We are lucky that we live in a cooler area of the country and our 1700's stone cottage is like a cave so the bedrooms stay reasonably cool. With careful management, not opening windows and keeping blinds shut, we have managed to keep to room temperature down to 20C in the bedrooms. Our main living space has been more challenging though, and has been 26C.

If I lived in the south east and needed AC, I'd be looking at one of these portable split units, like this one from Midea:

https://www.midea.com/uk/air-treatment/porta-split

I've seen a few reviews and from people who have one, and they are a lot more capable (and efficient) than the large hose through the window types.

Either that, or A2A for both heating and cooling would be the ideal solution in hotter areas, but then you have the issue of what to do for DHW.

Good question

I have aggressively managed window shading and opening/closing times.  Most of my windows have Low E glass or better and Go Outdoors sell a survival blanket for £6 (£3 if you are a loyalty club member) which has proved very good for the oly sunny one that doesn't.  The guy in front of me at the checkout was buying some for the same purpose!

I have also fired up the heat pump in (above dewpoint) cooling mode and run our portable dehumidifier.  I have one fan coil and two radiators with add on computer fans, not really a lot to provide a load or much cooling, but a start.  My feeling is that it has taken the edge off, but its far from true aircon.  The fancoil is noticably more effective than the adapted radiators.  The heat pump cycles because of the low load, which Im pretty sure reduces the effectiveness, because its only below 20C (the ceiling temperature for the fancoil) for part of the time.  I have tweaked one control parameter which has helped a bit, I have probably run out of time this time round to do much more tweaking.  More than even I now wish I had bought a few more fancoils for the rads that were marginal!

The heat pump is reporting just over 5:1 ratio of cooling to electricity supplied, however I suspect quite a bit of that goes towards cooling the outside given the cycling.

Here are some plots

IAT in the 'sunroom' (the clue is in the name).  This has the fancoil in one half of the room, the sensor is in the other half.  The very slow reaction time of the house is very evident in these plots.

OAT on a north facing shaded wall

Humidity ditto.  The drop towards the end is because I started running the dehumidifier on half power 24x7, rather than full power overnight.

FT, obviously including some DHW cycles.  The Heat pump is on 7.30am-7pm only.  The change in dehumidifier operating mode is also manifested here.  Before running it constantly the FT used to creep up during the day, because the heat pump was adjusting to an in creasing humidity by increasing its target FT.  On Thursday you can see that this did not occur.

Power consumption

@old_scientist looking at the photos, you still need the door/window ajar for the Midea unit, but it does look tidier than what we presently have.

Posted by: @editor

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@old_scientist looking at the photos, you still need the door/window ajar for the Midea unit, but it does look tidier than what we presently have.

Yes, I guess unless you have a professionally installed unit, any portable AC unit is going to require some connection between inside and outside units.

The umbilical linking them is quite thin (as opposed to large air vent hoses), and I've seen some reviewed with Velcro sealing kits to go around a door or window to seal and stop warm air entering.

These units are apparently a step up from the type you have and sit somewhere between what you have and a professionally installed A2A unit, both in terms of performance and price (somewhere in the £750-£900 range I think)

Unsurprisingly the Midea unit is out of stock! With Amazon anyway which is the link.

Posted by: @judith

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Unsurprisingly the Midea unit is out of stock! With Amazon anyway which is the link.

They were paying affluencers to pedal them like crazy on youtube. As I understand it they are R32 based so they've got to offload them all before they are banned next year. There have been other brands doing the same thing for some years.

They can be better - COP is about 4 which is better than even good dual hose portables, but they are noisy and the permanent attachment and weight is awkward.

If you have a sash window you can get the external fan block outside, lower the sash most of the way and make a pair of blocks to go each side of the elephant trunk out of knauf or kingspan or similar insulation and maybe a bit of sheepswool or a good dose of duct tape round the joint. It's also not hard to add some extra window locks at that height.

With tilt and turn good luck 8)

I'd probably go for a proper minisplit/multisplit if possible but if you are renting, it's awkward to do, it's listed so you want to dodge the whole planning farce by keeping it an appliance not part of the building then it's definitely an option - but always buy them in winter - prices are often 25% lower for winter sales 8)

Posted by: @editor

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What have you done this heatwave? What's worked, what hasn't and what are you planning before the next one?

I pushed the "cool" button on the air/air system that heats/cools the whole house. Kept the bedroom coolish, the lounge acceptable (it struggled versus the sun beating on the windows for that room) and the basement sits at 18C all summer whatever you do. Entirely ran off solar and battery from the solar in the day.

Very glad we went air/air. Might need to boost the cooling side at some point but need to look at the best approaches to deflect heat first.

You guys have it easy

It's engineering: calories in, calories out.

What I had: stone house, built 1732, 50cm thick walls, estimated thermal mass 600 tons. Zero insulation, single glaze windows probably a century old. Ground floor UFH, upper floor nada.

When our Dear Supreme Leaders decided on war with our main energy provider (Russia) I implemented:

- 200mm thick Rockwool exterior insulation

- All windows replaced with double glaze

- 400mm blown fiberglass in loft over airtight vapor barrier

- 12kWp PV + 20kWh LPF battery

- Electric car

- All windows on upper floor: louvred shutters. All windows on lower floor: solid wood shutters, except the two south facing enormous windows (10m² each): microperforated rolling shutters.

- Replace old failed ground source heat pump with 16kW A2W LG R290 monobloc

- Purchased 2x 3kW dirt cheap portable second hand aircon units

Results:

Strategy:

** When night time temperatures are cool (ie, minimum around 15-16°C) but day temperatures are hot (>30°C).

At night, open windows. Louvred shutters and perforated rolling shutters remain closed, these let air through without allowing in thieves or cats. Push "Auto ventilation" button in Home Assistant. 8000 m3/h fan in the corridor turns on if indoor temperature > outdoor temperature. This cools the thermal mass during the night. When morning comes, close windows. This keeps the whole house around 20°C during the whole day.

** When night time temperatures are above comfort level

As shown on the right side of the above plot, it is not possible to cool the house with outdoors air when outdoors air is hotter than the house. Therefore, close all windows and turn on portable second hand aircon units. But only if electricity is free obviously. They're on smartplugs, controlled by Home Assistant.

Posted by: @editor

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I've tried the portable AC route and I'll be honest, they're pretty useless in serious heat. You need windows open to run the ducting out, which completely defeats the purpose.

You're using it wrong 👌

Okay, it was designed to be used in a way that makes it useless, but that doesn't mean you have to!

Portable AC units have two airflow paths: one over the evaporator, which sucks air from the room, cools it, and blows it back in the room. And another path over the condenser, which sucks in air, heats it, and blows it out through the pipe.

For optimum efficiency, the condenser is placed outside and only handles outside air. The evaporator is placed inside the room and only handles indoors air.

If all you have is a mobile aircon unit, you can do the same by mounting it like so:

It isn't necessary to make it airtight. All that's needed is to plug the window with an alveolate plexiglas panel with a hole in it, put the AC unit in front of it, and push the button. 

Hmm I should have explained it better...

Problem with these devices: they have only one pipe. Thus they suck in already conditioned air out of the room, and blow it out. Air sucked out of the room then will be replaced with hot humid outside air that enters wherever it can. So these devices tend to only cool one side of the room, while hot air that is sucked in actually warms the other side of the room, and temperature climbs immediately after switching them off. Humidity is really an issue because a significant fraction of the power is used to dehumidify, so every bit of outside humidity entering means more power is wasted, and obviously using it with the window half open means a huge amount of humidity gets in all the time.

The idea is :

The window should be closed with insulating material with an opening in it, the result being reasonably airtight except the opening. 

The air inlet for the condenser, which is the bottom grille at the back on the device, should be placed in front of this opening.

This way, the evaporator fan sucks in outside air directly through the opening, this air runs on the evaporator and is blown back outside.

This does not create a low pressure zone in the room, so outside air is not sucked into the room, which massively boosts the performance of the device. Used as intended, it barely cools the room to 27°C, it's a total waste of power. With this simple and dirt cheap mod, it becomes a real aircon, capable of cooling a 50-70m² area to 20°C while outside temperature is scorching hot.

These units are "seasonal fruits" a bit like tomatoes: you can buy them second hand in February for 150€, or in July for 5-800€ lmao. Second hand units will most likely not work (or barely work) because both heat exchangers will be completely clogged by dust. Reason is, to clean the evaporator, the device must be disassembled with the whole back plastic shell removed. Once cleaned it works like new. Fins on the heat exchanger are very fragile so the best is the vacuum cleaner brush (the one with soft hairs).

Some pics of my heat solutions…

Bought the shutters as a job lot on eBay, stored in the garage over winter, bodged the outlet for the mobile in the conservatory and installed a Midea A2A in the lounge.

Shut the house down at 23c and open up at 23c evening.

We’ve got side hinged windows and no small openings in rooms that need it, so the the various bodges available to sash windows don’t work 

.So far I’ve learned that a single pipe solution will mess up our MVHR balance and a dual pipe one would be ok but the windows still limit it.

The dew point was 23C in the last heat wave here but even then the air to water system might help a bit if set to cool, and I’ve asked the installer to enable it at the next service (coming up soon).

What is the approximate price of a though wall permanent solution. Anyone have recent experience?