With a system that weeps cold and no temp sensors except for the one(s) on the side of your building measuring the ambient temp, all your doing is throwing water down the pipe based on a formula. Here's an analogy...doing this is like putting the thermostat to your house outside and asking your furnace to keep your house warm?
I weep hot water, for I believe you use a lot less water in the wintertime. Yes, you do use gas/propane to heat that water, and one could debate that all you're doing is moving the cost from one utility to the other. However, I believe you'd still be money ahead weeping hot water even if your boiler has to turn on every now and then. Think about the side benefits, heat in your trough keeping your other lines warmed...just bundle them together with velcro straps.
In order to weep hot, you need to do it intelligently, and it's not cheap to set up. Each one of my bays has a temp sensor as far out on the pipe as I can go (right before the swivel in the bay at the boom). You measure the temp of the pipe, and when it falls below whatever you set it to, your plc (or whatever you use) turns on the hot water. When the sensor is satisfied, the water turns off. Works really well.