Slab is a pre-processor program whose function is to calculate the ground temperatures taking into account that there's a building on top and so the soil "sees" a very different set of air temperatures than the outdoor air. Step back and take a big picture view of the problem. True, you don't know the exact air temperature of the building, but if it's a conditioned building it would be the control temperatures for heating and/or cooling, right? And if it's an unconditioned building, it would be similar to the outdoor air temperature, in which case there's probably little reason to use the Slab program.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx www.whiteboxtechnologies.com (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
On 1/18/2013 6:32 PM, academicryan wrote:
Hi Linda I have read that section at least 4 time trying to understand it. I still don't really understand it very well but I'm pretty sure its simply telling me to use the Slab program in the EnergyPlus Utilities.
I've mentioned that the Slab program gives unrealistic results. What I particularly don't understand about the Slab is why there is an input for monthly averaged indoor temperature. This means I need the indoor temperature to calculate the ground temperature. But to simulate the indoor temperature, I need the ground temperature. This seems like an impossible chicken/egg scenario of which one comes first. I've even read somewhere I'm supposed to start with an arbitrary indoor temperature and keep doing this chicken/egg cycle until both ground and indoor temperatures converge and stabilise. This seems really silly and tedious but maybe that really is what I'm supposed to do?
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Linda Lawrie wrote:
>
> Read the auxiliary programs document on Ground heat transfer with
> EnergyPlus. Look at the EPW file ground temperatures as well (which are
> not suggested for the Site:groundTemperatures values)
>
> On 2013-01-18 18:49, academicryan wrote:
> > Update: *EnergyPlus developer please respond*
> >
> > OK I now know how to calculate soil temperature as a function of
> > depth from Hillel, 1982.
> >
> > Essentially his equation says that at 0 m depth, monthly average soil
> > temperature is the monthly average air temperature plus 1°C. This is
> > basically a sine wave. With increasing depth, the soil temperature
> > gets closer to the annual mean air temperature plus 1°C.
> >
> > NEW QUESTION: Is this what 'Site:GroundTemperature:BuildingSurface'
> > wants? i.e. 0 m depth soil temperature. Or some other depth? Or some
> > other 'ground temperature' altogether?
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "academicryan" wrote:
> >>
> >> Can somebody please help me do a very simple task.
> >>
> >> Calculate/find the monthly ground temperature for Singapore. To
> >> clarify, this is the input for the
> >> 'Site:GroundTemperature:BuildingSurface'.
> >>
> >> ------
> >>
> >> Extra info - I've already tried the Slab utility, it comes up with
> >> very unbelievable results. Calculating some months below 17°C when
> >> Singapore air temperatures never drops below 21°C.
> >>
> >
> >
> >
> > ------------------------------------
> >
> > Primary EnergyPlus support is found at:
> > http://energyplus.helpserve.com or send a message to
> > energyplus-support@...
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> >
> > Attachments are currently allowed but be mindful that not everyone
> > has a high speed connection. Limit attachments to small files.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under
> > the Documentation link and press the "search" button.
> > Yahoo! Groups Links
> >
> >
> >
>
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Primary EnergyPlus support is found at:
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The primary EnergyPlus web site is found at:
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The group web site is:
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Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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