Selecting A Unit Heater For Use With Hot Water; Hot Water Correction Factors - Hach sc200 User Manual

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SELECTING A UNIT HEATER FOR USE WITH HOT WATER

DESIGN CONDITIONS
— Heating load
— Entering air temperature (EAT)
— Entering water temperature (EWT)* =
— Water temperature drop (WTD)
— Mounting height
— Spread required
— Standard horizontal projection unit required (model H).
SELECTING PROCEDURE
1 ) Calculate equivalent capacity at conditions of Table 8.
Equivalent capacity
From Table 8, choose the unit heater with this output, at
the condition 200°F EWT and 20°F WTD.
We select Cat. No. H-136 unit heater.
2) Calculate unit capacity at actual conditions.
Actual capacity = MBH (Table 8) x Factor (Table 10)
= 135.5 x 1.06 = 143.63 MBH
TABLE 10

HOT WATER CORRECTION FACTORS

ENTERING
AIR
TEMP. °F 160 170 180 190 200 210 220 230 240 250 260 270 280 290
30 0.96 1.04 1.11 1.18 1.26 1.33 1.41 1.48 1.55 1.63 1.70 1.78 1.85 1.93
40 0.88 0.95 1.02 1.10 1.17 1.25 1.32 1.39 1.47 1.54 1.61 1.69 1.76 1.83
50 0.80 0.87 0.94 1.01 1.09 1.16 1.23 1.30 1.37 1.45 1.52 1.59 1.66 1.74
60 0.73 0.79 0.86 0.93 1.00 1.07 1.14 1.22 1.29 1.36 1.43 1.50 1.57 1.64
70 0.65 0.70 0.77 0.85 0.92 0.99 1.06 1.13 1.20 1.27 1.34 1.41 1.48 1.55
80 0.57 0.63 0.70 0.77 0.84 0.91 0.98 1.05 1.12 1.19 1.26 1.33 1.40 1.47
90 0.48 0.55 0.62 0.69 0.76 0.83 0.90 0.97 1.04 1.11 1.17 1.24 1.31 1.38
100 0.42 0.48 0.55 0.62 0.68 0.75 0.82 0.89 0.96 1.03 1.10 1.16 1.23 1.30
For MBH at EWT other than those indicated in the tables, use 200°F MBH and multiply by factor in table 10. MBH obtained will be at USGPM of
*
200°F MBH used.
UNIT HEATERS
= 138 MBH
= 70°F
220°F
= 20°F
= 12 feet
= 30 feet
Capacity required
= —————————
Factor (Table 10)
138
= ——— = 130 MBH
1.06
E N T E R I N G W A T E R T E M P E R A T U R E — ° F
3) Calculate coil water flow (USGPM)
Actual BTUH
Water flow = ——————— = ———— = 14.36 USGPM
500 x WTD
4) Calculate coil water pressure drop (WPD).
WPD = WPD (Table 8) x —————————
( 14.36
= 1.31 x ———
13.55
5) Calculate final air temperature (FAT).
Actual BTUH
FAT = EAT + ———————
CFM x 1.08
143,630
= 70 + —————— = 123.84°F
2470 x 1.08
6) Determine mounting height and throw at actual conditions.
At Table 2 conditions (220°F EWT and 70°F EAT)
Mounting height = 14' x 1.15 (Table 6) = 16.1 feet
Throw = 44' x 1.15 = 50.6 feet
We can use this unit heater.
NOTE: See «GENERAL SELECTION» for application details
(page 3), and Table 7 for noise level.
300 310 320 330 340 350 360 370 380 390 400
2.00 2.07 2.14 2.22 2.30 2.37 2.44 2.52 2.59 2.66 2.74
1.91 1.98 2.05 2.12 2.19 2.27 2.35 2.42 2.49 2.56 2.63
1.81 1.88 1.95 2.02 2.10 2.17 2.24 2.31 2.39 2.46 2.53
1.72 1.79 1.86 1.93 2.00 2.07 2.14 2.23 2.29 2.36 2.43
1.62 1.69 1.76 1.84 1.91 1.98 2.05 2.12 2.19 2.26 2.33
1.54 1.60 1.67 1.74 1.82 1.88 1.95 2.02 2.09 2.16 2.23
1.45 1.52 1.59 1.66 1.72 1.80 1.86 1.93 2.00 2.07 2.14
1.37 1.43 1.50 1.57 1.64 1.71 1.78 1.84 1.91 1.98 2.05
143,630
500 x 20
( USGPM (Actual) ) 2
USGPM (Table 8)
) 2
= 1.47 feet of water