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[EnergyPlus_Support] Re: modelling misters

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: modelling misters
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Date: Sat, 02 Feb 2008 23:57:55 -0000
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Mike, I've only just seen this post, and it is the answer to the 
perplexing problem that I've been witnessing. So I guess I need a 
workaround (similar to what you suggested below) in order to transfer 
the latent heat gain of the zone air to an actual drop in the air 
temprature.

Unfortunately the latent heat gain variable output shows that it 
varies wildly depending on the "actual" moisture transfer rate. I 
would like to transfer the heat drop of the evaporation to the zone 
air temp. The options I considered are: 

1)use the drain water of the latent water use equipment to be an 
input into another water use equipment that is sensible. Then the 
reduction in temperature of the drain water will reach equilibrium 
with the zone air and the heat drop of the evaporation will be 
transferred to the air temp.

2) Use electric equipment to reduce the temperature based on 
the "Water Use Equipment Latent Heat Rate to Zone" output variable. 
This sounds like a good option to me.

The problem is I don't quite know how to implement either of the 
above options. I would prefer option 2 -so can you tell me how I use 
the output variable to drive the power of the electric equipment (or 
other suitable object)?

If you can give me an actual example of the code I would use it would 
be great!
cheers
Danny

\--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
<mjwitte@...> wrote:
>
> 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@...
> > <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@...
>




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References:
- RE: [EnergyPlus_Support] modelling misters
  - From: Michael J. Witte

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