Case 3

Energy Impacts of Infiltration and Ventilation in U.S. Office Buildings

[Emmerich, S. J., A. K. Persily, et al. (1995), Emmerich, S. J. and A. K. Persily (1998)]

The purpose of this study was to estimate the energy use in commercial buildings due to infiltration and ventilation airflows and to investigate the potential for energy savings that could be realized by envelope tightening efforts. A set of 25 buildings was used as a representative sample of the U.S. commercial building stock as of 1995. Buildings were located in cities throughout the U.S. so that a representative sample of climates was also taken into account. Leakage characteristics were assigned to each building based on limited envelope leakage data that exist for U.S. office buildings.

Infiltration airflows were estimated using CONTAM to account for the effects of weather and ventilation system airflows on infiltration. For each building, a relatively simple CONTAM model was created that consisted of three zones per floor - one for the main occupied area, one for the plenum, and one for the elevator and stairwell shafts combined. WYEC (Weather Year for Energy Calculation) weather data was obtained for each of the cities in which the buildings were located. A bin method was used to handle the large amount of data involved in the study. For each building, a set of simulations was performed based on bins of weather and ventilation airflow data to determine infiltration rates for each bin of data. These infiltration rates were then used in the form of a lookup table along with thermostat set points and inside-outside temperature difference (used to determine whether cooling, heating or free-cooling) to calculate hourly heating and cooling (both sensible and latent) loads attributable to infiltration.

The results of this study estimated that infiltration is responsible for about 15% of the total heating energy and 4% of the total cooling energy for U.S. office buildings. Results also indicated that potential energy savings on the order of 26% for heating load and 15% for cooling load could be realized by tightening building envelopes by 25% to 50%. The study also revealed the difference in the contribution of infiltration to the heating and cooling load depending on whether the building was pressurized or depressurized with respect to the outdoors.