Ground temperatures

9 posts / 0 new
Last post

Dear eQuest Users,

Would you please let me know which report would give me the deep ground
temperatures used in ground heat transfer calculations of eQuest? I used to
select an hourly report variable to make DOE-2.1e report these values, but
I am not sure how to get these values from eQuest. Would you help me with
this?

Thank you very much in advance for your help,
Best Regards,

Simge Andolsun, PhD.

SAndolsun's picture
Offline
Joined: 2013-09-11
Reputation: 0

In my opinion, the easiest way to get the ground temperatures would not be through DOE-2
Hourly Reports, although I'm sure that can be done, but by reading them from the weather
file using the WTHFMT2 utility program that converts the file from binary to text. There
are just 12 numbers for monthly ground temperatures, shown on line 2 of the *.FMT files.
By the way, I think that DOE-2 does some smoothing or interpolation of the monthly ground
temperatures; right now if you look at the hourly heat transfer through Underground walls
or floors, you'll see a wierd staircase effect with the same load for a whole month, and
then a jump to a different load the next month, etc.

Joe

Joe Huang

Joe Huang's picture
Offline
Joined: 2011-09-30
Reputation: 406

Correction to previous e-mail, meant to say

"By the way, I think that DOE-2 should do some smoothing or interpolation of the monthly
ground temperatures; right now if you look at ..."

Joe

Joe Huang

Joe Huang's picture
Offline
Joined: 2011-09-30
Reputation: 406

I haven't tried Joe's suggested tool (yet), but here's the hourly report variable you're looking for:
[cid:image001.png at 01CED0C7.28BC4720]
(Rankine conversion reference)

You get here double clicking one of the hourly report items in the component tree under the "project and site" tab. You can view the results by running the simulation then either opening the resulting .csv in the project directory or clicking the "hourly results" button on the top right of the "detailed results viewer," which opens the same file. Within that file scroll to the far right to check out any custom report variables you've included for the project.

Such an hourly report builds upon Joe's observation - it appears the monthly ground temperatures are averaged into 12 values over the year, then applied to each month on an hourly basis for the simulation. I can't speak to whether this is a trait specific to eQuest and/or the DOE-2 engine.

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

Nick-Caton's picture
Offline
Joined: 2011-09-30
Reputation: 805

Simge,
Do keep in mind that in DOE2 these are fixed monthly averages used for all hours of the month; these are derived by the ground reaching monthly-average outside air temperature at a lag of 3 months.

Ground Temperature will have little effect on loads/energy in Houston for typical buildings. If you are simulating geothermal heat exchange or radiant heating (thru slab-on-grade), then the investigation will be time worth spent.

Best,

Kapil Upadhyaya, LEED AP

Kapil Upadhyaya's picture
Offline
Joined: 2012-07-03
Reputation: 0

Kapil hi! :) Great to hear from you!
Dear Joe and Nick,

Thanks for all your responses.

I actually know what's happening to the ground temperatures in DOE-2, how
they are used in ground heat transfer calculations and their effect on
overall building energy consumption. I just wanted to know how to make
eQuest plot these temperatures for me. Thanks to y'all, I managed to do it.
But, thank you so much for responding with this much detail!

Best Regards,
Simge Andolsun, PhD.

SAndolsun's picture
Offline
Joined: 2013-09-11
Reputation: 0

Simge,

If you know what's happening to the ground temperatures in DOE-2, you should then know
that they are calculated by a sine-curve equation developed by Tamami Kusuda in the early
1980's that takes up only 10 lines of code in the DOE-2 weather packer, using default
values for soil diffusivity and ignoring the effects of water table, surface
evapotranspiration, or geothermal anomalies. In other words, these ground temperatures
are extremely approximate.

Joe

Joe Huang

Joe Huang's picture
Offline
Joined: 2011-09-30
Reputation: 406

Dear Joe Huang,

Yes, I am aware of this. I am trying to make the ground heat transfer
calculation parameters I will use in EnergyPlus as similar as possible to
those in eQuest in order to prevent them from being the cause of variation
between the two programs. So, regardless of how unreliable or approximate
these ground temperatures may be, I am OK with this at the moment. But,
thank you very much for making this point. It is very true.

SAndolsun's picture
Offline
Joined: 2013-09-11
Reputation: 0

The ground temperatures in the EnergyPlus EPW should be exactly the same
those in the DOE-2 BIN of the same weather file, because I remember
extracting the GTEMP subroutine from the DOE-2 weather packer and
providing it to the EnergyPlus development team some 15 years ago or so.

Joe

Joe Huang's picture
Offline
Joined: 2011-09-30
Reputation: 406