Overview

Bucknell University (Bucknell) has been continuously seeing campus growth over the last decade. With that growth, their campus utilities also needed to grow to match the extra capacities demanded by new square footage. A previous chiller addition to Bucknell’s chiller plant added 850 tons of capacity, which maxed out, both their current cooling tower capacity and electrical capacity. With their campus master plan complete, and four new buildings on the 10-year horizon, Bucknell knew additional chilled water capacity was going to be needed; they hired us to perform an analysis to determine how much will be needed and options to meet the future chilled water demands, so they could make an informed decision for their cooling utility needs.

Solution Details

It was determined that 1,000 tons of cooling capacity will be required to satisfy the projected campus loads of the next 10 years. Bucknell asked that we provide options to meet that capacity in two, 500-ton increments.

Four primary options were analyzed. Three options included additional campus chillers (water-cooled screw, water-cooled-centrifugal, and air-cooled screw) and the fourth option utilized a thermal energy storage (TES) tank and an existing 750 ton chiller to charge it overnight. Various location options for the three chiller options were provided, which varied by the chiller unit’s size and other factors.

Construction costs for each option and location sub-option were estimated first. Next, energy and operating costs needed analysis. With Bucknell’s input, future operating assumptions vital to projecting accurate operating/energy costs; allowed for true, real-world estimates to be made. Once construction and operating/energy costs were calculated, the total costs of each option can be aggregated.

After the cost analysis, we recommended that the first 500-ton increment of cooling capacity utilize the 600,000 gallon TES tank. Utilizing their existing chiller equipment, this tank could effectively be charged in 8 hours overnight, when electricity costs are their lowest. In fact, the storage tank was estimated to reduce Bucknell’s annual energy costs by $67,000.
For the second 500-ton increment of capacity, two options were recommended. First, if Bucknell wanted to add all 1,000 tons of capacity at once, the TES tank could be upsized to accommodate the capacity relatively inexpensively. Alternatively, if Bucknell wanted to stay with their 500-ton increment expansions, the low construction costs of the air-cooled screw chiller would be most beneficial, since this unit would primarily serve as a backup and its higher operating costs may not be incurred during non-summer months. Additionally, as an air-cooled unit, it could run in cold weather, if needed, without the worries of cooling tower freeze-ups.

Ultimately, with the options provided, Bucknell was able to make an informed decision and chose to install a larger thermal storage tank to accommodate all of its immediate cooling capacity needs at once.