IBC Technologies Inc.
17
VFC 15-150 and VFC 45-225
would remain off, the boiler shut down,
leaving primary circulation on until the
primary loop temperature drops into the
acceptable range for the floor.
Temperature sensing is done using
thermistors at the boiler supply and
return – no further sensors need to be
installed.
The use of the multi-temperature
modulating system is optimized when
the need to shutdown the boiler is
reduced or eliminated during the
transitional period. Methods to enhance
the system design include: (a) keeping a
relatively low thermal mass in the
primary loop, and (b) incorporating a
recommended manually set 3-way
mixing valve on the “cool” load piping.
If the installation involves small loads,
as in typical zoned baseboard heating
applications, use of a buffer tank is
recommended. Such buffer tank is best
located on a remote secondary loop to
avoid excess thermal mass on the
primary circuit. To aid in temperature
transition from hot to cool loads, a
manually set 3-way mixing valve can be
placed at the entrance to the cool load.
This will permit immediate circulation
of mixed flow into the cool loop. See
separate publication
Application Notes
for further comment. Use of a mixing
valve also provides independent floor
protection.
Always ensure that loads sensitive to
high temperatures (e.g. radiant floor) are
protected using appropriate means such
as a manual mixing valve, or an aquastat
(set to130°F, for example) wired to the
boiler's auxiliary interlocks.
Compared with the Primary/Secondary
approach, this design saves one pump.
Lost is the simplicity of constant head
and flow at the boiler, with reduced
flexibility in the handling of large
temperature differentials. Wiring: loop
the yellow & white “Primary Pump” pair
up to connect to the lowest pair of
contacts on the green Pump/Valve
terminal block. Then connect the two
load pumps to the chosen Load 1-2-3
contacts on the same green terminal
block. To achieve variable speed on each
load, the pumps would be wired to the
Pump/Zone Valve Terminal Block
(green colour, along controller’s right
Figure 8 – Parallel Pumped Zones
