LAARS Mighty Max HH (Sizes 320M - 400M) - Installation, Operation and Maintenance Instructions - Manual (Page 8)

Page 8
LAARS Heating Systems
2.7.2 Variable Water Flow Systems
There can be reduced water flow through the
boiler in heating systems using zone valves, zone
pumps or 3-way valves. This can result in a high
temperature rise across the boiler. Laars recommends
primary-secondary pumping for all variable flow
systems. The boiler pump in a primary-secondary
system maintains constant flow through the boiler
even though the system flow is variable. In a primary-
secondary system the pressure drop of the boiler is not
added to the system (see Figure 5).
2.7.3 System Pressure Requirements
The Model HH boilers are designed to operate
on closed, pressurized systems. Maintain a minimum
of 12 psi (81.8 kPa) on the system where boiler supply
water temperature is 200°F (93°C) or less. If higher
temperatures are required, the minimum system
pressure should be at least 15 psi (102.2 kPa) above
Figure 4. T-Fitting Sediment Trap Installation.
Gas Supply
Inlet
Tee
Fitting
3 In.
(76mm) Min.
Cap
Nipple
To Equipment
Inlet
Figure 3. Boiler Gas Valve Arrangement.
Note: The above diagram is a representation. Actual
venturi assembly may vary depending on boiler size.
Venturi
Air Shutter
Enclosure
Automatic,
Regulator
and
Redundant
Gas Valve
Mixture
Plenum
Filter
Housing Blower
Motor
the water vapor pressure corresponding to the elevated
water temperature.
The Model HH boilers are not suitable for open
systems unless the supply water temperatures are
kept below 180°F (82°C), and a minimum of 5 psi
(34.1 kPa) static head is maintained at the boiler.
2.7.4 Hot/Chilled Water Systems
When a boiler is connected to an air conditioning
system where the same water is used for heating and
cooling, you must prevent chilled water from entering
the boiler. When changing such a system from cooling
to heating, allow the chilled water to circulate through
the building, after the chiller has been turned off, for a
period long enough for the water to warm up to at
least 105°F (41°C) before the water flows into the
boiler. It is equally important to prevent hot water
from entering the chiller. The system shown in Figure
6 is suggested to make sure the system water is neither
too hot nor too cold when a changeover takes place.
When a boiler is connected to heating coils located in
air handling units (where they may be exposed to
refrigerated air circulation), install a flow control
valve or other automatic means to prevent gravity
circulation of chilled water through the boiler. Chilled
water in the boiler will create condensate on the boiler
NOTES: Sizes 320M and 400M use 4-pass heat exchangers.
*Pressure drop (head loss) through the boiler, expressed in ft. of H
2
O.
Shaded area is the recommended flow and temperature rise. Minimum inlet temperature is 120°F (49°C).
Table 5. Temperature Rise.
TEMPERATURE RISE IN DEGREES (°F / °C )
MODEL
10°F 6°C 15°F 8°C 20°F 11°C
GPM H/L ft. LPS H/L m GPM H/L ft. LPS H/L m GPM H/L ft. LPS H/L m
HH0320M 54 11.2 3.41 3.4 36 5.0 2.27 1.5 27 2.8 1.70 0.9
HH0400M 68 26.2 4.29 8.0 45 11.5 2.84 3.5 34 6.6 2.15 2.0
Flow High Normal Low
OUT OF
PRODUCTION