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RE: [EnergyPlus_Support] modelling misters
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]
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