Page 139 - Zero Net Energy Case Study Buildings-Volume 3

Simultaneous Heating and Cooling — Conventional Approach vs Innovation
Almost all large non-residential buildings in this climate require simultaneous heating and cooling at all times of the year, particularly in the case of laboratories and hospitals. To meet this type of demand, the Stanford campus at this time utilized a conventional approach for its central plant, generating steam for heating and chilled water for cooling, distributing these media throughout the campus to the various buildings using a large network of distribution pipes. When chilled water was made at the central plant, the heat removed was discarded to the environment via evaporative cooling, in the process using 25% of the entire campus demand for water.
The data collected suggested the study of heat recovery in some form as an adjunct for this sys- tem, with the expectation that about 10% of the time there would be sufficient excess heat from the cooling process to contribute to the simultaneous heating demand. Further study indicated, surprisingly, that excess heat could be harvested 75% of the time. In fact, analysis showed that about 90% of the heat requirement in campus buildings could be met through heat recovery from the central cooling system.
Stanford then focused on a truly innovative strategy to take advantage of the great potential for energy efficiency revealed by the data: heat pumps with hot and chilled water storage. There is some proven precedent of this approach: northern European countries had switched to hot water from steam for their district heating plants and experienced significant efficiencies due to reduced energy losses in the distribution network. The same principle would apply to a system based on heat pump technology.
There is also a huge cost efficiency to this approach since the electric-powered machines could be operated off-peak at lower rates using the large thermal storage. Because of this off-peak operation, the equipment does not have to be sized to meet the campus peak demand and therefore could also be significantly downsized, saving on initial system cost.
Heat recovery would be a major feature of such a strategy, but there would be inherently higher efficiency and potentially elimination of all carbon emissions because of the equipment em- ployed and the energy source contemplated—solar versus fossil fuel. The introduction of the solar component would require an operational management approach that would optimize en- ergy performance while minimizing operating cost. This would essentially require a new type of operating software—another challenge of this innovative strategy.
It was a strategy with highly desirable outcomes, but the implication was the total abandonment of the existing central energy plant. This had significant financial implications and operational risk, and would require major campus planning decisions by Stanford’s leaders.
The “Realistic” Opportunity Presents Itself
This “out of the box” strategy became realistic only because of a coincidental opportunity with regard to the existing gas-fired central plant. This existing central plant was actually owned by a subsidiary of General Electric Company, Cardinal Cogen Inc., and leased to Stanford University. As part of the lease agreement, Cardinal Cogen operated and maintained the equipment, with Stanford paying for replacement equipment when scheduled.
The lease contract was due to end in 2015 and a renewed 30(?)-year agreement would have to be signed at that time if Stanford were to opt for the “No Change” strategy instead of the decid- edly innovative green strategy. Since the design, construction and start-up period for an entirely new system would require 5-7 years, Stanford knew that there was no time to lose if the new strategy were to be realistically considered—all essential studies for the new system and review by university leaders would have to be completed by 2008 for a “Go – NoGo” decision.
Zero Net Energy Case Study Buildings, Volume 3
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STANFORD UNIVERSITY
PREFACE TO CASE STUDY NO. 17
(Left) The existing central plant in 2008, leased from Cardinal Cogen, located near the main part of the Stanford Universiity campus.
(Photo courtesy of AEI.)