Back To The Future

Engineered Systems, Oct, 1999 by Mike Shoulders

A major part of the heating-cooling system installation cost is tied up in distributing energy from wherever it is generated (the mechanical room) to where it is used (the classroom). Among the many system options available, two-pipe is proving to be the least expensive option.

For example, Mount Vernon (IN) Schools asked three firms to perform feasibility studies to air condition three elementary schools totaling 190,000 sq ft. Two of the proposed firms budgeted $2.2 million (four-pipe) and $1.9 million (DX cooling). Durkin and VPS budgeted and installed two-pipe systems in the schools for $1.4 million, helping the schools realize a $500,000 savings on the installation.

Meanwhile, Monroe County (IN) Schools asked three firms to provide feasibility studies to air condition four elementary schools totaling 220,000 sq ft. Two of the proposals estimated $3.9 million (neutral air) and $3.5 million (four-pipe). In this case, Durkin and VPS budgeted and installed two-pipe systems (and upgraded every light in all four facilities) for $2.7 million, realizing a $800,000 savings on the installation.

"If it weren't for two-pipe, we could not have afforded to air condition our schools," said Carl Culiver, assistant superintendent of buildings and grounds, Mt. Vernon (IN) Schools.

Bill Wiseheart, supervisor of energy services for New Albany Schools, seems just as impressed with the two-pipe system. "Two-pipe uses digital electronics and creativity to do what other systems do with pumps and piping. It costs a lot less, so more of our money can go to educate the kids."

In a geographical area where the average cost for school utilities is $0.70/sq ft/year, Indiana schools with two-pipe systems are typically operating at $0.50/sq ft/year, with several below $0.40. For instance, the annual utility bills for 20 two-pipe systems in the Evansville-Vanderburgh School Corp. (Evansville, IN) went down an average of $0.12/sq ft. (Figure 1.) This rate drop was accomplished while adding air conditioning to previously non-cooled facilities -- realizing a $500,000-per-year savings in operating costs.

"Gas consumption at Binford Elementary (Bloomington, IN) went down more than 60%," said Mike Scherer, director of extended services, Monroe County Schools (Bloomington, IN). "The utility company couldn't believe we were saving so much. They changed the gas meter twice."

'RIGHT TECH,' NOT HIGH-TECH

From any engineering standpoint, there are six special aspects to the two-pipe design. The first is electronic and speaks to the complexity of the system. Specifically, a sophisticated digital control scheme uses the power of computers to solve the workability issues of the two-pipe system.

The remaining factors are mechanical -- very straightforward -- and are to be admired for their simplicity. Simplicity is the essence of cost savings and maintainability. As Steve Johnston, manager of building and grounds, Evansville (IN) Schools, put it, "Two-pipe is cheaper to build, cheaper to operate, and easier to maintain. What's not to like?"