50 AGR 055A through 100A IOMM AGR
Figure 28, Outside Air Reset
LWRB
LWSP
OALL OAHL
OARB
(OALL=OAHL - OARB)
As the OAT increases above the Outdoor Air Low Limit (OALL), the Actual Leaving Water
Setpoint is decreased from its Leaving High Limit (Leaving Water Setpoint plus Leaving Reset
Band) to the Leaving Water Setpoint. When OAT reaches the OAHL, the Actual Leaving Water
Setpoint equals the Leaving Water Setpoint (AI4). If the OAT sensor is missing or unreliable, no
reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water Setpoint. If the
Leaving Water Sensor (AI1) becomes unreliable, the compressor command is forced to 0%.
Return Water Reset (optional Return Water Sensor is required)
When selected, a Return Water Temperature (RWT) sensor is connected to TB-7 terminals #134 and
#135. Four variables are used to setup the reset ramp that calculates the Actual Leaving Water
Setpoint. These are: Leaving Water Setpoint (AI-4), Reset Band selected with a Zone Terminal,
Return Water High Limit (RWHL), and Return Water Reset Band (RWRB).
Figure 29, Return Water Reset
LWRB
LWSP
RWLL RWHL
RWRB
(RWLL=RWHL - RWRB)
As the RWT increases above the Return Water Low Limit (RWLL), the controller decreases the
Actual Leaving Water Setpoint from its Leaving High Limit (Leaving Water Setpoint plus Leaving
Reset Band) to the Leaving Water Setpoint. When RWT reaches the RWHL, the Actual Leaving
Water Setpoint equals the Leaving Water Setpoint (AI-4). If the RWT sensor is missing or
unreliable, no reset occurs and the Actual Leaving Water Setpoint equals the Leaving Water
Setpoint. If the Leaving Water Sensor (AI-1) becomes unreliable, the compressor command is
forced to 0%.
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