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Question about air conditioner regulator implementation
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Just_another_Dave:
Recently we bough a new air conditioner which unluckily had some weird behaviors (temperature measurements that magically disappear, modes that behave differently to the described behavior in the user’s manual). After calling both the installer and the official technical service (neither of them had tested that model and both of them said that they didn’t know what was happening), the manufacturer sent a representative that showed us some confidential internal documents in order to prove that the device works as intended, but that they made a mistake writing the user’s manual (which is the only document that they officially provide to everyone else).

However, those confidential documents showed some interesting behaviors that I wouldn’t have imagined. In particular, I was surprised to find that it uses an on-off controller that turns it on if the temperature surpasses that the user sets in the control panel (for example 26ºC). Then, the controller turns it off if the temperature decreases more than 2 degrees (24ºC). I don’t understand this decision, as it means that setting a temperature of 26ºC causes the room to have an average temperature of 25ºC.
Do you know if this is a common practice in air conditioner controllers? Is there a reason for not using a PID controller?

On the other hand, the manufacturer says that their devices just work with the provided control panel, but it seems that some third-party manufacturers like tado sell vendor-neutral control panels compatible with them.
Do you know if air conditioner control panels follow any communication standard (like the ones used for heaters)? In that case, is the on-off controller implemented in the control panel (where it would be possible to replace it)?
BrokenYugo:
I'm thinking if it cut off right at 26 the building and stuff inside won't have had time to cool off, so it will just creep back up and short cycle if you don't program in some sort of correction overshoot.

Furnaces do similar stuff, cut off a bit early to account for the energy left in the hot heat exchanger after cutting the fire.
Just_another_Dave:

--- Quote from: BrokenYugo on September 16, 2023, 12:57:23 pm ---I'm thinking if it cut off right at 26 the building and stuff inside won't have had time to cool off, so it will just creep back up and short cycle if you don't program in some sort of correction overshoot.

Furnaces do similar stuff, cut off a bit early to account for the energy left in the hot heat exchanger after cutting the fire.

--- End quote ---

That would make sense, but I would have expected it to be centered (-25.5ºC to 26.5ºC) as it usually happens in heater regulators.

It can use the temperature measured by the control panel or in the return conduct (according to the preferences of the user). The last option leads to higher deviations, as more time is needed to sense temperature changes in the rooms
soldar:

--- Quote from: Just_another_Dave on September 16, 2023, 12:36:56 pm ---However, those confidential documents showed some interesting behaviors that I wouldn’t have imagined. In particular, I was surprised to find that it uses an on-off controller that turns it on if the temperature surpasses that the user sets in the control panel (for example 26ºC). Then, the controller turns it off if the temperature decreases more than 2 degrees (24ºC). I don’t understand this decision, as it means that setting a temperature of 26ºC causes the room to have an average temperature of 25ºC.
Do you know if this is a common practice in air conditioner controllers? Is there a reason for not using a PID controller?
--- End quote ---
A PID (inverter) machine and an on-off machine are completely different machines. Completely different.

I would not buy an on-off machine because inverter machines are much more efficient.

But, yes, the temperature differential between on-off is called hysteresis and it is necessary and designed like that.
EPAIII:
There may be some modern ones that work with fancier controls, but traditional AC control is a simple On/Off temperature switch, same as for a heater. Both heater and AC is either ON or OFF: normally there are no between states or proportional control. Usually the temperature sensing element is the same for both AC and heat. In both cases there is a temperature spread between the on and off points to prevent the unit from oscillating between on and off too frequently with only a small fraction of a degree of change. So the 2 degree spread sounds normal.

In the thermostats that I have seen that temperature interval is adjustable with an internal control that the installer should set for best performance with your particular heater and AC equipment.

The other thing that a furnace has is a timer that keeps the fan running for a minute or so after the heat source has turned off. That distributes the residual heat in it into the house so it is not wasted.
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