Why a Closed-Loop Cooling System?

1. Open-loop cooling tower water is exposed to airborne contaminants (dust, dirt, algae/biological organisms).

            »  This is then transported to the heat exchanger, where fouling can jeopardize proper heat transfer performance.

2. Closed-loop recirculating coolant can be aqueous glycol solution.

            »  This assures that freezing will never occur anywhere within the closed-loop.

3. WSAC systems can still be located remotely from the intercooler/facility.

4. Open-loop water on the WSAC system virtually freeze proof.

            »  Only when zero load conditions exist can there be any freezing. This is easily protected against using small

                immersion heaters to maintain a demand-ready system.

5. Temperature control using closed-loop is more assured.

Simple RTD monitoring of outlet fluid temperature can be combined with logic control of fans to effectively modulate heat rejection capacity of the WSAC unit. VFDs can be supplied for even better temperature set-point control during fluctuating ambient conditions. Inlet vs. outlet temperature monitoring (delta T – cooling range) can permit capacity control functions to further improve response times (set point control).

By contrast, cooling tower (CT) temperature control is more temperature-range limited with higher transient response times due to large volume of water in the circulating loop. Fan control will only be effective at capacity control at high-range of wet bulb conditions. At low ambient conditions, a CT will still evaporate a certain percentage of water even with fans cycled off. Thus, the water temperature will continue to ramp down if not balanced by heat load from the plant. Complete tower bypass yields pump head inefficiencies unless VFD control of pumps is provided.

Freeze protection of CT loop is large concern due to large volume of water contained in the system. KW consumption may become copious to maintain a thawed basin condition.

6. Closed-loop, evaporative coolers consume less parasitic energy that CT for same heat rejection. Typical fan horsepower reduced by 10-25%. Typical pumping horsepower reduction of 10-40%.

7. Water savings.

WSAC systems can operate at higher cycles of concentration leading to lower make-up and blow-down rates. This represents best use of water for facility water balance.

WSAC systems can be designed to allow cooling capacity without evaporation of water (wet/dry system). Finned tube bundles, spray water zone cycling are both viable options to consider. Water conservation is the big benefit of these upgrade options. This is not possible with a CT cooling system.

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