Thanks so much for your questions and so sorry for the late reply.
The need for hydraulic separation and/or a buffer tank is going to depend greatly on your system. Many boiler manufacturers will require a certain flow through their product and if you'll be using the boiler in a system with many zones that will turn on and off as needed, hydraulic separation will be a requirement. Because your system will end up with varying amounts of flow the hydraulic separator will be sure to allow your boiler to have the correct flow that it needs at all times.
In many systems, a buffer tank (hydraulic separation with added capacity) is a great idea. In conditions where only one small zone requires heat it will cause the boiler to short cycle (even modulating boilers) and greatly reduce efficiency. By adding a buffer tank, you not only get hydraulic separation but you add volume to the system and this will lengthen the run times of your boiler and increase efficiency.
Be sure to keep an eye out for our next edition of idronics, it will be covering the top of thermal storage and buffer tanks! Link below.
If you have any other questions please feel free to contact your local distributor, manufacturers rep or us directly at (414) 238-2360.