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RE: [EnergyPlus_Support] modelling misters

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] modelling misters
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Mon, 28 Jan 2008 13:16:30 -0600
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I am not sure exactly what your Ecotect inputs translate to in terms of 
EnergyPlus objects.  My guess it that the latent internal gain is described 
using ELECTRIC EQUIPMENT or OTHER EQUIPMENT.  All of the "* EQUIPMENT" objects 
for internal gains assume that the latent gain increases the enthalpy of the 
room air mass.  This means that the latent gain produces no sensible cooling 
effect, as an adiabatic evaporation process would do.  To model an adiabatic 
addition of moisture to the zone using OTHER EQUIPMENT, you would need two 
objects, one with a positive gain that is 100% latent, and another with a 
negative gain which is 100% sensible.  The two objects would use the same 
design level {W} if the water is entering at room temperature.  But more 
likely, the water is cooler than the zone, so you would need to calculate the 
energy rate required to heat the incoming water flow to room temperature and 
make the negative sensible gain that much greater.

My understanding of WATER USE EQUIPMENT (which Brent suggested a few days ago) 
is that it will compute the cooling effect of cold water exposed to the zone 
based on the current temperature difference.  There are report variables for 
the sensible heat gain (negative if a loss) and the moisture addition so that 
you can confirm how the model is working.

Mike


On 23 Jan 2008 at 18:29, Danny Bishop wrote:

> Hi All
> 
> As a follow up to my previous post (I've been working on it today seemingly in a
> different time zone from most of you all), I just wanted to get some more
> feedback on the approach to modelling cooling effects of water misters in a
> fresh fruit market overnight.
> 
> 
> 
> The recommendation I got for doing it in Ecotect was basically to have an
> appliance with a negative heat output. This sort of works (but the calcs for the
> power seem obscene, see footnote), but it obviously doesn't account for the
> following: 
> 
> 
> 
> 1)      Effect on humidity
> 
> 2)      You need to assume some sort of percentage of evaporation, and this
> needs to be the amount that changes to and stays as vapour, ie doesn't condense
> anywhere.
> 
> 
> 
> If I did this in E+ using the recommendations I've been given (see below),
> would they model the two above effects, instead of rely on me to estimate
> them?
> 
> 
> 
> Secondly, another option that occurred to me (that should minimise my
> interaction with E+ as I am very green) is to include a large latent
> internal gain for each zone. However, when I export these to E+ (Ecotect
> doesn't use the latent part in the calculation) I get only the slightest
> change in the temperature. I have uploaded these two files to the online
> file location, one named "Market export to E+-no latent", and the other
> "Market export to E+-latent". Perhaps the difference is the pesky HVAC loads
> which seemed to have activated themselves! If anyone can shed some light on why
> the difference is so small that would be great!
> 
> 
> 
> Cheers and thanks
> 
> Danny
> 
> ____________________
> 
> Footnote: latent power calculation of 1 litre of water vaporising per
> minute: 
> 
> 
> 
> Latent vapour heat of H20: 2270kJ/kg 
> 
> 
> 
> Power = 2270 (kJ/kg) x 1 min/60s x (1kg/min)/(1L/min)
> 
> =2270kJ/60s per L/min
> 
> =38kW per L/min
> 
> 
> 
> This seems huge! Can anyone tell me if I've made a silly error?
> 
> 
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Josh K
> Sent: Wednesday, 23 January 2008 4:29 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: [EnergyPlus_Support] modelling misters
> 
> 
> 
> I've used ECOTECT to create geometry for EnergyPlus simulations. It doesn't do a
> whole lot more than that; there are some options to create schedules,
> infiltration, and internal gains objects within ECOTECT, but frankly I've found
> it easier just to do these things within EnergyPlus.
> 
> That being said, it does a reasonably good job of creating geometry, as long as
> the geometry isn't excessively complicated -- when it is, ECOTECT sometimes has
> a hard time calculating adjacency properly, which results in the
> OutsideFaceEnvironment field of the SURFACE:HeatTransfer objects sometimes being
> specified incorrectly. In one instance, I created what was, in retrospect,
> excessively complicated geometry, and using the most sensitive settings for
> ECOTECT's inter-zonal adjacency calculations, I ended up with about 8% of the
> surfaces' OutsideFaceEnvironment field being specified incorrectly. In my
> opinion, if one were to simplify the geometry to the extent that simulation
> accuracy wouldn't be affected, this number would be pretty close to 100%.
> Unfortunately, I don't have enough experience at this point to state
> definitively if that's the case or not; what I can tell you is that after using
> the two systems together for a while, you definitely begin to get a sense of
> what geometric features ECOTECT will deal with correctly and which ones might be
> troublesome.
> 
> The biggest annoyance when using ECOTECT to create EnergyPlus geometry is
> the surface naming conventions. To my knowledge, there is no way to directly
> name surfaces in ECOTECT; they are all automatically assigned object numbers by
> the software. This wouldn't even be too bad, but these object numbers aren't
> static. That is, if you go in and modify your geometry in ECOTECT and re-export
> it to ECOTECT, it's possible that an unmodified surface could have a new object
> name. If one is importing and exporting entire geometries en masse, this isn't
> really a problem, but it can be really annoying if you have a big model and you
> just want to export chunks of it.
> 
> Anyways, if you learn to cope with the idiosyncrasies, ECOTECT is a usable
> tool for creating geometry for EnergyPlus. However, that's about all it does --
> no HVAC.
> 
> Hope that helps,
> 
> Josh
> 
> On Jan 22, 2008 10:05 AM, Griffith, Brent <brent_griffith@xxxxxxxx
> <mailto:brent_griffith%40nrel.gov>  > wrote:
> 
> > If you know a water flow rate and schedule for the misters, then it
> > should work to use the Water Use Equipment input object with a high
> > latent fraction. I suggest using a Water Mains Temperatures object for
> > your location to model the mister's inlet water temperatures.
> >
> > Hopefully someone else out there knows more about Ecotect ...
> >
> > ________________________________
> >
> > From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> <EnergyPlus_Support%40yahoogroups.com>
> > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> <EnergyPlus_Support%40yahoogroups.com>]
> > On Behalf Of Danny Bishop
> > Sent: Monday, January 21, 2008 5:48 PM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> <EnergyPlus_Support%40yahoogroups.com>
> > Subject: [EnergyPlus_Support] modelling misters
> >
> >
> > Hi All
> > I want to do a simulation modelling the use of misters to cool a fresh
> > food
> > market overnight. I want to see the benefit to the temperature, and also
> > the
> > effect on humidity. I would prefer to do import this to e+ via Ecotect,
> > but
> > suspect that I may need to do some post processing on the IDF. Can
> > anyone
> > tell me how to get my teeth into this, any examples perhaps?
> > Cheers
> > Danny
> >
> > [Non-text portions of this message have been removed]
> >
> > [Non-text portions of this message have been removed]
> >
> > 
> >
> 
> -- 
> Josh Kjenner, EIT, LEED AP
> Manasc Isaac Architects Ltd.
> 10225 100 Avenue :: Edmonton, AB T5J 0A1
> 780.429.3977
> 
> [Non-text portions of this message have been removed]
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]
> 
> 
> 
> 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 not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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Follow-Ups:
- [EnergyPlus_Support] Re: modelling misters
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References:
- Re: [EnergyPlus_Support] modelling misters
  - From: Josh K
- RE: [EnergyPlus_Support] modelling misters
  - From: Danny Bishop

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