A *sealed* bag for an aqueous solution? That's a *lot* of CaCl2 and effort for a small amount of ammonium chloride.
You're better off evaporating the solution with a hot plate or just by air exposure (very slow) and then cooling it.
ammonium chloride is very soluble in water and when concentrated, the vapor pressure of the solution is very low.
About 2 years ago, I neutralized almost a gallon of 5% ammonium hydroxide with a slight excess of HCl, and left the solution in a cut-off polyethylene milk jug with paper towels over the top to keep out dust and bugs. The heat in the summer evaporated much of the liquid, and when winter came, the very gradual onset of cold precipitated out gorgeous crystals of ammonium chloride. I filtered these off and left the wet, somewhat acidic NH4Cl in a dessicator over NaOH pellets, which do double duty of trapping the water vapor and excess HCl.
Since I've lowered the concentration by removing crystals and increased the vapor pressure, after the coming summer, I should be able to harvest another crop. Sure, I could do it with a hotplate and be done in a day or two, but where's the fun in that