OWB efficiency question

[sw18x]

So as per my last thread, I'm going with thermopex when I re-install the lines for our OWB. On a 60 foot run, at 180 degrees I was losing about 15 degrees of heat from the woodburner to the house. Since 15/180 = 8.3%, then double it for the return run = 16.5 % total heat loss.

Does that mean by refitting with thermopex, assuming a loss of maybe a degree and a half total heat with the new set up, I will use around 15% less wood? Or is it more complicated than that?

 

[leon]

OWB ugh

So as per my last thread, I'm going with thermopex when I re-install the lines for our OWB. On a 60 foot run, at 180 degrees I was losing about 15 degrees of heat from the woodburner to the house. Since 15/180 = 8.3%, then double it for the return run = 16.5 % total heat loss.

Does that mean by refitting with thermopex, assuming a loss of maybe a degree and a half total heat with the new set up, I will use around 15% less wood? Or is it more complicated than that?

----------------------------------------------------------------------------------------------------

Its more complicated than that simply because your boiler will shut down and smoke and it will also depend on your homes energy use and how much insulation you have,

If your buying the $13.00 per foot thermopex you will only lose 1 percent heat loss per per hundred feet if my memory of it is right.

 

[NSMaple1]

More complicated & very fuzzy.

Your 8.3% figure is based on a 0-180 temp range, which is quite flawed as your water would never see the bottom of that range. It might be more practically accurate to use a temp range based on useable temps. As an example, I don't know what you have for heat distribution, but lets pick something that uses low temps, like in-floor. That would give you a temp range of around 120-180, or 60°. So if you were losing 15°, that's a 25% loss. Anything else would likely turn out worse as in-floor gets about the most out of lower temp water than anything else.

Trying to extrapolate that to a decrease in wood comsumption would only be a guess as you'd likely still have some baseline losses that new piping won't fix.

But you'll definitely use less wood - a 15° temp drop is a lot. How that will affect how your boiler operates & the cycling it will do might require some burning & loading practice adjustments.

 

[sw18x]

Thanks - I had a feeling my estimate was missing a lot of science. Bottom line, I'm hoping to go through noticeably less wood, and to get by with a higher percentage of softer wood like silver maple and pine. True hardwoods (locust, oak) are just a fraction of the wood I'm able to scrounge.

 

[mtfallsmikey]

----------------------------------------------------------------------------------------------------

Its more complicated than that simply because your boiler will shut down and smoke and it will also depend on your homes energy use and how much insulation you have,

If your buying the $13.00 per foot thermopex you will only lose 1 percent heat loss per per hundred feet if my memory of it is right.

Correct, and maybe less, depending on your pump setup. I have 90' of lines betwen boiler/house, lose about 2 deg. between supply/return

 

[mtfallsmikey]

Thanks - I had a feeling my estimate was missing a lot of science. Bottom line, I'm hoping to go through noticeably less wood, and to get by with a higher percentage of softer wood like silver maple and pine. True hardwoods (locust, oak) are just a fraction of the wood I'm able to scrounge.

I burn a LOT of pine, it's down, close by.....especially in fall/spring during moderate temps., but use hardwood for the base, so the coals will keep the softwood lit.

 

[jrider]

----------------------------------------------------------------------------------------------------

Its more complicated than that simply because your boiler will shut down and smoke and it will also depend on your homes energy use and how much insulation you have,

If your buying the $13.00 per foot thermopex you will only lose 1 percent heat loss per per hundred feet if my memory of it is right.

Not all boilers smoke when they shut down. My neighbors don't even know when I fire mine up for the season.

 

[Butch(OH)]

Another perhaps larger reason your equation is flawed because you dont have not considered a very important factor, flow. 15 degrees of heat loss at 20GPM would be close to double the heat loss of that same 15 degrees at 10GPM.
All the science aside 15 degrees is a LOT of heat loss at the GPMs these systems normally are set up at. My run is 65 feet and heat loss each way is been very close to 1 degree every time I ever measured it or around 2 for the loop.

 

[sw18x]

Good point Butch, guess the only way to find out for sure is lay down those lines wait 'til November and fire her up!

 

[Iska3]

You might want to look in to ThermoFlex also.. I ran ThermoFlex 150 ft underground No heat loss or maybe 1 degree on my lines. The first year I ran it to the garage about 40 ft ontop of the now. What impressed me is the snow never melted off the outer pipe. My cost was $8.50 per foot and free shipping for a dealer. There is ThermoPlex and ThermoFlex... The key on both types is the closed cell polyethylene foam. Insulated Pex | Insulated Pex Pipe | Insulated Pex Tubing

 

[bower4311]

You guys mean to say that you're only getting a degree or two change running it to the house in the winter? That is mind baffling.

 

[mtfallsmikey]

You guys mean to say that you're only getting a degree or two change running it to the house in the winter? That is mind baffling.

Shouldn't be. Now, if you had a 150-200' run, you could lose some, but the insulated PEX is fantastic. You'll know if you lose a lot, snow will melt right over top of your lines, no matter how deep you bury them.

 

[Butch(OH)]

You guys mean to say that you're only getting a degree or two change running it to the house in the winter? That is mind baffling.

Ya, that's about it plus or minus a half degree. I used quite a bit different system than most as sold by Urecon corp. Expensive but I will never have to dig it up as the Pex can be pulled and replaced if ever needed. My lines are 30-36" deep and I have never seen any sign of them via snow or frost melt. I have seen installations that kept the snow melted all winter long in a 8 ft wide band across the lines :msp_scared:BAD deal!

URECON insulated conduit
View attachment 305472

 

[Richard@PM]

ya, that's about it plus or minus a half degree. I used quite a bit different system than most as sold by urecon corp. Expensive but i will never have to dig it up as the pex can be pulled and replaced if ever needed. My lines are 30-36" deep and i have never seen any sign of them via snow or frost melt. I have seen installations that kept the snow melted all winter long in a 8 ft wide band across the lines :msp_scared:bad deal!

Urecon insulated conduit
View attachment 305472

good stuff ayuh