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We should have installed air conditioning… now what?


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We took advice from two different architects, both of whom were against air con. The first advised that as long as we devised our sleeping quarters with the ability to have a cross breeze, we could cool bedrooms in that way. We have more or less done that, but for sufficient ventilation one needs to lift the blind with isn’t great in the morning. The second architect wrongly thought MVHR would make air con unnecessary. I wrongly thought that investing £££££ in wood fibre insulation to improve decrement delay of the roof, would keep the loft cool. If all that wood fibre is doing anything, I haven’t noticed. I think the heat from the rest of the house is rising and getting trapped at the top, despite me running a significant breeze up there by keeping rooflights and windows open.
 

The house is not passive, but is very well insulated and airtight. All west facing windows (including two big ones in the loft) have SN70/30 double glazing which is meant to reduce solar gain by 30%. The skylights in the loft are: two openable veluxes on the east side, and a fixed skylight on the west. I need to check the spec of the veluxes, but I think they are fairly high spec ones so will block some solar gain. The fixed sky light which is west facing definitely has SN70/30 glass.

 

The bedrooms are not the worst area in the house. The worst is my office which is in the loft, and I fear it will make working there in summer pretty unbearable. So I’m thinking of adding some sort of air con unit in that room. What options do I have? Do I have to install a box on the outside of the house that then needs to be plumbed to the air con unit and to the drains? Or could I get one of those units with a big water tank that I empty when I use it?

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You need to cut out any sunlight directly penetrating to reduce gains.  On Velux, external blinds work best.  For cooling a split A/C is best.

 

In my house we only have internal blinds and A/C is not practical to install.  Some of the bedrooms get hot in the mornings.  Luckily my office is on the ground floor so is tolerable.

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1 hour ago, Mr Punter said:

You need to cut out any sunlight directly penetrating to reduce gains.  On Velux, external blinds work best.  For cooling a split A/C is best.

 

In my house we only have internal blinds and A/C is not practical to install.  Some of the bedrooms get hot in the mornings.  Luckily my office is on the ground floor so is tolerable.

My two veluxes are GGL UK04 and GGL UK10. I think Velux make external shutters for the UK04 size but not for the UK10 size. Is that right?

 Luckily the one in my office is the UK04 size. Bloody expensive though.

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5 hours ago, Radian said:

How much better at keeping out the heat are the external shutters? I was looking at the velux solar powered blackout blinds

That’s a nice money saving idea, but Velux market the external blinds as blocking out 95% of the heat, whereas no such claims are made about the internal blinds.  I think this  makes sense as one needs to stop the heat passing through the glass. 
 

Has anyone got an external Velux blind? Did it really block out 95% of the heat gain? If so, as my Velux is East facing I would close it in the morning and open it in the afternoon.

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PV on the roof cuts down the heat getting in, if you haven’t got already?

2nd the external blinds.  Not that we have, but I’m sure they’d be effective.

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PV would have been a good idea. I did look into this, but couldn’t get a quote that was reasonable. Stupid prices really.

 My concern about spending money on fancy blinds/shutters is that the Velux is not that big, and I reckon the rising heat from the house is more of a factor. Anyone know how I can test to work out which factor is causing more of an issue. I have an optical thermometer which I guess I could use but not sure exactly what I’m looking for: The temperature of the glass on the Velux vs the temperature of the ceiling in the rooms below?

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7 hours ago, Adsibob said:

I reckon the rising heat from the house is more of a factor.


Where is that heat coming from? You have a well insulated house so you need to stop that heat getting into the house in the first place. 
 

We have external blinds on all windows…apart from 3 that face east that I didn’t think would be a problem. They most definitely are a problem. The solution that has worked so far through these brief hot spells has been to isolate the overheating rooms from the rest of the house by keeping internal doors closed, can you do that? Fortunately for us, the overheating rooms (plant room, master bedroom and en-suite) all have an MVHR extract so with the internal door closed we are chucking the heat away as quickly as we can and, so far, so good. 

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Floorplan?

 

AC on landing is nice. Performance of splits materially exceeds performance of portable units. Don't oversize; do check the detail performance docs; question units without docs available.

 

What is background "hotel load" that your gizmos and gadgets are contributing?

Air2Air Performance.xlsx

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4 hours ago, Russdl said:

Where is that heat coming from? 

Well that is my question. How do I work it out if it’s from the room below or the glazing within the room? The whole loft floor is warmer than comfortable, but probably only a degree or two warmer than the rooms below. I have tados in every room monitoring temp 24/7 (and recording the data to the Tado app), so I have plenty of data points, i also have an optical thermometer. But what am I looking for to diagnose the source of the heat?

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+1 on external blinds. We have a passive house, no AC, and if the heat gets in it is hard to get rid of.

 

We have external velux blinds on the east and south roof lights and internal blackouts on the west (these ones are huge).

 

While the external blinds are most effective, any shade will help.

 

While living in the caravan on site the summer before the build commenced, we noticed just how much solar gain came from the east and specified external blinds for those windows - this has been very effective at preventing morning overheating. We have curtains in the west bedrooms but the big west facing sliders in the living room were very problematic in the summer. This year we bought the internal Ikea motorised blinds and they are working really well.

 

Stack ventilation is handy in evening and then try to keep the house sealed up next day so you get the best of the cold air.

 

I also wish I'd installed a split air-con for these hot spells.

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17 minutes ago, markocosic said:

Floorplan?

 

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i don’t have a cross section to hand, but ceiling is quite high, about 3.1m and flat from the double doors to the left, whereas it drops diagonally at a 45 degree angle from the double doors to the right. So the Velux is on the diagonal roof.

 

17 minutes ago, markocosic said:

What is background "hotel load" that your gizmos and gadgets are contributing?

I have one pc and one flat screen monitor in the “home office” as it’s referred to on the plan. The pc does get a little bit warm to the touch, but not excessively and certainly not enough to warm up such a large room. plus one mobile phone and a MFC printer. Room was hot before I bought the printer. I really doubt the appliances are doing much to the room temp.
 

 

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Just had a look at temperatures: the second floor rooms are currently 23.6 and 23.5 whereas the rooms directly underneath them are both 23C. So maybe it is more solar gain than internal heat, no idea really. Outside it’s currently 18C, although that’s based on the bbc as I don’t have an external thermometer.

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@Adsibob

 

A note that relying on the decrement delay works only as long as it takes the heat pulse to soak through, then you need a cooling down period of some sort to let the heat back out again via whatever method.

 

Another tool you have could be light absorbent films if there are windows which are particularly a problem - with those you do not loose the visibility / light. Perhaps look at that big skylight or S facing or E facing windows?

 

For air cooling units, there are products that work with both parts inside and have 2 pipes going outside. I am not sure what they are called. Someone else will remember, but i have been away from renovations for a year or two. All it needs is one hole in the wall to take all the connections in one place.

 

I have an overheating problem on my S side, and I am eventually planning a veranda.

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4 minutes ago, Ferdinand said:

A note that relying on the decrement delay works only as long as it takes the heat pulse to soak through, then you need a cooling down period of some sort to let the heat back out again via whatever method.


 

yes good point. I try and ventilate upstairs by opening both veluxes on E and windows on W for a few hours each evening, though can’t be done when it’s raining. Also try and open a window lower down in the house to get stack ventilation going, but that’s tricky as the ground floor often doesn’t need cooling.

4 minutes ago, Ferdinand said:

Another tool you have could be light absorbent films if there are windows which are particularly a problem - with those you do not loose the visibility / light. Perhaps look at that big skylight or S facing or E facing windows?

All glazing on W elevation is Sunguard SN70/30. Does this film you speak of differ to that?

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21 minutes ago, Adsibob said:

yes good point. I try and ventilate upstairs by opening both veluxes on E and windows on W for a few hours each evening, though can’t be done when it’s raining. Also try and open a window lower down in the house to get stack ventilation going, but that’s tricky as the ground floor often doesn’t need cooling.

All glazing on W elevation is Sunguard SN70/30. Does this film you speak of differ to that?

 

We had a few conversations about it several years ago on BH. In answer to your q - I don't know. But it may be that they would send you a 500mm square sample for yo u to try, perhaps, or come and fit one? So you can see if the internal temp of the glass is cooler after application.

 

Somewhere there is a (c) Jeremy Harris thread about it, which I cannot find. He had a piccie of some test patches he did on his porch window.

 

Here is a quote from another thread:

We had about 12m² of external heat reflecting film applied two or three years ago, at a cost of about £100/m².  It was a mix of Solargard and 3M Prestige.  It works very well at reducing solar gain, and made a significant difference to our need for summer cooling.

 

 

When I was looking at my south facing bay windows, replacing the dg units in the main part of the window (which covers approx 80%) with solar control ones was surprisingly reasonable (but that does not help you):

 

 

Interesting looking at my potential need to sort out my south facing traditional bay windows, since mum has moved her bedroom downstairs and the rooms were running up to 35C when I measured it late August. The other one is my office. Expecting a sudden demand next summer.

 

The glass is 2G from about 12 years ago, and to replace 10 off of 450x900 units (ie the main windows not the opening toplights) with new ones with an anti-solar-gain outside pane would cost about £600 fitted, which might be a cost-effective solution given the extra lifetime over a solar film. Surprised at the relatively lowish price.

 

And here is an example of the type of "all in one box" aircon I was talking about above:

https://www.sunbeltsales.co.uk/olimpia-splendid-unico-air-8sf-18kw-all-in-one-air-conditioning-unit-copy

 

Various products are around, but you need to look carefully.

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28 minutes ago, Ferdinand said:

And here is an example of the type of "all in one box" aircon I was talking about above:

https://www.sunbeltsales.co.uk/olimpia-splendid-unico-air-8sf-18kw-all-in-one-air-conditioning-unit-copy

.

I’m confused, where does the heat go with such a unit. It sounds like a fridge that has been turned inside out. But in the same way the back of a fridge is warm, isn’t the back of this going to get very warm, which will then heat up the room thereby defeating the purpose?

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3 minutes ago, Adsibob said:

I’m confused, where does the heat go with such a unit.

 

Out through a wall duct.  I don't think they are anything like as efficient as a proper split A/C though.

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3 minutes ago, Mr Punter said:

 

Out through a wall duct.  I don't think they are anything like as efficient as a proper split A/C though.

I think I have space for an external unit, so long as they are not too deep. I have a bit of flat roof just outside and adjacent to the two loft floor rooms which has a footprint of about 100cm wide by 20cm deep, possibly 25cm. I need to measure though that involves climbing out the window and crouching there, which I’m not going to do on a day as windy as today. Presumably thee external unit needs to discharge water to a drain? Can I just let it trickle down some flashing and into our gutters? Would be very difficult to drain away waste water otherwise.

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I have a portable air conditioning unit, the sort that just exhausts it's warm air through a big pipe.  I found it next to useless.  Yes it is nice when it is blowing cold air at you, but it was way way too noisy to keep running over night in a bedroom, and insufficient cooling power to meaningfully reduce  the air temperature enough for it to stay cold when you turn it off.

 

I see nobody has mentioned a night purge?  This is what we do on the occasions it gets to hot. Once the evening / night temperature outside is less than inside temperature, throw all the windows open to let the house cool down overnight, then shut them all in the morning.  With a long decrement delay the house should stay cool through the heat of the day.  Repeat each night.

 

Not much help if the night temperature does not go below 25.

 

The "mistake" a lot of people make is "gosh it's hot, lets open a window" when the outside temperature is even hotter, you just let the heat in quicker.

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1 hour ago, ProDave said:

I have a portable air conditioning unit, the sort that just exhausts it's warm air through a big pipe.  I found it next to useless.  Yes it is nice when it is blowing cold air at you, but it was way way too noisy to keep running over night in a bedroom, and insufficient cooling power to meaningfully reduce  the air temperature enough for it to stay cold when you turn it off.


 

 

thanks, I think it’s clear that if I do go down the AC route, it will need to be a split system. Just had a quote from a company that recon they can supply and install everything and even match the indoor unit to any F and B colour, so that’s my neurosis covered. Bloody expensive though at c. £2k - £2.4k subject to “free” survey which is happening on Tuesday.

1 hour ago, ProDave said:

I see nobody has mentioned a night purge?  This is what we do on the occasions it gets to hot. Once the evening / night temperature outside is less than inside temperature, throw all the windows open to let the house cool down overnight, then shut them all in the morning.  With a long decrement delay the house should stay cool through the heat of the day.  Repeat each night.


 

well this is what I had planned, but I’m not sure why the house is not staying cool during the day. I’m sure the £5k of money I spent on wood fibre insulation is doing something, but I’m not sure what; is really bizarre. Here are a few graphs that tell you what my office has been like over the last week (blue dotted line shows my office’s  humidity level; yellow at the top indicates when the sun is shining; and the grey shaded area is my office room temp): 

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317A7562-8CAD-47D6-8716-4C2F3089C4FF.thumb.png.9b7fb1904d5e688c4f5a77e124c167ee.png

C6558BD0-86E2-433F-B2F8-41C2153D9CBC.thumb.png.7863a09727caf6938078bfd59f7f1800.png

64A347CA-0370-404A-A7B3-61617D91545F.thumb.png.5591629fed9baa37174f7c0cbfbac87b.png
53471C66-C6AD-4C90-A92A-81A36FC10664.thumb.png.42644e33dca7a71b98e739e20587b7c2.png

B6C8F981-6D65-45DE-A492-966DE2E7CEA7.thumb.png.39f903ac7efd7481c3e355dfda17d30a.png

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The evening purge definitely helps lower the temp, but the problem is during the day the temperature is often reaching too hot to comfortably work in. But maybe I need to purge more so that the starting temp is lower, but it’s not always possible as veluxes shut automatically when it rains.

1 hour ago, ProDave said:

Not much help if the night temperature does not go below 25.

 

The "mistake" a lot of people make is "gosh it's hot, lets open a window" when the outside temperature is even hotter, you just let the heat in quicker.



 

 

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3 hours ago, Adsibob said:

Just had a look at temperatures: the second floor rooms are currently 23.6 and 23.5 whereas the rooms directly underneath them are both 23C. So maybe it is more solar gain than internal heat, no idea really. Outside it’s currently 18C, although that’s based on the bbc as I don’t have an external thermometer.

That is today's OAT, hasn't London just had 30⁰C plus for a couple of days?

 

To only get internal temperatures in the low 20s when it is mid 30s outside seems a success to me.

 

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1 minute ago, SteamyTea said:

To only get internal temperatures in the low 20s when it is mid 30s outside seems a success to me.

Have a look at the graphs I just posted, tell me if that is the picture of success? Am I expecting too much?

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