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I thought I'd start a topic on cooling specifically. Although it's been covered as part of other threads I wondered what the options are for new builds and existing houses in this area? I've seen some great ideas in other threads:

  • Underfloor & ASHP cooling
  • MHVR cooling option
  • SunAmp to precool rather than preheat?
  • And of course opening the windows at night

When night time temperatures are too high to make opening windows useful, what then? Do we get dehumidifiers and air conditioning units like other countries? Shading to prevent solar gain is of course paramount during the day - also blinds, breise soleil, window film to reduce G value, adding trees, walking around stark naked.....!

What have people been doing this summer to keep cool and purge the heat? 

For my current house I'm just using blinds during the day and opening front and rear windows when I'm around too. Regularly 27 degrees in the bedroom overnight however. 

In the new house I'll have blinds, breise soleil, velux windows in the roof I can open but that's it. I would like to have other options but I can't see myself buying an ASHP at the minute, just MVHR. 

Thoughts?

 

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When all else fails, a fan in the bedroom is very helpful. I live in Sydney for several years, and even when the temperature didn't drop below 30 overnight, you could generally get some sleep with a fan on.

 

I'd still rather the room not be hot in the first place. As such, all the things you mention above that stop heat getting in in the first place are helpful. Screens that are outside the windows work a lot better than curtains/blinds etc that are inside the window.

 

Boosting the MVHR at night (assuming you have a summer bypass mode) helps on still nights.

 

You could also put a large fan near an open window at night and blow out hot air.

 

Oh, and insect screens are worth thinking about if you're interested in night purging.

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9 minutes ago, jack said:

When all else fails, a fan in the bedroom is very helpful. 

 

Have to admit I’ve been resorting to opening the bedroom windows on tilt when I get in from work that helps to cool things down a bit as that side of the house is shaded then, closing them when I go to bed, and then running a fan at night. The bedroom is about 22c which is ok in the living space but way too hot in a bedroom for me. 16-18 is my preference in a bedroom and I’d much prefer cooler upstairs than too hot. 

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Night purge works well if the night time temperature drops and if you can open windows o cross-ventilate, or have an MVHR with a 100% bypass option.  Turning the MVHR off during the day, when air temperatures outside are higher than you want the house to be, also helps, as does keeping doors and windows closed during the day.

 

Adding cooling to the MVHR is another option.  If you don't have an ASHP then a ground heat exchanger (like a GSHP heat collector - a long length of fairly deeply buried pipe) could be used to pump cool water around a heat exchanger fitted to the MVHR intake.  Water from a ground loop like this will be at around a constant 8 deg C or so in most of the UK, so could provide a useful source of cooling.  I'm looking at economic ways to fit a heat exchanger to our MVHR intake at the moment, and will post the details once I've finished working them out.

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Some observations.

  • Designing out cooling is quite easy and effective. I am doing it now with PHPP for my build. As mine is a modern house, I have more freedom to play with window sizes and architectural features, such as overhangs.
  • Floor to ceiling glass is to be avoided and I am doing so in my build. The glass below knee height offers little extra light but much extra heating gain.
  • Building regs require an openable window in every habitable room for purge ventilation. I wish it didn't, I don't want them in my modern house as it it does not have any conventional windows, just large frameless roof lights and architectural glass. Problematic.
  • Purge ventilation is sometimes defined as 4 air changes per hour (ACH). Most MVHR work at about 0.4 ACH. Trying to achieve it with an MVHR will lead to hugely over specifying the MVHR and require much bigger ducting. I know, I tried. The MVHR I needed was 271 kg!
  • Using water UFH for cooling delivers that cooling in a sub-optimal place, the floor. Sub optimal for convection. And if not carefully controlled can cause condensation. I decided against it.
  • In the end, I plan to put in a conduit for a split air conditioner in case I need it in my Passive House. Because split air conditioner are highly common they are very very cheap in comparison (about £800 tops) and finding someone to install or service it will be easy I imagine. I will try the house for a year and install an air conditioner if I need one.
  • Its easy to over engineer the solution and get carried away. I am aiming for a very simple, as simple as I can make it and for it to be cheap, and maintenance free.

 

 

Edited by Dreadnaught
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By luck more than anything, we have two large velux in the apex of the roof on the east side, one at the top of a full height atrium and the other at the top of the neighbouring stairs. Both have external blinds and we have them open all day, opening ground level doors or windows on whatever side of the house the sun is not at.

 

Helps create a decent through draft to keep the house cool, and as the house is airtight, when no other windows or doors are closed then there is no air movement.

 

I've been running around closing doors strategically during the day to max the airflow from cool rooms through warm rooms and back to hall  - seems to work.

 

Big west facing sliders still an issue in the evening, even with internal drapes (gauzy linen, not that heavy) pulled.

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Oh yes, on summer bypass, some MVHR models have "simulated" bypass. The Paul Climos 200, which I rather fancied, has this. As far as I can tell, this means it shuts down extract. It does not actually have a physical bypass of the heat exchanger. I assume the heat exchanger assumes you will open a window for the extract, which makes some sense. I am not sure how this can be called "simulated" but that's another matter.

 

As I don't want to open windows if I can avoid it, this means I will be choosing another MVHR model.

Edited by Dreadnaught

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Purge is good but I hate flies (and moths at night). Any purge windows I have will need fly screens.

 

As Jae Cottrell once told me, fly screens also help marginally with shading.

Edited by Dreadnaught

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Oh, and if you are playing with the summer overheating % in PHPP, as I am at the moment, there is a new advanced shading sheet available from Peter Warm. Warm said we are the first to be using it in the UK. It enables better modelling for transparent shading objects, such as trees. Useful for me because I have whopping horse chestnut slap bang between my new build and the southerly sun and about half a meter from my boundary.

Edited by Dreadnaught

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14 minutes ago, Dreadnaught said:

Purge is good but I hate flies. Any purge windows I have will need fly screens.

 

As Jae Cottrell once told me, fly screens also help marginally with shading.

 

Have to admit, only every notice the odd fly on the house where we are - edge of town and semi rural.

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17 minutes ago, Bitpipe said:

Have to admit, only every notice the odd fly on the house where we are - edge of town and semi rural.

 

True. Evening and night tends to be worse: moths, mozzies and worse.

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Ha, we got a bat in the house the other night because I opened a window, took for ever to persuade it back out the window , flies, pah ?

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2 minutes ago, joe90 said:

Ha, we got a bat in the house the other night because I opened a window, took for ever to persuade it back out the window , flies, pah ?

 

Ah, the bat to eat the flies and moths, clever tactic. I like it.

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1 hour ago, mike2016 said:

And of course opening the windows at night

You can get way more sophisticated with passive cooling than this. The trick as I see it is to create a thermal stack that drives a breezeway though the building. In our design there are 7 fakro tilting roof lights that can be controlled and we are hoping to install some low level automatic louvres to work with them - assuming we can find some suitable for a passive house. We will also have a reversable  ASHP to cool the slab via the UFH and the ability to cool the air coming in via the MVHR. We hope that will be enough. My other half is paranoid about over heating so we have gone for overkill on the cooling options.

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Wow - that's certainly enough to go full polar bear alright! I hope to have two velux at the top of the stairs which is open to roof level plus 4 more in the open plan living / dining area at the north of the house. Not sure yet about supplementing it using MVHR / ASHP / dedicated split unit but after this summer it's on my mind a lot more! I can always keep my options open but don't want to waste money over specifying. I've tall windows on the south facing side so might open for a higher G value for the lower portion of those windows as part of the specification. The briese soleil will take care of the rest. That or buy a few space chest freezers and leave them open.....!

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1 hour ago, joe90 said:

Ha, we got a bat in the house the other night because I opened a window, took for ever to persuade it back out the window , flies, pah ?

 

Butterfly net, preferably extending.

 

Or just leave a window open and close the door. It will probably find its way out soon enough .. they have sonar. We have had a few in in the old house, and that usually works.

 

 

Edited by Ferdinand

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Ceiling fans, 

having lived in oz, we will have ceiling fans in the vaulted section of the main living area. 

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3 hours ago, Dreadnaught said:

Some observations.

  • Designing out cooling is quite easy and effective. I am doing it now with PHPP for my build. As mine is a modern house, I have more freedom to play with window sizes and architectural features, such as overhangs.

 

 

 

I remain very, very unconvinced, I'm afraid.  A few days where the night temperature stays high and even the very best designed passive house will overheat badly.  The MVHR will pump in air at outside air temperature, and with the best will in the world that will end up overheating the house when combined with the internal heat gains that simply can't be removed.

 

You can get solar gain right down, as we have, but that doesn't overcome the fundamental problem of outside air at 30 deg C + during the day, and maybe 20 deg C+ at night (we've had four consecutive days where the night time air temperature was over 23 deg C).

 

PHPP will give you an overheating risk ESTIMATE, and it is an estimate, that doesn't take account of factors we've had in the past couple of weeks, like sustained high air temperatures.

 

We now have very good solar gain control, especially since planting the row of trees along the front, and with the reflective film we get very little solar gain overall.  However, when I went around with the big vacuum cleaner last week, the house shot up to 24 deg C within about an hour, and without the active cooling would quickly have become pretty uncomfortable.

 

Today was cooler, around 26 deg C outside, but the floor cooling was still on by midday and the MVHR air cooling came on by about 15:00.  The house stayed at a fairly comfortable 22 deg C, but it wouldn't have done without cooling, as with the MVHR on 100% bypass it was filling the house with air at 26 deg C every two hours.

 

 

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33 minutes ago, JSHarris said:

I remain very, very unconvinced, I'm afraid

 

Fair challenge. Its not about elimination of all overheating in all circumstances. Zero % overheating is unrealistic, as you say. I am referring to optimisation at the time of design. PHPP presents an average % of hours overheating per year, defined as a temperature over 25ºC. The standard for certification requires a modelled figure of 10% or less. Most aim for below 5% and I prefer below 2%. Architectural design optimisation of overheating is effective for this, as I am finding.

 

Oh and I plan to have the option of an air conditioner, should it prove required.

Edited by Dreadnaught

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2 minutes ago, JSHarris said:

.However, when I went around with the big vacuum cleaner last week, the house shot up to 24 deg C within about an hour, and without the active cooling would quickly have become pretty uncomfortable.

 

I think this is an interesting point, minimising generating heat within the house in summer.

 

We have PV that heats the UVC when not being consumed - obviously heat leaking out of that system (ours in plant room in basement so impact minimised somewhat).

 

Been avoiding using ovens, cooking out most nights. I also suspect that most fans generate more heat than they dissipate !

 

I've never been a fan of central vacuum systems but there is an argument that they are better suited to a passive house where the heat generating element is in the garage.

 

I think designing in provision for split air con and relying on PV to drive these for free in summer is a good approach - didn't think of it in time though!

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Overall fans in the room add heat, so make the house warmer.  They provide an illusion of making the house more comfortable (as long as the RH is low) by increasing the rate of sweat evaporation, so aiding body cooling.  For that to be effective you need to drink at least as much additional water as is being evaporated away by the forced air cooling effect of the fan.  If the RH increases to the point where body evaporative cooling, even with fan-assistance, isn't significantly increased, then fans are generally a bad idea, as they just add additional heat with little cooling effect.

 

One exception to this may be in a house with an actively cooled floor, like ours, with the UFH being capable of being reversed into a chilled water floor cooling system.  A fan that directs warmer air from the ceiling down towards the cooler floor may well be quite useful in cooling the whole house down.

 

 

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For a passive house, overheating in summer is generally the greater risk than an inadequacy of heating in winter.

 

Best practice: first step is to design-it-out to the extent possible (<2% ideally), then consider other solutions, including active cooling. 

 

I recommend The Passivhaus Handbook by Janet Cotterell if anyone's interested. Chapter 7 & 11 discuss overheating at length.

Edited by Dreadnaught

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I'd agree, I read every passive house publication available for several years before even starting on our build.

 

However, as a note of caution, I still screwed up...

 

I know others that have built passive houses that have found that theory doesn't translate well into practice, and have had to take some additional mitigation measures in order to avoid overheating, which in some ways is reassuring. 

 

If I were starting again now, then I would be very focussed on two things.  Reducing incidental heat gains (appliances, lighting, cooking etc) and providing adequate comfort cooling.  The two biggest problems to solve with a passive house are the provision of hot water and a way to provide comfort cooling in sustained warm weather, and the two are linked, as a lot of hot water systems can introduce a significant heat gain into the house right when you don't want it.

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10 minutes ago, JSHarris said:

Reducing incidental heat gains (appliances, lighting, cooking etc)

 

Agree. For example, in my design when I swapped from a hot water tank to a Sunamp, with its much lower heating losses, that change alone reduced my modelled annual over-heating rate by two full percentage points.

 

10 minutes ago, JSHarris said:

and providing adequate comfort cooling

 

Agree. For me that will be a simple and comparatively low-cost split air conditioner in the large double-height living room. I might also go for a second indoor unit in the master bedroom too (you can have up to 5 indoor units as I understand), not sure yet. I might try and build the indoor unit(s) into the ceiling as I have void where they could fit. I think it could look quite good.

Edited by Dreadnaught

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