Page 140 - Zero Net Energy Case Study Buildings-Volume 3

PREFACE TO CASE STUDY NO. 17
STANFORD UNIVERSITY
(Opposite page, top) Aerial view of the Stanford campus, with the existing central plant and new site for the CEF.
(Opposite page, bottom)
Diagram of the distribution network from the new CEF.
(Diagrams courtesy of AEI.)
Studies for the New Central Energy Facility
There were a number of technical studies necessary to be completed by 2008 and there were challenges along the way. One was to determine if large-scale heat pumps with the desired heat recovery features could be obtained competitively on the market. Stanford ultimately had to write a specification for the equipment so that the university could obtain multiple bids.
With that item checked off, the next challenge was essentially to model and optimize the opera- tion of the system based on system component performance characteristics and thereby deter- mine the size of the various pieces of equipment. Software to model this size and type of system did not exist, so Stanford wrote its own1. Published as the Central Energy Plant Optimization Model (CEPOM), the software calculates the most efficient hourly operational plan to meet loads based on demand, the price of energy and the equipment specification. The model analysis stud- ied five-year increments from 2015 to 2050 to map the complete cost and replacement schedule that would be required for the system. The result was an optimization for the equipment selection and system operation that set the basis of design for the new Central Energy Facility (CEF) that was most cost-, energy- and resource-efficient.
Another pre-design planning study involved what had to be done at all campus buildings and the distribution network. The changes were able to be tabulated in a straightforward engineering study, essentially requiring all the steam-to-hot-water heat exchangers be replaced by new hot water (HW) heat exchangers. As part of this study, the future chilled water (CW) demand was estimated for 2008-2015 to make sure that there was enough capacity in the current distribution network and the existing buildings, so that no special changes had to be made to that part of the system.
An additional study was done of the actual design of the large heat pumps, which were specified as ground source heat pumps. Rather than go the expense of installing a large new ground loop system connected to the heat pumps for rejecting and absorbing heat, staff studied the advan- tage of utilizing two existing horizontal networks of piping that circulated water: the landscape irrigation system in the turf playing fields, which used non-potable water, and the drinking water distribution system. The study showed that both could be used effectively as the ground loop components of the heat pumps. Connected to the irrigation system, the heat pump could use a heat exchanger to dump heat at night when the sport fields were being irrigated; warmer irriga- tion water was just as effective in keeping the turf healthy. During the day, the drinking water network was used as a “heat” source by heat exchangers, effectively chilling the drinking water before it was delivered to the buildings on campus—also a welcome outcome.
Finally, the cost of this major changeover, plus replacement and operating costs over a 30-year period were studied for the new CEF versus the no-change scenario. The cost study showed that the new CEF had a lower present-value cost than a renewed lease of the existing cogeneration plant and concluded that it was the best investment for Stanford University while meeting all the sustainability goals.
Campus peer review and Stanford’s own internal review of the studies supported the conclu- sions. This convinced campus leadership of the merits of this bold plan and the Board of Trust- ees approved moving forward.
1 Stanford University has made this patented software, Central Energy Plant Optimization Mod- el, publicly available, currently through Johnson Controls. The spreadsheet version, intended for non-profit institutions of higher education, is available at no cost, though this is temporarily on hold due to licensing issues.
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Zero Net Energy Case Study Buildings: Volume 3