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General Science => General Science => Topic started by: wolfekeeper on 24/02/2021 17:15:11

Title: Air conditioning condensate is thrown away?
Post by: wolfekeeper on 24/02/2021 17:15:11
Anyone happen to know why air conditioning condensate is usually thrown away?

I would have expected it to be sprayed over the condensing coil, to cool that off, and to evaporate the water away. Surely the lower the delta-t between the condensing coil and the evaporator coil, the better? Even if the air entering the condenser coil is at 100% relative humidity, it wouldn't be after having been heated, so there's always capacity for evaporation.

The physics is that you're spending (quite a bit) energy to condense that water (dehumidifying the room air), but if you evaporate it on the condenser, you get a lot of that heat of vaporization back by reducing the work load on the compressor.

Is the problem rust, or legionnaires disease or what?

Does anyone know?
Title: Re: Air conditioning condensate is thrown away?
Post by: alancalverd on 24/02/2021 18:44:19
From a legionella point of view I'd prefer any airborne bugs to be sent to the drain rather than recycled. And if you evaporate water from a warmish condenser it will accumulate its own biosphere which will reduce its efficiency. Dry dust is bad enough but green or brown slime can seriously spoil your day.
Title: Re: Air conditioning condensate is thrown away?
Post by: wolfekeeper on 24/02/2021 20:34:29
Right, but you can add biocides.
Title: Re: Air conditioning condensate is thrown away?
Post by: evan_au on 24/02/2021 20:48:16
Isn't the idea of condensate that they cool it down just enough to become liquid - so it's warm water, and not so effective at cooling as cold water?

Quote from: alancalverd
I'd prefer any airborne bugs to be sent to the drain rather than recycled
If it were airconditioning condensate in the ISS, I expect that the water would be filtered and recycled?
Title: Re: Air conditioning condensate is thrown away?
Post by: Bored chemist on 24/02/2021 21:04:34
If it were airconditioning condensate in the ISS, I expect that the water would be filtered and recycled?
It's recycled on earth too- as rain.
Isn't the idea of condensate that they cool it down just enough to become liquid - so it's warm water, and not so effective at cooling as cold water?
It's not as effective as cold water would be but, by evaporating, it can provide a big cooling effect.

I think Alan has pretty much nailed it. the "growing green slime" problem is too much trouble.
Title: Re: Air conditioning condensate is thrown away?
Post by: wolfekeeper on 24/02/2021 21:41:25
Isn't the idea of condensate that they cool it down just enough to become liquid - so it's warm water, and not so effective at cooling as cold water?
The condensate will be from the room-side evaporator coils, so actually will be cool water, but the temperature of the water doesn't matter a whole bunch, that energy is completely dwarfed by the latent heat of vaporisation.
Quote from: alancalverd
I'd prefer any airborne bugs to be sent to the drain rather than recycled
It would be on the outside of the dwelling anyway.
Title: Re: Air conditioning condensate is thrown away?
Post by: Petrochemicals on 01/03/2021 22:02:27
Isn't the idea of condensate that they cool it down just enough to become liquid - so it's warm water, and not so effective at cooling as cold water?
The condensate will be from the room-side evaporator coils, so actually will be cool water, but the temperature of the water doesn't matter a whole bunch, that energy is completely dwarfed by the latent heat of vaporisation.
Quote from: alancalverd
I'd prefer any airborne bugs to be sent to the drain rather than recycled
It would be on the outside of the dwelling anyway.
One reason for things like this is because of the small amount or unreliability of the supply. You have no idea how much you would get on any given day, so the apperatus would have to be designed for the WCS. Any extra condensate would just complicate things with drainage or over cooling. Convversley if you are going to supply water to the cooling area you will have to have a mains supply, to integrate an unreliable secondary source and design this into a machine is going to be expensive. Both these suggestions mean a worse in carbon footprint terms than just chucking the condensate. There are millions of examples of this sort of thing in design and management.

Secondly there is the fact that most airconditioners have 2 units, interior and exterior, condensate occurs inside and the water is required in the external unit for evaporation.
Title: Re: Air conditioning condensate is thrown away?
Post by: Bored chemist on 01/03/2021 23:15:13
Secondly there is the fact that most airconditioners have 2 units, interior and exterior, condensate occurs inside and the water is required in the external unit for evaporation.
If only there was some way to connect them in such a way that material could be passed from one to the other.

You have no idea how much you would get on any given day, so the apparatus would have to be designed for the WCS.
How big a problem do you think that is?
Essentially, instead of running the water down the drain, you run it over the outside coils.
On days when there's a lot of water condensed, that's because the A/C is working hard and will benefit from the extra cooling.
You can put a drip tray under it and run the drips to the same drain you would have used anyway.
The big problem is fouling.

Another entertaining one, is the idea of cold weather.
Cladding your air con with ice might cause problems- especially if it is meant to be reversible though, in that case, obviously you wouldn't get condensation on the indoor coils in the first place.
Title: Re: Air conditioning condensate is thrown away?
Post by: wolfekeeper on 03/03/2021 05:44:02
I looked into this some more, it seems that some window mounting A/Cs might be doing this, but separate interior and exterior units usually don't. Obviously with an A/C the outside coils are overwhelmingly likely to be hot and so icing isn't going to be a problem and the A/C can control the temperature of the inside coils to prevent freezing.

Even with heat pumps where the outside coils can freeze, they usually run a defrost cycle occasionally, so collecting the water can be done, but then you do have to worry about the quality of the water that is being collected, assuming you want to raise the humidity of the interior space, otherwise the water can simply be dumped.