Indirect tank circuit without air/dirt separation?

dave123

I've noticed in several boiler install manuals, where a piping diagram is provided for an indirect tank, the indirect is correctly piped in parallel, but the circuit typically does not include the air separation or dirt separation devices, which are placed either distant on the primary loop or on a secondary loop.

This means that during the non-heating months, when presumably only the indirect circuit is running (intermittently), that flow never sees the air or dirt separators.

Is this acceptable? Even if the indirect circuit is running only 45 minutes a day, over 6-7 months that's a lot of flow passing through the boiler without air or dirt separation.

So wouldn't it be best to ensure that the indirect tank circuit always includes air and dirt separation, even if that means longer pipes and more fittings?

STEVEusaPA

Many older manuals show outdated piping practices. Dirt mag is always on the boiler loop or at the bottom of a hydraulic separator, air eliminator on top, so it’s doing it’s job any time the boiler circ is on-heat or domestic call. Indirect usually have an air vent on top of the tank (second time this came up in one week).
Your better off looking here:
https://www.caleffi.com/usa/en-us/technical-magazine

dave123

But all these manuals can't be outdated. For instance, the manual for the Lochinvar Knight, pg 36, shows the indirect circuit not including air or dirt separation. Neither do the Weil-Mclain Aquabalance diagrams.

Is there some reason that the indirect circuit, running in isolation, doesn't need air/dirt separation like the rest of the system does?

SuperTech

The indirect circuit isn't running in isolation.  The fluid in its circuit will be mixed with boiler loop. The air and the dirt will make it to the separator.  No need for one on each zone.

dave123

SuperTech said:

The indirect circuit isn't running in isolation.  The fluid in its circuit will be mixed with boiler loop. The air and the dirt will make it to the separator.  No need for one on each zone.

I don't follow. Presumably the primary loop has check valves, specifically to prevent flow through the primary loop when the indirect circulator is running, so as not to waste heat. Otherwise there'd be heat lost to the primary loop all through the non-heating seasons.

STEVEusaPA

Can you post the specific diagram you are referencing?

mattmia2

also, many diagrams in manuals were drawn 35 years ago and they just keep reproducing them

hot_rod

if the indirect is a parallel loop off the boiler before the sep, true it does not flow through the sep, necessarily. But all the system fluid has made trips around the dirt and air separation device all during heating season. Really shouldn't be any air or dirt entering a sealed system?

Also, most boilers, mod cons for sure, have an air vent on the boiler itself, usually an auto vent. If it is a combi boiler they have air vents built into the DHW HX pump block for the same reason.

dave123

hot_rod said:

if the indirect is a parallel loop off the boiler before the sep, true it does not flow through the sep, necessarily. But all the system fluid has made trips around the dirt and air separation device all during heating season. Really shouldn't be any air or dirt entering a sealed system?

Also, most boilers, mod cons for sure, have an air vent on the boiler itself, usually an auto vent. If it is a combi boiler they have air vents built into the DHW HX pump block for the same reason.

The boiler's built-in air vent would capture much of the air I'd guess, but not microbubbles? Microbubbles form all the time just from heating, I thought, so even a closed, scrubbed system will still get them (?).

In Idronics #2, they make a point about including the DHW circuit in the flow through both the air separator and dirt separator, which they show in Fig 27. Some Siegenthaler diagrams show the same. Yet the boiler makers (Weil-Mclain and Lochinvar, at least) omit this step in their install manuals. You'd think they most of all would want the boiler protected at all times though.

The only downside I see is potentially the need for more pipe, more fittings, and more head loss through the indirect circuit. But maybe in the end, it doesn't add very much to the overall removal of air and dirt?

hot_rod

Correct the micro bubbles come out of solution when the water is heater. I like to run boilers up to 180 when installed to aid in that process of driving out ALL air. Once this is done the system should stay air free unless
The system is opened for service or repair
A small leak is allowing additional fill water, which has entrained air
Or you have an air vent on a system with an improper PONPC so points of the system could go negative and air enter through a float type auto vent, doesn't happen often, but certainly possible.

You see many drawings with the air separator right at the boiler, this eliminates your concern, and puts the air sep in the very best place in the system, the hottest water, or fluid.

motoguy128

Am indirect shouldn’t need a dirt separator. It’s a SS coil, won’ create any dirt. Dirt separator are because of steel piping and cast iron fittings and radiators. IF you have a copper fin tube system or PEX you don’t really need a dirt separator either.

hot_rod

The Munchkin and most mod cons like to show a Y strainer to protect the small passage ways. a dirt sep is a more engineered way to do particle removal, down to 5 micron size without obstructing flow, like a y strainer does.
Not required as @motoguy128 mentioned, but cheap insurance.

motoguy128

Navien have the strainer built in. Very small passage ways. But we add another Wye strainer or separator when installed to replace old boilers with steel and cast iron. Other cheap option to get some of the bigger stuff is a hydronic separator if you have a primary and secondary setup. Two 2” crosses, a pipe nipple and some bushings and you can build one on the cheap.