©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 8, August 2012.
By Charles C. Copeland, P.E., Fellow/Life Member ASHRAE
About the Author
Charles C. Copeland, P.E., is president and CEO at Goldman Copeland Associates in New York.
New York City’s compressed urban footprint and extensive mass transit system make it more sustainable than most American cities. Its greenhouse gas emission level, at 6.5 metric tons per person, is lower than that of 16 of the largest U.S. cities and well below the national average of 19.0.
The average New Yorker consumes less than half the electricity of a Dallas resident and approximately 33% that of a resident in Washington, D.C. Recent legislation, stricter energy codes, and incentive and cost-sharing programs have pushed sustainability goals to the forefront. As nearly 75% of the city’s carbon emissions result from building energy use, owners of the large commercial properties dominating the Manhattan landscape are driven to serve as models for efficiency upgrades.
Working with the New York State Energy Research and Development Authority (NYSERDA), our firm has had the opportunity to audit more than 32 million ft2 (297 290 m2) of this existing, mostly Class A, commercial building stock. This work includes one of the largest NYSERDA contracts of this kind.
This article is an introductory overview of the most effective technical strategies for improving HVAC energy performance in this important building type. Although real estate decisions can influence upgrade strategies in any locality, most of these techniques are transferable to other major cities.
Characteristics of HVAC Systems
Many of the city’s skyscrapers, especially in Midtown Manhattan, were built in the middle of the 20th century between the advent of the modern HVAC system and the acute awareness of energy issues resulting from the 1973 OPEC oil crisis. The invention of HVAC allowed architects to build these structures primarily using glass and steel, without concern for solar or thermal fluxes, or ventilation through operable windows; interior spaces could now be climate controlled. Energy was also relatively inexpensive, further reducing the need for designers to incorporate passive strategies to minimize heating and cooling loads. The predominant style of the time is known as the International Style, epitomized in New York City by the Lever House, the city’s oldest major “curtain wall” building, completed in the early 1950s.
HVAC systems in many of these legacy office buildings generally consist of:
- High-pressure (and high horsepower) perimeter air-handling systems supplying induction unit air systems (serving areas approximately 15 ft [5 m] from the exterior);
- Central air-handling systems, which serve the interior of multiple floors;
- Secondary water systems (perimeter zones);
- Constant flow chilled water pump systems and two-way chilled water valves on all heat transfer equipment;
- High-pressure steam turbine or absorption driven chillers (or, to a lesser extent, electric chillers) with heat rejection by cooling towers;
- Steam heating via air-handling steam coils or the secondary water induction system; and
- Building management systems (BMS), the majority still connected to pneumatically operated valves and dampers.
Table 1 reflects energy use information gathered during energy audits of 29 buildings, 84% of which were either built, or had HVAC systems retrofitted, between 1950 and 1970. Despite having similar vintages and systems, there is wide variety in the energy use of the audited buildings. This range is partly explained by the occupant and equipment density, and partly by the efficiency of the systems.
Citation: ASHRAE Journal, vol. 54, no. 8, August 2012
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