IBC Technologies Inc.
29
VFC 15-150 and VFC 45-225
achieve the desired comfort level. Fine
adjustment can be made at the keypad
using the
Indoor Setpoint Temperature
variable, located as Line 1 in the
User
screen. To increase heat (e.g. from 72°F
to 73°) - move the
Indoor
value upward
(warmer) from the level otherwise
chosen. This shifts the position of the
reset curve, will amend the boiler water
temperature by a similar amount. Do
not adjust the
Design Indoor Temp.
value - a movement upward in concert
with Line 1 adjustment will have the
effect of neutralizing the intended
effect.
An optional indoor temperature
feedback routine can be activated (with
field installation of an indoor sensor,
connected to the contacts located on the
controller) to automate adjustment of
the Outdoor Reset routine.
The key inputs on initial set up are (1)
Design Outdoor Temperature –
the
coldest expected weather typically
experienced at the installation site; (2)
the
Design Supply Temperature
– the
desired boiler operating level to occur at
that coldest day; and (3) the
Design
Indoor Temp.
- this is the value that
anchors the reset curve. The
Indoor Set
Point Temp
. variable is the primary
means for the user to “bias” the outdoor
reset routine to add or reduce heat.
If outdoor reset is selected and there is
no signal received from the sensor, the
controller assigns a provisional 0°C
value and will adopt the appropriate
temperature target from the relevant
reset curve.
(See Section 2.7 -
Set Up & Load
Definition
for activation procedure.
2.6.3 Variable Speed Pumping
One strategy to optimize combustion
efficiency across the boiler's wide
throttle range is to use a variable speed
system primary pump. This will better
match water flows with heat generation
- providing more stable
∆
T°
management. This generally has the
effect of lowering return water
temperature for any given heating duty,
promoting more condensation. Together
with Outdoor Reset, variable speed
primary pumping offers the prospect of
condensing operation with (otherwise)
high temperature baseboards.
The controller provides an electrical
signal (4-20mA) for connection to
pumps such as the
Grundfos 15-42 VS
or the
Taco 007
Variable Speed
. In the
variable speed configuration, the system
pump can receive its 120 V
AC
mains
power independently (wired to the
boiler); these pumps are typically
supplied with a 3-pin consumer plug,
although the installer will want to
amend to conform to code as
appropriate. The pumps signal leads are
to be connected to the harness provided
within the control wiring box.
The pump management routine seeks to
maintain a 20°F
∆
T° across heat
exchanger throughout the throttle range.
The actual
∆
T° achieved will be
dependent on the pump size selected
and the head of the piping system.
Using the recommended
primary/secondary piping configuration,
including a relatively short travel
primary circuit of 1
1
/
4
" piping, and a
Grundfos 15-42 VS(or 26-64VS) pump,
a 3:1 turndown ratio for waterflow
should be achieved. This will provide
stable 20°F
∆
T° management across the
majority of the boiler's operating range.
Where a conventional pump is correctly
wired in accordance with the wiring
diagram, the pump will operate at a
single, high speed.