Hot Water Heat

Select a hot water coil sufficient to meet the design heat loss.

Example:

Conditions:

VCWE, Hot Water Unit Heat, Size 17 (See Air Valve Selection)

Heating Airflow, Cfm = 850, 1.0 gpm

Winter Room Design Temperature, T=68F

Design heat loss, Q = 25 MBh

Select hot water coil from the coil performance table in the Performance Data section of the catalog.

Selection:

A Standard Capacity coil is sufficient to meet design conditions.

29.8 MBh

0.8 Ft. WPD

Air pressure drop (APD) of the hot water coil is included in the chart for VCWE with hot water unit heat. Chart P-3 shows a required static of 0.35 inches wg.

Acoustics

The acoustical data is found in the Performance Data section of the catalog. Locate the table for the VAV terminal unit of interest. Sound power data and an equivalent NC level for an ARI 885-90 transfer function is listed.

Example:

Conditions:

Cooling Only VCCE Terminal Unit, Size 17 Air Valve (See Air Valve Selection)

Cooling Airflow Cfm = 1700

Maximum Inlet Static Pressure = 1.5 in wg.

Downstream Static Pressure Requirement = 0.30 in. wg.

Maximum NC Criteria = NC 35

Maximum Inlet Static Pressure is the maximum static at the inlet to the box. Downstream Static Pressure requirement is the static loss downstream of the VAV box, which includes everything from right after the discharge of the box to the room.

The catalog assumes 0.5 inches of downstream static pressure for all but the minimum inlet static pressure valves. Since we have a downstream static pressure loss of 0.30 inches, the static across the box will be more than the catalog’s assumption using 0.5 inches downstream. Look into the catalog’s acoustic table at 1.5 + (0.5-0.3) or 1.7 inches.

Interpolation gives sound power data of:

To determine NC level, use either the catalog’s ARI 885-90 transfer function for the conditions shown in the acoustics table, or a transfer function of your own.

Using the catalog’s transfer function:

Radiated Path NC = 26

Discharge Path NC = 19

The maximum NC level is NC 26 which is less than the maximum NC for this example of NC 35. If the maximum NC level was exceeded, it would have been necessary to reselect the next larger air valve size. Computer selection of VAV terminal units greatly simplifies this task.