How to Reduce Runtime of Air-Conditioner During Peak Hours?

Electrical Technology

How to Override Air-Conditioner Thermostat Using Digital and Programmable Timers?

To reduce the excessive operation of the air conditioner during peak electricity hours, we can use digital and programmable timers with thermostats to regulate the AC’s runtime during periods of high electric prices. In the following post, we will show how to reduce the runtime of an air-conditioner using digital timer, LY2 relay and DH48S for both 120V and 240V AC circuits.

While doing so, it will not be possible to program it to limit the number of runtime minutes per hour. This means it will only lower/raise the temperature and reduce the number of hours during peak prices.

The following wiring circuit does the job without compromising and modification to the equipment and AC motors etc.

As any programable time will do the job for above mentioned scenario, but we have used Din Rail timer because they are available in 12 to 24V, and 120V to 240V AC.

Any programmable timer would do the job for the scenario mentioned above, but we chose to use a Din Rail timer because they are available in both 12 to 24V and 120V to 240V AC options.

We have used both digital and programmable twin timers rated for 120V and 240V in our wiring diagrams. They can be set up independently to operate between 0.01 seconds and 99.99 hours for repeated and endless cycles of ON and OFF operations.

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Controlling the Circuit Via 120V AC

In the following wiring diagram, the Din Rail timer is programmed and controlled using a separate breaker via 120V AC supply to be ON during peak hours. The further operation of the circuit is when:

1. the ST01 (or THC15A) DIN Rail timer is ON
2. It turns ON the LY2 Relay
3. The DH48S-S twin timer turns ON

Now, when the din rail timer is OFF, it will turn off both the relay and twin timer.

Click image to enlarge

As shown in the figure, one of the wires from the 24V thermostat is connected to the common terminal (5) of the relay. In this case

When the timer is off, obviously, the relay will be off, so the circuit operates under normal conditions through the 24V thermostat to control the AC contactor.

When the timer is ON, it activates the relay. Consequently, the 24V thermostat disconnects from the contactor and is redirected to the twin timer.

Working of the Circuit

For example, if you set the ON operation for 45 minutes and the OFF operation for 15 minutes, the air conditioner will run for 45 minutes in normal mode, during which the twin timer directs the 24V to the AC contactor. This configuration allows the twin timer to limit the AC’s operation to 45 minutes instead of 1 hour.

After the 45 minutes of running, the AC will then turn OFF for the next 15 minutes until the twin timer reset and back to the initial state. It means, the cycles is endless i.e. the AC will be ON for 45 minutes and OFF for 15 minutes until the timer is turn OFF.

You can adjust the timer settings to suit your needs for further energy saving e.g. setting the OFF period for 20 mins, 25 mins etc. especially in peak electric hours to save energy consumption and reduce the electricity bill.

As a summary:

When the Timer Turns ON → Relay Turns ON → NO terminals are ON, and NC terminals are OFF → 24V is routed through the twin timer → Twin timer turns ON.
When the Timer Turns OFF → Relay Turns OFF → NO terminals are OFF, and NC terminals are ON → 24V is routed to the contactor → Twin timer turns OFF.

Controlling the Circuit via 240V AC

The wiring circuit and its purpose are the same as above, except the control circuit is connected to a 240V supply instead of 120V AC. To do this, use a 10-15 amp fuse to protect the timer and relay circuit from the 40-60A contactor circuit.

Utilize the terminals on the contactor for smaller wires.
Avoid using wires with different gauges under a screw plate on the contactor.
To reduce the risk of sparks, use solid wires instead of stranded wires.
Install an inline fuse in the control circuit to protect it from high amperage.

Click image to enlarge

Controlling the Circuit Using DH48S-S Twin Timer

You can potentially reduce the runtime of the AC compressor using the twin timer DH48S-S without the need for an additional LY2 relay.

Since the twin timer has a 24VAC coil, it can be directly connected to the 24V thermostat wires.

Simply wire the entire circuit as shown in the modified circuit diagram below. Now, configure the example circuit with timer settings as follows:

For the ‘Disallowed off time,’ set Time-1 (T1) for 10 minutes.
For the ‘Allowed but limited to X minutes,’ set Time-2 (T2) for 20 minutes.

Click image to enlarge

How Does the Circuit Work?

When the cooling process is initiated by the 24V thermostat, it activates both the timer and the relay timer, allowing the AC to run for 20 minutes.
If the thermostat doesn’t initiate the cooling process before 20 minutes, the twin timer will turn off. When the process is initiated again, it starts in T2 (Allowed but limited) and allows the circuit to run for 20 minutes. That’s awesome!

You can also modify the circuit by adding an additional timer that can be set up to bypass the twin timer during peak hours, for example, from 4 to 10 PM.

The above circuit ensures that the air conditioner turns ON during regular prices and turns OFF during peak prices.

The 10-Amp inline fuse is connected to protect the timer circuit from the 40-60 amp contactor circuit. If the fuse blows, the twin timer will remain OFF until the fuse is replaced with a new one.

As a summary:

The 240V din rail timer operates during regular electricity prices.
When the din rail timer is ON, the air conditioner operates normally.
The din rail timer turns off automatically during peak electricity prices.
When the din rail timer is OFF, the circuit is redirected through the twin timer.
The 24V twin timer operates when the din rail timer is OFF.

Operation when the Din Rail Timer is OFF: