Heat loss calculation in mansion..help!

[mylocalplumber]

Hi,

Doing a heat loss calculation in a 8 bedroom house in central London. Currently has a light commercial Keston C90, 80l expansion on heating and 2 x 200 - 300l indirect cylinders.

Its a family house with 33 rads with a mixture of cast iron and single/double steel rads.

Wanted to do an exact heat loss calculation which I have never done to this extent.

So Ive measured every wall/internal space, window area etc but when I go to input it on a couple of the online calculators its either not giving me the options I require or mixed answers.

Has anyone got a definite way/software of calculating heat loss?

Should I get a mears calculator?

How exact is working out boiler size by counting exisiting rads?

 

[ShaunCorbs]

can i ask why you need to do a heat loss calc?

 

[mylocalplumber]

can i ask why you need to do a heat loss calc?

Hi Shaun,

Client has requested a full heating system survey including heat loss calc and I also think current boiler is possibly oversized

 

[ShaunCorbs]

COMMERCIAL HEATING - HEAT LOSS CALCULATOR

but tbh if you dont know what your doing could end up wrong if he or she is defo they want a full system spec i would get a firm in to provide the calcs and then you can check if rads are right etc and i would bother if the boiler is slightly oversize as it modulate down if its a newish one

 

[mylocalplumber]

COMMERCIAL HEATING - HEAT LOSS CALCULATOR

but tbh if you dont know what your doing could end up wrong if he or she is defo they want a full system spec i would get a firm in to provide the calcs and then you can check if rads are right etc and i would bother if the boiler is slightly oversize as it modulate down if its a newish one

Hi Shaun,

Its not that I dont know what I'm doing, I've just not done a a calculation of this size and wondering what techniques/software guys are using.

Youre right though, getting a firm to do it would be the easiest but I like to do things myself. Yeah it does modulate down to about 20kw I think but again, want to know exactly what the case is. Guess I just need to spend more time on it.

 

[stevetheplumber]

do one floor at a time and add the results

 

[ShaunCorbs]

Hi Shaun,

Its not that I dont know what I'm doing, I've just not done a a calculation of this size and wondering what techniques/software guys are using.

Youre right though, getting a firm to do it would be the easiest but I like to do things myself. Yeah it does modulate down to about 20kw I think but again, want to know exactly what the case is. Guess I just need to spend more time on it.

if you want to do it right and on your own i use this method nearly mines slightly modded (room by room)

TOTAL HEAT LOSS CALCULATIONS

 

[Sparkgap]

If you're wanting total heat loss from the place measure up areas of external walls, windows, roof and floor. Is it a new building or an old one, has any work been done to improve insulation, etc. etc.
For an old building, cavity walls, wooden windows etc. I'd be looking at a 'U' value of about 0.6 for floor and roof, 1.3 for standard cavity walls, 4.3 for single glazed windows, 2.5 for double glazed windows.
For a new building (last 30 years or less) you could halve those values.
Take the area for each element (wall, window, roof) and multiply by the U value and temp difference. I normally assume -3C outside and 21C inside but they might have higher temps. That will give you heat losses from the fabric, then you want heat loss due to ventilation: take volume of house, multiply by temp difference and 0.33 (this equates about 1 air change per hour). That's your total heat loss. For the boiler size you also want to know what the cylinder coil rating is as some cylinders can be 20-40kW depending on recovery rate.

I don't bother with online calculators as they make too many assumptions and use my own spreadsheet with the values from CIBSE or the architects spec depending on the job.

 

[joni os]

For boiler size I would calculate heat loss for whole building envelope. If you already have the dimensions a manual calc. is relatively simple and easily understood by client. Take into account air changes, one per hour is minimal. Normally I would then allow additional 20% for fast heat up but for a building this size, thermal mass and usage may allow lower figure. This is where art and science meet. Add for DHW demand.
Above all prevent comebacks by including everything. Agree construction details and air change requirements or if unknown agree worst case values.
Size boiler on output not input.

 

[mylocalplumber]

If you're wanting total heat loss from the place measure up areas of external walls, windows, roof and floor. Is it a new building or an old one, has any work been done to improve insulation, etc. etc.
For an old building, cavity walls, wooden windows etc. I'd be looking at a 'U' value of about 0.6 for floor and roof, 1.3 for standard cavity walls, 4.3 for single glazed windows, 2.5 for double glazed windows.
For a new building (last 30 years or less) you could halve those values.
Take the area for each element (wall, window, roof) and multiply by the U value and temp difference. I normally assume -3C outside and 21C inside but they might have higher temps. That will give you heat losses from the fabric, then you want heat loss due to ventilation: take volume of house, multiply by temp difference and 0.33 (this equates about 1 air change per hour). That's your total heat loss. For the boiler size you also want to know what the cylinder coil rating is as some cylinders can be 20-40kW depending on recovery rate.

I don't bother with online calculators as they make too many assumptions and use my own spreadsheet with the values from CIBSE or the architects spec depending on the job.

Thanks mate

 

[joni os]

As addendum to previous:- DHW fast recovery will require 60Kw. This is intermittent,but whoever calculated for the C90 seems to have made good choice. I would caution client against going smaller.