Altitude Also Changes How Office Towers Operate
- Elevation can affect HVAC system performance and reveal operational differences between seemingly comparable office buildings.
When people talk about the height of a tower, most attention focuses on the building itself. However, the altitude it reaches also depends on the ground it stands on, which determines not only where its rooftop ends up but also some of the physical conditions the property must address.
In the office real estate market, where topography can vary considerably between submarkets, that difference can amount to hundreds of meters. In Mexico City, for example, Torre Reforma, the capital’s tallest office building according to the Skyscraper Center, stands 246 meters tall on ground located about 2,242 meters above sea level, putting its highest point at approximately 2,488 meters. By contrast, the East and West towers of Arcos Bosques II are 161 meters tall but start at about 2,467 meters, placing their highest points at roughly 2,628 meters, according to measurements taken in Google Earth. Thus, although Torre Reforma is 85 meters taller, Arcos Bosques II ends up about 140 meters higher.
Those additional meters change not only a tower’s position relative to sea level, but also the conditions under which it operates, as the lower atmospheric pressure and air density that accompany higher elevations mean the same volume contains less air mass and, therefore, systems that move air must account for that difference from the design stage.
According to U.S. Bureau of Reclamation data analyzed by SiiLA, between 2,000 and 2,700 meters above sea level at the same temperature, air density decreases by about 1.2% for every 100 meters of elevation. Temperature also matters, as at an altitude of 2,300 meters, between 0 and 40 degrees Celsius, air density decreases by an average of about 0.32% for each additional degree.
Those density changes directly affect a building’s HVAC systems by altering variables such as pressure, mass flow, and the power required by the equipment. As a result, technical manuals and manufacturers’ specifications include altitude and temperature corrections for sizing fans and other equipment, such as chillers, condensers, and cooling towers, and warn that failing to apply them can result in undersized equipment.
The consequences are not limited to sizing, as altitude can also change the relationship between the energy equipment consumes and the capacity it delivers. For one line of Trane air conditioning units, for example, the manufacturer specifies that at an altitude of 8,000 feet, equivalent to about 2,438 meters, cooling capacity decreases by roughly 3% compared with the sea-level reference, while required power increases by about 2%. Combined, both factors amount to approximately 5% less cooling capacity per unit of power, a difference that can affect cooling costs, although its impact on a property’s total energy consumption also depends on climate, design and building operations.
Elevation therefore introduces physical heterogeneity within the same real estate market that can remain hidden behind seemingly comparable buildings, as properties intended for the same use and with similar characteristics may have been designed to respond to different conditions depending on where they stand. Part of what distinguishes them, then, comes not from the construction itself, but from the site conditions their design had to address and that remain embedded in their engineering and operations, making the site not merely the surface on which a building stands, but part of what the building ultimately becomes.
So, the next time you see a skyscraper, remember that not everything that defines it was built, as some of its characteristics were already there before the building even existed. And if you want to discover what else lies behind the buildings and markets transforming Mexico’s real estate sector, visit SiiLA Market Analytics or email us at contacto@siila.com.mx.
