York R-407C Acoustical Considerations, SELECTION PROCEDURE Given, Select Unit, Total, 1.46 IWG

FORM 100.50-EG1

The curb should be located according to the location recommendations above, and properly sealed to pre- vent moisture and air leakage into and out of the duct system. Flexible collars should be used when connect- ing the duct work to prevent unit noise transmission and vibration into the building.

Duct work should be supported independently of the unit.

ACOUSTICAL CONSIDERATIONS

The eco2 unit is designed for lower sound levels than competitive units by using flexible fan connections, fan spring isolators, double-wall construction, and lower speed and horsepower fans. For VAV applications, VFDs are used instead of inlet guide vanes. Additional sound attenuation can be obtained using compressor sound blankets and field-supplied sound attenuators when necessary.

Even with these equipment design features, the acous- tical characteristics of the entire installation must never be overlooked. Additional steps for the acoustical char- acteristics of a rooftop installation should be addressed during the design phase of a project to avoid costly al- terations after the installation of the equipment. During the design phase of a project, the designing engineer should consider, at a minimum, the impact of the equip- ment location, rooftop installation, building structure, and duct work.

SELECTION PROCEDURE

Given:

Required total cooling capacity of 600 mbh and sen- sible cooling capacity of 450 mbh with evaporator en- tering air conditions of 83°F dry bulb and 67°F wet bulb. Design ambient temperature is 95°F dry bulb. Supply air requirements are 17500 cfm of air at 2.25 IWG ex- ternal static pressure. Power supply is 460V/3ph/60Hz

and the unit requires a modulating economizer, 2-inch pleated filters, bottom supply and bottom return air open- ings and is constant volume.

Select Unit:

1.Determine the internal static pressure drop of the cabinet by referencing Table 8.

Wet evaporator coil	0.54
Bottom supply opening	0.14
Bottom return opening	0.13
2-inch pleated filters	0.10
Economizer openings	0.24
Modulating economizer dampers	0.31
Total	1.46 IWG

2.Determine the total static pressure by adding the internal to the external static pressure.

TSP = 1.46 IWG + 2.25 IWG

=3.71 IWG total static pressure

3.Determine the BHP of the supply fan from Table 6 using the supply air flow and total static pressure. From the table, we interpolate to get 15.1 BHP. As- suming a drive loss of 3% and a motor efficiency of 90%, we can calculate the heat rejection of the sup- ply fan motor as:

(2545 x 15.1)/(0.90 x (1-0.03)) = 44.0 mbh Required Cooling Capacities:

Total = 600 + 44.0 = 644 mbh Sensible = 450 + 44.0 = 494 mbh

4.Required total and sensible capacities are 644 mbh and 494 mbh, respectively. Using the Cooling Per- formance Data starting with Tables 2, locate the table with the correct ambient air temperature. Next, trace the 83°F entering air dry bulb temperature to match the 17,500 cfm and 67°F entering wet bulb temperature condition. The resulting conditions are, from the table, 645 mbh total cooling capacity and 497 mbh sensible cooling capacity. Thus, a 50-ton unit is selected.

YORK INTERNATIONAL 11