I wouldn't say that lol. That's unfortunately where half my paycheck comes from. Halliburton and NATO are two of our biggest costumers. I'd rather build green industry stuff but what do you do.
your firebox can hold 60cu.ft. of wood, if packed solid. so thats .46875 of a cord. lets call ash (seasoned) 21MBTU/cord per sweeps. so 9,843,750BTU can fit into your boiler in one load. now here is the cringe factor. OWBs are 30-40% efficient. that yields 2,953,130-3,937,500BTU per load. this actually falls in line with what you dealer stated of loading 4 times/day and gives you your 500,000BTU/hr at 30% efficiency (at least CB knows that they fall on the lower end of efficiency, right?). effinaye, thats almost 2 cords/day. what do we get from wet wood, 40% of the heat of seasoned? so 1,200,000BTU per load times 8 loads/day gets you 400,000BTU/hr. BTW, this is 3.75 cords/day. sounds about right? what can we take away from this? you should be able to get 80% of your design BTUs from 8 loads per day of wet ash wood. now, do you feel you are getting this 80% solution? if yes, great! go get yer wood seasoned and carry on. but man that is a lot of wood fetching. if no, you have heat loss or lack of pumping or both. back to square one...
Wow man thanks for all the work on this. I think so seasoned wood will be where I need to be. Plus I am about ready to start a large account requiring me to have about 4 employees. I am going to have help on keeping boiler up to temp in the future. Plus I will have much better wood. Like I said before when I put dry wood in there the boiler heated that greenhouse up pretty well when it was 10 below. I am also going to research better ways to insulate before next winter
Maybe I'm missing something but there is a lot of talk about slowing down pumps and blowers to ensure that the water gets to a higher temperature.. If pumps and blowers are slowed down, won't the water continue to return to the boiler at a low temperature thus having a negative impact on the firebox temperature causing a more inefficient burn? Why not just install a mixing valve that re-routes hot supply water back to the return side to ensure that boiler input temperatures are where they need to be? It would solve the problem of the "cold start" every time the boiler is reloaded by having a smaller closed loop through which the water circulates until higher temperatures are sustained. If this had no impact on the efficiency of the burn, it would of course cause lower temperatures at the heat exchangers. The theory, however, is that a higher temperature water jacket leads to a more efficient burn and thus more BTU's extracted from a given amount of fuel. Haven't seen anyone mention NoFossil's site yet.... Lots of good information there.... With good wood, Hydro Farmer will not only be heating his green house but an outdoor hot tub too!!!! http://www.nofossil.org/ Good luck....
Had a mixing valve. It cooled down in the greenhouse on a super cold night and rerouted water back allowing lines to freeze up. I removed it. Better off having Luke warm water circulating vs none that freezes. I will put glycol in this summer when I can afford the 2k
Fair enough... Too bad you couldn't locate the boiler inside the greenhouse so the heat from generation isn't lost to the outside.
Sorry, can't answer your question but had some thoughts. I agree with several suggestions posted so far... Compartmentalizing, using dryer if not ideally dry wood, etc. and while water barrels may not be ideal thermal mass/thermal lag and multi-step heat approach may help modulate things. Also thinking your boiler just can't keep up, unfortunately... And propane is pretty weak btu per unit but sometimes you have no choice if you can't run oil. Years ago I helped a friend with a smaller greenhouse, 24x90 I think. He wasn't super proud of it he ended up w/ two boilers; first one was piped pretty close to greenhouse and had 8 loops from the manifold (covered this in a eps and duct tape box) into a 6" 4000psi concrete slab, boxed on bottom and edges with 4" rigid, foil-faced polyiso, edges rose up about 18" with 12" block wall, reinf.'d/cores filled, double wythe (one each side of the insulation); ext. grade was only a few inches down from top of block walls. Had roughly 12" of #1 or #2 stone under it all, trying to keep it dry underneath. I don't recall the exact btu and efficiency, but these were not small boilers. He also had an airlock/vestibule, not sure how much that helped. In central Maine the slab could hold at about 35-40deg in light overnights in the single digits and teens without getting up every 3 hrs to pack it full again. I know, slab may not be in the cards but 24" bed of crusher run or #1 stone underneath, surrounded with insulation, may help. We didn't know how the slab would do, or whether he wanted to grow year round or what temp he absolutely had to maintain, but we figured it would need more if he wanted to grow all year. It's not the best thing but the second boiler fueled a couple exchangers a little bigger/deeper than yours, fans ran slowly and pretty constantly... three phase so not too worried about power. This did the supplemental heat for the rougher nights and got him through the -15-20F stuff in the 50s. He went through a lot of wood in any case but I also recall he was ok with temp fluctuations of about 10-20 degrees. Good luck tweaking your setup!
throttling back the pumps likely wouldnt help but it is something easy to try. theoretically it would return cooler water to the boiler but less volume so theres a chance the boiler would then be able to keep higher temps. if the fans were slowed down then less heat would be extracted out of exchangers thereby increasing return water temp.
If you are dropping 5 degrees between your boiler and your heat exchanger that is 100k btu like previously mentioned. That is some serious line loss. 40 gallons per minute x 60 minutes x 8.3 btu per degree per hour x 5 degree drop is 99600 btu. Now that is one way and you are loosing something similar on the way back. Now your 500k btu boiler is a 300k btu boiler. Lets say your boiler is really a 300k boiler to begin with using your wet wood. Subtract your 200k btu of loss and you have 100k of usable output or roughly 1/6th of your propane system.
i will say it again, 5* is a lot. especially with the volume you should be flowing. my lines are underground for ~120' and is see 1.0-1.5* loss at 3gpm. while we are on flow, your circs are working much harder than they were designed to. expect thier life to be short. if it were me, and even moreso if my business depended on it, i would have a spare one on hand. at a minimum i would take one pump offline and see how the system performed and decide if it could limp along running on one pump until a replacement can be installed. i guess not really a big deal if you have propane to back it up tho. idk if it messes with warranty, but maybe see if you could source old antifreeze from an auto shop. in the meantime keep the circs running constant and have the propane kick on if the temp in greenhouse falls too low.
revisiting this, 100kBTUs is IF 40gpm is true. but 40gpm is the max that pump can do, at 0 head. even with two pumps he is not cycling that much volume with little 1" PEX. kick me running if i can find a reason that most OWBs use 1". for things to work properly delivering 500kBTUs he needs 52gpm at deltaT=20*, 21gpm at deltaT=50*. thats with 30% glycol solution.
I agree 100%. That was just a quick back of the hand calculation. The heat loss is significant though and combined with wet wood and the 1" pex you are no where near 500k. My brother has an e-classic that is half that size and he ran 1 1/4 pex even though 1" is recommended.
I myself wood not worry about the glycol if your doing okay with the terrible setup and the way things are now next year as long as you learn and improve from this year (sounds to me like you know what you need to do) next year will be a breeze. As far as mixing valves and water return temps being low if anything i would put a faster pump in. You want the return temp to be within 10 or better degrees of supply temp. Of course your going to have heat loss between supply right front the boiler and return to the boiler that's kind of the point isn't it? More gallons per minute will help you achieve this. Also what do you have your boiler set at for a temperature and differential, mine right now is set at 175degrees and a10 degree differential. (Just a reference not telling you what to do)
Also with your homemade line holding your water lines how warm is it?can you put snow on it without it melting? How much line is exposed outside? If it feels warm to the touch,that's bad if it melts snow that's bad lol. See how much heat your losing just with that line and if it's significant i would build a small box around it abd insulate some more
I wonder if adding storage inside the greenhouse envelope would help or hurt? I really don't know. Seems like you could add some insulation even though it is a hoop house. What orientation is the house? If you have a long side with a N/S exposure you are getting little if any solar gain in the winter. Insulating the N wall even a little would help exponentially. I used to work in a wood fired green-house (later converted to NG). We didn't grow year round but when starting plants for spring (about now) we would insulate the end walls of the greenhouse because they added no value to solar gain that time of year and it was easy to do. We just tacked up some R13 batts. It helped a lot...and they came back down when we stopped heating. Insulating the side walls would be more difficult...but adding anything, even to the outside, would help. XPS fan-fold?
if no glycol, what then happens when there is a power outage in the winter? you are going to need a crazy high flow rate to deliver 500kBTU with only deltaT=10*!
