Refrigeration

[RODRIGO NUNAN G. MNONTEIRO]

Placing a refrigeration plant inside the mine, I thought that the heat rejected in the return should be as "latent heat", but in the Ventsim manual (as below) it says that it should be used as SENSIBLE heat, is that correct? Could you explain, since I simulated in this way and obtained extremely high dry bulb temperatures (68°C)??

21.4. Application of Refrigeration

......If the entire refrigeration plant is placed underground however, then the heat rejected by the refrigeration plant needs to be placed separately as a (usually) SENSIBLE heat source. This heat source needs to include an amount of equal value to the refrigeration value used, PLUS the input electrical or diesel power to the plant. The ventilation design implications are of course that the heat should not re-enter the cooled airflow, and sufficient airflow should be available to remove the heat.

[Martin Griffith]

Hi Rodrigo, it depends what the reject heat of the refrigeration plant is, is it just sensible heat, or is there moisture involved? If you input a large amount of sensible heat, with no latent, you would expect an air state of lower humidity, so it is not unreasonable to see high dry bulb temperatures. Presumably it would decrease further from the plant. 

Feel free to send us the model and we can investigate. Either DM it here or send it to ventsim.support@howden.com

[RODRIGO NUNAN G. MNONTEIRO]

Hi Martin!

Thanks for the quick answer. The heat will be rejected in our return airway, using a CSC (Condenser Spray Chamber): spraying 400 l/s of water at 41ºC and using 390 kg/s of return air at 28,5ºC (wet bulb temperature). If we should consider as mix of Sensible + Latent Heat, could you give me a tip on how to know the amount of each type of heat?

Rodrigo

[Martin Griffith]

Hi Rodrigo, thanks for the info, based on what you have there you can run the Heat Calculator in the Tools menu of Ventsim to calculate the sigma heat difference in and out of the spray chamber

 

You have more information than I do, so you should do this yourself with the correct information.

You can change the dry bulb temperatures as you like, and you will find that the sum of the sensible and latent will add up to nearly the same value. The wetbulb temperatures taken from your image are what set the sensible + latent total, it is the value of the dry bulb temperatures that will determine the breakup between sensible and latent heat. You can see this as you change the dry bulb temperatures. 

The other way to do it is with the second tab, which returns the total heat and then the latent heat expressed as a volume of water per time (ml/s). This is useful if you have some way of knowing what the volume of water is that is evaporated into the reject airstream. 

When configuring the heat in Ventsim you can do it this way if you want, entering the total heat as a Sensible Heat source, and then adding the water as a Moisture source. 

What you do depends on what information you have available. Is this an existing system and can you find out the dry bulb temperatures? Or is the amount of water evaporated in the reject airstream a known value from the plant design?

I hope this helps, I recommend having a play with the air heat tools in the calculator to get a feel for it.