[esp-r] Re: climate and snow

[Jeffrey D. Spitler]

Ida,
It has been probably 10 years since I looked at the esp-r surface heat 
balance and transient conduction routines for the surrounding ground.  
But, at that time, the answer was "no"  - it did not model the effects 
of snow by either changing the reflectivity of the surface or by 
accounting for the insulating effect of snow.  I strongly suspect this 
is the case for most or all other building simulation tools.

If you are only interested in getting an answer for a particular 
building in a particular location, you can STOP READING HERE and hope 
that someone else will give you some more useful advice! But, since I am 
involved in related research, I have a few thoughts on the matter...and 
am always interested to find out that I have missed some published work 
in the area, don't know about an unpublished technique or method, there 
is a better way to do it; I am plain wrong, etc.!
Then, from my perspective, the basic issues are:

(1) You need to have weather data that would support this kind of 
calculation.  I have looked at a lot of the EnergyPlus weather files for 
the USA and while there are fields for precipitation, in many cases they 
just have zero values.  On the other hand, I think you mentioned 
Östersund in an earlier message - I checked the IWEC-2 data file for 
Östersund and it does have precipitation depth in liquid equivalents, 
including values for hours that are below freezing.  With that, it would 
at least be possible to estimate when you have snow fall.

I suspect one reason for the paucity of freezing precipitation data is 
that you need a heated rain gauge to measure precipitation "correctly" 
in sub-freezing conditions; heating the rain gauge can introduce other 
errors; at least here, automated surface observation stations tend not 
to have heated rain gauges because of the power requirements.  That 
doesn't explain why there is a shortage of any precipitation data in 
weather files here in the USA, though.

(2) From an energy calculation standpoint, a typical snowfall year is 
problematic for calculating heat loss from the basement or foundation.  
In many locations, a year with an early snowfall will have much 
different ground heat transfer than a year with a late snowfall.  This 
seems to be highly random for many locations.

(3) To automatically predict, in a building simulation tool, when you 
would have snow and how much snow would be present and what its 
insulating value would be, you would need a full snow 
accumulation/melting model.  We have done this for bridge deck snow 
melting systems:

Liu, X., S.J. Rees and J.D. Spitler. 2007. /Modeling Snow Melting on 
Heated Pavement Surfaces Part I: Model Development/. Journal of Applied 
Thermal Engineering. 27:1115-1124.

Liu, X., S.J. Rees and J.D. Spitler. 2007. /Modeling Snow Melting on 
Heated Pavement Surfaces Part II: Experimental Validation/. Journal of 
Applied Thermal Engineering. 27:1125-1131.

and then later applied it to look at what is needed for prediction of 
undisturbed ground temperatures; I view this as a precursor to 
predicting disturbed ground temperatures - the issues are basically the 
same, though we found that disturbed ground temperatures could also be 
influenced by shading from the building in some of our work related to 
foundation heat exchangers:

Xu, H. and J.D. Spitler. 2011. /Importance of moisture transport, snow 
cover and soil freezing to ground temperature predictions./ Proceedings 
of the Nordic Symposium on Building Physics. May 2011.

(I should also note that we found freezing and thawing in the ground to 
be important.)  Modeling of snow accumulation and melting is 
computationally demanding and would take some time to implement in any 
building simulation program.  It may well be that some clever individual 
has developed an approximate algorithm that is faster and "good 
enough".  If so, I would be quite interested to hear about it.

I am also very interested to hear if anyone else is involved in related 
research.  Ida - I am sorry not to have a more immediately helpful answer.

Best wishes,
Jeff Spitler









On 5/24/2013 7:41 AM, Ida Auråen wrote:
>
> Hi,
>
> I have a question regarding climate file and snow.
>
> If you are modeling a building in a cold climate where there is snow 
> lying on the ground a significant time of the year, will ESP-r take 
> this into account?
>
> Snow will insulate the ground and minimize the depth of frozen ground. 
> The snow will also reflect solar radiation well and it will contribute 
> to more passive solar heat through windows or to solar 
> collectors/pv-panels.
>
> Is there snow on the ground for the simulations done in ESP-r in 
> colder climates?
>
>
> Best Regards
>
> Ida Auråen
>
>
>
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-- 
Jeffrey D. Spitler, PhD, PE
Regents Professor and C.M. Leonard Professor
School of Mechanical and Aerospace Engineering
Oklahoma State University
http://www.hvac.okstate.edu
Ofc: 405-744-6578

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