Zero Energy Band

Function

Zero Energy Band calculates the setpoints to maintain a predetermined comfort zone divided into heating, cooling, and zero energy bands. Zero Energy Band subdivides a predetermined comfort zone into:


The zero energy band represents a temperature range in which the room temperature may vary without a need for heating or cooling energy.


Setpoint optimization results in demand-related setpoint control (cascade* input) of the central air conditioning plant as a function of the individual room loads to use the lowest possible energy requirements outside the zero energy band.


*The term “cascade” implies that the outputs of this function are to be used as inputs for another controller.


Operation

The following diagram illustrates ZEB operation


Zero Energy Band Mixed Air Operation

When the parameter ZEB/ Load reset mode (P6) equal to 1 (Zero Energy Band), the application calculates the mixed air damper setpoint as follows.


If all three zone temperatures (“In HighestZoneTemp”, “In LowestZoneTemp” and “In AvgZoneTemp”) are within the zero energy range, Zero Energy Band controls the temperature only through the mixed air dampers. The average zone temperature (“In AvgZoneTemp”) is the determining factor for the calculation of mixed air setpoint.

Zero Energy Band generates a setpoint at “Out MixedAirSetpoint” as follows:

“Out MixedAirSetpoint” = P5, if “In AvgZoneTemp” > “In RoomTempSp” + P1

The mixed air setpoint is limited to the minimum mixed air setpoint, when the average zone temperature is at the upper end of the zero energy range.

“Out MixedAirSetpoint”= P5 + P11, if “In AvgZoneTemp” < “In RoomTempSp” - P1

The mixed air setpoint is limited to the sum of minimum mixed air setpoint and mixed air reset range, when the average zone temperature is at the lower end of the zero energy range and when the highest and lowest zone temperatures are within the zero energy range.

Inside of the zero energy band, the mixed air setpoint will have a linear dependence of the average zone temperature and will be limited by the minimum and maximum setpoint as described before.

“Out CoolingSetpoint” = P5 + P11 – P11/ (2*P1)*(“In AvgZoneTemp” - “In RoomTempSp” + P1)


Example:


Zero Energy Band Cooling Operation

When the parameter ZEB/ Load reset mode (P6) equal to 1 (Zero Energy Band), 3 (Cooling control), or 4 (Heating and cooling), the Zero Energy Band energy management function calculates the cooling setpoint as follows.


If the warmest zone temperature sensor value gets higher than the Zero Energy Band upper limit, cooling will be enabled. Cooling will maintain the cooling setpoint, “Out CoolingSetpoint”. To calculate the cooling setpoint, the maximum zone temperature sensor at the input “In HighestZoneTemp” is mandatory. Then the cooling setpoint is calculated based on a linear relationship with “In HighestZoneTemp” and sent to output “Out CoolingSetpoint”.


If the highest zone temperature is at or above the upper limit of the cooling band, then the minimum (lowest) cooling setpoint, P3, is used. This upper cooling band limit is specified by adding 3 times the comfort range, P1 (typically set to 4 K), to the room temperature setpoint (“In RoomTempSp”):

“Out CoolingSetpoint” = P3, if “In HighestZoneTemp” > “In RoomTempSp” + (3*P1)


If the highest zone temperature is at or below the lower limit of the cooling band, an offset called the “Cooling reset range” (P10) is added to the minimum cooling setpoint, P3, and this sum is used for the cooling setpoint, “Out CoolingSetpoint”. The lower cooling band limit is specified by adding the comfort range, P1, to the room temperature setpoint, “In RoomTempSp”:

“Out CoolingSetpoint” = P3 + P10 if “In HighestZoneTemp” < “In RoomTempSp”+ P1


When the highest zone temperature is inside the cooling band, the cooling setpoint, “Out CoolingSetpoint”, is calculated with the following formula:

“Out CoolingSetpoint” = P3 + P10 – P10/ (2*P1)*(“In HighestZoneTemp”-“In RoomTempSp” – P1)

Inside of the zero energy band, the mixed air setpoint will have a linear dependence of the average zone temperature and will be limited by the minimum and maximum setpoint as described before.


If the highest zone temperature sensor value is in the cooling band area (or higher), cooling will be enabled (“Out CoolingEnable” is set to 1).

Example:

Zero Energy Band Heating Operation

When the parameter ZEB/ Load reset mode (P6) is equal to 1 (Zero Energy Band), 2 (Heating control), or 4 (Heating and cooling), the application also calculates the heating setpoint as follows.


If the lowest zone temperature falls below the zero energy range, Zero Energy Band linearly increases the heating setpoint “Out HeatingSetpoint”. The minimum zone temperature “in LowestZoneTemp” is the determining factor for the heating and the calculation of the heating setpoint.

“Out HeatingSetpoint” = P4, if “In LowestZoneTemp” < “In RoomTempSp” - (3*P1)

This relationship means that the maximum heating setpoint (P6) is demanded when the lowest zone temperature is at or below the lower end of the heating range.

“Out HeatingSetpoint” = P4 –P9, if “In LowestZoneTemp” = “In RoomTempSp – P1

The maximum heating setpoint (P4) minus the heating reset range (P9) is demanded when the lowest zone temperature just falls below the zero energy range.


If the lowest zone temperature is in the heating range or lower, Zero Energy Band enables heating and assigns 1 to “Out HeatingEnable”.


Example:


Zero Energy Band Dehumidification

When the Zero Energy Band/Load reset mode parameter P6 is equal to 1 (Zero Energy Band), 3 (Cooling control), or 4 (Heating and cooling), the application also includes dehumidification as follows:


If the humidity measured by the “in Rel.orAbs.AirHumidity” sensor exceeds the value of P8 (Room humidity limit), Zero Energy Band initiates cooling. Relative humidity is the determining factor for cooling.


If you select an absolute humidity sensor in the parameters P2, Zero Energy Band performs a conversion to relative humidity.


To monitor humidity, select P7 Humidity sensor connected = true in the property sheet of the statement.


Note that with Heating and cooling applications (Zero Energy Band/Load reset mode equal to 4), Zero Energy Band only initiates cooling. This option does not inactivate heating. Cooling condenses moisture in the air so that it can then be removed. Because heating is still active, a downstream air heater can bring the air to the required temperature again.


With the Zero Energy Band application (Zero Energy Band/Load reset mode equal to 1), cooling takes place with a simultaneous inactivation of heating. In addition, the mixed air dampers setpoint will be activated and calculated depending on the maximum zone temperature.


With the Cooling control application (Zero Energy Band/Load reset mode equal to 3), when air humidity exceeds the allowable value, Zero Energy Band only initiates cooling.



Fig. 206.   Wire-sheet Icon

Fig. 207.   Property Sheet

Fig. 208.   Slot Sheet

Inputs and Outputs

Table 129.   Inputs

Inputs

Type

Functional description

In HighestZoneTemp

numeric

Highest zone temperature

In LowestZoneTemp

numeric

Lowest zone temperature

In AvgZoneTemp

numeric

Average zone temperature

In Rel.orAbs.AirHumidity

numeric

Relative or absolute air humidity

In RoomTempSp

numeric

Room temperature setpoint

In Enabled

boolean

If the input “In Enabled” is set to false disabled in the slot sheet, the output “Out” will be disabled and is set to the value “0”.


Table 130.   Outputs

Outputs

Type

Functional description

Out HeatingEnable

boolean

Heating system enable/ disable digital output

1 = Enable,

0 = Disable

Out CoolingEnable

boolean

Cooling system enable/ disable digital output

1 = Enable

0 = Disable

Out HeatingSetpoint

numeric

Heating setpoint

Out CoolingSetpoint

numeric

Cooling setpoint

Out MixedAirSetpoint

numeric

Mixed air damper setpoint

The three setpoint outputs can be used as be input variables to external controllers.


Parameter List

Table 131.   Parameter List

Description

Value Range

Default Value

Unit

P1 Comfort range

This value defines the width of the heating, cooling, and zero energy ranges. The width of each range is two times this value. All ranges are equally wide. The zero energy range is located symmetrically around the setpoint X5. The cooling range is located immediately above the upper limit of the zero energy range. The heating range is located immediately below the lower limit. See the Operation diagram later in this section.

0…30

2

K

P2 Humidity sensor type

0= Absolute Humidity

1= Relative Humidity

0/ 1

1

-

P3 Minimum cooling setpoint

This is the lowest allowable discharge air setpoint during cooling.

5   27

13

°C

P4 Maximum heating setpoint

This is the highest allowable discharge air setpoint during heating.

10…60

35

°C

P5 Minimum mixed air setpoint

Lowest mixed air, or discharge air setpoint while in the ZEB range.

5   32

13

°C

P6 ZEB/ Load reset mode

1 = ZEB (Zero energy band)

2 = Heating control setpoint

3 = Cooling control setpoint

4 = Heating and cooling control setpoint

1…4

4

-

P7 Humidity sensor connected

0 = false

1 = true

0/ 1

1

-

P8 Room humidity limit

0…100

65

%

P9 Heating reset range

15…25

15

K

P10 Cooling reset range

0…20

6

K

P11 Mixing reset range

0…25

7

K