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scaled vs unscaled media
    Unscaled (left) vs Scaled Media (right)

  • new unscaled media is shown on the left
  • client's scaled media - recirculating cooler after one cooling season

AZFlow coolers and Reduced media scaling and water savings

Patented AZFlow water distribution onto the cooling media is significantly different from that of recirculating coolers delivering significant performance and maintenance benefits.

In recirculating coolers, a sump is used to capture unevaporatived water as it returns from the media and combine this with makeup water added through a float valve connected to potable water system to maintain sump level. A submerged pump is located in this sump and pumps the mixture of fresh and recovered water to a spray bar where it is distributed over the media and to a bleed line that discharges to the sewer.

AZFlow patented water distribution system is designed to meter fresh water from the potable water system directly onto the evaporative cooler's media by opening and closing a control valve. The water flows from this control valve through a special valve that assures a constant volumetric flow of water per unit of time is delivered to the media. The water distribution system uses multiple high precision laser cut orifices and spray channels located and oriented to deliver water to the media in a profile that takes advantage of the wicking and water storage capability of the media and matches the evaporation taking place as air moves through the media.

The control system includes sensors and capability to determine the inlet temperature and relative humidity of the air along with the ability to determine the mass flow rate through the cooler. These are used by the control system to determine the volume of water needed to makeup for evaporation and match the cycles of concentration setting for the water leaving cooler.

The local evaporation rate changes with the wet bulb, dry bulb, evaporative cooler efficiency, and air flow rate. These change dramatically over the course of a day, from day to day, from week to week, and from month to month such that the local evaporation rate can change by a factor of 5 or more over the full season. AZFlow coolers are the only coolers that sense and compute the instantaneous evaporation rate and have the resolution in the control system to achieve a consistent cycles of concentration over the course of this constantly changing cooling season.

Recirculating coolers use either a constant bleed or timed blowdown process to account for the mineral buildup behavior of water during the evaporation process taking place in the media. As discussed earlier, the evaporation rate changes dramatically over the course of a cooling season while the feed and bleed rates and timed blowdown periods are typically fixed.  This results in excess bleed water and/or mineral build up to scaling levels.

Media scaling in AZFlow coolers is minimized by using the control system to control the cycles of concentration as discussed above and by incorporating rinse cycles to assure cooler operations are started and ended with the pads cleaned to one cycle of concentration and to periodically rinse the pads during operation. These rinse cycles are particularly effective on the AZFlow coolers since clean one cycle of concentration water is metered onto the media and the concentration of minerals increases as the water moved down the pad from the top to the bottom reaching the desired concentration just before exiting at the bottom. With this configuration of mineral concentration it only takes a small amount of rinse water to clean the pad. By making sure the pads are wet on startup and by cleaning the pads to one cycle of concentration before shutdown the pads are clean and saturated on startup and cleaned before they are allowed to dry.

Another factor contributing to media scaling is that media in evaporative coolers is a very effective particulate filter for particulate larger than 1 micron and capture of this particulate on the media provides a site for scale formation to start. This is a positive attribute of evaporative coolers in that they improve the quality of the air delivered to the conditioned space and since most airborne city and industrial dust is larger than this 1 micron much of this health challenging dust is removed by the evaporative cooler. While AZFlow coolers flush dust and particulate matter removed from the air down the drain, recirculating coolers capture this material in the sump where it is recirculated and redistributed back to the media where it can speed scale formation.

The following table was constructed to compare the volume of bleed water that would be discharged from coolers set up and operating per the manufactures guidance. Since all cooler manufactures supply different sized coolers and the guidance changes as the circumstances and cooler selection change, we normalized the performance of all coolers to 20,000 cfm and a static pressure of 0.75 "W.G. The recirculating cooler was set up on 20% of the maximum expected evaporation rate while the Aspen Pad and the MasterCool were set up based on recommended bleed rate per horsepower. This table shows the projected water savings for one cooler and for ten units. The AZFlow number includes both bleed water and rinse water.

To enlarge table click here.

Bleed Comparison for 1 year operation* of 20,000 cfm cooler in Phoenix using manufacturer recommended settings *Based on cooling season in Phoenix, AZ when dry bulb is > 62°F


Cooler Type (Adjusted for same delivery air flow) AZFlow Aspen Pad Cooler MasterCool Cooler Recirculating Cooler
Bleed Rate or water discharge Tracks Evaporation 0.55 gpm 33 gph 0.61 gpm 36 gph 0.33 gpm 20 gph
Annual water usage (6040 hrs) 35,000 gallons Rinse & Discharge 199,320 gallons Bleed 217,440 gallons Bleed 120,800 gallons Bleed
CFM (one unit) 20,000 20,000 20,000 20,000
Water Savings (Gallons) BASE 164,320 182,440 85,800
CFM (ten units) 200,000 200,000 200,000 200,000
Water Savings BASE 1,643,200 1,824,400 858,000