Zero-flow test: deactivation of base-load pump
In order to prevent the system from hunting, possibly leading to pressure fluctuations, the Comfort Vario controller deactivates the entire pressure boosting system only when there is no water drawn off whatsoever.
The preconditions for this state are established by the so-called zero-flow test as carried out by the Comfort Vario controller.
The minimum requirements are that only the base-load pump is still running and the system pressure and the speed of the base-load pump have remained constant for a specific, parame- terisable timeframe.
The zero-flow test is initiated and performed by the Comfort Vario controller if these require- ments are satisfied. The test involves increasing the setpoint pressure value by 0.1 bar (with set- point pressure values ⱕ 5.0 bar) for 60 seconds. With setpoint pressure values > 5.0 bar, the increase is 2% of the nominal value. After that the setpoint is set back to its original level. If the actual system pressure remains at the increased setpoint level, the pressure boosting system is deactivated as water is no longer being drawn off. However, if the actual pressure drops by a minimum of 0.1 bar relative to the increased setpoint level, the base-load pump continues to operate as water is still being drawn off.
Cut-out of peak-load pumps
When water requirements drop, the peak-load pump in operation is first run down until it no longer has any influence on the hydraulic per- formance of the pressure boosting system. This is the case when, because of the change in speed, its delivery head falls below the setpoint delivery head in the duty point and thus under the power range of the base-load or peak-load pump which up to that point was still running at locked maximum speed.
The Comfort Vario controller will then actuate the transfer of the next peak-load pump or the base-load pump (as applicable) to automatically controlled variable speed operation. The speed of the already run-down peak-load pump will be reduced to the minimum (20 Hz).
The peak-load pump will cut out completely after a time delay of 15 seconds.
If water requirements continue to drop, other still running peak-load pumps will cut out suc- cessively in the same way as described above.
20 40 4 0 0 8 12 60 80 100 120 2 6 10 14 Deliv ery head H [m] 16 Base-load pump Peak-load pump 1 Peak-load pump 2
Setpoint Standby pump
Authorised control range:
Setpoint <_ 5.0 bar = control range ± 0.1 bar Setpoint >_ 5.0 bar = control range ± 2 % of the setpoint
Volume flow Q [m3/h]
- Lowering of the speed of the peak-load pump - Transfer of control function to the base-load pump - Lowering of the speed of the peak-load pump to 20 or 26 Hz - Switch-off of the peak-load pump after 15 seconds Cut-out of peak-load pump
20 40 4 0 0 8 12 60 80 100 120 2 6 10 14 Deliv ery h ead H [m] 16 Base-load pump Peak-load pump 1 Peak-load pump 2
Setpoint Standby pump
- Lowering of the speed until speed and pressure constant - Then zero-flow test
- Cycle time 60 sec.
Volume flow Q [m3/h]
Increase of setpoint by 0.1 bar or by 2 % of setpoint
Reset of setpoint back to the previously set standard Zero-flow test: deactivation
System functions without frequency converter
During operation without a frequency converter, the system's operating range is between the switch-on level pONapplicable to all the pumps and the switch-off pressure level pOFF2for a) the base-load pump and
b) the switch-off level pOFF1for the peak-load pumps.
Once the 2nd switch-off pressure level (pOFF2) and a minimum run time of 0–180 seconds have been attained, the system is switched off at almost Q = 0 m3/h. As a result, pressure surges
and unnecessary switching on and off of the system for minimal extraction amounts is reduced to the greatest extent possible.
The base- and peak-load pumps are activated when the preset setpoint pressure level pONis reached.
2nd switch-off pressure level (freely adjustable) for the base-load pump
1st switch-off pressure level (freely adjustable) for the peak load pump(s)
p
OFF
p
OFF2
System head curve
3 Switch-on pressure level pON 2 1 Deliv e ry head H [m] Volume flow Q [m3/h]
System functions without frequency converter
System functions with frequency converter
When used with a frequency converter, the operating range of the unit will remain at set- point value. Only on reaching the 100% speed limit of each operating pump will the pressure fall to the switch-on level pONfor cut-in of the next (peak-load) pump. The same applies to cut- out of peak-load pumps: the pressure will only rise to the required switch-off level pOFFon
reaching the 100% speed limit. Any excessive pressure surges due to switching the peak-load pumps on or off will be mainly compensated for by the frequency converter lowering or raising the speed of the base-load pump, thus ensuring a soft transition in line with load variations commonly encountered in building services.
The pressure boosting system switches on without delay when the system pressure drops to the switch-on pressure level pON, with the base-
load pump starting softly under control of the frequency converter.
The pressure boosting system is switched off by means of the processor at Q = 0 m3/h. Fluid
hammer caused by immediate switch-ons fol- lowing premature switch-offs is thereby fully eliminated.
Switch-on pressure level, peak-load pump pON
Switch-off pressure level, peak-load pump pOFF
Setpoint System head curve
3 2 1 Deliv ery head H [m] Volume flow Q [m3/h]
System functions with frequency converter