Danfoss VLT 6000 HVAC Manual de servicio descargar pdf (Pagina 23)

VLT

6000 HVAC

23MG.60.B1.02 - VLT is a registered Danfoss trademark

Introduction to

HVAC

■■

■ Secondary pumps

Secondary pumps in a primary/secondary chilled

water pumping system are used to distribute the

chilled water to the loads from the primary production

loop. The primary/secondary pumping system is used

to hydronically decouple one piping loop from

another. In this case. The primary pump is used to

maintain a constant flow through the chillers while

allowing the secondary pumps to vary in flow,

increase control and save energy.

If the primary/secondary design concept is not used

and a variable volume system is designed, when the

flow rate drops far enough or too quickly, the chiller

cannot shed its load properly. The chiller’s low

evaporator temperature safety then trips the chiller

requiring a manual reset. This situation is common in

large installations especially when two or more chillers

in parallel are installed.

■■

■ The new standard

While the primary-secondary system with two-way

valves improves energy savings and eases system

control problems, the true energy savings and con-

trol potential is realized by adding VLT frequency

converters.

With the proper sensor location, the addition of VLT

frequency converters allows the pumps to vary their

speed to follow the system curve instead of the pump

curve.

This results in the elimination of wasted energy and

eliminates most of the over-pressurization the two-

way valves can be subjected too.

As the monitored loads are satisfied, the loads two-

way valves close down. This increases the differential

pressure measured across the load and two-way

valve. As this differential pressure starts to rise, the

pump is slowed to maintain the control head also

called setpoint value. This setpoint value is calculated

by summing the pressure drop of the load and two

way valve together under design conditions.

NB!

Please note that when running multiple

pumps in parallel, they must run at the same

speed to maximize energy savings, either with

individual dedicated drives or one drive running

multiple pumps in parallel.

CHILLER

∆P

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Danfoss VLT 6000 HVAC Manual de servicio Pagina 23

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