Differential Pressure Control In Heating/Air-Conditioning Installations; Pressure Control In Pressure-Boosting Installations P-C; Normal Operation - Wilo MVI 2..-6 Betriebsanleitung

Differential pressure control in heating/air-conditioning installations:

Adaptation of the installation to the constantly changing power requirements by altering the bulk current as a result of the speed control of the
base-load pump.
Pressure difference between forward and reverse, measured at central points of the circuit, is kept as constant as possible. Measurement
sensor is the differential pressure sensor. Gives signal to controller. Controller keeps differential pressure constant by setpoint/actual value
comparison over permissible feed current range.
Advantages: constant, stable conditions and good controllability of hydraulic system, especially with regard to controlling branch circuits.
Energy saving, low wear-and-tear on pumps, no flow noise.
p-c Differential pressure constant,
is picked up between two points of the installation.
Differential pressure is kept constantly at reference setpoint Wi over permissible delivery flow range (figure 8 a).
Control of single- and multi-pump operation possible.
2 different setpoints Wi1 and Wi2, e.g. for day and night operation, are to be set in the controller menu.
p-c Differential pressure volume-superimposed,
= f(Q)
is tapped before and after circulating pump. Compensation of pipework losses not recorded by fact that actual value follows a setpoint
[m 3 /h]
which rises with the flow rate (figure 9 b). Rise in setpoint is initiated by signal from a bulk current sensor to be provided by manufacturer,
and is assessed by the controller.
Control applicable for single- and multi-pump installations.
Advantage: No long lines for differential pressure measurements.
p-v Differential pressure variable: variant of p-c = f(Q)
Instead of flow-rate indicator of internal control signal (proportional to speed) of the controller for frequency converter. Is approximately
proportional to the bulk current (figure 9 a).
Advantage: No flow-rate indicator necessary. Only applicable with single-pump installations.
p-c = Differential pressure constant: is adapted linearly according to a superimposed reference variable, here outside temperature
f(T ) (figure 10 a).
A
For installations in which the differential pressure is not available as a variable to be controlled, the temperature can be used as the fundamental
operating parameter of the installation.
By adapting the hydraulics to the system it is possible to save energy, reduce wear-and-tear on the pumps and cut out flow noise.
n = f(T) Speed dependent on temperature: the speed of the pump is controlled via a linear sensitivity, e.g. by the outside temperature.
Only applicable to single-pump operation (figure 10 b).
T Differential temperature constant: between flowpipe and return of an installation. Fluctuations in heat consumption are
compensated for by changing the heat flow as a result of a change in pump speed (figure 10 c).
Pressure control in pressure-boosting installations
p-c Pressure constant:
Electronic pressure sensor provides actual system pressure value.
The controller keeps pressure constant by setpoint/actual value comparison over permissible delivery flow range (figures 7a/7 b).
4.1.4 Operating modes of the installations
Heating/air-conditioning installations

Normal operation

The first pump to start up and the one with a variable speed is the base-load pump. If in multi-pump installations the power required by the
system cannot be covered by the base-load pump, the controller connects a peak-load pump or additional pumps one after the other if the
power requirement continues to rise. The peak-load pumps run at constant speeds, whereas the base-load pump is always set to the setpoint.
Base-load pump operates at all times, except in case of
– faults,
– "External Off",
– during a setpoint change-over.
Pressure-boosting installations
Base-load pump operates at all times except in case of
– faults,
– "External Off",
– during a setpoint change-over
– zero-quantity switch-off due to lack of need.
In installations without an FC the base load is disconnected once the
maximum permissible level has been exceeded and after a set time
and immediately re-connected if the minimum level is fallen short of.
In installations with an FC the nominal frequency of the convertor is
reduced by 5 % if the pressure remains constant for more than 180 s.
If there is no change in pressure as a result of the resultant drop in the
speed of the base-load pump, the delivery rate is 0, and the pump is
switched off. If the pressure drops 5 % below the setpoint the base
load is re-activated.
ENGLISH
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