Properly Sizing Primary/Secondary Piping

chris87

Hi guys,
I'm new here, I always want to learn more and I have plenty of questions that I'm having a hard time finding the answer to. I have a decade of experience mainly in the commercial aspect of plumbing/heating and I'm getting more interested in residential hydronics. Whats the best way to size boiler piping? I'm sure there is a formula I just don't know it because most of the stuff I've done is engineered.

Thanks!

Gordy

It all depends on the btus, and flow rates the system needs to have delivered.

1/2" 15k
3/4" Cu 40 k
1" 72 k
1 1/4" 160k
1 1/2" 225 k

Flow rates are in the 2-4 fps range.

Henry

The proper way to size piping is by flow rate and not BTU. Get a Bell & Goddett System Syzer (it is free).
Here are a few sizes:
Iron pipe sizes
1/2 .8 to 2 GPM
3/4 2.7 to 4 GPM
1 3.3 to 8 GPM
1 1/4 7 to 17 GPM
1 1/2 11 to 26 GPM
2 20 to 50 GPM
2.5 32 to 80 PM
3 58 to 140 GPM

Never ever use the boiler connection size as the piping size! Don't use 35 or 40 F Delta T! The boilers that have Genonni type heat exchangers have very small passages like flat plate heat exchangers. The heat exchangers will block and fail. The past 3 years, we have replaced a number of installs by others that had insufficient pump and small piping.

chris87

Very helpful (I came to the right place). Can you explain Delta T a little bit more?

Henry

D T is the difference of output temperature versus return (input) temperatures. And no Gordy, it is not dependent on BTU but actual flow rates. 15000 BTU ar 20 DT is 1.5 GPM and 40K is 4 GPM. So I like to design my boilers to have a 25 DT. So 225,000 BTU is 18.5 GPM and 1 1/4 could do the job on the near boiler piping. 1 1/2 would be better on long runs as there is only .5 ft / 100 difference in head.

DanHolohan

With primary/secondary systems, you can usually work with temperature differences that are much greater than the standard 20 degrees. That can save you a lot of money on pipe- valve-, fittings- and circulator sizes. I wrote a book that explains all of this.

Mad Dog_2

Buy the book...it's excellent, inexpensive and helps support this site. "Pumping Away" is a great primer and segway in to P/S made simple. Mad Dog

Rich_49

Henry ,
Should one actually take manufacturers recommended Delta T for their HX design and their flow rates into account based on the fact that this is what they designed the controls around ?
Since the question was about primary / secondary , what are your thoughts on system side piping and sizing ? And won't all the flow rates throughout the system change based on real time heat loss ? Should we take what type of emitters are being used into account ?

Seems your math is a bit off too . 18gpm = 225000/12,500 . Is the extra 1/2 gpm for good measure . Maybe I should ask at what temperatures does the noted flow take place and what type of piping is used in your examples

Rich_49

Henry , I had a bit of time so for S & Gs I entered your numbers into B&Gs System Syzer program V4.4 and came up with the following that is attached .
We know a bit about Gil Carlson's system syzer wheel here . Did you know the original is now given as an industry award every 2 years and is called "The Carlson - Holohan Award " ? Right now it is in the hands of John Siegenthaler .
Anywhoo . Take a look at the 2 attached files , I think you'll find them interesting .
And if you used Pex then you'd be at about 4.88 fps and at 60* AWT with head of 3.9 , 167.5* AWT would have head loss of 3.06 .

chris87

I'm definitely going to buy that book. It sounds like it will handle all of my questions in depth. So a little variation of the original question. Of there's a high efficiency modulating boiler, say 30-100k btu example and the heating load is 70k total. Wouldn't the piping only need to be sized based on the flow for a 70k btu system? All of these comments are very helpful thanks again.

Rich_49

Forgot to attach file . Sorry

Rich_49

What kind of boiler is this ? Mean , what brand , model ?

chris87

Triangle tube pte 110 for this example.

Gordy

Henry said:

D T is the difference of output temperature versus return (input) temperatures. And no Gordy, it is not dependent on BTU but actual flow rates. 15000 BTU ar 20 DT is 1.5 GPM and 40K is 4 GPM. So I like to design my boilers to have a 25 DT. So 225,000 BTU is 18.5 GPM and 1 1/4 could do the job on the near boiler piping. 1 1/2 would be better on long runs as there is only .5 ft / 100 difference in head.

Henry,

How can you dictate a delta with out even knowing the boiler being used, or emitters being used?

I was giving a simple answer to the OP for starters. No idea of his knowledge. And I did include that those btu carrying capacities are in the 2-4 FPS flow rate. this all works together last I knew based on the universal hydronic formula.

To the OP get to know the universal hydronic formula well. once you understand it this all comes together.

Gordy

http://www.tabbcertified.org/site/public/download/index/Documents/formulas/HydronicFormulas.pdf

https://us.v-cdn.net/5021738/uploads/FileUpload/33/1bff6e16d99b9b4523b58024eec077.jpg

Gordy

So is this hypothetical......, or your new boiler? Was a heatloss calculated room by room? Emitter types? Also hydraulic seperators are a better option than P/S piping.

Paul48

First......You broke rule #1.....You over-sized the boiler. There was probably 20% fudge built into your 70k heat loss, then you over-sized it another 30%.

chris87

This is just a hypothetical example.

chris87

I guess what I was trying to get at was a modulating boilers that can do more of a load than required but modulates down to meet the actual need. Again just a hypothetical

SWEI

If you actually want your mod/con to modulate, you must pay attention to the minimum firing rate.

Size matters!

Henry

Rich said:

Henry , I had a bit of time so for S & Gs I entered your numbers into B&Gs System Syzer program V4.4 and came up with the following that is attached .
We know a bit about Gil Carlson's system syzer wheel here . Did you know the original is now given as an industry award every 2 years and is called "The Carlson - Holohan Award " ? Right now it is in the hands of John Siegenthaler .
Anywhoo . Take a look at the 2 attached files , I think you'll find them interesting .
And if you used Pex then you'd be at about 4.88 fps and at 60* AWT with head of 3.9 , 167.5* AWT would have head loss of 3.06 .

I used the wheel and not the program. It is quicker for me. We don't use pex as we do mainly commercial or very large residential.

Most manufacturers will have information for a DT of 20F to 35F. I had a meeting yesterday with the gas utility service company. Our installations are the only ones that are trouble free!

Henry

A typical install

Paul48

Sizing for more of a load than required, means less available minimum firing rate. For most of the heating season, you would require much less than the (hypothetical) 70k btus. No offense, but your last post's thinking is the reason many mod/cons are over-sized. We see professional, nice neat installs, here all the time, that will hardly ever condense because the units were sized incorrectly.

Rich_49

I see you use HTP . Very good . Is the Delta T you are speaking about on the boiler or system side ? Htp default programming modulates firing rates based on 20* Delta through the boiler . It can be set up custom though .

Henry

We custom set the settings on the HTP boilers. This set up gives a 20 to 1 modulation rate which allows for micro managing energy usage whiile keeping everyone cozy. We do not touch the original pump or pumps. 90% of the time the system DT is 20F. The original boiler was a large firetube Cleaver Vrook of 3,000,000BTU. They added two Laars 2.5 million BTU boilers that fed through the non-working CB. Plus there was a Raypak 305 for DHW. There were so many vents that I had to use a flashlight to get around. We have had one of the coldest winters on record, and there is still around 30% saving compared to the gas bills of 2 years ago.
The building's 10 year average consumption was 3,742,860 cu FT of gas. Each apartment consumed 93,571. The first winter we reduced the consumtion to 42,372. This year it went up to 65,490.

Rich_49

5:1 xs 4 = 20 . Gotta love diversity factors . How many units are in this building ? Is that 3,742,860 per year ? How often will your outfit maintain those Giannoni HXs in the ModCon 500s ? Did you use any system conditioners ? I did notice that you used the same size pipe for the boilers that the manufacturer supplied . Was there a reason for this ?

Henry

Yes, that is for a year. I converted the amount from cubic meters to cubic feet. We have replaced one Gianonni heat exchnager on a major job. The heating water was so bad, that we had to install bag filters. They had all sorts of leaks s there was a lot of fresh water. The condutivity was over 10,000 when we finally tested the water. Otherwise since we started to install the KBN and others, not one failure. This is due to maintaining a good flow rate that prevents particles suspended in the heating water from adhering to the surface. This is the same principle for flate plate heat exchangers. We install around 200 boilers a year, so our record is pretty good.