Like so many industries, pharmaceutical processing is increasingly focused on improving the operational energy efficiency. One challenge that often stands in the way: cleanrooms.
In these facilities, energy efficiency understandably takes a back seat to the mission of clean production. As a result, due to FDA-required filtration, high-performance processing machines and other factors, cleanrooms are energy intensive – with an energy load as much as 50 times more than a typical industrial structure.

But that doesn’t mean cleanroom energy efficiency can’t be improved. And as electricity costs rise, reducing these requirements is increasingly important to a pharmaceutical processor’s competitiveness. That’s why many processors continue to approach energy efficiency in new ways. One aspect that holds particular promise is process cooling.

The Drawbacks of the Usual Approach
Depending on the specifics of the application, process and facility, traditional process cooling approaches such as cooling towers and central chillers can account for as much as half of the energy demands of a cleanroom.

The dated cooling tower/central chiller approach uses a continuous evaporative process in an open loop combined with large compressors to cool the water used in process cooling. The overall process uses high amounts of energy and water, to deliver the same cooling water temperatures system wide that are often lower than needed at many of the processing machines. With clean operation remaining their top priority, many pharmaceutical processors have allowed these energy efficiencies to remain in the mix for far too long. But that’s changing.

Enter a newer approach: closed-loop adiabatic process cooling. Unlike a conventional cooling tower, the closed-loop system uses ambient air to cool the process water. When conditions permit, there’s no compressor-driven chiller needed.
The key is that this system uses a closed-loop adiabatic fluid cooler in place of the open-loop cooling tower. The process works like this:
1. A rise in ambient temperatures activates a part of the system called an adiabatic chamber.
2. A fine mist of water is pulsed into the incoming ambient air stream.
3. The mist evaporates instantly, cooling the air before it hits the cooling coils that carry the process water.
4. The newly humidified air drops the temperature of the process water to at or below the setpoint. Cooled water is then re-circulated to a facility’s process machines.
5. A microprocessor-based controller automatically maintains targeted cooling temperatures.

A Flexible Approach to Process Cooling
Instead of the “one temperature fits all” approach of a typical cooling tower/central chiller system, the closed-loop system can be configured to provide precise process water at each machine by pairing with machine-side chillers. This configuration not only improves part quality and cycle time, but also saves energy overall because the entire system can maintain a water temperature that’s higher than required at individual machines.

This capability is just one way the closed-loop system is more flexible in terms of energy use than a traditional cooling system. In fact, there are four different stages with varying levels of energy use depending on ambient conditions and setpoint requirements:
• Dry cooling – In moderate temperatures, the central cooler continuously routes water returning from the process through heat exchangers. Exhaust fans at the top of the central cooler ensure a steady stream of incoming cool air and outgoing heated air. The heat exchangers and exhaust fans together are all that’s needed to cool process water.
• Adiabatic cooling – As mentioned before, this function only activates in hot weather as needed to meet cooling needs.
• Increased adiabatic cooling – A patent-pending “adiabatic booster system” enables the unit to deliver even lower process cooling water temperatures in the hottest climates, still without the use of central chiller.
• “Free cooling” – The system automatically shuts down any chillers and lets the central cooler provide all the cool process water needed via ambient air flow.
Additional energy savings come from variable speed fans that reduce fan energy use by as much as 25% compared to typical on/off fans, as well as high-efficiency pumps that can also reduce energy consumption.

Taken together, these capabilities mean that a closed-loop adiabatic process cooling system can reduce energy consumption for process cooling by as much as 50% compared to a conventional cooling tower/central chiller system.

Central coolers equipped with available fan exhaust diffusers also keep hot discharge air from being drawn into the adiabatic chamber at the bottom of the unit – while allowing it to consume significantly less energy compared to models without the diffusers.

The Time Is Right for New Cooling Methods
Facing increasing competitive pressures, pharmaceutical processors with cleanrooms continue to upgrade their processing technologies for greater precision. Any one of these other improvements can be a good opportunity to reevaluate the process cooling system, as well.

One of the best reasons to do so is to reduce energy use in the cleanroom. Although energy efficiency hasn’t been a primary target for improvement in cleanrooms, it’s an increasingly important factor due to rising energy costs.

As you can see here, a closed-loop adiabatic process cooling system represents a significant opportunity for energy efficiency improvements. The efficiency extends to other resources as well – in particular, water savings. The closed-loop system uses up to 98% less water than an evaporative, open-loop cooling tower system. The closed loop also saves on the related maintenance and chemical treatment costs. n

About the Author
Al Fosco is the Global Marketing Manager for Frigel North America. He has a Masters degree in Heat Transfer and Fluid Mechanics Engineering from the University of Illinois.