Mini-tube distribution to 7 remote manifolds..

Rocky

Here is the scenario. Have 7 remote manifolds feeding 1.4 million BTUS to a new hanger. This equates to each manifold supplying 21 gpm each to the slab. Each manifold will need approximately 5.75 gpm on design day injection rate, assuming a 20 degree Delta T. That gives me 40.25 total injection gallons for the system. Will use a 2" Twin EcoFlex to bring this 40.25 gallons into building from a boiler room in another building approximately 40 feet away. Using 3 Buderus 315-7 oil boilers with Riellos. Question is: Since two inch pipe will carry the 40 gpm injection , can I have a two inch primary loop? Each Buderus has a 3" outlet, and they will tie in as a parallel primary/secondary. Seems kind of odd to think that the boilers will all tie together with three inch, then that three inch will tie into a two inch primary loop with closely spaced T's. Since we need 1.4 million BTU, I have to use the three boilers mentioned, but since it is all injection, we only have to carry the injection load, right? Which means 40gpm, which means two inch pipe, right? Seems as if I've heard somewhere where the primary pipe should be at least as big as the secondary piping. Do I have to upsize my primary loop to accept the three inch piping from the Buderuses (Buderi)? Line me out here folks.
Warm Regards,
Rocky

Tim Doran_2

A few questions

1- what is the required supply water temperature?
2- What is the required btu/sqft and total sqft?
3- Will you stage the boilers?


Tim D.

hr

The primary loop

will need to be sized based on the gpm and delta t you choose for the loop. Wider delta t will allow smaller pipe size. Always check with the boiler manufacture to see what they are comfortable with on the delta T through their boilers.

Siggys Hydronic Design Softwarehas a great injection pump and piping sizing module. It could also size your primary loop based on you inputs.

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Rocky

Tim, answer to your questions

The design system temp is 107. Supply temp is 180. BTU load per sq. ft is 49. Total sq footage is 29000. Boilers will be staged with a Tekmar 268, and each manifold will have a Tekmar 356 VSI control. I used the Tekmar essay regarding VSI injection to get the injection rate per manifold. That equals about 5.75 gallons on design day injection rate. That means 7 manifolds, times 5.75 gallons, equals 40.25 gallons. If thats all I have to supply to manifolds, then that means a two inch primary loop. How can I tie my 3" Buderuses (all three of them) into a two inch primary loop? Do I neck down the Buderuses? Seems as if the heat couldn't get out of the boilers that way, but if you only need 40 gallons, you only need 40 gallons. Delta T for the system was input at 20 on the Wirsbo ADS program. Any thoughts on this?
Regards,
Rocky

Rocky

Hot Rod, gpm is 40

and delta T for the system was input at 20 on the Wirsbo ADS program. The tekmar essay regarding VSI flow rates was used to come up with the 5.75 gpm injection rate. Gives me 40.25 gpm for total injection flow. If thats all I have to supply to the hanger, then 2" pipe will carry it. That means I only have to have a two inch primary loop, even though the Buderus have three inch outlets. Do I just neck them down and tie all three into a two inch manifold, then tie that manifold into my two inch primary? Something just isn't making sense to me but I just can't put my finger on it.
Best Regards,
Rocky

Boilerpro_3

You need to check with Buderus

about the flow rates through the boilers and very low temp returns. It sounds like you are injecting right from the boilers to the manifolds. This means you will be getting very low temps coming back to the boilers (Max return temp of 107F - 20F (delta tee) = 87F. If flow rate through boiler is okay, then this would work gret with a condensing boiler. If you need more flow, pipe the boilers with their own pumps as a loop and size the pipe accordingly and then use Primary/ secondary piping to pipe the injection loops to the boiler loop and the floor loops IE: If boilers are running a 20F delta tee, then you'll probably need a 3 or 4 inch common boiler main with two closely spaced tees and the two inch injection line running out to the manifold loop. This injection loop will be designed at a 180F -87F = 93F delta tee. The manifold loop will then have its own pump(s) to create a 20F delta tee for the system.

BTW, I am not sure why you would use 7- 356 VSI controls. One control could power a single pump (45 gpm max) or dual B&G NRF-33's (60 to 70 GPM max), depending on the head loss.

Boilerpro

Tim Doran_2

Thoughts and a drawing

Rocky,
You only need 40 gpm of injection because the delta T across the injection circuit is 73 degrees. The delta t across the boilers is usually a 20 but in this case I would open it up a bit to 30 or 40 to keep the pipe sizes and circ sizes reasonable. Just don't get below the manufacturers recommended return temperatures. The system flow is 142 gpm or so at a 20 delta T and to be honest I would open this up a bit as well. It's a hanger not a residence so a little wiggle room exists. I would however use a counterflow loop pattern if I opened up the delta T.

This is a conceptual drawing and I did not put in all of the valves, drains, controls,bells and whistles, etc. so don't use it for pricing.

If you want to discuss this project call me on Monday. I am certain that I can help you save some time and $$$$. 952-997-5334

Tim D.

Rocky

Boiler Pro

It is now Saturday. I met another frequent Wall poster (Weezbo) at the parts counter this morning and we started talking about this job. I was being stupid. You know how when you start to talk about things your mind starts going over all the steps and things become very clear, even to yourself!? Thats what happened. I realized that what I was missing was my SYSTEM delta T was 20, not my boilers! I was forgetting that if I am sending out 107 degree water to the slab, I am getting 87 water back. My boilers don't see a 20 degree delta T, my slab does. My boilers are actually going to see a HUGE delta T. Ran the heat balance equation from "Primary-Secondary Pumping Made EASY" (Thanks again, Dan). By the time my last manifold dumps back into the 2" return portion of the primary loop, I am going to have 40.25 gpm of 96 degree water! Boiler outlet of 180, return of 96 equals 84 degree delta T! If each boiler is capable of 550,000 btu, at an 84 degree delta T, I only have to move 13.1 gpm through the boiler. That means I can come out of each boiler with an 1-1/2" pipe, tie each boiler into a 2" common manifold, then tie this common manifold into my 2" primary with closely spaced T's. Right? Have a boiler pump on each boiler capable of moving 13.1 gpm, and a primary pump capable of moving 40.25 gpm at whatever head I come up with. Then each manifold in hanger can have its own VSI control with a small Grundfos or Taco pump tht will carry only that particular manifold's gpm needs (20.5 gpm).
Since Buderus have no minimum return water temp limitations, 96 degree entering water should be no problem.
Sometimes, just talking about something helps to crystalize it in your own (in my case, feeble) mind. Thanks for taking the time to post your response.
Regards,
Rocky

hr

Will that boiler

actually handle that cold of a return continously? Seem cold for a cast boiler? The copper tube boiler folks used to say 100° return temperatures were fine, also!

Make sure Bud is ok with that.

I, like Tim, would also look at a 25 or even 30 delta t in the slab. It is not generally a problem with commercial slabs and would also help with pipe sizing, loop lengths, etc.

Consider the Grundfos MixiMiser, if you injection flows get into it's range. a simple way to have multiple VS mixes fairly inexpensivly.

Behrends Mechanical of Juneau won a RPA award, and best of show, for their "Wings of Alaska" 25,000 foot hanger project in 1999. They may have some tips for you also.

Sounds like a fun project, need help Send pics!

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Weezbo

My Buddy is saying thank you for all of the help.:)

normally we drive past each other at 2 a.m. comming or going in late summer. its difficult to determine if hes going back to work or i am ) when it comes to helping others thats what we are about. You Guys Rock:)

hr

I used this method

on a commercial job, works great. I used figure #7 Bulge fitting method, shown in the link below.

I built the buldge with a t-drilled piece of 2-1/2" copper. Thanks John and Kitec! Two 200,000 boilers piped with 1-1/4", large delta T.

A Wirsbo Duomix handled two injection pumps. Earthlee built the custom steel manifolds for me, and I injected right into them.

I also went with long 3/4" loops, 30° delta t, and 15" oc by alternating 12" and 18" to have all the tube tied on the wire, as this was a pumped concrete job and keeping odd spacing ( tied between the mesh squares)rarely works. The force of the mud just pushes it to the side anyways.

I also used a Cliptie to save about 8 hours of hand tying!

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,73096,00.html

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Rocky

Hot Rod

Thanks for the posts. I remember seeing those photos in earlier posts on the Wall. I have two questions for you. What is a "cliptie" for tying the tubing down, and what type of insulation were you using. I am in a little bit of a debate with the owner and concrete guys as to how much, where and what type of insulation to use. Concrete guy wants an 8' perimeter with edge insulation, then, about 2 feet down, he puts down a "wing". This is a 4x8 sheet of blue board that anles out at about a 45 degree angle underground. It starts at about the footer and angles out from there. He does not want to put insulation under the main slab. I would like to have insulation everywhere, but realize many don't insulate the middle slab witht he thinking that once it developes a thermal root, heat loss basically stops in the middle. Is that Insultarp you have down in your picture? Have you ever tried the "bubble'wrap foil" type stuff? That is the one area I am not quite sure about yet and would appreciate any thoughts you may have on the insulation. Great idea on Wings of Alaska. I will give them a call. Yea, this should be a fun job. I might advertise here on the Wall for fellow Wallies to come help. They could help me install it, then I'll take them King Salmon fishing. Sounds like a WIN/WIN situation!
Regards,
Rocky

hr

The concrete guy shouldn't be dictating

the insulation detail, unless he is paying the fuel bill Seems in your climate it would be hard to over insulate! All commercial work in my area needs engineered stamped plans. Which is a good idea, to protect the owner and the subs!

Yes I use InsulTarp but had a band of 2" foam for the vertical edge down to the footing. And also a 4 foot wide perimeter band of the high load foam, then Insultarp.

The edge loss is the biggie, and next the perimeter area. the center only sees the soil temperature below, not the outside temperature, if the other insulation details are handled. IMO

I've not tried other bubble foams. I like the InsulTarp because the foam, and bubbles, are protected by the woven vinyl jacket. And the bubble portion is between two layers of closed cell foam. I know it works in concrete blankets, as we have poured in subfreezing weather with the use of concrete blankets. We have poured concrete year 'round in the mountains of Utah with blankets. That's pretty much what InsulTarp is, really.

Very hard to pop the bubbles. Unlike the other foil bubble products that sometimes pop as you walk over them!

I would never say it is a R-5, but my backyard testing proves it performs very close to 1" foam. Close enough for my area. And much better than nothing at all.

Yes at some point the downward loss stops. Industry experts still have not been able to model that loss. Too many variables as soil conductivity, moisture content, R value on top of the slab, operating temperatures, delta t between the slab and soil below, etc, etc.

I have seen a detail similar to what you describe with insulation outside the building. I think www.beaverplastics.com has some models of this detail.

http://www.beaverplastics.com/pdf/Insulation_Study.PDF

Watts radiant sells the ClipTie tool. Check with a dealer or rep in your area. If not I'll get a demo to you. It will save you hours of back breaking work. In the job I pictured I used 3/4 Watts pex (600 foot loops) with a 6X6 heavy gauge remesh. The wire was about 3/16" diameter heavy stuff, but it's what the structural engineer wanted. the ClipTie just makes it around that assembly.

The engineer also insisted on a compaction test for the subgrade. It actually failed the first test and had to be recompacted. They had a large vibratory Cat roller on the project. Something to do with the moisture of the base rock? This is a key detail for structural slabs. The slab is only as strong as the material below. He was wise to require this as a lot of fill was hauled in, and his stamp was on the drawings! This engineer did a lot of site visits. Good for him I say! The buck always stops at the P.E. stamp

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