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[EnergyPlus_Support] Re: Mechanical Rooms
Dear Josh,
I'm making this up as I go, since, as mentioned previously, I have not
done much more than think about these issues. Hoping that it
encourages some discussion, I'll plunge onward....
1) All conditioned spaces with > ~1W/square foot heating or
1.5W/sq.ft. cooling capacity must be modeled as having both heating
and cooling systems. It strikes me that some mechanical rooms might
not have this much heating / cooling capacity. If, for example, there
is only a ventilation fan for cooling, you might not exceed the 1.5W
threshold.
2)If I were you, I WOULD create an HVAC system, identical between
Baseline and Proposed. Of course, if the actual mechanical room is
served by a higher efficiency heating or cooling system than is
required for the Baseline, I'd take advantage of that benefit for LEED
points.
3)Rigorous energy accounting would make it important to add energy
from motor casings or boiler jackets to the mechanical room so that
its HVAC system "sees" a realistic load. Since those items are
already accounted for in the respective equipment object (e.g.,
Fan:Simple or Boiler:Simple), we need to have a means of separately
accounting for that heat so that it does not get double-counted in a
total (as you mentioned previously). I think this could be done by
assigning an equivalent amount of energy to, say, an ELECTRIC
EQUIPMENT object for that zone. I'd make a unique "End-Use
Subcategory" and report that energy with a Report Variable. You would
also need a Schedule that mimics the load. A simple approach would be
to make a reasonable estimate of the average, then make it a constant
for the entire year. For a boiler this should be reasonable, since
the jacket load would not vary too much. Another approach that may
work for a VAV fan, which I've heard others in this forum discuss,
would be to model the system, report the actual energy through the
year, then create a schedule for the motor inefficiency that mimics it.
Whichever method you choose, the seprate Report Variable provides a
convenient total that can be subtracted from the overall total. This
would be good to mention and explain in your final LEED submittal.
4) If you do NOT mechanically cool the mechanical room in the Proposed
system, you could still utilize a high cooling setpoint for that zone
to make sure the cooling system does not actually run. The fan
capacity and energy can be defined for the actual Proposed fan, and
the "cool" thing is that the room temperature should be predicted
reasonably closely by E+ and impose the proper load on adjoining zones
through their shared walls.
That said, the "less rigorous" approach is to provide HVAC to the
mechanical room, ignore the loads from inefficient motors or boiler
jackets since they're already accounted for once, and call it good
enough. Generally, I suspect that these loads are a tiny portion of
the overall energy use of any building.
So far, I've been working harder than at any previous time in my
moderately long life just trying to make E+ behave reasonably. I
haven't yet had time for this level of "rigor".
Congratulations on thinking through the details of the analysis and
not treating E+ as a magic box! That is both important and will pay
dividends for you and your clients.
Sincerely, Jim Dirkes
p.s., feedback always welcome! (or I wouldn't post it in the first place!)
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Josh K" <jeemang@...> wrote:
>
> Hi JV;
>
> Thanks for your thoughts. A few things:
>
> Just for background: the CaGBC version of LEED is in my
understanding pretty
> close to the USGBC version. One difference that is pertinent to this
> discussion is that the LEED Canada allows the use of either ASHRAE
> 90.1 *or*the Model National Energy Code for Buildings (a Canadian
> energy code based
> largely on ASHRAE 90.1 that was developed by the the Canadian
government)
> for the evaluation of EA credits.
>
> With respect to the mechanical room issue: so, were you me, would I be
> correct in understanding that because 90.1 requires the modeling of all
> spaces as heated cooled, you'd simply create a system, identical in both
> "proposed" and "baseline" cases, to condition the mechanical room space?
> Also, would I be correct in assuming that doing this renders the
question of
> process heat gains from equipment in the mechanical room somewhat
> irrelevant?
>
> Finally, with regard specifically to the process gains, the main
thing I was
> concerned about was the boilers. In this particular building there
are 3 of
> them, each with a seasonal efficiency of around 90%; it seems to me
that the
> "other" 10% of the heat they generate would be discharged to the
mechanical
> room, and would not be insignificant...
>
> Josh
>
>
>
> On Fri, Jul 18, 2008 at 12:00 PM, JV Dirkes II <jvd2pe@...> wrote:
>
> > Dear Josh,
> >
> > For your consideration:
> > 1) I'm not familiar with any variations of LEED that Canada may be
using
> > 2) LEED EA credits require compliance with ASHRAE 90.1, which in turn
> > requires modeling ALL spaces as heated and cooled (subject to some
> > anmormal exceptions noted in the Scope statement, par 2.2 and 2.3)
> > Also note Table G3.1, no. 4 regarding schedules.
> > 3) I think that you can model the mechanical room "cooling" system
> > with a very high setpoint so that it never operates. Just use the
> > same setpoints in "Baseline" and "Proposed" systems.
> > 4) You raise a good point regarding possible double counting of fan
> > and pump motor heat. Although they're small in the overall scheme, I
> > don't know where E+ puts that heat. For fans, at least, the motor is
> > often in the airstream and thus part of the cooling load. Not so with
> > pumps!
> >
> > --- In
EnergyPlus_Support@xxxxxxxxxxxxxxx<EnergyPlus_Support%40yahoogroups.com>,
> > "josh_miarch" <jeemang@>
> > wrote:
> >
> > >
> > > Howdy All;
> > >
> > > I'm preparing a model for a LEED Canada EAc1 submission third party
> > > review, and I'm curious as to how I should account for the
building's
> > > two mechanical rooms (this is the first LEED submission I've
done). In
> > > this building, they are both within the building envelope, and
neither
> > > is directly conditioned.
> > >
> > > The literature says that if they're inside the main building
envelope,
> > > they should be modeled, but doesn't provide much guidance beyond
that.
> > > My thought, based on this, was that I should keep them uncontrolled
> > > and add some internal gains objects to account for the heat
given off
> > > by the AHUs, pumps, boilers, etc, but I haven't the first clue about
> > > how I could accurately estimate the heat emitted by this equipment,
> > > particularly when it would be changing in response to the loads in
> > > other parts of the building and the ambient temperature in the room.
> > >
> > > Alternatively, it was suggested to me that I add a single-zone
system
> > > of some sort (UNIT HEATER perhaps; the building isn't cooled) to
> > > control it to a relaxed setpoint (16-18 C), which makes some
amount of
> > > sense to me, as it would avoid the problem of having to create a
very
> > > elaborate internal gains schedule. However, the problem I see (and
> > > perhaps I'm misunderstanding something) is that this would
> > > effectively double count the inefficiencies of the equipment in the
> > > mechanical room.
> > >
> > > Any suggestions on either method (or another) would be greatly
> > > appreciated.
> > >
> > > Many thanks,
> > >
> > > Josh
> > >
> >
> >
> >
>
>
>
> --
> Josh Kjenner, EIT, LEED AP
> Manasc Isaac Architects Ltd.
> 10225 100 Avenue :: Edmonton, AB T5J 0A1
> 780.429.3977
>
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