[TRNSYS-users] Air treatment unit / ground temperature model

Thu Jul 5 01:59:58 PDT 2012

The Trnsys Models are similar to this program that energy plus uses. As I'm
more familiar with eplus, I am pointing you to these references. The
principles are the same. The isothermal diagrams showing soil temperature
under the slab is interesting for you.

slab program uses a 3D explicit finite difference scheme to solve the heat
diffusion equation.

It is based on the PhD dissertation by William Bahnfleth:

Bahnfleth, W. (1989). Three-Dimensional Modeling of Heat Transfer from Slab
Floors. University of Illinois at Urbana Champaign.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA210826

see also:

http://www.dtic.mil/dtic/tr/fulltext/u2/a241567.pdf

and

http://apps1.eere.energy.gov/buildings/energyplus/pdfs/energyplus_slab-on-grade_tests.pdf

....to clarify the statement mentioned below: I suggest one calculates the
u-value (which is usually very resistive), and then apply a steady state
deltaT to get a "quick check" result for the heat flux lost or gained
through the slab. You will notice that mostly the W/m² of heat transfer
through the slab is quite small. This obviously depends on climate type and
building, but is not a bad generallization. The errors of W/m² from
inaccurate slab assumption, in relation to the errors inherrent in building
modelling due to unknown user profiles and user habits, natural
ventilation, etc. are far greater. Having more accurate scheduling usage
and equipment controlling are far more benifitial in my opinion. For
example, it is often assumed that the person load is 120 W/person...where
in actual fact this is quite a big assumption in facilities such as
schools. Another good point is building infiltration, which is either
assumed or calculated with large assumptions as to window usage by users. A
lot of modlers will simply put a fixed infliltration rate of 0.3 ACH for an
entire building.

Use the slab programs (types) if you have mastered some of the other
aspects of building modelling, like intergrating COMMIS (CONTAM) or can
better use the other infiltration models. Do "back of the cigarette packet"
calculations to check if it is worth while using the slab program, before
delving into it. As with all things, the actual answere is always "it
depends".

If you are in a warm climate, you may find using the slab programs are a
must...but it depends. ;-)

I had some other interesting links, but I can't find them now...will check
agian later.

All the best.

On 5 July 2012 09:34, <marcello.caciolo at cofelyaxima-gdfsuez.com> wrote:

> Dear Jeannieboef,****
>
> ** **
>
> I am really interested in modelisation of heat exchange of a building with
> the ground. Could you post the reference you mentioned?****
>
> ** **
>
> By the way, you say “the added accuracy [of modeling heat exchange with
> the ground] to yearly energy consumption is not that big”. Could you
> precise if this sentence is based on your feeling, on your experience or on
> some published results? In my experience, it really depends on the building
> type and on the ratio between height and floor area.****
>
> ** **
>
> Thank you for your help.****
>
> ** **
>
> Best regards,****
>
> ** **
>
> *Marcello Caciolo*
> Responsable Outils et Méthodes d'Analyse Energétique****
>
> [image: cid:image003.jpg at 01CD4E08.954D04D0]
> *
> *Cellule Efficacité Energétique et Environnementale - Pôle Projets et
> Réalisations
> 46 Boulevard de la Prairie au Duc
> BP 40119 - 44201 Nantes Cedex 02
> Tél.: +33 02 40 41 06 57
> marcello.caciolo at cofelyaxima-gdfsuez.com<prenom.nom at aximaseitha-gdfsuez.com>
> ****
>
> P *Pensez à l'environnement avant d'imprimer ce message*****
>
> ** **
>
> ** **
>
> ** **
>
> *De :* trnsys-users-bounces at cae.wisc.edu [mailto:
> trnsys-users-bounces at cae.wisc.edu] *De la part de* jeannieboef
> *Envoyé :* mercredi 4 juillet 2012 18:41
> *À :* Herve Gaël
>
> *Cc :* trnsys-users at cae.wisc.edu
> *Objet :* Re: [TRNSYS-users] Air treatment unit / ground temperature model
> ****
>
> ** **
>
> Just to re-itterate one of my favourite subjects...****
>
> The ground temperature objects are good to use with anytype of ground heat
> exchanger (for example the two mentioned by David, namely earth tubes and
> Geothermal). It should, however not be used as the boundry condition on the
> ground bounding contructions of conditioned spaces. This is inaccurate and
> a mistake I am seeing often by Trnsys users. If using a constant value, I
> suggest the mean (day + night) monthly conditioned space temperature minus
> 2 Kelvin, for bounding constructions in the range of 150 to 300 mm without
> insulation.****
>
> ** **
>
> If you want to accurately model this, I suggest using the slab/basement
> types that do the 3d calculation for this. If you are a begginer, don't
> focus your efforts here as the added accuracy to yearly energy consuption
> is not that big. If you do use the complex modelling types also bear in
> mind the effects of ground water level on apparent soil temps.****
>
> ** **
>
> If anyone is really interested, I can post the links to some papers about
> this topic when I'm back at my desk tomorrow.****
>
> ** **
>
> ---****
>
> ** **
>
>
>
> Sent from my iPhone****
>
>
> On 04.07.2012, at 14:00, Herve Gaël <G.Herve at ciat.fr> wrote:****
>
> Francis,****
>
>  ****
>
> You want to analyze your energy performance in heating and cooling, so
> first of all, I think you should do two separate simulations, one in
> heating and the other in cooling mode.****
>
> I suppose that what you need to know is the power injected by your
> terminal unit in each room depending of the delta of temperature between
> the set point and the real temperature. You don’t need to know the blowing
> temperature and the flow rate… I think your solution is creating a multi
> dimensional data interpolation in a file function of water temperature,
> speed of blowing, etc… ****
>
> I hope this can help!****
>
>  ****
>
> Best,****
>
>  ****
>
> *___________________________________*****
>
> *Gaël HERVE*****
>
> Ingénieur Numéricien LQAI****
>
> Avenue Jean Falconnier****
>
> 01350 CULOZ****
>
> Tél: +33 (0)4 79 42 64 30****
>
> Fax : +33 (0)4 79 42 40 13 ****
>
> *De :* trnsys-users-bounces at cae.wisc.edu [
> mailto:trnsys-users-bounces at cae.wisc.edu<trnsys-users-bounces at cae.wisc.edu>]
> *De la part de* Francis KERBER
> *Envoyé :* mercredi 4 juillet 2012 08:37
> *À :* David BRADLEY
> *Cc :* trnsys-users at cae.wisc.edu
> *Objet :* Re: [TRNSYS-users] Air treatment unit / ground temperature model
> ****
>
>  ****
>
> Dear David and Jean,****
>
>  ****
>
> Many thanks for your answer. I just need the ground temperature to
> modelise my basement. In my bui. I use an input Tsoil for "boundary
> userdefined" that's all. I will use your values if I don't find any.****
>
>  ****
>
> Otherwise to answer Jean question, I want to modelise to analyse energy
> performance, and to compare to reality my heat and cool needs.****
>
>  ****
>
> Many thanks.****
>
> Hope u will be able to answer to my second question about my air treatment
> unit and the final regulation system.****
>
>  ****
>
> Francis****
>
> 2012/7/3 David BRADLEY <d.bradley at tess-inc.com>****
>
> Francis,
>   There is no difference between Type77 and Type501. The component started
> out in the TESS Libraries as Type501 but was donated to the standard
> library and given a new number. It is still in the TESS Libraries for
> backward compatibility. The thing to remember about that model is that it
> is an undisturbed ground temperature model meaning that no matter how much
> energy you remove from the ground or add to the ground, the ground
> temperature will only ever be a function of the time of year. If you are
> using this in a geothermal application where you are rejecting energy to
> the ground and removing energy from the ground, the ground temperature will
> be impacted and you should look at using Type557. If you are drawing air
> through tubes in the ground then you should look at using Type460 (Pierre
> Holmuller's earth duct model as implemented by Transsolar)
>
>   If you aren't able to find data for Type501 then the following will get
> you started: For the mean soil temperature, use the average annual air
> temperature for your location. For the amplitude, plot out the monthly
> average temperature for your location and calculate the biggest difference
> between the average annual temperature and the monthly average
> temperatures. For the time shift, use 30.
>
> Best,
>  David ****
>
>
>
>
>
> ****
>
> On 7/2/2012 09:21, Francis KERBER wrote:****
>
> Dear all,****
>
>  ****
>
> I'm quite new on trnsys and I have few questions about my modelisation.***
> *
>
>  ****
>
> Firstable, I'd like to simulate the ground temperature instead of using a
> constant, which is less precise. I heard about type 501 and type 77. Is
> there any difference between those types? Which one is the best? Moreover,
> where to find the informations the type needs as inputs, like mean soil
> temperature, amplitude of Paris...?****
>
>  ****
>
> My project includes a Air treatment unit with a wheel heat exchanger, two
> fans, and two batteries (warm water and cold water batteries). I get a
> final regulation system, wich is a ventilating and cooling or heating
> system (by warm water and cold water batteries as well), depending on the
> set temperature. I do understand the system but I don't really know how to
> modelise it. Is ther any existing type I can use? Should I detail each
> system like my fans, my batteries...which seems to be complicated.****
>
> Moreover if I have this final regulation system in each room, must I
> create as much types as number of rooms?****
>
>  ****
>
> If u have any idea that would be helpful!!!!!****
>
>  ****
>
> Thanks a lot for ur answers****
>
>  ****
>
> Francis.****
>
>  ****
>
> _______________________________________________****
>
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>
> TRNSYS-users at cae.wisc.edu****
>
> https://mailman.cae.wisc.edu/listinfo/trnsys-users****
>
>
>
>
> ****
>
> -- ****
>
> *******************************
>
> David BRADLEY****
>
> Principal****
>
> Thermal Energy Systems Specialists, LLC****
>
> 22 North Carroll Street - suite 370****
>
> Madison, WI  53703 USA****
>
>  ****
>
> P:+1.608.274.2577****
>
> F:+1.608.278.1475****
>
> d.bradley at tess-inc.com****
>
>  ****
>
> http://www.tess-inc.com****
>
> http://www.trnsys.com****
>
>  ****
>
>  ****
>
> _______________________________________________
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