3. Multiple Fan Coil Units: Indirect Flowrate Measurement
Pressure
gauges
Supply
Return
FCU 1
FCU 2
FCU 3
The objective is the still the same, i.e. to measure the flow rate through each fan coil unit.
However, in this example, the pressure drop across each fan coil unit is measured and the flow
rate is then obtained indirectly from the fan coil water pressure drop performance charts. See
Appendix 19 for an example.
Such charts are available from the Technical Manual of the fan coil units.
Again, adjustments can be made to the flowrate by using the throttling valves in accordance to the
design specifications.
For both example 2 and 3, the balancing can be counter-checked by measuring the water
temperature difference between the entering and leaving. A result of 4 - 5 °C is expected.
3. Temperature measurement
In the absence of all the flowmeters, pressure gauges and balancing valves, the only possible
way to do a simple balancing is by measuring the water temperature difference between the
entering and leaving. A reading of 4 - 5 °C is then used as an indication of sufficient balancing.
However, this method is not so accurate due to several reasons:
a. The temperature difference is dependent on the entering air temperature.
Usually, colder air produces a lower temperature difference due to a lower loading.
b. The temperature difference is dependent on the amount of air flowing through the coil heat
exchanger. Lower air volume gives a higher temperature difference.
Section 13 Page 148
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