Boiler/Chiller Plant Energy Study| Project Profile

About the client

The client for this project is a Federal Court House building located in the Midwestern United States.

Scope of Project

Middough developed a building energy model and performed life cycle cost analysis of the building’s boiler/chiller plant that served a 500,000 SF high-rise courthouse.The purpose of this study was to perform a life cycle cost analysis on the major equipment in the boiler/chiller plant that may be near the end of their useful life.

Services provided by Middough

Middough providedProject Management, Mechanical and Electrical Engineering services for the study and project.

Results delivered to client

Middough performed an analysis for the following equipment options: 

1. Electric Steam Boiler vs. Gas Fired Steam Boiler

2. Standard Efficiency Water Cooled Chiller vs. High Efficiency Water Cooled Chiller

It was determined that it was physically possible to locate gas-fired boilers in the same general area where the existing electric boilers reside. However, the space was not large enough to adequately maintain the gas-fired equipment and it would be very costly to remove any major equipment from the mechanical room because the gas boilers would impede the removal of that equipment. 

Recognizing the feasibility for gas boilers was marginal, Middough still elected to make the comparison between gas and electric to determine the annual cost savings for gas. The resultant annual cost savings of $210,134 could conceivably pay for the relocation of the steam boilers to another location on the building site to facilitate gas-fired boilers. 

The feasibility of relocating the steam plant was outside the scope of this study. 

The cooling load calculation estimated the building peak cooling load to be nominally 1,400 tons. Based on this resultant load, the energy model analysis utilized three water-cooled chillers at 450 to 500 tons each. The electric power to the existing water-cooled chillers is 4,160 volts. 

This fact significantly curtailed the options for high efficiency chillers, so Middough elected to research chillers that utilize 480 volts to expand the options. As a result, the installed cost for the high efficiency option included an electrical transformation cost to reduce the voltage from 4,160 volts to 480 volts. 

The high efficiency chiller proposed has exceptional part load performance due to its integral VFD and magnetic bearings. The operational reliability for the high efficiency chiller is better than a standard chiller due to its oil-less compressor. The simple pay back for the high efficiency chiller is 15 years, and while this is not a great return on investment, Middough recommended the high efficiency chiller due to the increased reliability of the magnetic bearings.