[Editor's Note: This is a lightly edited version of an interview that originally appeared on Deborah Grove's website, Groves Green IT. It is reprinted with permission.]

I got to know Dr. Robert F. Sullivan through several Uptime Institute events over the years, and he was tremendously helpful to me two years ago when I was doing research on attitudes toward water conservation among data center operators. I caught up with him recently and had the opportunity to talk about one of his favorite topics: the Kyoto fan. Dr. Bob is best known for his Cold Aisle/Hot Aisle innovations.

Deborah Grove: Dr. Bob, tell my readers what the Kyoto fan is and why it is both a traditional and innovative product.

Bob Sullivan: Kyoto Cooling (named after the Kyoto Accord) is an idea created by four young engineers in The Netherlands. The basic concept has been used in building and industrial air conditioning installations for over 60 years. In building AC systems a heatwheel is used to precool hot air in summer and warm cold air in winter. The key component of the system is an aluminum honeycomb wheel that absorbs heat in one airflow stream and dissipates it in another.

In the traditional configuration the system is set up to draw fresh air into the building, precondition the air to lighten the load on the HVAC system and then exhaust the air after it has passed through the building.

In a data center, this design is tweaked so that there are two isolated circulation paths, rather than an intake and exhaust path. The computer room is configured with an isolated hot aisle and the hot air is circulated, the heat is absorbed by the honeycomb wheel, and the cooler air is recirculated back into the computer room.

The wheel is constantly rotating at low speed and the "hot" wheel rotates into a chamber where outside air is circulated through the honeycomb. Outside air is returned to the ambient environment, carrying the computer room heat load with it.

This cooling technique is not only extremely efficient on its own but also isolates the computer room from the ambient environment and all the problems associated with bringing huge volumes of outside air into the data center. This includes dirt, fine combustion particles, gasses, air with low or high dew point. In this way the energy used or lost to contain these elements is minimized.

Next page: Why Kyoto Fans haven't taken off in the U.S.