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EnergyPlus Variable that captures thermal loads?

asked 2021-02-25 09:06:19 -0600

sashadf1 gravatar image

updated 2021-05-21 03:34:42 -0600

Hi,

Is there a set of EnergyPlus reporting variables that capture the heating and cooling load on a building due to wind and solar gain? (IE loads not due to temperature difference between the inside and the outside but due to radiation and wind across wall surfaces).

Also useful would be EnergyPlus reporting variables that capture heating loads due to people in the building.

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answered 2021-02-25 16:41:07 -0600

See the zone output reporting variables described here:

'Zone Windows Total Heat Gain Energy',
'Zone Windows Total Transmitted Solar Radiation Energy',
'Zone Windows Total Heat Loss Energy'
'Zone People Convective Heating Energy'

Be careful about how you use these variables for design decisions - solar gain contributes to cooling load in summer but reduces heating load in winter. Incoming solar radiation may not be fully realized in the zone as load until hours later due to massing effects, or may not contribute to the zone load air balance at all in the case of a chilled radiant slab. If you explain how you want to use these results, we may be better able to guide you on what variables you want.

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I am using this in a transient energy balance for modeling for Transactive Energy. It is not for any design decisions but rather for an estimate of the gross conductivity and thermal mass of a single family detached residential building.

I was thinking of using the variable "Zone Total Internal Total Heating Rate" to capture all the gains from people, cooking equipment, etc

I think the way we are thinking about this model is considering sensible energy fluxes that will result in immediate change in temperature of the interior air, rather than heating of the floor or building shell.

sashadf1 gravatar image sashadf1  ( 2021-02-25 18:42:48 -0600 )edit

All of the heat fluxes either come from people, infiltration/exfiltration of air, solar, hvac, or temperature difference between the indoor and outdoor environment. Am I missing something? I think we have variables for hvac, the temp difference, and occupancy/equipment gains, but we need values that describe gains/losses from air exchange and solar radiation.

sashadf1 gravatar image sashadf1  ( 2021-02-25 18:48:06 -0600 )edit

how do you handle the radiant contribution of solar gain and internal loads in your model?

mdahlhausen gravatar image mdahlhausen  ( 2021-02-26 13:22:37 -0600 )edit

it is all handled automatically. I don't ever write an IDF file because ResStock automatically generates OS models, and OS models automatically write the IDF file.

sashadf1 gravatar image sashadf1  ( 2021-02-28 13:56:25 -0600 )edit

energyplus will capture the radiant components of load, assuming you have properly assigned radiant loss fractions to internal gain objects. A different question is what reporting variables you use to estimate internal gain contribution to radiant (delayed convective) loads. There isn't a straightforward way to do this. You cannot just report out the sensible internal gains and expect your "gross conductivity and thermal mass" estimate to be correct. You need to include the radiant, delayed release components in your calculation. I'm asking how you plan to include to those.

mdahlhausen gravatar image mdahlhausen  ( 2021-03-03 10:58:04 -0600 )edit

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Asked: 2021-02-25 09:06:19 -0600

Seen: 117 times

Last updated: May 21