38
timeguard, and 2 compressors are to be turned on, then
compressors A1 and B1 will be turned on immediately instead
of A1 and A2.
Low Cool Versus High Cool Mechanical Staging —
The num-
ber of compressors to be requested during a cooling mode are
divided into 2 groups by the control, HVAC mode = Lo Cool
and HVAC mode = Hi Cool.
If the economizer is not able to provide free cooling (
Run
Status
ECON
ACTV
= NO
) then the following staging
occurs:
• Lo Cool Mode mechanical stages = 2
• Hi Cool Mode mechanical stages = 3 (for 020 through 027
size units)
• Hi Cool Mode mechanical stages = 4 (for 030 through 060
size units)
If the economizer is able to provide free cooling (
Run
Status
ECON
ACTV
= YES
) then the following staging
occurs:
1. If the economizer’s current position is less than
Configu-
ration
ECON
EC.MX
– 5 and mechanical cooling
has not yet started for the current cool mode session then:
Lo Cool Mode mechanical stages = 0
Hi Cool Mode mechanical stages = 0
2. During the first 2.5 minutes of a low or high cool mode
where the economizer position is greater than
Configura-
tion
ECON
EC.MX
– 5% and mechanical cooling
has not yet started:
Lo Cool Mode mechanical stages = 0
Hi Cool Mode mechanical stages = 0
3. If the economizer position is greater than
Configuration
ECON
EC.MX
– 5% for more than 2.5 minutes but
less than 5.5 minutes and mechanical cooling has not yet
started then:
Lo Cool Mode mechanical stages = 1
Hi Cool Mode mechanical stages = 1
4. If the economizer position is greater than
Configuration
ECON
EC.MX
– 5% for more than 5.5 minutes but
less than 8 minutes and mechanical cooling has started
then Lo Cool Mode mechanical stages = 2 and Hi Cool
Mode mechanical stages = 2.
5. If the economizer position is greater than
Configuration
ECON
EC.MX
– 5% for more than 8 minutes but
less than 11.5 minutes and mechanical cooling has started
then:
Lo Cool Mode mechanical stages = 2
Hi Cool Mode mechanical stages = 3
6. If the economizer position is greater than
Configuration
ECON
EC.MX
– 5% for more than 11.5 minutes and
mechanical cooling has started then:
Lo Cool Mode mechanical stages = 2
Hi Cool Mode mechanical stages = 3 (for 020 to 027
units only)
Hi Cool Mode mechanical stages = 4 (for 030 to 060
units only)
NOTE: If some compressors are not available due to being
faulted, the Hi Cool Mode number of compressors are affected
before the Lo Cool Mode number of compressors. For exam-
ple, if a 4 compressor unit has one compressor faulted, and the
economizer is not active, then an HVAC mode Hi Cool
requested number of compressors is changed from 4 to 3. If
another compressor faults, then both Lo Cool and Hi Cool
requested number of compressors are set to 2. In addition,
compressors cannot be brought on faster than one every
30 seconds. If the control needs to bring on 2 compressors at
once, the first compressor will come on followed by the second
compressor 30 seconds later. Staging of compressors is shown
in Tables 38-45.
EDT Low Override
— There is an override if EDT drops too
low based on an alert limit that will lock out cooling. If the
supply air/evaporator discharge temperature (EDT) falls below
the alert limit (
Configuration
ALLM
SA.L.O
) cooling will
be inhibited. There is a 20-minute hold off on starting cooling
again once the following statement is true: EDT minus (
Run
Status
COOL
SUMZ
ADD.R
) has risen above
SA.L.O
.
The variable
ADD.R
is one of the SumZ cooling algorithm
control variables dedicated mainly for multi-stage control.
2-Stage Control and the Economizer
— The 2-stage logic will
first check for the availability of the economizer. If free cooling
can be used, then the control will first attempt to use the free
cooling.
If no mechanical cooling is active, and the economizer is
active, the economizer will first attempt to control to a cooling
control point of either the supply air setpoint high (
SA.HI
) or
supply air setpoint low (
SA.LO
) plus any reset applied,
depending on whether High Cool or Low Cool mode is in
effect, respectively.
If one stage of mechanical cooling is on, and the economiz-
er is active, then the economizer will attempt to control to 53 F.
Also If HVAC mode = LOW COOL, the second stage of
mechanical cooling will be locked out.
If the setpoint cannot be satisfied or the economizer is not
active, then cooling will be brought on one stage at a time
when the evaporator discharge temperature (EDT) is greater
the 1.5° F above the current cooling control point. A start-up
time delay of 10 minutes and steady state delay after a
compressor is energized of 5 minutes is enforced.
If both circuits of mechanical cooling are running, then the
economizer will attempt to control to 48 F. If the economizer is
active and the outside-air temperature (OAT) is less than the
cooling control point + 0.5 F, the compressors will be locked
off. When mechanical cooling is on, the control may also use
the economizer to trim the leaving-air temperature to prevent
unnecessary cycles of the compressor stages.
See the Economizer Integration with Mechanical Cooling
section on page 44 for more information on the holding off of
mechanical cooling as well as the economizer control point.
Table 38 — Capacity Control Staging Options —
48/50A020-027 Units VAV and Adaptive CV/SAV Staging Sequence with Variable Capacity Compressor
*On units with optional digital scroll compressor, compressor B1
modulates from minimum to maximum capacity to provide increased
stages.
STAGE
0
1
2
3
COMP
Compressor Status
A1
OFF
OFF
ON
ON
A2
OFF
OFF
OFF
ON
B1*
OFF
ON
ON
ON
UNIT
Unit Capacity 48/50A
020
0%
20 to 40%
50 to 70%
80 to 100%
025
0%
17 to 33%
50 to 66%
83 to 100%
027
0%
17 to 33%
50 to 66%
83 to 100%
Содержание Carrier Weathermaker 48A2
Страница 105: ...105 Fig 20 Typical Main Control Box Wiring Schematic 48 50A2 A3 A4 A5 Units...
Страница 106: ...106 Fig 21 Typical Auxiliary Control Box Wiring Schematic...
Страница 107: ...107 Fig 22 Typical 2 Stage Gas Heat Wiring Schematic Size 060 Units Shown a48 8357...
Страница 108: ...108 TO NEXT PAGE Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown A48 7296...
Страница 109: ...109 Fig 23 Typical Staged Gas Heat Wiring Schematic Size 060 Units Shown cont A48 8358...
Страница 110: ...110 Fig 24 Typical Electric Heat Control Schematic 50 Series Size 060 Units Shown a50 8228...
Страница 111: ...111 Fig 25 Typical Power Schematic 48 50A2 A3 A4 A5 060 Unit Shown...
Страница 112: ...112 Fig 26 Typical Low Ambient Controls Option Wiring...
Страница 113: ...113 Fig 27 Typical Small Chassis Component Location Size 020 035 Units...
Страница 114: ...114 Fig 28 Typical Large Chassis Component Locations Size 040 060 Units...
Страница 118: ...118 Fig 30 Economizer Control Board ECB1 and VAV Control Board ECB2 A48 7706...
Страница 142: ...142 A48 3733 Fig 56 Main Burner Removal...
Страница 176: ...176 APPENDIX C VFD INFORMATION cont Fig F Internal Enclosure Fan Replacement A48 7716...