Quantcast Flow Rates

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4.3.5 Flow Rates. If a flow meter is in the loop, compare the loop's flow rate with
the rate called for in the system's operation and maintenance manual. If this
information is not available, use Appendix B as a guide to the proper flow rate.
If a flow setter, with ports for measuring differential pressure, is in the loop, follow
the instructions for that unit. Compare the reading to the system's operation and
maintenance manual or Appendix B.
Some manufacturers supply pressure drop information for specific components,
such as collectors or heat exchangers. If pressure gauges or measurement ports
are available, this information can be used to determine flow rates.
The most common use of this technique involves reading the pressure on each side
of the pump when the pump is off, and again when it is operating.
After converting the pressure rise across the pump into feet of head, use the
manufacturer's pump curve, and estimate the flow rates. This technique is
described in greater detail in Section 3.1.4.
An estimate of flow rates can be made from the temperature changes through the
system. Table 4-6 describes some typical design conditions. It assumes a
reasonably sunny day, with storage temperatures of 120F. Collector loop
temperatures are measured at the collector feed and return lines. Storage loop
temperatures are measured at the storage water inlet and outlet at the heat
Remember that the temperatures are affected not only by flow rates, but by the
amount of solar energy striking the collectors as well. Therefore, use these as
rough guidelines only!
In general, the lower the collector loop temperature, the better. At first glance this
may not make sense. However, remember that if heat is being efficiently removed
from the collectors, their temperature will be lower. High outlet temperatures from
the collectors are an indication that too much heat is being left in them or that
collectors are inefficient.


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