Over Heat Loop Question

[mikes67]

Hi everyone,
Figured id run this by you guys. I'm installing an EB150 had this idea for the over heat loop.
Control it with an open on rise aquastat set at 210 that would cut power to an automag, in a power failure this would also act as a gravity loop? Run it in 30 feet of finned tubing on the ceiling. Am I on the right track here?
Could someone recommend an aquastat part (part #s) and also were to buy the automag.

Thanks, Mike

 

[jebatty]

If you're not on a track, I'm in trouble, because that's exactly what I have done and it works perfectly, including the finned tubing (mounted on the ceiling). A pointer: if your don't have an internal check valve on the boiler return circ (assume circ installed at the boiler), plumb the return from the overheat loop into the return line before the circ. This will allow the circ to put flow through the overheat loop and not depend on gravity in the event the overheat aquastat activates in a "power-on" situation. In a "power-out" situation, in my system I still get good gravity flow through the circ.

As to the aquastat, I have a strap-on type mounted on the boiler supply as it exits the boiler. Mine has both sets of contacts, and it is wired to break on rise (210F), or just get a break on rise aquastat. I bought mine off of ebay, but they are readily available from supply companies. You also can get the Automag off of ebay. Search "automag" in the Business/Industrial category.

BTW, I used enough finned tubing at 500 btu/ft to equal 10% of my boiler rated output.

 

[dogwood]

Does it make any difference how high up on the wall or ceiling you place the finned tubing for your overheat circuit? Is it advantageous or simply convenient that you put the finned tubing on the ceiling. I purchased my Automag from BioHeatUSA along with my boiler. I imagine they'd sell it to you separately if you can't find another source and better price. Their charge was $125.00, probably way too much.

Mike

 

[Gooserider]

Does it make any difference how high up on the wall or ceiling you place the finned tubing for your overheat circuit? Is it advantageous or simply convenient that you put the finned tubing on the ceiling. I purchased my Automag from BioHeatUSA along with my boiler. I imagine they'd sell it to you separately if you can't find another source and better price. Their charge was $125.00, probably way too much.

Mike

You need to configure it so that you get a good gravity or convection flow during a power-out situation - this means you need to pretty much come up out of the boiler and run the fin tube as high as you can above the boiler and then loop it back down. That way you will encourage the maximum heat dissipation. High on a wall might work, but the ceiling will get it out of the way more and is usually higher.

Gooserider

 

[mikes67]

I just chose to put it up on the ceiling, cause as goose said "its out of the way"
I have most of the parts together, should be installing this weekend

Mike

 

[in hot water]

Actually any zone valve with a N.O. normally open motor will work, so with power applied the valve shuts, power drops and it springs open. Doesn't have to be an Automag. Should be able to find a 24V NO zone valve for 70 bucks or so. In a Caleffi brand the Z131000 with end switch Z141000 without end switch for the motor. Body sizes Z200617 1" NPT, Z200635 in 1" sweat

Honeywell L4000 series aquastats come in many versions.

L4008A1015 breaks on temperature rise, 66" cap tube 5-30F adjustable differential.

 

[dogwood]

Do you start the finned tube section immediately after the automag, or normally open zone valve, or do you use regular pipe until you reach the ceiling, and on return from the ceiling? Also, do you leave the housing the baseboard normally comes in on, or do you take that off and utilize just the finned pipe. If any of you would be kind enough to share a photo of your overheat loop it would be appreciated. Is the 10% of boiler btu output Jim mentioned the norm for an overheat loop? Can't imagine he'd be wrong, but a confirmation would help me rest easier. I recently acquired a 170,000 btu unit and at one time thought I'd need eighty feet of Slantfin basebard for the overheat loop. Maybe that's way off. I'll have to find my old calculations now that its time to start the installation process and redo them prior to purchase. Any input woul be appreciated.

Mike

 

[jebatty]

My Tarm dealer recommended finned tubing at 500 btu/ft to equal 10% of boiler rating.

 

[Chris S]

This is an interesting topic. In my previous home, with a wood burning boiler, the boiler was in the basement, and I used my largest zone on a N.O. zone valve run parallel with the zone valve that controlled that zone. It had to work once, and it did. Because my boiler was in the basement, gravity convection was simple.
I am reading fin tube around the ceiling with interest. 3/4 fin tube in the enclosure is good for approx 600 or 650 btu/ ft at 180, more at higher temperatures, and the depending on whose you buy. Outside the enclosure it is substantially less however. Anyone who removes the front covers from their heat will confirm this.

Do those of you who have done, and advocate this have good experience with this? Does exposed fin tube up high behave better than it does down low and therefore emit more btus? or at least enough to accomplish your overheat protetction. Inquiring minds want to know. For those looking to do this, plumbing supply houses usually have plenty of bent baseboard which they will sell at a very good price for such an application, don't waste the good stuff.

 

[jebatty]

The intent is gravity feed, no power, so it must be mounted higher than the boiler supply with return lower than supply. To some extent, the higher the better, to improve gravity flow.

 

[dogwood]

Jim, mounting on a 10 foot high ceiling would be okay then, not too high? I was thinking if the baseboard was mounted flat on its back on the ceiling in its casing, the heat might have some problem escaping it's enclosure, as baseboard is designed to be on a wall with the heat escaping up and out. That's why I asked if the finned tubing should be taken out of it's enclosure. Also if I figured it right, 10% of 170,000 is 17,000; divide that by 500 btu/ft as you suggest and the result is I need 34 feet of baseboard. Sound right to you? Thanks for your help.

Mike

 

[jebatty]

I would be inclined to take it out of its enclosure and have the bare finned tubing on the ceiling. My ceiling is 9' high and I bought my tubing without the enclosure. I also hung the tubing about 1 ft down from the top of the ceiling to allow good air circulation to get rid of the heat, rather than trap it against the ceiling; hung it at a slope to aid the gravity flow; and put in air vent and an old shutoff valve at the high point to make sure I could purge the air out of it to not get an air lock. Once you put yours in, bring your boiler up to maximum temp with a good load of wood yet to burn, cut the power to the boiler and circs, and give the overheat loop a test.

 

[Chris S]

The numbers below give btu output at 4 gpm flow, and 1 gpm flow at various temperatures. This chart is from Haydon. First of all anybody using it for overheat will probably be up around 210-220, for which the numbers are pretty high, so thats good.
but...notice this is based on 65 degree entering air temp, which may not be the case, and I don't think a good convective flow will occur with the enclosure monted on the ceiling. I do believe that the initial displacement of the water will help lower the boiler temperature, but being able to contiunally disperse btus in the set up described, I wouldn't count on 500 btus /ft. Just my opinion


Table 1 - Heating Capacities, BTU per hr per lin. ft. 65 degrees entering air temp
GPM Hot Water Ratings
Average Water Temperature degrees F
Heat Base

- 150 160 170 180 190 200 210 220 230 240
4 410 480 550 610 690 760 820 900 970 1040
1 390 450 520 580 650 720 780 850 920 980

 

[dogwood]

Jim, didn't know you could get the finned tubing separately without the casing. Is it readily available on line or elsewhere? I will follow your tips on hanging it a foot below the ceiling and on a slant. God only knows what the inspector will make of that. Thanks for your info. Chris, how many btus per foot would you base your calculations on for how many feet of finned tubing are needed? Maybe I should add another ten feet of finned tubing for good measure. what do you think?

Mike

 

[Gooserider]

The numbers below give btu output at 4 gpm flow, and 1 gpm flow at various temperatures. This chart is from Haydon. First of all anybody using it for overheat will probably be up around 210-220, for which the numbers are pretty high, so thats good.
but...notice this is based on 65 degree entering air temp, which may not be the case, and I don't think a good convective flow will occur with the enclosure monted on the ceiling. I do believe that the initial displacement of the water will help lower the boiler temperature, but being able to contiunally disperse btus in the set up described, I wouldn't count on 500 btus /ft. Just my opinion


Table 1 - Heating Capacities, BTU per hr per lin. ft. 65 degrees entering air temp
GPM Hot Water Ratings
Average Water Temperature degrees F
Heat Base

- 150 160 170 180 190 200 210 220 230 240
4 410 480 550 610 690 760 820 900 970 1040
1 390 450 520 580 650 720 780 850 920 980

True, but I would also expect that the need to dissipate excess heat should also go down rapidly over time. In either a boiler overheat, or a no-power condition, the fans on the boiler should have shut down, and possibly other airflow, depending on the boiler design. This should rapidly cause the boiler to drop into "idle" mode where it is only getting natural draft, and not making a lot of heat that would need urgent dumping. Thus that initial surge of cooling should handle much of the excess heat that was present when the loop opened, and the heat production should be going down after that so any falloff in the cooling ability shouldn't be a big issue... The other thing I noticed is that your chart is suggesting that close to 900 BTU/hr would be possible, but Jim's number said figure at 500 BTU/hr - which seems like a pretty good margin right there...

Gooserider

 

[jebatty]

I think the supply houses sell it separately or as a package. I found mine on ebay, no enclosures.

 

[flyingcow]

I got my fintube(for my overheat loop) from an installer. This was given to me. But should be able to pick it up pretty cheap. They'll usually keep the old stuff.

 

[in hot water]

basic residential fin tube is fairly flimsy stuff. It's hard to handle and razor sharp on the fin edges, dents very easily.

If you can, find a section of commercial fin tube with a steel pipe and stiff steel fins, especially if it will be un-enclosed.

Apricus Solar sells a finned convector for a solar dump zone. Looks like a large finned surface inside a simple aluminum frame. The enclosure or box helps encourage convection currents.

hr

 

[Chris S]

Gooserider,
I agree that an EKO, Tarm, or similar boiler would need the initial cooling effect, abd then probably smolder, however some of the boilers do not operate this way. Also, if you were at a roaring burn- at the peak of your burn let's say, you wouln't want to be cut short. I don't know what the answer is as to what number to use.
IF the man. is suggesting 10%, I would consider that as 10% sustained, and test my system under the worst conditions. Hot rodmakes a good point, about the larger commercial stuff. I saved a cast iron radiator, I'm just not sure I want to hang it on my ceiling. I bought dented fin tube last year ( complete enclosures etc) for $ 1 / ft. for a customer who wanted me to heat behind a large whirlpool deck. I'm sure the supply houses dent the commercial stuff as well.

 

[Mushroom Man]

I am really foggy on how the overheat loop works. I hope someone will be patient enough to explain. I might be operating under a misconception but here goes.

Hot flows to cold by convection in the event of a power interruption. Let us suppose there is very hot water in one container say 210 degrees; and 70* water in an adjacent comparably sized container. The two are separated by a valve. You want the hot expanding water to mix with the cooler water to bring down the average temperature so you open the valve using an automated process. The boiler needs to lose 30* and there is ample capacity for the other container to dissipate the 30 degrees. Even if the height of both containers is the same; won't the hot water flow into the cool water and relieve heat from the higher temperature source.

What is the role of gravity here?

 

[Gooserider]

I am really foggy on how the overheat loop works. I hope someone will be patient enough to explain. I might be operating under a misconception but here goes.

Hot flows to cold by convection in the event of a power interruption. Let us suppose there is very hot water in one container say 210 degrees; and 70* water in an adjacent comparably sized container. The two are separated by a valve. You want the hot expanding water to mix with the cooler water to bring down the average temperature so you open the valve using an automated process. The boiler needs to lose 30* and there is ample capacity for the other container to dissipate the 30 degrees. Even if the height of both containers is the same; won't the hot water flow into the cool water and relieve heat from the higher temperature source.

What is the role of gravity here?

Gravity is what makes convection work... When you heat air or water, it expands, and thus becomes lighter than the air or water next to it that hasn't been heated, so it will want to rise. In the case of the heat dump loop, the water in the boiler is hotter than what is in the loop, so it will want to rise up into the loop pushing the cooler water in the loop out of the way. At the same time, the water leaving the boiler at the top pulls in the cooler water from the loop at the bottom, so that it can in turn be heated and repeat the cycle. The hot water that rises into the loop cools, and becomes heavier so it wants to go back down the other side of the loop pushing the warmer water out the top of the furnace - it is equally valid to see the loop as driven by rising hot water, or falling cold water, as both play a part.

However in order for this to work you MUST have enough of a loop for gravity to do it's thing - it also means that you can't have any significant dips in the loop, or the water will just go to the top of the dip and sit there as it can't "see" the rest of the path.

If you had a two bucket setup like you described without a loop, i.e. a single level pipe, there would be no convection flow - the only heat transfered would be by diffusion, which is a MUCH slower process as it depends on the random movment of individual molecules, rather than having a current that moves the entire volume in a single direction... OTOH, with a loop consisting of a pipes connecting the tops and bottoms of each bucket you would essentially see the contents of the two buckets changing places, without doing all that much mixing. If you just had one pipe on an angle, you might see some strange "ghost flow" patterns where the fluid would setup a loop within the pipe so that the top of the pipe flowed one way, and the bottom flowed the other, but it would be less effective than the true loop with separate pipes.

BTW, this is the way that the old fashioned "gravity systems" used to work back in the days before circulator pumps and the like... They were tricky to design and build, and only worked with certain architectures, but a well engineered gravity system was a wonderful thing - heat delivery with no added energy expenditure...

Gooserider

 

[dogwood]

Here is an address to the finned convector Hot Rod referred to: "http://www.apricus.com/html/solar_heat_dissipator.htm". I'll try and run down a price and how many btu's, or how big a boiler, one convector unit can handle Monday, when the dealer in Connecticut may be open. HR, do you happen to know? Looks like a neat and professional looking solution for this application. The product mentions it uses solenoids, and may use metric sized piping, both of which may be matters having to be dealt with. I don't know.

Another dumb question. What is the diameter of the tubing on typical residential baseboard. Is the commercial steel finned tubing HR mentioned typically larger in diameter as well as sturdier? What is typical there? BioHeat mentions in their installation manual that piping to the dump zone baseboard should be 3/4 inch but doesnt mention if the finned tube should be the same size too. What diameter baseboard finned tubing do some of you have in place already? Slantfin has a dizzying array of sizes and baseboards. Some practical advice would be appreciated to save me from making an uniformed choice. Thanks.

Mike

 

[Gooserider]

Here is an address to the finned convector Hot Rod referred to: "http://www.apricus.com/html/solar_heat_dissipator.htm". I'll try and run down a price and how many btu's, or how big a boiler, one convector unit can handle Monday, when the dealer in Connecticut may be open. HR, do you happen to know? Looks like a neat and professional looking solution for this application. The product mentions it uses solenoids, and may use metric sized piping, both of which may be matters having to be dealt with. I don't know.

Mike

The Apricus unit as I read it was meant to be used w/ solar tube systems, so I don't know if it would have enough capacity for a boiler or not. I think it was also designed for mounting on an exterior wall - at least that's what they seem to show in the pictures I've seen of it...

Gooserider

 

[in hot water]

SlantFin is the brand of fin tube I like. Their website has some good data including bare element sizes and output charts.

That Apricus "dump" radiator can handle a 30 tube array. It is small tube coil however, 15mm probably not suited for gravity flows.

The steel fin element is generally 1-1/4 and larger, threaded connections.

hr

 

[Gooserider]

Given that the stuff I've seen on gravity loops suggests that it works best to use large diameter plumbing on them, it sounds like the steel pipe / steel fin stuff would be the way to go. From the spec chart you posted, it also looks like that would give the highest BTU output per foot, which also is a good thing if only to minimize the amount of tube you have to put on the ceiling...

Gooserider