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RE: [EnergyPlus_Support] cooling load
The roof without insulation probably has a high night sky radiation that
cools the space. But it also has little resistance to solar gains
during the day, so although total cooling may be less, peak cooling load
may be more. I would check the solar absorption and emissivity values
you are using for the roof. A high reflectivity combined with high
emissivity is a "cool roofing" situation, but it may not be reliably
achieved in practice. Your roofing material, assuming galvanized steel,
should be a low reflectivity, low emissivity material that is more of a
heat trap.
Ned Lyon
Senior Project Manager
Simpson Gumpertz & Heger Inc.
41 Seyon Street
Building #1, Suite 500
Waltham, MA 02453
Phone: 781-907-9000
Fax: 781-907-9009
>>> chillarrahul@xxxxxxxxx 7/7/2004 1:08:34 PM >>>
Hello
Brents email gives a good explaination for the different loads in the
zone.
also i would like to say that adding the insulation would be Decreasing
the TOTAL Cooling Load on the Building , but the effect would only be
showing on the ground floor due to no insulation barrier on the ground
floor ceiling and it being able to release the heat to the upper floor.
If you do a Total SUm of COoling Loads for the entire building before
and After insulation i think it will be less after adding insulation.
Thanks
Rahul Chillar
Graduate Research Assistant
Building Systems laboratory
University of Illinois U C.
"Griffith, Brent" <brent_griffith@xxxxxxxx> wrote:
I bet that the ground floor slab is acting like a source of cooling in
an otherwise free floating building. Check that the ground temperatures
are reasonable. If you want better ground temperature values, you could
run slab.exe with the interior temperatures found in the first
simulation.
-----Original Message-----
From: zhen tian [mailto:tianzhen9@xxxxxxxxx]
Sent: Wednesday, July 07, 2004 10:04 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] cooling load
Hi, Rahul:
I underatnd the cooling load in the upper floor will increase with
added insulation because the insulation will be the barrier which
prevents the heat going out.
But I can not understand why the cooling load in the groud floor goes
down with added insulation in the upper floor roof.
Thank you.
Zhen
Rahul Chillar <chillarrahul@xxxxxxxxx> wrote:
Tek
this is what is happening.
Outside temperature is higher than inside, your insulation provides a
barrier for heat to go from outside to inside, this makes perfect
sense.
Now the building heats up all day in sun , its temperature rises.
The building is hot enougth and now needs to dissipate heat , The
insulation Blocks the heat from going out. This makes sense too.
Now what is happening is ,that when the building is trying to cool Or
lets talk each floor is trying to cool>>
Ground Floor is trying to Cool: It dissipates the heat to ground floor
ceiling which then goes into the upper floor zone. So upper floor gets
heat from lower floor and this lower floor ceiling is obviously not
insulated so there is nothing to block the heat being dissipated from
ground to upper floor.
Now
Upper Floor is trying to cool: It has heat from lower floor + its own
heat which it tries to dissipate and now there is insulation on the
upper floor ceiling (your roof) , THIS insulation will block the heat
going out from upper floor , so there will be an increase in the COOLING
LOAD for upper floor.
What you need to do is to vary the insulation parameters and find an
optimum which can get you the lowest cooling load .
This is the a wonderful capability of the E+ to vary the parameter and
see the effects which you should try.
I have neglected the heat dissipation from the walls of the building ,
cause they are unaffected.
Window heat gain depends a lot on the window area compared to wall area
, You may get more heat gain from window than the system cooling load
requirment , because your walls will also radiate heat , convect heat to
the enviornment outside. It is dependent quite a bit on outside
enviornment conditions which you need to look at when this happens.
Which hour / what is the temperature outside , wind speed etc.
Also just make sure you are comparing the same units for loads (and not
comparing rate Watt vs Load Joule) thought i am sure you might have
taken care of that.
Hope this helps
Thanks
Rahul Chillar
Graduate Research Assistant
Building Systems laboratory
University of Illinois U C.
Univerity of
teklay Weldeabzgi <teklay1979@xxxxxxxxx> wrote:
Rahul and Rohini you are right it may be the case.
but what i am confusing is, my building is a two story
(G+1) office building. when i see the results of the
simulation with and without insulation on the roof of
the upper floor of the building. the cooling load on
the ground zones decrease with insulation but for the
upper floor zones the cooling load increase with
insulation which seems an error.
another problem is on the window heat gain. does the
window heat gain directly sum up to the cooling load ?
if so in my report the window heat gain is greater
than the cooling load, why is this happens ?
--- Rahul Chillar <chillarrahul@xxxxxxxxx> wrote:
> Tek
> Since the building you are modelling is in a hot
> climate (equator) and there are no heating loads ,
> only airconditioning through out the year , The
> insulation would have negative effect. Infact your
> building would be heating up all day and will not be
> able to lose the heat due to insulation. This
> approach is suitable for cold climates. The
> explaination given by Rohini in email earlier
> justifies it well.
>
>
> Thanks
>
> Rahul Chillar
>
> Grad Research Assistant
>
> Building Systems Lab
>
> University of Illinois UC
>
>
>
> Rohini Brahme <rbrahme@xxxxxxxx> wrote:
> The reason could be that the heat from inside the
> building now has more difficulty in going out by
> conduction. This usually happens in office buildings
> which are dominated by internal loads and solar
> loads through windows. One way to check if this is
> true is to compare the internal temperatures without
> the system in the two cases. My guess is that the
> internal temperatures would be higher with
> insulation, and that these temperatures are higher
> than outside temperature on average. If you have
> enough air exchange with the outside (either by
> infiltration, or natural ventilation) then these
> numbers will be closer to the outside temperature.
> Also, make sure that the heating load is decreasing.
>
>
>
> Rohini
>
> -----Original Message-----
> From: teklay Weldeabzgi
> [mailto:teklay1979@xxxxxxxxx]
> Sent: Mon 7/5/2004 6:16 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Cc:
> Subject: [EnergyPlus_Support] cooling load
>
>
>
> when i simulate a ground plus one office
> building i
> gokt some confusing result due to insulation
> in the
> roofs. the roof in the upper floor is
> corregated iron
> sheet and a chip wood ceiling with an air
> space b/n
> them. when i see the annual cooling load for
> this base
> case and inserting an insulation just below
> the iron
> sheet the cooling load with insulation is
> greater than
> the cooling load with out insulation. but i
> doubt this
> result is correct b/c using insulation is to
> reduce
> the cooling load, but in my case it increases.
> can any one what will the possible reason. i
> have
> checked my idf file but i can't find any
> error.
>
> thanks
> tek
>
>
>
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