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NO. SUGGESTED ITEMS FOR INSTALLATION
1 Short pipe nipple and pair of boiler loop tees in piping
between system supply and return. One set per each
group of boilers
2 Boiler pipe loop. See piping sizing data above.
3 Boiler circulator. See pump sizing data above.
4 Thermometer.
5 Theraltimeter.
6 Plug cock to control flow rate.
7 Safety flow switches. For interlock with other systems or
instead of low water cutoff.
8 Relief valve.
9 With one -300, -399 or -420 item 9 is - sensing
element of remote control.
With a group of -300's, -399's or -420's, item 9 is - for
1st. boiler, the sensing element as above. For additional
boilers, install a 2nd. limit control if required by local codes.
With any -520, -610 or 670 boilers, install 2nd. limit control
here if required by local code.
BOILER INLET - OUTLET SIZES
10 HWB-300 - 1-1/4", HWB-399 - 1-1/2", HWB-420-1-1/2",
HWB-520 & HWB-610 - 2". Canadian Models
10 HW-300 - 1-1/4", HW-399 - 1-1/2", HW-420-1-1/2",
HW-520 & HW-670 - 2". U.S. Models
MINIMUM BRANCH SIZES TO BOILERS
11 HWB-300 - 1-1/4" HWB-520, 610 (Single boiler
HWB-399 - 1-1/2" per pump) 2"
HWB-420 - 1-1/2" Canadian Models
11 HW-300 - 1-1/4" HW-520, 670 (Single boiler
HW-399 - 1-1/2" per pump) 2"
HW-420 - 1-1/2" U.S. Models
12 Flow control valve. Required only if flow rate of system
primary is excessive for size of boiler branch tees or if
chilled water main is above boilers.
13 System supply temperature thermometer.
14 Boiler headers for three (3) boilers can be larger than pipe loop,
if desired, to aid in balancing.
The system flow rate is selected to give the desired system
temperature drop - depending on the design criteria.
The boiler generator flow rates, on the other hand, should be
selected to give the temperature rise through the generator that is
both economical and offers the best generator efficiency.
The boiler temperature rise is normally between 10
0
C and 20
0
C
(20
0
F and 40
0
F). The system temperature that will be introduced
to the boiler (inlet temperature) plus the selected boiler temperature
rise selected from PUMP AND PIPE SIZING DATA should not exceed
the high limit control setting of 115
0
C (240
0
F).
There should be a relation of the minimum system load to the size
boiler selected as the first firing or base boiler. This will stabilize
operation during minimum load periods.
B. Commercial Boiler Replacements
Application of
LINEAR-TEMP
®
to a commercial boiler replacement
with an old multiple pump installation is an excellent way to
modernize the system. The A. O. Smith boiler(s) should be
installed on a pipe loop with a separate circulating pump selected
from PUMP AND PIPE SIZING DATA TABLE.
Figure 3 shows a line drawing of how the system headers should
be connected to the pipe loop installed with the replacement
boiler(s). Make-up water connections and accessories are not
shown.
SCHEMATIC OF THE LINEAR-TEMP
®
SYSTEM
FIGURE 3
Supply and return headers of the old system should be connected
to the boiler loop with a pair of tees set close together. The boiler
loop pump and the boiler(s) should be wired to operate only when
any of the system pumps are in operation. The number of zone
pumps that may be in operation at any particular time will take their
required flow rate out from the first tee in the boiler piping. This
water will be circulated through the proper branches from the supply
header to the zones calling for heat. The water will be brought
back to the return header and then into the second tee in the boiler
pipe loop. There will be no conflict between the boiler pump and
the zone pumps when the two tees in the boiler loop are placed
close together.
Normal use of flow control valves is required to prevent cross
circulation of zones as with any multiple pump system. Flow control
is not required on boiler circuit.
Attention should be given to balancing gas inputs and water flow
rates. Large systems with multiple boilers should include main
water temperature control (with or without outdoor reset) to stage
the boilers on and off in relation to the load on the system.
3. WATER SUPPLY LINE
These boilers can be used ONLY in a forced circulation hot water
heating system. Since most forced circulation systems will be of
the closed type, install the water supply line as shown on piping
diagrams, fig. 1 or 2.
Fast filling of large pipe, old radiator installations and pressure
purging of series loop systems (where high pressures are not
available) requires bypassing of the pressure reducing valve.
Generally, pressure purging is not possible with a well pump
system. High point air venting is essential.
If the system is of the open type, a pressure reducing valve will not
be required as the water supply to the system will be controlled by
a manually operated valve. An overhead surge tank is required.
4. EXPANSION TANK
CAUTION
A closed system will exist if a check valve (without bypass), pressure
reducing valve (without bypass), or a water meter (without bypass)
is installed in the cold water line between the water heater and
street main (or well).