The FLEX-HEAT®System consists of a wide array of
components designed to provide high energy efficiency,
simple installation, and increased comfort from your
PB Heat, LLC Series GM™ boilers.
A. MODULAR VS MULTIPLE BOILERS
The FLEX-HEAT®System is designed to be installed as a
modular boiler system as defined by ASME1:
1. Modules can be no larger than 400 mbh gas input.
All Series GM™ boilers meet this requirement.
2. No isolation or stop valves can be placed between
modules and the main headers (installation requirement).
Modular boiler systems have the advantage of requiring fewer
limit controls than multiple boiler systems. On a multiple boiler
system, two limit controls are required on each individual boiler
(Figure 1.1). On modular boiler systems, only one limit control
is required on each module and one system limit control is
required (Figure 1.2).
The FLEX-HEAT®System may be installed as either a modular
boiler system or multiple boiler system.
Low Water Cut-off(s) - The Hydrolevel Hydrostat®limit controls
used on Series GM™ boilers meet ASME1low water cut-off
requirements when used in either modular or multiple boiler
installations. The Hydrostat®controls meet ASME CSD-1 low
water cut-off requirements when set to manual reset.
B. PB HEAT, LLC FLEX-HEAT®SYSTEM
1 Modular systems have higher overall boiler plant
efficiency. (Figure 1.3).
a) Higher part load efficiency. Atmospheric gas boilers
operate most efficiently at full gas input rate. The
FLEX-HEAT®system energizes each module at its
full gas input and efficiency and instead controls
the system by modulating the number of energized
modules.
b) Lower Stand-by losses. Since the FLEX-HEAT®
system energizes only the number of modules
needed to meet the heat loss, less heat is dissipated
to the boiler room and less heat escapes up the
chimney. Primary-Secondary inatallations further
reduce stand-by losses by preventing heated water
from flowing through idle modules.
2. Modular systems are redundant. If a single boiler
installation goes down, it’s a no heat situation. On a
modular boiler system, if a single boiler shuts down, the
remaining modules will provide heat until the problem
boiler can be corrected.
3. Modular systems can be faster to maintain.
Disassembling and reassembling a large boiler to
replace a section can take a large amount of time. Since
the FLEX-HEAT®modules are pre-packaged and fit
through a standard doorway, much less time is required
to replace a module.
1. INTRODUCTION TO FLEX-HEAT®
MODULAR BOILER SYSTEMS
INTRODUCTION TO FLEX-HEAT®MODULAR BOILER SYSTEMS
2
LIMIT/
LWCO
LIMIT
MODULAR BOILER SYSTEM
Treated as if a Single Boiler
400 MBH
or Less
Input
400 MBH
or Less
Input
400 MBH
or Less
Input
LIMIT/
LWCO LIMIT/
LWCO
LIMITLIMITLIMIT
2nd Limit Required if Boilers Over 400 MBH
MULTIPLE BOILER SYSTEM
Each Unit Treated as a Separate Boiler
STOP VALVES
LIMIT/
LWCO LIMIT/
LWCO LIMIT/
LWCO
Figure 1.2: Modular Boiler System
Figure 1.1: Multiple Boiler System
1ANSI/ASME Boiler and Pressure Vessel Code, Section IV: Rules for Construction
of Heating Boilers Figure 1.3: Boiler Plant Operating Efficiency
