Notice that the heated water and chilled water circuits are completely separated. As such, each should be equipped with make-up water systems, expansion tanks, air/dirt/hydraulic separators and safety devices.
Most air handlers are rated at specific operating conditions for both the incoming chilled water temperature and the incoming air. Those conditions are typically as follows:
• Entering chilled water temperature: 45ºF
• Incoming air conditions
Dry-bulb temperature = 80ºF, wet-bulb temperature = 67ºF
Dry-bulb temperature = 75ºF, wet-bulb temperature = 63ºF
The thermal output ratings for chilled-water air handlers are usually expressed as:
• Total cooling capacity (Btu/hr)
• Sensible cooling capacity (Btu/hr)
Sensible cooling capacity refers to the air handler’s ability to lower the temperature of the air as it passes through the unit. Latent cooling capacity is a measure of the air handler’s ability to remove moisture from the air stream. Total cooling capacity is the sum of sensible cooling capacity and latent cooling capacity. Latent cooling capacity can be obtained by subtracting sensible cooling capacity from total cooling capacity.
Other performance measures for air handlers include:
• Fluid head loss or pressure drop across the coil as a function of the flow rate through the coil.
• Airflow rate produced by the blower as a function of the external static pressure of the ducting system. This is typically stated in cubic feet per minute (CFM), versus the static pressure of the duct system, which is stated in inches of water column (e.g., inch w.g.). If the air handler has a multiple-speed motor, this information is often given for each speed setting.