i have two 1.5 ton capacity ac connected in a room of 10 ft by 10ft. my aim is to maintain the room temp nearly one degree centigrade.when two ac runs continiously for 30 minutes room temp comes down to zero degree. compressor is continios i.e no temperature control is installed.if i run the two machine for 2 hrs the room temp comes down to minus 4 degree centigrade.
is there any way to mantain the room temp nearly 1 or 2 degree centigrade by switching the compressor on and off by arduino. i have all the hardware setup like ssr, arduino, temp sensor and oled display.
any idea of writing algorithim in order to decide when to switch the compressor on.
A simple Arduino sketch using a temperature sensor such as the DS18B20 would be able to detect the temperature and then do something (even via relay) but how do you expect the compressors to be switched off?
I don't think you can just cut off the power, it's not good for them. Have they got a mechanism you can use to turn them off (I think they continue to run for at least 30 seconds after such a request for operational reasons).
in a room of 10 ft by 10ft.
A two-dimensional room?
no sir 8 ft height also
after switching off the compressor i think at least 3 minutes dealy is required to switch it on again
Is this an ideal room just in theory or something practical where heat loads such as people coming and going influence the outcome?
Either way, it calls for an inverter type system where the motor ramps up and down continuously.
Another possibility is a series of smaller compressors which might keep up with the tight temp control also but I doubt it with just 1.
Look into PID algorithms too...
Your requirement for 1-degree control will require that you eliminate overshoot on the heat/cool cycles.
Where are you measuring the temperature? There will be gradients.
You cannot hold all this enormous volume to a close limit unless you have large circulating fans.
Allan.
You must rest a compressor until the refrigerant has time to equalize. 3 minutes seems too fast.
Can we assume that you can only control with the units ?
turning them off is simple enough, turning them on is the problem.
you did not mention the heat load in the room.
people ? lights ? other ?
if you can monitor the load in the room, you can predict when you need cooling.
but trying to maintain 1 deg C is hard with good controls.
turn one on, run, turn the second on, run,
when needed alternate which one is on.
as you get too cold, turn of #1
as you get too warm, turn #1 back on. based on your times, this should not be under 15 minutes ?
then, when it gets too cold, turn off #2....
you did not mention how you turn them on an off. normally, a motor starter is used. often has a control coil that has low current. but it may be line voltage. you can control the signal to that coil with a relay that the Arduino can control.
If you have a large budget, there are ways to control very precisely.
allanhurst:
Where are you measuring the temperature? There will be gradients.You cannot hold all this enormous volume to a close limit unless you have large circulating fans.
Allan.
I would agree that this space should have multiple sensors. but the volume of air for one unit of about 600 CFM would keep the room air stirred up.
the control sensor should be in the return duct as that would be near the ceiling and the warmest part of the space.
It sounds like a refrigerated walk-in box. not sure what other type of room would have the need to be 1 deg C
I hope it is not fresh food storage, too close to freezing and letting the temperature to have such a huge swing (in food terms) would not stop the food from ripening.