Forum discussion
NC-2009 EAp2: Minimum Energy Performance
Forgive my ignorance, but I am not familiar with plumbing design. I need to calculate the domestic hot water usage as part of the energy model in EAp2. Is there a guide somewhere that explains how to estimate the annual hot water usage? I need a tutorial.
FYI I am using HAP for the energy modeling so I need to calculate this outside of the software.
Thanks.
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5915 thumbs up
January 17, 2014 - 10:31 am
There is a calculator for this within the new Table 1.4 (Dec 2012) spreadsheet you can download from LEED Online or the USGBC web site - http://www.usgbc.org/resources/eap2-section-14-tables-new-all-bdampc-pro...
Some of the assumptions used typically come from the ASHRAE HVAC Applications Handbook. It looks like Chapter 50 in the 2011 version.
There is also an example in the Advanced Energy Modeling Guide for LEED but it contains an error (do not assume 100% hot water for most applications). Also make sure that your assumptions are in alignment with the calculations for WEp1 as the reviewer check that for consistency.
Matt Scott
EngineerN.E. Fisher & Associates, Inc.
18 thumbs up
January 17, 2014 - 10:31 am
Thank you!
Matt Scott
EngineerN.E. Fisher & Associates, Inc.
18 thumbs up
January 17, 2014 - 11:53 am
Ok so looking over the Service Water Heating section of Table 1.4, it says the Service Hot Water Fixtures calculator (middle of the page) is only required if showing a savings between the baseline case and the proposed case. It seems the calculator only calculates the savings and not the actual usage. It looks like you still have to figure out outside of the spreadsheet how much hot water is to be used for either the baseline or proposed case.
Does the Advanced Energy Modeling Guide For LEED show you step by step how to go about calculating the actual water usage, not just the savings for low flow fixtures?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5915 thumbs up
January 17, 2014 - 12:32 pm
Sounds like you need the peak hot water demand for the project? When modeling you typically enter the peak demand, the hot water equipment and then schedule it. From those values comes the annual hot water energy usage.
The annual water usage is something different and is estimated by the calculations for WEp1. For those fixtures using hot water a common assumption it that 50% of the total water use is hot water but this can vary depending on the system.
This may not be of much help but as energy modelers for the project we will request the peak hot water demand from the project's plumbing engineer. They have to calculate it to size the equipment. Even if you calculate it yourself it must be coordinated to make sure it reflects the actual design value.
Some guidance is in Chapter 50 that I referenced above.
I am sure ASPE has some documents that outline the calculations - http://aspe.org/
Many engineers use rules of thumb and sizing charts provided by the hot water heating equipment manufacturers.
The Advanced Energy Modeling Guide does not show water usage calculations.
Matt Scott
EngineerN.E. Fisher & Associates, Inc.
18 thumbs up
January 17, 2014 - 1:45 pm
Thanks for the advice. I think I know where to take this now. Much appreciated.