HVAC Question

Bury your house.

Build a shade cover over it.

Blow air over a 500 pound block of ice with a big fan. Use the melt water for drinking.

Add a second "air conditioner".

Buy a room air conditioner. (A real one with a compressor)

Move to Switzerland.

The most cost efficient way is to reduce the heat load by adding insulation and other methods....of course they are other factors at play here, your climate and geographical location, square footage of the space you are conditioning....You can't really hope for more than 500 sq ft per ton of cooling to work well....If your A/C unit was sized correctly originally, then you have probably experienced some loss of capacity, this calls for a pro to check out the system and do required maintenance and repair...your condenser coil could have some scale buildup or you may have a refrigerant leak or dirty evaporator coil, any number of problems could be effecting the performance of your unit....this is most often the case...

http://www.advantagehomeperformance.com/cooling-load-reduction

Solar,

If you have a high efficiency unit, you can get more than 500 sq ft/ton. I think the minimum efficiency allowed here in So Cal is a SEER 13. I heard about a new Westinghouse system that has a SEER rating of 25.5.

Don't complain if your getting 25° temperature drop from your "air conditioner", most air conditioners, with compressors, only wish they could achieve a 25° temperature drop.

Like Lyn said, either "bury your house" or find a deep cave to move into. It's either that or cover all of your, roof, walls and windows with 100% reflective coating

I think he said down TO 25°C/77°F.

I'd think 25°C would be considered cool where the OP is.

I did over look his location. Living Dubai you'd think he could afford an AC with a compressor?

I could live with 77°/25° room temp. California's central valleys get pretty dang hot too, it's not uncommon to be 100°+ during the summer

It might be in Zimbabwe, though, where the OP is working on a prospective irrigation dam/reservoir project.

Some local design dry-bulb and wet-bulb info might help. A "swamp cooler" like the OP's can asymptotically approach actual wet-bulb temperature, but no lower.

"or cover all of your, roof, walls and windows with 100% reflective coating"

dj's got the good oil.

<...25 degrees...> is <...at least 18 degrees...>!

A swamp cooler(using only water evaporation for cooling)can never get temperature below the local dew point.

A larger unit will not help,no matter the size.

A larger size has a greater ability to remove sensible heat,but a poor ability to remove latent heat,so the air is very humid and will feel uncomfortable.

To get below the dew point,you must remove latent heat,by using a method that will remove latent heat.

A normal air conditioner removes humidity and heat,that is why they call it an "air conditioner",not an "air cooler".

If you look at the condensation on the evaporator coils of an air conditioner,the condensation is due to the removal of latent heat from the room air.

The lowering of humidity allows your body to evaporate moisture more efficiently.

You feel cooler at a higher temperature because of this effect.

I am sure you have heard "But it's a dry heat",which speaks to this effect.

A dry heat is more comfortable.

Do some research on air conditioning principles,and you will understand why this is true.

As far as I am aware, the OP has not told us exactly "why" he needs such a temperature in the first place, which might be a very good idea.....

I think there must be more to the situation than he has told us...Maybe he is dramatically over weight? That could easily explain why he needs such a low temperature......Overweight people are simply too well insulated and feel hot all the time....it shortens their lives quite dramatically....

I lived in Singapore many years ago starting at age 17, mostly without air conditioning/cooling or any sort, other than ceiling and table fans.

But having air conditioning set to too low a temperature (18°C is very low to my mind!), makes going outside (I assume that will happen occasionally!) torturous.

Also, it seemed that we got colds far more often with air conditioning.....thats an opinion only, not proven fact!! So it may be not a "healthy" move for anyone, fat or not!......

Its better to have only a 5 - 10°C lower temperature difference between in and out and to use the air-con mainly to get as much of the moisture out of the air as possible, down to around 50-60% is very comfortable then....

Singapore for example, usually has around 100% humidity, a dry day is 95%!! It does take several weeks for an average European to acclimatise, but once you are, its really great, but I found that you need to dress up warmly if the temperature drops below 35°C!!

That was when I got goose bumps.....

Our Aircraft carrier Engine and boiler rooms were usually around 90°C, a working environment that melts the fat off you no matter how much you eat!! A positive side effect!!

Others call that a "cool" sauna!!!

What is the cooled space needed for?

Is it an equipment shelter, workspace, home, airport, restaurant, boat....?

Second law of thermodynamics: Heat cannot spontaneously flow from a colder location to a hotter location.So this tells you that you can't get a room cooled without putting in energy. (first law)
Try sucking out the hot air from a high point in your room, (this has the most heat)and pump in air that passes through a cold area like a bath of water or shade into the bottom of said room.
this will give you a circulation that will feel colder than the outside air.you'll only need a pump for getting the air out, and air in, this should reduce cost.In a building the coldest place will always be the ones on the bottom (if there are no people generating excess heat)

18° is cool?? That's summer in the UK :-)

I must have missed that.

A desiccant cycle to dry the incoming air to the cooler.