FB_BA_RcvMonit

The function block is used for calculating the efficiency of an energy recovery system.

The function block requires the following measured temperature values for calculating the efficiency (heat recovery rate):

• Outside air temperature rTOts
• Exhaust air temperature rTExh
• Air temperature of the energy recovery system in the inlet air duct (alternatively: in the outlet air duct) rTAftRcv

The function block logs the temperature values every 10 seconds and forms minutely averages from 6 consecutive values. The results are used to check whether the plant has reached a "stable" state.

• This is the case when the recorded temperatures of outside air, exhaust air and air after energy recovery are almost constant, i.e. none the 6 individual values deviate by more than 0.5 K from the respective mean value.
• The temperature difference between outside air and exhaust air is at least 5 K.

If this is the case, this measuring cycle is acknowledged with a TRUE signal at output bStblOp, and the calculated efficiency is output at rEffc. If the state is not "stable", a FALSE signal appears at output bStblOp, and rEffc is set to 0.

In any case, each measuring and analysis cycle is marked as completed with a trigger (a TRUE signal lasting one PLC cycle) at bNewVal.

Enable (bEn) and Reset (bRst)

The function block is only active if a TRUE signal is present at bEn. Otherwise its execution stops, and all outputs are set to FALSE or 0.0.

An active measuring and evaluation cycle can be terminated at any time by a TRUE signal at bRst. All outputs are set to FALSE or 0.0, and the measuring cycle restarts automatically.

Selection of the temperature value "after recovery" (bSnsRcvTExh)

A FALSE entry at bSnsRcvTExh means that the temperature measurement after the heat recovery in the supply air duct is used for calculating the efficiency.
To use the temperature measurement after the heat recovery in the exhaust air duct, TRUE must be applied at bSnsRcvTExh.

Limit violation (rContrVar, rLmtEffc, bLmtRchd)

A limit violation has occurred, if the calculated efficiency is less than the specified limit value rLmtEffc, and at the same time the control value for the heat recovery is at 100%. To this end the control value must be linked to input rContrVar.
The limit violation message can be delayed by an entry at udiLmtVioDly_sec [s]: If the two criteria, violation and override, are met for longer than udiLmtVioDly _sec [s], this is indicated with a TRUE signal at bLmtRchd.
A warning message, which may have occurred, is canceled if a complete measuring cycle provides "good" values, or with a rising edge at bRst or deactivation of the function block.

This warning message only occurs if the plant is in a stable operating mode (bStblOp=TRUE).

Taking into account the temperature increase of the outlet air due to the fan motor (rTIncFan)

It is possible that the outlet air is warmed by a fan motor, resulting in distortion of the measurement. This temperature increase can be specified through rTIncFan. Internally, the measured outlet air temperature is then reduced by this value.

VAR_INPUT

bEn               : BOOL;
bRst              : BOOL;
rContrVar         : REAL;
rTOts             : REAL;
rTExh             : REAL;
rTAftRcv          : REAL;
bSnsRcvTExh       : BOOL;
rTIncFan          : REAL;
rLmtEffc          : REAL;
udiLmtVioDly_sec  : DINT;

bEn: Function block enable.

bRst: Reset - all determined values are deleted.

rContrVar: Control value for the heat recovery, i.e. the actual value.

rTOts: Outside temperature.

rTExh: Exhaust air temperature.

rTAftRcv: Temperature after energy recovery.

bSnsRcvTExh: Temperature at the measuring point after energy recovery: FALSE -> in inlet air duct (SupplyAir) - TRUE -> in outlet air duct (ExhaustAir).

rTIncFan: Temperature increase due to fan.

rLmtEffc: Limit value efficiency.

udiLmtVioDly_sec: Limit violation delay [s]. Internally limited to a minimum value of 0.

VAR_OUTPUT

bNewVal      : BOOL;
rEffc        : REAL;
bLmtRchd     : BOOL;
bStblOp      : BOOL;

bNewVal: Output trigger for new value rEffc.

rEffc: Efficiency

bLmtRchd: Limit value reached

bStblOp: Stable operation.

Requirements