My main motivation in installing a heat recovery system is to get silent ventilation - that is, ventilation without the annoying neighbours, etc.

How do I keep the house cool in the summer?

Thanks Damon

However opening windows at night is the last thing I want to do, because I want the silence! I will look into blocking light out of rooms though thats a good point

Of course, life may be more complicated than that, and you may want to air the house if there's a nice breeze, but just doing the above makes a huge difference to comfort.

I think that's it; the short term solution in a "Crap House" (TM) is very situation dependent.

If it's warm but breezy *and* the occupant is present, having the windows open may be a decent short term solution, because of the effects of the breeze on evaporation etc.

You can't have windows open everywhere due to security concerns.

I often wonder about the use of ventilation - if air is such a poor holder of energy, why would it be much help here? But then I guess it's the other side of the relationship - time.

I like the idea of thermal capacity and decrement delay personally... but that's a gut feel and is as such worthless.

Solar gain through any surface is of course the enemy.

Keeping cool in summer, design out too much glass, insulate well, shade windows externally, high mass and lots of thermal inertia, MHRV,

If desperate use night time cooling via the ventilation system.

How do I keep the house cool in the summer?

By not heating it!

A heat recovery system is also a cool recovery system if the house is cooler than the world and the summer bypass facility is not active. Thing is, the amount of air it moves to keep the air fresh inside the house is so insignificantly small that it can easily be massively overwhelmed by a few I'll placed windows.

It makes no sense to consider an MVHR as a causative factor in overheating a house in summer, or keeping it warm in winter, because the contribution it makes is so small in all but the most finely balanced passive houses

Returning to the not hearing it comment; the sunlight streaming in through your window and striking a surface such as wall or floor, turns it into a heater and it can be worth anything up to a kilowatt per square metre. I have a row of roof lights 9m by 1.5m that are South facing and my office reaches 40 degrees. I look at them and think "I wish there was a way of turning that 16 bar electric fire down an bit"

So as others have mentioned; stop it getting in in the first place rather than looking at systems to get rid of it once it's inside. If you can't change the orientation of the house (are you new building?) and vary the glass angles/design in useful solar gain, you're really looking at shading methods externally. It's possible to build things on some windows that let the low winter sun in but screen out the high summer sun. If after all this you're still too warm, you can turn to technology; one of my next steps I'm considering is putting an air source heat pump inside the house- I need hot water on a daily basis and they produce it in exchange for cold air. Normally this is a byproduct that blows away because the pump is in the world outside, but migt be the thing I need to mass cool the house before I get home and take a shower..

@gravelld asked about air being a poor holder of energy so why does it help? Because if you can move a lot of it (and when I open the barn doors at the front, and the windows in the 4m semi circle in the top floor side, I can arrange a through draught that takes a 40 degree office down to 20 degrees in an hour if there's a good breeze) then it doesn't matter that it's a crap holder of energy. If you could run at a hundred miles an hour you could empty a bin full of sand faster with a teaspoon than your grandpa can with a shovel, so to speak. Critical is that you have to cool the structure of the house - a room at 40 degrees will pretty rapidly reheat to 39.9 degrees if you take all the 40 degree air in it and replace it with 20 degree air - here's so much heat energy stored in the plasterboard, floorboards and room objects that you have to mass change the air on a continuous basis, and then stuff cools down

Agree,

1) Keep the heat out in the first place.

2) Purge it overnight.

Not as if we have that many days a year when this is a problem (unless you've built a stupidly over-glazed mansion with no blinds/curtains (i.e. most Grand Designs)).

Largely agree with Tony, except thermal mass only seems occasionally a benefit in the UK climate. Shifting a bit of the heat to release later will not always be helpful. Low thermal mass will tend to heat up a bit faster, but purge the heat faster overnight, High thermal mass will mean the building will be a bit cooler in the day, but release some of that overnight; I guess it depends on your heating strategy and just how much solar gains you get and how you control them.

In the winter high thermal mass tends to be less responsive - again depends on your heat strategy and demands as to whether or not this is a problem.

<blockquote><cite>Posted By: tony</cite>design out too much glass, insulate well, shade windows externally, high mass and lots of thermal inertia, MHRV,</blockquote>

Seconded. We're overglazed. While external shading would be better we've just fitted some internal roller blinds to the west facing windows so we can screen out some of the solar gain.

thermal mass works both ways - at the moment the sun through our kitchen windows heats up the concrete floor which carries on emitting heat after the outside temperature has dropped.

Chimney stack ventilation is a good aim if you can make it work we get a good effect from our rooflight but it's most effective with internal doors and windows wide. Fine for a purge but not great while in bed.

Yes external shading is best, even dust sheets hung up outside work

Struggling with the same problem on our recent PassivHaus standard self build. This hot and humid weather is proving difficult, especially at night, and the low thermal mass of the timber frame / timber clad doesn't help. Working my way through the options - trying to avoid the wife's favourite of A/C - and looking o fit external fabric blinds to the poorly designed (yes, this a retired architect admitting to errors!) south facing windows in our bedroom and the west facing ones in another bedroom. The cleverly designed large overhanging eaves obviously don't work with the morning and evening sun, but we'll persevere.

Has anyone any experience of external blinds - recommended suppliers perhaps? Thanks.

All the ones I have seen have a drain, usually 15mm pipe from a tray in the unit.

Some roof light makers do Brie sollei blinds that fit their windows externally.

The films work a bit, look blueish and go on the outside I think.

Posted By: richardelliotHas anyone had any experience of using solar films on windows to minimise summer solar gain?

I appreciate that external shades are better, but I have a hard to access externally roof light, but I could get to the inside to apply a solar film.

I had solar film fitted last year to a large 3/4 glazed gable. It has made a big difference to the temperature in the sitting room. It's fitted to the outside of the glass, which in my case is triple glazing. AIUI if an internal film is used on double or triple glazing there is a heat build up in the glazing unit. I used Clearview Vista80X.

http://www.sun-x.co.uk/products/clearview-solar-film

We self-installed film from https://www.windowfilm.co.uk/residential/heat in the flat we were living in with only South facing windows. Made an appreciable difference.


>>AIUI if an internal film is used on double or triple glazing there is a heat build up in the glazing unit.

Ours were double glazed - this is the first I've heard of it.

I chose to fit solar screens over all glazing - my windows are quite large relative to room volume, as seems common in many 60s and 70s properties. I chose a black mesh with 20% open area.

They made a big difference. I used to get overheating in all rooms (ranging from "uncomfortable" to "unbearable") as the sun swept around from E to NW. The room on the SW corner was particularly bad - a 22degC exterior shade temperature around mid-day would result in that room reaching temperatures of around 30degC on a clear day. A sofa under a SE facing window was very noticeably faded within a year. Cellular shades on one SE window resulted in 50degC+ temperatures measured on the room-side.

Now, with the screens fitted my indoor temperature measured in the same location in the SW corner room with the same device has never been more than 1-2degC higher than outside air temperature, and it always feels cooler walking in from outside.

I still have some screens to fit - if I stand in front of those windows at this time of year, even at 8am, the sun feels very warm on my skin. Stand in front of a screened window on the same elevation and there's no sensation of heat at all. This is backed up by IR temperature measurements of interior blind temperatures.

So fitting screens has completely solved the rapid rise in temperature during the day. My peak temperatures now occur in the late evening, due to what expect is the stored energy making its way in through exterior walls and the ceiling (very hot attic).

Solar film should have a similar effect - I believe that in the US, it's often a toss-up between the two, as they both have pros and cons. One pro for US homeowners is that they might already have insect screens over their sash windows, so fitting solar screens is as simple as replacing the mesh. In my case, it was down to cost and ease of DIY - I didn't fancy attempting to apply 1.2x1.2m squares of film :)

The solar screen mesh is certainly fine enough to block the same type of insects are regular aluminium mesh does, but with less airflow. I can't comment on the effectiveness as an insect screen since my screens are static over each glazing unit, but if it works as you hope, then you might find that the reduced airflow is offset by the reduction in solar gain.

What type of windows do you have? Mine are all casements, and because I wanted optimal solar performance, I mounted them externally onto the casements themselves and sacrificed the insect screen usage. With tilt-and-turn or sliding/sash, you get the best of both worlds.

I came across some mounting hardware for tilt and turns that means you wouldn't even need to drill or fix permanent hinges or turn buttons - they just clip into the frame opening.