Ventilation / Fans

Forward-Thinking Design Enables Efficiency

March 25, 2013
Trans

It takes a bit of ingenuity and a healthy dose of elbow grease to transform a 30,000-square-foot abandoned Sears auto center into a 91-point LEED Platinum certified office space, but that is exactly what Bremerton, Wash.-based Rice Fergus Miller (RFM) Architecture did. After sitting idle for over two decades, this concrete square block is now RFM’s high-performance headquarters.

The building features clerestory windows, locally harvested and milled lumber, a reflective roof, photovoltaic (PV) panels, super-insulated walls, and a hybrid mechanical/natural ventilation system with ceiling fans to maintain occupant comfort.

The project was recently awarded a first place ASHRAE Technology award for 2013, and is currently performing at energy usage intensity of 19 kBtu per square foot, per year.

“We knew we didn’t want a ducted, conventional HVAC system, and we were going to rely on variable-speed heat pumps scattered throughout the space in localized places along with ceiling fans to mix the air around,” said Steve Rice, principal at RFM. “We had the goal of a building that had the ability to be net zero — we knew we couldn’t afford to get there from day one, but we wanted nothing that we designed to preclude us from getting there in the future.”

Simulating Savings

Starting with a computer simulation of the abandoned space, RFM partnered with mechanical engineers from Seattle-based Ecotope to calculate the necessary energy use allowing them to achieve net zero status. Using the region’s mild (heating) climate to their advantage, coupled with astute engineering design, Ecotape calculated the amount of energy generated by covering every horizontal surface with PVs while determining energy budgets for all of the end uses within the building.

Factoring heavily into the design of the building’s mechanical system was the addition of a 14-foot large-diameter Element fan from the Big Ass Fan Co.

“We designed the building around the design of the fan,” said Rice. “We have a hole in the upper area so we could incorporate the fan instead of running ductwork all over the place. That saved us quite bit of money, and with the fan it is just more efficient.”

One of the large contributors to energy use in commercial buildings is fan energy associated with central air systems. With the Element fan, RFM was able to move the same amount of air as traditional ducted air-handlers using 30 times less energy input.

Plus, the fan significantly reduced the amount of ductwork needed, resulting in an initial savings of $42,000 in material costs. Operating at no more than 50 percent of maximum speed, the fan successfully circulates air throughout the office. In addition, smaller fans were installed in each of the smaller offices and meeting rooms to circulate air and maintain occupant comfort.

Efficient Ventilation

Another innovation with the building design was to control the load so that simultaneous heating and cooling is not required, opening up the opportunity to turn off HVAC systems and use natural ventilation and ceiling fans.

The building is designed to operate in active mode when outdoor temperatures reach extreme levels and in passive mode upon milder outdoor conditions (55-75˚F). First year data indicates the building operates in passive mode for 42 percent of the year with the fan being used in lieu of the HVAC system. Total energy use for first year operations was 21.5 kBtu per square foot, per year, with HVAC energy use making up 3.1 kBtu per square foot, per year.

“It makes sense if you are in a heating climate or if you are well-insulated like an igloo. Also, if you are getting your heat sources from the people, the lights, or the computer servers,” explained Rice. “We have enough insulation around us that basically that’s our heat source for most of the year.”

This is where the effectiveness of fans comes in. In facilities that must contend with cool-to-cold winter temperatures, heating system efficiency can be drastically improved with the use of large-diameter, low-speed fans. Through destratification, warm air trapped at the ceiling level is circulated down to the occupants. Heated air from a forced-air system (90-125˚F) is less dense than the ambient air (75-85˚F) and naturally rises to the ceiling. Slowing the fan speed 10-30 percent of its maximum revolutions per minute (RPM), the warm air is redirected from the ceiling to the occupant level, increasing comfort and reducing the amount of heat loss through the roof. At the same time, the fans can be tied in with a facility’s automation system allowing the speed to fluctuate along with capacity, which, in this case, is critical to occupant comfort.

The simplicity of the design works with air’s natural tendencies. By letting convection take place, the hot air rises and the windows are opened at the top to let it out. When this warm air is needed, the large-diameter fans are employed to bring it back down.

SIDEBAR: LEED Points

The Rice Fergus Miller (RFM) office space achieved 91-point LEED Platinum certification. These are the areas in which Big Ass Fans contributed to the LEED qualifications:

Thermal Comfort Design: With the addition of Big Ass Fans, the project met the requirements of ASHRAE Standard 55-2010, Thermal Comfort Conditions for Human Occupancy, indicating increased air movement extends occupant thermal comfort range.

Optimized Energy Performance: Fans are used for destratification to reduce heating energy loss. The warmer air at the ceiling level is circulated back down to the occupant level, reducing the conductive losses through the roof. Ceiling fans with high-efficiency direct-drive motors contribute to reduced energy usage that effectively moves the air around compared to a typical HVAC system distributing air. The RFM project received all 20 LEED 3.0 EAcr1 energy points possible.

Controllability: During large community events, windows are opened and the Big Ass Fan speed is increased to offer a cooling effect to occupants. With the addition of natural ventilation from the operable windows, mechanical cooling is not required.

Publication date: 3/25/2013 

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