Re: [TRNSYS-users] Heat transfer between building and ground

<I am looking for a methodoly and tools which can be considered as a good practice for application in building simulation to model the heat transfer between a building and the ground on which it is built. I insist on the fact that I need it for a real building project and not a research project. This means that the "material" I am looking for should be quite simple to apply but also accurate enough ..>

As many of you know, TESS participated in the International Energy Agency Task 34/43 which sought to compare and contrast methods used to predict ground heat transfer in building simulation. Using TRNSYS, and a series of fully 3-D models that we developed, our approach was deemed to be one of only three "reference standards" (along with a FLUENT model and a MATLAB model) for accurately predicting slab-on-grade heat transfer. The IEA exercise consisted of comparing our models to an analytical solution and then taking the model and predicting the heat transfer for a wide variety of slab-on-grade applications, shallow boundaries, deep boundaries, large slabs, narrow slabs, sinusoidal boundary conditions etc. As one might expect, we learned a lot by participating in the exercise and our ground heat transfer model is better for having undergone the rigorous testing.

Using the methodology from the IEA model, along with quite a few lessons learned, we have created a series of ground heat transfer models that will be part of the new TESS library package for TRNSYS 17. We've added models for slab-on-grade, slab-in-grade, a single-zone basement model, a single-zone walk-out basement model, a multi-zone slab-on-grade model, a multi-zone slab and basement model, buried storage tanks and pipes and a detailed ground heat exchanger model. I've attached a few screen captures from one of our projects that shows results from the multi-zone slab-on-grade model for a building equipped with high temperature radiant floors, low-temperature radiant floors and walk-in coolers. It's pretty interesting.

Some of these models will likely end up in the standard TRNSYS libraries as they are useful to almost everyone that studies buildings. I can tell you that the results using the detailed approach are VERY different from some of the simple approaches that are commonly used today (large zone, tied to ambient temperature with fictitious insulation etc.). We're in the process of writing a paper on this topic for the next IBPSA international conference.

We have made many of these models available to TRNSYS users so they won't have to wait for TRNSYS 17 and version 3 of the TESS libraries. I would be willing to have you send me the geometry of the building which you wish to study and I can recommend a model that will meet your needs. Feel free to ask us any questions that you may have on our approach.

----- Original Message -----
From: benoit.cogne@dh-technologies.fr
Sent: Fri, October 3, 2008 11:13
Subject: [TRNSYS-users] Heat transfer between building and ground

Dear Trnsys users,

I am looking for a methodoly and tools which can be considered as a good practice for application in building simulation to model the heat transfer between a building and the ground on which it is built.

I insist on the fact that I need it for a real building project and not a research project. This means that the "material" I am looking for should be quite simple to apply but also accurate enough to give results in which I can be confident. The authority of its source is therefore also important.

I have been already advised to use the European standard EN ISO 13370. This standard has the advantage to exist, however it is difficult to apply and I have great doubts on the quality of the results of my interpretation. More over I did not find yet some one ready to control my application (!)

This subject is of a very high importance as I found the results on the simulation I am doing (calculation of summer indoor conditions without air conditioning) are very sensitive to the numerous hypothesis.

Thank you in advance for your help

Benoît Cogné

France

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