Supply Air Temperature Cooling

Professionals call this temperature difference the evaporator delta t.

Supply air temperature cooling.

Why use cold air distribution. The cold air systems distribute air at a temperature much lower than 55 f. Mixing systems generally supply air such that the supply air mixes with the room air so that the mixed air is at the room design temperature and humidity. The supply air temperature can be always maintained at its design setpoint 55 f by modulating the outside airflow using the outside air and return air dampers.

For generations large commercial air conditioning systems have been designed around a constant supply air temperature setpoint of 55 degrees. Since the lowest supply air temperature is already achieved without any mechanical cooling supply air temperature optimization is not necessary in this outside air condition. First let s start with 55 degrees. All the stages of cooling have been on for 10 or more minutes.

For example if the air supply system is designed for a constant air supply temperature of 55 f the valve controlling the supply of hot water to the heating coil will close as the supply air temperature approaches 55 and will open wider if the supply air temperature begins to drop below 55 f. So even though there s no single ideal temperature you do want a 16 22 f difference from the supply air and return air. When the outdoor dry bulb temperature odb is at or below 15 6c the setpoint is 18c. The unit controller compares the supply air temperature to the supply air temp alarm for cooling and initiates the alarm based on the following criteria.

In cooling mode the cool supply air typically around 55 f 13 c saturated at design conditions exits an outlet at high velocity. In between the setpoint is varied linearly. Your cooling schedule that sets cooling setpoint temperature changes values between 0 and 24 on weekdays and the summer design day which is the design day used for cooling sizing. For a given air conditioning load as the supply air temperature is reduced the supply air volume is reduced proportionally.

2 outdoor air temperature reset reset the cooling supply air temperature based on the following default rules. The temperature your ac puts out is relative to the temperature you set on your thermostat. The coldest practical air temperature is about 38 f with most cold air designs using 42 48 f.