Primary/Secondary Piping Concept

[WoodNotOil]

I currently have a series hookup with storage that works fine most of the time. However, I don't like the temp drop that happens when multiple zones are on. When I add on to my house and put in more zones this is going to be more of an issue than it is now. I am trying to understand how P/S hookups work with zone pumps instead of zone valves. I don't want to have to change that part of my system. I know pybyr is doing something similar to this, so hopefully people will have some input. I don't plan on changing my piping until next summer.

In my drawing the boilers are connected to the main loop via closely place tees. The primary loop can be supplied heat from wood, storage, or oil and each zone has its own pump. The zones are not connected via closely spaced tees so each zone can get the highest temp water available. Here are my questions:

1. Will the zone pumps supply flow through the primary loop or does the primary loop also need a pump?

2. Assuming there is no need for a pump in the primary loop, when the wood circ is on the water in the primary loop would need to flow clockwise for zones to get the feed and if the storage circ or the oil circ were on then the primary loop would have to flow counterclockwise to feed zones. Would that flow change happen automatically from the direction the boiler loops flows through the common pipe? Would a flow change happen at all? Should the boiler loops all enter flowing in the same direction and be on the side of the loop between the supply and return? (The reason I ask is that physically it would be easier to pipe the way I drew it based on the position of everything.)

Any help understanding this application would be greatly appreciated. Thanks

 

[Nofossil]

My understanding is that you need a circulator in the primary loop, and it should flow more than any of the secondary loops. I think the zones are usually configured just like the boilers, with closely spaced tees.

This setup gives you excellent control over flow in each heat load and source at the expense of always having multiple circulators running. here's an excellent sticky on theis forum that describes the approach.

 

[Adios Pantalones]

If the wood boiler return pump is on, what is to keep it from just short-circuiting the loop (as in- water goes out of the boiler to the loop, then just gets sucked back to the boiler)? Another pump would have to be on drawing from the loop much more to keep that from happening I think. Your tank loop- does that have to push the charging pump backwards to draw heat?

I'm new at looking at these, so please bear with me.

 

[pybyr]

you definitely need a pump in the primary loop, too

the down side of primary/ secondary is the additional pumps needed and associated power draw; the bonus is tremendous flexibility for both current configurations and later adaptability.

google "primary secondary back by popular demand" and you will find a great article by John Siegenthaler on the hows & whys of this approach

later on I should take a photo and post it of my primary loop, which is made, but not yet connected or fully installed- the rest of life keeps interfering with my schedule

 

[Jim K in PA]

They way you have drawn it, without a primary pump and the secondary loops pumping through the closely spaced Tees, you will likely just recirculate the water, and induce little if any flow in the primary loop. Based on my understanding, you will need to have the primary pump circulate the water in the primary loop, and the pump for the secondary loops for the oil, storage and wood circuits will each have their own pump pulling water out of the primary loops on the upstream side. All secondary loops must be plumbed in the same way (same direction of flow through the primary).

As to the zone circs, you can run them the way you have shown, albeit they are not set up in a true P/S layout. That is more of an injection hybrid than a P/S. Depending on how long the primary loop is, and the diameter of the primary relative to the zone loops, you may not have much of a problem with ghost flows through the zones when the zone circs are off.

That is the one advantage of the zone valve over the circ. The valve prevents flow whereas the pump cannot.

Hope this makes sense.

 

[WoodNotOil]

Alright, I am starting to understand this a little better now. Here is a revised version based on feedback so far.

If the wood boiler return pump is on, what is to keep it from just short-circuiting the loop (as in- water goes out of the boiler to the loop, then just gets sucked back to the boiler)? Another pump would have to be on drawing from the loop much more to keep that from happening I think.

I assume it would short cuircit unless there was another pump on. That must be why there has to be a pump in the primary loop.

Your tank loop- does that have to push the charging pump backwards to draw heat?

Yes it would. Pumping through another idle pump may not be conventional, but it works great and had the blessing of the Taco guy I talked to about it. It saves a great deal of complexity and cost. An additional hx or lots of piping with zone valves would be required to make this happen otherwise. I have this configuration on the tank side of my plate hx currently with a DPDT relay that makes sure they both don't try to run at the same time. Works perfectly!

google “primary secondary back by popular demand” and you will find a great article by John Siegenthaler on the hows & whys of this approach

later on I should take a photo and post it of my primary loop, which is made, but not yet connected or fully installed- the rest of life keeps interfering with my schedule

I'll check out the article, thanks. I would love to see pictures of your install. Did you end up going with closely spaced tees for zones or did you do something like in my drawing where the supplies are together and the returns all together?

Thanks for the help guys!

 

[Jersey Bill]

its better with the primary pump, but its still NOT primary-secondary.
to make it primary-sec. you need to bring the zone returns back to the primary loop right next to, and after where the supplies are taken off. its the so-called "close spaced tee"
arrange the zones after the boiler from highest to lowest temperature, or proirity.

 

[WoodNotOil]

its better with the primary pump, but its still NOT primary-secondary.
to make it primary-sec. you need to bring the zone returns back to the primary loop right next to, and after where the supplies are taken off. its the so-called "close spaced tee"
arrange the zones after the boiler from highest to lowest temperature, or proirity.

What your saying is true. I should have been a little more clear from the start. I am not looking to use a true purist P/S piping arrangement because I do in fact want all zones to have access to full temp water.

From what I have read in several articles there is another option as well. I could use a hydraulic separater which would eliminate the need for a pump and for a full primary loop. It would also require less change to my existing system which doesn't really have enough piping room for the space required after the closely space tees, etc. in a P/S system to "minimize turbulence." Here is a link to a piping example that uses the hydraulic separator (broken link removed to http://www.radiantandhydronics.com/RH/Home/Images/0508rh-GF-Fix-lg.jpg)
Anyone have experience or comments on this approach?

That drawing comes from a funny section of a website called "Glitches and Fixes" (broken link removed to http://www.radiantandhydronics.com/CDA/Articles/Glitch_and_Fix/BNP_GUID_9-5-2006_A_10000000000000349101) where amatuers designs are reworked by a pro. The fixes are done by John Siegenthaler the same guy that wrote the article pybyr refered to above.

 

[Nofossil]

One minor point - it feels like the primary loop circ ought to be on the right hand side just above the oil boiler connections. As it's drawn, you could just get circulation through the zones with the boilers circulating back to their own inlets. I think that's a risk of a less-than-pure primary / secondary approach. I haven't finished my first cup of coffee yet, so I may be way off. However, I think moving the circ would make it a viable solution. That primary circ does need to be bigger than all of the load ircs put together to ensure that you don't get reverse flow up the left hand side of the loop.

 

[in hot water]

The Caleffi HydroLink would fix all of that. Here is a link to what it does and how it works, click on the video.

www.caleffi.us/caleffi/en_US/Utilit...ude=/applications/search/results_catalogo.jsp

Here is a quick conceptual drawing on how to pipe 2 boilers, buffer and several zones. Move the buffer tank pump to the red supply line, sorry moving too fast

 

[kabbott]

I posted some pics of my separator here https://www.hearth.com/talk/threads/29488/ if you want to check it out.

Kris

 

[pybyr]

I was going to post a photo of my primary loop, but some aspect of my wireless network has taken a dump... causing me to only be able to kludge in with a machine that cannot handle photos.

Photo soon, I hope

 

[WoodNotOil]

The Caleffi HydroLink would fix all of that.

That looks like a very useful device. However, I want to leave my zone supplies and returns exactly as the are if possible.

I posted some pics of my separator here https://www.hearth.com/talk/threads/29488/ if you want to check it out.

Kris

Very cool! Where did you get the large diameter pipe? Is it 3"? Copper?

I would be interested to know how much it costs to buy one new if anyone has a link or price to where you can buy one. Also, does the separator have to have its own expansion tank? My system has one on the wood boiler and one on the oil boiler already.

 

[kabbott]

Yes the pipe is 3" copper and the rest of the story is my dad is a retired plumber so I kinda raided the shop for some pipe and fittings. He still has a ton of short pipe and fittings in the bins, hate to see them go unused. :coolsmirk:
No need for another expansion tank if you already have enough capacity, better if the pumps all pump away from tank but I have seen many less then ideal setups work fine for many years.

There is no crime in using a hybrid system like in post #5 or you can extend the legs on the secondary side of the separator to catch your zones. just pay careful attention to pressure drop on that part of the system
I went with hydraulic separator because it eliminates 1 pump, pure P/S needs minimum three pumps running to get any heat moving.
To me P/S really shines when you have a ton of zones spread out over a large area, you can run the P/S loop through the building and pull your zones off where you need them.
If everything is already in one area(like my basement) A separator and manifold make more sense, the manifolds can be over-sized without great expense because they will be very short anyway.

 

[pybyr]

Yes the pipe is 3" copper and the rest of the story is my dad is a retired plumber so I kinda raided the shop for some pipe and fittings. He still has a ton of short pipe and fittings in the bins, hate to see them go unused. :coolsmirk:
No need for another expansion tank if you already have enough capacity, better if the pumps all pump away from tank but I have seen many less then ideal setups work fine for many years.

There is no crime in using a hybrid system like in post #5 or you can extend the legs on the secondary side of the separator to catch your zones. just pay careful attention to pressure drop on that part of the system
I went with hydraulic separator because it eliminates 1 pump, pure P/S needs minimum three pumps running to get any heat moving.
To me P/S really shines when you have a ton of zones spread out over a large area, you can run the P/S loop through the building and pull your zones off where you need them.
If everything is already in one area(like my basement) A separator and manifold make more sense, the manifolds can be over-sized without great expense because they will be very short anyway.

I got really intrigued by some of what I'd read about the separators before I then eventually pointed myself back to P/S. I sorta got the separator concepts, but I think that the things that make them work, and how to tie them in (especially on a residential scale), are still under-explained and under-understood on this side of the Atlantic (where even P/S is still seemingly considered complicated and avant garde on a residential scale, even though, now that I've fooled with hydronics, I spot it everywhere I go in places like stores, school gyms and cafeterias with exposed HVAC plumbing overhead).

Someone should do a "sticky" (please) on theory and implementation and construction of residential-size hydraulic separators and how to tie them into various multiple heat sources, loads, and storage. I've got too much effort and material already spent to turn back from the P/S on my main loop--- but I am wondering about someday using a separator to drive various radiant panel and radiant floor sub-zones out of a secondary off of my primary...

 

[pybyr]

I'll check out the article, thanks. I would love to see pictures of your install. Did you end up going with closely spaced tees for zones or did you do something like in my drawing where the supplies are together and the returns all together?

I am using Taco Twin Tees -- not the lowest cost option, but I really like how they don't take up a lot of linear room in a big multi-secondary loop, and how they are entirely oblivious to the direction of flow in the secondary-- this opens up interesting options about how any circuit can be a heat source under some conditions and a heat load under others. not sure where I will go with that in the long run, but I want to build in a lot of flexibility in this core of my system from the get-go

my install is not yet done- no catastrophic snags, just the rest of life means that time is way harder to find than originally hoped, and of course, like any project, each step takes longer to complete in practice than it does in theory. so right now, nothing is particularly photogenic, overall-- just lots of really exquisite pieces of metal waiting to come together, and partially put together, and making good progress, in an old stone farmhouse cellar.

this place was the first for miles to have running water and indoor plumbing, and also the first to have electricity (via a kerosene fired DC generator out in the barn) long before utility power came here in the '40s. I like to think that old man Parker who did a lot of that (and he was a DIY-er at all of it) is smiling knowingly and encouragingly at me as I beat my head against this stuff

 

[in hot water]

Yes the pipe is 3" copper and the rest of the story is my dad is a retired plumber so I kinda raided the shop for some pipe and fittings. He still has a ton of short pipe and fittings in the bins, hate to see them go unused. :coolsmirk:
No need for another expansion tank if you already have enough capacity, better if the pumps all pump away from tank but I have seen many less then ideal setups work fine for many years.

There is no crime in using a hybrid system like in post #5 or you can extend the legs on the secondary side of the separator to catch your zones. just pay careful attention to pressure drop on that part of the system
I went with hydraulic separator because it eliminates 1 pump, pure P/S needs minimum three pumps running to get any heat moving.
To me P/S really shines when you have a ton of zones spread out over a large area, you can run the P/S loop through the building and pull your zones off where you need them.
If everything is already in one area(like my basement) A separator and manifold make more sense, the manifolds can be over-sized without great expense because they will be very short anyway.

I got really intrigued by some of what I'd read about the separators before I then eventually pointed myself back to P/S. I sorta got the separator concepts, but I think that the things that make them work, and how to tie them in (especially on a residential scale), are still under-explained and under-understood on this side of the Atlantic (where even P/S is still seemingly considered complicated and avant garde on a residential scale, even though, now that I've fooled with hydronics, I spot it everywhere I go in places like stores, school gyms and cafeterias with exposed HVAC plumbing overhead).

Someone should do a "sticky" (please) on theory and implementation and construction of residential-size hydraulic separators and how to tie them into various multiple heat sources, loads, and storage. I've got too much effort and material already spent to turn back from the P/S on my main loop--- but I am wondering about someday using a separator to drive various radiant panel and radiant floor sub-zones out of a secondary off of my primary...

 

[in hot water]

www.caleffi.us/caleffi/en_US/Site/T...gazine_detail_0000054/type/magazine/index.sdo

This link has some excellent info on hydraulic separation, how and why.

hr