To avoid the use of antifreeze and, later on, the disposal of water & additives mix and to continue Testing during winter time also avoiding possible brittle fractures, the most simple solution could be the performance of Tests inside a tunneled habit with the use of scaffold sheeting and heating injection from each end.
Under extreme temps, - 15 °C to -20 °C we could maintain a steel temp + 10 °C to 15 °C with the only issue we could have is the wind-chill (here in Kazakhstan it's very common).
The sheeting improves heat retention and reduces wind-chill factor inside the contained area but the only time we get problems is with the wind; it creates cold spots which are very difficult to control.
During winter time, the wind generally comes from the east so to help and try to keep under control the degree of wind-chill we can try to place the items on the west side of the main shed or somewhere with the same kind of protection.
It all sounds a bit basic but it would work.
About demi-water storage tank and feed lines can have applied the same philosophy or can be insulated and power traced to avoid freezing of the water.
The only missing part, that it's still under evaluation is the recovery of the flushing water (required by client 150 l/min.).
If anubody have suggestions, it will be welcome as usual.
Wind chill applies to living beings, not inanimate objects like your pipe. If the ambient temp. is -20C, the temp of your pipe will not be lower than -20C even if the the wind is blowing at 70 km/hr. I guess what you are trying to say is that the rate of heat loss of your pipe would be faster with higher wind speeds.