Cooling the home, methods?

[Harry Bloomfield]

So what do other do to keep their home cool, and cost, be it a heat pump or fan, and how to control, lets have some ideas in action.

I cool the house fabric down, during the night, aim to restrict solar gain during the day. During the night, front bedroom window(s) are flung wide, along with rear window(s), to take advantage of cooler night air, to cool the house fabric down. During the day, we close blinds, to bounce heat back out, all windows are closed, we just have the back door open, which has a permanent for the summer fly screen up. My routine works for several days, even in the worst of the heat, to keep the house a few degrees cooler than outdoors.

For a little extra comfort, during the night, in bed - I swapped the ceiling light, a while ago, for a fancy, combined remote controlled, variable speed fan, variable brightness LED light. It's much better, more useful than a portable one.

 

[Why Not Indeed]

How about opening the loft hatch? Heat rises, so in theory the warmest air from the habitable space should go up into the roof void.

 

[big-all]

How about opening the loft hatch? Heat rises, so in theory the warmest air from the habitable space should go up into the roof void.

old thread but worth comment

a well insulated house may be perhaps 24 to 28 degrees the loft space with all day solar gain may be mid 30s to 50 degrees so heat tranfer would be very negative

 

[Why Not Indeed]

Yes indeed, at 1800 it was 26°C in my office yesterday and 37°C in the loft. I wasn't expecting conduction, it was more convection I had in mind.
But I think you pointing out that the gradient is the "wrong direction" to cool down the habitable space means that opening the loft hatch won't work.

 

[Harry Bloomfield]

old thread but worth comment

a well insulated house may be perhaps 24 to 28 degrees the loft space with all day solar gain may be mid 30s to 50 degrees so heat tranfer would be very negative

This is our situation, this morning... Yellow is the indoor temperature, blue the outdoor- it is already 27.1C out there. We've had two bedroom windows wide at the front, bathroom window wide over-night, now closed, as are blinds on the sun facing side. You can see a dive in indoor temperature, when the windows are opened at 11pm last evening. The dive in indoor temperature, wasn't as pronounced as usual, because there was absolutely no breeze through the house.

Opening the loft hatch, will not be very effective, unless the rising air has somewhere to escape, once it rises into the loft. A well sealed uninsulated roof, the temperature up there could easily be 50C. Open the loft, and warmth from the house, will rise into the loft, initially causing that 50C air to drop into the house, the opposite effect to that required. A well insulated roof, with some sort of open, opening window up there, can be very effective.

 

[robinbanks]

a well insulated house may be perhaps 24 to 28 degrees the loft space with all day solar gain may be mid 30s to 50 degrees so heat tranfer would be very negative

Insulation works both ways, and I expect you'd find a heat gradient established so there wasn't a huge transfer down to the extent that you'd notice at head height in a room. The biggest meaningful effect of a loft hatch would be if one opened a door or window elsewhere and a breeze was blowing from a direction where the roof profile formed an aerofoil making the loft slightly lower pressure, increasing the draw of air from the house into the loft.
That said, loft hatches aren't typically very big so the major limitation to cooling effect would be the amount of air that could be moved through the opening. Opening more doors and windows on the prevailing windward side would help but overall one would probably be better forgetting the loft and trying to arrange a through draught of air, in at the bottom on the windward side and out at the top on the leeward

A well sealed uninsulated roof

Most lofts aren't; well ventilated loft spaces dispel moisture buildup before it condenses, so tend to be how they're constructed

Yes indeed, at 1800 it was 26°C in my office yesterday and 37°C in the loft.

Indeed, and I suspect that opening the loft hatch and letting the breeze through would have done relatively little to counter N square metres of roof insolating at the tulle of thumb rate of 1kW per sqm; that's a big ole electric fire equivalent

because there was absolutely no breeze through the house.

Having been in a similar situation for many years, of circa 6sqm of south facing non opening roof glazing in the office, the ceiling of which has 300mm of PIR (not so bad on winter), I've finally installed the 21 inch extraction fan I was gifted several years ago, such that I can open a cupboard door, switch it on and evacuate all the house volume in about 3 minutes
It just irks me that it costs 350W minimum to run. Thinking of having 4 desk fans mounted in plywood instead.. Slower but less than half the running costs

 

[JohnD]

Open the loft, and warmth from the house, will rise into the loft, initially causing that 50C air to drop into the house,

I'm very interested in your suggestion that hot air falls.

The Montgolfier brothers didn't know that.

 

[Why Not Indeed]

I'm very interested in your suggestion that hot air falls.

If all this was about, was convection, then you might have a point, but the loft isn't airtight and there is a breeze, so air moves both ways.

When I opened the loft hatch, after a while I could smell the smell of the loft. So air from the loft definitely came down.

 

[Harry Bloomfield]

If all this was about, was convection, then you might have a point, but the loft isn't airtight and there is a breeze, so air moves both ways.

When I opened the loft hatch, after a while I could smell the smell of the loft. So air from the loft definitely came down.

Exactly! Loft lid closed, the hot air will be trapped up there. Open it, and cool it, but in the process some of the 50C hot air will be displaced out through the hatch. Once the air currents get going, the open hatch, will cool the house.

My loft is a little different, the centre section is well insulated, remains cool, but is fitted with a Velux. Open the hatch, open the Velux, and an outside door, then there is a substantial positive flow, through the house. As an alternative to opening the Velux, I can open either of both doors, to the loft wings for through ventilation.