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UH-PRC001-EN20
Selection
Procedure
Step 4.
Determine the pressure drop at 6.53
GPM. Pressure drops are cataloged for
both standard wall (SWT) and heavy
wall. (HWT) tube coils. In this example, if
a SWT coil is selected the pressure drop,
by interpolation is
2.38 feet of water.
Step 5.
Calculate the final air temperature
F.T. = E.A.T. +
Btu/hr
CFM x 1.085
= 70 +
96000
=
70 + 53.2
= 123.2°
1661 x 1.085
Note:
If a constant water temperature drop is desired, apply the conversion factor to the WTD and to the desired MBH and enter 200° EWT column at these conditions. Select the unit which will
provide the equivalent MBH at the adjusted WTD. The GPM can then be interpolated from the table at the adjusted WTD. To determine the actual capacity at operating conditions proceed as
outlined in example #2.
If a constant GPM is desired, enter the 200° EWT column at the given or calculated GPM. Select the unit which will provide the equivalent MBH at this GPM. To determine the actual capacity
at operating conditions in this case proceed as outlined in example #1.
Example 2
Determine the capacity of a Model 336P
unit heater operating at 180° (EWT), 100°
(EAT) and 15° (WTD).
Step 1.
Find conversion factor (in Table SP-11)
= 0.546
Step 2.
Adjust the water temperature drop
Adj. WTD =
15
= 27.5°
.546
Step 3.
Multiply the MBH (interpolated) at
27.5° WTD, 200° EWT and 60° EAT by the
factor to obtain the MBH at desired
conditions.
0.546 x 224.9 = 123.0 MBH
Step 4.
WTD = 27.5 x 0.546 = 15°
Step 5.
GPM =
Btu/hr
=
123,000
= 16.9
485xWTD (485)(15)
Step 6.
Pressure drop interpolated at 27.5° WTD
for a SWT coil is 1.82 feet of water.
Step 7.
Calculate final temperature
F.T. = E.A.T. +
Btu/hr
CFM x 1.085
= 100° +
123,000
= 121.8°
5210 x 1.085
Table SP-11 – Unit Heater Hot Water Conversion Factors (Applies To Tables PD-1 - PD-5)
Ent.
Air Entering Water Temperature
Temp. 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
30 .962 1.036 1.110 1.182 1.259 1.331 1.408 1.482 1.554 1.627 1.702 1.780 1.850 1.925 2.000 2.070 2.142 2.220 2.295 2.370 2.440 2.515 2.590 2.660 2.735
40 .880 .954 1.024 1.100 1.171 1.249 1.318 1.391 1.468 1.539 1.612 1.686 1.759 1.831 1.909 1.976 2.048 2.120 2.193 2.268 2.348 2.417 2.488 2.560 2.632
50 .795 .869 .940 1.011 1.085 1.158 1.230 1.301 1.374 1.448 1.520 1.590 1.664 1.735 1.809 1.882 1.953 2.024 2.095 2.168 2.242 2.312 2.388 2.459 2.530
60 .715 .785 .859 .929 1.000 1.071 1.141 1.215 1.285 1.359 1.429 1.500 1.571 1.642 1.715 1.785 1.858 1.930 2.000 2.070 2.140 2.215 2.285 2.360 2.430
70 .634 .704 .774 .845 .917 .988 1.058 1.129 1.200 1.270 1.340 1.410 1.482 1.552 1.622 1.694 1.764 1.838 1.907 1.976 2.045 2.116 2.188 2.258 2.332
80 .568 .628 .698 .768 .838 .908 .978 1.048 1.118 1.188 1.258 1.328 1.398 1.468 1.538 1.604 1.674 1.742 1.815 1.884 1.952 2.020 2.091 2.162 2.230
90 .484 .552 .622 .690 .760 .829 .898 .967 1.036 1.106 1.173 1.244 1.311 1.380 1.450 1.515 1.585 1.655 1.723 1.795 1.862 1.930 1.998 2.067 2.137
100 .410 .478 .546 .615 .684 .753 .820 .889 .957 1.025 1.095 1.161 1.230 1.300 1.368 1.433 1.499 1.569 1.638 1.705 1.776 1.843 1.910 1.977 2.046
Apply to the 200 F entering water capacities only.
Table SP-12 – Trane Unit Heater Nomenclature (Applies To Tables PD-1 - PD-5)
Abbreviations Definitions
MBH 1000 BTU Per Hour
GPM Gallons Per Minute
FT Final Temperature °F
PD-S.W.T. Feet Of Water Pressure Drop - Standard Wall Tubes.
PD-H.W.T Feet Of Water Pressure Drop - Heavy Wall Tubes
Correction Factors for Propylene
Glycol/Water
When sizing equipment for systems that
will utilize a propylene glycol solution,
consider the following factors:
1. Heat transfer @180F with no increase
in flow rate
Propylene
Glycol
20% solution .97*
50% solution .90*
Propylene
2. GPM required @180F, Glycol
20°D (no correction to
pump curve) 1.10%
3. Pump head required
@180F w/increase in
GPM 1.23%*
4. Specific gravity
(water = 1.0) 1.045-1.055*
5. Pounds/Gallons@60F
(water = 8.3453
Pounds/Gallons) 8.77
Propylene
Glycol
7. pH@50% by volume. 9.5
8. Freezing Point 55% by volume —
50% -28F
40% -13F
30% +28F
20% +17F
**Compared to water