Assessments - 2, GPA: 5
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SF Frame Datum Dia. (in.) Bore (in.) Model Datum Dia. (in.) Bore (in.) Model BP090 1-1/2 1725 80% 1.15 56 3.4 - 4.4 7/8 1VM50 7.5 1 AK79 A55 2 1725 80% 1.15 56 3.4 - 4.4 7/8 1VM50 6.5 1 AK69 A53 BP120 2 1725 80% 1.15 56 3.4 - 4.4 7/8 1VM50 7 1 AK74 A54 4 1725 80% 1.15 184T 4.3-5.3 1-1/8 1VP56 6.2 1 BK72 BX56 Unitary Products Group 66307-YIM-B-0606 AIR BALANCE Start the supply air blower motor. Adjust the resistances in both the supply and the return air duct systems to balance the air distribution throughout the conditioned space. The job specifications may require that this balancing be done by someone other than the equipment installer. CHECKING AIR QUANTITY METHOD ONE 1. Remove the dot plugs from the duct panel (for location of the dot plugs see Figure 10). 2. Insert eight-inches of 1/4 inch metal tubing into the airflow on both sides of the indoor coil. NOTE: The tubes must be inserted and held in a position perpendicular to the air flow so that velocity pressure will not affect the static pressure readings. 3. Use an Inclined Manometer or Magnehelic to determine the pressure drop across a dry evaporator coil. Since the moisture on an evaporator coil can vary greatly, measuring the pressure drop across a wet coil under field conditions could be inaccurate. To assure a dry coil, the compressors should be de-activated while the test is being run. NOTE: De-energize the compressors before taking any test measurements to assure a dry evaporator coil. 4. The CFM through the unit can be determined from the pressure drop indicated by the manometer by referring to Figure 23. In order to obtain an accurate measurement, be certain that the air filters are clean. 5. To adjust Measured CFM to Required CFM, see ’SUPPLY AIR DRIVE ADJUSTMENT’. 6. After readings have been obtained, remove the tubes and replace the dot plugs. Failure to properly adjust the total system air quantity can result in extensive blower damage. METHOD TWO 1. Drill two 5/16 inch holes, one in the return air duct as close to the inlet of the unit as possible, and another in the supply air duct as close to the outlet of the unit as possible. 2. Using the holes drilled in step one, insert eight inches of 1/4 inch metal tubing into the airflow of both return and supply air ducts of the unit. NOTE: The tubes must be inserted and held in position perpendicular to the airflow so that velocity pressure will not affect the static pressure readings. 3. Use an Inclined Manometer or Magnehelic to determine the pressure drop across the unit. This is the External Static Pressure (ESP). In order to obtain an accurate measurement, be certain that the air filters are clean. 4. Determine the number of turns the variable motor sheave is open. 5. Select the correct blower performance table for the unit from Tables 13 - 28. Tables are presented for horizontal and downflow configurations. 6. Determine the unit Measured CFM from the Blower Performance Table by utilizing the measured External Static Pressure and the number of turns the variable motor sheave is open. 7. To adjust Measured CFM to Required CFM, see ’SUPPLY AIR DRIVE ADJUSTMENT’. 8. After readings have been obtained, remove the tubes and seal holes. NOTE: With the addition of field installed accessories repeat this procedure. Failure to properly adjust the total system air quantity can result in extensive blower damage. Unitary Products Group 66307-YIM-B-0606 Predator 50 Hz Heat Pump Units Indoor Coil Pressure Drop vs. Airflow 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 2000 2500 3000 3500 4000 Airflow (CFM) FIGURE 23 -DRY COIL DELTA P SUPPLY AIR DRIVE ADJUSTMENT Before making any blower speed changes review the installation for any installation errors, leaks or undesirable systems effects that can result in loss of airflow. Even small changes in blower speed can result in substantial changes in static pressure and BHP. BHP and AMP draw of the blower motor will increase by the cube of the blower speed. Static pressure will increase by the square of the blower speed. Only qualified personnel should make blower speed changes, strictly adhering to the fan laws. At unit start-up, the measured CFM may be higher or lower than the required CFM. To achieve the required CFM, the speed of the drive may have adjusted by changing the datum diameter (DD) of the variable pitch motor sheave as described below: Required CFM ()• Existing DD = New DD Measured CFM Use the following tables and the DD calculated per the above equation to adjust the motor variable pitch sheave. 7.5T 50 Hz HP 10T 50 Hz HP 4500 5000 5500 EXAMPLE A 12.5 ton unit was selected to deliver 4,000 CFM with a 3 HP motor, but the unit is delivering 3,800 CFM. The variable pitch motor sheave is set at 2 turns open. Use the equation to determine the required DD for the new motor sheave, 4,000 CFM ()• 4.0 In. = 4.21 In. 3,800 CFM Use Table 32 to locate the DD nearest to 4.21 in. Close the sheave to 1 turn open. New BHP 3 = (Speed increase) • BHP at 3,800 CFM 3 = (Speed inc...
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