Among the many technical sessions and meetings that occurred at this summer’s ASHRAE meeting was a session by a group of professionals assessing central chiller plants with a focus on establishing standards for monitoring, measuring, and benchmarking central plant performance.

One issue in this task is determining the ways chilled water plant performance can be stated. Questions such as, “Does the kW/ton include the ancillary equipment energy?” are being asked as part of the data collection process. The final results will be valuable management tools for assessing and point of referencing one segment of facility management operating costs.

A Shared Goal

Along this line of study, while at the ASHRAE conference, I had the opportunity to share central chilled water plant experience and thoughts with John Vucci, assistant director for HVAC Systems at the University of Maryland. It seems that we are both pursuing energy consumption improvements for central plants and system distribution projects along a parallel course for totally different projects.

For him, it was the university’s goal to reduce operating costs with one of its targets, the energy associated with the chilled water distribution system that serves the campus. For me, it was three individual projects: a central cooling system for a 150,000-sq-ft college laboratory building, a similar private school laboratory building, and a professional sports complex.

Our mutual approach to energy conservation measures and associated operating cost was to begin to monitor, measure, and manage air conditioning capacity at the individual buildings and then work our way back to the central chiller plant. With this approach, we will have established the lowest possible chiller load, which could then be measured and benchmarked for energy/operating cost/sq ft. This concept would provide the owner with a means to goal set the lowest cooling load and allow the focus to then be on establishing the best central plant kW/ton performance.

When discussing this idea, the analogy I use is of two automobiles leaving from the same point for the same destination, with both vehicles consuming 30 mpg. The difference is that the first car takes a more direct route to the destination while the second car takes a longer, roundabout route to the same destination. While both vehicles are benchmarked at the same energy consumption rate, the results will be significantly different operating costs. In other words, similar chiller plants with similar benchmarked performance in kW/ton (e.g., 0.75 kW including ancillary equipment) will not necessarily result in the same operating cost.

Managing Space = Energy Saved

So how does our approach to central plant performance work? It begins with program management and focuses on building space usage. This approach is ideal in a school environment where space usage within each and every building during the summer months may be very low. Unlike other building types, school facilities will most likely peak around May and again late August with the new school year. Using my 150,000-sq-ft building project, which has 20% occupancy in the air conditioning season, it will make sense for the education program to consolidate its teaching to a specific area of the building.

For my client, this means limiting access in the laboratory building to the first floor corridor and the second floor classroom/lab space or use of 30% of the building. The remaining area 105,000 sq ft (first floor, third floor, and fourth floor) will remain vacant and in the unoccupied mode of HVAC operation throughout the summer sessions.

The operating cost savings breaks out as follows with you filling in the numbers:

  • 70% less HVAC and electrical energy with systems and lights off: $____
  • 70% less work orders: $____
  • 70% less custodial requirements in the unoccupied space: $____
  • Access to vacant space for repairs, etc. during normal work hours: $____

Did We Miss Anything?

With any energy management program today, the equipment involved with the plan has most likely been designed and installed after the energy crisis of the 1970s. Therefore, much of this equipment already has relatively good energy performance. Before someone sets out to fine-tune or retrofit this performance, the individual should first inventory big-ticket items (e.g., shutting down buildings and systems wherever possible).

Addressing the building program can result in significant operating cost savings by consolidating summer programs into a single building and shutting down other buildings and/or major portions of those buildings for reasonable periods of time.

Next, don’t overlook all the operating costs associated with managing the building(s). Credit needs to be taken for all the realize benefits whether immediate ROI or lifecycle ROI. This approach is ideal for owners pursuing LEED™ certification of existing buildings. It is also a great template for a campus-wide, energy master plan. Remember, managing central plant operating costs begins with managing the programs.