Octopus Heat Pumps

Strummer22

Spies said:

Does anyone know if its possible to calculate heat loss of the property yourself? If I know the outdoor temp, the indoor temp and the amount of gas (in kwh) to maintain a temperature surely theres a formula that can provide me with an answer?

Yes. Your gas boiler will be somewhere around 90 - 95% efficient. Say 90% for any potential losses for getting the heat to your radiators.

Heat loss at a given (constant) temperature difference = gas usage * 0.9 / time over which gas usage is measured, in hours. The units of the result will be kW.

That's it.

Heat loss per m2 of floor space is this value divided by floor space. You can calculate the same value for m2 of wall space if you know it.

Theoretically, the heat loss should double if the temperature difference between inside and outside doubles. So if you measure the loss at a temperature difference (delta T) of 10C, you would expect it to be twice as high for a delta T of 20C.

However, heat loss will decrease if you've got solar gain, and, unless you have a passivhaus, will increase in windy conditions. So if you plan on measuring this, do it on days that when:

• weather is calm, cloudy, and with a steady outdoor temp; 
• the heating is maintaining temp, not raising it; and
• you can measure usage over several hours.

matelodave

Plenty of heatloss calculators on t'interweb - have a shufti at this and then download the calculator and try it yourself - https://openenergymonitor.org/heatlossjs/

or you could try the MCS one - https://view.officeapps.live.com/op/view.aspx?src=https://mcscertified.com/wp-content/uploads/2021/04/MCS-Heat-Pump-Calculator-Version-1.10-locked.xlsm&wdOrigin=BROWSELINK

Reed_Richards

Those are all valid points, @Magnitio .  We had an outside oil boiler so it was just a matter of replacing one ugly monstrosity with a different ugly monstrosity that took up the same space.  You'll lose a lot of space in the airing cupboard too, but you'll gain a heat source that will greatly aid with any actual airing required.  Heat pumps might be marginally cheaper to run that a gas boiler but there's little in it at present.  By the time there is, the government will probably have cut or abolished the grant.      

Spies

Strummer22 said:

Spies said:

Does anyone know if its possible to calculate heat loss of the property yourself? If I know the outdoor temp, the indoor temp and the amount of gas (in kwh) to maintain a temperature surely theres a formula that can provide me with an answer?

Heat loss per m2 of floor space is this value divided by floor space. You can calculate the same value for m2 of wall space if you know it.

Would that be based on a standard ceiling height?

Strummer22

Spies said:

Strummer22 said:

Spies said:

Does anyone know if its possible to calculate heat loss of the property yourself? If I know the outdoor temp, the indoor temp and the amount of gas (in kwh) to maintain a temperature surely theres a formula that can provide me with an answer?

Heat loss per m2 of floor space is this value divided by floor space. You can calculate the same value for m2 of wall space if you know it.

Would that be based on a standard ceiling height?

Depends whether you've got a stepladder and a tape measure! ;-)

QrizB

I worked my way through the MCS heat loss spreadsheet linked above. It was straightforward enough once I'd got my head around it.

Strummer22

The MCS spreadsheet and other heat loss calculators are useful and interesting to play around with. However as you can see you need to know what materials the building is constructed from etc. 

@Spies wants to know whether you can calculate actual heat loss from measured indoor and outdoor temp and gas usage. The answer is yes, and it's a relatively simple calculation.

Spies

So I went with the quick and dirty method that @Strummer22 provided, there was a period today of 3 hours where indoor and outdoor temp were stable, 18c and 10c respectively, this works out to 2.37kWh heatloss, however the room this is based on is double height and has a vaulted ceiling.

Does this sound about right? 

QrizB

Spies said:

So I went with the quick and dirty method that @Strummer22 provided, there was a period today of 3 hours where indoor and outdoor temp were stable, 18c and 10c respectively, this works out to 2.37kWh heatloss,

If you are saying that:

• Over a period of three hours;
• The temperature in a room was maintained at 18C, while the outdoor temperature remained at 10C; and
  
• To maintain that temperature you added 2.37kWh of heat;

... then you can calculate the heat loss for that room under those conditions as 0.79kWh/h, ie. 790 watts.

You can go further and say that, since this was with a temperature difference of 8C, your heat loss was ~99 watts per degree C.

Spies said:

... however the room this is based on is double height and has a vaulted ceiling.

The size and shape of the room is immaterial to these calculations. It could be a broom closet or an aircraft hangar.

Spies

Sorry the 2.37kw is the hourly heat loss, I had already divided by 3 so would that make my heat loss 296w per degree c? 

Is that quite high?