Before you even try to think about Thermal Vent.. You have to know how this work exactly. And so far as i can see no one in this thread could know how it work.
Here we go..
In fact Thermal vent don't do anything to make your temperature low. Actually this effect simply CAN'T make your ship more cold than it is already.
The main design of this effect is to allow pilot to have 5GR OC PP and fire Beams. So this effect ONLY lower temperature of WEAPON that you use. Only weapon that have Thermal vent.
How it works?
You have stock temperature for about 40% ok? And you fire 2 huge beam without Thermal Vent with 4 pips. You will get like 80% of heat while firing this beam.
And second example: You have now stock temperature for about 40% and you firing 1 or 2 huge beam (same Thermal load as a 2 stock beams because of secondary) with Thermal Vent while in 4 pips. If we assume that your % of accuracy is 80% or close to 90% or even 100% then your temperature while firing will be... 40%.
Yes, same 40%. As i already say, this effect only about your WEAPON and not ship. Ship can't have low temperature with such effect. It ONLY make your weapon COLD ( like not firing at all. That is exactly a reason why this effect feels broken in Silent Run. Because it is not broken. It is a main design of this effect to not cooling your ship BUT WEAPON.
While without effects 2 beams will deal only 80% of heat. 2 beam with effect will be like 4!!! stock huge beams if you did not hit your target.
Oh and by the way. If you understand what i am talking about. You will realise that the effect is not stacking at all.
Oh, and one more thing. If you have firing not only beams but also some MC. What will be with your temperature? Just fire with MC and look for your temperature. See? Let's take for example 55% of heat while firing MCs.
So after firing beams with Thermal vent + MCs we will get.. 55% of heat. Ofc it is depends on how good is your accuracy.