Hey Greg or Yanche: Water Coil Question for Ya

 
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SMITTY
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Post by SMITTY » Sat. Aug. 09, 2008 1:34 pm

I was thinking of buying the 21T coil http://www.hilkoil.com/product.htm#table , or 2 of them, & installing in my new Mark III (92K BTU)

What I want to do is plumb the coil (or coils in series) into my oil furnace with a continuously running circulator. I don't need to maintain 180*(although, the more the merrier ;) )-- I'd like to have a minimum of 150*, just to be able to make hot water for the Amtrol indirect-fired tank I have ( set @ 125* ) & heat 1 room upstairs (has 22' of hydronic baseboard). What I plan to do is disconnect the electrical connections to the oil burner, but leave power to the aquatstat & Amtrol unit so that the Amtrol circulator will run when called for & the circulator for the baseboard heat for that 1 room will run by thermostat upstairs.

That one room will get down into the low 50's to upper 40's on a single-digit night, even with the stove running -- so I figure that even if I had 120* flowing thru the baseboards it would be enough to at least warm the room somewhat.

I read a post of someone who had 7.2 feet of coil in their stove & was getting 180*. So 2 of the 21T coils should do the trick, I'm thinking.

What do you guys think? Also, how close to the fire can you put these? Can you pile coal right on them & have them in the center of the heat, or will it melt the outside of the stainless?


 
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Post by LsFarm » Sun. Aug. 10, 2008 9:42 am

Do not bury the coils in the coal, leave room between the coils and the fires so you can stack the coal and not hit the coil with the shovel.. I'm not sure you will get enough heat for 22' of baseboard, but it's worth a try,, and like you said. even warm water circulating in the baseboard will help.

I'm not sure I'd use two in series,, if you try this, I'd plumb them with ball valves so you can swap between parallel and series.

Greg L.

 
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Post by SMITTY » Sun. Aug. 10, 2008 10:33 am

Thanks for the info Greg.

I was thinking that if I plumbed the 2 coils in series that I would get more heating ability out of the furnace.

If I did the 2 in parallel, I could run one to the Amtrol coil, & plumb the other directly into the zone (but then it would have to run continuously without thermostat). I've thought about both ways, but I figured that series into the furnace would be the easiest & simplest install -- that way I only connect one pipe to the boiler return, & the other to the boiler drain (circulating through the coolest part of the water).

What would be the advantage to parallel plumbing? Do you think the 2 in series would be too much?

 
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Post by LsFarm » Sun. Aug. 10, 2008 10:41 am

My concern with running them in series is that you will hit boiling temps inside the coil when the water makes it's second pass,, Traderjp made a custom coil that has many passes in his stoker stove,, but that is a much smaller fire.. and a much better controled fire than in a hand fired stove.. You don't want the water to flash to steam, and blow off the PRV all the time..

I'm sure some of the people with coils installed will soon add their experiences and ideas...

if you set it up to circulate continously, then maybe the temp drop through the baseboard will be enough to keep the temps under steam..

Greg L
.

 
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Post by SMITTY » Sun. Aug. 10, 2008 11:09 am

Ahhh....now I see. ;) I didn't think of the steam scenario! :lol:

This could work out good, because I can just leave that room's thermostat at 85*, then when I go to bed I can turn that one off & turn on the one upstairs. I have a circulator that's been kicking around since I installed the Amtrol, so I'll use that one wired to either a switch or something that will turn it off below a certain temp. I think I have plenty of heat loads to prevent steam.

I think I'm going to order those coils now. 8-)

Thanks again for your help Greg! :up:

I'll keep everyone posted on the results this winter -- I should have it up & running by the first week of November, unless it's in the 80's that week :funny:

 
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Post by Adamiscold » Sun. Aug. 10, 2008 6:44 pm

Smitty don't forget the pictures ;)

 
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Post by coaledsweat » Sun. Aug. 10, 2008 7:17 pm

LsFarm wrote:You don't want the water to flash to steam, and blow off the PRV all the time.
It can't flash to steam without a headspace (air present).


 
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Post by LsFarm » Sun. Aug. 10, 2008 7:55 pm

Hi Ian,
Maybe my terminology is wrong,, but if water gets hot enough, and there is inadequate pressure in the system, won't water start to boil and create steam?? This then takes up more space than the water, and the combination of the heat, expansion and resulting pressure causes the PRV to open?? This then drops the pressure, and more water 'flashes' or instantly turns to steam... ??? I think this is the right scenario that could occur in an overheated coil in a stove??

Greg L.

 
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Post by coaledsweat » Sun. Aug. 10, 2008 8:05 pm

Yes, over time the boiling water will eventually build up a head of steam but flash is instantaneous. If the water is circulating it would need to exceed 300*+ or so before that starts I would think.

 
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Post by PelletstoCoal » Mon. Aug. 11, 2008 7:32 pm

Steam is governed by the noble gas laws, pv=nrt, thus pressure is directly proportional to temp. Greater pressure in the system so increases the boiling temp. remember science class, place water in a vaccume and it will boil at room temp. as long as the circulator is running full time (24/7) there should not be any problems (guess on my part) as per your upstairs heating requirements. Perhaps you should consider eliminating the human error factor from the system and design the pump to run on parity with the stove via a thermal snap switch (stove hot/pump on)and let the thermostats operate some zone valves or install another circulation pump for the upstairs room. If I understood your post, you would have to jockey thermostats to control pump, and there is a chance of zero circulation while the stove may be running. This could result is serios damage to you, your stove and your home. Water to steam in confined areas can be explosive. If I repeated things already said , sorry did not mean to, just airing caution.

Found some data regarding baseboard, @ 1gpm 130 deg supply yields 260 btu/hr/ft vs. 580 btu/hr/ft @ 180 deg. supply @ 1gpm, increasing flow to 4gpm gets you 220 and 610 btu/hr/ft. I did this in a section of my home (135-140 deg. water into baseboard) with mixed results. Ok until temp drops below 30 deg.

Frank

 
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Post by SMITTY » Mon. Aug. 11, 2008 9:30 pm

Adamiscold wrote:Smitty don't forget the pictures ;)
I'll be taking many! ;)
PelletstoCoal wrote:Found some data regarding baseboard, @ 1gpm 130 deg supply yields 260 btu/hr/ft vs. 580 btu/hr/ft @ 180 deg. supply @ 1gpm, increasing flow to 4gpm gets you 220 and 610 btu/hr/ft. I did this in a section of my home (135-140 deg. water into baseboard) with mixed results. Ok until temp drops below 30 deg.Frank
Frank, that's some great info -- a 50* rise in temp yields over double the BTU's -- :shock: I wouldn't have never figured that! I'm familiar with the pressure/boiling temp. relationship from automotive & motorcycle cooling system work, but I forget the details.........is it a 10 degree increase in boiling temp for every 1 PSI or do I have that backwards .. or am I thinking elevation to boiling temp? I think that was 10* per 1000' rise.

The coil is going to be plumbed from the stove directly into the furnace, which is basically a tank of water. My only concern is what you mentioned -- what if my circulator of unknown age decides to take a dump 15 minutes after I leave for a 14 hour day! :blowup: NOT good. But I'm figuring that the volume of water, plus the PRV & expansion tank on the furnace already will take care of a pressure spike, & may even circulate by convection -- although I'm not sure on that due to the way I may plumb this. The plan is to circulate the water thru the lowest part of the boiler (which is coolest) & then return to the stove thru the other side of the boiler at that same height -- the bottom. I figure the circulator will mix the water of different temps. & send the heat up top, where the baseboard & hot water supply are. But if the circulator craps out, now the hottest part is higher than the coolest -- not conducive to convection. A sudden spike in pressure would force some movement in the water, I would imagine.

I'll have to do this project on the weekend so I can monitor things! :gee:

 
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Post by PelletstoCoal » Tue. Aug. 12, 2008 12:14 am

Not sure regarding the altitude/temp question, but I can get back to you about that. I have an old data table around here somewhere. However, to answer your circulation question, I think you are refering to a Thermal Siphon. The principle operates with the water storage tank (i.e. cold water) elevated above your heating source. Cold water has a greater density so when heated water is introduced into storage tank a thermocline is formed, warm on top to cold to the bottom. In on top, out on bottom, but the question is what is the elevation differential of the stove vs. storage tank (your case the boiler). I do not think 22' or so of baseboard upstairs would give a sufficient push of water. Your thermal siphon flowrate (gpm) may be too low allowing too much contact time within the coil assembly for a comfortable saftey factor. Designs can be worked out on paper, but sometimes it is best to do as you stated, do a controlled test and modify as required. Just remember to place a PRV close to the coil, preference to be at the high point of the coil assembly.

Frank

 
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Post by beatle78 » Tue. Aug. 12, 2008 3:39 pm

As water temp rises, the amount of space the water consumes rises. When there is no place for the water to go the pressure of the water in the system rises. I think this is what makes the PRV valve blow.......

Disclaimer: I have no clue what I'm talking about. But a read "pumping away" last night and I think that topic was discussed. :D

 
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Post by BIG BEAM » Tue. Aug. 12, 2008 8:00 pm

BB heat doesn't do much at 140F like the old cast iron radiators.You need 180F and up for BB to work well.I would run that zone with 1 coil and a constant run circulator to start.Keep in mind that you are only trying to raise the temp in the room 20F or so and with 22' of BB puting out 250ish BTU's/ft even at 140F your getting 5000 BTU's.That's about equil to a 1500W electric heater on high.
BUT KEEP IN MIND THAT WHEN NOT IF THAT CICULATOR FAILS THAT COIL WILL GO INTO STEAM.You could just run a gravity system
DON

 
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Post by SMITTY » Tue. Aug. 12, 2008 10:05 pm

I'll probably buy a Taco just to have a backup & install both on some type of relay -- one fails, the other takes over. If this was a 12VDC system I'd have this all figured out by now. AC is semi-uncharted territory for me (except for the basics - black white green). Never seen an AC relay -- can't think of a use for one either :gee:


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