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UW Tower: A Template for Radical Energy Savings in Existing Office Buildings

Our existing building infrastructure consumes tremendous energy resources. This creates an opportunity for conservation on an expansive scale if progress can be made toward identifying a replicable technical and economic template for deep-energy renovations. Fundamentally, this is a question about what our existing buildings of today will look like a generation from now.

To envision a technical path to transforming the energy use of existing high-rise office buildings, the University of Washington Integrated Design Lab (IDL) with Solarc Architecture and Engineering and TBD Consultants have developed bundles of integrated energy efficiency measures aimed at reducing the operational energy use of existing high-rise office buildings by more than 50%. We call these bundles Integrated Measure Packages (IMPs). As part of our research, we have selected the UW Tower to serve as a platform for a simulation-based investigation of these IMPs. This work is being performed as part of the Northwest Energy Efficiency Alliance’s (NEEA) Existing Building Renewal (EBR) Initiative.

 UW Tower is 40 year old. What will it look like in 40 years?

The UW Tower is an existing 24 story approximately 500,000 square foot high-rise. Built in 1973, itis now almost 40 years old. The total complex consists of a Pavilion (4-stories and a basement), and a tower (18 stories and a mechanical penthouse). To assist with our research effort, the building manager and engineer have provided the UW IDL with comprehensive data including a full set of architectural, mechanical, and electrical drawings, and utility consumption data. They have also provided access to the site to perform a complete systems and central plant audit. This data was used to document architectural systems performance, to calculate annual and peak energy use, and for the development a calibrated energy model.

UW Tower’s existing mechanical system

Four simulation models form the basis of the analysis. The first is a “baseline” model which is calibrated to the existing performance of the UW Tower (as indicated by current consumption). The current building has an Energy Use Intensity (EUI) of 82.6 kBtu/ft²-yr.

The second model includes core architectural upgrades (single-pane window replacement and lighting system replacement) and an upgraded air-side HVAC system. This model achieves an EUI of 37.9 kBtu/ft²-yr, a 50% reduction over existing performance. and is essentially equivalent in energy performance to current Seattle Energy Code for new construction.  The savings in this model is comparable to the annual energy consumption of three Poplar Residence Halls (the new dormitory on Campus Parkway and Brooklyn Avenue west of the University of Washington Seattle Campus).

The third model, including core architectural measures and a radiant heating and cooling system with a dedicated outside air (DOAS) ventilation system achieves a 60% reduction over existing conditions and includes significant plug load control. This model achieves an EUI of 31.9 kBtu/ft²-yr. Energy cost savings is $1.01/ ft²-year. The energy saved could power 270 typical single family homes in Seattle.

We constructed a fourth model to include heat capture from an adjacent data center. This supplemental energy efficiency measure reduces energy use to 25 kBtu/ft²-yr, which is less than one third of the current energy consumption of the tower.

Diagrams of UW Tower’s exiting system and two renewal options

Energy Savings comparison of two modeled packages

It is unlikely that energy savings alone will motivate an owner to take a comprehensive approach to improving existing building energy performance. Non-energy benefits will play a substantial and motivational role in compelling building owners to implement a deep energy renovation. In our example project at UW Tower, all bundles of energy efficiency measures yield significant non-energy benefits. The first, and likely most lucrative, includes the realization of approximately 7,000 ft² of additional leasable floor area recaptured through the removal of existing perimeter induction units. At a lease cost of $25/ ft², this measure alone yields approximately $175,000 of rental value to the owner. Secondly, the existing chillers are near the end of their service life. The replacement of these large chillers within the top floor mechanical penthouse is expected to require a very substantial investment. The use of modular chillers as described in the IMPs will make replacement less expensive and on-going maintenance of the chiller plant less costly due to ease of transport through the building. Finally, occupant thermal comfort is expected to be substantially improved. Increased thermal resistance and improved solar gain control from higher performing glass and window frames will decrease unwanted fluctuations in mean radiant temperature at the perimeter Mitigating this problem is likely to lead to increased occupant productivity.

Renewing Seattle’s office buildings with projects similar to the ones simulated on the UW Tower can make a significant impact on the energy use in the region and their viability for the next 40 years. Of the commercial office real estate buildings ten stories or greater in Washington State, 93% are in the Seattle Central Business District (CBD). There is more than 88 million square feet of commercial real estate in the Seattle CBD.  More than 30million square feet of this total is in non-owner-occupied commercial office real estate, in high-rise buildings of ten stories and greater, constructed before 1996. Buildings constructed prior to 1980 were not subject to any energy code requirements. This means that these buildings typically underperform current minimum energy code requirements by a substantial margin and will continue to do so indefinitely without a major intervention.

These buildings are not going away. What will they look like 40 years from now?

 Written by Aaron Helmers and Christopher Meek.

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