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[woodman]

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?

[mlappin]

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.

[hondaracer2oo4]

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.

[wreckit87]

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

[E Yoder]

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.

[woodman]

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.

[wreckit87]

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

[wreckit87]

Or was the term "domestic" misplaced and you're using the closed side for heating purposes? That's a different can of worms

[woodman]

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.

[E Yoder]

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.

[wreckit87]

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

[woodman]

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?

[hondaracer2oo4]

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.

[woodman]

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?

[hondaracer2oo4]

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.