[Equest-users] HHW reset controls in eQuest

[Aaron Powers]

Dominique,

Short answer: You're getting negative/zero savings because you haven't
defined any loop losses or a UA for the HW loop.

According to your inp file, you have a normal natural gas boiler.
 Non-condensing boilers operate more efficiently with reduced HW supply
temperature only due to reduced jacket and piping losses.  The
stoichiometry of the process isn't changed when you change the supply
temperature, but the savings of a HW reset are because cooler water looses
less heat to the environment.  This is very different than the savings
associated with a CHW reset and a chiller in which the operating efficiency
of the chiller is improved.  Defining the losses (either by dT or UA) is a
tricky business though in my opinion.  For an existing building, you must
account for all losses through the system as geometries change and
environmental conditions change, and it would be easy to miss the mark.
 For a new building, the losses should be minimal with a good installation,
so the savings with a HW reset should be minimal.  The danger for any case
is that you can make the savings be whatever you want depending on what
value you give the loop UA.

Note that reducing your HW supply temperature will also decrease the
capacity of your HHW coils which will cause an increase in either pump or
fan energy, which is probably the source of your negative savings.  This is
a real concern in practice, and the HW supply temperature should really be
optimized globally to minimize all system energy usage.  Lower HW supply
temperature is not always the less energy intensive option.

Boiler lockout is another issue (mentioned in your earlier email).  Right
now, I don't see it defined in your inp file.  To model this, you want to
give some availability schedule to the HHW loop either based on time of the
year or outside drybulb.  This will show savings in eQuest, possibly at the
cost of unmet space conditions.

Aaron

-- 
Sent from my DynaTAC 8000x

---------- Forwarded message ----------
From: "Dominique Michaud" <dominique at scengineers.net>
To: <equest-users at lists.onebuilding.org>
Cc:
Date: Tue, 17 Sep 2013 09:51:22 -0700
Subject: Re: [Equest-users] HHW reset controls in eQuest

Fellow eQuest modelers,****

** **

I’m reposting my last query (see below) with an example of one of the
eQuest models that I have been having trouble with. Again, I’m having
trouble modeling some very simple (IMO) heating hot water/boiler energy
efficiency measures. I’m just not seeing the amount of savings I’m
expecting. I’m even seeing negative savings for some measures (this is
especially frustrating).****

** **

My offer of a beer to anyone who helps me solve my problem still stands,
though I’ll have to restrict my offer to US/Canada destinations. Did I
mention I’m in San
Diego<http://travel.nytimes.com/2012/05/27/travel/san-diegos-thriving-craft-beer-scene.html?pagewanted=all&_r=0>
?****

** **

Thanks in advance for your help.****

** **

*Dominique Michaud *| Project Engineer**

*SC Engineers, Inc.* <http://www.scengineers.net/>**

17075 Via Del Campo, San Diego, CA
92127<http://maps.google.com/maps?hl=en&cp=40&gs_id=2&xhr=t&q=17075+Via+Del+Campo,+San+Diego,+CA+92127&gs_upl=&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=583&wrapid=tljp132371020953200&um=1&ie=UTF-8&hq=&hnear=0x80dbf72707811bcf:0xafda74b7e473e651,17075+Via+Del+C>
****

P: 858.946.0333 | C: 858.436.4213 |F: 858.946.0334****

dominique at scengineers.net | www.scengineers.net****

** **

** **

** **

*From:* Dominique Michaud [mailto:dominique at scengineers.net]
*Sent:* Friday, September 13, 2013 5:35 PM
*To:* 'equest-users at lists.onebuilding.org'
*Subject:* HHW reset controls in eQuest****

** **

Fellow eQuest modelers,****

** **

I am experiencing a great deal of grief trying to model HHW/boiler energy
efficiency measures using eQuest. I am trying to model HHW temperature
resets based on outside air temperature and boiler lockout strategies.****

** **

Under the DD Wizard, “Hot Water System Control and Schedule > Setpoint is:”
 drop-down list I’ve selected “OA Reset” and allowed the resulting hi/low
temperature values to default, namely HW Max Temp: 180.0F and HW Min Temp:
140.0F (see attached screenshot).****

** **

Digging into the BDL, I noticed this issue:****

** **

     *5356 * "B5HW Lp Heat Reset Sch-D" = DAY-SCHEDULE-PD****

     *5357 *    TYPE             = RESET-TEMP****

     *5358 *    SUPPLY-LO        = 140****

-CAUTION-------------------------- ===
-------------------------------------------------------****

-CAUTION--- VALUE GREATER THAN MAXIMUM OF 0.1200E+03****

     *5359 *    SUPPLY-HI        = 180****

-CAUTION-------------------------- ===
-------------------------------------------------------****

-CAUTION--- VALUE GREATER THAN MAXIMUM OF 0.1200E+03****

     *5360 *    OUTSIDE-LO       = 30****

     *5361 *    OUTSIDE-HI       = 65****

     *5362 *    ..****

** **

However, it looks as though the values are accepted for the reset schedule:*
***

** **

-NOTE- - -         DATA FOR     B5HW Lp Heat Reset Sch-D****

-INPUT - - - - - - - - - - - - - - - - - - - - - - - -  TYPE             =
RESET-TEMP****

-INPUT - -                                              OUTSIDE-HI
=                      65.0000 F****

-INPUT - -                                              OUTSIDE-LO
=                      30.0000 F****

-INPUT - -                                              SUPPLY-HI
=                     180.0000 F****

-INPUT - -                                              SUPPLY-LO
=                     140.0000 F****

-DEFAULT - - - - - - - - - - - - - - - - - - - - - - -  DAY-HOURS
=                       1.0000****

-DEFAULT -                                              DAY-HOURS
=                      24.0000****

** **

** **

When I run the model I end up negative natural gas savings (i.e. more gas
usage than in my baseline case). No matter what dials I try to turn with
this EE measure, I consistently end up with negative savings. Even more
frustrating, when I try to run a OA temperature lockout for the boiler, I
get even more energy use than my baseline model!****

** **

Can anyone provide me with some guidance on what I need to do to get my
model to run these EEMs correctly? Help put me on the path to solving these
problems and I will buy you a beer…****

** **

(Note: I am using eQuest 3.64 Build 7130 – the latest release)****

** **

Thank you for any assistance you can provide.****

** **

Yours,****

** **

*Dominique Michaud *| Project Engineer**

*SC Engineers, Inc.* <http://www.scengineers.net/>**

17075 Via Del Campo, San Diego, CA
92127<http://maps.google.com/maps?hl=en&cp=40&gs_id=2&xhr=t&q=17075+Via+Del+Campo,+San+Diego,+CA+92127&gs_upl=&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=583&wrapid=tljp132371020953200&um=1&ie=UTF-8&hq=&hnear=0x80dbf72707811bcf:0xafda74b7e473e651,17075+Via+Del+C>
****

P: 858.946.0333 | C: 858.436.4213 |F: 858.946.0334****

dominique at scengineers.net | www.scengineers.net
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