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INSTALLATION AND OPERATION INSTRUCTIONS

2-8

VFC 15-150 - VFC 45-225 MODULATING GAS BOILERS

In an “open loop” reset system, a room or zone thermostat is used to send a call

for heat over a 24VAC lead; this opens the respective zone valve, and signals the

boilertoreusingonwardleadstotheboiler’sdrycontacts(useoneofthepairs

marked “Therm 1, 2 or 3” on the orange connector terminal located on the right

edge of the controller). Gang such leads in parallel from multiple zone valves for

single connection to the boiler. Note that typical room thermostats simply provide

a call for heat, they do not control the circulating water temperature from the

boiler in an open loop reset system. Adjustment of a room thermostat from 23°C

to30°Cwillmakenofurtherdifferencetothedeliveredtemperatureiftheoor

slab has stabilized at the boiler temperature served up by the reset curve.

Where Outdoor Reset is applied without the indoor sensor feedback option, some

manual adjustment may be required to 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eld

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 Denition for activation procedure.

Figure 30: Outdoor reset curves

IBC VFC 15-150 Manual

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