ASHRAE Journal - September 2012 - 65

2012 ASHRAE Technology Award Case Studies
The total residential portion of the building is approximately 275,000 ft2 (25 548 m2), with eight typical units on 30 floors for a total of 232 condominium units. The building has a two-level attached heated garage of approximately 52,000 ft2 (4831 m2). The exterior envelope of the building is comprised of concrete, brick and glass, and the building has new tinted, double-pane windows. In 2008, the engineering team conducted an objective energy audit and building pressurization study that included the heating, cooling and ventilation systems. The resulting report identified opportunities for improvement in energy efficiency, comfort, maintenance and especially, reliability. Shortly after delivery of the report, the design team laid out a complete mechanical upgrade of the condominium building, which included replacing the existing boilers, chiller, cooling tower and makeup air unit (MAU). Additional energy savings strategies included demand controlled ventilation (DCV), variable frequency drives (VFDs), carbon dioxide control for garage exhaust and a webbased building automation system. Because 525 W. Hawthorne is a residential condominium building, the entire mechanical upgrade project needed to be completed with the building occupied throughout construction. This required minimal downtime of all building services and careful planning during design and construction phases. and repair burdens with no redundancy. The recommended design called for replacing the original single boiler with two separate hot water boiler plants, forming a hybrid boiler system. The hybrid boiler plant design was cost-effective because an elevated-temperature, near-condensing boiler plant was located in the existing basement boiler room, and a low-temperature condensing boiler plant (for space heating only) was located in the mechanical penthouse, eliminating the need for a 30-story stainless steel stack. By installing condensing boilers, overheating was reduced as a more aggressive water reset schedule is used. The new elevated-temperature boiler plant was constructed entirely within the footprint of one of the existing boilers, allowing the remaining boiler to provide steam throughout construction. The elevated-temperature boiler plant uses eutectic cast-iron sectional boilers with high turndown (12:1) linkage-less burners, and serves domestic hot water, pool, garage and lobby-level heating. Installing the low-temperature condensing boiler plant in the penthouse presented structural, spatial and equipment ingress constraints. As a result, the design featured carbon fiber reinforcement of the existing penthouse floor and structural steel grating for access to the new boilers. New double-wall heat exchangers were installed for domestic hot water (DHW) and pool heating, while new piping and pumps were installed to serve the garage. Both new boiler plants were designed to offer redundancy, which was missing in the existing equipment. The design for the hybrid boiler plant is innovative because it allows for maximum efficiency by separating the hot water loads and, therefore, distinct hot water temperatures can be used. This improved resident comfort by allowing the first floor common areas to be heated during cool nights and shoulder months prior to the low-temperature condensing boiler plant’s annual startup. Also, the selection of low NOx condensing boilers and low NOx power burners (high-temperature hot water boiler plant) reduced the amount of harmful emissions.

Single-wall original DHW heat exchangers.

Chillers & Cooling Tower
Cooling for the building was originally provided by a steam absorption chiller, rated for 366 tons (1287 kW) of cooling and was designed to use 6,850 lb/h (0.86 kg/s) of 10 psig (170 kPa) steam. The absorption chiller, controls and cooling tower were original to the building and were also 38 years old. The cooling tower was in extreme disrepair and failed to start during the spring 2008 system startup. Large amounts of scale,

Building at a Glance 525 W. Hawthorne
Location: Chicago Owner: 525 W Hawthorne Condominium Association Principal Use: Residential high-rise condominium Occupants: 400 Gross Square Footage: 327,000 Conditioned Space: 327,000 Substantial Completion: 2010 (building was occupied throughout project)

Boiler Plants
The building was originally served by two fire-tube steam boilers located on the first floor with a seasonal efficiency of approximately 67%. The boilers operated continuously throughout the year and were maintained at approximately 11 psig (177 kPa). The steam was distributed to users in the building (garage heaters, absorption chiller) and a number of steam-to-hot water heat exchangers. The boilers were original to the building and, at the time of the energy audit, were more than 38 years old. The boilers had also undergone several repairs over the previous three years (totaling $78,000) and represented maintenance
September 2012

ASHRAE Journal

ASHRAE Journal - September 2012

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