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# Head calculation for proper pump size: Stumped

Member Posts: 278
edited October 12

I'm going crazy trying to figure this out ... Hot Rod was nice enough to figure out the head and flow for my 11 loops of 3/8 Pex feeding the radiant panels on what I call Manifold #4. Can't find such a cool calculator. Can anybody direct me to one .. or an online table?

I'm trying to understand how to do the calculations for the 3 other manifolds and how they all interact with a single pump. #1 is 7 loops of 200' in 1/2 PexAL #2 is 5 loops of 200' PexAL and #3 is 8 loops of 225' Pex. Just for information #1 and #2 are in my Warmboard and #3 is a slab.

The Viessmann boiler is piped w/ LLH and the 1 1/4 copper line off the LLH has the branches off to the manifolds -- My goal is one pump. The only thing I can find when I punch in the numbers keeps coming up with about 4ft of head for each loop -- but I don't think I am doing it correctly. The Alpha 2 is 19ft head .. that's tight if I am correct with the 4ft each. Do you just add them up 4+4+4+6 = 18. The 11 loops of 3/8 has a zone valve for the whole manifold ... but I really think it's going to end up being "on" most of the time. I went with Cross manifolds for the other 3 as some of the loops many need some high limit control and the Cross make connections to Tstats easy.

The guys doing this would normally used 4 more pumps -- one for each manifold ... that seems crazy. I already have the 3 speed for the indirect and an Alpha for the boiler loop -- and one for the hot recirculation. It seems with modern pumps one should work.

• Member Posts: 13,412
Pressures in a parallel flow arrangement such as you have don't add -- but flows do. The pressure loss will be the same on all the loops -- which means, unless you have balancing valves, the flow through zone 3, with longer loops, will be less than that through the other zones -- and the flow through zone 4 with 3/8 inch pex will be much less (if they are the same length, about half). So figure the flow in each loop at your 4 feet of head loss, and see if you selected pump can handle that much flow at that head.

You will almost certainly need balancing valves, and if you want any degree of independent control of the various you will have to have zone valves as well.
Br. Jamie, osb

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 278
What's occurring when a system just has one static pump and zone valves ?

I am zoning -- the manifold with 11 loops has a zone valve and the other manifolds are Cross with a valve control on each loop ... some will always be open ... some controlled. They all have balance valves on the individual loops like most manifolds.

It was my understanding with a Alpha 2 type pump -- it will ramp up and down depending on how many loops are open -- and balance valves are not needed.
• Member Posts: 13,412
It will ramp up and down depending on the load on it. There are several operating modes. There is a definite upper limit as to how many gpm it will pump, depending on the model.

Problem is, if your various loops which are open have different head loss characteristics -- which they will, unless they are identical -- you have no control of how much flow goes to which loop, and the results may not be quite what you want Solution? Balance valves.
Br. Jamie, osb

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 124
I recommend that you quit trying to calculate everything - even the pro installers don't, and never have, done that. Just put in balancing valves and a multi-speed circulator, and adjust it to suit your own comfort. Much simpler.
• Member Posts: 13,838
I think the way that manifold operated, every time a loop opens or closes the circulator will adjust. If you had loops of vastly different lengths in one zone, you would need to balance each loop
As @Jamie Hall mentioned, the most restrictive loop dictates the required head. Add all the gpms. That circ will be real close, usually the calculations have some fudge factor, give it a try.
The real test is at or below design temperature days.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 278
I was very careful to not only match the loop lengths on each manifold but to keep them on the shorter side for the whole project. All the manifolds I purchased have both flow meters and the adjustable valves for each loop.

I told the installers to pipe with the idea of using the one Alpha 2 pump but leave space in the layout just in case we need a pump for each manifold. They are doing it today ... The more powerful Alpha pump looks to be the same physical size as far as piping ... so, that I guess would be plan "B" before going to more pumps.
• Member Posts: 13,838
yes, most all the common circulators will fit that spacing, plenty of options from B&G, Taco, Wilo, Armstrong, certainly you can find one that matches any circulation need.
Bob "hot rod" Rohr
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
• Member Posts: 13,412
Well, I'm glad you have both flow meters and the balancing valves on the manifolds. You are going to need them, as the loops -- even if you had matched the lengths, bends, and all fittings exactly -- will flow differently. This is the real world, not a digital simulation, and things are never, ever, exactly the same.
Br. Jamie, osb

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 278
I'm a good copier. Had the heat loads done by a few different people using different calculations. All come in around the same numbers for overall building load. The main building is an old stone church ... so it's not a typical building .... plus I'm spray foaming it. The addition is typical stick w/ foam. I have used Warmboard on a few projects -- slab and plates as well. The problem here is I have very little space -- tight mechanical room and the need to remote two of the manifolds in crawl spaces made for them.

My calculations also show that with the loads and the delivery methods there is no reason for mutli temps. Given the space problems -- using one pump is preferable.

It's a question of I know the radiant delivery method can give me more BTU's than I need ... but -- I have to get the water to the manifolds. I have also never used a condensing wall boiler.

All of my previous projects have been conventional Buderus cast boilers running natural gas ... mostly because I love old houses and I'm typically rehabbing something with radiators The last project I got one of the last small cast that can run on ODR.

This project is propane as well
• Member Posts: 1,872
Does the boiler have a pump and is piped primary-secondary or is there just one combination system and boiler pump? There is a minimum flow you need to maintain through the boiler even when only the most restrictive zone is calling if it is not primary-secondary.

BTW, mod cons usually do great with cast iron radiators, they usually are sized such that they will run at lower temps quite nicely most of the year.
• Member Posts: 278

Going to install another Alpha2 for the secondary. Run the system initially with everything fully open. With the loops almost matching on each manifold I don't see where I'm going to have a problem with any one loop in a manifold causing short cycle problems.

It's possible that I may need everything open and running on a cold evening night .... but my guess is there will alway be some parts on and off. I would feel better knowing the pump is strong enough for it all ... but, switching out to the larger Alpha2 is easy enough down the line.

The property being an old church -- five levels with high ceilings and rooms open to each other. There will be some adjusting.

Because the property needed AC -- There is also a zoned propane furnace/ heat pump ducted system for the old stone church as well as mini-splits for the addition and a loft. The Carrier system will be on -- so when it gets really cold the floor heat is not going to have to supply it all .
• Member Posts: 13,412
May I make a suggestion having nothing to do with the radiant? One of the buildings I care for is a church -- still in use as such. The single most important thing we've done in terms of heating comfort in the sanctuary (high ceilings, balcony) has been installing big overhead fans. Two of them. They're very discreet -- most of the parishioners don't even know they're there -- and silent and use almost no power. And make heating and cooling the space very simple indeed, and very even.
Br. Jamie, osb

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 278
Jamie: We will have two ceiling fans up in the peak of the ceiling. We used this property as a weekend getaway for about 6 years before a fire damaged it. The old HVAC was oil forced air (2 units). The larger unit did the stone church and much of the duct work was buried in the old slab. Place was very comfortable as long as the main unit was running .. lots of heat went up to the peak ... so I understand what you are talking about. The fans ran on low all the time. The smaller unit was for the addition and part of the church. It also had an oil hot water tank. We would use over 2000 gallons of fuel oil in the winter just using it on the weekends -- painful when oil hit \$4.

I was willing to go a bit overboard with the new HVAC systems because we plan on using this full time and I want to be comfortable w/o spending a fortune