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prestart mode and de-energizes the condenser water
pump relay. This diagnostic is automatically reset if flow is
established at any later time.
Note: This diagnostic would never automatically reset if
Symbio™ 800 was in control of the condenser
pump through its condenser pump relay since it is
commanded off at the time of the diagnostic. It
could however reset and allow normal chiller
operation if the pump was controlled from some
external source.
Chilled Water Reset (CWR)
The controller will reset the chilled water temperature
setpoint based on either return water temperature, or
outdoor air temperature. The Return Reset option is
standard, Outdoor Reset is optional.
The following is selectable:
•
RESET TYPE Setpoint.
This can be set to: DISABLE, CONSTANT, RETURN or
OUTSIDE AIR. The MP shall not permit more than one
type of reset to be selected.
•
RESET RATIO Setpoints.
For outdoor air temp. reset, both positive and negative
reset ratios will be allowed.
•
START RESET Setpoints.
•
MAXIMUM RESET Setpoints.
The maximum resets shall be with respect to the
chilled water setpoint.
When the chiller is running, if any type of CWR is enabled,
the controller will step the CWS toward the desired CWS'
(based on the below equations and setup parameters) at a
rate of 1 degree F every 5 minutes until the Active CWS
equals the desired CWS'. When the chiller is not running
the CWS will be fully reset immediately (within one
minute). The chiller will then start at the Differential to
Start value above a fully reset CWS or CWS' for Outdoor,
Return, and Constant Return Reset.
Equations for calculating CWR
Equation used to get Degrees of Reset:
Outdoor Air:
Degrees of Reset =
Reset Ratio * (Start Reset - TOD)
Return Reset:
Degrees of Reset =
Reset Ratio * (Start Reset - (TWE - TWL))
Constant Return:
Degrees of Reset =
100% * (Design Delta Temp - (TWE - TWL))
To obtain Active CWS from Degrees of Reset:
Active CWS = Degrees of Reset + Previous CWS
Note: Previous CWS can either be Front Panel, BAS, or
External
RTHD-SVX01K-EN
Reset Ratio calculation:
The Reset Ratio on the User Interface is displayed as a
percentage. To use it in the above equation it must be
converted to its decimal form.
Reset Ratio percent / 100 = Reset Ratio decimal
Example of converting Reset Ratio:
If the Reset Ratio displayed on the User Interface is 50%
then use (50/100) = 0.5 in the equation.
Abbreviations used in equations:
•
TOD = Outdoor Air Temp
•
TWE = Evap Entering Water Temp
•
TWL = Evap Leaving Water Temp
Programmable Relays (Alarm and Status) -
Optional
Symbio™ 800 provides a flexible alarm or chiller status
indication to a remote location through a hard wired
interface to a dry contact closure. Four relays are available
for this function, and they are provided (generally with a
Quad Relay Output LLID) as part of the Alarm Relay Output
Option.
The events/states that can be assigned to the
programmable relays are listed in the following table.
Table 14. Chiller events/status descriptions
Event/State
Description
This output is true whenever there is any active
diagnostic that requires a manual reset to clear,
Alarm - Latching
that affects the Chiller, the Circuit, or any of the
Compressors on a circuit. This classification does
not include informational diagnostics.
This output is true whenever there is any active
diagnostic that could automatically clear, that
affects the Chiller, the Circuit, or any of the
Alarm - Auto Reset
Compressors on a circuit. This classification does
not include informational diagnostics. If all of the
auto resetting diagnostics were to clear, this output
would return to a false condition.
This output is true whenever there is any
diagnostic effecting any component, whether
Alarm
latching or automatically clearing. This
classification does not include informational
diagnostics.
This output is true whenever there is any
Warning
informational diagnostic affecting any component,
whether latching or automatically clearing.
Installation Electrical
45
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