Simulated VRT?

[Fred_K]

Hello!

 

In VentSim, the simulated VRT appears to be calculated from this line function: Geotheromal Gradient * Surface Datum of Mine Grid + Surface Datum RockTemp

 

It is this simulated VRT that is used in other calculations, correct?

 

I have a geothermal gradient, from temperatures that can be considered VRT, obtained from borehole data (several boreholes, different locations). However, the simulated VRT for a target level does not match the measured temperatures at all. To match my temperatures, Surface Datum RockTemp or Geothermal Gradient would need to be a lot higher.

 

Since it is theoretical and not calculated from other values, I would think that I can simply change the Surface Datum RockTemp to match my temperatures? Or would this affect other calculations beyond those making use of the simulated VRT?

 

By the way, the manuals from the Howden website do not have page numbers beyond the table of contents. Makes things just a little harder to find quickly 😉 

 

Thanks!

Frédéric

[Fred_K]

I think I answered my own question, changing the theoretical Surface Datum RockTemp is what I will be doing...

 

I also played around with the settings a little too much. I made corrections and it's much closer to the measured VRT now.

[Martin Griffith]

Hi, yes it sounds like you are on the right track. The Surface Datum Rock temperature is not something you can directly measure, its value should be extrapolated from the underground borehole measurements. 

[Fred_K]

Thanks Martin!

[Fred_K]

I have a small follow-up question here.

 

When I run my simulations, why does Ventsim auto-adjust the surface datum of my mine grid?

[Ivan R]

Hi @Martin Griffith,
Can you explain me this issue?


Thank you 

[Martin Griffith]

Hi Ivan, 

This warning indicates that the airways associated with the warning have a Date Mined setting which is further into the future than the year specified in Settings | Simulation | Environment | Current Year.

If you set a Date Mined value on your airway, then each Heat Simulation, Ventsim will calculate the age of the airway based on the difference between the Current Year setting and the Date Mined value. If the Current Year is earlier than the Date Mined, this age is negative and Ventsim throws the warning. 

So the fix is to make sure the Current Year setting is correct and the Date Mined setting on the airway is correct. You can find the Date Mined property on the Heat Tab of the Airway Edit Box.

Hope this helps.

[Martin Griffith]

On 9/8/2021 at 8:57 PM, Fred_K said:

I have a small follow-up question here.

 

When I run my simulations, why does Ventsim auto-adjust the surface datum of my mine grid?

Hi Fred, 

Apologies I appear to have missed this question from you. 

If you set your surface datum mine grid to zero, it will auto-adjust. It could also be that there is a large distance between the top of your mine and the entered surface datum. Whatever the case if it's not making sense, please send us the model or some screenshots at the Ventsim support email and we will work out what is happening.