Outside Air Temperature Compensated Control

The mixed water temperature setpoint depends on the:

Optionally the mixed water temperature setpoint can be compensated by the room temperature control deviation. This can happen only if no heating curve adaptation is configured HCA-04 = 4. Room temperature compensation and heating curve adaptation are not compatible.

The mixed water temperature setpoint is calculated according to the formula:

CalcMWTempSp = Heating Curve Setpoint + RMT-01 * FADAPT * (RoomTempSp +/- CPA – Room Temperature)

Heating Curve Setpoint = HC (RoomTempSp +/- CPA, FilteredOATemp, HCA-01, HCA-02)

CalcMWTempSp = 0, for total cool down

FADAPT = 1; if HCA-01 = [4]

FADAPT = 0; if HCA-01 = [0; 1; 2; 3]

CPA is the control point adjustment set with the wall module's setpoint potentiometer.
RMT-01 = room temperature compensation factor


Any kind of start or stop optimization requires a time program for the room temperature setpoint.

Note: during heating curve adaptation, we do not compensate the mixed water temperature setpoint with the room temperature control deviation.


Mixed water temperature setpoint calculation with outside air temperature reset

The heating curve considers the following facts:

The colder the outside air temperature, the more heating energy is needed and the higher the mixed water temperature has to be. This happens due the heat losses of the building, which are higher the bigger the temperature difference between the room and the outside air temperatures are. Each building behaves differently, this behaviour depends on the:

The conclusion is that the required heating energy depends on outside temperature and building characteristic. The building characteristic is optimally represented by a heating curve. Each building has a specific curve defined by slope and curvature. If the room temperature setpoint rises e.g. by 5 K (+/- CPA) control point adjustment, the demand to the boilers is increased accordingly still considering the building characteristic. The set of heating curves is moved along the inclined room temperature axis as shown in the next figure:

Fig. 1.   Heating curve

During occupied periods the mixed water temperature setpoint is calculated using the heating curve. The heating curve curvature, the heating curve slope and the heating curve slope limit are defined by the settings shown in the next table.

Table 1.   Parameter List

Description

Value Range

Default Value

Unit

RMT-01: room temp. compensation factor

0…50

4

K

HCA-01: heating curve curvature

1,0...2,0

1,33


HCA-02: heating curve slope

0...4,5

1,6


HCA-03: heating curve slope limit

0...4,5

2,0



Un-occupied Period

With the parameter SYS-01 occupied/ un-occupied changeover, the user can decide whether he wants to run the heating circuit with night setback or with total cool-down.

If the room temperature setpoint is higher or equal than SYS-01, the mixed water temperature is controlled by the room temperature setpoint, otherwise it is set to 0.

Table 2.   Parameter List

Description

Value Range

Default Value

Unit

SYS-01: occupied/ un-occupied changeover

0…50

16

°C


Total cool-down is possible only if one of the following conditions is true:

Fig. 2.   Heating circuit control modes

The next picture shows an example of a heating circuit with total cool-down and a heating circuit with night setback control with optimum start / stop. The high mixed water temperature setpoint shows the boost heating during optimum start. The "0" setpoint during the occupied period is the optimum stop.

During total cool-down the room temperature setpoint of the time schedule has to be lower than the setting SYS-01 (16°C default)

T2boost is the mixed water temperature setpoint during optimum start with room temperature – see chapter optimum start.

Fig. 3.   Transition from un-occupied to occupied mode with optimization

The next picture shows an example of a heating circuit with total cool-down and a heating circuit with night setback control without optimum start / stop.

During total cool-down the room temperature setpoint of the time schedule has to be lower than the setting SYS-01 (16°C default)

Fig. 4.   Transition from un-occupied to occupied mode without optimization

Fig. 5.  un-occupied mode flow temperature control with/ without roomsensor