Supply Air Temperature Cooling

In cooling mode the cool supply air typically around 55 f 13 c saturated at design conditions exits an outlet at high velocity.

Supply air temperature cooling.

2 outdoor air temperature reset reset the cooling supply air temperature based on the following default rules. In between the setpoint is varied linearly. All the stages of cooling have been on for 10 or more minutes. 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.

For generations large commercial air conditioning systems have been designed around a constant supply air temperature setpoint of 55 degrees. 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. Why use cold air distribution. When the outdoor dry bulb temperature odb is at or below 15 6c the setpoint is 18c.

The well known fact that 55 degrees is the preferred supply air temperature comes to us from the commercial world. The temperature your ac puts out is relative to the temperature you set on your thermostat. First let s start with 55 degrees. 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.

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. Professionals call this temperature difference the evaporator delta t. When the odb is at or above 26 7c the setpoint is the off coil air temperature set point. For a given air conditioning load as the supply air temperature is reduced the supply air volume is reduced proportionally.

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. The cold air systems distribute air at a temperature much lower than 55 f. The coldest practical air temperature is about 38 f with most cold air designs using 42 48 f.