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The ‘Combined Heat and Power’ template consists of CHP combined with a storage tank and a basic control strategy.

CHP - Basic control

Working principle

The programmable controller controls the CHP. It gives the setpoint to the external PI-controller for controlling the 3-way valve to achieve a certain return temperature. Internally it will enable or disable the CHP and it will calculate the modulation based on the measured return temperature (see figure below).

The CHP is enabled on 4 conditions:

  • Measured return temperature is lower than maximum return temperature.

  • Once the CHP has been disabled the sequence to enable the CHP shall be inhibited for 10 minutes -> check of this timer has run out.

  • Number of starts within 24h is lower than 6.

  • Temperature in TES is lower than 70°C.

 

The CHP is disabled on 1 condition:

  • If the measured return temperature is greater than the maximum return temperature during a specific time, the CHP will be stopped.

Controls

The following settings can be changed by the user in the programmable controller:

  • SetpointReturn = 70;
    (= setpoint return temperature for CHP in °C)

  • ReturnX1 = 70;
    (= return temperature at maximum modulation in °C)

  • ReturnX2 = 75;
    (= return temperature at minimum modulation in °C)

  • MaxReturn = 80;
    (= disabling return temperature for CHP in °C)

  • TimerValue = 600;
    (= delay timer of 10 minutes after disabling CHP)

  • TimeReset = 8640;
    (= counter reset after 24h or 86400 seconds)

  • MaxStarts = 6;
    (= number of allowed starts per 24h)

 

The CHP is released based on 4 conditions:

  • Measured return temperature is lower than maximum return temperature.

  • Once the CHP has been disabled the sequence to enable the CHP shall be inhibited for 10 minutes.

  • Number of starts in 24h is lower than 6.

  • Temperature in thermal store is lower than 70°C.

 

The modulation signal for the CHP is based on the measured temperature as follows:

  • Return temperature < 70°C
    => 100%

  • 70°C < Return temperature < 75°C
    => between 100% and 60% depending on the return temperature, visualised in the figure below

  • 75°C < Return temperature
    => 60%

Notices/Remarks

  • The user should lock the nominal thermal power and return temperature of the CHP. If not, the software will calculate with the propagated power and return temperature from the installation.

  • When using a thermal store, the user should lock the temperature regime of the CHP. If not, the software will calculate with the propagated power and return temperature from the installation.

  • It is possible to upload electrical and thermal efficiency tables, by clicking on the pencil icon. The user can download an example file by clicking on the grey arrow icon. After adjusting this file, the user can upload it back to the CHP by clicking on the blue arrow icon.

  • The user can change the design temperatures, thermal power, end units… But keep in mind that the controls have to be changed as well. This can be done by changing the “settings” in the programmable controller which are listed in the top of the code. After changes in the settings, the correct operation has to be checked again. The user should only change the “settings” and nothing else in the code to make sure the correct control strategy is still valid.

  • If the user changes the power of the end-units, the thermal capacity of the CHP doesn’t change automatically. The user should implement a correct capacity corresponded with the thermal power of the CHP.

More information about the CHP can be found in ​CHP (Combined Heat & Power).

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