Dear Cronin’s Corner:

I believe the most practical free cooling system (Cronin’s Corner, Spring 2008) is a combination of water- and air-side economizers that offers all of the benefits and none of the risks. This can be achieved with an air-cooled chiller with integrated free cooling where the face area of the coils is larger than a standard chiller to maximize the free cooling.

In warmer weather the chiller operates just like a standard air-cooled chiller. When the outside ambient air falls below the RETURN temperature, a motorized three-way valve automatically diverts the return through the free-cooling coils before it enters the evaporator. As the ambient falls further the free cooling effect is increased and the compressors unload, saving energy. At approximately 20 F below the SUPPLY chilled glycol temperature the chiller will achieve 100 percent free cooling and the compressors are switched off. The system allows for partial free cooling, with the condenser fans controlled by refrigerant head pressure whenever a compressor is operating. When the compressor is off, fan control is automatically switched leaving chilled glycol temperature to minimize fan power and prevent over-cooling. The change from mechanical to free cooling (and back again) is seamless with no temperature variation and no operator intervention required.

This system allows the indirect use of cold ambient air to cool the glycol in a carefully controlled sequence via a customized PLC. The data center is always isolated from airborne contaminants, and there is no make-up water required. This system offers optimum energy savings while eliminating the risks and shortcomings of water- or air-side economizers. Historical ASHRAE weather data can be used to project and verify free cooling savings for any location. Any location north of the Mason-Dixon line will easily justify free cooling. Typical payback is one year.

Graham Whitmore
President - Motivair Corp

Dear Editor:
Doug Sandberg’s Mission Critical Care column advises readers that stored diesel fuel needs to be treated due to deterioration (Spring 2008, page 16).

Better practice?

Facilities should implement the Joint Commission’s emergency generator testing requirements. Why? Like the American Red Cross driving requirements for its 300-some Emergency Response Vehicles (ERVs), diesel engines would get regular power ups that cycle the fuel and fluids before getting stale.

Thanks to the monthly 30-minute nameplate load testing, and the quadrennial 4-hour testing, our hospital’s generator reliably worked throughout all my 15 years here.

Chief Donald E. White, CHSP, CHCM
Director of Safety and Security
Northern Virginia Mental Health Institute