Fläkt Woods has built a reputation for large chilled beams projects in Europe, but this technology is still relatively unheard of in North America, so it was a demanding test to prove to some initially sceptical building owners that chilled beams, when used with advanced energy recovery, would work in a leading architectural university in Pennsylvania.
Colleges and universities are changing the way they approach construction projects and Marywood University is no exception. This private, Catholic university in Scranton, Pennsylvania, unveiled its new Centre for Architectural Studies amid enormous excitement and pride from faculty, students, and the architecture/engineering team.
The Centre is the academic facility for the University’s new School of Architecture. Inside the restored walls of a former gym, Marywood students will pursue undergraduate and graduate architectural degrees. Lessons in sustainability, energy efficiency and indoor air quality literally surround these students as they prepare for a career in architecture. This includes the use of chilled beam technology and advanced energy recovery.
The University instigated an efficiency-focused design, proposed by the engineering firm of Greenman-Pedersen. Their team suggested using 42 Fläkt Woods chilled beams to provide 100% of the cooling for both floors of the renovated building.
Chilled beams were a good choice for this project because of the limited floor-to-floor space and a cooling dominant load. Since a second level was added to the centre of the former gymnasium, there was limited space for ductwork; this led the engineer to choose a dedicated outdoor air delivery system to provide all the necessary ventilation (and proper humidification or de-humidification). They opted for a chilled beam system to satisfy the sensible load.
All chilled beams are fitted with Flakt Woods patented Comfort Control. This enables velocity control to be regulated by means of variable geometry slots and offers both uni-or bi-directional supply and enables adjustment of air diffusion into the room. Regulation of capacity increased flexibility for future planning.
Since large ductwork is not required for the beams (when compared to a VAV system), they are remarkably space efficient, requiring only ceiling space and minimal space for wiring, piping, and ventilation ducting.
Passive chilled beams are also whisper quiet, making them ideal for an open, educational application like the School of Architecture. In fact, the only noise associated with chilled beam cooling is the almost imperceptible flow of water through the coils. They also integrate well with the exposed steel structure and the parallel lighting units suspended from the structural deck above.
Chilled beam systems offer exceptional comfort and indoor air quality, however, to avoid the issue of condensation on cold surfaces the dew point temperature of the air needs to be controlled at a level below that of the cold surface in question. The dew point temperature of outdoor air in the summer in the US can often be well above the surface temperature of the coil in a chilled beam.
This means that moisture must be removed before supplying it to the room. The traditional method is to use a cooling coil to condense out the water and then a re-heater to warm the air to a suitable supply-air temperature. This method demands a large cooling plant and is costly to run.
The use of the Pinnacle Primary Ventilation System, which dehumidifies and preconditions supply ventilation air is an important part of the puzzle since chilled beams handle sensible loads only, not latent loads.
Craig MacFadyen, Applications Manager at Fläkt Woods explains: “Using our knowledge of twin wheel technology and active chilled beam systems, engineers have created a more efficient method of providing dehumidification to the primary fresh air in order to avoid problems with condensation.”
“I thought it was a great idea,” said Myron Marcinek, Assistant Director of Buildings and Grounds at Marywood. “It seemed like a great energy saver and we are very proactive in that.”
How it works
The chilled beams are supplied with cold water from the campus’s central chilled water system. A three-way control valve blends chilled and return water to maintain the temperature within a few degrees above dew point to prevent condensation. Typically, chilled water through the beams is maintained between 13°C to 17°C - substantially warmer than the chilled water temperature used in a typical VAV system.
Although chilled beams offer many advantages, it is critically important to address dehumidification as a separate issue, which is what led Steve Daiute, Assistant Vice President of Greenman-Pedersen, to choose the Fläkt Woods’ Pinnacle unit. He says: “It was the only system that could provide the humidity control we desired without any active regeneration of desiccant material. The design of the entire system was built around the specific inclusion of the Pinnacle unit, which offers a wide operating range and can be highly customised for the application.”
The passive dehumidification wheel in the Pinnacle system dehumidifies the supply air to a dew point far lower than any standard air conditioning equipment can provide. This deep dehumidification satisfies the building latent load with much less airflow than what would be required by typical air conditioning equipment. Combining the most energy efficient ventilation/latent load system (Pinnacle) with the most energy efficient sensible load system (chilled beams) is a win-win combination for the school.
The Pinnacle system pre-cools and dehumidifies outdoor air during the cooling season; it also preheats and humidifies the outdoor air during the heating season. Pre-tempering and dehumidification are both accomplished by recovering (or rejecting) heat from the exhaust air stream via the heat wheels. The Pinnacle system responds to variations in temperature and humidity by modulating the rotational speed of the passive dehumidification wheel, and/or adjusting the energy input to the cooling coil. The rotational speed control may be adjusted to control the level of temperature and moisture exchanged by the passive dehumidification wheel.
The first wheel, a total energy wheel, and the second, a passive desiccant dehumidification wheel, work in series to pre-temper and dehumidify supply air, ultimately bringing it down to an arid 7.2ºC dew point. The Pinnacle system responds to variations in temperature and humidity by modulating the rotational speed of the passive dehumidification wheel, and/or also adjusting the energy input to the cooling coil, which is positioned between the two heat wheels.
The Fläkt Woods twin wheel system is best controlled by their stand-alone control unit, which ensures proper operation and needs a minimum of input from the main AHU controller. The nominal efficiency of thermal wheels is typically between 70 and 85% depending on air velocity.
“In practice, with today’s emphasis on energy recovery, most systems will include some method of heat recovery. Nevertheless, this configuration shows a marked efficiency improvement in the summer cycle and is better in the winter cycle than most systems with some form of heat recovery”, adds Craig “Pinnacle is a very valuable addition to the range and although predominantly for overseas use, there would always be end user savings wherever the technology is employed.”
The University’s School of Architecture anticipates earning LEED Gold certification for the newly-renovated building (equivalent to our BREEAM excellent rating). The application of the chilled beams and energy recovery technology will enable Marywood University to achieve several points under “LEED Energy and Atmosphere, Credit 1: Optimise Energy Performance.” More important, the students and faculty are enjoying a healthier, more comfortable environment at a reduced carbon footprint.