Selection Example
Air Handler Selection Conditions:
“I want a ceiling mounted air handler that gives 35 tons of cooling and 35 tons of heating. I have 44°F. water for
cooling and I have 200°F. water for heating. My entering air temperatures on the coil are standard, that is 80°F. dry bulb and 67°F. wet bulb (50% relative humidity) for cooling. For heating, the entering air temperature is 60°F. I will supply duct work,
you should select the motor to handle a half inch of external static pressure. Select the smallest air handler possible and tell me what kind of CFM, flow rates, fluid pressure drops, and sensible cooling performance your selection will give me. I want a filter too.”
Selection Procedure:
1. Which air handler for cooling performance? |
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Look at index of air handler performance |
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on page 11. Find that tables 6 through 9 |
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give chilled water performance. | You need 35 tons or 35 x 12 = | 420 | MBH | ||||
Compare 1/2" and 5/8" and 4 row and 6 row performance: |
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Select size 20 air handler with six row 1/2" tube coil with capacity of: | 430 | MBH | |||||
Note that 4 row 5/8" tube coil is not enough at: |
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| 374 | MBH | |||
2. Which air handler for heating performance? |
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Look at index of air handler performance on |
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page 11. Find that tables 12 & 13 are for hot |
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water performance with 60°F. air. | You need 35 tons or 35 x 12 = | 420 | MBH | ||||
Compare 1/2" and 5/8" and 1 row and 2 row performance: |
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Select one row 5/8" tube coil for size 20 air handler with capacity of: | 502 | MBH | |||||
Note that 1 row 1/2" tube coil is much too small | at capacity of |
| 395 | MBH | |||
3. Comparing steps 1 & 2, select: |
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Size 20 air handler at 10025 CFM with |
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6 row, 1/2" tube chilled water coil with |
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1 row, 5/8" tube hot water coil. |
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4. Look at page 38, “Characteristics of standard coil sections “ and confirm that: |
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| 1 row depth coil casing: | 3.25 | inches |
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| + 6 row depth coil casing: | +9.75 | inches |
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| Total |
| 13.00 | inches fits into HCS type cabinet |
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5. Look at page 40 & 41, “Air pressure drop tables” and calculate total pressure drop:
0.17 | inch | Pressure drop through 1 row coil, see dry 5/8" tube at: 10025 Divided By 19.25 = 521 FPM | |||
0.79 | inch | Pressure drop through 6 row coil see wet 1/2" tube at: 500 FPM | |||
0.22 | inch | Pressure drop for flat filter section, pleated 2" filter at: 10025 Divided By 24.4 = 411 FPM | |||
+ 0.50 | inch | External static pressure |
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| 1.68 | inch | Total static pressure |
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6. Look at page 27, “Fan performance”: |
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| Select a 5 HP motor for the condition of 10000 CFM and less than 1.75 inches of water. | |||
7. Air handler description and performance: |
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| Description: |
| Performance: |
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| HCS model size 20 |
| 10025 CFM at 1.68" total static and |
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| with 6 row 10FPI, type A, | cooling coil | 0.5" external static pressure |
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| with 1 row 10 FPI, type 5, | heating coil | 430 MBH total cooling capacity and |
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| with open 5 HP motor at 230/3/60 volts | 292 MBH sensible cooling capacity with | |
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| (See page 10) |
| 80°F. DB/ 67°F. WB entering air |
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| with 120% adjustable drive | and 44 °F entering water at | |
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| with motor starter |
| 85.8 GPM and 13.5 feet of |
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| with flat filter section |
| fluid pressure drop |
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| with 35% efficient 2" filters | 502 MBH of heating capacity with | |
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| with (6) rubber in shear vibration isolators | 60°F. entering air and 200°F. | |
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| for ceiling mount (see page 38) | entering water at 64.5 gpm | |
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| and 12.3 feet of fluid pressure drop |
8.To estimate performance of coils at other than 10 FPI, or different row depths, or different air speeds or temperature conditions see tables on page 20 - 23, or call your representative. With your representative, you can have specific computer selected coils for your job conditions.
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