[Dan Robinson]

Kind of ironic you refusing to do a gas rate when you consider the title of the thread innit .

But that's right - you're god's gift to engineering with your making of MLG and whatnot.

 

[Dan Robinson]

Guys I wouldn't of gave this bellend 2 mins of my time , hats off to ya

Like I said - beats writing estimates

 

[jeff the gasman]

I can't believe the 8 pages I've just read. He really is a twonk.
Someone tell him if it's only getting 20 KW worth of gas you can only get 19 KW out of the boiler.

 

[jakeycrx85]

You're talking out of your a7se, but at least you found the mass flow rate formula.... Now if you gas rate your boiler you can do things properly.

Why does the formula not use gas rate then?

Look on the bright side at least you learnt something today

Kind of ironic you refusing to do a gas rate when you consider the title of the thread innit .

But that's right - you're god's gift to engineering with your making of MLG and whatnot.

You like to think you're God's gift to RGI's but you're clearly not.

Guys I wouldn't of gave this bellend 2 mins of my time , hats off to ya

Bellend? Pot, kettle, black?

I can't believe the 8 pages I've just read. He really is a twonk.
Someone tell him if it's only getting 20 KW worth of gas you can only get 19 KW out of the boiler.

I'm only interested in the output. The input is obviously higher than 23 KW. 2.5 m3/hr is a fair bit more than 23 KW.

 

[Nozzle]

I'm only interested in the output. The input is obviously higher than 23 KW. 2.5 m3/hr is a fair bit more than 23 KW.

Take a look at the back of your gas bill and you can tell what the power input would be for 2.5m3/hr. I suggest most of the heat input is put into the circuit, the rest lost to the exhaust. Unlike say a car, power station, jet engine etc where most is rejected to the environment.

Nozzle

 

[Stadan20]

It appears my comment was deleted , just like I said it would , I hope my 2 likes wasn't taken from me hahahaha... This time I didn't have a notification saying they got taken off , it must be a ninja mod

 

[AGAS]

 

[AGAS]

in a weird way i did enjoyed his contribution it certainly made me giggle

 

[jakeycrx85]

Nozzle[/QUOTE]

I'm only interested in the output. The input is obviously higher than 23 KW. 2.5 m3/hr is a fair bit more than 23 KW.

Take a look at the back of your gas bill and you can tell what the power input would be for 2.5m3/hr. I suggest most of the heat input is put into the circuit, the rest lost to the exhaust. Unlike say a car, power station, jet engine etc where most is rejected to the environment.

Nozzle

The calorific value on my bill is stated as 39.2 so 2.5 m³/hr equates to 27.84 Kw.