What to do with heat loss calculations

[Jilly]

I've just spent the afternoon resurrecting my memory of trigonometry lessons to fill in Jeremy's heat loss spreadsheet. I've left the weather values as I can't seem to find accurate local ones. What do I actually do with the figures to calculate what I need for heating and hot water? 

 

Sorry to be a bit thick!

Edited February 10, 2021 by Jilly

[SteamyTea]

Try this for local weather.

https://www.metoffice.gov.uk/research/climate/maps-and-data/historic-station-data

[Bitpipe]

The heat loss only tells you your space heating requirement - from memory you plug in your desired year round inside temp (say 20^o) and you'll get a w/m2 value.

 

This is what your heating system needs to inject to get the required temp on the coldest day of the year so helps you size the system.

 

If the house is well insulated and airtight, MVHR etc then you'll probably be looking at a low temp UFH system with additional underfloor (electric or wet) in tiled bathrooms for comfort plus towel rads.

 

If your house is going to perform very well, you likely don't need heating in bedrooms as convection will circulate heat in the house - note MVHR does not significantly move heat around, it is intended to ventilate and minimise heat loss while doing so.

 

Domestic hot water (DHW) is a function of how many people in the house, how many concurrent baths and showers there are likely to be etc - more a consideration of storage (UVC vs Thermal store, and litres stored) plus acceptable recharge time, cost to run etc.

 

If you are on mains gas and want to continue with that, you'll have a nice efficient boiler (e.g. greenstar) which will deliver hot water for DHW and then mix it down for the UFH.

 

If you're all electric then you may use an ASHP and follow the same plan or target it at the UFH temp and consider a means to boost for DHW - Jeremy used inline electric impulse heaters. Others have used Willis heaters etc for their hot water generation and timed with PV generation or E7 etc.

 

Plenty of more knowledgable people will now come along and polish what I've said

 

 

[Jilly]

In cold weather (I've plugged in minus 2), the total daily heat loss power for average outside temp in W is calculated at 1479. 1.5KW cant be right... I must have done something wrong. We have no MVRR as it's a conversion so I put 0.    The house is not being very air tightly built as far as I can see...

[TonyT]

Have you done it for all the rooms and added it up?  
sorry had to ask?

[SteamyTea]

10 minutes ago, Jilly said:

In cold weather (I've plugged in minus 2), the total daily heat loss power for average outside temp in W is calculated at 1479. 1.5KW cant be right... I must have done something wrong. We have no MVRR as it's a conversion so I put 0.    The house is not being very air tightly built as far as I can see...

To get the energy needed, the kWh, from the thermal load, the W, multiply by the hours it is being heated.

So if it is on for 10 hours, then 1479 W times10 hours is 14790 Wh or 14.79 kWh.

Power and energy are not the same thing. 

Edited February 11, 2021 by SteamyTea

[Jilly]

6 minutes ago, TonyT said:

Have you done it for all the rooms and added it up?  
sorry had to ask?

Yes, I think so ?

[Jilly]

1 minute ago, SteamyTea said:

To get the energy needed, the kWh, from the thermal load, the W, multiply by the hours it is being heated.

Do if it is 10 hours, then 1479 W, for 10 hours is 14790 Wh or 14.79 kWh.

Power and energy are not the same thing. 

OK, but how do I decide how long the heating will need to be on for? 10 hours seems reasonable, is that standard for a cold day or just decimalisation for a numpty mathematician? ?

[SteamyTea]

6 minutes ago, Jilly said:

OK, but how do I decide how long the heating will need to be on for? 10 hours seems reasonable, is that standard for a cold day or just decimalisation for a numpty mathematician? ?

Well it depends if you want to keep the house at a constant temperature 24/7, or are happy to have it vary a bit.