Air conditioning question

[Kenny202]

Recently installed an 18kw Samsung Air con. Standard cool only / non inverter. Room is 8m x 4m, block home.....all walls are not exposed to the sun. Have insulation and a suspended tile ceiling. Not the most efficient set up in the world but I would have thought the 18kw unit would have smashed it. The air output feels cold but seems to struggle pulling the temperature down below say 24 degrees and doesn't cycle on and off. It is anywhere from 37-41 degrees here ATM. Is it reasonable to expect it to chill down to where I want or could there be a problem?

[Crossy]

An 18kW unit would freeze you to death, you have 18,000 BTU.

The standard sizing guestimate for Thailand is 600 BTU per m² which gives about 19,200 BTU.

18,000 BTU is a little undersized using that calculation (which is usually an over estimate).

It's marginal asking that unit to achieve a delta-t of 17C, turn up the thermostat a bit (try 26C) and see if it manages to achieve that, your aircon and power bill will love you.

[Kenny202]

Thanks Crossy. Did that last night and it is cycling now and still nice and cool. The room temperature is far lower than 26 degrees so I guess the setting doesn't have so much to do with the actual room temperature, or lets say where we are sitting. I should have really put the unit at one end of the length of the room but not practical. I had to put it at one end of the room but not on the shorter 4m wall but on the longer 8m wall so the unit is blowing across 4 meters instead of the length of the room if you can imagine from all that waffle :-( I would have assumed the air would have only had to travel across the 4m and bounce back to the air con to operate the thermostat, albeit it would dissipate through the house. Don't think the Samsung has the grunt my Mitsubishi in Australia had.

[billphillips]

I would say that considering the outside temp, 24 and below is an unrealistic room temp to try and achieve. A setting of 27/28 would give you a very cool room on a hot day and your unit should be able to maintain that temp without overheating (if it's working ok).

I'm going to state the obvious: keep all the windows and doors closed. Close the curtains or blinds for windows letting sunlight in.

Your aircon compressor should be idle more than it runs once the room temp is attained. Is it producing water from the drain away pipe? Is the outside unit in strong sunlight, fitted on the ground or not in a clear air space?

[IMHO]

To achieve the temperature drops you want during the day, you'll need 800-900 BTU per sqm. The 600/sqm rule-of-thumb is a baseline for nighttime-only usage.

It seems increasing the thermostat got you an improved result at night, but you'll need to see how it does again today before you start any celebrations

I wonder - has the indoor wall unit been mounted at least 10cm below the ceiling?

Also, IIRC your house has unusually high ceilings too? That also demands more BTU.

Edited March 21, 2015 by IMHO

[IMHO]

I would say that considering the outside temp, 24 and below is an unrealistic room temp to try and achieve. A setting of 27/28 would give you a very cool room on a hot day and your unit should be able to maintain that temp without overheating (if it's working ok).

I'm going to state the obvious: keep all the windows and doors closed. Close the curtains or blinds for windows letting sunlight in.

Your aircon compressor should be idle more than it runs once the room temp is attained. Is it producing water from the drain away pipe? Is the outside unit in strong sunlight, fitted on the ground or not in a clear air space?

Agreed, you're not going to get 24c inside with 41c outside temps, with 560 BTU/sqm.