Piping concept

marc

The only way the rfh zone will work is when the radiator zone is on. We usually repipe into p/s piping, this gives the customer separate temp. control on the new zone.
Marc

Don Robertson_2

piping concept

I'm just looking for feed back on this piping diagram. Any comments or suggestions would help. There are existing radiators and the RFH will be new. I have seen other hybrid installations but I was wondering if this arrangement works.

Brad White_9

So long as your radiators work

with the diluted water temperatures (they are existing, they must), and your RFH can work with the residual temperature, I think it is fine. Are the TRV's new? If the PD is of concern you might consider monoflow tees on both S & R.

Does the RFH have priority control? I would think that it would. The TRV's are always a good idea.

My $0.02

Brad

Mike T., Swampeast MO

Should work fine. Presume you've measured or estimated the available supply temp at the radiant floor connection?? A reset controlled three-way mixing valve for the radiant floor might prove to be a valuable addition.

Empire_2

Wow...I am pondering this one

I have a problem with the availiable positive remaining pressure at the end of the run before serving the RFH. Availiable temps are not the issue. In my thoughts, when the RFH calls, that circuit changes the whole dynamics of the entire loop before it. If momo-flow,... considering this is a whole house set up, the drop in pressure in the RFH loop which will probably be 2X the loop pump. Since Delta "P" dictates where the water flows, my thoughts are that the RFH loop will actually cause bypass to some degree of the radiators as a result. I would think that taking the feed to the RFH off the main loop pump supply and returning to the back side of the loop would be more affective..... My thoughts.........Feed back appreciated..

Mike T.

Mike T., Swampeast MO

Great observation Mike T. Certainly a possible problem if that circulator for the radiant floors is too large. It should be sized to be BARELY able to overcome the increased head in the radiant floor loop(s) while delivering the same amount of flow that would ordinarily be flowing through the closely-spaced tees--e.g. the system flow

While such a degree of accuracy is likely impossible, the TRVs [should] be able to compensate for marginally different flow rates (either higher or lower) when the radiant floor circulator is running. Don't forget that the TRVs will already be varying delta-p across each rad and throughout the system as a normal course of operation.

To the original poster: Have you studied the paper regarding TRVs on one-pipe systems available here in "The Library" under "Thermostatic Radiator Valves"? VERY good paper by Danfoss that's no longer available through any of their websites.

Don Robertson_2

Thanks

Thanks for the feed back guys. I will check out the Library. I have not seen the job yet but from what my customer explained to me this is how I saw it. I think a primary/secondary repipe may be the best thing. When I see the job I will repost w/ actual numbers. Thanks again!

Brad White_9

What am I missing?

The RFH circuit has it's own circulator. The closelyspacedtees decouple the two loops such that one circuit will not affect the other in a measurable way. What goes into the closelyspacedtees has to come out. Balancing of course is key. And you are only talking a trickle anyway of primary water. That is what I see anyway.

Don Robertson_2

That's how I saw it

but because I don't have all the specifics yet I didn't want to get too far into it.

Mike T., Swampeast MO

Closely spaced tees or no, I believe that the floor heat circulator will appear in series with the one-pipe loop circulator. Any residual power the floor heat circulator after the head loss to the floor heat loop is satisfied will appear as increased flow through the one-pipe loop.

Brad White_42

I respectfully disagree...

The RFH circuit is likely small diameter stuff (granted it is not shown but could easily be 1/2" diameter as an injection point and carry an awful lot of BTU's).

[EDIT: My assumption here is that the RFH circuit will only draw a minor portion of what the main branch is carrying, that it is in fact an injection situation, not full system flow.]

That circuit (the RFH branch) also has a mixing valve -read: Pressure Drop- and a flow-check after it's own circulator.

The main closelyspacedtees have nothing in comparison to that.

My point being when the RFH circulator is off, all of the factors I mentioned will effectively stop flow and the two circuits will have no measurable effect on one-another.

If not, then an awful lot of marketing people selling flow check valves has some serious 'splainin' to do. And the concept of closely spaced tees would then be a myth.

Unless I am missing something, that is what I see.

My $0.01,



Brad

Empire_2

Brad, it think I understand.....

I guess what I was thinking was, if you have multiple moniflow loads in the main loop, all of which are slightly lowering the total availiable pressure and gpm towards the end before the RFH....Wouldn't that possibly give you a questionable delivery to that RFH? If 3.0 gpm (lets say) is needed, you have to make sure the end flow is there to feed your RFH. I am trying to understand :-)

Mike T.

Brad White_42

Multiple Monoflow Loads

No matter what the system or piping arrangement, the supply pressure always decays as it moves away from the pump. (It has to, for without a pressure differential, you have no flow of course.)

The pressure decays but not the gpm. Each monoflow circuit give it back right away.

Another way to look at it:

The water in the main circuit is going to make it back to the pump no matter what; that is it's mission in life.

All the RFH circuit is doing is "borrowing" from the main, reducing it's temperature in the process of course, but giving it right back to the main in kind.

(The main barely knows it lost a passenger for it picked one up right after the drop off. A little chillier perhaps, but the flow is the same.)

When the RFH circuit shuts off (AS-IF! ), the primary flow cannot be bothered to go anywhere but straight. Take a hard 90 degree turn, through a mixing valve, an inoperable pump, flow check, manifold, 100 feet of PEX, another manifold and back to the main. Probably not.

Hope that helps!

Brad

Donny

check valve ?

I think you will need a check valve between the closely spaced tees [flow back to boiler] to guanantee hot water supply for the rfh. water might short cycle if rfh is only zone calling for heat

[Deleted User]

I agree with your disagreeance...

Is that even a word? Disagreeance...

The two closely spaced tees make the RFH loop a secondary loop, and provided that the primary is moving fluid through its primary, it will work. It is entirely possible that the water would be flowing backwards through the common set of tees.

For example, If you have 3 GPM going through the primary, and 5 GPM going through the secondary, you would have 2 GPM going backwards through the closely stacked tees when the RFH pump is on. Unlikely and unnecessary, but possible, and of no real consequence to the operation of the system as a whole.

In fact, on large district heating systems, backwards flow is used to temper the fluid going into the secondary tees.

The ONLY way (other than going through the flow/pressure drop calcs) that you would know this is to do the oohhh aaahh test on the three branches of the P/S piping at that point. Your hands can see (feel) what the brain has trouble conceiving, and the brain STILL doesn't believe it to be true... But it HAS to be, because its simple math. What ever enters a tee must exit a tee.

The residual pressure generated by the primary circulator has NOTHING to do with the flow through the RFH secondary branch. Nada, nothing, zip, zero. Now, if it wer ein PARALLEL to the primary, it would be a WHOLE nuther story.

I'll find you some graphics to demonstrate backwards flow potentials...

ME

Donny

load seperation

in addition to the check valve I think I would install between the closely spaced tees, to prevent the rfh's circ sucking in its own discharges, to truly seperate the heating loads, I think I,d install zone valves on the tee branches [supply side]as close to main as possible. wire them to open when the appropriate circ starts.

Adam_23

Don why dont you just get an Iseries 4 way mixing valve from Taco it should solve any problems you might have .The arrangement you have is workable it may require alot of time balancing .Time is money an iseries valve would allow your RFH circuit to modulate itself . They cost about four times the price of a standard Three way tempering valve but money well spent and less future hassles .

Mike T., Swampeast MO

Thanks Mark! Didn't see a problem at first then I started thinking too much when someone questioned. Sorry about that!!

So...

The close spacing of the tees forces the differential pressure produced by the 2nd circulator to appear only between the tees--not to the main loop circulator. Right?

Mike T., Swampeast MO

Mark (or anyone):

What's going on in the attached illustration?

What keeps the boiler circulator from seeing increased flow from the circuit (assumed to be radiant floor or other panel) with the added circulator? Surely it's a variable-speed circulator, but still...

[Deleted User]

The 3 way valve...

at most times will only be partially open. Therefore, the majority of the flow/pressure differential that the F pump is creating is spent in the RFH loop. If the 3 way goes fully open, then you have two pumps in series, which possibly would increase the flow rate through the boiler as opposed to just running with the boiler circulator only. However, knowing the Viessmann way, the master control on the boiler would be aware of that condition if it were to occur, and probably adjusts the burner based on that condition.

Typical true run time scenario, the boiler would be supplying water temperatures above the needs for the RFH demand, hence the 3 way is barely cracked open. If it were a cold start situation, then the 3 way is wide open, but at that point you WANT all the flow you can get.

One thing that cracks me up about the Viessmann piping is the fact that their boiler pump is pumping towards the PONPC. Wonder why that is :-) Their solar systems are the same way...

ME

Brad White_44

PONPC on Viessmann

I have the same issue with my Monitor MZ. I do however have it P/S so where it counts, I do pump away. I think the thread about pumping into the boiler to keep the Pressure Switch happy has something to do with it. But if they pumped away propery, I would argue, the pressure switch would still be a happy camper. Pumping INTO the PONPC would obviously wreak havoc if the pressure switch were on the suction side.

There but for the Grace of God go I....

Jim Eastman_2

I don't think you want a check valve between the closely spaced tees. See Mark's post, above. If your RFH system needs more flow than the primary loop can provide, then it MUST take some of the flow from the second branch of the closely spaced tee and send it to the supply branch. Nothin' wrong with that! Your themostatic mixing valve or automatic reset valve will compensate for the cooler water in the supply branch if this happens. If you had a "one position" mixing valve, the temperature control may not be adequate at very high flow rates.

Brad White_9

I agree with Jim.

Messing with closelyspacedtees by inserting a check valve defeats the purpose and may promote secondary flow. Have faith. As ME noted, reverse flow is possible and even desirable. (What goes into a tee comes out of a tee). My own system has that effect when at high speed. Some T-mix occurs. Not an issue in my system just neat to see (feel) the phenomenon.