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

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.

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

....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.

On 5 July 2012 09:34, <marcello.caciolo@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

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@cofelyaxima-gdfsuez.com

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De : trnsys-users-bounces@cae.wisc.edu [mailto:trnsys-users-bounces@cae.wisc.edu] De la part de jeannieboef
Envoyé : mercredi 4 juillet 2012 18:41
À : Herve Gaël

Cc : trnsys-users@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@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@cae.wisc.edu [mailto:trnsys-users-bounces@cae.wisc.edu] De la part de Francis KERBER
Envoyé : mercredi 4 juillet 2012 08:37
À : David BRADLEY
Cc : trnsys-users@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@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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