Primary-Secondary Piping Design Tweak

08GeezerGlide · November 2022

After digesting a few hours of Dan and others' expert commentary/discussion/videos, I am trying to apply Dan's "K.I.S." approach to solving what may be an occasional low-temp. return water issue. There was also some minor flue pipe rot at the insertion to the masonry chimney and also what looks like some flue tile degradation in the clean-out.

A new oil-fired W. McL. WGO-3 (Beckett) is now going in to replace a second cracked Burnham in 24 years. The home, about 1600 sq. ft., has 3 active zones (1st - 2nd floors & a small, breezeway room). A new 4th zone will be added as a standby for rare use to temper the basement on cold N.E. days.

Attached is a drawing of the proposed modified piping based around work within a tight area, inclusive of a very low unfinished basement ceiling. With regard to the supply header & return leg from the return header, they will tie into an abbreviated primary loop, which makes use of the Taco 007e supplied with the boiler. Heeding Dan's concerns for keeping secondary loop tees closely spaced, these tees will be kept within 6" of each other. This will be pushing the water, after the compression tank and Spirovent, with the newly supplied circulator.

The existing zone piping has the 3 zone circulators on the return, with flow-checks on the supply. The 4 new circulators going in will have built in flanged shut-offs & flow-checks. And, respectful of Dan's growing phobia with gravity heat (garden hose also?), I will install flow-checks on the returns as well. The design also assumes the primary circulator to run only when burner runs. There is an existing Taco 4 zone control panel handling the circulators.

Any input directed to possible design flaws would be appreciated. I do question whether such a short primary loop having a circulator pumping down to the return port will prevent the supply header from efficiently drawing hot supply water from the tee without creating disruptive turbulence and possibly conflicting pressures elsewhere, but the design also seems to be in line with the concepts discussed.
At any rate, open to criticism and comment. Thanks for either.

hot_rod · November 2022

primary secondary loop does not necessarily protect the boiler unless you have a way to sense and react to return temperature. It will cost another pump, and you will get some temperature blending at the close tees, depending on various flow rates as zone pumps turn on and off.

A "moose antler" primary loop could work if you added an aquastat to turn off the boiler pump when return drops below 130F. Called a bang/ bang method as you turn the boiler pump on and off until temperature rises. The German boiler brands use this method on cast boilers for protection.

A boiler return protection valve is another option. It modulates flow to the system and boiler until the return gets to 140F, for example.
An explanation on how it works.

Jamie Hall · November 2022

I don't see any problems, although others will have more detailed input. Not to worry about whether the water is going "up' or "down" -- once a pump gets into the game, the orientation of a pipe relative to gravity becomes almost irrelevant. What drives water flow in a pumped system is pressure differences, not gravity.

08GeezerGlide · November 2022

Thanks Bob! Your response options made me look a bit deeper. So with regard to your inked note-pad dwg., I do not see a circulator on the primary loop. Was this intentional to allow the loop to simply convect/flow on thermodynamics? I do see the bypass valve, which in my project would be a 1 1/4" bypass valve. Available in NPT? Very expensive? Can I assume that these valves can be set for a minimum 150 degree return water before the valve starts letting return water through? And I guess a bit more curious as to how the supply loop(s) that may be still calling will perform when the return path is shut off. If the tank, in the depiction, is replaced with a loop of emitters that are calling for heat, when the return leg is shut off, wouldn't flow out to the zone be stopped?

As far as the last attachment, showing the closely spaced tees, or possibly even a specialty fitting designed to do the same thing, where does the protection to the boiler come into things? I am looking at this and seeing the potential for below-acceptable temp. water coming home on the return and flowing right back to the boiler. No?
Thanks again!!

08GeezerGlide · November 2022

Jamie- Thanks. One brain-block I continue to have with this concern for low-temp return water and its effect on combustion condensation is this. How is this issue addressed when a boiler cold-starts after sitting for a while? It would seem in these cases, sub 140 degree water either sitting in the jacket or being pumped in would have the same effect.
And back to my drawing, are there any issues created when the elevation of the headers are dropped down from where their supply line is hung? i.e. Do I need to worry about pressure changes or undesirable trapping when forced water piping is running horizontal at one level and then drops down, say 1-3 feet, before heading up to a level above its previous horizontal level? I ask this as work conditions, especially with low ceilings and raised boiler platforms, can create a real need to fit a few components into the line(s) and then drop down to allow adequate room for a neat, serviceable header/circulator assembly. Would be nice to rule this out when faced with physical obstacles that crop up. In this case for instance, trying to get the compression tank, CW service tee, and air separator above the boiler and out of the way of the vertical flue pipe is a challenge which leaves me with a supply run to the supply circulators at a height that just won't permit a header, valves and circulators starting at the same height. No room on the right to speak of and limited on the left.

hot_rod · November 2022

08GeezerGlide said:
Thanks Bob! Your response options made me look a bit deeper. So with regard to your inked note-pad dwg., I do not see a circulator on the primary loop. Was this intentional to allow the loop to simply convect/flow on thermodynamics? I do see the bypass valve, which in my project would be a 1 1/4" bypass valve. Available in NPT? Very expensive? Can I assume that these valves can be set for a minimum 150 degree return water before the valve starts letting return water through? And I guess a bit more curious as to how the supply loop(s) that may be still calling will perform when the return path is shut off. If the tank, in the depiction, is replaced with a loop of emitters that are calling for heat, when the return leg is shut off, wouldn't flow out to the zone be stopped?

As far as the last attachment, showing the closely spaced tees, or possibly even a specialty fitting designed to do the same thing, where does the protection to the boiler come into things? I am looking at this and seeing the potential for below-acceptable temp. water coming home on the return and flowing right back to the boiler. No?
Thanks again!!

The first drawing with the 3 way protect valve is not primary secondary. Any zone pump pulls from the boiler, but that valve only allows enough flow into the system as the temperature returning allows. Think of slipping the clutch in your truck when you start on a hill or with a heavy load.

Them last drawing is primary secondary, does not offer protection unless you add a temperature control in the boiler. When the boiler drops below say 130, it turns off that boiler pump until the block it heats back up over 140F. It's not a nice smooth method but it works. And you have primary secondary to keep the various circulators happy with one another.

Really, the boiler protect valve is a simple non electric, automatic device that gets the job done.

08GeezerGlide · November 2022

Bob - I have labored over your response here trying to fully comprehend your own ink drawing referencing the three-way valve and just can't see what role the vertical bypass pipe plays given there is NO circulator dedicated to pull or push water through the 3-way valve to the return. If we assume the boiler is up to temperature allowing zone circulation, and 1 or more zone circulators create a cold return ( -140), and the 3-way valve closes off the return water from the circulators, it would seem that now there is no flow in the zones nor is there any flow through the bypass pipe. I would think that because we have stopped the source of the colder return water, at some point the valve may sense an increased return water temp simply due to migration of the rising block water temp. But again, what is the bypass pipe doing when there is no circulation induced? I do like the idea of this 3-way valve but just can't see it here in your ink drawing.
Would it just be easier for me to install three speed Taco 007 pumps in all the zones and a temp gauge in each of the zone returns? Maybe with that, I could monitor return temps on a cold day and adjust pump speeds to regulate the offending zone(s). Thanks for any follow up.

hot_rod · November 2022

Good eye and good thought process. That sketch only works on one zone single pump.
We still need that hydraulic disconnect via primary secondary with multiple pumps, or zone pumps.

Here are two options with thermostatic mix valves for protection. One with close tees, one with a hydraulic separator

hot_rod · November 2022

Some additional reading and piping options.This article shows high mass radiant connected. But the same principles apply for any high mass, high volume systems like gravity conversions.

https://www.supplyht.com/articles/100650-myths-and-methods-for-protecting-boilers-against-flue-gas-condensation

Primary-Secondary Piping Design Tweak

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