Our firm has come across a way to substantially lower energy use in many commercial buildings using a simple, readily implemented measure. This observation arose from our work on two large energy conservation efforts for NYC office buildings. The first was NYC’s Energy Conservation Capital program (the largest municipal program at that time) highlighted in this 1980s article. The other was our more recent effort to identify and implement energy efficiency projects in high-rise commercial buildings in New York City (August issue of ASHRAE Journal). Despite the intervention of almost three decades, at least one large wasteful concern persists: the excessive amounts of outside air most buildings draw in through defective outside air dampers.
Though not always inexpensive, this is a relatively straightforward issue to correct and one that most building owners and managers should consider.
In one major office building, after the outside air quantities were field tested, we found that leaking dampers allowed several times more outside air in than that recommended by ASHRAE Standard 62.1-2007 (see Test Building 1 in Table #4 below, taken from our ASHRAE article). Even with ostensibly closed dampers, the leakage rate exceeded 40% in this building. Testing in subsequent buildings confirmed that a large majority of the ubiquitous 1960’s and 70’s commercial office buildings are over-ventilated, resulting in wasted energy, some for heating, but mostly for cooling. Many of these dampers date from the original construction of the building. Table #4 shows the results of air testing of a number of other properties.
Table #4: Excess outside air is common in older large, commercial buildings
If a majority of Manhattan office buildings have excess outside air quantities similar to Table #4, installing new dampers would significantly reduce wasteful energy use as well as overall energy costs.
Another measure connected with curbing excess outside air is demand controlled ventilation (DCV), a process for reducing the cooling and heating costs associated with excess air. It has wide ranging applications not only in office buildings but in hospitals, recreation spaces, auditoriums, museums and many other facilities. The DCV technique employs equipment that measures the freshness of air in a building, typically done by measuring carbon dioxide (CO2). Although typically associated with global warming, in this case CO2 turns out to be an excellent proxy for determining appropriate ventilation conditions. (Because people breathe CO2 out, the concentration of CO2 reflects the number of people in a space.) Typically outside air in New York City is 400 to 450 ppm of CO2. An occupied air environment is normally considered “fresh” when the CO2 level is less than 1100 ppm. Clearly, unless tightly-closing dampers are in place, DCV will not be fully effective since it relies on being able to stop outside air exchange when ventilation is not needed. Using Test Building 1 as an example, Figure #2 shows the extent to which installing low-leakage dampers can be key to the effective use of DCV.
Figure #2: Test Building 1 proportional outside air savings; low-leakage dampers vs. DCV.
Unfortunately, some dampers constructed by local shops are not always engineered appropriately. The linkages and damper motors often do not properly close the large damper assemblies and the damper blades become deformed, further limiting closure. Outside air dampers must be installed on a modular basis, with appropriately sized damper motors and linkages, to provide adequate torque to close the dampers leaktight. High quality dampers, properly installed and adjusted, are the key to reducing outside air to appropriate levels and employing DCV effectively.
