Air Conditioning in Bedrooms

Heat Pumps in UK bedrooms : what I've learnt.

I have air conditioning units to heat my bedrooms. These have work well for me over 3 years. If I had to start again, I'd follow a few tips I've found and am documenting here.

AirCon is a type of ASHP used for decades in the pacific regions mostly for cooling but also heating. In the UK they are mainly fitted in commercial premises by the refridgeration/air conditioning industry. Many installers just follow the usual procedures for the few domestic units they sell. They fit high-wall fan units with exposed or ducted pipework and recommend leaving them on automatic. The system sets the fan speed and the heat or cool mode to achieve a set temperature. You can buy single, triple or quin models, meaning a single outside unit (compressor) runs one, three or five inside fan units. These are referred to a wall-splits, triple-splits, multi-splits. I found the triple option was best value for my needs.

My first novice question to my installer was whether I can have a heating-only unit. They said it didn't exist. Reecently and much too late I hear from an expert on a facebook group that isn't true. I'm told there is a link on the internal control panel of some models that can select heat-only mode. Few sales or fitting staff know about this, you have to get deep into the technical hierarchy to find this out and it's not mentioned in the installation manuals. I didn't find which manufacturers have this, but probably all the major japanese production will.

There are two reasons why this matter. First, a normal UK bedroom can be cooled in the few hot days we have by better means. Bedrooms should be empty with blinds closed against the sun anyway. More annoying is that for cooling mode you must have a condensate drain pipe. Obviously this must flow downward under the unit and through an outside wall. You could have an external pump to raise it but all this is ugly and expensive work.

All wall-fan units are similar in size and layout, usually 300-ish high and requiring about 100mm above for cover access. There's a grid-net above that needs dusting off occasionally. The connection duct runs along the bottom and has knockouts at each end. All connections are on the right, so pipes usually enter from the left side about 40mm out from the rear wall, so suitable for normal surface duct pipe. There is no space inside the unit for vertical pipe runs, so if you feed down from the ceiling then you need 400mm of vertical pipework on the left side. This is two insulated pipes, usually in black foam wrap and about 26-28mm diameter. Exposed it looks horrible and you need space for the bottom corner to turn into the unit too.

In one room I managed to avoid this by placing all pipes through the wall. Three one-inch holes aligned horizontally, 380mm down from the ceiling. I drilled the left two at an angle sideways to reduce the bend on the copper pipes behind the unit, the 3rd on the right square to the wall and angled slightly down for the drain, then a final small hole for the 4-core electric cable. I got these in before the wall was plastered and the FGAS fitter just positioned the wall unit over them so all were hidden behind the bottom space. My far-left hole is about 30mm inside the left edge of the unit, the cable hole about 200mm. You need about 300-400mm of pipe tail for the FGAS fitter to work with, just a stub or elbow for the overflow, but 500-600mm for the 4-core cable to reach the far right side terminals.

You can see why this was a half-DIY job. I didn't want to decorate around a wall fixture, easier to get piping done early along with other renovation work and call the professionals in later. Since then, there has been an influx of pre-charged chinese units that have to be fitted in one session. Easier for the installers, cheaper both to buy and fit, but creates decoration problems. Pre-charged systems come with custom fixed-length pipes which can't be shortened. If I do another install, I'll stay with copper rolls, which are easily available from any refridgeration supplier and can be routed by any builder/plumber. You usually need 1/4 and 3/8 imperial pipes (all aircon follows USA standards) or occasionally 1/2 pipe for a big model. Make absolutely sure you keep the insides clear and clean!

Each wall unit will come with a TV-tyle remote controller. For a multi-split, I suggest you hide all but one then use the last to cotrol all units. All must always be in the same mode, you can't heat one bedroom and cool another. I don't use the automatic setting which allows the systen to change the fan speed: that's annoying in a bedroom. Fix the louvre flaps to avoid drafts, fix the fan speed to avoid noises (I use lowest fan setting). I turn each bedroom on just before the occupant goes through the bathroom before bed, that 10-15 minutes is usually enough to warm the bedroom adequately, if it's a standard size with loft insulation above and plenty of soft furnishing and clothing in it. I find a continuous 19 degrees makes for a comfortable night and we don't notice the fan's whisper after a few minutes.

My outside units are on wall brackets, well away from bedroom windows to avoid the noise. These certainly do attract your attention as the big fan, the size of a dustbin lid, zooms up and down its speed range between tick-over and airoplane takeoff speed. The blast of cold air can whither plants, I'm glad mine are above head level. Lots of water condenses from them, but it's just cold water, not acid like from a gas boiler. It could fill a water butt, or just drain away through gravel.

And downstairs? Well that's different. Room use varies widely, central heating is expected, hot water has to be provided too. Radiators or under-floor heating? Heat storage? Bedrooms are simpler, as long as they are night-sleep use only and not teenage studies.