Delta T vs. TD Lots get mixed up or interchange these. There's a simple way to remember. When speaking about delta t, we are speaking about the "same" medium. For example, air in and air out, or water in and water out. The temperature change of that particular substance before and after a coil or a boiler for example. Another good one is liquid line temperature before and after a filter drier, the medium is refrigerant and is the same medium before and after the component. Where TD is the temperature difference between two "different" mediums. We usually refer to TD in refrigeration or air conditioning by referring to evaporator TD or condenser TD. Evaporator TD is the difference between return air and the saturated suction temperature (the corresponding temperature of a refrigerants pressure). Example, if the return air is 72⁰F and your evaporator saturated suction temperature, read from your gauges is 40⁰F, your evaporator TD is 32⁰F . Condenser TD is the difference between ambient air around the condenser and saturated condensing temperature of the refrigerant. For example, if the ambient air is 100⁰F and the saturated condensing temperature, read from your gauges is 80⁰F. The condenser TD is 20⁰F. I hope this helps...

Posted by HVAC Know It All at 2021-02-27 12:35:24 UTC