500mm for a loft? 300-400mm CAT say, as the payback falls right off after that. If fuel rises dramatically in the next 3,4,5 years then 500mm is feasible.
Let me see. In winter the bedrooms 20c and the loft 1C. Hot goes to cold so a difference of 19C. the larger the difference the greater the heat flow. In summer, a loft at 48c and the bedrooms below at 25C, a difference of 23C. Appears better pack the loft with insulation in order to cool the house.
What kind of calculation is that? All you have mentioned is the temperature difference. THe heat flow depends on the U value of the material and the thickness as well. That's the whole point......
Good grief!
I really don't believe you can be any kind of HVAC professional (or any kind of professional for that matter) when you seem incapable of understanding two of the most fundamental formulae:
I'm not 100% convinced: at the weekend I pointed my laser thermometer up into my loft and it was 52C - there's a long south facing slope acting like a giant solar panel. But of course at night the reverse happens and the roof acts like a big cooling radiator.
If I use my example of the 8m x 8m house and the current Building Regs U value of 0.16, and let's say the room temperature of the upstairs rooms is 25 degrees.
Through the upstairs ceiling, the major heat gain would be transmission through the insulation (and I suppose bridging through the ceiling joists if they weren't covered.
Heat gain would then be
64 x 27 x 0.16 = 276W.
Also, due to convection, that heat would remain near the ceiling. This doesn't suggest a major heating effect to the rooms and I can't see any other mechanism for heat transmission through the ceiling.
I suppose one could do the solar gain calculations, but it would seem to me that this and air changes are the major reasons for the house growing warmer....
I found that by ventilating the loft with a fairly chunky fan using air from outside, the temperature drops fairly quickly after late afternoon. When it becomes less than the first floor average air temperature, it's worth opening the loft hatch. In that scenario the loft insulation doesn't help
A pool of heat (hot air) is trapped against the ceiling. This pool of heat heats the thermal mass ceiling plaster and joists and in turn this acts as large radiator radiating down haeting the people and room below. That is why with windows not up to ceiling level it is best have a small ventilator at ceiling height, or on the ceiling. The vent extracts this pool of trapped hot air making the room far cooler and actually cooling the ceiling plaster. This means not requiring an expensive needless a/c.
Victorian houses had high ceilings to take the fumes of gas lights. With Georgian windows up to ceiling level you can pull down the top sash for effective cooling.
Most people don't understand any of and go out and buy expensive a/c equipment. Understand nature and go with it.
Verandahs that's what you need in a hot climate. Ask the Australians. Build them to the right depth and the low sun will still come in the windows in the winter.
What a sweeping generalisation. I currently live in Sydney and there are more double (or more) floored houses than not.
However, I will grant that verandas are only effective for the ground floor. We do have a two to three foot overhang on the first floor which is not as effective as the larger one downstairs, and it would get very hot without effective cooling (we tried it last summer and it was unbearable).
Good to hear about the weather in the UK at the moment - it's cold here.
? Must have been hallucinating whenever I've been there then. Same with the two storey verandahed builidings In New Zealand where I grew up. Sure, many houses are single storied but by no means all. House I spent most of my teenage years in you entered at first floor level from the road and descended to the recreation room, laundry and two bedrooms. On the back of the house there were decks on both levels with cover on the upper deck, guess that makes it a verandah. You could get under the lower deck on one end as the slope was compound. So is this a single story house, a two storey house or a one and a half storey house?
Au contraire, ventilation wont bring a house's temp below the outdoor temp. The keys are insulated roof plus earth floor. The earth floor is a constant source of damp, and as this damp evaporates it cools. Same principle as an evaporative cooler, only big.
In the winter tho, it'll be damper and colder.
Overhanging roof will help as well, and a hgh ceiling with ventilation at the top means the hottest stratum of air escapes. Be grim in winter tho.
No - but there was a slight draught which, as we slept between the doors, was refreshing.
That's true ... but not so's you'd notice. In fact the hens made dust baths in it. But we did notice a slight dew on the underside of the damp barrier under our bed.
Not necessarily, there's a big firepit.
The windows can be closed with shutters. The ill fitting doors can be stuffed with straw. The fire can be lit.
We've done it in similar buildings in very cold winters and have been cosy.
You may find that there is a lot of grass around outside. Any air entering the house, especially from ground that is at a lower level on the north side, will also do the same
During the day am running a fan temporarily mounted in place of the vent in one eave end of the roof. Temperatures have been what are considered, here, hot. That is
75+ Fahrenheit but we do find high humidity worse than the temperature.
The fan keeps the attic roof space at the same temperature as the air; without it the heat build up due to the sun shining on the built up pitch and gravel over tongue and groove lumber on trusses is very high, probably plus 20-25 deg. F. And our roof has plenty of vents all round the soffits and at the two ends! It's now dark the air temperature is lower and I'm still running the fan to remove any residual heat in the roof structure, I'll turn it off when we go to bed. Our ceilings are well insulated but even so cooling the roof space/attic does seem to make the house cooler.
Guys, enough already!!! Everything that can be said has been. IMM - it's apparent you're not any sort of technical professional as all the engineering stuff just goes way over your head, so stop replying with such silly postings. If you don't like a/c's, then fine - don't bloody use any! For the rest of us, the temperatures recently have been way above what any natural cooling will make comfortable. That's not to say some of what you've been saying isn't correct - it is, just your arguments for how much they are correct compared to Andy and other's calculations are pure bullshit!
Suggestions:
Trust Andy, he knows of what he speaks Don't go buy an a/c and be a proud wee martyr Use your good suggestions for ventilation to make you house vaguely bearable in this heat (not the foil under roof one though, that was utter bo**ox!) Get yourself a spell and grammar checker for when you post to NG's
I took the tyke reference to infer small, but I guess it depends where you come from ... doesn't it mean child in most cases? Is there some Black Country meaning I've missed?? ;)
If not a gal ... a woman or a lady I wonder ....??
Yes it does. I thought everyone knew a Yorkshireman (causing more confusion) was a Tyke!
Some authorities suggest that "tyke" (lower case) is a naughty or scruffy child. Not the same thing at all as a Tyke, fully capitalised.
I have nothing to do with the Black Country ... it's not personal, just a matter of geography.
Well, "gal" suggests someone young. I'm not young. A woman definitely. I have no title - except Mistress (normally shortened to Mrs but in the line I'm in I'm usually known as Mistress.
"Miss" is also short for Mistress but I'm properly married and have the fading monochrome photographs to prove it.
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