best control for 3 boiler system please

Kevin O. Pulver_2

Hello Wallies, my customer is doing a gorgeous timber frame and sips home, with radiant in slab and warm board. Zoning by Circulator with MVAs on the 3 main floor Warm board zones.. Also has a basement, garage, and DHW zones. Simple 3 way mixing valves for floor supply temps. HX for outdoor wood boiler.

Primary Secondary piping with two Raypak non condensing boilers and one outdoor wood boiler. Load is 86k at design conditions the 2 Ray Pacs will just cover that. But most of the time one would probably be enough. The Raypacs have built-in bypass boiler protection.

Of course he wants the wood boiler to be priority when it is fired, and only one gas boiler to fire unless another is needed. I know Tekmar probably has what I need but I've always been mystified by their selection. Do I need a solar control to for the wood boiler, or is Tekmar alone what I need. any advice welcome and thanks in advance for the help guys.<img src="https://us.v-cdn.net/5021738/uploads/FileUpload/c4/9782a63b7c4030e84585b7134872fc.jpg" /><img src="https://us.v-cdn.net/5021738/uploads/FileUpload/c4/9782a63b7c4030e84585b7134872fc.jpg" />

Empire_2

I haven't read through all Tekmar's technical literature, but they have a wide variety of control for applications like the one you are working on. I believe it is located @ Tekmar.com.

Mike T.

Zman

I am not sure I would call that "primary/secondary" piping. I am not saying it won't work, I just does not have the hydraulic separation you get with primary/secondary.
As far as controls go, the challenge with these is how do you prevent the backup boilers from dumping heat into the wood boiler when there is no wood fire? Do you need to dump some heat to the wood boiler to prevent freezing?
A simple 3 stage boiler controller with the the wood boiler set as "fixed lead" will do just fine if you are not concerned about heating a cold outdoor boiler. If you want to turn off the outdoor boiler circs when the backup boilers are firing, you could use an aquastat and a DP/DT relay which would turn off the OWB circ anytime the temp falls off and the backup boiler fires.

Carl

Kevin O. Pulver_2

I contacted Tekmar but didn't hear back from them. I had been wondering about an aqua stat on the boiler, but wasn't exactly sure how to tie this all together. I figured it's been done plenty of times already by guys who learned a lot about it. I want to learn from their successes and failures. thanks for the input guys. Anybody else have any other ideas or anything a little more definitive please?

Zman

Is the outdoor boiler at risk of freezing when not fired?

GW

I did a wood boiler tie-on with one wall hung boiler and indirect with Bb zones, the control wiring was a bit busy, it was fully automated.

In my opinion you can do this a million ways. Tekmar is excellent stuff and does what it says it will do.

a lot depends on how much human intervention you want vs how much total automation you want. Both choices are fine as long as you know the pros and cons to both.

Please share about your t drill.

Kevin O. Pulver_2

Zman, this is in Kansas, and owner is gone sometimes for a week or so. He is concerned about freezing, though the wood boiler is in its own dedicated small garage, so that will help. He wanted to use glycol, but the wood boiler manufacturer is really frowning on that. I don't have any experience with glycol in open systems, but have read that it can form glycolic acid or other nasty things.

Kevin O. Pulver_2

GW, most of what I do is Lochinvar mod cons but we're using these Raypak non condensing boilers because the owner had them and wanted to use them, then he came up with the outdoor wood boiler too. We wanted to go fairly simple on this system, thus the Caleffi 3 Way mixing valves as opposed to dual variable speed injection mixing. I have a couple of Caleffi isolar controls on the shelf, and wondered about using one of those somehow in conjunction with a Taco pump relay so that on a call for heat, the wood boiler would come on if it was up to temperature, otherwise the LPG boilers would come on sequentially according to load. I've read all Carol Fey's books several times, and do all my own wiring. But I don't have a real concrete plan for this project, so I really appreciate the help. Concerning the Tee drill, I use it mainly to pull half inch branches in making manifolds for smallish commercial projects. But for the price of so many inch and a quarter by inch copper tees, I decided to use it here also. I started maybe 10 years ago with a rothenberger, and now have the Tee drill brand which I got used. the well used half inch head is not very sharp,so I usually use a Unibit step bit for accuracy and ease in getting things started, then finish with the T drill.

Zman

I think this would do the trick http://tekmarcontrols.com/images/_literature/274_d_07.pdf

On page 6 you would be in mode 1.

On page 8 you want "Fixed lead first on/first off"

The OWB heat exchanger circ would be wired to relay 1, The other 2 boilers "TT" connections would be wired to relay 2 and 3.

Take the time to read the whole manual and set the boiler mass, stage delay, ect. setup correctly.

Carl

Kevin O. Pulver_2

Thank you very much! I've installed several 201s, and even been to a Tekmar class. but that was all before the mod cons came along. I'll read this thing thoroughly before I order and let you know how it goes or if I have any questions. any other advice or options from anyone is more than welcome, as I agree there's probably various ways to do this.

Paul Rohrs_14

Kevin,

How much piping do you have remaining? You and I need to make a trip to BufferTank-Mart and just re-pipe a little. Is the BPHX the isolation for the wood boiler and is the next circ to the right w/o mixing valve for the DHW?

Paul

Paul Rohrs_14

Zman, As it pertains to staging on page 8, I agree with fixed lead but wouldn't you want the wood boiler to be "first on/last off"?

Kevin O. Pulver_2

Thanks Paul, Yes you are correct the HX is to separate the open outdoor wood boiler and the supply return without mixing valve is for the domestic hot water. we're going to put a 3 Way mixing valve on the discharge side of the indirect.

GW

Kevin, yes I consider myself "good" when it comes to controls, but sometimes simple trumps total automation, and sometimes it's the other way around.

Paul has a point- you should consider a buffer tank especially if you're gonna be stoking the fire on milder days.

I'm not super familiar with this control Zman outlined- if you are required to run outdoor reset, then this isn't ideal. Wood boilers will trump the ODR; another reason you need a buffer tank

So- if i buy a T-drill, is it pretty easy to learn? You braze those joints? Is it hard to clean up and make it shiny? I have been buying Alberta Tees for over 10 years

Zman

Paul,
Good to see you back.
Buffer tank is an excellent idea.
You are correct it should be first on last off. I thought that setting pertained to the remaining 2 boilers, my mistake.
Carl

Paul Rohrs_14

This is the representation I sent to Kevin. An argument could be made for the DHW to be piped on the source side but since it is a single gentlemen, DHW recovery can easily be handle on the load side. In this manner, the buffer is the thermal flywheel and the tekmar will see the system sensor in the buffer tank as the setpoint for all boilers as reset will happen only on the load side downstream of the DHW.

(Edit: Expansion tank, make-up water, other components not illustrated)

Good to be back on The Wall. I actually bumped into Dan at ASHRAE in Chicago. Good times, good friends.

Best,

Paul

SWEI

If money is tight on this one, and there is sufficient space inside the building envelope, you might look into re-purposing a 499 LPG tank.

Kevin O. Pulver_2

Thanks again for the input guys. Yes Gary the T drill is very easy to use. You braze it with the long flat Sil-Fos sticks like the HVAC guys use. No flux or even pre cleaning the copper is required. I sand blast the manifolds but the pipe you see on the wall has 0 cleaning done on it. (though the owner is talking about polishing it and leaving it sans insulation)

Paul actually sold me my first T puller years ago. That Rothenberger worked very well but I was disappointed it came without a manual, and with ZERO instructions at all. You can't even buy a toaster these days without getting a booklet with tips for best use and service for crying out loud! It came with a ratchet, but I turned it with a Milwaukee Super Hole Hawg which worked very well. It was MUCH cheaper than the T drill brand, and just as fast... almost, except the drilling and pulling are two operations instead of one. But it's more compact to operate. REMS makes the "Hurricane" that will do the job also. If you watch eBay you may find a good deal on one of those three. One advantage of the T drill is its extractor is fully adjustable for larger or smaller extruded hole adjustment and it comes with a branch pipe notcher for better fit of the connection. Though for simple manifolds with half inch branches the notcher is not necessary and I never had a problem with fit. Tee drill, T drill, puller, extruder, notcher, REMS, Rothenberger are good search words.

GW

Thanks Kevin, I think i spend $1500-2000 a year on Alberta Tee stuff; I'll look into it.

Gabriel@HBX

HBX makes a control, the CPU-1000 that can handle 3 boilers and a fixed first for your wood boiler. Let me know if I can be of assistance