HHW reset controls in eQuest

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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 

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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
?

Thanks in advance for your help.

Dominique Michaud 

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Joined: 2013-02-14
Reputation: 0

Thank you very much for your input, Ante. I hope you don't mind that I'm
sharing your explanation with the group.

Your suggestions were all hypotheses that I was contemplating, and you've
validated them with your clear explanation.

Due to time constraints I was asked to cut corners on zoning. And as you've
alluded, I think I'm paying for it now. Since the reset savings will result
when there is a large diversity in zone thermal needs, by not modeling them
the building doesn't act like it might in reality. Modeling one zone per VAV
system will not get me very far.

I didn't quite have a specific energy savings number in mind; I just wanted
a positive number that I could start working with. But now that I can
conclude that my model lacks some precision, I know where to start
troubleshooting.

Thank you again,

Dominique Michaud 

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Joined: 2013-02-14
Reputation: 0

Dominique,

Let me preface by saying that for years I've joked that the San Diego climate is so benign you could remove the walls and roof (or at least their insulating values) and it won't affect loads much.

I only had time to look at a few things quickly, which might explain some of your questions. I've noticed in the past that using the EEM wizard inserts some default values that you might not be aware of. For example, on air-cooled DX equipment if you specify an evaporative pre-cooler before the condenser, pumping power gets inserted. If you have a pre-cooler with no pump that operates on building supply pressure, you have to go into detailed edit mode to zero out the pump power. In the DD wizard you can also see some of the default values on the air-side or water side tabs and clicking on a component.

Anyway, your gas goes up a little in the economizer run. The baseline for system #1 shows 0% outside air in the DD Wizard Project Navigator. Without looking at hourly zone loads, it's possible the system is trying to satisfy the cooling of a zone with O.A. and causing some additional heating in other zones.

In the HHW variable flow run, electric only goes down 1% and gas goes up 5%. If you click on the waterside tab of the DD Wizard screen, you'll see you have an atmospheric boiler located outdoors. In this instance, this might not make much difference, but this boiler type and location could have higher standby losses. If you click the airside tab, you'll see that you have 3-way hot water valves. A 3-way valve system design is going to be virtually constant volume all the time. Looking at the PS-E end use energy report shows that the reduction in electric is from pumping. Not a lot of kWh, but this will result in less pump heat added to the HHW and the amount of increased gas is within reason if you convert the kWh to therms (about 127 therms of heat, not gas). Not all of the electric is going to end up as pump heat gain. If the motor is air-cooled, that drops the difference between the 127 therms of heat and 72 therms of increased gas, so the increase is within reason.

The 5 kWh in electric for the HHW supply temp reset run may be the result of a few hours that the VFDs have to speed up to satisfy zone temps. It's so small to be insignificant. No difference in gas consumption is hard to comment on without studying the input file or consulting the DOE-2 manuals. You might want to do this to see what calculation algorithms are used, how much piping is assigned and how it is assigned, what pipe insulating values, or if the program defaults to the piping being located in conditioned or unconditioned space.

Sorry I couldn't be more helpful but I don't have the time today to explore this deeper. For shakes and giggles, you might try changing the weather file to someplace like Chicago and see what kind of results you get.

My best,

Mike Busman

Michael R. Busman, CEM

Busman, Michael R's picture
Joined: 2012-07-12
Reputation: 0

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" To: 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 ?****

** **

Thanks in advance for your help.****

** **

*Dominique Michaud *

*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 *

Aaron Powers2's picture
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Joined: 2011-09-30
Reputation: 0