Heating Help

Hydraulic separator yes or no?

@ August 11, 2010 3:11 PM in Hydraulic separator yes or no?

My partner and I have been debating the necessity of  hydraulic separators for a while and frankly are having a hard time seeing the need and justifying the added expense.

Our basic radiant system is built with a mod/con boiler with a dedicated pump injecting into the radiant distribution loop through closely spaced tees. Most of our systems employ constant circulation through non-electric remote thermostatically controlled zone valves (TRV's).

We are told that besides venting air and collecting dirt, the advantage of a hydraulic separator is that at certain points in system operation, the gpm through the boiler will exceed the gpm of the heat distribution loop. The design of the separator then provides a path for the boiler supply water to mix with return water and divert directly back into the boiler return pipe.

I have spent more hours than I would like to admit, in wet-head obsessive fascination, watching boilers run and playing with my clamp-on thermistors. My conclusion is that when gpm's through the boiler exceed gpm's through the heating distribution loop, a portion of the boiler supply water goes back upstream, where it diverts right back into the boiler return pipe. Just like in a hydraulic separator, but without spending half a grand to do it.

I can see separation piping scenarios for buffer tank applications, but on most residential situations I am thinking it is better to put the money into Uncle Hydronoids retirement fund. Am I missing something or is this just more gear being foisted on the unwitting?

high temp solutions

@ August 11, 2010 3:09 PM in stagnation...

Pressurized glycol systems need to have work to stay cool. Cooked glycol becomes acidic and requires replacement, it doesn't take long either. Many controls have night-time cooling and other tank heat management functions.
You might consider larger storage if that works for your winter scenario and you might consider heat dumping. Use the heat elsewhere like a hot tub or pool. You can also divert heat to some soft copper in the ground outside the structure or run some fin tub mounted outside where it wont bother anyone. With the help of your panel manufacturer you can figure out your panels output in high summer and size your heat dump accordingly.
Expansion tanks should be sized to accept the volume of fluid in the panels so that in the event of overheating during stagnant periods or pump or control failure the h2o in the glycol can flash to steam and push back into the expansion tanks without popping off on high pressure. Popping off creates a cascading set of problems. DOW makes a highly resilient glycol.
For your next system you might consider piping for "drain-back" and you would avoid all these concerns and collect at a higher efficiency as well. We service a number of four panel drain-back systems with small fan-coils that have been plugging away for thirty years making dhw and space heating with barely any maintenance other than monitoring storage water levels and replacing thermistors and one or two pump cartridges.