Currently, the loop is operating according to the pump performance curves
below:
Often times, capacity changes will require that the
cooling loop flow be increased or decreased. Traditionally, single speed pumps would
require that the system curve be altered to change the flow. For example, if the
loop flow is to be decreased to 10 L/s, the FIC valve must offer more resistance to change
the system curve as seen below:
Let's think for a moment. We are now requiring
less work from the pump, but the pump is using the same amount of power. This is
where variable speed pumps come into play. Rather than increasing the loop
resistance, the pump speed is just decreased. In the past, the additional costs
associated with variable speed pumps made them less attractive. Now that they have
become more affordable, the energy savings and maintenance cost reduction with a variable
speed pump can actually make them less expensive over the life of the pump. With a
variable speed pump, the pump curve, rather than the system curve is altered to obtain the
necessary flow.
While variable speed pumps are not necessary for all
applications, it can be very beneficial in many applications. Give your valves and
your pumps a break, don't make them do work that isn't necessary.
References:
Turley, Roger S., "Variable Speed Pumping Benefits", Chemical Processing,
December 1998, p. 27-30.
