Conservatory cooling part II

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Conservatory Cooling - What works?

In my previous article on conservatory cooling I described how in attempts to cool my 3.5x3.5m area south facing conservatory I had considered a solar coating, tried blinds, a ceiling fan and also used a pedestal fan but nothing worked. I had also previously purchased a rather noisy 12000 btu air conditioning unit which went back as the conservatory is mainly used as a treatment room for my wife's back pain clinic.

Quieter portable air conditioning unit

Despite my previous claims that I would call several air conditioning companies and ask advice on which would be the quietest I fell back to my scientist roots. This involved finding and reading the technical datasheets for several popular portable air conditioning units to see how many dBA they were quoted. My previous 12000 btu unit produced noise up in the 55-65dBA level. The dBA is the measure of noise adjusted to the frequency sensitivity of the human ear. Roughly a 10dBA increase is perceived as a doubling of loudness. The unit I chose was a 12000 btu Amcor air conditioning unit from Ebuyer. It had a quoted noise level of 49dBA and so should be at roughly half the loudness of the previous unit I bought. The unit cost £280 including VAT and delivery.

Installation

Air conditioning units produce heat in cooling the air they blow into the room. The warm air they extract and the extra heat they produce has to be vented out of the room via a pipe or permanent ducting. For a portable air conditioning unit it is usually via a flexible ribbed pipe that is either stuck out of the window or through a door that is slightly ajar. The key is to vent the hot air without letting the warm air outside back in. The flexible pipe is anywhere between 1.5 and 3m in length. The instruction warn that you must not try and extend this pipe or have to many extreme bends in it as the air conditioning unit may over heat. Why? Well, in order for the unit to expel the hot air down the pipe it has to provide a certain amount of pressure. The amount of pressure required depends on how fast the air is needed to travel, the diameter of the pipe and its length. If air cannot be expelled quickly enough then the air con units motor will get hot. The issue with this method of hot air extraction in a conservatory is that they don't usually have 'normal' windows. The windows that open in our (and indeed most) conservatory are at the tops of the window pane a good 1.5-2m above floor level. Problem! The connection point for the pipe into the air con unit is maybe 30cm above ground and so the pipe only just stretched to the window opening. I 'solved' the problem by using the expanded polystyrene packaging as a stand for the unit to sit on. Still the pipe isn't ideally situated as it has a 90 degree bend in it and had to push the hot air up the pipe to get out of the window. To help seal off the room from hot air getting back in through the open windows the unit came with a cover plate that fits around the exit of the hot air venting pipe and should fit in the gap made by the open window. In practise this doesn't work for our windows.

Cooling effectiveness

Firstly in the absence of any cooling our conservatory gets extremely hot. Prior to writing this article I have measured the inside temperature at 41C when the blinds have been down all day. That's as hot as India in summer! This is in a cloudless day at 3pm with an outside temperature of about 25C in the shade. The unit can attempt to maintain an air temperature between 18 and 23C. Whether it can do that depends on how much heat it can expel compared to how much heat is being generated inside the room. After running the unit for about half an hour I measured the air temperature at about 31C or 10C cooler, but still hot. This is for a unit that is rated at 12000 btu and so should be adequate for the size and location of the conservatory we have.

Air conditioner noise level

It certainly is quieter than the previous unit we had, even when it is in turbo mode, that is with the compressor running (actually air conditioning) and the fan on at full speed. I wouldn't say it was quiet, you couldn't easily watch TV whilst this thing was on in the room, but it isn't too obtrusive. My wife thinks it will be OK for noise level when treating the clients. Actually positioning it on the packaging helped reduce some of the noise due to vibrations.

Can it be improved?

I think both the noise level and the cooling ability would be improved by have the air vent at the same level as the exit hole in the air conditioning unit, rather than run up the flexible pipe and out of the window. This would also allow the pipe to be shortened in length and hence improve the rate of air expelling. To do this I would have to cut a large diameter hole the wall under the window similar to the vent for a tumble drier.

The other option is to buy a more powerful air conditioning unit. I did see some units that were quieter than 49dBA but had the price tag to match as £900. Typically a portable 15000 btu unit would also be louder than a portable 12000 btu unit. A split unit, where the compressor is outside the room, would be quieter per btu of cooling power but expensive. The actual units themselves aren't too bad. A 11000 btu unit can be found for £299 and is quoted at 41dBA for the inside part. The next size up on the site in question is a 18000 btu unit which should be powerful enough, the dBA has gone up to 46 and the price is £400. This price does not include installation costs. I'm not sure I would be confident in installing these units. Some of them require hard wiring into the mains and pressurising with the coolant gas before use. I think I would be looking at paying £500 for a fitted unit capable of cooling the conservatory and that's too much at the moment. Maybe next year.

Conclusions

We've spent quite a bit of money trying to cool our conservatory

And managed to achieve a 10C reduction on a hot sunny day outside, but this temperature drop makes the difference between whether the room can be utilised as a clinic or not. If it had the chance to spend the money again I would have maybe bought and installed my own roller blinds on the vertical windows (rather than the more complicated shape of the roof) and used the money I saved to have a professionally installed split air conditioning unit (of maybe 18000 btu) fitted. The total cost would have been less than £1000 and saved a lot of time and resulted in a cooler room. If anyone has any other ideas and wants to try them on my conservatory (such as solar coatings) I would be happy to let you do so for free! ( as long as you are a professional company). The results positive or negative would be published in an article on this site.

By Jonathan Pearson