Multiple Closely-Spaced Tees (CST's) vs Manifold off one set of CST's from Primary Loop

WrightTrack

I'm relatively new to this, but taking a big stab...so be gentle if I'm missing some kind of "flow effect" or perhaps reinventing the wheel.

System: Multiple boiler sources (solar, wood, gas - hopefully in that order, eventually).

3 zones, 1 big, 1 small, last 1 is an indirect w/h for domestic use water.

The gas w/h shown also doubles as a buffer tank, as I plan to manifold the solar, gas and wood burning sources into it as the hub of my primary loop.

Last note: This application is located in the upper midwest in an off-grid cabin, so an alcohol mix is preferred, rather than simple tap water, for all the obvious reasons.
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So the question: Which version of the secondary loop/loops is most effective?

I have seen and read many iterations of CST and non-CST arrangements, all with great rationale - so many that I can't figure out which one is most efficient. Assuming use of CFT's is the best option, it seems to have come down to 2 options:

1. One set of CST's off the primary loop, with 3 zones using in/out manifolds.
-OR-
2. Three sets of CST's directly providing h/w to the 3 zones.

Option 1 seems a little more involved, but a more even distribution of the hot fluid to the 3 zones - and seems to [require] the backflow preventers (check valves).

Options 2 seems less complicated, but it also appears that the [1st] secondary loop may 'rob' the hottest fluid, from the following secondary loops, making initial heat-up take longer. The check valves may or may not be necessary, but appear to 'force' positive forward flow into the primary loop.

WrightTrack

No one has responded to the scenario I posted yet, so I'll update it with an additional (albeit seemingly obvious) observation.

Each scenario [seems to] require a pump for each secondary loop, which starts adding up, especially since my intended tiered, multi-source system also requires a pump for each source.

So, contrary to the 2 options in the post above, what if CST's are -not- the best option? Another option I'm considering (and I'll add a schematic later) is pumping directly [thru] the buffer tank into the manifolds without CTS's, and use zone controllers to stop flow to the in-floor zones as required by their respective thermostats.

I wouldn't necessarily need to control flow to the indirect water heater, since its thermostat should be a [final] determination of whether or not the 'backup' source (gas water heater) needs to fire up or pump hot fluid. Or in the case of a solar boiler moving hot fluid all the time, wouldn't the 80 gallon indirect water heater be able to continually absorb that heat?

This scenario cuts out the complication and electricity used by the secondary loop pumps, which is especially significant in my off-grid (solar/wind) home, but for any home that 'pays' for electricity.

hot_rod

With solar and wood you definitely need some buffer capacity. Ideally sized to the number of solar collectors and or the size of the wood boiler. I'd start with 200- 350. It really depends on how long you want to run off the buffer. Many wood burners end up with 1000 gallon, a couple used 500 LP tanks, for example..

The buffer becomes the central part of the system. All inputs pipe to it and all distribution starts there. I'll include a drawing of what I ended up with after a 1/2 dozen different piping and tank size options.

Solar drainback is the only way to go with large thermal arrays as you have very small summer loads typically and you do not want to stagnate glycol collectors all summer.

With that in mind the buffer can also serve as the drainback. I stood a 500 gallon LP tank on end, left about 35 gallons of air space up top. That is the drainback "bubble" and the system expansion tank. Just plain tap water in the tank. That same water is in the solar, wood boiler, LP boiler and all the distribution piping.

So DHW is generated from the tank via a plate HX, any time a faucet opens that pump runs to make continuous HW. It works down to 120F tank temperature.

Any or all heat generators can add heat. Solar and wood were priority, LP only when needed. LP went directly loads, it did not heat the 500 gallon buffer ever. So the LP boiler just connected up high on the tank, enough to keep the plate HX hot for DHW.

There really is no super simple way to pipe that much stuff together and prevent one from heating the other, some sort of separation is needed. Using the tank as the sep and buffer is the best way.

Piping can be complex, control logic even more so if you want at least some automation instead of manual valves

WrightTrack

Thank you for the tips, Bob, and for sharing your progressive knowledge and experience - these things are valuable to know. Unfortunately, the scenarios in question weren't actually addressed, which were the [better] choice of the 2-3 variations on the primary/secondary loop CST arrangement:

1: Individual sets of CST's off the primary loop - one for each zone.

2: One set of CST's into two manifolds - manifolds serving all loops.

3. Direct feed from buffer into manifolds to serve all loops, metering with zone controllers.

Piping the 3 sources into the buffer isn't an issue, and seems to be pretty straightforward handling with hard logic and only a simple control module.

I have also updated the original post to mention that use of tap water [as part of the in-floor system] is not an option since I live in the upper midwest and winter temps could cause problems.

hot_rod

I not a fan of series primary loops, drawing 2 as you always have mixing and temperature drops at every set of tees. the temperature mixing will vary depending on which loads are running, what gpm etc.

The concept I was showing puts everything in parallel and avoids all the "blending"

My system was in the midwest, my current system is in Utah, both areas experience sub zero weather. Un less you have outside piping or exterior walls, extended power outages, really no reason to use glycol. The shop I'm building now will have constant circulation in the floor loops, instead of glycol. A basic UPS or small generator could keep the system goin g in a power outage, at least power a few ECMs.

Of your option, one set of tees would eliminate the temperature drop you will get with multiple CST off the primary loop.

P/S piping does get pump intensive, that is part of the concept, provide each circuit with dedicated flow without interfering with other connected circuits.

If the garage loop kicks on after a period of no heat in cold weather, it will overpower that LP heater, I assume it is a tank type heater?, and cause condensation, ideally that would be a condensing type WH?

Even so that cold slab "flywheel" will prevent other loads from getting adequate heat on design conditions from a cold start. You might configure a priority load control logic of some sort.

Still not sure why you want a primary loop? Separation could be accomplished by headers at your tank, then any inputs or loads come from that piping, all loads see the same temperature, use mix valves for lower temperature loads.

WrightTrack

Hot Rod Bob! Thanks again for the tips and comment! I'm understanding more and more as I try things on my own as well as glean knowledge from folks like you that have already been through the school of hard knocks!

My off-grid electricity at this point is pretty reliable, but I have personally experienced small anomalies that give me the impression I should "hope for the best and plan for the worst". My main reason for this old adage is that I'm not always out there, but will want/need it to work on its own. This goes for electricity and heat or cooling, depending on the season. Therefore, glycol is going to me my choice, even with the significant up front expense.

I agree wholeheartedly about the consecutive CST's, as I wrote in my original post, that they could potentially "rob" heat from one another - at least at startup, as you mentioned. With giant heat sinks, like my garage floor slab, heating after startup is more a maintenance than anything else. Thank you for confirming that notion.

The reason for my primary loop buffer and secondary loop zones comes from all the opinions that I've read online, as well as some seeming logic in the matter. If you heat fluid in a continual loop, it will always be available for the zones as needed. I agree that 'cold starts' would be a big burden in that scenario, all the way until everything is heated.

I agree again with you regarding the LP water heater shown, which doubles as one of the "boilers" as well as the buffer tank. It is a source in addition to the (3 other) boiler sources I am using though, because I have another LP water heater in conjunction with the solar array (not yet in place) and the wood boiler (in place).

The reason for skipping an expensive condensing boiler at this time is based a number of great YouTube DIY videos, as well as a strong opinion across several videos and articles that discuss gas water heaters being more efficient than boilers.

Note: I am thinking way ahead with my system circuitry for desirable or necessary changes that will inevitably appear. It is piped in a very modular and easily changed fashion, so that I'm not stuck with a ton of "undoing" as I dial in the system. Adding, removing or replacing components will be a pretty painless task...even if it's the previously mentioned CST's and one pump per zone.

PC7060

Ok, I’ve tried to figure it out but no luck. What does CST stand for?

ratio

Took me a while too: closely spaced tees.

PC7060

lol, that’s really forcing a acronym.  I’ll have to start calling my decking fasteners RSN now (ring shank nails) 🙃😝😎

psb75

For the OP (original poster): I too struggled with CST--seeing it in the thread title and then never seeing it "expanded" in the following text. Here is a good rule when using these acronyms: good to type all the words--at least once. Usually ITB (in the beginning).
BTW, I'm a firm proponent of CSTs, and HSTs (heat storage tanks) as hydraulic separators--especially with multiple heat sources, with one being a solid-fuel burner.

WrightTrack

Regarding the acronym "CST's" - I didn't make it up. I read it in a number of articles here on HeatingHelp while doing my best to do my due diligence before posting. I figured it was a common-use term in this group and on this forum.

My apologies for any confusion. I will update the original post.

hot_rod

I like the CST acronym, much quicker to type. P/S is commonly used for primary secondary.

WrightTrack

PSB75 wrote: [ "BTW, I'm a firm proponent of CSTs, and HSTs (heat storage tanks) as hydraulic separators--especially with multiple heat sources, with one being a solid-fuel burner." ]

I don't have a problem with the CST setup, I was originally just wondering which is a better option between the two original schematics (and descriptions).

However, I admit that removing the [pumps per zone] and controlling flow with zone control valves is a pretty attractive alternative.

PC7060

@WrightTrack - we are just busting your chops since you did such a good job of stumping several of us.  

and re the design of your system. I try to do whatever @hot_rod says.  

WrightTrack

Update (theoretical): As may have occurred to some of you, the multi-source, multi-zone design [may not] actually need a pump for every zone. If I don't add a larger zone on an upper floor, for instance, a single pump could be placed between the 'exit' manifold and 'return' CST, and adding zone control valves to supply whichever zone is calling for heat. In this schematic, I chose not to bother with a zone control on the indirect water heater, because - especially with a solar supply option - keeping that loop flowing keeps hot fluid circulating through my buffer tanks. This is, of course, another theory that seems solid, but may be just my undereducated logic dictating design direction.

hot_rod

Probably just my old eyes, any way to put all that piping on a white background? Easily

WrightTrack

Here you go, Hot_Rod. I tried to edit the post, but somehow it vanished. I'm trying to remember what I wrote, so it won't be word for word, but also notice that I switched the two original schematics to white background, too. Thanks for the heads up on the difficulty - I look at this kind of stuff all day, and didn't notice.

Rewritten post:

THEORETICAL UPDATE: As many of you may already have realized, I wouldn't likely need a pump for each zone, as originally posted in CST/Manifold scenario one above. If I never had to add another zone, like a large zone on an upper floor, I could simply place a single pump on the exit side of the exit manifold, and use zone controllers to manage their respective need for heat. Note that the indirect water heater doesn't show a zone controller, as it can maintain ongoing circulation, which will be especially good if the solar boiler array does the job I hope it will.

hot_rod

Getting there.
Flow comes out of the LP, by solar or the wood boiler upstream? The left 1/2 of the schematic doesn't show up on m y screen.
The indirect running wild could get to 190 or more if the wood boiler runs away? It will need a check valve, maybe those are below the zone valves? The circuits with zone valves should not need checks

An expansion tank somewhere? depending on where it is tied in, "P" may be better on the red, supply line.

Erin Holohan Haskell

@WrightTrack, if you edit a post too many times within a set time period, it gets held by our spam filter. I've sent it through here. Thanks!