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[EnergyPlus_Support] Re: Mechanical Rooms
This is from the Bldg-Sim List and seems relevant. Just passing it
on.... (Didn't remember this before posting the last time.)
I have a mechanical room that is conditioned to 95 in cooling through
exhaust fans and heated to 65 with unit heaters.
Do the exhaust fans constitute as a cooling system? The system would
need to provide a sensible capacity of 5 btu/h*ft2 for the mech room
to be considered to be a cooled space, which I have not yet calculated.
The reason I as is that if these exhaust fans are not considered a
cooling system then the baseline cooling system will need to be
modeled to complete an accurate LEED model.
Any suggestions?
There definitely seems to be some variability out there on how it's
handled.
There are several LEED CIRs posted on the LEED website for situations
that seem similar to this. My take on it is that if you are only
ventilating the spaces, the ventilation fans don't need to be counted
as a cooling system; thus, you do not need to model a cooling system
for these spaces. However, the fan energy does need to be accounted
for in both the proposed and baseline models. So, they basically
become energy neutral in the models and/or are treated kind of like a
process energy load.
If others have a different interpretations, I'd appreciate hearing the
feedback.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "JV Dirkes II" <jvd2pe@...>
wrote:
>
> 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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