System Balancing - Daikin ARQ Installation And Maintenance Manual

Figure 37: 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 38 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.
Figure 38: Typical system balancing circuit
Typical water system consisting
of reverse return mains feeding
branch circuits
IM 1083-3
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.
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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