Ventilating a 1 1/2 story house.

[Rorschach]

That's OK then 22 inside is bearable and will feel lower if there's a draught.
Sorry I forgot your are anti science so weather forecasts and a lot of these things won't mean much to you!

It isn't 22c inside, it's 27c because the house is already hot, I can bring in some air but it doesn't cool the house sufficiently to bring it back down to the outside temp and we have had no breeze for a week.

Look buddy, you are talking rot as usual, temperatures inside huge thermal stores like houses don't change on a dime when the temp outside falls for a few hours overnight.

 

[Jacob]

...
I can bring in some air but it doesn't cool the house sufficiently to bring it back down to the outside temp

not enough air

Look buddy, you are talking rot as usual, temperatures inside huge thermal stores like houses don't change on a dime when the temp outside falls for a few hours overnight.

If you have insulation (in the right places) the inside temperature won't rise so high and if you have enough ventilation it can be brought down to external air temperature. There are other passive measures of course but these are top priority.

 

[Rorschach]

Insulation means nothing in prolonged periods of constant temperatures and no active heating or cooling, even you know that.

 

[Jacob]

Insulation means nothing in prolonged periods of constant temperatures and no active heating or cooling, even you know that.

Surfaces in sunlight can get very much hotter than the air temperature and if not insulated can raise internal temperature too.

 

[Rorschach]

Surfaces in sunlight can get very much hotter than the air temperature and if not insulated can raise internal temperature too.

Yep but I am just talking about air temperature. Have a constant average air temperature of 25c for over a week and it doesn't matter how well insulated your house it, the house is stuck at at least 25c unless you have active cooling.

EDIT: Just looked at the actual recorded temperatures for a 24 hour period this week, the average air temperature was 24c over that 24 hours and we had more than 12 hours of constant sunshine so there is an awful lot of solar gain to add onto that. How exactly without active cooling do you propose to get a house down to a reasonable temperature with just ventilation? It isn't physically possible. Insulation will keep out *some* of that solar gain but conversely it will keep in radiated heat overnight making it harder to cool the house.

 

[Jacob]

Yep but I am just talking about air temperature. Have a constant average air temperature of 25c for over a week and it doesn't matter how well insulated your house it, the house is stuck at at least 25c unless you have active cooling.
......

You won't have had constant 25º for over a week, especially not with clear skies.
Check your local weather reports.

 

[Jamesc]

I would suggest you look up passive cooling. Thsi is a very involved subject but the basics are to minimise heat gain during the day and maximise ventilation when the air is cooler.
As others have said insulation will help, your roof covering will inevitably be a dark material which will absorb heat (just put you hand on the roof or walls after a few hours of full sun). The insulation will help to stop the transfer of this heat into the house.
Next is solar gain through the windows (think greenhouses), Ideally you want to shade the windows from direct sunlight. This is what the projections you often see on commercial buildins above the windows are for (Google 'brise soleil' for more info). Pulling the curtains or blinds especially if they have a white lining can help.
Finally ventilation. Warm air rises so always try to work with that. if you can create an air path with downstairs windows open on the cool (shaded) side of the house and upstairs windows open on the warm side you will create an natural air flow bringing in cool air. The natural inclination to throw open every window in the house just does not work unless there is a good breeze. The downside to this is the the sun moves so you have to monitor where the sun is falling and adjust your arrangements accordingly. This is why there are many companies out there now selling fully automatic natural ventilation systems. If you are interested one of the bigger players in this country is Monodraught.
Regards
James

 

[Terry - Somerset]

Some years ago I suggested to my dear wife it would be very straightforward (power, access etc all easy) to put a split unit AC to service the three bedrooms at the back or the house which get late afternoon and evening sun.

No - quite unnecessary, I can cope. Regret is not doing it - will be on the list for later this year.

But a few related thoughts:

• meditteranean countries often fit shutters - allow airflow but reduce solar gain - a reasonably cheap fit
• I have wondered whether a water spray onto the roof would dramatically reduce internal temperatures through evaporation. This could be a very cheap fix - hose pipe, garden sprinkler, run for 30 mins as sun sets. Any views??
• we have tried with some success putting a small fan blowing air into the bedroom (with the bedroom door opento allow airflow) from an open window. This could be improved with a larger fan and ducting to ensure the fan only blows cooler external air in rather than churn what is probably a mix of external and internal air.

 

[Jamesc]

Hi Terry,
Your second point is called evaporative cooling and could indeed work. The downside is the risk of Legionella. Evaporative coolers are all but banned for this very reason. Without getting into any kind of debate, Legionella is present in pretty much all water sources, it is only a problem if the concentration gets high (usually stagnent water - think gutters) and the particles are breathed in from a mist of vapour (splashing water from your hose).
It is a small risk but something to be aware of.

 

[Adam W.]

The only time this old place gets hot is when it's 36ºC outside for a couple of weeks. So we had the heating on and the woodburner going for a few hours yesterday.

Lovely!

 

[Rorschach]

You won't have had constant 25º for over a week, especially not with clear skies.
Check your local weather reports.

Check my previous post, I did the math based on actual recorded temps. Just so you know I added together 24 numbers and then divided by 24, I can do simple math like that

 

[Jacob]

Check my previous post, I did the math based on actual recorded temps. .....

In that case your recording methods may want looking at more closely. You should be down to about 20º this evening.

 

[Rorschach]

In that case your recording methods may want looking at more closely. You should be down to about 20º this evening.

Speak to the MET office, I used their figures.

 

[Adam W.]

Now, now boys!

Anyway back to the hot bungalow.

Cooling the exterior of the roof in the evening will not reduce the temperature of the air trapped between the rafters and the ceiling fast enough to reduce the temperature inside the house overnight. So really cross ventilation throughout the upstairs rooms is probably the only solution in the short term.

Reducing the quantity of trapped hot air by filling the void will stop the space heating up, but if the air outside is 26ºC and you open the window, the air temperature inside will eventually increase. Cross ventilation will help by increasing evaporation of perspiration from the skin and I find that a cold shower before bed helps enough to get to sleep when I'm staying in London.

If it's really hot I sleep in a tent in the garden.

 

[Jacob]

Speak to the MET office, I used their figures.

You must have misread them. Try again with your own post code/location Wirksworth (Derbyshire) weather

 

[Rorschach]

You must have misread them. Try again with your own post code/location Wirksworth (Derbyshire) weather

I didn't misread them and I did use the nearest weather station which is only a couple of miles away.

 

[RichardG]

You can also use Wundeground to get actual readings from a site nearby. Here’s one in Bradford.

Personal Weather Station Dashboard | Weather Underground

And the temp graphs.

So looking at those with good thermal management (minimising daily heat, maximising even cool) with good insulation I see no reason why the house can’t be kept to a more reasonable inside temp in the low 20s. But it’s an on going process as eventually the thermal mass of the house will reach above the mean outside temperature, but its rare for the U.K. to have prolonged hot nights and days, well at the moment anyway.

 

[Rorschach]

Thanks @RichardG for that site. The numbers I calculated from the MET office were actually almost exactly spot on with the numbers provided on that site, within a few 10ths of a degree.

 

[Jacob]

Thanks @RichardG for that site. The numbers I calculated from the MET office were actually almost exactly spot on with the numbers provided on that site, within a few 10ths of a degree.

Accuracy and precision are not the same thing.
Do you in some sort of anomalous zone of steady temperature? Everywhere else in the country gets these big shifts - down to 15º in Bradford! You'd need to keep the duvet on!

 

[Jacob]

..... it’s an on going process as eventually the thermal mass of the house will reach above the mean outside temperature, but its rare for the U.K. to have prolonged hot nights and days, well at the moment anyway.

On the thermal mass point - insulation is most effective when it is at or close to the internal surfaces. This reduces thermal mass which means more rapid and better control of heating and cooling. Mine is a chapel conversion but insulated within so the effective thermal mass is just the plasterboard, studs, joists, flooring, room contents. The 100s of tons of masonry construction behind it is not relevant.