Good morning all,
I am brand new to bikepacking.  I have hiked in the past and camped in a tent.  To cut down on weight and bulk, I decided to try a bivy sack as my shelter. 
Last night I camped in my back yard to test the bivy before I venture out on the bike.  Temps were sub freezing, and I was warm for most of the night.  My set up is a EMS Boreal 0° Sleeping Bag inside an Outdoor Research Alpine Bivy. 
My problem:  By morning, condensation had built up so much that my sleeping bag was moist and starting to constrict, and the zippers of the bivy were frozen shut.  Should I switch back to tent for cold weather overnights, or is there a way to control humidity in the bivy?   
Any insights people have would be greatly appreciated.  I have a week to rectify this problem for next weekends adventure.