COMBOMAX
MC
Electric boiler Set-up, use and care guide
(revised Oct 2015)
, Page
7.
3.5.7 Circulator zoning
A flow-check valve must be installed in each
zone, preferably at the outlet of each circulator,
to prevent water flowing to zones where no heat
is currently required. (see figure 4).
3.5.8 Zone valve zoning
Zone valves with low pressure drop are
recommended. (see figure 3)
3.5.9 Circulator selection criteria
The COMBOMAX
MC
boiler includes a pre-
mounted circulator. The information below will
help you select additional units for multiple
circulator set-ups.
3.5.9.1 Pump flow rate calculation
The boiler output rating must correspond to the
calculated heating load. Use the equation below
to calculate the pump flow rate:
Pump flow rate = Boiler output
÷÷÷÷
BWTD
÷÷÷÷
500
•
Pump flow rate is expressed in U.S. gallons
per minute or GPM.
•
The Boiler output ( in net BTU per hour) is
the maximum amount of heat to be
transferred through the heating circuit to
meet the hot water demand.
•
BWTD is the boiler water temperature drop
through the heating circuit.
For example, a 24 Kw COMBOMAX
MC
boiler has
a rated output of 81,964 BTU/hour. The system
is designed for a boiler water temperature drop
(BWTD) of 20°F.
Pump flow rate = 81,964
÷
20
÷
500 = 8,2 GPM.
The following table shows the required flow rate
as a function of boiler water temperature drop
(BWTD) and rated power output.
Table 5 : BWTD vs. flow (GPM)
BWTD
Model
Kw
10
o
F
20
o
F
30
o
F
40
o
F
COMBOMAX XX-8
8
5,5
2,7
1,8
1,4
COMBOMAX XX-10
10
6,8
3,4
2,3
1,7
COMBOMAX XX-15
15
10,2 5,1
3,4
2,6
COMBOMAX XX-18
18
12,3 6,1
4,1
3,1
COMBOMAX XX-20
20
13,7 6,8
4,6
3,4
COMBOMAX XX-24
24
16,4 8,2
5,5
4,1
3.5.9.2 Selecting a circulator
Consult the manufacturer’s operating
characteristic curves to select the proper model.
These curves plot flow versus pressure, together
with other information such as efficiency and
power. Ask your pump dealer or HVAC
wholesaler to recommend the circulator which
best fits your needs.
3.6 DOMESTIC HOT WATER CIRCUIT
3.6.1 Connecting the domestic hot water
piping
The COMBOMAX
MC
domestic hot water coil may
be set up alone or in parallel combination with
other COMBOMAX
MC
units or storage tanks.
Parallel connections should be made using the
reverse-piping method to ensure equal flow
through each boiler.
The HOT WATER OUTLET and the COLD
WATER INLET connections are clearly marked.
Inlet water connections (COLD WATER INLET)
are to be made to the copper pipe (sweat
connection) at the bottom of the heater. Outlet
water connections (HOT WATER OUTLET) are
to be made to the three-way thermostatically
controlled valve (sweat connection) at the top of
the heater.
The installation of copper unions or copper alloy
unions is recommended on the HOT and COLD
water lines, so that the water heater may be
easily disconnected for servicing if necessary.
These unions must be dielectric (insulating) if
you are making steel-copper connections.
A shutoff (ball) valve is present on the
COMBOMAX
MC
domestic hot water outlet for
servicing convenience.
Use only clean copper or approved plastic pipe
for water connections. Local codes or
regulations shall govern the exact type of
material to be used.
Insulate all pipes containing hot water,
especially in unheated areas.
Thermometer(s) should be installed to indicate
the temperature of the water at or near the outlet
of the water heater and storage tank(s), if
provided.