ASHRAE Journal - May 2012 - 19

dations on when condensate collection should be considered mandatory.

Prior Studies
Several attempts to estimate condensate have been previously published. A typical hourly condensate production rate was reported by Guz3 for buildings in San Antonio, Texas, of between 0.1 and 0.3 gallons of water per ton of cooling (0.11 and 0.32 L per kW of cooling), or approximately 0.5 gallons/hour per 1,000 ft2 of conditioned floor space (2.0 L/hour per 100 m² of conditioned floor space). At these rates of collection, condensate recovery systems were determined to be financially viable for buildings in excess of 100,000 ft2 (9300 m²). While this provides a useful guide- Figure 1: Location of cities studied. line for areas with a climate similar to San Antonio, it is not readily applicable to other areas and Selection of Cities and Weather Data Parameters climates. A set of 47 cities in the United States was selected for this Bryant and Ahmed4 reported in 2008 a simplified model based study, with these shown on the map in Figure 1. Although on empirical data from a case study in Qatar, predicting con- this study only looked at cities in the U.S., developing corredensate generation for a “normal” commercial air-conditioning lations between the amount of condensate and weather data system to be 8 gallons of condensate per ton of cooling (8.6 L parameters allows the results and conclusions to be appliper kW of cooling) for each day with a dew-point temperature cable anywhere. The first step toward this goal is to check in excess of 60°F (15.5°C). Painter5 reported a methodology if correlations can be derived for the amount of condensate to predict condensate production from dedicated outdoor air- collected with respect to readily available weather data pahandling units with energy recovery systems for buildings in rameters. This list of weather data parameters used in the Dallas, Houston and San Antonio, Texas, comparing the differ- correlation study, and the descriptive abbreviations reference in humidity ratio across the system cooling coils. enced in this paper, are given in Table 1. The values for all Lawrence, et al.,6 developed a method for evaluating the but one of these parameters were taken from one source, the amount of condensate collected from a typical air-handling unit ASHRAE Handbook—Fundamentals,9 while average annual based on the amount of incoming outdoor air and its temperature dew point was computed from the Typical Meteorological and relative humidity. This method predicts the collected con- Year (TMY3) data.10 densate using hourly weather data for when mechanical cooling would be expected, and accounts for the potential of using econo- Condensate Prediction Regression Study mizer cooling when that would make sense. The method was valThe amount of condensate collected annually was deidated using data collected from a field study during the cooling termined for each site using a methodology developed season of 2009.7 The method predicts the volume of condensate and verified using field site data collected during an entire annually collected from a unit volume flow of incoming outdoor cooling season.7 It would be ideal if a prediction method air. Application of this method to the varied climatic conditions of for the amount of condensate could be characterized with the U.S. was described in Lawrence and Perry.8 only a few parameters. Multivariate linear regression equation correlations were therefore developed using various Methodology combinations of the weather data parameters. The initial This study approached the topic of condensate collection regression was done using all weather data parameters, and with three specific purposes. The first was to develop a meth- then subsequent modifications made to evaluate using seod to characterize the total annual amount of condensate col- lected groups of the parameters, steadily reducing the numlected using correlations with local weather data parameters. ber of parameters in each regression step of the evaluation Next, was to evaluate the economics associated with a typical study. The combinations selected were based on factors that condensate collection system. Finally, these results would be should strongly influence the amount of condensate, such analyzed for generalizations regarding regions where con- as humidity levels and the amount of time mechanical cooldensate collection would be recommended from an economic ing is required (as opposed to “free cooling” using air or and/or environmental impact perspective. water-side economizers).
May 2012 ASHRAE Journal 19

ASHRAE Journal - May 2012

Table of Contents for the Digital Edition of ASHRAE Journal - May 2012