LX Series Unit Ventilator Controller User's Guide
47
Morning Warm-up State
The Unit Ventilator Controller enters the morning warm-up state when
nviApplicMode has the value of HVAC_MRNG_WRMUP. This value of
HVAC_MRNG_WRMUP may be the result of binding nviApplicMode with a
network variable from a supervisory network system such as nvoTerminalLoad.
The morning warm up period uses occupied setpoints. The fresh air damper is
closed if there is no cooling demand. Morning warm up ends when
nviApplicMode commands another state.
Using Night Purge and Morning Warm-up with DCV
The UV provides DCV by using the CO
2
sensor to measure air quality. While CO
2
is a reliable gauge of the effect of human metabolism upon air quality, it does not
provide any measure of other effects upon air quality. For example, various glues
and plastics release gases for an extended period of time after installation in a new
building. These gases can produce unpleasant odors and cause eye, nasal, as well
as bronchial irritation. The accumulation of these gases does not affect the CO
2
level. If CO
2
alone is considered, the concentration of these gases may not be
sufficiently reduced during occupied periods to ensure the comfort and health of
the building occupants.
Similarly, an unoccupied building can accumulate gases and odors caused by
clothing left in lockers, damp drains, and photocopiers programmed to produce
manuals during the night. None of these detriments to air quality is detected by a
CO
2
sensor.
Such problems can be solved by over-ventilating, which is expensive, or by
providing a minimum airflow during unoccupied periods. Another solution is to
use the night purge or morning warm-up to exhaust the accumulated gases before
the start of normal occupation.
While the building is unoccupied, CO
2
levels do not increase. Yet the levels of
other contaminants increase. During occupied periods, these contaminants may not
be removed by a DCV system that responds only to CO
2
levels. Night purge and
morning warm-up remove all contaminants by flushing the building with fresh air
before the occupied period.
Fan Operation
Three fan speeds are available in the UVC. Fan speeds are started according to the
heating or cooling demand and according to the outputs configured in the Unit
Ventilator Controller configuration wizard. Normal operation sequence begins
with the UVC commanding the first fan speed to turn ON. After this, the UVC
starts or modulates all cooling and heating outputs to their maximum capacity
according to their respective demands. Finally, all other fan speeds are started
according to their respective demands.
