If you are asking what PSI the spunding valve should be set at to allow for carbonation to occur during the fermentation then you will first want a Pressure gauge on your spunding valve setup so you can monitor the actual pressure. In my experience with my valve, the numbers on it don't mean jack. Secondly, you do not want to allow the pressure to build up to the amount that you would want to let it carbonate at room temp until the majority of the fermentation is complete or else you won't finish attenuating.
Lastly, yes, to calculate what pressure the vessel should be under at room temperature to gain a particular volume of CO2, use the same calculator used when force carbing cold. Just change the temp!
