[TRNSYS-users] Type 997 - horizontal ground heat exchanger

[Jeff Thornton]

Henk, 

<How could I find acceptable values for the emissivity and absorptance
of the soil surface. The soil is probably earth/grass but could perhaps
be paved.> 

Paved surfaces vs grass surfaces will have very different absorptivity
and emissivity values. There are some great resources online - do a
search on emissivity of materials. However, with that being said, we
rarely use that approach when we studt horizontal GHX systems. The model
does not take into account evapotranspiration and therefore the surface
temperatures likely swing more in the model than they do in real life. I
would suggest using the surface temperature mode corresponding to the
long-term averages (Kusuda). 

<With the input Zone convection coefficient, the comments state this is
only used in zone surface mode 1 (energy balance), where is this set?> 

Parameters in the model: 

Insulated surface mode
Soil surface mode 

<Also, what would be an appropriate value or how could one estimate
this?> 

It depends entirely on what is happening in your zone. Is the air
stagnant, moving, etc. Refer to the Type 56 documentation for examples
on convective heat transfer in zones. 

<The incident short wave radiation (also used in surface mode 1) should
be read from the weather file, does this need to go through a radiation
processor as in other models? What output of that processor or weather
file would be a good one to use?> 

Be careful here. If the surface is within a zone then the incident short
wave is likely from lighting although there could be solar radiation
hitting the floor. If it's not within a zone then the incident radiation
is solar and should come from the weather component (type 15). Most
likely the total incident radiation on a horizontal surface. 

<Sky temperature and incident solar radiation - same question> 

The sky temperature input should be connected to the sky temperature
output from the weather component, 

Jeff 

---
Jeff Thornton
President - TESS LLC
22 N. Carroll Street, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 02/14/2018 10:00 am, henk witte via TRNSYS-users wrote: 

> Dear fellow TRNSYS users, 
> 
> I am currently building a model with the TESS type 997, horizontal heat exchanger, for the first time and have some questions about the parameterisation and inputs: 
> 
> 1) How could I find acceptable values for the emissivity and absorptance of the soil surface. The soil is probably earth/grass but could perhaps be paved. 
> 
> 2) With the input Zone convection coefficient, the comments state this is only used in zone surface mode 1 (energy balance), where is this set? Also, what would be an appropriate value or how could one estimate this? 
> 
> 3) Same question for Zone radiant temperature 
> 
> 4) The incident short wave radiation (also used in surface mode 1) should be read from the weather file, does this need to go through a radiation processor as in other models? What output of that processor or weather file would be a good one to use? 
> 
> 5) Sky temperature and incident solar radiation - same question 
> 
> Any suggestions more then welcome! 
> 
> Thanks, 
> 
> Henk Witte 
> 
> Groenholland Geo-energysystems 
> 
> Valschermkade 26 
> 
> 1059CD Amsterdam 
> 
> T: +31 (0)20 6159050 
> 
> M: +31 (0)628176535 
> 
> E: henk.witte at groenholland.nl 
> 
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at lists.onebuilding.org
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