Your refrigerator should be on its own breaker.

You could safely run your grow equipment on a 20 amp breaker. honestly I wouldn't run anything on the same breaker as the refrigerator. Turn off the breaker that you believe it to be on and see what turns off. Then go around and plug an alarm clock or small lamp into each. After you've done this to EVERY outlet and every breaker in your place mark which is on which and go from there.

Also the electric usage is normally printed some where on the appliance so that would give you a better idea of the watts your working with.

Good Luck