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Hot Climate, Cool Laboratory

Fri, 12/14/2012 - 10:45am
Todd See, Senior Vice President, WSP Flack+Kurtz, San Francisco

Chilled beams can provide an energy-efficient laboratory environment even in a tropical paradise.

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The University of Hawaii Cancer Center during construction in June, 2012. All images: Todd See, WSP Flack+Kurtz   

The goal of the University of Hawaii Cancer Center is "Creating a world where cancer no longer exists." The mission of the building's designers was to create energy-efficient laboratory space to help researchers achieve this goal.

Located on the John A. Burns School of Medicine campus of the University of Hawaii at Manoa, the Cancer Center is a 160,000-square-foot laboratory located along the water. The project, completed in September 2012, is the first project in Hawaii to utilize chilled beam technology. The building is projected to earn a LEED Gold Certification and have an energy use approximately 30% lower than the minimum requirements for energy-efficient designs for buildings as specified in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 90.1.

The new facility provides state-of-the-art facilities for cancer biology, prevention and control, and epidemiology studies, as well as clinical and translational research. The design, a collaboration between executive architect Shimokawa+Nakamura of Honolulu and design architect Zimmer Gunsul Frasca (ZGF Architects) Los Angeles, also features building systems engineering by WSP Hawaii in collaboration with WSP Flack+Kurtz of San Francisco. Sustainability consulting was provided by WSP Built Ecology, San Francisco.

The building is well integrated in its concept. A primary east-west orientation provides excellent daylight opportunities and views to the Pacific Ocean to the south (Makai–“to the water” in Hawaiian) and the mountains (Mauka) to the north. The office wing, separated from the laboratory and laboratory support wing by a breezeway, is designed to provide views to Diamond Head, a sacred place in Hawaiian history. The design locates write-up spaces at the perimeter, separated from the laboratories by glass partitions, allowing natural light into the laboratories. By maximizing the use of natural light, the lighting energy for the building is reduced by approximately 5%.

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Typical write-up space located at the perimeter. Chilled beams can be seen above the windows.   

HVAC system selection and design
The design of laboratories and the supporting heating, ventilation, and air conditioning (HVAC) systems has changed dramatically over the last 25 years. Where previously the driving force behind laboratory safety was moving as much air through a space as possible—usually at a constant rate of 20 air-changes per hour minimum—the industry today recognizes the moving of that much air is not appropriate or necessary. Better laboratory safety practices and procedures and the development of variable air volume systems have improved energy efficiency and safety. Since all of the air supplied to a laboratory is exhausted, moving less air though a laboratory saves energy in a number of ways.

First, fan energy is reduced, both in supplying air to the space and exhausting air from it. Less energy is required to cool and de-humidify the supply air. And, the need to re-heat the air to keep the space comfortable is decreased.

Three criteria are considered when determining the maximum and minimum airflow required for each laboratory space: The minimum safe ventilation rate for a laboratory is typically six air-changes per hour—the cooling required to offset heat generated by people, lights, equipment, and transferred through the building envelope and the exhaust required by laboratory equipment such as hoods, cabinets, or snorkels.

From the outset of design, the goal was to make the Cancer Center as energy efficient as possible. Because the Cancer Center’s HVAC system was such a large energy consumer, the focus was on how to minimize that energy use.

Chilled beam strategy
The three critical design criteria for a laboratory space are sometimes at odds with each other: The minimum ventilation rate may provide too much or too little cooling for a particular space as it will be used. The ideal design should provide the correct amount of ventilation air at a temperature that will not over-cool the space, requiring additional heat to keep the space comfortable.

Wet laboratory space with views through the write- up space to the outside.With a room-temperature setpoint of 72 F, the ideal supply temperature to the space is between 58 and 65 F. In cases where the minimum ventilation air supplied at this temperature would not meet the cooling load, supplemental cooling is required. For the Cancer Center, a system of active chilled beams was chosen to provide that supplemental cooling.

Chilled beams offer a low-energy solution for cooling a space. Active chilled beams have been used successfully in Europe for the last 20 years, but only recently used with frequency in the United States.

The HVAC design for the Cancer Center was selected after a series of studies prepared by WSP Built Ecology. Options included active exterior shading, a zone re-cool scheme (think the opposite of re-heat), and several chilled beam applications. The final design includes baseline cooling within the laboratories from the ventilation system that supplies a minimum six air-changes per hour of 100% outside air.

Active chilled beams are placed in laboratory areas where the cooling load exceeds that provided by ventilation, as well as in all office spaces.

A run-around heat recovery system pre-cools the outside air. The system includes a direct evaporative section in the exhaust airstream to lower the exhaust air temperature before the heat recovery coil.

Re-heat is provided at the laboratory areas by utilizing condenser water leaving the chillers at approximately 95 F, eliminating energy use associated with re-heat typically associated with laboratory design requiring high ventilation rates.

Exhaust air heat-recovery system
The local climate for this project is both hot and humid. Coupled with a requirement for 100% outside air for laboratory ventilation, a large cooling load exists just for the ventilation of the building. On this basis, the building was a prime candidate for combined sensible and latent heat-recovery systems. Two exhaust-air heat-recovery systems—one with only a sensible heat-recovery coil and one that combined latent and sensible heat recovery—were evaluated.

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Schematic of a typical chilled beam. 1. Cool, dehumidified ventilation air is introduced; 2. Mixing box; 3. Room air is induced over the chilled beam cooling coil; 4. The cooling coil; and 5. Supply air to the room is a combination of ventilation air and room air.   

The sensible heat-recovery coil system captures waste heat from the exhaust airstream by using two coils. One coil is in the exhaust airstream and extracts heat from the warm (87 F outside air). This heat is rejected to the cool (75 F) building exhaust air. The weakness of this approach is that it does not recover latent heat from the relatively dry exhaust air.

The indirect evaporative cooling and heat-recovery coil system is a modification of the sensible heat-recovery coils described above. By adding evaporative cooling to the exhaust airstream, exhaust air is first cooled to the wet-bulb temperature (65 F) before it pre-cools intake air. Ideally, cool condensate from the dehumidification process would be the water source for this approach, improving performance and reducing water consumption.

Unlike the sensible-only heat-exchange option, the evaporative process leverages the relative dryness of exhaust air for latent recovery.

The final product
For years, there has been concern about using chilled beams in tropical climates due to the potential for over-condensation. The University of Hawaii Cancer Center is proof that this relatively simple, low-energy cooling system can be applied in hot, humid climates. The key to success was maintaining the chilled water temperature above the room dew-point. Coupled with a straightforward heat-recovery strategy, the University now has a state-of-the-art building that will save energy for years to come.

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