HI..
the table was made with the equation that I gave you before, as i told you you cannot find the triggering time for a specific Vrms, thats because i dont know how maybe it can if there is a some way to solve for t in the equation. I made a little mistake (sorry), these are the correct values for 50Hz..
as you can see the minimum value Vrms that you can get is 0 when you wait aprox 9.96ms after you detect the cross by zero, it must be exactly 10ms its like the triac goes off just when you want to trigger it, and you have the maximum voltage when you wait 0.0ms after you detect the zero cross, thats mean bla, bla bla, i think you should know.
if you want to calculate in the uC the triggering with a temperature measured value i think you should use a table conversion, because if there is a way to calculate that, i dont know it, this is not my speciality, this is only part of my power electronics basic knowledge.
if you finish your project, i'd like to make me know, or even if you have more doubts maybe i can help.
good luck..