Process Equipment Power Consumption

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Dear All,

One of the things that cause most trouble for us in modelling is the power
consumption of equipment such as dishwashers, ovens, food warm-up
equipment and so on that have varying levels of power consumption during
operation (even PCs and laptops). We are sometimes using nameplate
installed kW values, but deep inside we know that this is quite wrong -
but we have no other more reliable source / guideline for such equipment.
I would appreciate any feedbacks on how others are modelling such
equipment.

Thank you,

Omer Moltay, LEED AP

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Omer,

Absolute agreement - modeling plugload with any degree of certainty is a
headache.

At least for Office equipment, there is some information, albeit dated:
"Heat Gain From Office Equipment", pp33-39 ASHRAE JOURNAL June 2000 issue.
This article summarizes some information from ASHRAE research projects
RP-822 and RP-1055.

Someone else on the list may know of research that's a little more
up-to-date.

Steven

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Hi Omer,

On recent projects, I have had to pay more attention to the process loads for the types of equipment you mentioned below. In the past, I would just ensure that my process energy cost was 25% of the total energy cost because I knew that the types of buildings I was modeling (commercial offices, mostly) would never have an actual process load even close to 25%.

However, recently I have been modeling process loads in a more exact way. What I do is I take the kW rating of the equipment, then I talk to the electrical engineer to get an idea of whether that equipment will ever run at its rated load and, if not, I apply the appropriate reduction to it based on what the electrical engineer says.

Once I have this maximum energy use for process loads in the building, I then create a custom schedule for this process energy. Sometimes I need to create more than one custom schedule based on the type of equipment in the space. This can become very tedious if you get too far into the weeds, so I try to keep the schedules realistic, but simple and I keep the number of different custom schedules I create to a minimum. As we all know, you can never know the actual occupancy and use schedule of a building until it is occupied for a certain period of time, so keep your assumptions simple and logical.

I'd love to hear what other folks are doing if it differs from my process.

Kristy Walson, PE, LEED AP

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Please refer to the Chapter 18, Nonresidential Cooling and Heating Load
Calculations of the 2009 ASHRAE Handbook of Fundamentals.

Best regards,

Gaurav Mehta

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Whenever you have an equipment, aka process, load it is proper to apply
first a diversity factor, aka % on at one time, and then a schedule. Whether
your building is new or existing doesn't matter. This is an Art not a
Science. Experience is the primary teacher. You can always ask us old farts.
We are relevant and have information that one only can get with time. Yours
to chose to listen to or not.

Peace out,
Carol

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I do not believe we are double discounting. Try this: think of when you turn
your computer on and off however you do so during the day, lets say on at 9
am off at noon on at 1 pm off at 5 pm. That is your schedule. Now think of
how when you walk away from your computer for any length of time and it goes
into sleep mode, that's your diversity.

Comments, thoughts are welcome. Is this what you were maybe getting at with
the multiplier, Nick.

Waiting to learn more,
Carol

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The schedule, with multipliers (fractions), as found in DOE-2 for example, will have in fact already accounted for both run time and diversity.

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Demba NDIAYE

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Carol et al,

Here's my current understanding of the options we have (specifically in
eQuest) to specify equipment loads (from my head - correct me if I'm
off):

- You may enter one (optionally, up to 5) distinct W/SF or kW
value for a zone to represent the full equipment load(s). You may
optionally apply a diversity to the full load at this step here, but if
doing so you should modify your operation schedules as follows...

- Each equipment load specified must be assigned a fractional
schedule. You may choose to use 0's and 1's to model ON/OFF behavior,
but eQuest left to its own devices generates hourly schedules which
apply such diversity here.

- The hourly thermal effects of each specified equipment load
may be reduced further by means of specifying the sensible and latent
load factors - values from 0 to 1. By default, I believe equipment
loads generated by the wizards will have whatever you may have specified
for sensible (1.0 by default) and 0.0 for the latent portion. The sum
of these two factors cannot exceed 1.0, and these factors have no effect
on the amount of energy consumed - only the heat contributions.

In the referenced and on-going (?) thread (discussing the intent and
means of handling/satisfying the LEED 25% default process load rule) I
brought up the possibility of specifying additional equipment loads with
a sensible/latent fraction of 0.0 - effectively consuming additional
energy to reach the 25% mandate, but also contributing nothing to
internal heat gains. It was suggested, and I'm currently in agreement,
that an easier and less seemingly subversive approach to meeting the 25%
rule and achieving the same intentions would be to instead specify a
direct internal load to the electric meter. It should be noted some
feel strongly that the 25% rule itself ought to be ignored entirely, but
if this topic interests you I'd suggest replying to that discussion
thread for clarity's sake ;).

NICK CATON, E.I.T.

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So sorry! The user is the only one who accounts for anything.
DOE2/eQUEST/EnergyPlus are all just tools. The schedules found in DOE2 are
just *advice and suggestions.* (user beware! GIGO can happen). We the
modelers, and Demba, I mean you no disrespect at all, are responsible to
review and revise these suggestions.

I am so outdated, I remember when we had to create each and every schedule
on our own in BDL. Now that would be an energy modeling competition I'd be
interested in IBPSA.

Love to all,
Carol

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Has anyone looking at the COMNET recommendations. They are trying to provide
a more comprehensive guide for energy modeling. They include a lot of
recommendations on plug load density and scheduling. The recommendations
appear to be a combination of the 90.1 users manual, ACM and their own
recommendations.
http://www.imt.org/comnet.html

In general I think it makes more sense to consistently apply reasonable plug
load assumptions rather than chase 25%.

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I agree with Austin. All of these are resources for us that can be used
along with good judgment, sound engineering practices, and any available
real information. We just have to remember that we are the users and the
model is just a model.

C

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What I meant is that if you input a schedule of that type, both factors are embedded into it.

_________________
Demba NDIAYE

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1) How about an excessively low discharge air temp (assuming that you have a
reheat coil)
2) a site in the Sahara desert ;)
3) a corrupt weather file?
4 I know those weren't too helpful, but it seems that an energy modeler is
always solving a similar mystery.

p.s., Good for you to be checking your output critically!

The Building Performance Team
James V. Dirkes II, P.E., LEED AP

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The schedule, with multipliers (fractions), as found in DOE-2 for example, will have in fact already accounted for both run time and diversity.

_____________
Demba NDIAYE

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Carol et al,

Here's my current understanding of the options we have (specifically in
eQuest) to specify equipment loads (from my head - correct me if I'm
off):

- You may enter one (optionally, up to 5) distinct W/SF or kW
value for a zone to represent the full equipment load(s). You may
optionally apply a diversity to the full load at this step here, but if
doing so you should modify your operation schedules as follows...

- Each equipment load specified must be assigned a fractional
schedule. You may choose to use 0's and 1's to model ON/OFF behavior,
but eQuest left to its own devices generates hourly schedules which
apply such diversity here.

- The hourly thermal effects of each specified equipment load
may be reduced further by means of specifying the sensible and latent
load factors - values from 0 to 1. By default, I believe equipment
loads generated by the wizards will have whatever you may have specified
for sensible (1.0 by default) and 0.0 for the latent portion. The sum
of these two factors cannot exceed 1.0, and these factors have no effect
on the amount of energy consumed - only the heat contributions.

In the referenced and on-going (?) thread (discussing the intent and
means of handling/satisfying the LEED 25% default process load rule) I
brought up the possibility of specifying additional equipment loads with
a sensible/latent fraction of 0.0 - effectively consuming additional
energy to reach the 25% mandate, but also contributing nothing to
internal heat gains. It was suggested, and I'm currently in agreement,
that an easier and less seemingly subversive approach to meeting the 25%
rule and achieving the same intentions would be to instead specify a
direct internal load to the electric meter. It should be noted some
feel strongly that the 25% rule itself ought to be ignored entirely, but
if this topic interests you I'd suggest replying to that discussion
thread for clarity's sake ;).

NICK CATON, E.I.T.

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So sorry! The user is the only one who accounts for anything.
DOE2/eQUEST/EnergyPlus are all just tools. The schedules found in DOE2 are
just *advice and suggestions.* (user beware! GIGO can happen). We the
modelers, and Demba, I mean you no disrespect at all, are responsible to
review and revise these suggestions.

I am so outdated, I remember when we had to create each and every schedule
on our own in BDL. Now that would be an energy modeling competition I'd be
interested in IBPSA.

Love to all,
Carol

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I agree with Austin. All of these are resources for us that can be used
along with good judgment, sound engineering practices, and any available
real information. We just have to remember that we are the users and the
model is just a model.

C

cmg750's picture
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What I meant is that if you input a schedule of that type, both factors are embedded into it.

_________________
Demba NDIAYE

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