Transmitted Heat Gain Through Structure?

Squall Leonhart

Hi,

I am really hoping that somebody will be able to assist me in working out the heat gain of a building, as the transmitted heat gain through a structure.

I.e., the sun will be shining on a building all day (well, ideally.. not so much in Ireland ), heating the walls, and the roof of the building. The heat of which will slowly be radiated into the house in the evening/night. Perhaps not to any perceptible level (winter) but can be quite notable (Summer).

Can somebody assist with formula for this?

It's a standard 300mm block wall, with a U-Value of 0.21 w/m2K.
The roof has a U-Value of 0.16 W/m2K, and is just tiles on timber battens/rafters.

Any further information needed I'll provide it as needed, I've quite a lot of information about the building.

Thanks,
Paul.

Supertech

Try Green Design - Sustainable Building for Ireland, A Green Vitruvius, and Environment and Energy in Architecture. You'll probably only get them in academic libraries, but yo should find something useful in them. (Definitely Green Design - I used it for a similar purpose last year)

Also have a look at Thermal Mass - useful publication here -

http://www.irishconcrete.ie/downloads/Thermal_Mass_and_Sustainable_Building.pdf

Some of the CIBSE Guides may be of help aswell.

Squall Leonhart

Oddly enough, I have a PDF copy of Green Design on my hard drive... Perhaps it was silly of me not to check it out, I never even thought of it. I'll look into it, cheers!

Squall Leonhart

After a good look through the Green Design - Sustainable Building for Ireland book, I'm no further on. It contains useful information about the heat gained through glazing, but I have already figured this one out.

I'm still concerned more so about the heat coming through the opaque elements of a building.

sydthebeat

id suggest you enquire of one of the passive house designers listed here.

the amount of heat gain can be worked out by reference to solar gains as listed in DEAP, and heat retention and emmitence as reference by the window manufacturers tech details.

however, the ability to store and release heat (decrement delay) is harder to calculate. some materials are better at releasing heat when need than others, eg concrete is actually a bad thermal store when compared to say dense insulation or fibreboard. Concrete releases heat quickly so say 12 hrs of daytime stored heat may be released back into the house in 6 hours of night... preferably there should be equal storage and release times.

http://www.viking-house.co.uk/decrement-delay.html

http://www.greenspec.co.uk/decrement-delay.php


this may also be of some use, i havent looked at it myself
http://www.designbuilder.co.uk/component/option,com_docman/task,cat_view/gid,11/Itemid,30/


pm for pdf document with mathematical calculations of solar absorbtion etc (way over my head kinda stuff )

Mellor

I don't know if there is much point chasing that route.

It will be significant in the summer. but not so much in the winter.
Built to current standards you won't need to use the heat in summer so we aren't really concerned with gains. In winter the exteranl temps will be colder than the internal, so most of the heat will radiate away from the house.

IMO heat gains through opaque elements during the time of year when the heat is on are small enough to be ignored.

jonniebgood1

Mellor wrote: »

I don't know if there is much point chasing that route.

It will be significant in the summer. but not so much in the winter.
Built to current standards you won't need to use the heat in summer so we aren't really concerned with gains. In winter the exteranl temps will be colder than the internal, so most of the heat will radiate away from the house.

IMO heat gains through opaque elements during the time of year when the heat is on are small enough to be ignored.

What is 'current standard' for heat gain. Applying a 'standard' to what should be a developing part of construction is a dismissive & negative outlook. You are correct to point out that a trombe wall (being a regular component of heat gain) is not best suited to Irelands climate. Potential problems with overheating in summer compared to winter can be designed out with roof ovehangs extended so that the optimum results occur in winter when they are most required. If the heat gains are insufficient as you point out then there is the possibility of upgraded design on the south facing wall.

http://books.google.ie/books?id=1Yj-fzAhyCsC&pg=PA137&lpg=PA137&dq=trombe+wall+in+winter+uk&source=bl&ots=zeB-JGGLGh&sig=bAsQTU7-QH0HnCMiOUx7HLhnhsA&hl=en&ei=b5-mTehKk4GFB_3Esc0J&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCoQ6AEwAw#v=onepage&q=4.3.3&f=false

Mellor

jonniebgood1 wrote: »

What is 'current standard' for heat gain. Applying a 'standard' to what should be a developing part of construction is a dismissive & negative outlook. You are correct to point out that a trombe wall (being a regular component of heat gain) is not best suited to Irelands climate. Potential problems with overheating in summer compared to winter can be designed out with roof ovehangs extended so that the optimum results occur in winter when they are most required. If the heat gains are insufficient as you point out then there is the possibility of upgraded design on the south facing wall.

Current standard refers to building standard.

The heat gain via opaque elements are so small during winter that they can be ignored.
A standard house isn't going to over heat ever in an irish climate.


On the other end of the scale you have passive houses. Which won't need any heating so they already are design to maximise gains, focusing on opaque elements in winter is unnessecary.

In summer there may be an overheating situation. But here the problem is mostly due to windows, opaque elements are not the problem. My point is that while is is possible to get gains through opaque elements, they aren't the biggest concern.
Overhangs and such are design features for glazed elements not opaque elements by the way.

jonniebgood1

Mellor wrote: »

Overhangs and such are design features for glazed elements not opaque elements by the way.

An overhang can be used wherever required, not just on an one particular element.

Mellor

It would be a waste of time.

1. Overahangs work on windows as they are generally higher the facade.
2. They don't work as well on walls as the the whole wall lets in heat, so they cover a much lower proportion of the wall. The base of the wall lets in heat too.
3. The majority of heat through opaque elements is through the roof, where the over hang has zero effect.

A overhang, or similar structire can reduce the heat through a window by a significant amount. An over hang will reduce heat through opaque elements by next to nothing.

Have you honestly ever had to do this for a house, in ireland. I honestly think you are jsut spouting theory and not thinking of the application.
We aren't concerned with what happens in other climates. (i live in a climate where overheating is an issue. And still windows are the huge factor. When ever over heating is high through opaque elements, its sky high through windows. Trying to factor in and combat opaque elements is pointless as its much easier (and cost effective) to control the windows.

jonniebgood1

Mellor wrote: »

It would be a waste of time.

1. Overahangs work on windows as they are generally higher the facade.
2. They don't work as well on walls as the the whole wall lets in heat, so they cover a much lower proportion of the wall. The base of the wall lets in heat too.
3. The majority of heat through opaque elements is through the roof, where the over hang has zero effect.

A overhang, or similar structire can reduce the heat through a window by a significant amount. An over hang will reduce heat through opaque elements by next to nothing.

Have you honestly ever had to do this for a house, in ireland. I honestly think you are jsut spouting theory and not thinking of the application.
We aren't concerned with what happens in other climates. (i live in a climate where overheating is an issue. And still windows are the huge factor. When ever over heating is high through opaque elements, its sky high through windows. Trying to factor in and combat opaque elements is pointless as its much easier (and cost effective) to control the windows.

I agree. None of this is a contradiction