Pipe/Manifold and Circulator Sizing

mdmccool

I have an old, hacked up single zone mono-flow system feeding cast iron radiators in an old two-story farmhouse I recently purchased and I am hoping to convert to a two zone system, one for the first floor and one for the second. There are seven radiators on the first floor and seven radiators on the second floor. I am planning on two sets of manifolds, a "send" and a "return" for each of the two floors, PEX from new manifolds to 1/2" copper that is currently feeding each radiator (individual home run) already piped through the floors and walls. It has been recommended that I control zones with individual circulators, not zone valves.

Boiler is a conventional oil-fired 100k Burnham.

I am looking for some guidance regarding pipe and circulator size...

If my math is correct....

Calculating flow rate from BTU/EDR calcs (20deg delta T), adding-up GPM requirements of all radiators per floor (zone), I will need approximately 6.5GPM for the first floor zone and approximately 5.5GPM for the second floor zone. Boiler IN/OUT piping is 1.25" which I believe can supply 16gpm. My thought is to "T" two 1" manifolds off of the 1.25" boiler supply, 1" manifolds able to carry 8GPM each, I believe. These 1" manifolds will then be feeding 7 radiators each via 1/2" PEX requiring 6.5gpm first floor and 5.5 GPM second - which I believe will be enough flow.....

Finally I am not sure about calculating total head-feet to make a fairly accurate circulator pump selection. While piping and fitting data is available I'm sure, how would I calculate for these radiators?? I have two Taco 007's I can reuse from the old system if applicable.

Any help provided is much appreciated, as I am hoping to make any mistakes on paper, not in practice...
Matt
NJ

hot_rod

So you have the gpm required at 12 gpm, now you need to calculate the circuit resistance to come up with the head.

Here is a link to a Journal that explains the concept and gives you the information needed to size the circ correctly.


https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

Zman

For 2 zones, going with zone circs is not a bad idea. Make sure you put check valves on them.
The radiators themselves usually have very little resistance at low flow. The pex runs and the manifolds will be the areas you need to pay the most attention to.
Unless you are doing something really unusual, the 007 circs will work just fine.

mdmccool

Thanks guys for the help. That Caleffi journal is really packed with good info, thanks for passing that along! Thanks also for the circ info.

Do my calculations above seem correct that I can use 1" manifolds to supply the radiation?

Snowmelt

1 inch can carry roughly 100,000 btu so I would stock with 1-1/4

mdmccool

Snowmelt - thanks for your comment. The heat loss calc for the building came in at about 71kbtu, one of the reasons I was planning on 1 inch manifolds, which I forgot to mention. (figuring 1" could carry about 80k btu @ 20 deg delta T). Two 1" manifolds, one for each floor (fed from the boiler supply 1.25) would need well below the maximum capacity. The other reason was it seems as if "no-frills" 1-1/4 copper sweat X 1/2 crimp pex (8 port) seem hard to come by.

But...there is a good chance I am missing something, or everything, which is why I am here! Would you still recommend 1-1/4?

Thanks again,
Matt

Snowmelt

If it’s 71,000 btu then 1 inch is fine,I’d use a delta t pump

mdmccool

Thanks for the info on the "Delta T" pump. Didn't realize these were available. More reading to do....thanks!

mdmccool

Another question comes to mind:
Are ball valves an acceptable way to regulate flow?
I know water will generally take the path of least resistance and I anticipate the radiators near the supply manifold will tend to get more flow than those farther away (in a home run type setup). Was hoping to add a ball valve in each loop as to regulate flow. Was actually thinking of adding a valve in the supply and return of each radiator for individual isolation without having to drain the entire system if there is ever a problem.

Zman

Ball valves aren't really the right tool for the job. It is hard to find the sweet spot, and you can't tell what the flow is. A manifold with balancers and flow meters is best.

mdmccool

Zman- Thanks for your comment. I can understand how ball valves aren't the best solution.

In my past home I installed an under-floor radiant PEX system using an expensive brass manifold with built-in balancers, flow meters and valves to accept zone actuators. Almost every portion of the manifold failed within five years. The flow meters leaked and the sight glass filled with water, one out of five balancing valves failed, every single "zone valve" eventually leaked contaminating and causing failure of all the electric zone actuators. I replaced all these items only to experience failure within five years again.

From that experience I am *hoping* to keep things simple with this install: simple copper-to-pex crimp "no frills" manifold, separate (and easily replaceable) "balancing" valves etc...

Thanks again,
Matt

Larry Weingarten

Hello, You might want to look into globe or needle valves for balancing. Also, some flow meters should be useful as they can give you instant feedback when making adjustments.

Yours, Larry

Ironman

GOOD manifolds, such as Caleffi, Rehau, Uponor, Watts, etc, don't have the problems that you mentioned. Cheap Chinese one's do.

You need to use GOOD quality manifolds rather than trying to piece together stuff. You may think you're saving $$, but when you see the total picture, you're not. Trust me, I've come behind enough of these scenarios to know.

hot_rod

Repeated failures of wetted parts is often related to water quality. Minerals, chlorides assembly oils and flux, etc

The more accuracy you need in balancing, the better the balance valve you would use. Wheeled type valveswith fine thread, for example, give you better accuracy when balancing to 1/10 gpm rates