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Tim: As usual, the answer is 'it depends"... The (annual) efficiency of instantaneous hot water heaters is a controversial topic and is a function driven primarily by whether or not the a standing pilot is used, the frequency and duration of hot water loads, and the estimated amount of cold water usage 'wasted' if/when users are waiting for hot water to be delivered or when the minimum flow requirements are exceeded and the hot water draw becomes cold. At any rate, the TREAT (Targeted Residential Energy Analysis Tools) software suite allows one to model the annual effects of changing from a tank storage type of system to a tankless type of system. More importantly, TREAT employs a very unique savings determination algorithm which allows users to combine multiple individual improvements into 'packages' to see the interactive effects - which more accurately capture and quantify the 'interactive' savings that occur when multiple improvements are simulated. For example, TREAT could accurately quantify the interactive savings from changing out existing shower-heads and faucet aerators with 'low flow' devices, while switching hot water heaters from say a tank type 40 gallon electric to a tankless propane model, combined with improving the insulation of the DHW piping (piping surface areas are user specified) in unconditioned spaces from from R1 to R4, and resetting the DHW temperature from 135 degrees F to 120 deg F. As always, users must provide accurate input (GIGO), if they expect accurate output, which is especially important when working with simulating an existing building. To assist with this, TREAT integrates a billing analysis tool for use against the baseline building model which compares baseload (weather independent) and heating/cooling slope (weather dependent) energy consumption of the model against utility billing data. Good data from residential utility bills are required for this feature, and the data is weather normalized (corrected) using daily high/low temperatures correlating to the billing data period, while the model uses TMY2 30 year average weather data . If billing analysis is used to 'match' the baseline model , users can improve the confidence of their predictions when investigating baseload (hot water, appliance and lighting) energy improvements. This is probably more than you wanted - but I wanted to make sure you were aware of the possibilities when you are considering annual simulations. You can download a 30 day fully functional trial version of TREAT (including program documentation) from http://www.treatsoftware.com. Have fun - Chris Chris Balbach, P.E., LEED AP Manager of Energy Engineering Services Performance Systems Development http://www.psdconsulting.com (607)-277-6240 tim wrote:
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