Fig. 24 - Cv Space Sensor Stepped Heat Algorithm - York eco2 050 Installation Operation & Maintenance

Sequence of Operation
When the space temperature is 1.5
the Economizer 1 stage or Economizer 2
st
point, destaging compressors is accomplished by tempo-
rarily requesting an SAT setpoint of 90
assures that ere is no need for compressors even at the
hightest outdoor air temperature and/or enthalpies.
Note that the destaging process still occurs in cooling
state, so there is no possibility of heating being ac ti vat ed
due to the temporarily high SAT setpoint, or due to
space temperature dropping below its cooling set point
and towards space heating setpoint.
Staging of Compressors When Exiting
Economizer Mode
This situation occurs when one, or more compressors
are running in the economizer mode, and free cooling
becomes unavailable. The sensor control mode chang es
– sensor algorithm is no longer selecting the active econ-
o miz er SAT setpoints, but now is used to directly control
the compressors. The control mode changeover process
involves turning off the com pres sors that were running
during the economizer op er a tion, and then turn ing back
on the compressors needed during mechanical cooling
only. The compressors will continue to operate until
the minimum run time criteria has been met.
Heating Operation With a Space Sensor
For Heating operation, the space temperature will be
controlled to either the Unoccupied Heating Setpoint or
the Occupied Heating Setpoint based on the Occupied/
Unoccupied state of the unit (i.e. Occ/Unocc Input, or
Internal Scheduling).
Heat Step
Stays OFF
OFF-Time
OFF-Time
(minutes)
Min.
ON-Time
(6 minutes)
0%
Output of Cooling Zone
Temp. Control (PI)
Low Saturation
FIG. 24 – CV SPACE SENSOR STEPPED HEAT
ALGORITHM
56
F or more less than
0
Stage set
nd
F. This setpoint
0
Heat Step
Stays ON
ON-Time
On-Time
(minutes)
Min.
OFF-Time
(6 minutes)
100%
High Saturation
LD06555
Control Algorithm For Space Sensor Stepped Heat
• The Space Sensor Stepped Heat control algorithm is
as illustrated in Figure 22. The controller will read
the number of Heat Steps parameter to de ter mine
the heat steps available. Heat steps will be used in
number se quence.
• A direct acting, proportional – integral space tem-
per a ture controller generates a 0 – 100% output
signal that responds to space heating demand.
• The output of the controller is used to calculate on
and off time of the heat step most recently started
based on the calculation method in Figure 22.
• PI gain values are to be determined by such that all
heating steps are on within 42 minutes with a 10°F
space temperature error.
• When the duty cycle reaches 100% (the PI algorithm
reaches a "High Saturation state" and a saturation
time delay expires), the modulated heating step
stops cycling and remains on.
• An additional heating step is started every time the
space control PI algorithm reaches a high satura-
tion state and a programmed saturation time delay
expires.
• A heating step is stopped when the PI algorithm
reaches a Low Saturation state and a programmed
saturation time delay expires.
Control Algorithm For Space Sensor Hydronic
Heat
In CV heating operation using hydronic heat, the SAT
is controlled by algorithm as shown in Figure 23.
Table 16 details the modes of CV operation and provides
an overview of the control methods in all modes.
Hydronic Heat
2nd Stage
SAT Setpoint
Hydronic Heat
1st Stage
SAT Setpoint
Zone Satisfied
(No Heat)
-1.5˚F
Space Temperature Deviation From Setpoint (˚F)
FIG. 25 – CV SPACE SENSOR HYDRONIC
HEAT ALGORITHM
FORM 100.50-NOM1 (604)
+0.5˚F +2.0˚F
Zone Temperature
Setpoint For Heating
LD06556
YORK INTERNATIONAL