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desCrIptIon of operatIon
Temperature Comparison with Enthalpy Comparison Economizer (optional)
If the optional Leading Edge economizer function is selected, the unit ventilator is
provided from the factory with both the IA humidity and OA humidity sensors, which
are used along with the IA temperature and OA temperature sensors to calculate IA
enthalpy and OA enthalpy. In this case, the UVC is factory set for the Leading Edge
Economizer Strategy and uses the Temperature Comparison with Enthalpy Compari-
son Economizer function.
Note: Temperature Comparison with Enthalpy Comparison requires both an optional OA
humidity sensor and an optional IA humidity sensor.
Table 18: Economizer enable/disable tests defined
Tests
Economizer enable/
disable tests
Enable test Disable test
A OA temp set point Effective OA Temp < (Econ OA Temp Setpt – Econ Temp Diff) Effective OA Temp >= Econ OA Temp Setpt
B IA/OA differential temp Effective OA Temp < (Effective Space Temp – 3.6°F – EconTempDiff) Effective OA Temp >= (Effective Space Temp – 3.6°F)
C OA enthalpy set point Effective OA Enthalpy < (Econ OA Enthalpy Setpt – Econ Enthalpy Diff) Effective OA Enthalpy >= Econ OA Enthalpy Setpt
D
IA/OA differential
enthalpy
Effective OA Enthalpy < (Effective Space Enthalpy – Econ Enthalpy Diff) Effective OA Enthalpy >= Effective Space Enthalpy
Table 19: How economizer enable/disable tests are selected
Economizer
strategy
Space temp sensor OA temp sensor Space humidity sensor OA humidity sensor
Economizer enable/
disable tests
All
Unreliable Ignored Ignored Ignored OA damper closed
Ignored Unreliable Ignored Ignored OA damper closed
Basic
Reliable Reliable Ignored Unreliable Test B
Reliable Reliable Ignored Reliable Test C
Expanded Reliable Reliable Ignored Reliable
Test C and Either Test B
or Test A
Leading Edge
Reliable Reliable Reliable Reliable Test D and Test B
Reliable Reliable Reliable Unreliable Test B
Reliable Reliable Unreliable Unreliable Test B
Reliable Reliable Unreliable Unreliable Test B
Note: The hard-wired sensor and the equivalent input must both be unreliable for the value to be considered unreliable.
Networked Space Humidity Sensor Capability
A networked space humidity sensor can be network interfaced with the Space Humidity
Input variable. When the Space Humidity Input variable is used (valid value), it auto-
matically overrides the hard-wired space humidity sensor (if present).
Networked Outdoor Humidity Sensor Capability
A networked outdoor humidity sensor can be network interfaced with the Outdoor Hu-
midity Input variable. When the Outdoor Humidity Input variable is used (valid value), it
automatically overrides the hard-wired outdoor humidity sensor (if present).
CO
2
Demand Controlled Ventilation (optional)
Ventilation equipment typically uses xed damper positions to determine the amount
of OA for proper ventilation within the space. Most commonly, the xed position of the
OA damper is based on the maximum number of occupants the space is designed to
accommodate. However, this xed OA damper operation ignores the fact that most
spaces during the day have varying occupancy levels and may only rarely reach
maximum design occupancy levels. This type of xed damper control for ventilation is
energy wasteful since you are treating OA not actually needed for ventilation during low
occupancy levels.
People produce CO
2
when they breath; the CO
2
level within the space has a direct
relationship with the number of people within that space.
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