Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 100

end excess flow due to high water pressure and timers with auto-
matic shut-off limit disposal over-operation. A solenoid valve can
also be used to control water flow to the disposal.

• Recirculating hot water systems, typical for most larger non-resi-

dential applications, are the source of energy loss (both heat loss in
the piping and pumping energy required for water circulation), but
typically reduce water waste. To reduce the energy burden imposed
by the recirculating systems, pumps should be turned off during
unoccupied periods and low low restrictors installed on each hot
water outlet.

• For both cooling towers and boilers, the amount of blowdown for

deposition control can be minimized by using automatic water
treatment systems. For automatic blowdown control, the blowdown
requirement is determined by measuring the boiler water electrical
“conductance,” a measure of the amount of conductive solids in the
water, since pure water has zero conductance. The recommended
boiler water conductance level for HVAC boilers operating at less
that 350 psig is 3500 mega-mho/cm or less, where a “mho” is the
conductive equivalent to an “ohm” of resistance. For cooling tow-
ers, the water conductance setpoint must be determined based on
the water chemistry.

• For cooling towers and evaporative condensers, the term cyclesof

Table 4-5. Blowdown Cycles of Concentration vs.
Make-Up Water Requirements
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GPM/Ton %

Make-up
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2 0.0300 0.0300 0.0600 100
3 0.0300 0.0150 0.0450 75
4 0.0300 0.0100 0.0400 67
5 0.0300 0.0075 0.0375 63
6 0.0300 0.0060 0.0360 60
10 0.0300 0.0033 0.0333 55
15 0.0300 0.0023 0.0323 54
20 0.0300 0.0015 0.0315 53
————————————————————————————————

Cycles Evaporation Blowdown Make-up