Before talking about setpoints, first you need to have the right HP for the room size. That's called rightsizing. If HP is too small you will never reach the set point and the compressor doesn't cut off. That's like trying to drive a kancil at 300kph.
If the HP is too large, the cut off will happen too soon before the compressor reaches optimum efficiency. That's like driving a Ferrari in a traffic jam. Either scenario is wasteful.
Using the right size HP and selecting correct setpoint both need to be done.
Your uncle likely failed to do either, accounting for the excessive bills. Also setting the setpoint at 18oC is the wrong way to use the air-conditioning. Setting at 25 is correct. That is where inverters come into the picture. Basic Air-conditioning compressors work by turning on and off to maintain the set point.
Inverters work by reducing the need to turn off completely. Not only it saves energy, but it reduces wear and tear.

Having a lot of money doesn't mean he knows everything. Do you even know how cold actually 25oC is? There is a range of combination of temperature, humidity and air movement which is known as the thermal comfort zone, in which human perceive themselves to be comfortable. 25oC is usually the upper limit. In HVAC design, that approximates the max temperature you can go in Summer before it is deemed uncomfortable. On the other hand, 20oC is the minimum temperature you set for heating in Winter before things are deemed too cold for comfort.

To be fair I absolutely agree with your earlier contention that passive cooling and better structural design reduces the need for active regulation via air conditioning. However I cannot abide by the fact that you dismiss setting 25oC as a good practice. It *is* the norm (it should be even higher if we really want to save on carbon emissions). To use another car analogy, you don't floor the pedal if you are just intending to drive at 80kmh

The whole point of all the technological advances in HVAC and environmental design such as inverters etc is that you would want to adjust your living environment so it is comfortable with the minimum drain on resources.
It's not just about the money here.

It's just absolutely wrong to even justify setting 18 or 19 or even 20oC in our Malaysian climate as it is extremely difficult to achieve. To be honest with you I think the majority of Malaysians are ignorant about how air-conditioning is supposed work. An expat friend of mind once remarked how silly and ironic it was to see Malaysians set 18-19oC in their office thermostat and yet come to work clad in sweaters and jackets, complaining it was "too cold".

FYI until recently I lived in a 3 storey house with 8 air-conditioners, (including 2 energy-sucking 2.5 and 2HP cassette units) and my monthly bill was rarely above RM170. That was because I minimized usage of the air-conditioning to just a few hours at night, not seeing the need to blast it on 24x7 and tried my best to use electricity saving devices like inverter fridges, LED lighting etc. It's no point bragging about electricity costing RM700-800 and being able to afford paying for it. It think it's downright shameful nothing more is done to lower it.

just my 2 cents'

I'm just pointing out some facts and trying to correct some potentially misleading points you brought up. A lot of what I say is backed up by sound theory. Some of the things you are saying are clearly based on practical experience, but not fully informed by theory, and that makes it dangerous.

If I tell you 25oC is cold enough a setting, then if you are not getting it "cold" enough, it means that something is not right. It means *potentially* one or the other of the scenarios I pointed out. (assuming there is nothing wrong with the workmanship or the installation)
The more common scenario in Malaysia is I believe, people buying air-conds which are way too small because of initial cost consideration, and then switching it at lower temps because they can't get it cold enough. You NEED to right-size.

Having a lot of air conditioners doesn't mean I have to switch all at once in order to get a humongous electric bill: I do accept that usage of air-conditioning will always be higher slightly than having none at all; I *understand* the potential impact on the environment of excessive electricity usage and try to keep within acceptable bounds; I am *willing* to pay for that *small* premium for additional comfort within a reasonable amount, but that is as far as it goes: It's mainly there so that I can have it when I *need* it, e.g. when there's a party and I have like 50-60 guests milling around the premises. I don't think I'm the one being childish or presumptuous here.
I don't need you to salute me because that is not the intention I brought up the matter: you can't fight the laws of physics. You use electricity, there is a price to pay, not just money, but in terms of impact to our environment. That is why we must use what we have responsibly.
If I say 25oC is the correct set point, and you are not getting that, you need to find out what really is the matter. That's all I'm telling you.

Care to elaborate on this?
Unless you are replacing/refilling the gas, which is not all the time, the labour cost of just cleaning should be about the same.
Even then it's not always true, because not all inverter air-conditioners use the more-expensive R410A gas, which should be around RM2xx~ (but dropping fast)

You don't have to be so defensive or evasive. I'm neither interested in massaging nor bursting your ego, and anything you feel is really a reflection of yourself rather than what others say. None of us here claims to know everything, and we all learn from each other. If something I say is wrong, I'd sooner recant than defend the indefensible because the advice and information given here could potentially cost people money and a lot of inconvenience if taken at face value. Let me remind you that this is a forum for sharing information and seeking advice, not /k or RWI where people thrash talk each other and show the world how stupid they are.

As far as I know there are at least 2 makes (one of them is Daikin, the other I can't remember) in the local market which carry R22 inverters.
When we talk about cost, there's cost of purchase/installation and there's cost of ownership (i.e. maintenance/operation).

When we buy air conds, inverters carry a premium over non-inverters for the same brand due to the extra features.
When we install air conds, we have to consider the gas type, especially for retrofit: New houses that come with air cond piping tend to have thicker piping ok for use by both R22 and R410a type gas. Older houses on the other hand, may not have the thicker pipes and there is the additional cost of retrofitting if you want to use R410a inverters.

When we use air conds, provided they are install correctly and optimized for their environment/use-case, inverters will tend to result in greater savings in electricity bills and maintenance cost due to reduced wear and tear.

In general, you will also find that when air conditioning is installed professionally, there is not a lot of need to refill the gas.

In the case of refilling R22 inverters should cost about the same to refill as normal R22.
R410a inverters on the other hand, have a premium of about RM100 on gas cost last I checked.

I also know that some installers *cheat* a little by saying they completely replace the gas when actually they are just topping up. Comes with the territory and everyone has to cari makan.

I'm sharing what I know based on what I researched when I bought my air-conds because I think we can all benefit. I'm not interested in playing word games with you.

I agree! My Daikins are really quiet and you would be hard pressed to hear the compressors running from inside the house.

For those of you who are more technically inclined, here's some sharing

http://fire.nist.gov/bfrlpubs/build02/PDF/b02186.pdf

A Comparison of an R22 and an R410A Air Conditioner Operating
at High Ambient Temperatures


The TLDR version: in an extreme use case (not necessarily applicable in Malaysia), i.e. extra high ambient temperature, R410A actually performs worse than R22, with greater loss of efficiency.



This post has been edited by oe_kintaro: Feb 4 2014, 06:59 PM

A lot of distance to the living for the 2HP wall mount to cover IMHO . Maybe a 2.5HP ceiling cassette in a more central location? Or you can keep the 2HP wall mount there and have another 1 HP one for your living.

OYL manufactures York under license. York is owned by Johnson Controls worldwide. Acson is OYL's "house brand" I think