A/C Control - Automatic Changeover Unit

[Pravin]

Hi All,
Looking for a design of a programmable automatic changeover for an unmaned station with two A/C units being used on a duty/standby basis and in the event of duty unit fails, standby unit switches automatically.

Tks & regards

Pravin

[The Viking]

Depends on what brand A/C units you go for.
Most Major manufacturers offer this.

I know that the Toshiba one has all the bells and whistles, changes over every day or so depending on interval set, changes over at warning or alarm from duty unit and runs both units at high temp alarms.

[Jase]

Both units would have to be wired through a control panel which should have a high temp stat wired into the circuit, i.e say the temp reached 25oC then the standby unit would be switched on.
Also if the unit(s) in question have contacts for alarm conditions then this would be wired through the panel, so upon fault condition a signal would be sent to the standby unit.

Regards
Jase

[Dharmil]

Is any one aware of master slave configuration where at high temperatures both units start simultaneously, the slave units cuts off first and then master unit cuts off at setpoint. After this condition is achieved, and later when there is demand for cooling, the unit which first went off starts cooling and later cuts off at setpoint now at next demand the other unit which has now greater time in off condition would start and so.... on.

[BritCit_Juve]

Thats not a function that I have ever seen outside a close control unit where the unit has full control.
As has been mentioned most of the manufacturers offer an interfacee which will change over after a set period, on fault or if a stat is fitted on overtemperature.
3D/HRP offer a setup for MHI which can be 'modified' to integrate with other manufacturers equipment. It comprises two parts the 'comptrol light' (one required per system) which converts 12vdc signals from the indoor unit to volt frees and the 'comptrol vario' which does the changing over and if a thermostat is fited can provide the overtemp function. What it doesnt do though is alternate starts.
they can also do n+1 as the 'comptrol vario 3' has connections for 3 indoor units so ready for the extra equipment load :-)
Brit

[frank]

Have you considered the Mitsubishi Alpha series of controllers, where you can write your own programming?

I've had some success with these on a couple of projects. A choice of inputs/outputs/timeclocks and the programming is done by 'dragging & dropping' icons into the programming window. Quite easy when you get the hang of it.
http://www.automation-applications.com/alpha2.pdf