Oregon Sustainability Center

building partnerships : advancing best practices : creating green jobs

The Path to Net Zero Energy

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Ask Omid Nabipoor of Interface Engineering about energy strategies for a net zero building, and he’s likely to tell you first about a towel.

“Imagine you have a wet towel,” he’ll say, as he did last week during a meeting with OSC tenants, “and you are wringing it out, getting every last drop of water out of this towel.”

For emphasis, he gestures with his hands, twisting an invisible towel, and we imagine a stream of water – all the inefficiencies of a standard office building – spilling onto the floor.

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Sounds easy enough. Eliminate waste, first. Gone is the soggy (conventional office building) towel. Make note of the inefficiencies that comprise the puddle on the floor, and cut them from the building’s design.

Next, design the highest performing building envelope possible, relying on passive energy systems primarily, and the most highly efficient active energy systems where necessary, and hey presto…a well wrung-out towel becomes a net zero building?

Not quite, but it’s a good place to start.

With regard to the Living Building Challenge, the Oregon Sustainability Center is considered an energy-driven building, much of its design tracing back to the LBC’s Prerequisite Number Four, Net-Zero Energy, which requires, “One hundred percent of the building’s energy needs supplied by on-site renewable energy on a net annual basis.”

The intent behind this prerequisite speaks to the most pressing environmental issues of today. As the LBC explains:

“The majority of energy generated today is from unsustainable sources including coal, gas, oil and nuclear energy. Large-scale hydro, while inherently cleaner, brings widespread damaging ecosystem impact. The effects of these energy sources on regional and planetary health is becoming more and more evident, with climate change being the most worrisome of major global trends due to human activity. The intent of this prerequisite is to signal a new age of design, whereby all buildings rely solely on renewable forms of energy and operate year in and year out in a pollution-free manner. Since renewable energy sources are inherently more expensive than energy efficiency measures, efficiency as a first step is assumed.”

Assuming efficiency as the first step…back to Omid Nabipoor and his wrung-out towel. Just how efficient is the OSC striving to be?

According to the 2003 Commercial Building Energy Consumption Survey on energy use in office buildings, published by the Department of Energy’s Energy Information Administration, the average facility in the United States has an EUI (energy utilization intensity) of approximately 92 kBTU/square foot/year.

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With Oregon’s more stringent energy code and the climate of the Pacific Northwest, the EUI average around here drops closer to 74. The Terry Thomas in Seattle, ranked last year as one of the Top Ten Green Projects by the AIA, has an EUI of 37. The Oregon Sustainability Center, by comparison, has set an EUI goal of 18-20.

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In order to achieve this unprecedented level of efficiency, the OSC will incorporate the following load reduction and mechanical strategies:

  • Improved building envelope (overall wall U value of .04)
  • A heat recovery ventilator with heating / cooling coils, supply / exhaust fans and air filtration
  • A geothermal, high efficiency water-to-water heat pump to provide heating to radiant floors and a heat recovery ventilator
  • Plate heat exchangers
  • An injection well with regenerative turbine / pump and 3R control valve
  • Radiant heating and cooling integrated into a topping slab on the structure
  • Low velocity underfloor air distribution for ventilation throughout
  • Night ventilation of the building’s thermal mass
  • Carbon dioxide sensors throughout the building
  • 35% vision glass that will be triple glazed with an overall glazing to be tuned to respond to each elevation.  For example, the south side will have a higher shading coefficient and the north side will have a higher U value.
  • Exterior shading devices with integrated photovoltaic panels to generate electricity while reducing heat load on building.  Interior light shelves will help bounce daylight deeper into the interior spaces.
  • Single gender bathrooms on alternate floors, which will make the floor plate more efficient.
  • A higher floor-to-floor height, allowing more light to penetrate the building interior
  • Roofs shaded with photovoltaics to minimize heat gain
  • Daylight controls with continuous dimming for a minimum of two zones (0-15’ from the window and 15’-25’ from the window)
  • Highly efficient fixture optics that allow for individual control of fixtures
  • Occupancy sensors for lighting throughout
  • Individual tenant control of light levels
  • LED lighting for corridors and lobby areas
  • Dual day / night lighting in corridors and egress stairs with occupancy sensors and time clock control

With each of these features and strategies plugged into the OSC’s energy model, the building achieves an EUI of around 23 kBTUH/sf. Bringing the EUI down to its final targeted range requires the engagement of the least predictable component in the building: the tenants themselves.

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The design team has added to the OSC energy model the following occupant enhancements, changes to typical office usage that are dependent on the building users, and that, if successful, will bring the building’s EUI down to even less than their original forecast, to 17.7 rather than the targeted 18-20.

Occupant enhancement strategies include:

  • Plug loads that are occupancy sensor controlled
  • Cleaning scheduled during unoccupied daylight hours, such as early morning or late afternoon, when there are fewer people in the building but natural light available
  • Hot water use reduced to little or none
  • Computer use limited to 80% laptops with a secondary screen / 20% desktop
  • Printer use reduced by 50%
  • Phantom loads completely removed
  • Personal energy budgets monitored daily

Tenants will be able to actively draw comparisons between different plug loads (from task lighting, space heaters, small appliances) as well as compare their energy usage power metering, with software that provides power quality information and feedback on actual power usage compared to others in the building.

At the individual scale, feedback will be possible with either a plug strip with integral power metering or a plug-in meter for workstations in open areas.

The team is still looking into additional enhancements such as thin client technology and a DC (direct current) loop, which would allow the energy generated by the photovoltaic panels (described below) to go directly to an end use without changing its current type (thereby eliminating the inefficiencies that come with conversion from DC to AC power).

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After all energy conservation measures have been included, the nearly final push for the building’s net zero strategy will be the incorporation of photovoltaics (PVs). For the building’s energy model, PVs were analyzed using the most efficient panel on the market today – the Sanyo HIT 205. Bifacial PVs are also being considered, for the soaring canopy panels described in our previous discussion of the ground floor design.

The OSC rooftop, 10th floor canopy, sunshades, and plaza canopies contribute more than 85% of the energy needs of the building, while building integrated photovoltaics at the south facing spandrels account for the rest.  Altogether, the building has approximately 54,000 square feet of PV.

Greatest efficiencies, passive and active energy sources…so what, then, is the final-final push for net zero energy?

As one of only two governing principles for the Living Building Challenge, the priority is clear: Designation of a Living Buildings is “based on actual, rather than modeled or anticipated, performance. Therefore, buildings must be operational for at least twelve consecutive months prior to evaluation.”

As usual, the final responsibility for the success of a Living Building floats back to the people. We won’t know whether the OSC will reach its 17.7 EUI, or its net zero energy strategy, for a couple of years. Planned efficiencies and sourcing from renewables takes us halfway there. The rest is up to every individual who commits to working in the building each day. At the risk of becoming a broken record, we’ll say it one more time: People are (still) the life in a living building.

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Filed under: Design Progress, Project History

One Response

  1. […] to the building’s strategy for net zero energy, the design team added water conservation measures first, incorporating into the basis of design […]

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