Description of Operation
Emergency Heat Mode (Super State)
The Emergency Heat mode is provided for situations where the UVC is in a mode that does not normally allow heating, such as OFF, Cool, Night Purge, or Fan Only. If Emergency Heat mode is enabled, the UVC can automatically force itself into the Emergency Heat mode from OFF, Cool, Night Purge, Fan Only, Purge, Pressurize,
Software model 05 does not have the primary or secondary heating devices. The UVC uses auxiliary heat (if field provided and field connected) when emergency heat is required.
When the Emergency Heat mode becomes active, the UVC automatically determines which state to make active, Full Heat [7], or Cant Heat [D], based on the transitions for each of those states.
Figure 10: Emergency heat state diagram
Emergency Heat Mode
Super State
Full Heat
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Cant Heat
D
Full Heat State (State 7)
The Full Heat [7] state is the “normal” state that the UVC goes into when Emergency Heat mode is active. It is activated when the space temperature is lower than the EHS.
When Emergency Heat mode becomes active, the UVC goes into 100% heating until the space temperature raises to the EHS plus a fixed differential (5.4°F/3°C). In the Emergency Heat mode, the space fan is set to high speed, and the OA damper operates normally.
If the UVC automatically forces itself into the Emergency Heat mode from another mode (e.g., Cool, Fan Only, etc.), then the UVC returns to the appropriate unit mode once the space temperature rises to the EHS plus a fixed differential (5.4°F/3°C).
The UVC monitors the DAT to ensure it does not exceed DAHL. If the DAT does exceed DAHL, then heating is set to 0% for a minimum of
Cant Heat State (State D)
The Cant Heat [D] state is a
Heat mode is active. An IAT or DAT sensor fault during Emergency Heat mode causes the
UVC to make this state active.
When the Cant Heat state becomes active, the space fan remains at high speed as set during the Full Heat state.
The UVC will remain in the Cant Heat state until heat becomes available.
16 | McQuay OM 751 |