High on the energy hog
An example of a carefully planned successful energy and cost savings program was carried out by the Harley Davidson Motor Co. during the late 1990s. At that time the corporate facilities occupied several floors on the original historic site. The site was comprised of several buildings with a total floor area of approximately 300,000 sq ft; offices and support areas occupied about 40,000 sq ft. These areas had been upgraded to a low-temperature variable air volume (VAV) system with partial ice storage for peak shaving. The remaining facilities were used for warehouse and storage areas. As the need for additional corporate space and training facilities was rapidly increasing, Harley realized the potential of the existing facilities and set about preparing a master plan to convert the facility to meet the future needs.
There were three fundamental requirements: the first was that the historical significance of the site had to be preserved. Second, the facilities had to be flexible with respect to function and operating schedules. Third, the HVAC system had to be designed to respond to a variety of operating conditions such as conference centers, corporate office, archival storage, and engine testing laboratories. Another requirement was that the HVAC system had to be designed in a manner such that it could be easily expanded to meet the new building loads throughout the multiyear project. Also, the firm wanted to maximize energy efficiency and minimize operating costs.
The plan built off the existing ice plant design, which served the current corporate facility. This allowed a majority of the main piping to be salvaged. The warehouse facility was converted to include a conference center, two floors of training facilities for dealers, a printing facility, and office space. The system selected would ultimately be made up of three 250-ton chillers, variable speed chilled water, condenser water, and hot water pumping systems. A water side economizer system was selected, which also allowed pre-cooling of the return chilled water during intermediate months. This was driven by limitations imposed on air side economizers, which prevented large louvers on the building face with respect to the historical significance. Changing the cooling tower fill surface area and increasing the fan size resulted in a net savings compared to air side economizers. Precooling the return chilled water temperature resulted in operating cost savings for some additional piping and valves.
The remaining floors of the original corporate facility were converted to office space with VAV systems. The ice storage system was upgraded to provide approximately 2200 tons/hr of cooling. Ice building was accomplished by a 250-ton air cooled chiller; this avoided the costs of additional chillers. The converted warehouse and office cooling plants were interconnected in the final phase. This allowed the ice to work with the water side economizers and the water cooled chillers, which have a higher operating efficiency. Minimum additional costs were incurred because piping was extended through a tunnel that connected both complexes during one of the earlier phases. The interconnection created an operational savings due to the diversity of the entire complex, which ultimately deferred the purchase of an additional 250-ton chiller. The initial added cost to install the pipe in the tunnel was a fraction of the cost of an additional chiller and tower; the end result provided an overall demand reduction of approximately 300 kW per month and an annual energy reduction of approximately 500,000 kWh per year.
Peter D. Zak is a principal with Graef-USA Inc., where he manages the MEP group. He is a member of NCEES and is on the editorial advisory board of Consulting-Specifying Engineer. He was an adjunct assistant professor at the Milwaukee School of Engineering for 20 years and is a registered professional engineer in 24 states.