FB_BA_DHW2P

This function block controls the 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 variable rSp is used to transfer the setpoint 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. The charge request is disabled if rTMin is above the setpoint of rSp.
Due to the fact that 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. The charge request is disabled once rTMin is above the setpoint 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 temperatures [°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 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