Awareness is growing about the need to conserve and reuse freshwater supplies across the U.S. and around the world. In much of the U.S. and other developed nations, there is commonly a basic assumption that there will be always be plenty of water to supply and feed a lifestyle that we have become accustomed to. Other areas of the globe have continually lived with water shortages, and in these regions water is treated like the valuable commodity that it is. Supply (or lack of it) and demand does influence the price of water, although in most developed nations the price of water does not fluctuate much in the near-term. ASHRAE recognizes the importance of water to society and the consumption of water by buildings and building systems. Some now consider water concerns to be just as important as energy within the green building circle. Two ASHRAE Standards are being developed or recently released that address water use within buildings. Standards 189.1-2010 (Standard for the Design of High Performance Green Buildings Except Low-Rise Residential Buildings) and 191P (Standard for the Efficient Use of Water in Building, Site and Mechanical Systems) each provide requirements for water using systems and condensate collection.

Since existing buildings comprise approximately 98% of the building stock (the other 2% being new construction), a significant and immediate benefit to society in terms of energy or water consumption savings exists with the existing building stock. In the right situation, retrofitting existing buildings has the potential to provide significant water consumption savings. This paper presents a methodology for predicting the amount of water collected from an air handling unit. The prediction model could be used to estimate the water collected for either a retrofit or new construction scenario. Data taken during the 2009 cooling season on a 100% outdoor air unit were used to validate a model for the amount of condensate collected. The data included the amount of condensate collected, outdoor and supply air conditions (temperature and relative humidity), and supply airflow (the unit has a VFD control for the fan). Results indicate that it is possible to predict the amount of condensate, but the accuracy of the prediction strongly depends on the accuracy of the relative humidity sensors used.