circulator sizing for 1 pipe monoflo tee system

Uni R

Warning:
If I were any more handicapped at complex math I'd probably be allowed to get special plates so I could park in those big parking spots near the stores' doors. ;-)

I was hoping to do the same calculations as you. Even went as far as buying a copy of Modern Hydronics the other day to help me in that pursuit but unfortunately black iron and diverter tees aren't covered in the pumping calculation chapter - I guess they aren't modern.

In my mind the factors for calculations would be the diameter and length of main pipe and flow for all the fittings (including the boiler etc) when there are no branches combined with calculations where there are branches. The latter calculations are tough because part of the water is following the mains and part is following the branch (for different lengths because mains are normally much shorter) and then there may be one diverter tee or two per branch and furthemore the branches often start in the middle of another branch which means the overall flow of the water could be down three or more paths concurrently.

What would be nice is a machine that you could own or rent that you just bolt between the circ flanges and it pumps at a variety of velocities and gives you a nice paper printout of the corresponding flow rates.

ralman

Please check my calculation for accuracy.

I am trying to verify I have the correct circulator on my system and figure the flow rates for my baseboards.

Boiler gross output is 121,000 BTU divided by 10,000 = 12.1 GPM.

The monoflo distribution system is 1.25" and has a split return. I measured the total length of the longest side to be 132 feet. I only measured the main pipe, not the risers and baseboard lengths.

132 x 1.5 = 198. 198 x .04 = 7.92 feet of head.

I checked the taco pump charts and selected a 007.

If I understand what I have read, this is the method used to size a circulator. The reason I ask is I am not sure if the monoflo system is calculated differently than other systems.

The manufacturers literature on baseray cast iron baseboard shows BTU outputs for 1 gpm and 4 gpm. I assume I should be getting somewhere between 1 and 4 gpm of flow through these baseboards. How this is achieved, I have not been able to find. Is there a method to calculate the flow rate through my baseboards?

Brad White_39

MonoFlo Pumping

The gross theory of it all is that the pressure drop of the main has to be more restrictive in total than the longest branch run served. Otherwise you would not be diverting flow.

Each MonoFlow tee has a defined pressure drop at a given flow rate (as does everything else in hydronics -if not life...)

Still, the way I was taught (a former Bell and Gossett representative who used "milli-inches" as units of pressure drop in the classic B&G way) was to take the sum of the main circuit (pipe, elbows, normal and MonoFlow tees), PLUS the longest branch run and emitter pressure drop, plus the boiler. In your case what you figured was straight pipe, 50% for fittings (a guess let's admit it) and a pressure drop of 4 feet per 100 feet of pipe. You have to add the cumulative MonoFlow fitting losses to that plus the longest branch is how I was taught. (That was in 1977-78 by the way.)

He did admit that the need to consider the branch run was theoretically redundant but it was his way of making sure the water made it to the attic radiator.

Go get the B&G literature and map out the flow along your worst-case side. Take all fittings into account and see what you get. From what you are saying, the 12 GPM and 8 feet of head might be cutting it close even as it is. If you have say 10 feet of head, a 0010 may suit you better from the Taco line. But calculate the head first.

I like that you split the return, Ross. Keep those pressure drops nice and low.

As to assure yourself of proper flow in each branch, I am certainly a big fan of balancing valves such as Macon, Tour and Andersson, Mepco and others. These are valves which turn 4 times between fully closed and fully open (10 turns for Macon, the most precise of all). Knowing the valve setting and the pressure drop you can figure flow rate.

You can also balance by temperature, sending water out at as constant a temperature as you can maintain, letting they system come to temperature and throttling down until the return water meets your expectations. Can be time consuming.

Size the balancing valves for flow not pipe size.

I tend to use 1/2" size valves for individual runouts. They will work fine for up to 3.0 gpm even if I increase to the running pipe size. Because you have finite flow, water management in my opinion is critical. Too much in one is less for another, although one may argue it will pass through warmer than if less flow.

Because you split the flow, you may want to balance each branch or at least the short one.

Just some thoughts.

Brad

ralman

Thanks for the info.

I also am planning to purchase that book and I am disappointed to hear that the monoflo system isn't covered. At any rate, in the library section of this website, you can access the Bell & Gossett handbook, 1949 2nd edition which gives detailed instructions on the way monoflo systems were designed. The problem is, You wouldn't be able to find a space to park your car because my car would be in the way. My math, reading and reasoning skills are terrible and I was hoping some experts here would be able to clear the air on this issue. Basically, the formula I used is the rule of thumb version from the book which doesn't take into account each individual fitting. From what I understand, The flow rates in the radiators are strictly a function of the riser pipe diameter. The radiators are sized to room heat loss, then there is something about a conversion to millinches (this is the point where I got lost), then you refer to a chart in the back of the book to select the riser pipe size. There is some fine print disclaimer stuff that cautions the designer about using the correct chart, one is for using 1 monoflo fitting, the other chart is for using 2 fittings. Also some discussion about pipe lengths. All of this was difficult for me to grasp and I don't have radiators. I have Burnham baseray and that is not covered at all. Good luck and if you get it figured let me know.

ralman

Brad, thanks for weighing in on this one.

I have been getting a lot of help from you and I do appreciate your help. If you had a chance to read my reply to UNI R in this thread you will understand my dilemma on figuring this out. I can't take credit for splitting the supply main or anything else about this system design. I bought the home this way and I am trying to make it more comfortable and cost efficient. Some of the questions I post here have led to questions back to me about what my flow rate is. My system currently has a Taco 007 and works so I was trying to reverse calculate to see if I could nail down my GPM flow rate. Yes, this also relates to my recent posts and inquiries as to what the effects of total water content is to my system. And YES I am still losing sleep over the complexity of this heating system. As for balancing valves; there is a valve with welsbach stamped into the metal near the boiler on both return mains. I learned a valuable lesson on this one. When I moved in, I didn't know their purpose and they didn't look fully open so I did what any idiot would do. I opened them fully and over the next several weeks I struggled with trying different combinations of settings until I got good heat in all the baseboards. Thanks again!

Brad White_39

I do hope this helped you, Ross-

I appreciate that you as a homeowner are really "getting into this". It can be fascinating and when you have control over your comfort and energy costs, you take steps yourself. What it is all about IMHO. Uni R intimated in another subject post I think you were a part of, that he wanted me to take this on.

Remember my posting about flow rates and outputs? How you can pare back the flow by half and still get about 90% capacity? That works here too. My cautionary note is that you do not want your return water temperature to get so low that it affects your (non-condensing) boiler adversely. If so you may need a bypass to protect the boiler. That said, if you have or are getting a condensing boiler, go for it!

If you want to nail down your flow rate (did not know that was what you were trying to do), install T&P Ports ("Pete's Plugs" but Petersen Equipment Co.) or a 0-15 psi range pressure gauge on either side of the pump. Measure the PSI difference across the pump and divide by 2.31. That will give you feet of head. Spot that on your 007 pump curve and read down to your GPM. Not perfect but a reasonable way to do this.

Let me know what else you may need, OK? If you get stuck, contact me off-line and maybe send me a diagram.

Best,

Brad

ralman

It does vey much.

The fact that a 50% reduction in flow rate will still give me 90% output is significant. I picked this up from your post in the other person's thread. So I am not sure if eventually finding the exact flow rate is going to benefit me greatly. Yes, my boiler is currently non condensing, non modulating, about 6 years old and I would rather not have it replaced unless absolutely necessary. I do have low water return temps. I was advised by you and others in some previous posts about boiler decoupling, so I have been working on a plan to make that happen. I am going to Google these plugs you mentioned and check for them at the local supply house. Thanks!

Brad White_9

Pete's Plugs

are generically known as T&P (temperature and pressure) Ports. They consist of a brass nipple with a cap, within which is a rubber grommet which is self-sealing. You need a pressure gauge with a needle adapter (cheap money). The needle is inserted into the grommet to take your reading. A needle type digital thermometer can also be used for the temperature side.


If you buy the aforementioned multi-turn balancing valves, there are the very same ports built in to the valves themselves to take delta-P readings. So if you opt for those you will have them and you will, I believe, love them.

If you are having low water temperatures you may want to consider a larger pump to narrow your delta-T also. That pending your system reconfiguration.

Brad

Uni R

Thanks Brad n/m

John Starcher_4

Wait a minute, Brad.....

.....Don't you MULTIPLY the pressure drop by 2.31??????

Or am I confused as usual........


Starch

Brad White_9

My Bad, Starch, you are correct

Multiply PSI by 2.307 (OK 2.31...) to get feet of head. Of course...
No excuse, I am usually wide-awake at 5:30 AM when I wrote that...
Thanks for being vigilant!

Brad

John Starcher_4

Whew!!!!

Ya know, I just found my mind again last week, and here I thought I had already lost it again!!!!!!!!!

Starch

Jerry_15

Wow-workin hard

It's nice to balance these things perfectly, but a simple check of the delta-t would tell you in a minute if the pump was big enough to bother balancing. I would have started out with a 0010, and maybe, on a convoluted system with long runs a 0014, which I find a cure-all for existing problem systems. A little head pressure on the discharge side of the pump is not a hangin offense, especially if there are no zone valves. If so, a pressure by-pass is easily installed. A two sensor temp meter will tell you everything you need to know on a small system like this. Of course, you could always hire an engineer.

Jerry_15

PS

I realized right after I posted that what you are talking about is the same re-pipe series system that I run into constantly on the Eichler houses out here. They didn't usually bother with monoflow tee's, just in and out in a daisy chain. 3/4 pipe too. Use the 0014, your problems are over. With a continuous loop on 1" pipe with one thermostat you won't have any pressure issues, or velocity noise issues. Good luck

Uni R

The 3-Speed Grundfos Test

Two years ago I replaced my B&G 100 with one of these little circs (and has already paid for itself in electrical savings 0.75A vs 1.75A). I did take the flow check valve out of it.

I have a single zone of almost 150' of 1.25" mains, with 16 diverter tees (3 being double teed below the mains) and some fairly long circuits (3/4" branches) that rise to a second storey. I found no real difference between the medium and the highest speed (other than some circ sound). This was with 2 of the diverter tees being capped while waiting to finish the basement walls (which can't help flow). When I tried the lowest speed some of the circuits would not get any flow or the heat would vary - there has to be enough pressure to force flow down the branches.

Diverter tees systems aren't as restrictive as some people tend to think. It's not like a 3/4" main system with 1/2" branches. If you have good flow (heat) in each of your branches with your 007 you're set.

I finally piped in the heat in the basement on Sunday so now I'll have to see what happens with it on the low speed.

nb_4

old monoflow tees

generally in the past the cast iron tees were set to have a pressure drop equivalent to about 12 feet of straight pipe. in order to calculate the pressure drop you have to know the hydraulic resistance of the pipe. for 10 feet of pipe R=0.028 approx at 170 degrees.
once you know R the head loss can be calculated, where H loss =Rx flow rate in gpm to the exponent of 1.75.
say for example you want your flow rate to be 4gpm on the main run then the head loss through the run of the monoflow tee would be 4 to the power 1.75 = 11.3
11.3 x 0.028= 0.32. then 0.32x 1.2= 0,38 feet

0.38 feet is the head loss through the old style monoflow tee, new versions may have different values.
add the number of tees to obtain the total pressure drop, also do not forget to include the pipe itself, then cross reference the mains head loss against the pump curves to obtain the flow rate.

now when it comes to the emitters themselves the math can become very complicated. this is beyond my simple explaination laid out here. remember that all flows will eventually recombine into the return for the total flow rate that you desire.
the R value for 1-1/4" pipe is 0.0031 for 10 feet so for 132 feet it would be 0.04 thus at 12.1 gpm if that were in fact the flow rate the head loss would be 12.1 to the power 1.75 = 78.5 x 0.04= 3.17 feet.
since you rough guessed an etra 50% then 3.17x 1.5 =
4.76 feet.
this may be an underestimate as you still have to consider the monoflow tees.
good luck.

nb_4

sorry i meant to write R = 0.028 for 10 feet of 3/4" type M copper pipe.