Flat Plate HX for 93 MBTU?

[Sawyer]

I am trying to size the HX for my system to transfer 93MBTU to my closed boiler system from the Garn. I am running 2- 1” lines 175’ from the Garn to a 1-1/4” tee at the LP boiler in the house. I want to transfer 93MBTU to the closed system. I am figuring 7.5gpm per 1” line, or 75MBTU per line. I was told a 5x12- 50 plate HX with 1-1/4” ports is required, it is $1175. I was not prepared for this expense. Am I being told the correct information.

Thanks, George

 

[jgrimm]

George,

Go here to size the HX, registration is free. I sent you a PM also.

John

 

[Sawyer]

I will check with you today.

 

[Captain Chaos]

Sawyer,

I have a GARN2000 on order also and am sizing my lines, pumps, HX also. I need 125,000 BTU at my boiler, and when I told my Garn distributor this, he reccomended a 200,000 BTU flat plate HX 1" in/ out , 20* drop send/return w/ 16gpm flow. He sells them for $371.00. I priced it at a plumbing supply house and they wanted $990. I have been doing a lot of learning/ figuring with the help of my plumber friend. I have found that Garn has zero customer support so far...5 calls with 5 messages left and no return calls...zipo This forum with its past threads has been extremely helpful.

 

[Sawyer]

Hi Captain,

Isn't 16gpm flow through a 1" pipe quite a high velocity? I thought 75-80MBTU was about max for 1". I am learning slowly so I am open to correction

George

 

[Captain Chaos]

I agree, makes no sense to me, however I am an electrician and not a heating contractor. It must work becaue HX is rated at 200,000BTU with 1" in/out@ 16gpm with 20* drop. It is made by AIC and its cat# is LB-3150. My project has come to a halt over these sizing issues. My plumber tells me that i will need 1 1/4 to 1 1/2" pex and a very expensive odd ball pump set up to meet the HX rated capacity. I can't figure out why I need such a big HX when I only have a 125,000 BTU max load at my oil boiler. The Garn Distrubutor doesn't give me much info when I talk to him, and GARN still will not return my 5 phone calls to their "tech support" I am really starting to regret going with GARN.

Have you had any luck with your distributor or contacting Garn directly?

Capt

 

[heaterman]

I agree, makes no sense to me, however I am an electrician and not a heating contractor. It must work becaue HX is rated at 200,000BTU with 1" in/out@ 16gpm with 20* drop. It is made by AIC and its cat# is LB-3150. My project has come to a halt over these sizing issues. My plumber tells me that i will need 1 1/4 to 1 1/2" pex and a very expensive odd ball pump set up to meet the HX rated capacity. I can't figure out why I need such a big HX when I only have a 125,000 BTU max load at my oil boiler. The Garn Distrubutor doesn't give me much info when I talk to him, and GARN still will not return my 5 phone calls to their "tech support" I am really starting to regret going with GARN.

Have you had any luck with your distributor or contacting Garn directly?

Capt

Patience there Sparky The Garn will be worth it both now and 20 years from now when it's still pounding out clean heat.

Heat exchangers are normally spec'd out with a 20* difference from side A to side B. A wood boiler is a different can of worms. In most cases where you are using a plate type HX to dump heat into an existing hydronic system you need to keep your ^T closer than that. You don't want to run your wood boiler at a constant 200* to get 180* out of side B which moves the heat into your existing system. That's why your plumber is recommending a larger HX and more flow.

The issue would be the same regardless of what particular brand of wood burner you choose. It's just physics. I just met with a customer who has a lack of heat transfer problem with a setup put in by the Central Boiler guy in these parts. Probably the 8th or 9th person who has called me to correct what is invariably an undersized HX & lack of flow. The solution for him is basically what your plumber is recommending only in his case we have to rip out 170' of 1" tube and start over.

I would suggest a careful analysis of your existing system to see how low you can actually let the water temp get and still heat the house. You may find that you have enough excess capacity in the baseboard to allow adequate heat output with only 140 or 160* water. This would mean you can get the job done with a smaller HX and circ. If the person who originally sized your baseboard scrimped on the lineal feet you may be stuck with having to run high water temps and a larger HX, circ and tube. It all starts with a heat loss calc of your house. Heating with wood is the same as anything else. You have to do it right or it won't work.

PS 1" pex will not flow 16GPM unless you hook a nuclear powered pump to it. Not something I'd attempt under any circumstance. If you need 16GPM 1-1/4" pex is your minimum, probably 1-1/2" if the tubing length is much over 100'................I'd have to do the math...........

 

[Sawyer]

I agree, makes no sense to me, however I am an electrician and not a heating contractor. It must work becaue HX is rated at 200,000BTU with 1" in/out@ 16gpm with 20* drop. It is made by AIC and its cat# is LB-3150. My project has come to a halt over these sizing issues. My plumber tells me that i will need 1 1/4 to 1 1/2" pex and a very expensive odd ball pump set up to meet the HX rated capacity. I can't figure out why I need such a big HX when I only have a 125,000 BTU max load at my oil boiler. The Garn Distrubutor doesn't give me much info when I talk to him, and GARN still will not return my 5 phone calls to their "tech support" I am really starting to regret going with GARN.

Have you had any luck with your distributor or contacting Garn directly?

Capt

Hey Capt, glad to see another future Garn owner posting!

I have not heard anything about delivery of my Garn either. I do think you will be happy you waited when you are firing this winter. I am 62 and put a lot of thought into whether I would be able to last as long as the Garn, hope so! Fortunately in my case I am too busy with other building and landscaping projects to worry at this point. I do not have my pipe buried as I am waiting for my insulator to get the 30kw generator fixed on the foaming unit. I do hope he is ready next week so I can finish the concrete work that has to be done over the buried and insulated pipe line.

I was glad to hear from heaterman, he always seems to clear the clouds and give good direction. I guess with my sizing situation I am trying to get my Btu’s with a low velocity so I can use a smaller pump as others have suggested. I guess that leaves me a degree of safety if I miscalculated with the SlantFin calculator.

 

[heaterman]

Here's a resource.

(broken link removed to http://www.aicheatexchangers.com/images/application) request form.pdf

Simply put in the temps you want to achieve and the flow rate you want to do it with and they'll size one for you. If that link doesn't get you there try this one. The upper right corner of the page has a link for a sizing request.

http://www.aicheatexchangers.com/

 

[jebatty]

It must work becaue HX is rated at 200,000BTU with 1” in/out@ 16gpm with 20* drop.

When I run the calc on this, I come to 160,000 btu/hr: 8.35 lbs/gal x 16 gpm x 60 min/hr x 20*. Did I miss something?

 

[Captain Chaos]

Thanks for the pep talk Heaterman, I was a little frustrated yesterday. I will try and get some pics of the project on this site soon. I'm thinking of using 2 parallel 4" electric conduits (I have extra) going from the slab to the house (80ft), have a insulation contractor blow some insulation around them, then pull 1 pex through each conduit. I bet I might be able to install the premolded foam around the pex as it is fed intio the 4" conduit. This way I can proceed with the project while still not sure on the pex size Hmm...need to think some more on that one..

Capt.

 

[heaterman]

If you want to size your own HX you can go here

http://www.flatplate.com/resources_SOFT.htm

You have to create an account and log in first. On the main page you'll see resources listed on the side. Once you have established an account, just a user name and password, you can proceed to input the temperatures required for the supply side (A) and the load side (B). The software will calculate your required flow rate and the size of HX you need along with how many plates. Use no more than 2PSI drop on both sides to keep the head in the system reasonably low. It's amazing to see how much 5* drop on the supply side or 5* more demand on the load side changes the size of the HX. This sizing software will be fairly close with any brand of plate type HX. Remember to drop the manufacturer a note of thanks for providing the resource.

I think a lot of you running 5x12 30, 40 or 50 plate HX's will be surprised at the actual output.

 

[Sawyer]

Heaterman, I think I am going to wear out the calculator! What a great learning tool, watching the effect of different temps, DT, flow rates, and pressure drops. I now understand better the reason for properly sizing the HX to accommodate the various temperatures available through storage temperature swings. Hopefully I will understand the plumbing before my Garn arrives.

Your idea of thanking GEA is a good one.

 

[heaterman]

Heaterman, I think I am going to wear out the calculator! What a great learning tool, watching the effect of different temps, DT, flow rates, and pressure drops. I now understand better the reason for properly sizing the HX to accommodate the various temperatures available through storage temperature swings. Hopefully I will understand the plumbing before my Garn arrives.

Your idea of thanking GEA is a good one.

Glad that it helps you out. Hydronic heat is not rocket science. Heck, even I can grasp most of the concepts It does demand a fair amount of design work and thinking through the whole system before pulling the trigger and just installing something because it "should" work. It's gotta be right or you'll be doomed to fighting with the system forever.....or at least until you change it and make it right.

I like the way you think Sawyer. Your wood shed is full BEFORE the wood burner arrives. Too many get it the other way around.

 

[jebatty]

With all the discussion on pro/cons of plate and coil hx's, is there a similar calculator for coils so that a comparison could be made?