Economizers For Your Roof Top Unit

By Glenn Caunt, Account Executive

Economizers are a great way to save energy by introducing the cool outside air into a building to help cool the space.  Usually you can use an economizer on a packaged rooftop unit ranging from 3 to 25 tons.  You can add an economizer to a rooftop unit when the unit is being built in the factory, or a technician can add the economizer in the field.  A simple economizer will use two sensors to measure the outside temperature of the air being supplied to the space. 

One sensor is called the outdoor air sensor, and the other sensor is called a mixed air sensor.  Both sensors are wired to the controller.  The other components to make the economizer work are the dampers, actuators, and the thermostat.  The actuator will open and close the dampers when the thermostat calls for cooling.

Now that you know the parts needed to make an economizer work, let’s put it all together.  When the thermostat calls for cooling, the sensors will read the outside temperature to determine if the outside air is cool enough to cool the space inside the building.  If the outside air is cooler than the preset temperature, the economizer will tell the actuator to open the dampers, to bring in cool air from outside and mix with the return air.

The thermostat usually has two stages of cooling.  If the supply air still isn’t cool enough, the thermostat will call for the second stage of cooling, starting the first stage of mechanical cooling to be introduced. The mechanical cool air can be mixed with the outside cool air. 

If the building has high occupancy, and the desired temperature still isn’t satisfied at the thermostat, some newer digital economizers can work with two stage compressors and call for the second stage of mechanical cooling after a certain amount of time.

Remember, all rooftop units don’t have economizers installed; This is an add on feature. 

Tristate Filter is an official distributor of Siemens with the economizers in stock. Save on your energy bills by using an economizer.

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