Bryant 549B - Manual (Page 168)

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Outside air enthalpy — EconoMi$erIV will be enabled
based on the outside air enthalpy curves as shown in the
EconoMi$erIV Changeover diagram below. The A, B, C,
and D curves shown have been in use for many years and
have been included as part of the latest ASHRAE 90.1
energy efficiency code. The curves are designed to take
into consideration both outdoor temperature and humidity.
These curves are used to set up the EconoMi$erIV control-
ler to use the EconoMi$erIV for free cooling when the condi-
tions to the left of the curve exist. When the conditions are
to the right of the curve, then outdoor air cooling will not be
used and the outdoor air damper position will be set at the
minimum position.
Deciding which curve is used is a function of the outdoor cli-
mate and the type of economizer utilized. Since
EconoMi$erIV is a fully integrated economizer, the range
where outdoor air can be utilized for free cooling is
expanded and the A and B curves may be used. The con-
trol point table in the EconoMi$erIV Changeover diagram
below provides assistance for whether the A and B curves will be suitable. In general terms, a hot and humid climate
may be a reason not to use the A curve, while a cooler cli-
mate might be more applicable for using the A or B curve.
The EconoMi$erIV has expanded outdoor air capability. For
a changeover economizer which cannot utilize simulta-
neous economizer and compression, both A and B curves
would potentially be undesirable since the temperature and
humidity levels are too high without compression assistance
to provide effective cooling. Therefore, most changeover
economizers utilize the D curve.
Differential enthalpy — The EconoMi$erIV will be enabled
based on the comparison of the enthalpy of the return air
and outside air. When the outside air enthalpy is lower than
the return side, the unit will be in economizer mode.
Using the EconoMi$erIV controller for implementing differ-
ent control changeover strategies requires the use of differ-
ent combinations of dry bulb and humidity sensors as
outlined in the EconoMi$erIV Sensor Usage table.
ECONOMI$ERIV SENSOR USAGE
*CRENTDIF004A00 and CRTEMPSN002A00 accessories are used on many different base units. As such, these kits may contain parts that will not be needed
for installation.
†CGCDXSEN004A00 is an accessory CO
2
sensor.
**CGCDXASP001A00 is an accessory aspirator box required for duct-mounted applications.
APPLICATION
ECONOMI$ERIV WITH OUTDOOR AIR
DRY BULB SENSOR
ECONOMI$ERIV WITH SINGLE
ENTHALPY SENSOR
Accessories Required Accessories Required
Outdoor Air Dry Bulb None. The outdoor air dry bulb sensor is factory installed. CRTEMPSN002A00*
Differential Dry Bulb CRTEMPSN002A00* (2) CRTEMPSN002A00*
Single Enthalpy HH57AC078 None. The single enthalpy sensor is factory installed.
Differential Enthalpy
HH57AC078
and
CRENTDIF004A00*
CRENTDIF004A00*
CO
2
for DCV Control using a
Wall-Mounted CO 2 Sensor
CGCDXSEN004A00
CO
2
for DCV Control using a
Duct-Mounted CO 2 Sensor
CGCDXSEN004A00†
and
CGCDXASP001A00**