Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: woodman on December 03, 2017, 07:04:01 AM
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Hi guys. Will a flat plate hx have output water that eventually is the same temp as the owb input hot water if that same water is circulated through the hx on the domestic side. In other words if I am using 180 degree water from my owb will the hx put out 180 degree water if there is no load, or is there a loss through the exchange that is not recovered in the water?
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Most aren’t plumbed to continuously circulate thru the plate, normally you install it on the could side of the water heater, when you open a tap water flows thru the plate and into the hot water heater tank, only the amount you use flows thru the plate, fill a gallon jug with hot water and a gallon of cold flows thru the plate.
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My 50 plate on my indoor boiler loop gets the water to within about 10 degrees of my owb water if I run it continuously circulating water. I would think with a no call for heat that it would get close but according to my temp gauges it doesn't. It doesn't make much sense to me but those this is what I see on my gauges even after calibrating them to the same temp on the same thermowell and then putting them in their respective wells.
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You can easily match temps within a couple degrees with a properly sized plate. This will depend entirely on plate size and flow rate. A typical water heater is piped in 3/4" pipe which can only flow ~4 GPM with all fixtures running, while a typical boiler loop flows 6-8 GPM constantly. For example, I run a 5x12" 40 plate in my own house. A week or two ago we were having this discussion and I took some numbers from my system. With 2 showers and 3 faucets all running wide open I was getting about 162 off the inlet to the tank. With just one shower running which is typical in my house, the inlet was 168. Boiler water temp was also at 168 on the inlet of the HX. That's only 1-1.5 GPM of domestic with 8 GPM of boiler flow so apples to oranges, but it is possible to do when properly sized
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Do you want the domestic water to get up to furnace temp? I personally prefer about 140, safer and you don't run out. I've seen dairy barns need to go hotter though..just asking to understand how you're using it.
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Do you want the domestic water to get up to furnace temp? I personally prefer about 140, safer and you don't run out. I've seen dairy barns need to go hotter though..just asking to understand how you're using it.
Well its kinda a long complicated story but to summarize I am separating a open system from a closed system.
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Do you want the domestic water to get up to furnace temp? I personally prefer about 140, safer and you don't run out. I've seen dairy barns need to go hotter though..just asking to understand how you're using it.
Well its kinda a long complicated story but to summarize I am separating a open system from a closed system.
Well, yeah. Domestic always needs to be separated. Can't drink boiler water. Anything hotter than your water heater setting will keep it from kicking on, but the more, hotter water you pour into the tank the longer it will last after you mix it on the outlet of the tank. It's all a matter of personal preference how hot you want it to be
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Or was the term "domestic" misplaced and you're using the closed side for heating purposes? That's a different can of worms
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Or was the term "domestic" misplaced and you're using the closed side for heating purposes? That's a different can of worms
Lol! I'm not too smart but I know better than to shower in boiler water. This is not a dhw application it is a buffer tank application. I'm making a change and incorporating 1000 gallons of storage. I was going to seperate the buffer from the storage to promote stratification within the storage and buy some time while I make some plumbing changes on the house side.
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OK, making more sense now. I bunny trailed off on water heater ideas... :)
I would imagine on the storage tank side you'd want to minimize flow to promote stratification, so a variable ecm circulator like a B&G Ecocirc Vario would allow you to turn it way down. A really long flat plate helps match temps better than a shorter one. Counterflowed of course. Pull off the bottom of the storage tank to be heated in the flat plate and dump in the top.
Just some ideas.. hope I'm following you and giving accurate info.
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I don't know that I'm following.. Separating the buffer from the storage? They are the same thing, do you have 2 tanks? I think I need to sit this one out- what I'm understanding of your setup is that you want to have 1000 extra gallons of hot water to continue heating a space while you change some plumbing in the house. Storage between the boiler and tank won't do any good if you can't keep flow in the house right? I must be looking at this all wrong because I don't understand what you're trying to do
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I don't know that I'm following.. Separating the buffer from the storage? They are the same thing, do you have 2 tanks? I think I need to sit this one out- what I'm understanding of your setup is that you want to have 1000 extra gallons of hot water to continue heating a space while you change some plumbing in the house. Storage between the boiler and tank won't do any good if you can't keep flow in the house right? I must be looking at this all wrong because I don't understand what you're trying to do
Yes I have 2 tanks and storage and buffer are not the same in this case but that is beside the point. Let me ask it in a different way. If I was installing a open owb system to a closed indoor boiler rated at 100,000 btu with a plate exchanger between them, what plate hx would give the highest water temps in the indoor boiler. And what would the expected water temp be in the indoor side assuming 180 water from the owb?
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I have a owb open system that is plumbed to my indoor oil boiler system through a primary/secondary loop system. I have a primary loop that has a 50 plate plumbed into it. The primary loop has a circulator on it that is powered up when the house thermostat calls for heat. My oil boiler and my hydro air box are both secondary loops off the primary loop. I used to have my primary pump 24/7 and my water temp in the primary loop would run around 8-10 degrees below what the owb was supplying to the flat plate. It has never made any sense to me since a no load on the primary loop should result in temps on both sides of the flat plate reaching very close to the same temp. I don’t know why this is but it is my expierence.
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I have a owb open system that is plumbed to my indoor oil boiler system through a primary/secondary loop system. I have a primary loop that has a 50 plate plumbed into it. The primary loop has a circulator on it that is powered up when the house thermostat calls for heat. My oil boiler and my hydro air box are both secondary loops off the primary loop. I used to have my primary pump 24/7 and my water temp in the primary loop would run around 8-10 degrees below what the owb was supplying to the flat plate. It has never made any sense to me since a no load on the primary loop should result in temps on both sides of the flat plate reaching very close to the same temp. I don’t know why this is but it is my expierence.
OK now we are getting some where. Think of my buffer tank as the primary loop.
Next, I like to have the water constantly circulating through the forced air hx. This way it always produces a little heat radiating out of the registers even when the blower is off. To me that provides a very even heat feeling rather than the shivering than sweating feeling of a traditional cycling forced air furnace.
However If I went directly from my storage to furnace hx with a 24/7 circulator I would not get much in the way of storage tank stratification. This is why I was thinking buffer tank in the middle. I would like this tank to mix and act similar to the way a owb water temp does cycling between setpoints.
Honda, is your flat plate plumbed counter or parallel? Would a larger hx allow you to get water temps closer to the owb?
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Lets attack this one point at a time here.
On the running water through the water to air hx 24/7. This can lead to undesired temp rise in the home depending on what your heat loss is like for your house. The way that modern hot air systems run is low cfm and lower register temps. What this does is it keeps your house from getting hot super fast and then cooling down resulting in that uncomfortable feeling that traditional hot air systems have. So what I have done is I run my fan speed on number 1, slow and my register temps are around 110-120. This keeps my house even all the time. Balancing your system with the dampers in the hvac ducts also keeps a nice consistent flow of heat to the home and you can direct a little more to larger rooms and less to smaller rooms. My whole house is 1 zone and the entire house is at the same temp all the time. I used to get the hot and cold swings. Those are gone. I have also calculated with my temp drop of my boiler being 3 degrees of 200 gallons and my indoor hvac running for 8 mins every time it cycles it comes out to be about 900 btus per minute that my system puts out.
Why do you want a buffer tank?
So a larger flat plate would give you more surface area to exchange more heat in one pass through. The thing is with my system I would run the pump 24/7 circulating water around the primary loop through the flat plate with no load. It would only get within 8-10 degrees. I don't know why that is, it doesnt make sense. Adding more plates shouldnt help this because again, there is no load.
My flat plate is plumbed counter flow.
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Honda what are you measuring to come up with that 8-10 degrees? Is the oil boiler side of the HX circulating at the same time the OWB side is? Assuming just a short loop through your fan box and back or is there a bypass on the A/W exchanger or what? If they are both circulating you will catch up at some point right? Return temps will get higher and higher every exchange under no load until you are matched.
Woodman, storage and buffer tanks are the same thing- it's how you choose to use them that differentiates. Potato/potato. That's neither here nor there though. If you want constant circulation through your coil, as you said this will limit stratification by drawing through the tank 24/7 so a secondary tank with a shunt pump to keep mixed is what you're after, right? That way when the entirety of tank #2 gets below temp, it will draw hot water from stratified tank #1, and that replacement water will be reheated by your plate HX from the OWB loop. Am I on the right page now?
As for the plate, the short answer is yes- bigger is better. A 5x12 HX with 20 plates let's say will pick up 60 degrees at 5 GPM. Now that same 5x12 with 40 plates, you may be able to pick up 100 degrees with all other things equal. There comes a point where flow becomes a factor and you may need to go to a bigger plate (like 10x20) for port sizing to keep X amount of flow, but residentially that's all but unheard of. You need to know the GPM, heat load, and desired temp on both sides of the plate to be able to properly size an exchanger. As I said before, it's entirely possible to match temps on both sides but it depends completely on the aforementioned variables to size the plate accordingly. For what I think you have going on, assuming 7 GPM on the OWB loop and 7 GPM through your A/W exchanger, I would assume you'll want to minimize recharge time for the storage/buffer tanks. Matching temps with equal flow on both sides is going to require a BIG plate- like an 80 or 100 plate 5x12 or a 20 plate 10x20. You can downsize a little bit by reducing flow through your A/W coil to say, 4 GPM which will help recovery time across the plate but to minimize recharge time go big. Keep in mind this is going to pull your OWB down like a freight train during the entire recharge cycle, so hopefully it's got a full firebox at recharge time
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I should revisit this conundrum that I had with the two sides of the plate not being able to reach equal temps because it has never made sense. Thinking about it some more I bet what is happening is that the oil boiler which is plumbed into the primary via a secondary loop and is cast iron would thermosiphon some cold water from the boiler into the loop keeping it from reaching equal temps. I bet that if I had run the flat plate with the oil boiler up to temp the issue would go away. I ll have to do some investigating by turning off the boiler valves on the secondary loop.
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Wreckit, Yes I believe we are on the same page now.
Wreckit, Honda,E Yoder, So are we all now in agreement that given enough time with constant circulation during a no load situation on the house side the temps on both sides of the exchange should equalize regardless the size of the Hx? And that the size(number of plates) will determine how quickly the temps equalize?
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Correct.
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Yes, the size (there are lots of sizes) and # of plates and flow rate on both sides of the flat plate determine the rate of heat transfer- how fast it equalizes, the last few degrees will be very slow.
Counterflowing is critical. I would agree with Honda that convection flow in the ducts can be problematic in warmer weather. Some ducts are worse than others (low returns).
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I hope your 1000 gallon tank is very well insulated or you will be loosing an appreciable amount of heat from it. Any size plate exchanger will have some temperature difference from one side to the other unless there is no flow at all. The slower the flow the closer the temps but they are not 100% efficient thus the difference.
For my DHW I use a 10 plate in the hot discharge line of my electric w/h and flip the breaker off to the w/h. We do have to be careful with the water temp but have gotten used to it over the years.
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I hope your 1000 gallon tank is very well insulated or you will be loosing an appreciable amount of heat from it. Any size plate exchanger will have some temperature difference from one side to the other unless there is no flow at all. The slower the flow the closer the temps but they are not 100% efficient thus the difference.
For my DHW I use a 10 plate in the hot discharge line of my electric w/h and flip the breaker off to the w/h. We do have to be careful with the water temp but have gotten used to it over the years.
I will disagree with this as I've done it several times. It's very possible. Might I ask what your temps are off the 10 plate? I recently dropped from a standard 30 plate to a 20 on my DHW installs and have been having very good luck so far keeping outgoing water above 120, but I pipe them pre-tank for some storage with a mixer on the tank discharge. Just curious how a 10 does
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I think some of what we're dealing with is theoretical v. what we normally see in real life. (The equalizing temp thing). So many little variables, heat loss off piping, etc.
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I'm working on a shop/house combo right now with a combined floor area of 9120 square feet. 29 loops of radiant in 3 zones, a 200k forced air unit heater, 120k A/W furnace coil, and domestic water all served with an OWB. Boiler is supposed to arrive Friday, so as soon as the overhead doors get installed I'll have it fired up for the drywall crew and let you know how the 20 plate 10"x20" exchanger performs, but it'll be apples to oranges with double the GPM on the radiant side over the OWB side at full draw. Despite my repeated nagging about getting bigger underground, he only buried 1" Thermopex because the CB dealer said it would be enough. This one I don't want to match temps since it's only radiant, but it should be interesting nonetheless
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I'm working on a shop/house combo right now with a combined floor area of 9120 square feet. 29 loops of radiant in 3 zones, a 200k forced air unit heater, 120k A/W furnace coil, and domestic water all served with an OWB. Boiler is supposed to arrive Friday, so as soon as the overhead doors get installed I'll have it fired up for the drywall crew and let you know how the 20 plate 10"x20" exchanger performs, but it'll be apples to oranges with double the GPM on the radiant side over the OWB side at full draw. Despite my repeated nagging about getting bigger underground, he only buried 1" Thermopex because the CB dealer said it would be enough. This one I don't want to match temps since it's only radiant, but it should be interesting nonetheless
Ok I appreciate that. I hope this guy has a mountain of firewood ready! I also don't see how that system will work with that 1" line though. Even if he forces 10-12 gpm with a oversized pump a Delta t of 20 would be what 100k-120k btu's? Try to pull more and send ice water back to the boiler that 3 way valve won't allow much heat to the system. Should be interesting alright
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Wreck. Do you think maybe he'll need a buffer tank to make that 1 inch line work? The floor can eat off the buffer tank on a call for heat and the owb can charge the buffer while no Zones are calling.
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Wreck. Do you think maybe he'll need a buffer tank to make that 1 inch line work? The floor can eat off the buffer tank on a call for heat and the owb can charge the buffer while no Zones are calling.
I was thinking the same thing. I bought my 1000 gallon propane tank for a 100 bucks at a scrap yard.
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Wreck. Do you think maybe he'll need a buffer tank to make that 1 inch line work? The floor can eat off the buffer tank on a call for heat and the owb can charge the buffer while no Zones are calling.
That has already been discussed, but he doesn't like the idea. I told him a dozen times to upsize the underground and explained why, but his dealer "does it all the time" so he listened to him. Crappy part is that the line is buried under the building and is not in a sleeve for future replacement, with the mechanical room being dead center of the building. There will only be room in the mechanical room for about a 60 gallon buffer if anything. The upside is that the boiler holds 400 gallons of water and he has 10" walls in the building, so we may or may not be alright. All three zones calling at once is going to pull 15-18 GPM of mixed water so probably 6-9 across the plate. Putting a 26-99 on the boiler so I'm hoping for a full 7 GPM in 3rd gear but who knows. There will only be 1 PEX elbow and 4 male adapters in the loop to choke flow, the rest is full 1" copper inside. I'm afraid the return temps are going to be pretty cold but if we bump the supply temp up to the top hopefully stay above 150. The thermostatic valve is not getting installed, I want to see how it performs without it first. Didn't mean to hijack your post woodman, sorry about that
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Maybe Marty can bump this to a new thread.
What about doing a primary loop in the back of the owb, then run a big delta on the line to the building. Could cut the needed flow rate in half.
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Was a heat loss calc done?
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No heat loss calc was done. As far as the primary/secondary deal, that was my thought if the return temps end up being too low. The building will still require the same amount of flow P/S or not, so the way I see it there will be no benefit unless the return temps are too low but perhaps I'm missing something. Huge delta shouldn't hurt the boiler as long as return temps are above condensation right? The damper will probably be open forever, but if the same load is applied to the other end, I'm thinking the boiler is going to run just as often with P/S as it would in a single loop
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Woodman has your question been answered? I only brought up my deal to say I might have an example in the near future- totally wasn't planning on hijacking your thread. I'd rather keep on your topic if you're still needing information
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Woodman has your question been answered? I only brought up my deal to say I might have an example in the near future- totally wasn't planning on hijacking your thread. I'd rather keep on your topic if you're still needing information
I think I am good. I have a hx on order but will be out of town for a couple weeks so it may take a while before I can report back, between vacations and Christmas. It's fine with me to keep this thread going the direction it is. It will be interesting to see how this turns out. I too have a very large and complex heat load and am making changes to address some of the possible problems I think your customer may run into. It will be interesting to compare notes when both are up and running.
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No heat loss calc was done. As far as the primary/secondary deal, that was my thought if the return temps end up being too low. The building will still require the same amount of flow P/S or not, so the way I see it there will be no benefit unless the return temps are too low but perhaps I'm missing something. Huge delta shouldn't hurt the boiler as long as return temps are above condensation right? The damper will probably be open forever, but if the same load is applied to the other end, I'm thinking the boiler is going to run just as often with P/S as it would in a single loop
My thought with P/S was that if the radiant ran at a lower temp than typical 180 furnace temp you could could mix down at the manifolds and supply in from the owb at 180, back at perhaps 120 or 140 (or whatever the return floor temps are). Your delta can double or triple and the primary loop prevents condensation. The huge delta reduces the required flow rate to move the same btu's.
But this is all depending on the mixed down radiant temps. So may or may not be of much use. Almost an injection mixing idea.
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Yoder, I think we may be on different pages. My boiler loop here hits the domestic HX first, then to the A/W in the furnace, then to the 200k unit heater in the shop, then the 10x20" HX before going back to the boiler, all in series. If there is P/S at the boiler, the heat loss will be the same through the building as it is now, so the temps in the underground loop would be identical regardless of how it's piped at the boiler, right? The radiant is all run in a closed system (you know how I like atmospheric radiant) off of that 10x20 HX, with all 3 zones having their own pump and mixing valve. I'll start with all 3 zones at 100 degrees as a baseline and see how it performs, that way the flow rate through the boiler loop remains the same regardless of load. P/S inside the mechanical room may have a little benefit from a no-load flow standpoint, but P/S at the boiler would only be for boiler protection if the return temps get to be too low due to the huge delta T. With all 3 radiant zones pulling at once, say 100 degrees, while the boiler loop is hypothetically still 170 into the 10x20 HX at 7 GPM, we're still looking at only 6-8 GPM through the plate on the radiant side instead of the full 15 because much of the return water will be recycled. With that, let's call it 80 degree return temps from the floor. Doesn't take a ton of new heat to inject from the plate to make it back to 100 right? So even if I'm getting 130 off the plate, should still be great plenty to feed all 3 zones while keeping the boiler loop above condensing temps. This is why I push closed systems, to keep max flow in the boiler loop. I spent many a night awake designing this system to work with what he's got, and I'm fairly certain it'll work just fine. The unit heater in the shop will almost never run at the same time as the 21 loops of radiant in there, it's only backup if he brings a semi in and wants to heat it up quick- at which point the air temp would satisfy the radiant stat and shut it down, so that's a huge weight lifted right there
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Makes sense.
I mentioned P/S at the owb for return water protection, not to change the BTU load.
The main loop to the building doesn't change temp or delta whether it's one loop or P/S like you said. And yeah, it would need the flow you mentioned to be enough for dhw and fan coils. I missed that, Duh Eldon.
You've got a good plan, sorry about the bunny trail.
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Something more on subject-
I'd love to find a flat plate sizing calculator online to input various flow rates and temps and it would give you BTU rates, delta t, pressure drop. I can email our supplier but it's slow.
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Yoder. Can the company give you the equation they use?
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That would be a fantastic option. I'd love to have it simplified vs guessing but I feel the variables may be too great?
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I don't know what formula they use, there would be quite a few #'s in the mix. And flat plate sizes. Probably would have to buy a program.
Would be interesting to swap plate numbers , sizes and watch the output temps change..
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Here is the cluster in question Yoder, just finished piping last night. Waiting on insulation and the OWB delivery before I can fire it up and put it to work
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:thumbup:
How many feet of the 1" Thermopex underground?
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Too many. I think he said 170ft :-\ Looking at some online calculator thing this morning, it's looking to me like even if I'm able to keep 7 GPM through the boiler loop and put 170 into the plate, the return temps will need to be down in the 110 range in order to get 130 out of the plate on the radiant side :bash: Looks like P/S is in order. 15-58FC in the primary between supply and return ports with a pair of closely spaced tees and a 26-99FC pumping the secondary loop to the building? I can honestly say I've never done a P/S at the wood boiler before.
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That's kinda the temps I was (very roughly) guessing would be if everything runs at once. I see why you wanted bigger piping, I'm sure it'll heat though. Post some temps when you fire up.
We did a 400'+ one way run with 1" Pex this year, less than 3 gpm with an NRF-25, got 130℉ domestic water by doubling flat plates in series, but ran a huge delta t during showers. Extra large heat exchangers were cheaper than larger pipe.
I've never done P/S in the back of an OWB either.
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That's kinda the temps I was (very roughly) guessing would be if everything runs at once. I see why you wanted bigger piping, I'm sure it'll heat though. Post some temps when you fire up.
We did a 400'+ one way run with 1" Pex this year, less than 3 gpm with an NRF-25, got 130℉ domestic water by doubling flat plates in series, but ran a huge delta t during showers. Extra large heat exchangers were cheaper than larger pipe.
I've never done P/S in the back of an OWB either.
You got 3 GPM out of an 800+ ft loop of 1" with an NRF-25?!?! That's incredible! It'll be a couple weeks before I get this contraption fired up probably. Sounds like they're going to start insulating next week sometime and sheeting the lid toward the end of next week. Overhead doors are 2 weeks out yet, but I think he's going to double poly the openings until then if we need heat. Kind of a cluster, because I need water to fill the boiler but the well guys need heat to turn the water on lol. Once it's insulated I think we'll Nipco heat it up for a day and get the water on, then I can get the boiler fired and at least run the unit heater for awhile while I purge the floors and whatnot. As far as the P/S goes I just ordered parts a half hour ago here, I think a 1" copper loop between the supply and return ports at the boiler with a 15-58 in 3rd gear, and a pair of closely spaced tees with a 26-99 in 3rd gear running the building loop. Temp gauges on the supply and return lines of the building loop and another gauge on the return port of the primary loop to keep an eye on the mixed return water. Should keep everything in check, I hope
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I'm guessing it was about 2.5. According to the charts the resistance dropped off dramatically when the velocity got that low. So I tried it, through two flat plates, close tees for house blower coils loop and back to the owb.
And I didn't measure the flow, just what I calculated on that distance with the NRF-25 pump curve. A 26-99 would have gained a bit more than 1 gpm if I remember right. Would have never gotten air out except it's all uphill to the OWB.
Customer says it's heating well and has good hot water, but I'll bet the delta t climbs to 80+ degrees at times. A new house so the heat load isn't very high. Domestic water is the big one. First flat plate pulled the domestic up to maybe 100, second up to 130-ish. Not as hot as normal, but it'll do.
That sounds like a fun one, juggling everything. With new construction seems like its always hurry up and wait. :)
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Too many. I think he said 170ft :-\ Looking at some online calculator thing this morning, it's looking to me like even if I'm able to keep 7 GPM through the boiler loop and put 170 into the plate, the return temps will need to be down in the 110 range in order to get 130 out of the plate on the radiant side :bash: Looks like P/S is in order. 15-58FC in the primary between supply and return ports with a pair of closely spaced tees and a 26-99FC pumping the secondary loop to the building? I can honestly say I've never done a P/S at the wood boiler before.
I would put the new 15-58 pump from supply to return at the boiler but only connect the main loop into the return and leave both pumps drawing directly out of the boiler. That would get you more hot water to mix before it goes back into the stove return and also won't lose heat if the extra pump dies.
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:post:
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Been busy on a friends install. Not sure what you were disagreeing with after my post on page 2 wreckit? No plates are 100% efficient, check the manufacturer specs. My 10 plate (5"x12") produces hot water temps in excess of 145 with single use drawing from it. It drops if multiple faucets are used at the same time. My set up is a primary 1 1/4" pex line in the basement with secondary 1" pex lines using monoflo tees to feed each of my loads, DHW is first load. I only have 1" pex coming from the OWB and upsized to 1 1/4" in the basement and shed once indoors. Would have buried 11/4' but got some ill advice on my first install.
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One more thing. As I mentioned my 10 plate is in the hot discharge of my water heater. If installed in the cold inlet to use the w/h as a storage tank you usually have to leave the water heater on or the temp drop in idle time, i.e. overnight or gone at work all day, will leave you with tepid water when you go to use it. I shut my breaker off to the w/h for additional savings during the heating season.
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My disagreement schoppy, was that temps can absolutely be matched across a plate if properly sized. With my 40 plate at home, I checked it a couple weeks ago to have this discussion elsewhere and with the shower running, I had 168 coming off the plate into the tank. At the same moment, I had 168 coming into the plate from the boiler. Exact temp match. That's my residential example. I work commercially as a pipefitter and build hydronic systems every day, and I can assure you that there are thousands of commercially installed exchangers out there that match temp as well. Most are shell and tube design, but there are a handful of gasketed plates out there as well. As for the storage ordeal, that is a very common misconception. I fill my tank with 160-170 degree water, but it'll last a week in there without firing up the burner. To prove this point, I shut the gas valve off to my water heater last year and used a ton of hot water the day before I left for Aruba. I was gone for 6 days, and had enough hot water left to shower when I got home. I think having my plate below the WH allows for some thermosiphon, because the line is always hot.
RSI, I don't see how that would be of any benefit? First, it would eliminate hydraulic separation. Second, if the 15-58 dies the 26-99 will still pull the same water from the boiler right through the 15-58 while piped with closely spaced tees. What am I not seeing?
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I think in most residential applications cost dictates that the exchanger is sized to not attempt to match temps during a load. Maybe that's what we're missing each other here?
How would the 26-99 pull through through the 15-58? Wouldn't it just recirc back through the tees? With the assumption the goal was higher return temps, not hydraulic separation.
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I thought the point of adding the pump was for a higher return temp. Why does hydraulic separation matter. If setup like I suggested, you could even put a sensor on the return pipe and only need to run that pump when the return temp drops way down. If there is some other reason than simply not wanting cold water being returned into the boiler then primary/secondary setup may be better.
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I guess my thought behind the close tees/ hydraulic separation is that if the 15-58 would die, the 26-99 wouldn't recirc through the tees because it is hydraulically separated. But then again as RSI pointed out, there really is no need if piped in that fashion. Very good points guys, thanks
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Will this work for you Eldon for a flat plate sizer?
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Hmm.. I'll check it out. Thanks.
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Trying to figure out their model #'s but this is very useful. Thanks, Honda.
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No problem. Took a little digging to find it again but that is what I used when I sized mine.
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What I'm seeing is they size their models that don't quite fit the dimensions I use.. but it's a good place to start.
I actually already had a password, but forgot I had used it in the past. My brain's getting fuzzy in my old age I think.
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Just getting back from Texas where it was almost as cold there as here in Wisconsin before this weekend anyway.
Well wreckit87 if you want to put in a 40 plate heat exchanger that's rated anywhere from 250,000 to 400,000 BTUH at close to twice the price for a 40,000 BTUH water heater you could probably keep incoming and outgoing temps very close to the same. But installing it in the cold inlet to the w/h you still need to keep your water heater on to prevent tepid water during prolonged off cycles. Extreme overkill in my opinion.
E Yoder you hit the nail on the head with properly sizing equipment to loads.
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Just getting back from Texas where it was almost as cold there as here in Wisconsin before this weekend anyway.
Well wreckit87 if you want to put in a 40 plate heat exchanger that's rated anywhere from 250,000 to 400,000 BTUH at close to twice the price for a 40,000 BTUH water heater you could probably keep incoming and outgoing temps very close to the same. But installing it in the cold inlet to the w/h you still need to keep your water heater on to prevent tepid water during prolonged off cycles. Extreme overkill in my opinion.
E Yoder you hit the nail on the head with properly sizing equipment to loads.
A respectful disagreement ( 2 actually); I don't know where you buy your exchangers, but a 40 plate can be had for under $200 all day. Last time I bought a water heater which was 3 months ago, was right at $400 for the cheapest piece of crap Menards sells. Secondly, unless you're leaving the house for a week at a time, the WH can stay off. Mine hasn't run once since I installed the boiler 6 years ago, and I often leave for several days at a time with nobody else around to use any hot water. 40 gallons of 170 degree water isn't going to be "tepid" overnight unless you were born on the sun and need 150 degree showers. I'm mostly baffled at where you are finding $100 water heaters; I could save a lot of money with those.
If I read that wrong and you were saying the 40 is double the price of say, a 10 plate, then yes you are absolutely correct. For $60 though, I'd still rather have a tank full of hot water for when I want to do laundry and dishes and shower at the same time. Nothing worse than running out of hot water in the shower IMO. Especially if I'm in a hurry and the boiler isn't up to temp, there's nothing you can do about it if the plate is after the tank. Personal preference I suppose, it's just what I like
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I would agree with wreckit that I haven't seen water heaters cool down much when preheated with a flat plate. Maybe 10 degrees after 24 hours at most. We've done quite a few that way with very happy customers, endless hot water, with fairly even temps. We use 3X8" 30 plates and aim for about 140℉ water in the water heater to avoid needing a mixing valve. A bigger flat plate (hotter water) and mixing valve would allow a longer idle time between drawing hot water as the mixing valve would even things out... Hmm... I learn things every day. I like these discussions.
Years ago we did sidearms and those were much harder to get right. I hope whoever invented the flat plate was treated real well, he made my life easier. :)
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Yes, I was comparing plate to plate cost. Of course if you have the temp high enough in a water heater it will maintain an adequate temp but 170 is crazy IMO. I can run hot water all day with my 10 plate and never run out. Obviously this is with the OWB running in operating temp range. Even when water isn't being used a flat plate will transmit some heat into the tank which can help hold temp as well.
To each their own, I like to keep it simple.