Evaporative cooling fail

[Garald]

I'm still trying to figure out how to make my attic comfortable during heat waves. I live in the Paris area, where heat waves are comparatively dry (in fact, they are the only time when it is comparatively dry).

So, I decided to get a medium-sized evaporative cooler: https://www.amazon.fr/KLARSTEIN-Skyscraper-Rafraîchisseur-Humidificateur-Refroidisseur/dp/B085HM8N2Z?th=1

 

It does produce a cool breeze, so I suppose it is helpful if you stand or sit literally in front of it and quite close to it. I didn't notice enough of an effect if sitting at 1-2m from it. 

 

So, wanting to determine the truth, I ran an experiment. 

 

My attic consists of two compartments (not counting the bathroom): I closed the windows in both, and ran an evaporative cooler (Klarstein Skyscraper ICE) in one of them; I put a thermometer/hygrometer in each compartment. After a while,

- the half without the cooler was at 30.9 C, 50% humidity,

- the half with the cooler was at 30.9 C, 60% humidity.

That's a remarkably total and precise failure! The cooler was humidifying without cooling. My question is: how is this even possible?

 

Wouldn't a simple decorative indoor fountain do better than this? How can a tool manage to be so bad? How do you set out to make an evaporative cooler that doesn't work?

 

 (Some data (from https://www.kwangu.com/work/psychrometric.htm😞 30.9 C at 50% corresponds to a wet-bulb temperature of just 22.75 C (i.e., we could be very comfortable if were just willing to do math while wrapped in wet towels). An evaporative cooler that keeps enthalpy constant (I thought that was a reasonable assumption - these are low-powered devices, so the heat they dissipate by operating is likely negligible) would keep wet-bulb temperature constant. Then, at 60% humidity, we would have expected the temperature to be lowered to 28.7C, a significant change.)

 

I ran the experiment again the following day. Starting conditions (at 4:50pm): outside temperature 28C, attic room with cooler: 32.8C, 42% humidity; attic room without cooler, 32.9C, 47% humidity. 

End conditions (at 11:25: attic room with cooler - 30.3C, 60%, attic room without cooler - 31.2C, 51%). All right, this time, the cooler did *something*, but it seems to be remarkably bad at what it does.   

[ProDave]

The clue is in the name "evaporative".  It "cools" by evaporating water.  So it puts water vapour into the air.  What else do you think will happen to the humidity in the room?

 

Many will say this sort of "cooler" is snake oil.

 

The only way to cool the room, is to remove heat from it.  Something your ASHP is likely capable of doing?

[Garald]

  On 01/07/2024 at 21:42, ProDave said:

The clue is in the name "evaporative".  It "cools" by evaporating water.  So it puts water vapour into the air.  What else do you think will happen to the humidity in the room?

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Well, obviously, the humidity will go up, but the temperature should go down.

 

  On 01/07/2024 at 21:42, ProDave said:

The only way to cool the room, is to remove heat from it.  

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If by "cooling" you mean lowering the heat, then yes, obviously and tautologically.

 

If by "cooling" you mean lowering the temperature, no, not necessarily. Without refrigerative means, the wet-bulb temperature will not go down, but the temperature may and in fact should be lowered as humidity is added, no?

>Something your ASHP is likely capable of doing?

 

Nah, it's not reversible. (It's air-water; if it had a different, more polluting refrigerant coolant, it could produce cold water).

[dpmiller]

why can't your air-to-water cool?

[Garald]

  On 02/07/2024 at 05:43, dpmiller said:

why can't your air-to-water cool?

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The model doesn’t. Mitsubishi models that could used an older, more polluting cooling fluid - and all installers I talked to expressed profound skepticism as to whether producing cold water was ever useful, particularly without underfloor heating (I have radiators).

[ProDave]

Post the exact model number, I would be surprised if it can't do cooling.  It might need an internal switch changing to enable that function.

 

Cooling to radiators will work, just keep an eye on cooling water temperature so you don't get condensation on the radiators.

 

ASHP cooling on a sunny day is free if you have solar PV as well.

[Garald]

  On 02/07/2024 at 08:29, ProDave said:

Post the exact model number, I would be surprised if it can't do cooling.  It might need an internal switch changing to enable that function.

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ERST20D-VM6D
PAC-ISOCH
MITSUBISHI UE ECODAN SPLIT ZUBADAN SILENCE 12KW 1PH R32 ZUBADAN SILENCE

 

  On 02/07/2024 at 08:29, ProDave said:

 

Cooling to radiators will work, just keep an eye on cooling water temperature so you don't get condensation on the radiators.

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Won’t they just cool a thin layer of air at the bottom?

 

  On 02/07/2024 at 08:29, ProDave said:

 

ASHP cooling on a sunny day is free if you have solar PV as well.

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Will have it, don’t have it yet.