45
Mode 5 – 0-10 V Input to Modulate Firing Rate:
This feature also requires the use of an optional PFA-1
Interface Adapter kit (54271). With this adapter, this
mode allows the boiler input firing rate to be controlled
by an external source using a 0-10 VDC analog signal.
In this case, voltages below 2.0 volts DC prevent the
boiler from operating. An input voltage of 2 volts will
cause the boiler to operate at it minimum input (1%
modulation) and 10 volts will cause the boiler to
operate at maximum (100% modulation). Between
these points, the input rate will be proportional. Note
that the boiler high limit is set at 210°F and will cause a
lockout if this temperature is reached.
Mode 6 – Hydro-Air Unit
: This mode is specifically for
boilers supplying hot water to a hot water coil in a
forced air heating system using a User defined boiler
target setpoint temperature.
This mode is nearly identical to Mode 1 except that
the response parameters are adjusted differently. The
boiler control targets the setpoint temperature and
modulates based on this temperature.
2. Setpoint operation:
When operating in CH mode 0, 3 or 6 the user can
select a target temperature for the boiler supply. The
control modulates the boiler based on three conditions:
1) The difference between the current supply
temperature and the target; 2) The speed with which
the supply temperature increases; and 3) The speed at
which the system reacts to the temperature increase.
When the boiler supply temperature approaches the
target setpoint, the burner will modulate down to
decrease the input. If the temperature begins to
decrease, the control will increase the input rate.
3. Outdoor Reset Operation:
To maximize fuel savings, P
UREFIRE
®
boilers are factory
equipped for outdoor reset operation. The following
describes the operating principal of this feature.
Operating Principle:
• Heat Loss decreases as Outdoor Temperatures
increases.
• Heat distribution system is sized for Design
Conditions (Coldest Outdoor Temperature).
• Boilers operate more efficiently at lower water
temperatures.
• Condensing boilers have no minimum return
water temperature.
The integrated control system on the P
UREFIRE
®
boiler
adjusts the boiler supply setpoint based on outdoor
temperature. In the installer menu, under “CH
Settings” there are two parameters that define the
design point of the boiler. The design point represents
the conditions for which the boiler was sized.
Boiler Design Temperature
: The boiler supply
temperature required to heat the building under its
design load is called Boiler Design Temperature. For
example, if the building was designed with copper
finned tube baseboard with 180°F water, this is the
design temperature that should be entered. The
factory default for the Boiler Design Temperature is
180°F (82°C).
Outdoor Design Temperature
: The outdoor design
temperature is the outdoor temperature used to
calculate the heat loss of the building to determine the
maximum heat load.
Commonly used values for this can be found in Table
8.7 for many North American Cities. The factory
default for this setting is 0°F (-18 °C).
Mild Weather Boiler Temperature
: This is the
temperature required to heat the building under a
minimum load. Table 8.8 shows recommended values
for this temperature setting.
The default for this is 70°F (21°C). However,
depending on the type of heat distribution used, this
value should be increased.
For example, if the boiler targets 70°F when a kick
space heater or unit heater is used, the heating unit is
likely to supply cold air if there is no thermostat to
prevent it from running.
Mild Weather Outdoor Temperature
: This is the
outdoor temperature at which the boiler should
operate at its minimum heat load. The default value
for this is 70°F (21°C).
Example:
Figure 8.9 shows how the Design Point and the
Mild Weather Point define a line used to calculate
boiler supply temperature based on outdoor
temperature.
The design point is shown for an outdoor design
temperature of 0°F and a boiler design supply
temperature of 160°F. The mild weather point is
shown for an outdoor temperature of 70°F and a
boiler supply temperature of 95°F.
From this, the P
UREFIRE
®
control calculates a boiler
supply temperature of 130°F when the outdoor
temperature is 32°F.
System Type Presets
: The PUREFIRE
®
Control allows
the installer to select preset values for Boiler Design
Temperature and Mild Weather Boiler Temperature
based on the type of heat distribution used. Table 8.7
shows the system types and the corresponding boiler
temperatures.
Type #7 is designated user defined and shows the
default boiler temperatures. Once this choice is
selected, the installer can change the numbers as
desired.
BOILER CONTROL: INTERNAL WIRING & OPERATION
System Type
Temperatures
Boiler
Design
Mild Weather
Boiler
1. Finned Tube Baseboard 180 140
2. Hydro Air Unit 190 140
3. Cast Iron Radiator 160 120
4. Cast Iron Baseboard 150 110
5. Low Mass Radiant 140 70
6. High Mass Radiant 120 70
7. User Defined (Default) 180 70
Table 8.7: System Type Presets
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