Cutting-edge cooler hits 90% efficiency with help from networked controls

Jan 1, 2010 12:00 PM

An AXFlow cooler in place and a cooling fan regulated via SNAP digital output modules and a Linux-based controller.

Despite the fact evaporative coolers can use only a small fraction of the power needed for traditional chillers, they have a reputation for losing efficiency over the first few months of operation. These and other drawbacks have limited the situations in which the technology can be used.

There are no such problems with novel evaporative cooling designs fielded by Azevap LLC, however. The firm's AZFlow coolers use a patent-pending metered distribution system that lets out water uniformly onto media at a rate that factors in the rigid media's water storage capacity, wicking ability, and heat transfer properties. The system senses inlet temperature and relative humidity and computes the instantaneous evaporation rate for the air flow rate. A controller then adjusts for the local water chemistry to determine how much fresh water to meter onto rigid media for evaporation.

This contrasts with ordinary recirculating coolers, which bathe their media in water pumped from a sump at an average rate more than 2.5 times the evaporation rate. Recirculating the water in this manner, among other things, tends to promote scaling on the media which eventually degrades energy efficiency.

The AZFlow coolers can operate scale free and hit efficiencies of 85% to 90% even after operating for several years, without changing the media. This scheme is also more efficient than in ordinary evaporative units because there is no pump to recirculate the water, no float valve to add water to the sump, and no water sump to capture and store water for recirculation.

An AXFlow cooler in place and a cooling fan regulated via SNAP digital output modules and a Linux-based controller.

The AZFlow water distribution system uses an embedded SNAP control system from Opto 22, Temecula, Calif., as its central component. The system gathers sensor data about factors such as surrounding air temperature and humidity, then send this data to the SNAP processor via analog I/O modules residing on a SNAP rack. The system uses a proprietary algorithm executed by a Linux-based controller to correlate the instantaneous water evaporation and water application rates so the proper volume of water is delivered across the media, ensuring that it never gets too wet or too dry. More specifically, the algorithms determine just how long the cooler's water application valve stays open to keep the cooling pad damp.

The Linux controller was programmed and implemented by Opto-Solutions, a consulting and integration services company. The software lets the Azevap Linux controller communicate with Opto 22 I/O modules and execute cooling-related strategies.

Besides reading the I/O, aggregating all the data, and controlling the valve used to wet the media, the Azevap control system also connects to other evaporative cooler components. For instance, an RS-485 serial interface reads the operating status of the variable frequency drives controlling the cooler fans. Interfaces to SNAP digital output modules let the controller manage these fans (along with the entire cooler itself). Also, within the coolers, SNAP modules connect float switches and valves to the controller to give warning of clogged drains so any water accumulation can be identified and corrected.

A typical Opto22 module setup for an AZFlow cooler. Input modules measure ambient temperature and humidity, note the status of a float switch, door position, and control switches, and record VFD performance. Outputs power the solenoid and motor-operated valves and send commands to the VFD. The AZFlow gateway is Linux, apache, php, and ajax-based software on a microcomputer which controls the outputs that meter water onto the media and control the operation of the fan via the VFD to manage building air flow.
Select chart to enlarge.

Operators can view all cooler system control processes and acquired data via a Web-based HMI. The HMI also permits the entering of alarm levels, devising fail-safe contingency actions, and so forth.

AZFlow cooler controls are structured to interface with Local Area Network (LAN) and building energy management systems (where installed) at existing facilities. Internet explorer can be used to access the cooler controls and manage cooler performance. A locally administered, multilevel, password-protected, security system is integrated into the control system used to manage access and interface with these computer controls. Control system features include the ability to trend cooler performance, diagnose and both send alerts/alarms and take compensatory/corrective actions when components fail or performance degrades.