MHS Boilers Ultramax 115, Руководство по эксплуатации и техническому обслуживанию, Страница: 25 / 46

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Table 8 Water flow rate and pump data
* The maximum power consumption of the pump is given for pump speed 3. The optimum operating point in
relation to efficiency and minimum power consumption can be determined from the related pump curve
** 3-phase pump available.
Pumps supplied by others.
The primary pump must be sized to have an optimum duty when ∆T = 22 K. When running
at ∆T’s less than this the pump size should be checked to ensure suitability.
The water flow rate can be measured by making a ∆P measurement via the filling and drainage valve
in the supply and return pipe of the unit. The measured head can be compared with the boiler
resistance (table 8). At full capacity the water flow rate can be very accurately compared with the ∆T,
measured across the flow and return of the boiler.
The unit has a standard pump control. When the boiler is enabled, the pump is switched on. When
the enable signal is removed, the pump will continue to run for several minutes. This run on time
is adjustable. The standard time is two minutes.
When the system includes air heaters (ventilation, air treatment), it is usually desirable to have a
small ∆T over these components. Because of this, the quantity of water flowing through the total
secondary circuit is usually greater than that flowing through the boiler units.
The low velocity header must be dimensioned such that the
water speed does not exceed 0.5 m/s
.
In this case the diameter of the header must be calculated for the water volume flowing through
the secondary circuit. When the water volume flowing through the secondary circuit is greater
than that flowing through the primary circuit, a mixed temperature will exist which is lower than
the desired temperature of the supply from the appliance. The regulation system reacts to this
and opens the control devices (valves, etc.). Usually the supply temperature from the boiler(s)
must be adjusted to obtain the desired temperature in the connected circuits.
For additional energy savings a speed controlled pump should be considered.