FB_BA_DHW2P

Functional description

This function block controls the charging (heating) of a hot water tank via an on-off controller. Tank heating is activated at input bEn. If tank heating is active the output bLd is TRUE. The variables rSp is used to transfer the set value for the hot water temperature to the function block. At input rTMin a minimum selection of all temperature sensors for the hot water tank is connected, at input rTMax a maximum selection of all temperature sensors.
Due to the thermal stratification in the hot water tank, the sensor at the top is generally the one showing the highest temperature, the one at the bottom the lowest.

The tank can be charged in two ways via the variables bKepFul:

bKepFul = FALSE

Charging is requested if rTMax falls below the value of rSp-rSpHys. Charging is disabled if rTMin is above the set value of rSp.
Since the sensor at the top generally measures the highest temperature, the heating is not switched on until the hot water tank has been discharged.

bKepFul = TRUE

Charging is requested if rTMin falls below the value of rSp-rSpHys. Charging is disabled if rTMin is above the set value again.
Selecting the minimum of all tank temperatures ensures that the coldest point of the tank is used for control purposes. Recharging takes place when the tank is no longer full.

VAR_INPUT

bEn     : BOOL;
rSp     : REAL;
rSpHys  : REAL;
rTMax   : REAL;
rTMin   : REAL;
bKepFul : BOOL;     

bEn: enable boiler charging

rSp: service water temperature setpoint [°C]

rSpHys: hysteresis, recommended 1°K to 5°K

rTMax: maximum selection of all tank temperatures [°C]

rTMin: minimum selection of all tank temperature sensors [°C]

bKepFul: control temperature selection:

FALSE = rTMax is used to request bLd, rTMin to switch off

TRUE = rTMin alone controls switching on/off of bLd

VAR_OUTPUT

bLd    : BOOL;
rSpOut : REAL;

bLd: enable of the charging mode

rSpOut: setpoint transfer to charging circuit

• rSpOut = rSp (input) if the function block is enabled
• rSpOut = 0 if the function block is not enabled

Requirements