Heat Loss Calculation for my renovation

[wcavanagh]

So I am trying to do a heat loss calc for my renovation project. Im not sure if I am doing it right. Wonder if someone could help.


First off I am using Stelrad STAR App to calculate as it seems the most detailed.


It is a 1900 solid stone cottage, that I have insulated big time. 100mm Kingspan built in all external walls via a new timber frame. 150mm in between the roof apex, 100mm in the concrete solid floor, then a further 40mm under the self levelling screed. All windows are Argon triple glazed.


So questions.....


When I calculate each room, do I need to take into account U value of internal stud walls?


The cottage is about 150 sqm floor area, and calculations are coming in at about 14KW load? This seems very low.


I am keen to get this right as it will need an oil boiler and want to avoid short cycling as much as possible.


One last thing, its heated by all UFH in the screed. Does this make any odds?


Many Thanks

 

[muggles]

14kW could be right, it's a similar size house to mine and that's what I'm running on. Get yourself a Hounsfield Tuscan 12/19 and that'll give you headroom if you need to increase the output a bit, or allow you to reduce if you can get away with it

 

[wcavanagh]

Many Thanks,

So its not totally crazy. haha. Been doing many calculations and they all seem to hit that. I guess I am meant to ass 3000W for hot water on top.

Is that right?

 

[muggles]

Depends on your setup but not necessarily - I haven't bothered, I just time my hot water to come on an hour before the house needs to start warming up when we get up in the mornings, then boost again for an hour in the evening. With a well insulated modern cylinder they don't lose much heat through the day.

 

[John D v2.0]

I'm not a pro but you are always sizing your boiler for the maximum heat loss situation ie -1c, including heating up in a reasonably time.
So you would avoid cycling at the coldest time of year but it would still cycle if the demand is below the minimum which would be late autumn and spring.
Is your insulation all internal, or do you have some thermal mass on the inside of your insulation? If you have plenty of thermal mass you should have less of a problem of fluctuating temperatures.
Some people advocate having some kind of heat dump radiator to prevent cycling at low demand but that wouldn't comply with efficiency regs.

 

[wcavanagh]

It is all insulated internally and I have poured a self leveling screed around the UFH pipes, it has about 11 cubic meters of screed if that helps size the mass. I was also advised a buffer tank can help with the short cycling.

 

[John D v2.0]

11 cubic metres is pretty good. Short cycling would be caused if there's not much water/heat loss in the system, so it would be influenced by whether you want to heat the whole house or just one room most of the time.
Maybe some of the more experienced members would advise on the practicality of buffering the heat on such a system.

 

[wcavanagh]

Many Thanks,

Guess we will have to see how it goes, at least its an option, and maybe someone will help. The Mrs likes the house warm, and we are in Scotland, so guess it will be on a fair amount. It will have stats in each room, as i have divided it into 12 zones. So i guess, when the floor only needs a small top up of heat, the boiler could short cycle.