This is a Simple Outside Air %% calculator. We are an HVAC company and this simple calculation has been very well used by us over our 20 years in the HVAC business. We hope you too, will find that it's a helpful app to have around.

**NOTE***
This equation works best on cold days. If the unit has a heat wheel it should be shut down for this equation to work.

The primary design intent behind most economizer systems is to provide free cooling any time the outdoor temperature is below the required system supply temperature. The economizer cycle will also reduce the mechanical cooling load when the outdoor temperature is higher than the required supply temperature but the outdoor air enthalpy (or total heat content) is less than the enthalpy of the return air. They key is to minimize energy – a task that relies on accurate control system and component operation.

The outdoor air damper modulates from minimum position, when the full cooling load can be met by the minimum outside air volume, to the 100%% outdoor air position as the outdoor air temperature approaches the required supply air temperature. When outdoor air temperature (or enthalpy) is greater than the return air (or enthalpy), the outdoor air damper should revert back to the minimum setting for ventilation.

Check out our up-coming apps for HVAC service on our website: www.tractree.com

此版本中的新功能：

Version 8.0: Adjusted the %'s out to 4 decimal places if needed.