[EnergyPlus_Support] Re: Indoor air temperature LOWER than ambient temperature

["academicryan" <azianzheep@xxxxxxxxx>]

Hi Jason,

Thank you! You are absolutely right! (And thank you Richard as well). I put a massive cover over the glass house and indeed the phenomenon stopped. Thank you for providing the solution as well as a way to test it. 

Cheers

Ryan



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Jason Quinn <jason.e.quinn@...> wrote:
>
> Richard hit it on the head - it is most likely radiation cooling to the
> night sky.
> 
> Actually if you've eliminated thermal lag effects ( the interior
> temperature is below the LOWEST nighttime temperature) and the ground
> temperature under the slab is above this than the only variable that can
> produce a lower temperature is radiation cooling. Frost on your car window
> when it clearly did not go below freezing is a good example of this but
> I've seen refrigerators that use this as well - essentially with a clear
> sky if your object is insulated from seeing the ground objects it can get
> quite cold.
> 
> Thinking this through for buildings the night cooling effect due to
> radiation cooling to the clear night sky would be largest for small thermal
> inertia and large exposed glass. You can prove this by adding an exterior
> shading element over the windows (actually just stick it over the whole
> building and let it extend a bunch so the building cannot see the night
> sky). Then run just the night of concern and you should see the
> temperatures not go below the lowest ambient.
> 
> Jason
> 
> 
> 
> On Fri, Aug 17, 2012 at 8:39 AM, academicryan <azianzheep@...> wrote:
> 
> > **
> >
> >
> > Hi Dr. Li,
> >
> > Thank you for taking the time to reply me.
> >
> > The ground temperature argument is a good one, however in my case the
> > night time ambient is around 11-16C (and ground temp is constant at 18).
> > Thus it cannot be due to this effect.
> >
> > To clarify, you are right, ambient does mean outdoor dry bulb temperature.
> >
> > please have a look at the file "glass_house.xlsx" in the Files section of
> > this Yahoo Group. You will see what I mean. The inside temperature goes
> > below the lowest night time temperature, which to me seems impossible in
> > real life.
> >
> > The simulation is of a glass house rather than a regular house,
> > nevertheless this phenomenon is still against common logic and has occurred
> > for me when I model regular houses as well.
> >
> > Many thanks
> >
> > Ryan
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
> > >
> > >
> > > When you say ambient temperature, I assume that you are referring to the
> > outdoor dry bulb temperature. The dew point has a lower temperature. The
> > building surface ground may have a lower temerature, and assumed to be
> > 18°C, if you did not not enter a set for the bulding. The radiation
> > component always acts faster than the covection component. The exterior
> > surfaces are facing the sky temperature, which is also lower than the ODT..
> > >
> > > The ODT is usually the lowest at around 5 am. The building will follow
> > this with a delay. Therefore, there are many possiblilities. After sun
> > rise, the indoor temerature can still be lower, because of ground cooling
> > through the floor. So list the variable for floor temperature ro confirm.
> > If it is due to the low building surface ground temperature (18°C),
> > increasing the temperature will raise the indoor temperature by a similar
> > amount.. Dr. Li
> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > > From: azianzheep@
> > > Date: Fri, 17 Aug 2012 07:47:37 +0000
> > > Subject: [EnergyPlus_Support] Indoor air temperature LOWER than ambient
> > temperature
> >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Hi
> > >
> > >
> > >
> > > I've been doing E+ simulation for over half a year now and feel like I
> > have a good grasp of it. But one thing I can't figure out is why I
> > sometimes get results of indoor temperature being lower than ambient
> > temperature. This often occurs during the early morning, 3am-9am. In
> > reality this is impossible so I'm very confused by this result.
> > >
> > >
> > >
> > > Can someone please explain to me why E+ produces this result?
> > >
> > >
> > >
> > > If requested, I can attach additional information such as .idf or excel
> > graph.
> > >
> > >
> > >
> > > Many thanks,
> > >
> > >
> > >
> > > Ryan
> > >
> >
> >  
> >
> 
> 
> 
> -- 
> Jason Quinn
> Lead Engineer
> Sustainable Engineering Ltd.
> 82 Liverpool Street
> Wanganui 4500
> New Zealand
> 
> +64 21 1846 911
>




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