Burnham 8HE Series Application Instructions page 28

3
Water Piping
(continued)
3.21.1 Water heater size may be determined in the
following manner:
1. From Table 3-14, find the appropriate factor
for each fixture in the building and add them
together to find the total fixture units.
2. From Figure 3-15, convert the fixture units to hot
water capacity in gallons per minute based on
40-140°F temperature rise.
3. Select water heater based on gallons per
minute from 2) above.
3.21.2 The addition of water heating may not
necessarily add to the size of the boilers. Since
the maximum space heating load and the
maximum water heating load rarely occur at the
same time, only a portion of the water heating
load is added to the space heating load to size
the boilers as follows:
1. Calculate the water heating load in Btuh:
___gpm x 8.33 Lb/Gal x 60 Min/Hr x 100
∆T = ___________Btuh
2. Calculate ratio = Water Heating Load Space
Heating Load
3. From Figure 3-16, using the ratio found in 2),
find factor for sizing the "boiler added capacity".
4. Calculate "boiler added capacity" by
multiplying factor from 3) by water heating load.
5. Total the space heating load and the "boiler
added capacity".
6. Select boilers from Table 1-2 using the total net
input.
7. Divide water heating load by gross output of
one boiler to determine the number of boilers to
be used in the water heating circuit.
Example - An office building has 10 basins and 1
slop sink and a space heating load of 1,000,000
Btuh.
Size the water heater and boiler.
Solution:
1. 10 basins x . units = 7.5 Fixture Units
1 slop sink x 1. units = 1.5 Fixture Units
Total = 9 Fixture Units
2. In Figure 3-15, using curve "C" for office
building, find that for 9 Fixture Units 6 gpm is
required.
3. Select water heater at 6 gpm and 40-140°F
temperature rise.
4. Calculate water heating load in Btu.
6 x 8.33 x 60 x 100 = 299,880 Btuh
28
8HE
Multiple Boiler Application Instructions
5. Calculate ratio = Water Heating Space Heating
= 299,880 = .30
1,000,000
6. From Figure 3-16 find that for a ratio of 0.3 is
10%.
7. Determine the total load:
1,000,000 + 10%*1,000,000 = 1,100,000 Btuh
8. Determine number of boilers from Table 1-2
using the Total Net Output column. Select (4)
805HE and (1) 806HE boilers for a total net
output of 1,136,000 Btuh.
9. The water heating load of 299,880 Btuh can be
handled by any two of the boilers.
3.21.3 The domestic water heater sizing procedures
outlined in this section are based on methods
recommended in the ASHRAE Handbook and,
HVAC Applications Volume, "Service Water
Heating" Chapter.
3.22 Oxygen Corrosion
Oxygen contamination of the boiler water will
cause corrosion of the iron and steel boiler
components, which can lead to failure. As such,
any system must be designed to prevent oxygen
absorption in the first place or prevent it from
reaching the boiler. Problems caused by oxygen
contamination of boiler water are not covered by
Burnham's standard warranty.
There are many possible causes of oxygen
contamination such as:
• Addition of excessive make-up water as a result
of system leaks.
• Absorption through open tanks and fittings.
• Oxygen permeable materials in the distribution
system.
In order to insure long product life, oxygen
sources should be eliminated. This can be
accomplished by taking the following measures:
• Repairing system leaks to eliminate the need for
addition of make-up water.
• Eliminating open tanks from the system.
• Eliminating and/or repairing fittings which allow
oxygen absorption.
• Use of non-permeable materials in the
distribution system.
• Isolating the boiler from the system water by
installing a heat exchanger.
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