6
NG-IOM-ATT Release 1.2
July 12, 2019
2.2 Cooling Control
The DAC/WAC unit provides the primary shelter cooling. The secondary HVAC mechanical-only cooling units operate in
the event that internal temperatures exceed a threshold or failure of the DAC/WAC unit. When commanded to run, the
DAC/WAC unit fully opens the its internal damper and the remote exhaust damper then regulates the blower speed
dependent on internal shelter temperature.
DAC/WAC Cooling:
PARAMETER
THRESHOLD
DAC/WAC
INSIDE TEMP
< 55°F (13°C)
BLOWER OFF
INSIDE TEMP
>= 55°F (13°C)
BLOWER SPEED 5%
INSIDE TEMP
> 77°F (25°C)
BLOWER SPEED 5%-100%
INSIDE TEMP
> 90°F (32°C)
BLOWER SPEED 100%
INSIDE TEMP
>= 104°F (40°C)
BLOWER OFF
INSIDE TEMP
>= 109°F (43°C)
See note
Table 1: DAC/WAC Cooling Stages
HVAC Cooling:
PARAMETER
THRESHOLD
MECHANICAL
INSIDE TEMP
>= 104°F (40°C)
HVAC ON
INSIDE TEMP
<= 89°F (32°C)
HVAC OFF
INSIDE TEMP
>= 109°F (32°C)
See note
Table 2: HVAC Cooling Stages
Note:
For a DAC/WAC with one HVAC unit, if HVAC cooling is active and the indoor temperature rises above the local high
temperature alarm set point then the HVAC unit is disabled and the DAC/WAC assumes cooling responsibility. For a
DAC/WAC with two HVAC units, if HVAC cooling is active and the indoor temperature rises above the local high
temperature alarm set point then the lead HVAC unit is disabled and the lag HVAC unit assumes cooling responsibility. If
both lead and lag HVAC units are unavailable the DAC/WAC assumes cooling responsibility. Three consecutive events of
this type will set the HVAC Fail alarm for the HVAC unit.
2.3 Heating Control
The HVAC units exclusively provide shelter heating; the DAC/WAC unit does not run if heating is required. Note that if
the cooling and heating temperature set points overlap, the system will only allow cooling to be active.
DAC/WAC Heating:
PARAMETER
THRESHOLD
DAC/WAC
INSIDE TEMP
< 55°F (13°C)
BLOWER OFF
Table 3: DAC/WAC Heating Stages
HVAC Heating:
PARAMETER
THRESHOLD
MECHANICAL
INSIDE TEMP
< 45°F (7°C)
HVAC HEATING ELEMENTS ON
INSIDE TEMP
>= 55°F (13°C)
HVAC HEATING ELEMENTS OFF
Table 4: HVAC Heating Stages
