[Bldg-sim] Equipment Sizing

Varkie C Thomas thomasv at iit.edu
Sat May 22 08:35:16 PDT 2010


 
I changed the topic name to �Equipment Sizing�.  I thought I would add my 2 cents worth also.  So now Bldg-Sim has 8 cents worth.
 
The first building project that I was associated was at the tail end of the M-E design at JB&B of the Federal Reserve Bank Building in Minneapolis.
http://www.lera.com/projects/ofc/federalreservemn.htm
The building opened in January (I think) in the early 70s.  ASHRAE winter design at 1% is -16 F.  When the building opened it was about -30 F (it can go down to -40 F there) with strong winds.  Occupants in the US are not dressed (with full arm and leg heavy woolen underwear) to tolerate low indoor temps even for one day.  
 
Summer design in Minneapolis at 1% is 92 DB 75 WB but the DB can exceed 100 F.  Occupants can tolerate a little discomfort on the few days that extreme summer conditions occur.  It�s still better than no AC.  Few, if any, buildings were air-conditioned, even in the US, before 1940.  The moral of this story is design for extreme winter conditions in very cold climates.  Judgment, experience, and common sense have to be applied.  It depends on the location.  In a place like Singapore the temp varies from a low of 75 F to 95 F all day and all year.  There are no extremes.  All buildings in tropical countries do not need heating systems.
 
Inefficient energy use occurs when there is only one unit of the equipment and it is oversized.  When there are two or more units, one unit starts until it reaches maximum, then second unit comes on and the two shares load.  The units are rarely operated at minimum load.  This is the default in DOE2 but LOAD-MANAGEMENT allows you to sequence the use of primary equipment in any way you want that is appropriate for the project.
 
The lighting and equipment design criteria was 5 watts /sf and 3 watts /sf for buildings designed before the energy crises in 1974.  No one cared about energy before then.  Actual lighting density was nowhere close, and there was very little equipment in offices.  This means for a million sqft building you end up with three chillers.  One is standby which comes into operation when a chiller fails or one chiller has to be shut down for maintenance.  Specifying standby primary equipment affects first costs and does not affect equipment efficiency.
 
Energy programs are for comparing alternative energy conservation measures.  There is no need to size equipment for occasional extreme weather conditions.  But I think auto-sizing is based on weather data (not design data or median weather data) so equipment is sized for the worst condition of that year.  This means at every other hour of the year the equipment is operating inefficiently at part load conditions.  Equipment sizes estimated by energy programs are used in the design process.
 
Equipment schedules in design documents are based on actual equipment selected from manufacturers catalogs.  The name of the manufacturer and the model number are specified and then �or equal� added.  Equipment schedules are not based on design calculations or generic data because it is possible that real equipment cannot meet the performance data.  You need the dimensions of the equipment (with clearances for maintenance) to design them into the space.  TRACE energy program is based on actual real equipment performance data specified my model numbers.  HAP is based on real equipment, but they don�t mention model numbers.
 
I think the Code of Federal Regulations 10CFR434 (ENERGY CODE FOR NEW FEDERAL COMMERCIAL AND MULTI-FAMILY HIGH RISE RESIDENTIAL BUILDINGS) used to allow you to size two identical units of primary equipment each at 66% of the maximum design.  This would be commercial buildings with large heating and cooling loads where you would have two units.  Perhaps it was a special case where failure to perform at all times was not an option.  I couldn�t find it the latest register.
http://www.wbdg.org/pdfs/10cfr434.pdf
 
10CFR434 - 403.2.2 Equipment and System Sizing.
Heating and cooling equipment and systems shall be sized to provide no more than the loads calculated in accordance with subsection 403.2.1. A single piece of equipment providing both heating and cooling must satisfy this provision for one function with the other function sized as small as possible to meet the load, within available equipment options. Exceptions are as follows:
(a) When the equipment selected is the smallest size needed to meet the load within available options of the desired equipment line. 
(b) Standby equipment provided with controls and devices that allow such equipment to operate automatically only when the primary equipment is not operating.
(c) Multiple units of the same equipment type with combined capacities exceeding the design load and provided with controls that sequence or otherwise optimally control the operation of each unit based on load.
 
 
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Jason,
 
Thanks for your insightful response.  To a large degree I concur.  You
encounter various situations out there as a design consultant, and you
need to understand the plans and needs of your client.  But surely you
recognize that there are some cases where over sizing is not required,
and the client may actually prefer to pay less up front and get a better
operating system than always be able to maintain set point under the
most extreme combination of conditions.  When maintaining perfect
environmental control is critical, then you must oversize accordingly,
but when it isn't, you may assign more priority to proper sizing, or, in
rare cases, under sizing.
 
I personally would prefer a slightly undersized AC system in my home to
an oversized one if I had to choose between the two.  I understand the
advantages, and prefer to risk having to tolerate a little discomfort
for a few hours a year than to pay for and operate an excessively
oversized system for the next 15 to 20 years.
 
But to offer this to a client may be risky business unless you get him
to sign a waiver, and then it is still risky.  On the other hand, if you
can determine the maximum probable system load and add a reasonable
10-25% to that, you will have satisfied the client's needs with a
reasonable margin of safety.  The only angry clients I have ever
encountered were angry because their system was failing to deliver a
significant amount of the time when circumstances were only normal, in
which cases the engineer had made a serious error and specified a system
that was grossly undersized.  I don't recommend over sizing to make
certain this doesn't happen.  Instead I recommend checking and double
checking your sizing calculations so you don't make such a mistake.
 
This is a hot issue because nearly every HVAC engineer is going to
sooner or later make that proverbial mistake, lose self-confidence, and
from then on join those that oversize their systems more than necessary
just to cover potential mistakes.  Most clients are none the wiser
anyhow, and, after it has all been paid for, some actually enjoy the
feeling of knowing they have a "honker of an air conditioner" that is
capable of cooling the place down in 60 seconds or less.  So what do we
have to lose?  I think it might be some of our own professional and
personal integrity!  Not much else comes to mind.
 
Now I have said too much, so I will bow out of this, knowing that last
paragraph may ruffle some feathers.
 
Glenn

________________________________

From: Jason Humbert [mailto:jhumbert at sesnet.com] 
Sent: Friday, May 21, 2010 3:57 PM
To: Haynes, Glenn
Subject: RE: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering


Glenn,
 
For load sizing, over sizing equipment can be bad with them short
cycling and energy hogs.  But on the other hand under sizing a system
can be just as bad.  When you size equipment you normally can't select
equipment that will meet your building load exact so most engineers
normally go to the next size up in equipment. Very rare do I see or hear
any one pick the size down in equipment.  Its the nature of the beast.
Everyone has the fear of being sued from an owner it is easier to
oversize the equipment that way you have the extra capacity if you need
it, than having to deal with an angry owner.  
 
My view on energy simulation is like trying to kill a fly with a bullet.
Everyone is trying to predict exactly what a building will do and how it
will perform, and you just can't.  There are so may variables in an
energy simulation, some variables you can predict and even control and
other variables you just can't predict or possibly even know.  That is
why I believe it is important to relay the bases of your energy
simulation to whomever you are presenting it to.  That the simulation is
based on these parameters and based on these parameters this is how the
building should perform.  And then when the building is build and its
performance is better or worse than what you predicted then you can
compare the variables and see which ones are off and how bad.  And the
most common variables that is normally off is infiltration and weather.
But no one goes back to a building after it has been build to adjust
there model to see what was off.  And that is also the nature of the
beast as well.
 
Jason Humbert
 
4000 W. Eleven Mile Rd.
Berkley, MI  48072
p: 248.399.1900 ex. 215 
f: 248.399.1901
jhumbert at sesnet.com
 
 
 

________________________________

From: Haynes, Glenn [mailto:Glenn.Haynes at kema.com] 
Sent: Friday, May 21, 2010 11:49 AM
To: John Aulbach; Chris; backer at uidaho.edu; paul at zed-uk.com;
thomasv at iit.edu
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering


John,
 
Looks like I might have awakened a sleeping giant...been around awhile,
huh?  Are you going to tell us how it worked out?
 
Glenn

________________________________

From: John Aulbach [mailto:jra_sac at yahoo.com] 
Sent: Friday, May 21, 2010 11:34 AM
To: Haynes, Glenn; Chris; backer at uidaho.edu; paul at zed-uk.com;
thomasv at iit.edu
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering


I did all that 30 years ago using the Meriwether ESAS program for Hilton
Hotels. Before DOE-2. Before DOE-1 !!


________________________________

From: "Haynes, Glenn" <Glenn.Haynes at kema.com>
To: Chris <chris at zed-uk.com>; backer at uidaho.edu; paul at zed-uk.com;
thomasv at iit.edu
Cc: bldg-sim at lists.onebuilding.org
Sent: Fri, May 21, 2010 8:22:53 AM
Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering

Chris,

You make a good point, and it also can apply to centrifugal chillers,
which are sometimes most efficient at 60-80% loaded.  But you still have
to remember that the client has to pay for the larger equipment, which
costs more, plus larger system components (which cost more) and more
space (which costs more).

You also maake a good point about the system loads 90% of the time,
which raises an interesting question regarding sizing for optimum
operating efficiency.  What if we sized certain types of equipment to
meet the most predominant loads within their most efficient capacity
ranges?  That is not difficult when using hourly simulation software.
Of course, you have to keep an eye on peak loads and capacities.  I
haven't thought this through yet, but I'll bet someone else has.

Thanks,
Glenn

-----Original Message-----
From: "Chris" [mailto:chris at zed-uk.com] 
Sent: Thursday, May 20, 2010 7:13 PM
To: Haynes, Glenn; backer at uidaho.edu; paul at zed-uk.com; thomasv at iit.edu
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering

Glenn,

Oversize isn't always bad! A condensing boiler is generally at its most
efficient at < 20% of its capacity.

All the same, the mid-season is largely ignored when it comes to sizing.
Ridiculous really, when you think this is where the plant will be 90% of
the time.

Perhaps this is more of an issue when you are shifting large amounts of
chilled water to various pieces of zone equipment but has anybody
considered Valve Authority? Unfortunately my experience is limited when
it comes to the nitty gritty of piping networks. But, I do know one
thing: valve response is not linear, especially if there is a
substantial head in the system. My hunch is mid season control could get
really messed up if plant has spare capacity but designers haven't been
quite as generous with pipe sizes.

Such questions should be in the domain of simulation in the next few
years.

Chris

on 20/5/10 8:15 PM, "Haynes, Glenn" <Glenn.Haynes at kema.com> wrote:

> Brad,
>
> I did HVAC design consulting for 14 years, and I used to oversize 
> systems just like everyone else.  Now I am an energy conservation 
> programs evaluator, and have discovered the extent and negative 
> impacts of over sizing.  Not speaking for all designers who oversize, 
> I did it mainly out of willful ignorance.  It was easier for me to 
> loosely calculate the peak loads and then beef those estimates up 
> enough to safely cover and mistakes or false assumptions than it was 
> to calculate the loads with enough confidence to properly size the 
> systems.  I believed in the old adage that too much is just right from

> my perspective, because it minimized risk.
>
> But now I have to measure the effects of excessive over sizing and see

> the results, some of which are poor humidity control, short cycling, 
> reduced system operating efficiency and higher first cost to the
owner.
> My DOE2 models usually indicate peak (I mean absolute hourly peak 
> loads) at about 20% less than Manual J loads, on average, for 
> residential applications.  But even Manual J allows up to 20% above 
> their calculated loads, which have already been calculated using 
> conservative estimates for most inputs that are not explicitly 
> defined.  The observed
> (measured) field results have proven the average residential AC system

> to be about 70% to 75% oversized, with some as high as 200% (that's 3 
> times the peak load).  20% to 25% over ASHRAE's 2.5% design standard 
> is acceptable to me now, but anything above 25% without some 
> overriding owner requirement (plans to add on to the current building,

> etc.) begins to waste the owner's resources (from first cost to energy

> and maintenance costs) and reduce the lifetime of the equipment while 
> at the same time decreasing his overall level of comfort through 
> limited latent performance.
>
> There!  You obviously rubbed a sore spot in my emotional make-up, but 
> I appreciate the opportunity to make a point.  And the point is this: 
> no matter how good your modeling software is, the outcome is still in 
> the hands of the user.
>
> Glenn
>
> -----Original Message-----
> From: bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Acker, 
> Brad
> Sent: Thursday, May 20, 2010 1:45 PM
> To: Paul Carey; Chris Yates; Varkie C Thomas
> Cc: bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering
>
> I do not do modeling on a daily basis so I'm not as experience as many

> other here. I do agree modeling just for LEED is silly. I have seen 
> modeling inform designs, reduce loads, and SIZE SYSTEMS. This last 
> part is what most bugs me. Why do people put so much effort into 
> models and then not use them to size the systems? Preventing over 
> sizing is a great benefit of modeling. What is your experience with 
> using models to size systems? Why do engineers fall back on the vendor

> based programs and 9 out of 10 times end up over sizing systems?
>
> Brad Acker, P.E.
>
> -----Original Message-----
> From: bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Paul 
> Carey
> Sent: Thursday, May 20, 2010 3:42 AM
> To: 'Chris Yates'; 'Varkie C Thomas'
> Cc: bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering
>
> Just to add a couple of points to this interesting debate.
>
> I see the problem being that, as we increasingly set more defined 
> limits regarding energy modelling and its role in building regulation,

> we are seeing buildings that are being built and designed to purely 
> meet compliance.  This is in some part is useful as it brings all 
> buildings up to a minimum standard, the flip side of that problem is 
> that it also means, that to many developers this means there is no 
> incentive to strive for alternatives or innovative solutions.  It can 
> also allow therefore lead to the use of simpler tools that meet those 
> prescribed limits, but really don't push the boundaries of engineering

> design enhancement of buildings.
>
> The correct implementation and use of energy modelling need not be a 
> hindrance to projects nor be seen as a necessary "extra" or evil if 
> you consider the design process as a whole.  If you use the tools at 
> the concept or schematic design phases, this can quantitatively 
> confirm an engineer's instinct or gained experience in way that will 
> enable them to show compliance later on. It will then allow the team 
> to come to a decision on the most energy efficient but also compliant 
> route of design earlier on in the design stage and should stop the 
> repeat iteration of designs as the building design progresses and 
> therefore reduce design costs and with luck increase productivity and
profit accordingly.
> Fanciful dream perhaps, but it does work.
>
> I visited an architect a while back and he said to me "Why do I need 
> to do modelling, I know the principles of good low energy design, I 
> can read books
> and learn more if I need to".  To which I replied, "Well every time
you
> send me a job to check for building regulation compliance 3 weeks 
> before it goes before a planning team, I normally have to tell you 
> what you need to do in terms of meeting compliance as your buildings 
> are consistently failing and you then have to rush to make those 
> changes.  I am effectively designing your buildings for you, so if you

> want to continue without using energy modelling then please carry on, 
> and I'll continue to design your buildings."
> As you can imagine this was one of those Eureka moments for this 
> Architect, as I waved my red rag in front of his face.
>
> My tuppence worth.
>
> Paul
>
> -----Original Message-----
> From: bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Chris 
> Yates
> Sent: 20 May 2010 07:55
> To: Varkie C Thomas
> Cc: bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Fwd: Re: RE: Voodoo Engineering
>
> Varkie
>
> Vast subject. Kudos for condensing it whilst conveying all the 
> necessary meaning.
>
> We are now at a point where Energy Modellers are at the very least 
> specialist engineers. In fact, you could say the best are indeed 
> "wizards"!
>
> Chris
>
> Sent from my iPhone
>
> On 19 May 2010, at 21:35, Varkie C Thomas <thomasv at iit.edu> wrote:
>
>> Since my response has ended up on Bldg-Sim, I might as well include 
>> the attachment with the response which gave my views 
>> <Building-Energy-Programs-VCT.doc>
>> I am including the attachment that I included with my earlier 
>> response
>
>> to John Eurek. Using energy programs is like voodoo engineering if 
>> you
>
>> don't understand its engineering basis.  It analyzes the various 
>> options quantitatively.  It cannot be used as a magic black box.
>> Experience and judgement have to applied to the results.
>>
>> ----- Original Message -----
>> From: Eric O'Neill <elo at MichaelsEngineering.com>
>> Date: Wednesday, May 19, 2010 12:03 pm
>> Subject: RE: Voodoo Engineering
>>
>>> John,
>>>
>>> The purpose of energy modeling is to identify differences between 
>>> two
>
>>> energy related setups. The idea is to tell you how much you could 
>>> conceivably save by switching from one design to another. This is 
>>> usefulfor a payback analysis or life cycle cost analysis.
>>>
>>> Hope this helps, (I'm really not trying to be inflammatory :) )
>>>
>>> Eric
>>>
>>> -----Original Message-----
>>> From: Eurek, John S NWO [mailto:John.S.Eurek at usace.army.mil]
>>> Sent: Wednesday, May 19, 2010 11:19 AM
>>> To: Varkie C Thomas
>>> Cc: Eric O'Neill; cmg750 at gmail.com
>>> Subject: RE: Voodoo Engineering
>>>
>>> Varkie, I read your attached paper.
>>>
>>> "Energy programs are external to the design process. The results are

>>> not used to generate construction drawings."  This may be my #1 beef

>>> with energymodeling.  What is the purpose?
>>>
>>> If you say, to save energy...  It does not.
>>>
>>>
>>> John Eurek
>>> LEEP AP
>>>
>>>
>>> -----Original Message-----
>>> From: Varkie C Thomas [mailto:thomasv at iit.edu]
>>> Sent: Wednesday, May 19, 2010 10:08 AM
>>> To: Eurek, John S NWO
>>> Subject: Voodoo Engineering
>>>
>>> Academia institutions and research centers tend to attach 
>>> disproportionate amount of importance to energy modeling.  Most them

>>> have not dealt withreal buildings.  Attached are my views on energy 
>>> modeling.
>>>
>>> ----- Original Message -----
>>> From: "Eurek, John S NWO" <John.S.Eurek at usace.army.mil>
>>> Date: Wednesday, May 19, 2010 8:14 am
>>> Subject: Re: [Equest-users] Compliance rule set for Oregon
>>>
>>>>
>>>> I would prefer Lynn work to ban/destroy/do-away-with energy
>>> modeling.>
>>>> Any chance this voo-doo engineering will go away any time soon?
>>>> It is only
>>>> statistical analysis with no meaningful/useful results for anyone.
>>>>
>>>> As a community I think we are going in the wrong direction for
>>> the
>>>> rightgoals.
>>>>
>>>> -----Original Message-----
>>>> From: equest-users-bounces at lists.onebuilding.org
>>>> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
>>> Carol
>>>> Gardner
>>>> Sent: Wednesday, May 19, 2010 12:30 AM
>>>> To: Scott Criswell
>>>> Cc: equest-users at lists.onebuilding.org; curt.strobehn at eesinet.com
>>>> Subject: Re: [Equest-users] Compliance rule set for Oregon
>>>>
>>>> All,
>>>>
>>>> Lynn Bellenger will soon be the first female president of ASHRAE..
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