LCD Series Finned Copper Tube Gas Boilers & Water Heaters – Boiler Manual
18
Pump Requirements (Primary/Secondary)
This low mass boiler requires a continuous minimum water flow
for proper operation. The boiler pump must be sized to overcome
the head loss of the boiler and the near piping in order to achieve
the required temperature rise. Table 7 provides the heat exchanger
pressure drop and temperature rise figures. The temperature rise
across the boiler must never exceed
35°F
,
19.4°C
.
A temperature rise outside of the range listed in Table
7 indicates that the flow rate through the heat exchanger
is incorrect which will damage the heat exchanger
voiding the warranty! The maximum allowable
temperature rise is
35°F
,
19.4°C
.
The maximum allowable flow rate through a LCD
boiler with copper heat exchanger is
92 GPM
,
5.8 L/s
on 400-1200 models and
115 GPM
,
7.3 L/s
on 1480 to 2300 models. The cupro-nickel
heat exchanger allows for
100 GPM
,
6.3 L/s
on 400
to 1200 models and
125 GPM
,
7.9 L/s
on 1480 to
2300 models.
Low Water Cutoff
If a boiler is installed above any radiation elements it must be fitted
with a low water cutoff device.
Refer to wiring diagram supplied with the boiler/water heater for
proper wiring connections.
Expansion Tank & Air Separator
An expansion tank or other means to control thermal expansion
must be installed in the heating system. An expansion tank must
be installed close to the boiler on the suction side of the pump. An
air scoop and automatic air vent must also be installed to eliminate
air trapped in the system.
Primary/Secondary Piping
Boilers connected to heating systems using zone valves, zone pumps,
or systems that have excessive flow rates or return water temperatures
less than 125°F, 52°C must be isolated from these systems to protect
the boiler. Figure 11, shows a typical primary/secondary piping
system. A dedicated pump is used to maintain a constant water
flow through the boiler. This boiler pump is sized to overcome the
head loss of the boiler and near-boiler piping system while supplying
the flow rate required to maintain the desired temperature rise across
the boiler heat exchanger. The system pump is sized to provide the
required flow to the heating system. The boiler piping connections
to the heating system piping must be a maximum 10X pipe diameters
between centers to ensure zero pressure drop in the primary system.
Flow must be properly accounted for in the design of primary/
secondary systems. In order to prevent boiler(s) short cycling the
system flow must be equal to or higher than the boiler(s) local flow.
Low Return Water Temperatures
To prevent the problems associated with condensation of the
products of combustion due to low return water temperatures a
primary/secondary piping system with a bypass and bypass valve
must be installed, see Figure 12 and 12A. The bypass and bypass
valve must be sized the same as the secondary piping. A balancing
valve must also be installed in the supply side of the secondary
piping downstream of the bypass. The balancing valve should be
adjusted to divert some of the heated discharge water into the return
water until the required inlet water temperature is achieved. The
primary and secondary pumps should be sized to provide the required
flow through each system. The secondary piping connections to
the primary system piping must not be more than 10X pipe diameters
apart to ensure zero pressure drop in the primary system, see Figure
12 and 12A.
Multiple Boiler Systems
Systems using multiple boilers can also be installed using a primary/
secondary manifold system, Figure 13.
Piping For Use With Cooling Units
The boiler, when used in connection with a refrigeration system,
must be installed so the chilled medium is piped in parallel with
the boiler. Appropriate valves must be used to prevent the chilled
water from entering the boiler.
When a boiler is connected to a heating coil that may be exposed
to refrigerated air from an air handling device, the piping system
must be equipped with flow-control valves or some other automatic
means of preventing gravity circulation of the boiler water during
the cooling cycle.
