[Equest-users] Hot Water Usage Percent

Nicholas Caton ncaton at catonenergy.com
Thu Dec 3 15:02:56 PST 2015

Regarding the mixed hot water % example:

Yes, the % hot water for mixed water is proportional to the relative
deltas... this can be figured/proven from basic energy balance equations but
I'm too rusty/forgetful to derive it from memory.  Here's how it looks in
*my* brain if I type it out:

% hot water = ( Tmixed - Tcold ) / ( Thot - Tcold)

Regarding baseline/proposed concerns... this is simpler than it may seem.
Here's my typical workflow outlined:

1. Figure out your proposed case hot water supply temperature to the service
hot water loop.  This is technically the temperature leaving the heat
exchanger for your case, but you might interpret this to be the temperature
leaving the hot water boilers (to exclude piping/exchanger losses from the
2. Calculate the loop demand flow rate (gpm) based on the fractional
schedule used and the outputs the Table 1.4 spreadsheet provides you to
effect matching annual hot water consumption  (gph/60 = gpm).
3. Baseline case supply/storage temperatures MATCH the supply/storage for
hot water in the proposed case.  Fractional consumption schedules match
also.  Baseline case however will provide the higher annual consumption you
calculated by way of entering a higher demand gpm for the loop.
4. Concerning storage, the only other typical difference in inputs between
baseline/proposed would be to account for differing rates for standby
losses.  There are other threads in the archives that go into detail on that
topic, but a "one stop shop" for most conversion effort cases is the
'Domestic Hot Water' tab in RMI's EMIT spreadsheet:

Hope that gets you moving!


Caton Energy Consulting
  306 N Ferrel
  Olathe, KS  66061
  office:  785.410.3317

-----Original Message-----
From: Sefa Şahin [mailto:ssahin at mimtarch.com]
Sent: Thursday, December 03, 2015 8:42 AM
To: Nicholas Caton; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Hot Water Usage Percent

Hi Nick,

For example: the annual ground water temperature is 60 F , delivery
temperatures of SHW equipment is 120 F and the mixed fixture outlet
temperature is 104 F. In this case, hot water percent is 73.3, cold water
percent is 26.7. Is it true?

Our proposed design uses the heating hot water boilers to provide service
hot water through a heat exchanger. Baseline case uses gas-fired water
heater with storage tank. How can we calculate percent of hot water or cold
water When delivery temperatures of proposed and baseline case are
different? Additionally, How can we adjust Baseline service water storage
temperature ?

Thank you for helping,

02.12.2015 21:18 tarihinde Nicholas Caton yazdı:
> I advise grabbing a copy of your project's reprequisite preliminary
> documentation (as occurring) to avoid conflicts in your calculations,
> then to leverage the 'Service Water Heating' tables in the Seciton 1.4
> tables spreadsheet to work out the % of hot water consumption per
> fixture.  This will account for cold water usage.
> I typically leverage the annual ground water temperature
> (representative of cold water at delivery), the delivery temperature
> from the SHW equipment, and the mixed fixture outlet temperatures
> weight the % of hot water delivered for each fixture type consuming hot
> water.
> The spreadsheet will then calculate the "peak" gal/hr (provided the
> "annual equivalent hours" determined from your fractional schedule)
> w0hich you can easily convert to gal/min for equest input.
> It's a relatively easy number crunching exercise.  Hope that helps!
> Owner
> Caton Energy Consulting
>    306 N Ferrel
>    Olathe, KS  66061
>    office:  785.410.3317
> www.catonenergy.com
> -----Original Message-----
> From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org]
> On Behalf Of Sefa Sahin
> Sent: Wednesday, December 02, 2015 10:03 AM
> To: equest-users at lists.onebuilding.org
> Subject: [Equest-users] Hot Water Usage Percent
> Dear All,
> We have received the following  from GBCI regarding the energy
> modeling
> review:
> "The percent hot water listed in Table 1.4.5 does not appear to be
> calculated based on the storage and fixture supply temperature and
> adjusted to account for expected cold water only use"
> How can we adjust hot water usage percent?
> Thanks for all replies,
> Sefa Sahin
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to

Sefa Sahin

More information about the Equest-users mailing list