Aircondition Conundrum

[CapraIbex]

I am going to increase my open plan living area to about 60 sqm.; The ceiling height is 2.80m. The room is well insulated, the windows may leak a little but have no afternoon sun.

My existing air-condition unit (Carrier 38FCE018-R1, 18,700 BTU) is maintained on a regular basis and working extremely well but am unsure if adequate for cooling down the new room (my Internet searches yield  mixed results) .

Would installing a 2nd air conditioner (equal brand/model) in the same room be an option or would I have to bite the bullet buying a new unit and dispose of the old one?

[Crossy]

Ok. The standard Thai guesstimate for A/C is 600-700 BTU/m² this actually over-sizes a bit but it's a good starting point.

 

So you 60m² room is going to need about 36,000 to 42,000 BTU, it's well insulated / low gain so the lower end should be just fine.

 

So you need to add about 17,000 BTU. 

 

Another similar sized unit to your existing one at the other end of the room should be a good fit.

 

I'd certainly go inverter for your new unit.

 

[CapraIbex]

36 minutes ago, Crossy said:

Ok. The standard Thai guesstimate for A/C is 600-700 BTU/m² this actually over-sizes a bit but it's a good starting point.

 

So you 60m² room is going to need about 36,000 to 42,000 BTU, it's well insulated / low gain so the lower end should be just fine.

 

So you need to add about 17,000 BTU. 

 

Another similar sized unit to your existing one at the other end of the room should be a good fit.

 

I'd certainly go inverter for your new unit.

 

Thanks for recommendation and technical advise.

In terms of power consumption, would an inverter unit be compatible with a 'non-inverter'? And how to ensure that one of the units is not 'overworking' and used in concordance?

[sometimewoodworker]

8 minutes ago, CapraIbex said:

Thanks for recommendation and technical advise.

In terms of power consumption, would an inverter unit be compatible with a 'non-inverter'? And how to ensure that one of the units is not 'overworking' and used in concordance?

There is no compatibility problem.

 

the way that most people would use a dual AC setup like that is to only run 1 AC until it’s obvious that you need more cooling then turn the other one on as well. This has the advantage of reducing the wear on the secondary AC so you will be unlikely to need to replace both at the same time.

 

My preference would likely to run the inverter as primary when the weather is not too hot, then when the weather heats up swap and run the inverter as secondary.

Edited February 23, 2022 by sometimewoodworker

[bankruatsteve]

I adequately cool 55m² well insulated rooms with 11k BTU inverter (Daikin).  Just sayin.

Edited February 23, 2022 by bankruatsteve

[Crossy]

15 minutes ago, bankruatsteve said:

I adequately cool 55m² well insulated rooms with 11k BTU inverter (Daikin).  Just sayin.

 

It certainly wouldn't hurt for our OP to "suck it and see" with his existing unit.

 

But it depends upon what is defined as "adequately cool", he may keep penguins as pets ???? 

[bankruatsteve]

42 minutes ago, Crossy said:

what is defined as "adequately cool",

For me, the AC is set to 25^o.  Actually, the AC is in our 20m² bedroom.  I open the door and shutters to let it spill out to the 35m² living area which, with ceiling fans, will maintain at 26^o.  When it is 40^o outside, it will run up to 28^o but still feels cool.

[CapraIbex]

Thanks to all for useful input.

The advise for using the inverter as a primary unit is certainly most helpful.

Based on the replies, I just may try using my existing aircon first and check for cooling effects power consumption. I generally set the the temperature to 27C, comfortable enough for me but may be inadequate for arctic duckies. And I do make use of ceiling fans.

[CapraIbex]

Apropos inverter air-cons.

I recall a thread posted many moons ago stating that the inverter unit did not perform to its specification. The poster claimed that the brand new inverter unit was not producing the intended cooling effect. I can't locate this particular post - maybe some of the readers here can.

[OneMoreFarang]

2 hours ago, Crossy said:

The standard Thai guesstimate for A/C is 600-700 BTU/m²

Do you know where that and other numbers come from?

I.e. it makes a huge difference if I want to cool down a room to 25 degrees or to 18 degrees.

And it makes a huge difference if I have huge uninsulated windows with lots of sun.

If someone would declare that i.e. 650 BTU/m^{2 i} is good enough to to cool down a "normal" room with not too many windows to 25 degrees that would be interesting.

So how about cooling that same room to 20 degrees?

Any formula?

[Crossy]

34 minutes ago, bankruatsteve said:

For me, the AC is set to 25^o.  Actually, the AC is in our 20m² bedroom.  I open the door and shutters to let it spill out to the 35m² living area which, with ceiling fans, will maintain at 26^o.  When it is 40^o outside, it will run up to 28^o but still feels cool.

 

Yeah, we run similar temperatures, anything cooler than 26C is just too cold! (been here too long evidently).

 

We recently replaced the aging 18,000 BTU conventional unit in our bedroom with a 12,000 BTU inverter. The installer was worried it was too small, but was happy when I said we ran at 26C. 

 

We are gradually replacing the conventional units with inverters, mainly because they soft-start and don't stress our power generation system. What I have noticed is that they don't have that "instant gratification" arctic blast on starting (that might be why some people think they are not cooling as expected) but leave them alone to get on with the job and they really do cool just as fast.

[OneMoreFarang]

10 minutes ago, CapraIbex said:

Apropos inverter air-cons.

I recall a thread posted many moons ago stating that the inverter unit did not perform to its specification. The poster claimed that the brand new inverter unit was not producing the intended cooling effect. I can't locate this particular post - maybe some of the readers here can.

It seems for some people they want to sit right in the cold air stream of a normal aircon.

Inverters don't produce this super cold airstream all the time.

And, as far as I know, the idea is that people should not primary sit in that cold stream. The cold stream should mix with the rest of the air in the room and the result should be a comfortable temperature. 

[Crossy]

2 minutes ago, OneMoreFarang said:

Do you know where that and other numbers come from?

I.e. it makes a huge difference if I want to cool down a room to 25 degrees or to 18 degrees.

And it makes a huge difference if I have huge uninsulated windows with lots of sun.

If someone would declare that i.e. 650 BTU/m^{2 i} is good enough to to cool down a "normal" room with not too many windows to 25 degrees that would be interesting.

So how about cooling that same room to 20 degrees?

Any formula?

 

There are "accurate" sizing programs, feed in 1,000 variables and it will select the "correct" size of A/C. You then get to pick one from a range of maybe 4 or 5 cooling capacities.

 

Thing is, so long as it's not massively over (yes, you can over size an A/C although it's less of an issue with inverters) or under sized, the thermostat will even out the bumps and all will be good.

 

The Thai guesstimate comes from loads of local experience, as noted it does tend to over-size somewhat for what we feel comfortable at, but we have to keep those penguins happy. 

[warrima]

Last year i pulled out an old 24000 BTU LG unit that was in our 35 sqm living/kitchen area. It was 12 years old and getting expensive to run - which was usually only when guests came over. The compressor was massive and took a sizable chunk of the balcony as well. 

 

I self replaced it with a little 12000 BTU Sharp inverter. The compressor is tiny (and light)  in comparison and really freed up some valuable space. I deliberately chose an undersize unit at the time thinking it was only gonna be in use maybe one week a month and i wanted it to run as a dehumidifier as much as anything.   

 

Roll on a year and its perfect. As opposed to my earlier thinking its now used pretty much daily - set at 27 deg - which it has no issue with and very comfortable. Lecky bill is still less than compared to running the old one only occasionally. 

[bankruatsteve]

49 minutes ago, Crossy said:

Yeah, we run similar temperatures, anything cooler than 26C is just too cold! (been here too long evidently).

At night, I put on "Dry", close the shutters and door and it maintains at 26^o.  ????

[Banana7]

I like to oversize using inverter AC. For 3 rooms, a total of 96 sq. mt. I have 3 Hitachi inverter AC each 18,000 BTU, one in each room. When I come home, on a hot sweltering evening with sweat dripping, all 3 get flashed, and 20 minutes later the place is down to 25c. The inverters are full power initially and then throttle back, both fan and compressor, when the desired temperature is reached and eventually, 1 or 2 are turned off, depending on the ambient heat coming from the walls and outside air.

 

In the bedroom, 32 sq. mt., night-time sleeping temperature is 23c, and one 18K BTU does a nice job. Quick to initially cool and maintain a nice temperature all night. On cool nights, the compressor turns off, on hot nights, it just throttles back to a low setting. Got to keep it cool so the girlfriend snuggles up to the hot man.

 

 

[Yellowtail]

I would wait and see if it will keep up, and if it will not, depending on the budget. I would:

1. Low budget: Buy another low-end unit and add it to supplement the existing unit. ~B20-30K

2. Mid budget: Buy a new higher-end, higher capacity unit to replace the existing.  ~B30-40K

3. High-budget: Buy a new higher-end cassette unit to replace the existing. ~B50-70K 

 

I'm not a fan of two units unless in a single area unless the room is very long and narrow. How old is the existing unit? If you go with two units and one unit is old, you may end up having to buy another new unit in the next few years. If you pay someone to service your units, your service cost goes up as well. If the room is very long and you want a unit on each end, consider a multi-split, this will run cheaper and cool more effectively than two separate units, particularly if you are only running one of the units occasionally.

 

If you have the budget, go with a nice cassette unit in the center of the ceiling. It will run cheap, require less maintenance, and cool all areas of the room more effectively than wall units.