Smith Cast Iron Boilers GB100W - Manual (Page 10)

Page 10 GB100W NATURAL OR PROPANE BOILER
INSTALLATION AND OPERATING INSTRUCTIONS
CAUTION: To prevent damage due to excessive
condensation, one of the following piping options
should be used.
System Bypass
For systems using a circulator on the return as either a
single zone, or multiple zones with zone valves, install
a system bypass line between the supply and return
on the suction side of the circulator, see Figure 7.
Install a metering valve in this bypass line to regulate
the amount of flow that will be diverted to the return. A
plug valve offers the best control for this application.
Although other valves may be less expensive, a plug
valve will be easier to set accurately.
In the absence of a flow indicator, set the metering
valve using temperature as a guide. The accompanying
diagram suggests one scenario. This addition requires
only two tees, a plug valve, and a small amount of pipe
and offers the simplest approach to reliably control
condensation. For this system and those that follow,
be aware that you are using a percentage of the pump
capacity to blend, but the friction loss for the entire
pump flow has been reduced. In most cases, the
standard pump packaged with the boiler has enough
capacity to feed the baseboard distribution system and
the bypass line.
Figure 7: System Bypass
Pump Away Bypass
For systems that use a single circulator to pump away
from the boiler, the bypass should be installed on the
discharge side of the circulator, see Figure 8. Full
temperature water supplies the baseboard distribution
system as before. Half of the circulator’s volume moves
through the bypass, blending and heating the cooler
return water. Again, the cost of installing the bypass is
small and setting it by temperature can be accomplished
with a contact thermometer.
Figure 8: Pump Away Bypass
Pumped Blend
An additional circulator can also be used to provide a
return water temperature blend. This method works
well with systems with multiple zones with circulators,
see Figure 9. The dedicated bypass circulator provides
a strong blending flow without diminishing the flow
available to any heating zone. Any residentially sized
circulator is adequate for this purpose.
Each of these bypass solutions also has the added
benefit of increasing circulation in the boiler which will
maximize tankless coil output and increase the accuracy
of temperature sensing controls.
Figure 9: Pumped Bypass
SUPPLY RETURN
50%
120° F
100%
140° F
100%
160° F
50%
160° F
50%
160° F
SYSTEM
BYPASS
SUPPLY RETURN
50%
120° F
100%
140° F
100%
160° F
50%
160° F
50%
160° F
PUMP AWAY
BYPASS
SUPPLY RETURN
100%
120° F
200%
140° F
200%
160° F
100%
160° F
100%
160° F
PUMPED
BYPASS