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      OPTIMIZATION OF ELECTRIC HOT WATER RECIRCULATION SYSTEMS FOR COMFORT, ENERGY AND PUBLIC HEALTH

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          Abstract

          Hot water recirculation systems (RECIRC) are labeled green and are sometimes mandated in local plumbing codes. Previous work conducted under non-optimized operation schemes demonstrated that these systems actually waste energy and water versus standard (STAND) water heater counterparts. Optimization of RECIRC system operation by minimizing pump operation did improve energy efficiency 6–60%, saving consumers 5–140% annually in associated utility costs. However, STAND systems were still more energy efficient than any of the RECIRC systems. With respect to factors that might influence pathogen growth, reducing RECIRC pump operations increased disinfectant residual by as much as 560% as compared to the baseline RECIRC system; however, STAND systems still had 25–250% more total chlorine residual than any of the RECIRC systems. At 60°C operating temperature, STAND systems have 30–230% more volume at risk for pathogen growth (e.g., volume with temp 37–46°C) than any of the RECIRC systems. Thus, in the context of “green” design, RECIRC systems provide a convenience to consumers in the form of nearly instant hot water, at a cost of higher capital, operating and overall energy costs. RECIRC systems have distinct advantages in controlling pathogens via thermal disinfection but disadvantages in control via secondary disinfection residual.

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          Most cited references 8

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          Differential growth of Legionella pneumophila strains within a range of amoebae at various temperatures associated with in-premise plumbing.

          The potential effect of in-premise plumbing temperatures (24, 32, 37 and 41°C) on the growth of five different Legionella pneumophila strains within free-living amoebae (Acanthamoeba polyphaga, Hartmannella vermiformis and Naegleria fowleri) was examined. Compared with controls that actively fed on Escherichia coli prey, when Leg. pneumophila was used as prey, strains Lp02 and Bloomington-2 increased in growth at 30, 32 and 37°C while strains Philadelphia-1 and Chicago 2 did not grow at any temperature within A. polyphaga. Strains Lp02, Bloomington-2 and Dallas 1E did not proliferate in the presence of H. vermiformis nor did strain Philadelphia-1 in the presence of N. fowleri. Yet, strain Bloomington-2 grew at all temperatures examined within N. fowleri, while strain Lp02 proliferated at all temperatures except 41°C. More intriguing, strain Chicago 2 only grew at 32°C within H. vermiformis and N. fowleri suggesting a limited temperature growth range for this strain. Identifying the presence of pathogenic legionellae may require the use of multiple host amoebae and incubation temperatures. Temperature conditions and species of amoeba host supported in drinking water appear to be important for the selection of human-pathogenic legionellae and point to future research required to better understand Legionella ecology. No claim to US Government works. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.
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            Survival of Mycobacterium avium in a model distribution system.

            A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50microg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53 degrees C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.
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              Is Open Access

              A REVIEW OF THE SUSTAINABILITY OF RESIDENTIAL HOT WATER INFRASTRUCTURE: PUBLIC HEALTH, ENVIRONMENTAL IMPACTS, AND CONSUMER DRIVERS

               Randi H Brazeau (corresponding) ,  Marc Edwards (2011)
              Residential water heating is linked to the primary source of waterborne disease outbreaks in the United States, and accounts for greater energy demand than the combined water/wastewater utility sector. Furthermore, home water heating is the second largest energy consumer in the home and thus represents an integral part of the water-energy nexus. To date, there has been little practical research that can guide decision-making by consumers, public health officials and regulators with regards to water heater selection and operation to minimize energy costs and the likelihood of waterborne disease. Scientific uncertainties associated with existing “green” advice have potentially created misguided policy with long-term negative repercussions. This review is aimed at defining the current state of knowledge related to hot water infrastructure and in highlighting current gaps in the research. While there are many sustainability claims of certain water heater types (i.e., hot water recirculation systems and instantaneous water heaters) these claims have not been substantiated in head-to-head testing of the interplay between water temperature, energy, microbial growth, and scaling, all measures that need to be better defined.
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                Author and article information

                Journal
                jgrb
                Journal of Green Building
                College Publishing
                1552-6100
                1943-4618
                1943-4618
                Spring 2013
                : 8
                : 2
                : 73-89
                Author notes
                aCorresponding Author: Metropolitan State University of Denver, Campus Box 22, P.O. Box 173362, Denver, CO, USA 80202, rbrazeau@ 123456msudenver.edu , 303-556-2699 (p); 00-1-303-556-4436 (f)

                bVirginia Tech, 418 Durham Hall, Blacksburg, VA, USA 24060, edwardsm@ 123456vt.edu

                Article
                jgb.8.2.73
                10.3992/jgb.8.2.73
                ©2013 by College Publishing. All rights reserved.
                Page count
                Pages: 17
                Product
                Categories
                RESEARCH ARTICLES

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