This is also the reason why you need to cover a solar collecter with a transparent heat insulator, if you want to use it to collect night cooling. Otherwise, the convection current will keep it at ODT.
Sky temperature is also one variable that you can display. When it rains, the sky temperature is almost the same as the ODT
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: azianzheep@xxxxxxxxx
Date: Sat, 18 Aug 2012 06:42:56 +0000
Subject: [EnergyPlus_Support] Re: Indoor air temperature LOWER than ambient temperature
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
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Sky temperature is also one variable that you can display. When it rains, the sky temperature is almost the same as the ODT
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: azianzheep@xxxxxxxxx
Date: Sat, 18 Aug 2012 06:42:56 +0000
Subject: [EnergyPlus_Support] Re: Indoor air temperature LOWER than ambient temperature
Hi Dr. Li,
Thank you for that suggestion. I have found that the reasoning is 100% due to radiation cooling. I ran your suggestion and indeed the glass house showed energy loss at all times during the night (even when the zone temperature is below ambient). However if I put a big shading cover over the whole glass house (blocking radiation cooling), the night time energy loss drops to 0 and the phenomenon of cooling below ambient no longer occurs.
Thank you for helping to solve this mystery!
Kind Regards,
Ryan
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
>
>
> For the glass house, simply list the window heat gain/loss at night. Then you know whether the zone is gaining or loosing heat. The exterior roof surface temperature will also give you some indication, it it is not glass.
>
> Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: azianzheep@...
> Date: Fri, 17 Aug 2012 12:39:49 +0000
> Subject: [EnergyPlus_Support] Re: Indoor air temperature LOWER than ambient temperature
>
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> 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
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> >
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> > Hi
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> >
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> >
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> >
>
> > 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.
>
> >
>
> >
>
> >
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> > Can someone please explain to me why E+ produces this result?
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> >
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> >
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> >
>
> > If requested, I can attach additional information such as .idf or excel graph.
>
> >
>
> >
>
> >
>
> > Many thanks,
>
> >
>
> >
>
> >
>
> > Ryan
>
> >
>
Thank you for that suggestion. I have found that the reasoning is 100% due to radiation cooling. I ran your suggestion and indeed the glass house showed energy loss at all times during the night (even when the zone temperature is below ambient). However if I put a big shading cover over the whole glass house (blocking radiation cooling), the night time energy loss drops to 0 and the phenomenon of cooling below ambient no longer occurs.
Thank you for helping to solve this mystery!
Kind Regards,
Ryan
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
>
>
> For the glass house, simply list the window heat gain/loss at night. Then you know whether the zone is gaining or loosing heat. The exterior roof surface temperature will also give you some indication, it it is not glass.
>
> Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: azianzheep@...
> Date: Fri, 17 Aug 2012 12:39:49 +0000
> Subject: [EnergyPlus_Support] Re: Indoor air temperature LOWER than ambient temperature
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> 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
>
> >
>
> >
>
> >
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> >
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> >
>
> >
>
> >
>
> > 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
>
> >
>
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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