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[wreckit87]

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

[hondaracer2oo4]

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.

[woodman]

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?

[hondaracer2oo4]

Correct.

[E Yoder]

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).

[schoppy]

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.

[wreckit87]

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

[E Yoder]

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.

[wreckit87]

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

[woodman]

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

[hondaracer2oo4]

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.

[woodman]

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.

[wreckit87]

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

[E Yoder]

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.

[hondaracer2oo4]

Was a heat loss calc done?