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Estimation of Envelope/Fabric load for an unconditioned and unoccupied thermal zone

asked 2019-10-21 03:38:25 -0500

Manu4Energy gravatar image

updated 2020-01-07 17:15:10 -0500

A simple building room with walls, roof and window is modeled in Sketchup 2017. It is assumed that there is no ventilation system, no infiltration and no internal load generated through people or lighting equipment's. In short, the room is unconditioned, empty and well-confined. Need to estimate the envelope load/fabric load through openstudio platform. In openstudio, which all “output variables” need to be activated to check the fabric load for the above scenario in the openstudio/energyplus report session.

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answered 2019-10-21 10:35:13 -0500

The typical way to calculate a load in EnergyPlus is to add a ZoneHVAC:IdealLoadsAirSystem and then look at how much heating/cooling energy the system transferred. You will also need to provide heating/cooling setpoints for a load to be calculated.

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Thank you so much for your response. So, if i reiterate what i understood from your comment, in order to maintain a certain indoor temperature (based on set-points), we need to either reject/accept a certain amount of thermal load by integrating an ideal HVAC system and energy consumed by this system can be estimated through district heating/cooling data. In my scenario, indoor thermal load or envelope heat gain is solely due to conduction through walls, windows and solar heat through windows. Is there any specific output variable to estimate this envelope heat gain in Openstudio/Energyplus?

Manu4Energy gravatar image Manu4Energy  ( 2019-10-22 01:34:08 -0500 )edit

@Manu4Energy, the Envelope and Internal Load Summary reporting measure on BCL may be useful for you. It breaks down the heat gain and loss components for the building. This post has a screenshot and link to the measure. The post also lists the output variables which you can use outside of this measure.

David Goldwasser gravatar image David Goldwasser  ( 2019-10-22 09:41:51 -0500 )edit

@David Goldwasser, thank you very much for your valuable feedback. The measure was very helpful to segregate the heat gain and loss from building components. To further enhance my understanding of the concept, may i clarify that, while I consider the space to be unconditioned, would this heat gain into the thermal zone(room) through roof,wall,window change when the space is conditioned? If it changes, what would it mean?

Manu4Energy gravatar image Manu4Energy  ( 2019-10-23 22:00:37 -0500 )edit

@Manu4Energy yes, the heat gain and loss for envelope components would change if the spaces were not conditioned.

David Goldwasser gravatar image David Goldwasser  ( 2019-10-24 11:33:55 -0500 )edit

@David Goldwasser, I very much appreciate your help. Thank you.

Manu4Energy gravatar image Manu4Energy  ( 2019-10-25 00:50:59 -0500 )edit

answered 2019-10-22 06:37:35 -0500

It the zone is unconditioned, then it doesn't really have an envelope/fabric load. It might have some heat transfer across the envelope at times but that would be due only to the thermal mass delay. To me a "load" is really only present if some level of conditioning of the zone exists.

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@JasonGlazer, thank you very much for your response. Doesn't this thermal lag or thermal mass delay that partly play a role in varying the indoor temperature. And this ingress of thermal energy/thermal load indoors is either rejected/accepted by a HVAC system to maintain indoor temperature within certain predefined set points. Kindly correct me if I am wrong.

Manu4Energy gravatar image Manu4Energy  ( 2019-10-24 04:17:39 -0500 )edit

Of course, thermal mass plays a very important role in computing the loads. Perhaps it is the semantics of your original question that prompted my response. A "load" is how an HVAC system maintains the space conditions at a fixed setpoint. Heat "gains" and "losses" are instantaneous additions and subtractions of heat into a space. If the zone is not conditioned, it doesn't have loads but that doesn't mean it doesn't have gains and losses. In your comment in response to my answer you are now talking about HVAC. So which is it, conditioned or not?

JasonGlazer gravatar image JasonGlazer  ( 2019-10-24 08:03:04 -0500 )edit

@JasonGlazer, thank you very much for your valuable feedback. Initially, I had kept the space unconditioned to analyze the impact of envelope materials on the indoor temperature. With help of "Envelope and internal load breakdown" measure, heat gain and loss was estimated (thanks to fellow forum contributors). And with reference to my first comment to your response, my objective was to clarify a few conceptual doubts, for which you have fittingly explained the concept in a broader sense through your second response. Thanking you again for your time and consideration.

Manu4Energy gravatar image Manu4Energy  ( 2019-10-25 00:42:24 -0500 )edit

answered 2019-10-22 08:16:31 -0500

Manttech gravatar image

You can use the measure "enveloppe and internal load breakdown". This measure is in the OS library and reports the heat gain/loss thought wall/floor/roof. It also reports Surface average face conduction energy gain/loss for each individual surface and subsurface.

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@Manttech, thank you very much for your valuable feedback. Much appreciated.

Manu4Energy gravatar image Manu4Energy  ( 2019-10-24 04:19:53 -0500 )edit

In my opinion "door" surfaces are neglected in this measure gravatar image  ( 2019-10-28 07:36:11 -0500 )edit

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Asked: 2019-10-21 03:38:25 -0500

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Last updated: Oct 22 '19