Ground Temperature

rahmiandarini · Posts: 56

Hi Arturo,

Thanks for the idea. Yesterday I also thought that it could be done like that. But, still I get stuck with the initial point.
1. Which comfort conditioning temperature should I use for the first step using Slab? I have 2 storeys building, and there is a hole (I assume for staircase). Is it ground floor, or first floor? or take for whole building?
2. In Slab program, there is option of DEEP temp, which temperature is this? is it temperature the I got form CalcSoilSurfTemp?
3. In DB, I have possibility to use separate construction and add ground construction layers to surfaces in contact with ground, in your suggestion, for the first option (Conditioned building), do I need to do this as there is SLAB DEPTH in Slab Program?

Thanks,
Rahmi

lklawrie · Posts: 189

Ground OSC Example File:

The slab program determines and produces monthly temperatures corresponding to the average outside temperature of the slab, the outside temperature of the core region, and the outside temperature of the perimeter region. Generally most users input the average outside slab temperatures in the GroundTemperatures object, but if a user wants to use both the core temperature and the perimeter temperature, the slab surface must be divided into appropriate regions, and one of the region's temperatures need to be supplied using the OtherSideCoefficients object. The Slab program produces the needed objects but they have to be named to fit the model. The example file just demonstrates the use of the OtherSideCoefficients object and the corresponding monthly temperature values in a CompactSchedule object. check the outside surface temperatures of the South wall to see that the temperatures from the CompactSchedule object were applied to the outside of the surface.

AOG · Posts: 172

Hi all,

About Rahmi questions:

1. I used theoretical comfort temperatures for each month calculated with a simply formula, e.g. thermal neutrality (Tn = 17.6 + 0.31 Tave).

2. If you are referring to TDEEPin, it is the fixed temperature you can set to the lower surface of the model, if the field FIXBC: is the lower boundary at a fixed temperature is set as TRUE (you can define the deep of model lower surface in the field ZCLEARANCE: Depth of region below slab, in the EquivAutoGrid object). I think you can estimate this temperature from .stat file related whit your .epw file, if it provides calculated undisturbed ground temperatures at least for 4m deep, or use a value near to average annual dry bulb temperature for the site. Otherwise, as I understand help document, if you set FIXBC as FALSE the program will calculate by itself an undisturbed temperature profile (please Linda tell me if I�m wrong).

3. Well, I understand this issue as follow. In DesignBuilder ground monthly temperature applies for outside surface of every surface adjacent to ground. Then, if you are using combined constructions, ground monthly temperature applies for outside surface of ground floor slab. If you use separated construction, and add a ground construction layer, ground monthly temperature applies for outside surface of this layer. So, in the last case, depth at which ground monthly temperature applies will depend on the thickness of the added layer. Said this, I think values obtained within Slab are more accuracy with first option (combined construction) or with the second one if don�t add any layer.

Daniel:

It�s really nice to meet a Mexican colleague in this forum. You can contact me through my web site (see it in my profile) or directly at arturo at sol-arq dot com. It will be great to collaborate in such study. Un gran saludo desde Chihuahua.

Regards,

Arturo

andfranz · Posts: 105

I know that the subject is dealt with by the Annex D (Application to dynamic simulation programmes) of the European technical standard EN ISO 13370:2008 "Thermal performance of buildings - Heat transfer via the ground - Calculation methods", but I have never used it…
Has someone got more experience?
With Regards

andfranz · Posts: 105

andfranz · Posts: 105

jean marais · Posts: 95

Just a thought...
I've done this for a project in Germany. Somethings to think about are
1) Where is the ground water level...this will have the "deep ground temperature"
2) A good reason that the temp under the slab is different is that it is not "exposed" to the ODA environment at the top and has no wind or radiation effects on it as does the gound in the cow field.
3) The slab thickness has a big effect on the outside temp of the slab.
4) The Slab program does a good job. It is a 3d FDM program and even takes into account shading from the height of the building on the ground next to the building.
The cyclic average inside temperature variation is also accounted for. Because the slab has a certain thermal "inertia" the average room temp is good enough for the simulation.

jefh25 · Posts: 2

The slab program is the best option, look for the tutorial named: "leture 24 ground heat transfer".

In this presentation you will find and example, and an easy explanation of how to use the slab program.

I will try to attach the document.

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