[Equest-users] Hot Water Usage Percent

Nicholas Caton ncaton at catonenergy.com
Fri Dec 4 21:29:53 PST 2015

I do believe domestic hot water supply (and delivery temperatures, though
that isn't an input) should match between cases.  Do you have some sort of
energy saving measure that would most easily be captured with such a
differentiation and could not be accounted for in an increase/reduction in
hot water consumption volume (i.e. kgal per year)?

I'm guessing your reviewer didn't offer any more specific guidance / clues
for how they want you to separately account for cold water only usage?

To date I have not been called to make a "cold-water-only-usage" distinction
between residential and other lavatories, for LEED projects outside of
multifamily highrise (where SHW is a relatively bigger deal).  Perhaps I've
been lucky.  For multifamily projects there's a much more developed/involved
procedure for residential HW consumption between the energystar simulation
guidelines and their 'performance path calculator'.

This is the first time that sub-passage has been called to my attention in
the 1.4 Tables workbook.  I'm not aware of an 'official' source for
residential "cold-only operation percentage" or similar.  Perhaps you are
meant to rule-of-thumb it based on what you know about the occupancy,
whether there's hot water recirc present, whether the climate lends itself
to chilly hands, average dental hygiene ... etc.  Perhaps you could just
state something in response like "Based on XXX, we estimate these lavatories
operate in cold-only operation approximately 30% of the time.  Therefore we
apply a factor of 0.70 to the percentage calculated for the mixed condition
delivery temperature."

I think in reality, there are many site and occupant-specific factors that
would make "cold-water-only" operation percentage a highly variable thing
(i.e. this is a case-by-case thing).

If someone knows of a study/publication that nails this down however, I'd be
interested to know as well!

If you are really motivated, I suppose you could try, for each such fixture
type, working some of the current energystar guidance for multifamily
highrise backwards to contrast against the annual consumption you would
otherwise calculate for a fixed mixed delivery temperature at all times.
This will again involve site/occupancy specific variables such as
residential occupant density / usage patterns / etc...  The associated
baseline hot water consumptions involve a specific fractional schedule which
I suppose ought to be informed by the sort of data that would help us here
(but I truly do not know its origin).



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

-----Original Message-----
From: Sefa Şahin [mailto:ssahin at mimtarch.com]
Sent: Friday, December 04, 2015 4:05 AM
To: Nicholas Caton; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Hot Water Usage Percent

Hi Nick,

First of all, thank you for your kindly helping. Your advices are make
easier to my workflow. I have also two question. Do we have to use same
service hot water temperatures for baseline and proposed design case?
How can you adjust baseline service hot water temperature ?
Additionally, my project includes residential lavatory faucets and common
lavatory faucets and these faucets fixture temperatures are same.
Residential lavatory faucets %hot water and common lavatory faucets % hot
water are must be different because of  the following sentence that exist on
Table 1.4.5.  "e.g. residential lavatories would be expected to have cold
water usage associated with brushing teeth".
How can we calculate this difference?

Thank you

04.12.2015 01:02 tarihinde Nicholas Caton yazdı:
> 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 simulation).
> 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:
> http://www.rmi.org/ModelingTools
> Hope that gets you moving!
> Owner
> Caton Energy Consulting
>    306 N Ferrel
>    Olathe, KS  66061
>    office:  785.410.3317
> www.catonenergy.com
> -----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.or
>> g To unsubscribe from this mailing list send  a blank message to
> Sefa Sahin

Sefa Sahin

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