LAARS Rheos RHCV - Install and Operating Manual - Manual (Page 22)

LAARS Heating Systems Page 22
Figure 15. Control Parameter Graph.
through the heater is 25°F, the outlet temperature will
be 175°F (150°F+25°F). Therefore, set the manual
reset high limit to 195°F (175°F + 20°F).
Example, Metric units: If the tank temperature
is set to 60°C, set the heater’s temperature control to
66°C (60°C+6°C). Further, if the temperature rise
through the heater is 15°C, the outlet temperature will
be 81°C (66°C+15°C). Therefore, set the manual reset
high limit to 92°C (81°C+11°C).
5.4.2 Internal Water Heater
Temperature Control
When an external control is not used, the
circulator between the heater and the storage tank
must run continuously, so that the heater’s temperature
control can detect and control the water temperature in
the storage tank. The Rheos water heater’s temperature
control is adjusted to its lowest temperature position
when shipped from the factory. This is the preferred
starting point for setting the temperature control. Set
the manual reset high limit 20°F (11°C) plus heater
temperature rise above the temperature control’s
setting.
Example, Imperial units: If the heater’s
temperature control is set to 130°F, and the
temperature rise through the heater is 25°F, the outlet
temperature will be 155°F. Set the manual reset high
limit to 175°F.
Example, Metric units: If the heater’s
temperature control is set to 55°C, and the
temperature rise through the heater is 14°C, the outlet
temperature will be 69°C. Set the manual reset high
limit to 80°C.
Caution
Should overheating occur or the gas supply fail to
shut off, turn off the manual gas control valve to the
appliance.
5.5 Temperature Control Features
The Rheos temperature control is versatile and
will allow the user to better match the modulating
control to the application. Settings that can be changed
are temperature setpoint, differential, offset, throttling
range, and minimum output.
The temperature setpoint is the setting at which
the unit will shut off, having satisfied the controller’s
call for heat.
The differential determines how far the
temperature in the Rheos can fall before energizing
again.
The offset determines where the throttling range
begins.
The throttling range is the temperature range
through which the unit will modulate from minimum
to maximum firing rate.
Important Note: These control parameters work
together. Therefore, setting one parameter may have
an affect on another. Figures 15, 16 and 17 show the
relationships between these settings. Figure 15 follows
the examples that are shown in the following sections,
and Figures 16 and 17 are examples of how the
parameters can interfere with each other.