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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
Btu/hr
F .T . = E.A.T . +
CFM x 1.085
96000
= 70 +
= 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.
Table SP-11 – Unit Heater Hot Water Conversion Factors (Applies To Tables PD-1 - PD-5)
Ent.
Air
Temp.
160
170
180
190
200
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.
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
20% solution
50% solution
20
Selection
Procedure
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°
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
210
220
230
240
250
260
Table SP-12 – Trane Unit Heater Nomenclature (Applies To Tables PD-1 - PD-5)
Abbreviations
MBH
GPM
FT
PD-S.W.T.
PD-H.W.T
2. GPM required @180F ,
20°D (no correction to
pump curve)
3. Pump head required
@180F w/increase in
GPM
Propylene
4. Specific gravity
Glycol
(water = 1.0)
.97*
5. Pounds/Gallons@60F
.90*
(water = 8.3453
Pounds/Gallons)
.546
Entering Water Temperature
270
280
290
300
310
320
Definitions
1000 BTU Per Hour
Gallons Per Minute
Final Temperature °F
Feet Of Water Pressure Drop - Standard Wall Tubes.
Feet Of Water Pressure Drop - Heavy Wall Tubes
Propylene
Glycol
1.10%
1.23%*
1.045-1.055*
8.77
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
Btu/hr
F .T . = E.A.T . +
CFM x 1.085
= 100° + 123,000
5210 x 1.085
330
340
350
360
370
380
7 . pH@50% by volume.
8. Freezing Point
55% by volume —
**Compared to water
= 121.8°
390
400
Propylene
Glycol
9.5
50%
-28F
40%
-13F
30%
+28F
20%
+17F
UH-PRC001-EN
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