Raypak 5000.72A, Installation & Operating Instructions Manual

Page: 45 / 80

45
Additional Operational
Features
Outdoor Reset Operation
When a building is being heated, heat escapes
through the walls, doors, and windows to the colder
outside air. The colder the outside temperature, the
more heat escapes. If you can input heat into the build-
ing at the same rate that it is lost out of the building,
then the building temperatures will remain constant.
The Reset Ratio is an adjustment that lets you achieve
this equilibrium between heat input and heat loss.
The VERSA
®
control can change the System Set-
Point based on outdoor temperature (Outdoor Reset).
The VERSA
®
control varies the temperature of the cir-
culating heating water in response to changes in the
outdoor temperature. The heating water temperature
is controlled through the modulation and/or sequenc-
ing of the cascade.
The VERSA
®
control can also control the system cir-
culating pump with an adjustable Warm Weather
Shutdown temp (WWSD) See page 46. When the out-
door temperature is above the WWSD Cutoff, the
pump is turned off and no heating water is circulated
through the system. When the outdoor temperature
drops below the WWSD Cutoff, the system pump relay
is activated and the heating water circulates through
the system. The temperature of the heating water is
controlled by the Reset Ratio, Water Offset, and
changes with the outdoor temperature.
Reset Ratio/Outdoor Reset
The starting point for most reset systems is a 1:1 ratio
of outdoor temp changes to heating water temperature
changes. This means that for every degree the out-
door temperature drops, the temperature of the
heating water will increase one degree. With the
VERSA
®
, both ends of the slope are adjustable. It is
factory set at 70°F water temperature (Boil START) at
70°F outdoor air (OUT START), and 180°F water tem-
perature (Boil DESIGN) at 10°F outdoor air (OUT
DESIGN). Each building has different heat-loss char-
acteristics. A very well-insulated building will not lose
much heat to the outside air, and may need a Reset
Ratio of 2.00 (OD):1.00 (SYS) (Outdoor: Water). This
means the outdoor temperature would have to drop 2
degrees to increase the water temperature 1 degree.
On the other hand, a poorly insulated building may
need a Reset Ratio of 1.00 (OD):2.00 (SYS). This
means that for each degree the outdoor temperature
drops the water temperature will increase 2 degrees.
The VERSA
®
control Reset Ratio allows for full cus-
tomization to match any buildings heat loss
characteristics.
A heating curve that relies not only on Outdoor temper-
ature but also on the type of radiation will improve heat
comfort. The user can fine-tune these adjustments
based on the needs of the specific building.
Reset Ratio
The control uses the four following settings to deter-
mine the reset ratio:
Outdoor Starting Temperature (OUT START)
This is the outdoor temperature at which the control
starts to calculate a reset when Outdoor Reset is
active. This value is only available for set/change
when the PIM™ identity is “H” and the TARGET =
RSET. The range of adjustment is 35°F to 85°F. The
default value is 70°F. See Figure 9 for Outdoor Reset
curve information.
Outdoor Design Temperature (OUT DESIGN)
This is the outdoor temperature that is typically the
coldest temperature of the year where the building is
located. This temperature is used when doing heat
loss calculations for the building. This value is only
available for set/change when the PIM™ identity is “H”
and the TARGET = RSET. The range of adjustment is
-60 to 45°F. The default value is 10°F. See Figure 32
for Outdoor Reset curve information.
Boiler Design temperature (Boil DESIGN)
This is the water temperature required to heat the sys-
tem when the outdoor air temperature is as cold as the
OUT DESIGN temperature. This value is only avail-
able for set/change when the PIM™ identity is “H” and
the TARGET = RSET. The range of adjustment is 70°F
to 200F (200 = Boiler Design max value, user selec-
table). The default value is 180°F. See Figure 32 for
Outdoor Reset curve information. The Highest TAR-
GET calculable value is determined by Boil Design
setting.
Boiler Start Temperature (Boil START)
This is the starting boiler target temperature that the
system requires when the outdoor air temperature
equals the OUT START temperature setting. The Boil
START is typically set to the desired building tempera-
ture. This value is only available for set/change when
the PIM™ identity is “H” and the TARGET = RSET.
The range of adjustment is TARGET MIN to 150°F.
The default value is 70°F. See Figure 32 for Outdoor
Reset curve information. The lowest target calculation
will be truncated based on the target minimum setting.