System Balancing - Daikin ARQ Installation Manual

Figure 40: Typical Piping Through Grommets in Back of
Unit

System Balancing

The recommended method, and the one most commonly used, for
balancing a system is called "proportionate balancing." Figure 41
shows a water system consisting of reverse return mains feeding three
branch mains. Branch A and Branch C are designed as reverse returns,
while Branch B is designed as a direct return upfeed riser. Each of the
branch circuits has a balancing valve in the line going back to the system
return main. In addition, each unit has a balancing valve in its return
line. The prescribed method of proporationate balancing is as follows:
1. Open all valves fully.
2. Beginning with Branch A, take readings to determine the
GPM flowing to each unit in the branch.
3. Determine the ratio of the actual/design flow for each of
the coils in Branch A. This is called the proportionate flow
rate. For instance, if Coil A-1 had a design flow rate of 10
GPM and the measured flow rate was 15 GPM, then its
proportionate flow rate would be 1.5.
Figure 41: Typical System Balancing Circuit
Typical water system consisting
of reverse return mains feeding
branch circuits
IM 1083 Self-Contained WSHP Unit Ventilator Models ARQ, ERQ, GRQ
4. Assume Coil A-1 has the lowest proportionate flow rate, A-2 the
next lowest, and so on. Leaving the balancing valve to Coil A-1
wide open, begin to throttle the balancing valve on A-2 until the
two coils have the same proportionate flow within an allowed
tolerance. (This usually is set by the balancing contract at around
5 percent.) Proportionate balance now has been achieved between
these two coils.
5. Proceed to Coil A-3 and establish proportionate balance between
it and Coil A-2 by the same procedure. Coil A-2 need not be read.
It will change in direct proportion to the change in A-2 and will
remain in balance with it.
6. Adjust the balancing valve in Coil A-4 until it is in proportionate
balance with Coil A-3. Likewise, bring Coil A-5 into proportionate
balance with Coil A-4. This is the end of Branch A. All coils on
this branch will be proportionately balanced and any increase or
decrease in the total system GPM, or the branch, will increase or
decrease the GPM at each coil proportionately. They will remain
in balance with one another.
7 By the same process, achieve a proportionate balance of all coils
on Branches B and C.
8. The next step is to balance the branches. To do this, select at random
one coil on each of the three branches. Use the same procedure
as for coil balancing and proportionately balance the branches
against one another, using the selected coils. Note the balancing
valve on the lowest proportionately flowing branch will be left
wide open.
9. The final step in the procedure is to adjust the flow from the pump
to the system to bring all coils to their design flow rate. As was
previously discussed, this can be done by imposing additional
resistnace at the pump by means of a balancing valve and throttling
the system back until the flow rates are equal to those called for
by the design, or decreasing the output of the pump
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