radiator calculations

[MP plumb]

hi,

Can you please break down how to do rad calcs. I done them a few years back at college but paperwork is lost.


i dont want to use one of the web sites as i need it to be accurate as poss.

thanks

 

[SimonJohns]

You need to work out volume of room

U values of walls

Floor construction

Ceiling construction

Or. Invest in a mears gauge

 

[PlumbBobBob]

best way to do it without using online calculators is as simonjohns says get a mears gauge.

 

[MP plumb]

thanks for the replys, i know i can use a mears calc and i know i need to find what simonjohns suggested, but there is a way to be accurate to the 'tee'! i was taught it ages ago but my memory is failing me!

 

[Billy Bob Bob]

Clair buy a mears it will be spot on trust me

 

[dancinplumba]

volume, air changes, temp of room, m2 of each surface, u values, glazing, heat gain/loss
av forgot calc tho too

 

[dancinplumba]

then add 10% for rapid heat up ??

 

[MP plumb]

thanks for the help...

i beleive a mears is ok for one room, or a small house but this is for a big job in london, and the last thing i want is for the client to come back saying the room isnt hot enough, and the complaints fall back on me!

 

[tamz]

Big room big rad. Small room small rad.

Get yourself the Stars program from Stelrad
Stars App | Heat loss calculator for any room
Myson used to have a free download called heatloss manager which you will find if you look for it
Barlo (Quinn) do one too.
Or just buy a mears calculator
Mear's Calculators

 

[Mike Jackson]

I've found that mears tend to oversize so if your competing on price it can lead to you being uncompetitive. I've not got the faintest idea where my course notes are and that is the last time I calculated a heat loss longhand. Out of college it was mears all the way until PCs appeared on the market and the first version of STARS came out (which you had too pay for). Since then it's been quick calc on site - mears. Full system - software. I'm looking for a decent app for the iPad now so that I can use it for everything.

 

[CMairiD]

Heatline have a nice computer app. Visit their website and they'll send you a CD.

Quinn have an app for iPad/iPhone. Mind the iPhone as for some reason you can't use the minus sign. Defaults to -1 outside temp, so on the iPhone you can't change to -3.

Stelrad just redone their Stars app and it's all online now: Stars App | Heat loss calculator for any room Not convinced yet. Poor selection of walls, etc and it doesn't appear you can change to custom U values.

 

[fuzzy]

hi,

Can you please break down how to do rad calcs. I done them a few years back at college but paperwork is lost.


i dont want to use one of the web sites as i need it to be accurate as poss.

thanks

fabric loss + vent loss x 15 %

u value x area x temp diff
vent factor x temp diff x volume x air changes
add all up
x by 15%
= rad output

 

[desalman]

Pardon my ignorance but.....If you have worked out the heat requirement for each room using the appropriate U values for the different surfaces plus the air changes etc, why add another 15% ?

I was under the impression that the total heat requirement per room gave you just that - the heat required ( as decided by your choice of outside minimum air temperature. From that you pick your rad size, use the appropriate rad factor then round up to the rad which meets the numbers.

Obviously it's not quite as simple because of heat gains / losses from / to adjacent rooms but the principle is surely the same.

Where have I gone wrong?

 

[fuzzy]

Pardon my ignorance but.....If you have worked out the heat requirement for each room using the appropriate U values for the different surfaces plus the air changes etc, why add another 15% ?

I was under the impression that the total heat requirement per room gave you just that - the heat required ( as decided by your choice of outside minimum air temperature. From that you pick your rad size, use the appropriate rad factor then round up to the rad which meets the numbers.

Obviously it's not quite as simple because of heat gains / losses from / to adjacent rooms but the principle is surely the same.

Where have I gone wrong?

15% is for the initial heat up time, if you only replace what is being lost you cannot increase the temp

 

[Howsie]

Domestic Heating Design Guide is something you should own. eBay or Amazon is where you should head now.

 

[MP plumb]

Thanks everyone.
Fuzzy, that has rung some bells, so I'll give long hand a go again. Thanks

 

[CMairiD]

Domestic Heating Design Guide is something you should own. eBay or Amazon is where you should head now.

A very good book!

 

[desalman]

I understand what you say, but the amount calculated to be lost will not be lost until the temperature differential reaches the design figure.

eg, if a room needs (say) 5kw to maintain an internal temp of 20 deg C against an external temp of 0 deg C then 5 kw will not be lost until the delta T reaches 20 degrees. At that point the input and output will balance with the internal temperature remaining constant at 20.

Is this not so??

 

[fuzzy]

I understand what you say, but the amount calculated to be lost will not be lost until the temperature differential reaches the design figure.

eg, if a room needs (say) 5kw to maintain an internal temp of 20 deg C against an external temp of 0 deg C then 5 kw will not be lost until the delta T reaches 20 degrees. At that point the input and output will balance with the internal temperature remaining constant at 20.

Is this not so??

well as its normally designed on an outside temp of -1 itsa often over sized, you have to have a benchmark somewhere. you can also do some further quals to allow for diffferential in design temp and mean temp of f&r, tbh for most domestic situaTIONAS this is over the top imo

 

[MP plumb]

thanks for the help. after the reminder from fuzzy, i found my old book that has it all in. (plumbing NVQ and technical certificate level 3)

there is one website that lets you do a really easy calcuation, and its not too far off the long hand way. but i guess long hand allows you to show the architect all the workings out.

 

[jam1979]

the best way is to calculate the walls and window heat loses calculate the external wall areas height of rooms how many rooms and floor and loft heat loses all the u values

 

[MattWeth]

Don't forget infiltration losses.

 

[Howsie]

the best way is to calculate the walls and window heat loses calculate the external wall areas height of rooms how many rooms and floor and loft heat loses all the u values

A comma/full stop would help your post no end!

 

[AWheating]

i normally put the calculations into a table to show working values for each room, with heat losses from each wall, floor, ceiling, door, window including u values, air changes etc...... with a totals table for property at the top of the page. Normally this is exceptable for builders needing proof of calculations.

 

[Michael R]

Start with volume LxWxH xsay1.5 (ACHR)x temp rise etc can send details hopefully too many years ago college

 

[MP plumb]

I've done it now, made a spreadsheet so now it looks very professional!

 

[fuzzy]

does the spreadsheet work well?