Primary/Secondary??

Dave_13

What is the difference, between having the Primary connected with closely spaced tee's as in the picture or having the secondaries using closely spaced tee's to the Primary? Are these the same things and my head is playing games with me???? It seems to me, in the picture, that I could have all the same water temps out to my secondaries... Any help? Thanks.

Mark Eatherton1

The INS and OUTS of P/S piping...

Dave, what you posted is a picture of a boiler set up as a sceondary INPUT to a parallel primary. The pumps pumping away are not true primary secondary pumps. If they were, their returns would be right next to their supplies. If set up this way, with everything running at the same time you'd get an effect on temperature drop that would be the equal to running the loads in series with each other.

You can header a set of secondaries off the primary, thereby allowing all secoindaries to see the same water temp tho...

ME

Dave_13

W/M

Was just looking at literature for the W/M Ultra and this is the exact piping they showed for their boiler and was listed as "Primary/Secondary"......

Dave_13

And..

The Munchkin manual I have shows the same thing!!!!

Mark J Strawcutter

clarification?

I don't think ME was saying your diagram _wasn't_ P/S

He was just pointing out that your system pumps and attached "zone" did not each constitute a secondary.

The W/M diagram you "quote" isn't the same as what you initially posted - it doesn't have circs to the zones.

The designation "primary" vs "secondary" is illdefined. I tend to view the loop with the expansion tank as the primary.

Like ME, I'd classify the W/M diagram as a parallel primary with the boiler on a secondary (input) loop.

Also, on the W/M diagram, the loop for the indirect is not done P/S - when the indirect's circ runs it will cause flow thru the boiler (and also up thru the rest of the boiler loop toward the common/close Ts on the primary - I don't understand why they don't have check valves to prevent this)

Mark

Joe_20

Primary / Secondary....W/M

The W/M boiler has priority for domestic hot water, so when the water heater calls for heat, I believe everything else shuts off....flow then would be through the easiest path or just through the water heater? YES/NO ..?

I think W/M's drawing is confusing....why don't they just come out of the boiler with 1 1/4 or 1 1/2" pipe to form a primary boiler loop and then plumb the zones off the closely spaced T's for secondaries?

The first sketch, I would agree...all zones would receive the same temperature supply water....but only the last circuit is plumbed as a typical secondary....???

Just trying to learn myself....!

Dave_13

P/S

I also have the W/M drawing for circ. pumps in the secondary. It is exactly like the one above, but with circ. pumps. I guess the reason they don't do closely spaced tee's in the secondary is lowered water temps as you move through the loop. This is still something I don't understand. If you design for lower water temps down the secondary loop, and the upstream loops aren't calling for heat, your lower temp loops will get hotter water supplied to them. I do like ME's post about a header off the secondary. I too, am trying to learn... Thanks for all the input.

Mark J Strawcutter

circs

You do closely spaced Ts to hydraulicly isolate one loop from another. Each one needs it's own circulator.

In your original drawing, if each zone was piped off the (what I call) primary loop with closely spaced Ts, then you'd need an additional circ for the loop itself.

Concerning your question about low-temp zone being "downstream" and getting too-hot water when upstream zones not calling - you're right, but you design this way to get a guaranteed _minimum_ temp at design with all zones calling. Max temp control, if needed, is done with some other mechanism such as a mixing valve.

Mark

Dave_13

So...

What do you think about this Munch. drawing??? Right or wrong? Isn't the Munckins loop hydraulically isolated from the rest because of its own closely spaced tee's????

Mark J Strawcutter

two loops

The primary loop is the one with the expansion tank, and includes all the zones and the indirect.

The boiler is piped as a secondary "input" loop.

Yes, the boiler loop is hydronicly isolated from the primary.

Mark

Joe_20

So, if you are zoning with circulators, the pump labeled P2 becomes a cost adder and system complicator doesn't it? At that point would it be wiser just to make the boiler loop the primary and secondary off from it?

Also, does anyone out there have a good sketch of how you would plumb an injection pump into a secondary to get 120 degree water from a 180 degree system for two different zones?

This is great stuff, eh?

Thanks

hr

Different ways

to look at it. In the Munchkin drawing I would say the indirect is in series with the primary loop.

Also pump P2 needs to be there to supply the indirect, as in this drawing it has a zone valve.

The goal of this piping is to assure the Munchkin has enough pump, and flow. Depending on the Munchkin size it may need a 26-99. The zone pumps could be much smaller, depending on the loads of that zone, as they are hydrauliclly seperated.

Also in a DHW only "call" the primary loop to the right may not see any flow if the indirect coil could handle all of P2's flow.

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Mark Wolff

Joe, here are some sample drawings.

Mark J Strawcutter

I'm curious

why you view the indirect as being in series with the primary?

Mark

hr

For primary secondary

you need closely spaced tees. Usually 6-12" apart. In the drawing the indirect pulls from a supply and return side of a loop.

Here is an example and some logic. On this job I had a cast boiler, an indirect, a buffer tank and Danfoss ZCP. For DHW loads that occur out of the heating season there is no need to circulate the buffer or the primary loop through the Danfoss.

I coupled my indirect right at the boiler. So the boiler fires directly into the indirect without any other piping involved. Of course you need to use check pumps at the boiler and indirect.

This puts the indirect in series.

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Mark J Strawcutter

I agree

that it's not P/S

But in the Munchkin diagram above, the indirect looks to be parallel off the primary. Granted, under certain circumstances where the heating zones are off and if the pressure drop thru the indirect is low enough, it could effectively be series. But in practice I think you'd still end up with flow thru the rest fo the primary loop.

If your setup has priority for the indirect, and that priority has no max time over-ride (not sure if that't the right term) then I'd agree it's series. But if/whenever the buffer and indirect are running together it's parallel?

Mark

hr

I think You are right Mark

I'm going to backpedal on my call, and that the indirect, in that example could be best described as in parallel

My system does have a priority on DHW. The Crown circuit board conviently provides that. a nice feature! I have never tried the "time out" on DHW call function. As of yet I have not had a problem with an extended DHW call effecting the heat loads. Yes there is a small potential for something to stick and not switch back to the heat. Slim, I feel.

In this install the entire radiant is a gyp pour. Generally those could be "off line" for an hour or more before, considering the mass, the output would be noticed.

I imagine with a baseboard or panel radiator system a looooong dhw call on the indirect call could be noticed.

Yet another reason to be sure you size boilers to the largest load, which can easily be the DHW indirect, in many homes. Thanks for keeping an eye on me

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Joe_20

Thanks! we'll keep on plugging.

Joe

F Reynolds

P/S Pipe Length

Ok, I'm back.

WM Manual shows primary/secondary connections, i.e. boiler loop and in some instances, Zone 1. So which one is the primary and which one is the secondary? I assume the boiler loop is the primary, and the secondary is Zone 1.

If so, how long or short must or can the boiler loop be? I've noticed the only thing the book says is "do not exceed 12 inches apart. I'm making the assumption the boiler loop can be very short, only needing enough room for the closely spaced "Ts", and circulator. Am I correct? Also, the principal behind the pri/sec is to prevent cold water entering the boiler and condensing the flue gasses (or something like that), and that the goal is to keep it above 135 degrees. Am I all wrong here?

Dave_13

Hmmm.......

I thought the main reasons for P/S is to get the required amount of flow through the boiler without any problems and to hydraulically uncouple the secondary from the primary...... Most condensing boilers say they require P/S and they thrive on low return temps. Correct???

F Reynolds

I thought I read that

Ok, I'm trying to look for the reference. I've been reading so much, maybe I'm confused. Anyway, still looking for the pipe distance. (Oh, still looking for that reference, about the flue gas stuff)

F Reynolds

Found it

"When using a non-condensing style boiler, it is important that the flue gases released from the combustion process be vented out of the boiler. When the water in the boiler is at a temperature below the dewpoint of the flue gases, these gases will condense back to water inside the boiler. The results can be very damaging. Boiler thermal shock is another reason for controlling the return temperature."

Ok, I have the Ultra, and it is condensing, so that doesn't count. Sorry about that. Ok, now that the condensing thing is not an issue for me, how short can the boiler loop be, could/would that be considered the primary?

Joe_20

Yea, On that W/M drawing there is a Boiler Loop, then there is a Primary Loop...Then the secondaries come off the Primary....If your return water temp is above 135°F is it alright to use the boiler loop as the primary and run your secondaries off from that?

My understanding is that anytime a zone calls for heat, the boiler pump is going to start creating a flow through the "primary" loop and the zone that's calling for heat will also have a pump starting and pulling water into that secondary....Why does W/M and others suggest plumbing as the sketches show? Any help? Seem like you are just adding more complexity to the system...pumps and pipe....

Joe

F Reynolds

Primary/Secondary?

In the Zoning with Circulators diagram, the only thing referred to specifically as primary/secondary connection, is the 12" pipe connection......... I think THAT is what creates two "primary/secondary" connections....

Wait, I think I've got it. There is not necessarily any particular size for the boiler loop. It will only be in operation during a call for heat, and the zones will be pulling water from it. Interesting. Don't let this lame revelation cause anyone from piping in (no pun intended).

radiantdave

2piping sketches

i would love to send you a couple of coolpiping ideas e mail me a fax number

Cliff Brady

Two ways to P/S boiler loops

The conventional way of P/S for boiler protection has the system return water going through the second P/S tee it sees (boiler return) while boiler supply is coming in the to the system loop from the first P/S tee the return water sees. This mixes warm boiler supply water with the cooler system return water in the closeley space tees before the boiler return.

With condensing boilers you do the opposite and have the first tee the system return water sees be the boiler return and the second tee the boiler supply. This way your cold return water goes righ into the boiler return without much mixing with the boiler supply.

Hope this helps and is understandable.

F Reynolds

Is it because

I think it was clear as day. Is it becuase with a condensing boiler, you want colder water to return into the boiler, and not mixed hotter water?

radiantdave

yep

the piping can be as long or as short as you would like . the most common reason given by boiler manufacturers for the 12 spacing or less is to prevent the primary pump from pumping directly through boiler
(path of least resistence ). primary pump is there to protect boiler by keeping return water and supply water at mix temp above 140 for the most part . this pump serves a second purpose as in radiant systems this pump should be sized for the head of the entire system to keep flow at design.if one temp radiant system theese designs are fine .especially for munckin it can take lower temp on return .cast iron boilers would be different as we should all know. if on secondary loop you were to pull off say three zones radiant each with differant temps spacing for those tees would be 6"or less to stop ghost floww from large secondary pumptheese would be tertiary loops this pump ,boiler pump and zone pump would all run at same time boiler would not fire until reserve water heated were exhausted as sensed by aquastat. variable speed injection can be pulled from secondary loop to supply a many number of radiant zones if all work on single same temp. if hi temp and low temp zones you would need seperate variable speed injection pumps .pipe size of primary should be that of boiler tapping size 1.25 or 1.5 .pipe size of secondary should be sized to accomadatefloww of entire system.tertiary zones those that would be supply and retun to floors should accomadate flow of zones they supply.injection is cool !yeah cool.radiant is way cool ! and piping is awesome cool !i am always trying to come up with smaller neater cooler performance orientd piping designs ... I JUST LOVE THIS @#$T!!!!!!!! HOPE THIS HELPS

Cliff Brady

Exactly the reason

It's a key concept to understanding the P/S biz. This just sank in for me recently. I would still rather avoid P/S for one zone cast iron systems unless there are flow imbalance issues.

Condensing boilers are most effecient heating cold water. Having lots of radiation emmitters so heat can be satisfied at lower temps for effeciency. Of course those emitters cost money. Lower temperatures emitters give out more radation relative to convection than at higer temperatures, which equals greater comfort.

Mark J Strawcutter

get the book

Dan's "primary secondary pumping made easy" will answer a lot of your questions.

Mark

Joe_20

Got it....you are right, it's a great book...top shelf, must read, and easy to read. The tables and calculation examples are "the BEST"!! Everybody should have this book....I think I paid $20 for it and also got all kinds of neat stuff with it!!

J