| AFX SERIES AEROFLO HEATER HOW TO SELECT AN AFX AEROFLO
Figure 2
| Step 1 - |
Calculate the total space heat
loss in MBH for the building to be heated including transmission, ventilation and
infiltration losses less any appreciable internal heat gains. |
| Step 2 - |
Determine the net building volume
(NBV) to be heated, exclusive of stored materials, office cubicles, large machinery, etc.
|
| Step 3 - |
Select a desired air volume
turnover per hour (VTOH). Experience indicates that 3 to 4 VTOH results in optimum
operation of the AFX Aeroflo. For reference, Figure 2 presents an empirically developed
relationship of floor to ceiling temperature difference as a function of volume turnover
per hour for a typical structure. It should be noted that very high or low ceilings, or
high localized internal heat gains could cause variations in the distribution shown.
|
| Step 4 - |
Calculate required air flow in
SCFM using the net building volume (NBV) from Step 2 and volume turnover per hour (VTOH)
of Step 3 in the following formula: |
|
|
| Step 5 - |
Select the AFX Aeroflo. |
|
a. |
Use Selection Table to pick AFX model whose
Maximum SCFM and Burner Output (MBH) meets both the SCFM requirement of Step 4 and space
heat loss of Step 1 |
|
b. |
Discharge air temperature from the AFX Aeroflo
heater, that is, the total of design space room temperature plus the temperature rise, is
recommended to be approximately 100ºF, not exceeding 120ºF |
Note : Your local Hastings
sales representative will be pleased to offer assistance in estimating heat losses, in
proper equipment location, or other AFX Aeroflo application information. Your
representative can also furnish information on the AFC Series Aeroflo heaters equipped
with steam, hot water or electric heating coils.
| EXAMPLE OF AFX SELECTION PROBLEM
Heat warehouse
Size of warehouse: 200' wide x 360' long x 25' high
Warehouse stock and office cubicles occupy 40% of total
building volume
Design space temperature: 65°F
Fuel: No. 2 Oil (140,000 Btu/Gal.)
Desired burner control: Hi/Lo/Off
SOLUTION
| Step 1 - |
Calculate total space heat loss |
|
Total heat loss was calculated to be
2,074,000 |
|
Btuh or 2,074 MBH
|
| Step 2 - |
Net building volume |
|
NBV = 200 x 360 x 25 x (1 00% - 40%) |
|
NBV = 1,080,000 Cu. Ft.
|
| Step 3 - |
Volume turnover per hour |
|
Design for 3 VTOH
|
| Step 4 - |
Total air flow required
|
|
|
|
| SCFM = |
1,080,000 x 3 |
= 54,000 |
|
60
|
|
|
| Step 5 - |
Select AFX Aeroflo |
|
From Selection Table - |
|
Note : |
a. Proceed under the "Maximum SCFM"
column to determine which model to select for the required 54,000 SCFM. This air quantity
falls in the AFX 260 range. Fans with 5 HP motors have a maximum of 52,000 SCFM so the
selection is an AFX-260 with (2) 7-1/2 HP motors capable of a maximum of 58,000 SCFM. (The
belts and drives will be set at the factory for the desired 54,000 SCFM.) The next step is to check burner capacity in the SCFM and motor HP
range selected .The total heat loss was calculated to be 2,074 MBH . The smallest burner
in this category which satisfies the heating requirement is 1,500 MBH.The final selection
is thus completed :(1) Model AFX-260-L02 with (2) 7-1/2 HP motors,a 2,250 MBH output
light oil fired burner and Hi/Lo/Off burner control.
Check discharge air temperature.
| Temp. Rise = |
MBH Output x 1,000 |
or use Table |
|
SCFM x
1.08 |
|
| Temp. Rise = |
2,250 x 1,000 |
= 38.6°F |
|
54,000
x 1.08 |
|
| Discharge Air Temp. |
= 65° (design) + 32.2° |
|
= 103.6° F |
Cost considerations may warrant an alternate selection of a Model
AFX-260 with (2) 5 HP motors and an air delivery of 52,000 SCFM, thus yielding 3.00 VTOH.
As shown in Figure 2, there is only a small increase in the floor to ceiling temperature
difference for a typical building when reducing the volume turnover per hour from 3 to
2.89. |
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