Heat loss calculations

mail

Hi when doing heat loss calculations for a building are the total results in kW per hour for when the heating is operating or for the full 24 hrs, thanks

BryanF

mail wrote: »

Hi when doing heat loss calculations for a building are the total results in kW per hour for when the heating is operating or for the full 24 hrs, thanks

We could do with more details about how your calulating but generally : kwh/m2/yr -
See current part L technical guidance documents from DOE website

mail

Thanks, I have calculated the total heat loss from the house as 15kW which includes all the elements, walls roof windows floor. My heating will operate for 40 weeks of the year. The floor area of the house is 140m sq. I suspect I am doing something wrong but cant find what, any help appreciated.

kW/hr = kW x time
140m sq. / 15kW = 9.33 kW
8hrs x 7 days x 40 wks = 2240 hrs
9.33kW x 2240 hrs = 20899 kW/hr
20899 kW/hr x e 0.058 Gas per kw/hr = 1212.14( euro)

brdboard

mail wrote: »

Thanks, I have calculated the total heat loss from the house as 15kW which includes all the elements, walls roof windows floor. My heating will operate for 40 weeks of the year. The floor area of the house is 140m sq. I suspect I am doing something wrong but cant find what, any help appreciated.

kW/hr = kW x time
140m sq. / 15kW = 9.33 kW
8hrs x 7 days x 40 wks = 2240 hrs
9.33kW x 2240 hrs = 20899 kW/hr
20899 kW/hr x e 0.058 Gas per kw/hr = 1212.14( euro)

How did you calculate the heat loss?
Is it based on u-values of the different elements?
The heat loss is dependent on the internal and external temperatures

This line of your calculation doesn't make sense to me

140m sq. / 15kW = 9.33 kW

Is the 15kw the heat loss per hour?
I think if you gave an insight into how you calculated the heat loss it might help

mail

The heat loss is based on all the individual elements and their u value and yes the inside temperature and outside temperature are taken into account.
I arrived at a figure of 15kW and I am unsure as to how to proceed from here. I want to know how much money is being lost and dont know if the 15kW is for when the heating is on or is it divided up over the year, thanks.

brdboard

mail wrote: »

The heat loss is based on all the individual elements and their u value and yes the inside temperature and outside temperature are taken into account.
I arrived at a figure of 15kW and I am unsure as to how to proceed from here. I want to know how much money is being lost and dont know if the 15kW is for when the heating is on or is it divided up over the year, thanks.

How did you get the answer of 15kw? Could you include some calculations of how you got to that answer.

Is that heat loss per metre squares per year?
15kw itself doesn't mean much without knowing the area and time span it refers to.

sinnerboy

Have look here

mail

This is how I arrived at the figure, I want to know how to calculate the cost of the heat being lost over a year.

Element Area M² U Value Temp Dif ° Watts

Windows and Doors 32.00 1.6 22 1126
Walls 229.00 1.65 22 9312
Roof 108 2.9 22 6890
Floor 108 0.19 22 451

Ventilation
number of air changes per hr. 4
volume of building m³ 514
sp. Heat factor of air 0.34
temp difference ° 22

heat loss in Watts 15378 15378
Total heat loss in Watts 33157
1000 watts = 1 kw 33.1 kW

Andrew_Doran

I don't know all the necessary details but I do know it's an awful lot of work to calculate what you want, a lot more than you have there. For instance you'll need to include solar gains and account for the difference in temperature across the seasons.

Is it the method you're interested in or the result?

If it's the result, then there is government provided software that is free, tailored for Ireland and will do all the calculations for you:

http://www.seai.ie/Your_Building/EPBD/DEAP/Download/

sinnerboy

+1 and look at post #7.

fclauson

Or use the PHPP spread sheet

as said above U values is one thing - but there is also solar gain which also then needs to know the construction type and the thermal mass of the internal materials

MOTM

fclauson wrote: »

Or use the PHPP spread sheet

as said above U values is one thing - but there is also solar gain which also then needs to know the construction type and the thermal mass of the internal materials

...along with other internal gains (metabolic, appliances, gains from water heating system etc).
If you're feeling really adventurous, you could look at this for ideas:

I.S. EN ISO 13790:ENERGY PERFORMANCE OF BUILDINGS - CALCULATION OF ENERGY USE FOR SPACE HEATING AND COOLING

mail

Apologies Sinerboy I should have posted here,
Hi thanks for your recent replies regarding heat loss, could you explain why you divided by 1000 here

(20-9) X 24 x 365 / 1000 =96.3 kKhra.

Also what does kKhra mean
Would this example work for a wall,
u value 1.65 x 96.3 x 0.058 x 229m sq = 2110 euro
0.058 is the cost of gas per kWhr, this seems like a way out figure. I dont need to be exact as in the calculations in DEAP just looking for a ballpark figure.
Thanks again for your help

sinnerboy

/1000 to go from watts to kilowatts

kKhra means kilo kelvin hours per year which means the same thing as kWhrs / year

Your example calculation looks right i.e. to cost allocateble to walls alone to maintain 20 degrees internal temperature year round in Ireland with un-insulated hollow block walls of that quantity would be over €2k. More when you add in losses through the floors and roofs and add on for hot water.

You are only finding this incredible because in Ireland we are not used to 20 degrees constant internal temperature as we could never ever afford that. Thr house holder pays €2k + for fuel to keep the house barely tolerable in winter in my experience. Untill now - current building regulations will deliver to those that embrace them thermal comfort and affordability.

mail

Thanks very much for your detailed reply, it has opened my eyes to what can be achieved by careful building.