©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 7, July 2012.
By Murdoch MacPherson, P.E., Member ASHRAE
About the Author
Murdoch MacPherson, P.Eng., is president of MacPherson Engineering in Regina, SK, Canada. MacPherson is a member of ASHRAE’s Regina Chapter.
Having surpassed 42 employees, the continued growth of AODBT Architecture + Design necessitated a larger office space. In 2009, the firm purchased an existing 13,442 ft2 (1248 m2) inner-city warehouse, built in 1973 in Saskatoon, SK, Canada, with the intent to renovate it into its new LEED-certified office space. The location for the new office would help keep costs down while helping to revitalize the inner-city neighborhood.
The design team was challenged with turning the warehouse into a comfortable working environment in spite of the harsh outdoor ambient design conditions (ranging from –35°F [–37°C] in the winter to 88°F (31°C) db/68°F [20°C] wb in the summer).
During the pre-design, design and construction phases, an integrated design approach was used, which involved the owners, the design consultants, the construction manager and the subcontractors. The integrated design approach helped the designers meet the project requirements by evaluating different proposed systems and determining how they would affect overall constructability, budget constraints and the construction schedule. The mechanical systems were fully commissioned on site with the contractor present so deficiencies could be addressed at the time of discovery.
The existing envelope was supplemented with a new high-efficiency R-31 wall system and a new R-30 roof. High-performance glazing was used with exterior perforated metal solar shading. The solar shades also worked as an architectural and security feature of the building. Reuse of the existing structure, rather than constructing a new building, resulted in reduced construction waste, lower construction costs and reduced overall embodied energy (Figure 1). The enhanced building envelope was thermographically tested to confirm the integrity of the vapor barrier and wall construction.
The uninsulated floor slab edge and perimeter grade beam posed a particular challenge to the mechanical consultants as the floor would be very cold during the winter without proper treatment.
Radiant floor heating would have been a logical system alternative, except that the existing floor slab was to be polished as an architectural feature, so it wasn’t possible to embed hydronic piping.
The use of a perimeter hydronic radiation heating system could have been considered and would have met our heating season space comfort goals but would also have needed a non-condensing (20°F [11°C]·T ) boiler system. This alternative was too costly, energy inefficient and maintenance intensive to be considered.
The mechanical system that was ultimately designed and installed included seven horizontal condensing high-efficiency forced-air furnaces with direct expansion (DX) cooling. The furnaces were zoned from a cooling standpoint based on combining interior spaces, and on combining offices and areas with similar solar exposures. Supply air was distributed to the individual offices and areas through thermostatically controlled bypass diffusers.
The attractiveness of the system was the manner in which the perimeter offices and areas were kept warm and comfortable to ASHRAE Standard 55-2004 comfort requirements during the heating season. This wasn’t an easy task with diffusers 12 ft (4 m) in the air and a potentially cold concrete floor.
Citation: ASHRAE Journal, vol. 54, no. 7, July 2012
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