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Re: [EnergyPlus_Support] Sensible Heat ratio in EPlus
Warning! This gets philosophical.
So as Jim said, e+ breaks it down to
Radiant+Convective+Latent+Lost=1. Mostly, we don't need to enter the convective as e+ calculates it from unity, i.e.
Fraction Convective=1-(fraction radiative + fraction latent + fraction lost).
Our model of energy transfer has four modes:
- Conduction
- Radiation
- Convection (which is a fudge term for kinetic and radiative energy transfer effects at a molecular level, similar to conduction...and the closer you look the more theoretical this becomes)
- Mass transfer (in our e+ world, water vapour, or "latent")
If we take a (floating) plate of hot food and want to study how energy transfers into the control volume of the room air then we "see" how the different energy flow paths transmit energy from the food to the air.
Most mechanical electrical equipment does not have (notable) mass transfer (via vapour) so there the fraction is zero.
Radiation of warm equipment may "delay" the radiative fraction getting to the air as it first must fall on a receiving surface (wall, ceiling, floor, etc.), heat that surface and then be convected from there to the air (is if even the same energy? Ha, ha). Radiation exchange with the air molecules itself is negligible.
Because my plate is floating, I have no direct contact to the ground, and to the air conduction effects are lumped into the transfer mode that we call convection.
Lost can be used for accounting for energy that does not even make it into the control volume and is lost before it gets there via mass transfer or other means (like a kitchen exhaust), but indeed is not further accounted for by the model.
Our modelling of most things uses fudge factors that we humbly call "coefficients" to sound a bit less like we're fumbling in the dark. We base these on experience, i.e. lot of experiments and data collection in the lab and the field.
I like the term modelling (UK spelling). It reminds me that even our mathematics is a model. There is no certainty until after an event has occurred, and even then you can't be certain of what you think you're certain of. If a tree falls in the woods and no one was near to hear it, did it make a noise. (I always say yes)
Douglas Adams wrote a book where a super computer figures out that the answer to life, the universe and everything = 42. Problem was that it didn't calculate why.
Our models need not be perfect, just good enough to get the job done (fit for purpose).
On 7 Mar 2016 8:31 am, "Javed Iqbal
eee.javed@xxxxxxxxx [EnergyPlus_Support]" <
EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Â
Hi,
I am trying to simulate a internal equipment in a zone with a known sensible heat ratio that would be transferred to the zone air heat gain. I referred I/O reference file an found following are the three heat ratios types based on source type. In my case, Fraction latent and Fraction radiation is "0" as given in the specification sheet.  My question is what would be the correct value to simulate Sensible heat ratio of 65% in the following heat ratio objects?
--
Javed Iqbal, LEED AP, CEA
Sr. Energy AnalystÂ
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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>
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