Sizing a circulator, general questions

here_to_learn

While planning for a retrofit of my original 1950s boiler, I'm trying to determine a proper circulator pump. I've followed Taco's Selecting Circulators — TD10. After realizing the pages were out of order, it went more smoothly . The old system has a single loop of 1-1/2" steel pipe made by Crane (going to multiple 3/4" copper feeding the cast iron baseboards). This is run with one circulator. The current retrofit plan will keep this main zone, add another zone of radiant floor heating, and have future potential for a zone in the garage.

Now, assuming the design load of the home is 50k btuh, I'm calculating a 5 gpm flow rate.
I have not been able to locate any tables to determine the equivalent length of piping for this 1-1/2" steel. The longest run at our test home is about 200 feet. Using a rule of thumb of adding 50% to this length for fittings and a pressure drop of 4 feet per 100 feet, we have

200 × 1.5 × 0.04 = 12 feet of head.

I'd like to be more precise or at least know this is close. If you can point me in the direction of some relevant tables, it would be most appreciated. From the Taco site, I see a head loss formula in terms of tubing size, correction factor, total equiv length of piping, and more (see numbered page 4). Yet, all the Taco info is based on coper or PEX pipe. Again, I have steel pipe that is likely larger than needed.

Overall, I trying to determine a proper circulator for this retrofit. I'm figuring that to do so, I need the flow rate and head loss. It's the head loss with 1-1/2" steel pipe that I need. Thanks for any help!

If interested, the first post in my other discussion provides more details about the project.

hot_rod

EL is basically turning the fittings and devices into pipe length.
Idronic 16 takes you through and example.

The engineeringtoolbox website has all the tables you need for various steel and copper tube. PPI website for plastic pipes and tubes..

https://www.caleffi.com/sites/default/files/media/file/idronics_16_na.pdf

Jamie Hall

The friction loss in the pipe depends so much on the condition of the pipe particularly for steel. Copper and PEX have friction loss characteristics which are so similar to each other that it is safe to use tables for one of the other as you please -- provided the velocity of flow is closely similar. Steel and iron are different, and it depends on the age and condition of the pipe. If you are dealing with steel pipe, the head loss for a given velocity will be about twice the head loss for copper or PEX (again, it's velocity you care about, not gpm). Brand new galvanized is about the same as copper or PEX, but it's galvanized steel it will change rapidly (within a few years) to values more like plain steel. If it's galvanized iron, however, it will become -- at worst -- only about one and a half time copper or PEX Cast iron ages slowly; initially it's a little worse than copper or PEX, but by the time it is 40 years old in normal service it can be as much as four times the head loss (my own experience with cast iron on, admittedly somewhat larger sizes (think 48 inch diameter) is that it doesn't actually age that fast -- if the velocity is high and relatively constant).

hot_rod

One issue with large pipe diameter and low flow like your 5 gpm in 1-1/2" pipe is velocity.
.75 fps in your case.

Below 2 fps the air tends to be left behind, not traveling with the flow back to the air purger. High point vents are important at radiators, etc.

EBEBRATT-Ed

@here_to_learn

Download the "Bell and Gossett system sizer" you can google it and it is free.

hot_rod

A very handy tool, the System Syzer
Here is the EL chart from the manual version of the System Syzer.
A 5 gpm example showing the velocity and friction numbers as the chart above.

EdTheHeaterMan

I have found this book to be very helpful with several Rule of Thumb charts on the last page https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf. Page 12 shows the SHARED PIPING SIZE chart. I wonder if this is the info you are looking for?

hot_rod

That same engineeringtoolbox has pipe flow charts.

Here are numbers based on hydraulic calculations.
Rules of thumb tend to be conservative.
Here are 3 common tube sizes for residential work.

3/4 copper M at 5 gpm flow= 3.1 feet per second velocity. pressure drop per 100' 2.5 psi or 5.7 ft.head

The System Syzer uses type L copper, smaller ID, so velocity and pressure drop is a bit higher.

EBEBRATT-Ed

I never left the office to look at a job without my B & G Wheel

here_to_learn

hot_rod said:

A very handy tool, the System Syzer
Here is the EL chart from the manual version of the System Syzer.
A 5 gpm example showing the velocity and friction numbers as the chart above.

Thanks Hot Rod! This helps me find the EL.
I wish I had one of those B&G System Syzer calculators. Looks cool!

here_to_learn

EdTheHeaterMan said:

I have found this book to be very helpful with several Rule of Thumb charts on the last page https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf. Page 12 shows the SHARED PIPING SIZE chart. I wonder if this is the info you are looking for?

Thanks EdTheHeaterMan! I'm under the impression that shared piping would not be needed, since we will have separate pumps for each zone. Yet, I am still learning what a retrofit of these fascinating systems involve.

here_to_learn

Thanks Jamie Hall and EBEBRATT-Ed, too.

I’m finding that many of the head loss calculations involve some type of friction loss guesstimate. I assume that this comes more naturally to those who regularly work in this field.

I will calculate a more precise EL of pipe and try to estimate the head loss with all the ideas above (after the busy times at work cease which is hopefully soon). I will try to post back soon, but in the meantime how would someone working in this field normally size a circulator pump for such a retrofit? Do you use the System Syzer app, B&G System Syzer wheel, tables/charts, or some other method?

Overall, I’m trying to ensure this retrofit (replacing 1950s CI boiler and 15 year old hot water tank with modcon and indirect tank) goes smoothly, works efficiently, and last a long time. I find hydronic heat to be extremely fascinating and enjoy learning more about it. If you have other good references for a newbie wanting to learn about retrofits, please share them.

I found the idronics “Lowering Water Temperature in Existing Heating Systems” very informative.

Thanks everyone so far!

Joe Mattiello

Sizing the correct circulator is fun stuff.
TD10 is a great tutorial for calculating load, and losses for flow and head, two variables necessary for selecting the correct pump.
taco tech support can help with any questions you might have after reading the document. 

Based your system description, you’ll probably end up with 007e or comparable pump, depending on how fancy you want to get.
give Tech a call at 401-942-8000
curious to know how you make out. Let us know
thanks for considering Taco

here_to_learn

Woah!! Using the table for steel pipe provided by @hot_rod, I'm finding an equivalent length of pipe (EL) of around 513 ft, which is way more than the rule of thumb used above. I did not realize the large EL for screwed fittings. By the time you sum the 16 tees, 14 venturis, 10 regular 90s, and other minor adjustments, that 200 feet of 1.5" steel pipe seems to pale in comparison to all the fittings!

This changes my initial thoughts. Using an Engineering Toolbox (ET) online calculator, I found the following copied from their site:
(inputted values on the left)

513    l - pipe or tube length (ft)
120    c - roughness coefficient determined for the type of pipe or tube (using Galvanized Iron)
   5    q - flow rate (gal/min)
1.5    d - inside diameter (inch)

ET OUTPUT:
Actual Head Loss (ft H2O): 2.09

Does 2.09 ft head loss seem reasonable with this setup?
(This is way different than the rule of thumb mentioned earlier.)