80K Btu through 3/4\" iron, Possible?

gasfolk

Could you put 80K Btu/Hr through a 3/4" iron loop of several feet, a few elbows, and a pump (Taco 007 or Grundfos 15-42). Only full-port valves.

System delta T 10. Design temp 130. Boiler aquastat: High 170, Low 140.

Any practical problems with this plan?

Thanks,

gf

JBH_2

Won't you need more GPM out to the system with a 10 degree delta T opposed to a 20?

16 vs 8?

Ron Schroeder

You will need 16gpm for 80KBTU at 10 degrees delta T. Pressure drop thru 1 feet equivilent of 3/4" iron is about 5.6'. The velocity would be almost 10feet per second.

Can you go with a higher delta T to get a lower flow rate?

Ron

Empire_2

YEP...

SInce 3/4" pipe will only carry 40000BTU/HR @ 20*Del T, the senerio you are proposing will make a nice humming sound all thru the house. Water moving too fast even at 20*Del T. I doubt you will be able to get your 80M out of this loop. not only are you trying to double it, but transfer the heat in only several feet of base if I read you correctly. 40m-3/4" at 67 feet effective base =40M @ 20*DEL T

George Peteya_2

Anything's possible, but ...

... here's some info from the Grundfos P/H Handbook:

Head loss in 3/4" Schedule 40 steel pipe is 56.4 feet of head per 100' length, or 0.564 feet of head per foot of length, at 16 gpm. Let's say that "several" means five.
Each standard 90° ell is equivalent to 2.3 feet of pipe. Let's say you have 4. Since the valves are full port, let's assume they are not there. Let's say the ells equal 10 feet. ("Let's say ...": this is how engineers talk)
So, you have the equivalent of 15 feet of pipe. At 16 gpm, the head loss is (15 x 0.564) = 8.5 feet of head.
A 15-42 will move 16 gpm at about 4 feet. A 007, 16 gpm at 5 feet. So if you insist, use a 15-58 or a 008. Wouldn't recommend it though ... please read on.
Velocity in 3/4" steel is over 9 feet per second. So at a minimum, this system will sound like a running toilet. That is, until erosion/corrosion sets in and you have to replace the loop with something bigger ... this isn't already installed, is it?

gasfolk

Tekmar Literature

Thanks for your comments and help. We are trying to understand this Tekmar essay on Mixing Methods and Sizing. It's not that we don't trust the essay. We're just not sure we are reading it right, and we DO trust the practical experience on The Wall.

The table on page four shows "Design Injection Flow Rate (US GPM)", suggesting that short injection piping ("5 feet of pipe, 4 elbows, and 4 branch tees") allows a 3/4" pipe to carry a maximum flow through of 10.5 gpm. At a Tb-Ts of 20 that could carry 100K Btu?? Note also the warning on page 3: "Do not oversize the injection system. If the heating system is not able to get enough heat, the boiler's operating temperature can be increased."

For our low-temperature application (max Ts 130, delta Ts 10), by simply increasing the buffer tank's operating temp and widening Tb-Ts to 30 (for example), 3/4" pipe could easily inject 150K Btu?? Of course, with two 3/4" tappings, we have even more capacity??

Our heat loss by Manual J is 90 MBH, and boiler clocking suggests a lower value.

We don't want to find our error on a chilly night. Thanks for any crticisms, positive or negative.

gf

gasfolk

Tekmar Literature

Thanks for your comments and help. We are trying to understand this Tekmar essay on Mixing Methods and Sizing. It's not that we don't trust the essay. We're just not sure we are reading it right, and we DO trust the practical experience on The Wall.

The table on page four shows "Design Injection Flow Rate (US GPM)", suggesting that short injection piping ("5 feet of pipe, 4 elbows, and 4 branch tees") allows a 3/4" pipe to carry a maximum flow through of 10.5 gpm. At a Tb-Ts of 20 that could carry 100K Btu?? Note also the warning on page 3: "Do not oversize the injection system. If the heating system is not able to get enough heat, the boiler's operating temperature can be increased."

For our low-temperature application (max Ts 130, delta Ts 10), by simply increasing the buffer tank's operating temp and widening Tb-Ts to 30 (for example), 3/4" pipe could easily inject 150K Btu?? Of course, with two 3/4" tappings, we have even more capacity??

Our heat loss by Manual J is 90 MBH (boiler clocking suggests a lower value). If this works it simplifies our piping and eliminates a pump, but we don't want to find our error some chilly night next winter.

Thanks for any crticisms, positive or negative.

gf

Boilerpro_3

I was going to point you towards that.

If you look carefully, your delta tee across that 3/4 inch injection piping is not 10F, but more like 170F boiler supply - 120F system return = 50F delta tee. Your system temp drop is 10F, not the injection loop.

Boilerpro

Brad White_33

I agree

The injection loop delta-T can be as wide as the coolest primary hot water temperature will allow. System delta-T can be quite wide and the remaining boiler flow will keep the boiler delta-T low. As stated you have to be prepared to set your boiler (primary) temperature high enough to do the job on a design day.

gasfolk

We're surprised because...

3/4" seems awfully small, but sounds like we got lucky with a very low design temp.

The buffer tank has potential for two 3/4" supply tappings. OK to use just one, or is there any benefit to combining the two 3/4" tappings into a 1' injection loop?

This really saves us a lot of work and heartache.

Thanks everyone.

gf

gasfolk

We're surprised because...

3/4" seems awfully small, but sounds like we got lucky with a very low design temp.

The buffer tank has potential for two 3/4" supply tappings. OK to use just one, or is there ANY benefit to combining the two 3/4" tappings into a 1' injection loop?

This really saves us a lot of work and heartache.

Thanks everyone.

gf

George Peteya_2

That's the nice thing ...

... about injection loops. With relatively small pipe, you can move a lot of Btus. My biggest injection loop ever (it's been running 9 years now) was 1", 80 feet each way, with a 0010 injection pump. The design load was 530,000 Btuh with a design water temp of 95°F. So let's see, the delta T across the injection loop is 95°, assuming 180° boiler supply, and 85° return. You don't want to knowhow much a 4-way valve (3"?) would have cost.
Most residential injection loops are 3/4" because it's hard to believe 1/2" can carry all that heat ... but look at that tekmar essay now and believe it later ...

Empire_2

Thanks for chimming in Brad.

I was gonna say that Brad has a grip on this topic...I didn't know that it was injection application. Thanks Brad...

Mike T

Ron Schroeder

Hi gf,

Remember, you don't have to limit your pipe size to the same as the taping. You can use reducers from larger pipe to the 3/4" taping. The taping and reducer would be most likely less of a restriction than a typical zone valve. You can even get smooth tapered reduction nipples from McMaster-Carr.

Ron

gasfolk

Sounds like we have options...

gasfolk

Sounds like we have options...

Looks like 1/2", 3/4", or even 1" would be OK. If we understand you guys, larger pipe will have less flow noise, and the Tekmar article suggests a globe valve for throttling/balancing.

And as you all suggest, when we right size our primary pump (gravity conversion, EDR 750s, so 007 instead of current 0010), BOTH delta tees should increase--in the system loop and between boiler supply and primary return.

We're actually a little sad getting to this answer, because it has been great fun bouncing ideas off of you guys these last 6 months. Mark Eatherton says "pay it forward," and the best we can do is share all of your good ideas and articles with our plumber (a great guy whose father was a plumber). He tells us, if this works, he will be putting a buffer tank in his house next.

Very best to all of you,

gf

gasfolk

Does this mean...

an inch and 1/4 (1 1/4") primary loop could be piped right off the buffer because flow restriction through the 3/4" orifice is relatively negligible?

If true, then with falling heat loads of well-insulated houses, current Ergomax tappings would appear more than adequate for most piping schemes. True?

Thanks again,

gf

hr

adapters

you can but 3/4mip X 1 adapters, even 3/4 mip x 1-1/4. I'd guess you add 1 foot of head into the calcs for that short restriction.

I've used the adapters below to build buffer connections on water heater tanks, compression tanks, LP tanks, just about any pressured vessel I can get my hands on Have not had an issue with pumps, excessive noise, or erosion corrosion.

Look down the throat of just about any circuit setter any you will see a small opening. This B&G has about a 3/4" port.

As Ron mentioned you can also find reducing nipples. If I'm not mistaken the Munchkin has a 3/4" x 1-1/4" brass reducing nipple on the supply and return. Even on the 199,999. Moving a lot of flow into the 3/4" header

hot rod

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