calculating heat required to heat a room, for idiots

[Lin]

Not sure this is the right place for this question.....

Can anyone point me in the right direction to find out how to understand or make a basic calculation for the heat requirement for individual bedrooms. Just an idea not 100% accurate

My blood pressure is rising just thinking about having to do this.

What sort of professional should know how to do this if I give up.

[le-cerveau]

@JSHarris has a good spreadsheet, however you need to know the make up (u-value) of the floor, walls and ceiling, temperatures of adjacent rooms/outside, u-values for windows and doors, areas for them all..

There are lots of heating calculators out there but without the specifics inputs they are 'gestimates' at best.

[Visti]

This is the spreadsheet in question:

 

I'd suggest that you do the calculations for the entire house rather than per room as that can get quite complex, which is exactly what that model does. 

 

First you need to know the following for each of the external surfaces of your house (Foundation, Walls, Roof, Windows, Doors)

• Surface Area (m2)
• U-Value (U)
• Temperature difference (dT) - usually 21 degrees inside, minus the ave outside temp. This will change with the seasons mind!

That loss in Watts is equal to m2 * U * dT

 

You can convert that to kWh to identify the total cost of heating your home given your current £/kWh for electricity by your energy supplier.

 

 

 

[Luckylad]

Are the Asterisk symbols representing multiplication?

[Jeremy Harris]

49 minutes ago, Luckylad said:

Are the Asterisk symbols representing multiplication?

 Yes.  some of the more common standard keyboard symbols for mathematical operations (because keyboards don't have all the mathematical symbols we often need), are:

 

Addition +

Subtraction -

Division /

Multiplication * or . (I tend to use . some use *)

Raising to a power, say taking the square of a number ^2 (or ^5 for raising by the power of five).  This forum is handy in that it also allows superscript text for powers, like 4² for four squared, or 16 (4*4)

 

There are quite a few other common keyboard abbreviations, but we could probably do with putting together a glossary.

 

 

[Luckylad]

Ok thanks 

Ive tried clicking on the link above to your fabric and ventilation heat loss calculator but it just appears as a lot of question marks.

Could it be to do with the fact ive only got an iPad?

[SteamyTea]

Yes the * is multiply

 

Sometimes a  . is used, as is an x, and sometimes there is nothing.

 

U-Value is a measure of power, with the unit W. W means watts and is what is called a derived unit.  It is derived from the basic SI units of mass, distance and time.

This may sound a bit odd when you think of electricity or solar power, but it really does all make sense.

The other derived unit is the joule, J, and is the unit for energy.  The old name for energy was heat, and is descried as the ability to do work, the rate at which work is done is  called power, which is watt, W.

So you can see that there is a relationship between energy and power, with the only difference being time, which is measured in seconds, s.  We sometimes use hours (h), 1 hour is 3600 seconds.  You may also often see 8760h which is 1 year.

 

So U-Value is W.m^-2.K^-1

All that means is power divided by metres squared multiples by temperature difference.  It may also be written as W / (m² . K).

So if you have a wall, or window, or anything that allows energy to pass though it because of a temperature difference between one side and another, you need to know 3 things initially.

 

The U-Value of the element you are looking to calculate, say a wall with a U-Value of 0.15 W.m^-2.K^-1 (°C and K are interchangeable) , the surface area on the cold side, say 7.5 m² and the temperature difference between the two, say 12°C.

 

Multiply them all together (called the product) gives you the power loss in W (watts)

 

0.15 [W.m^-2.K^-1]  x  7.5 [ m²]  x  12 [°C]  =  13.5 W

 

Now say you have those exact conditions for 8 hours, you can work out the energy loss in watt hours.  This is useful as we buy our energy in kWh, or 1000 Wh.

So 13.5 [W]  x  8 [h] = 108 Wh, which is 0.108 kWh.

 

If you pay 3p per kWh for gas, then the losses will cost you:

0.108 [kWh]  x  0.03 [£] = £0.00324 (or about 0.33p).

 

Now what you have to actually do is work out all your areas and the associated U-Values, get some local weather data, and work out the losses for a whole year.

This may sound daunting, but it is what spreadsheets are made for.

 

Hope that helps and feel free to ask about any bit you do not understand (and I may have made an error anyway).

 

Here is a power loss calculator I knocked up a while back.

https://steamytea.wixsite.com/u-valuecalculator

Edited January 11, 2018 by SteamyTea

[Jeremy Harris]

6 minutes ago, Luckylad said:

Ok thanks 

Ive tried clicking on the link above to your fabric and ventilation heat loss calculator but it just appears as a lot of question marks.

Could it be to do with the fact ive only got an iPad?

 

It's a spreadsheet that should run on any spreadsheet software, it certainly works fine on Excel and Libre Office Calc, under Mac OS, Windows or Linux with Excel or Libre Office installed.  I'm not an iPad person, but there are spreadsheet apps for the iPad.  Sadly I've no idea how compatible any of them are with Excel or Libre Office Calc.  You may be able to get Excel for the iPad, I think.

Edited January 10, 2018 by JSHarris

[SteamyTea]

You can get LibreOffice for the iPad, and it is free.

Most of us work with Excel and there may be the odd incompatibilities, but generally for basic stuff there is not a problem.

If you have a PC, it may be easier to do all this calculations and stuff on that.

[Luckylad]

Thank you both for your help.

I haven't got a pc at home although I can  sometimes access one at my wife's work.

I'll have a proper go at heat loss calculations with my ipad at the weekend.

[SteamyTea]

Does the iPad have Numbers on it, if so, that will be perfectly good enough.

[Luckylad]

I'll have a look when I get home tonight.