Flat Plate HX works - My tank is charging!

[WoodNotOil]

After an extra month of work than I expected, my tank is done and charging. The flat plate works perfectly and the tank while charging has a 10* temp differential from top to bottom. Stratification looks good and charging seems efficient. Check out my web page for more details.

 

[pybyr]

Go, man, go!

I and probably many others are aiming to follow in your footsteps of a plate HX + circulators "aiming at" one another.

Can't wait to see more details on your Googlepages, and to hear them here on Hearth.

I hereby hoist an appropriate cold beverage to your project, your hard work, and progress!

 

[hkobus]

Great work and nice web-page to go with it. I have also narrowed it down to this system. I am still looking for reasonable priced supplies however. I have a hard time finding plate exchangers at a reasonable cost.
How does it perform at the end of the charge, when the tank reaches it's high temp? Just wondering if the HX is the right size ( can't seem to get anywhere near what you paid for a 30 plate around here!)

Thanks again for blazing a trail here and enjoy your success!

Henk.

 

[MrEd]

Congrats - I also an eagerly waiting for someone to get one of these up and running. I have a 500 gallon propane tank that I plan on hooking up but have kept thinking that a bigger unpressurized tank in the basement , with heat exchanger would be a better option - and cheaper.

Besides the 500 gallon tank (which I got for free but I could probably sell for $500), I would need to add a $500 expansion tank, plus I am looking at another $1000 (almost) for an indirect fired DHW heater (a superstor). I had this nagging feeling all along that I could take that $500+$500+$1000 and invest it in a 1200 gallon or so home built setup and get more bang for less buck - but like many others, that fact that no one so far had proven it would work with a heat exchanger was holding me back. I am still not committed, so keep the details coming. I can be swayed and I would like nothing more than to just follow in someone else's footsteps instead of blazing the trail.

A few question for you from you website.

1 - the liner you used is only rated to 175 degrees...aren't you worried that you are pushing the limits of it? Or are assuming that the max temp under-rated?

2. You went with series, not parallel, was that a conscious choice? or just what would more easily work in your setup?

3. When is the open house? :>)

 

[mysticfalcon]

Sign me up for that open house too.

 

[mpilihp]

Hi WoodNotOil nice job, I have a few questions for you, on your diagram what are you using for a purging valve? Are you just using a T with a drain valve on it?

Second, I see your diagram on how to wire up the back to back pumps for the HX but dont quite get how the DPDT relay is keeping only one set of pumps running. Is it that when the charging pumps Aqustat applys power to the relay it is opening up contacts so that the drawing pumps cannot come on? If so does that mean if the charging aquastat is OFF-no power applied to the DPDT relay then the contacts for the drawing pumps are normally closed and if the drawing aqustat applys power it will go to the drawing pumps with no action from the DPDT relay?

Also, how does it work when a zone is calling for heat, looks like it draws through the oil boiler when the draw pumps are on correct? so is your oil boiler the center of your heat system and the zones run off of the oil boiler?? Is your DHW in the oil boiler?

Thanks

 

[WoodNotOil]

Thanks everyone for the encouragement. I was not aware how many were following my "experiment." I had every confidence it would work all along and that is why I went ahead.

Mr Ed - I plan to only charge the tank to the 175 limit. (My PEX and CPVC max out at 180* anyway) To go above that would have cost significantly more for a liner, so this is a cost compromise. Maybe someday I will buy a more expensive higher temp liner. My system was series to begin with and though it is less efficient that way, I decided to take it as a challenge. I am working on insulating all pipes in my system and on making an additional polyiso jacket for the oil boiler and attempt to compensate that way. I have a DHW coil in the oil boiler and I was concerned about letting it sit stone cold all year. This way it is kept hot and the coil can be utilized when needed.

mpilihp - The drawing pumps pass through the relay when it is not charged. When the charging aquastat charges the relay then connection to the drawing pumps is broken until the relay is uncharged. It actually works perfectly!

I hope to have some concrete data soon on charging times and all that. I will keep adding info to the web page.

 

[WoodNotOil]

Hi WoodNotOil nice job, I have a few questions for you, on your diagram what are you using for a purging valve? Are you just using a T with a drain valve on it?

Yes it is a cpvc T with a copper drain valve threaded into it. Above it is a cpvc ball valve. I close the ball valve to prime the lines or to drain the tank. The charging pump will actually pump the tank out, all but the last 1-2".

 

[MrEd]

How will you prevent the tank getting above 175? Also, it seems you have DHW coil in the tank, and also in the boiler - are you feeding hot water out of the tank into the DHW coil of the oil burner?

Once statistic I'd be very interested in is after you charge the tank, especially in the summer, how long can you get DHW before the temp is too low. When my system is done I'd like to use no oil at all for DHW, but I'd like to be able to go 7-10 days between fires in the summer.

 

[WoodNotOil]

How will you prevent the tank getting above 175?

Right now I have the Tarm set at 175 so the temp will not exceed that. Once I figure out the temp differential on the plate I could probably push that higher as there is usually a 5* difference across the plate. Also, I do plan to eventually put some aquastat on the tank for high and/or low temp cut offs with more DPDT relays to make the whole thing a little smarter.

Also, it seems you have DHW coil in the tank, and also in the boiler - are you feeding hot water out of the tank into the DHW coil of the oil burner?

The coil in the tank is meant to preheat the water before hitting the coil in the oil boiler. The oil boiler will be kept warm by the tank as well. That way no oil will be burned. Also, I plan to try getting the hot water only off the tank coil in summer. Not sure yet if I put in enough copper for that. My original intention was only as a preheat.

Once statistic I'd be very interested in is after you charge the tank, especially in the summer, how long can you get DHW before the temp is too low. When my system is done I'd like to use no oil at all for DHW, but I'd like to be able to go 7-10 days between fires in the summer.

I will certainly pass those figures on when I get them. I am curios as well!

 

[mpilihp]

Hi again thanks for the explaination. Have another dumb question, whats 'cpvc T' mean? Coper Pipe V?? C?? I too have my DHW in the Oil boiler and will run series until I can get an indirect hot water heater or have my storage up and able to put the DHW in the storage tank.

~ Phil

 

[kabbott]

Hi again thanks for the explaination. Have another dumb question, whats 'cpvc T' mean? Coper Pipe V?? C?? I too have my DHW in the Oil boiler and will run series until I can get an indirect hot water heater or have my storage up and able to put the DHW in the storage tank.

~ Phil

Chlorinated polyvinyl chloride (CPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. Uses include hot and cold water pipe, and industrial liquid handling

 

[kabbott]

How will you prevent the tank getting above 175?

Right now I have the Tarm set at 175 so the temp will not exceed that. Once I figure out the temp differential on the plate I could probably push that higher as there is usually a 5* difference across the plate. Also, I do plan to eventually put some aquastat on the tank for high and/or low temp cut offs with more DPDT relays to make the whole thing a little smarter.quote]

I am curious if the exchanger maintains the same temp difference recovering as it does charging since you are only reversing one side?
Sure makes things easier than reversing both sides if the performance is close to the same.

 

[jebatty]

Great set-up. I used a flat plate hx last year to heat 1000 gal LP pressurized. 5* temp differential through the hx is about as close as I could get.

Another idea related to CPVC. I used that for some connection piping from my old OWB. Although it worked fine, at the high temp exposure it did not hold up permanently. Joints began to fail (cracks in piping) after about 3 years.

For my current setup I'm using hot water hose, rated at 200F, with brass hose barb fittings. Steel fittings also are available and cheaper. The hose is really easy to use, bends, snakes, etc. with ease. 3/4" runs about $1/ft. I saw another setup where radiator hose (looked like about 1") was used.

 

[WoodNotOil]

Great set-up. I used a flat plate hx last year to heat 1000 gal LP pressurized. 5* temp differential through the hx is about as close as I could get.

Another idea related to CPVC. I used that for some connection piping from my old OWB. Although it worked fine, at the high temp exposure it did not hold up permanently. Joints began to fail (cracks in piping) after about 3 years.

For my current setup I'm using hot water hose, rated at 200F, with brass hose barb fittings. Steel fittings also are available and cheaper. The hose is really easy to use, bends, snakes, etc. with ease. 3/4" runs about $1/ft. I saw another setup where radiator hose (looked like about 1") was used.

That is good to know. I will have to keep my eye on that potential problem. I suppose in a few years I can always replace my to the tank piping with something like you suggest.

On another note, it didn't occurred to me how long it would take to bring 1000 gallons from cold tap water up to 170 degrees. After 3 full, no idling burns I was up to 140 this morning. I lit another full burn and hope to get the last bit by this evening. Those first degrees take a lot of btus and the return water is quite depleted before it hits the termovar and is compensated for return to the tarm. I guess that is a good sign that the flat plate is doing its job.

This first charge is unique in how much it has to raise the temperature. I think I will get better time, temp differential, etc. data off of the next charge when it has a smaller amount to raise the tank temp. Everything looks good so far. I will keep the updates coming.

 

[pybyr]

I wonder whether perhaps the "gray" PVC that is used for electrical conduit, and is sunlight resistant and also generally built to take more potential physical abuse than pipe (especially the thickwall Schedule 80 PVC conduit) might by chance also be more resistant to high temperatures without becoming brittle like the domestic water type PVC.

In other things I've built and fooled with, the concuit PVC has always seemed more resistant to various forms of long term degradation and brittleness than the plumbing stuff. I wouldn't use the grey PVC conduit for potable water, but that's not what we're talking about here, anyway.

Interesting about " how much fire " it takes to bring the temp of a big tank up from stone cold. I suppose that this is definitely a "pro" in favor of the boiler + tank over the Garn for systems where one might sometimes be away and where the tank temp would drop to cold-- the stand alone boiler would let one push heat from the boiler straight to the living space, and skip the storage in the short haul- whereas a Garn type (which I have always admired for its ability to omit all the pumps and controls between firebox and heat storage) that's been allowed to get cold could take a _long_ time to start yielding BTUS to heat with.

 

[jebatty]

That really cold tank start is interesting. Last winter, before switching to pressurized, I had used oil tanks-open storage. When gone for 13 days in mid-winter, also one of our coldest spells, on return there actually was some ice in the tanks. Now that's a cold start. It took several (don't remember how many) full load burns to finally bring the tank above 140.

 

[WoodNotOil]

So the good news is that the fire burned for two days straight without idling and charged the tank to over 150*. That should be enough heat for my DHW for now. This shows that the flat plate is large enough to transfer all the heat my Tarm 40 can throw at it.

I am a little concerned with the tank readings I am getting. I have capped 1/2" copper pipes running through the lid as wells for the probes from my Alez digital temperature guage. The problem is that my bottom tank temp is being read as higher than the top temp. Even if the tank was mixing, I find it hard to believe that these are accurate readings. I am wondering if the 42" length of the copper well is picking up heat from the entire tank and making the reading higher than it should be.

I find it hard to believe that my tank is mixing either. There is 10' of pipe running horizontally with holes drilled every inch pointing to either side on both the top and bottom that move the water in and out of the tank. This should be creating at least some degree of stratification.

I will probably have to come up with a new design for a well for the tank bottom. Anyone have any ideas on that?

 

[kabbott]

You could use a piece of cpvc and change to copper just near the bottom.
Have you checked all the probes against one another to make sure they are reading correctly?
Really does not make sense the bottom would be hotter, not to be smart but you didn't cross up the pump wiring pumping hot to bottom?

 

[hkobus]

So the good news is that the fire burned for two days straight without idling and charged the tank to over 150*. That should be enough heat for my DHW for now. This shows that the flat plate is large enough to transfer all the heat my Tarm 40 can throw at it.

I am a little concerned with the tank readings I am getting. I have capped 1/2" copper pipes running through the lid as wells for the probes from my Alez digital temperature guage. The problem is that my bottom tank temp is being read as higher than the top temp. Even if the tank was mixing, I find it hard to believe that these are accurate readings. I am wondering if the 42" length of the copper well is picking up heat from the entire tank and making the reading higher than it should be.

I find it hard to believe that my tank is mixing either. There is 10' of pipe running horizontally with holes drilled every inch pointing to either side on both the top and bottom that move the water in and out of the tank. This should be creating at least some degree of stratification.

I will probably have to come up with a new design for a well for the tank bottom. Anyone have any ideas on that?

That is the reason I am watching your progress. I had some concerns about this, we use in some barns air plenums and distribute air through holes in a plastic tube. The "jetting" action caused by this is staggering. I would not be a bit surprised with this happening in your tank. I have thought about this, but not put any numbers to it, I was thinking of cutting "slots" in an over sized pipe ( to reduce the velocity of the entering flow). With the slots pointing to the sides.
See if it is left overnight without the pump running if it changes and stratifies.

Good luck and Thanks for all the information and hard work. I hope to get back to working on my storage soon.

Henk.

 

[jebatty]

You can check this easily by putting a thermometer on your return line a short distance from the tank. I use a meat-type probe thermometer with nylon cable binders to fix the probe to the pipe, and then wrap with insulation.

I did the same thing on my hx in/out on both the boiler and system sides; gives quick reading of approx performance. You can see the temp drop on the boiler side as well as the temp rise on the system side.

As to the mixing issue, my tank supply pipe projects about 6" into the tank and then has about a 6" right angle aimed away from the tank return fitting. This "shoots" the hot supply water across the "top" of the water in the tank and not down into the tank. I get good stratification within a 3' diameter LP tank.

 

[WoodNotOil]

Kabbot - My piping is correct. I double checked it.

hogstroker - I am not discounting mixing as the problem. However, I ran the pumps with the tank full and the lid open before I sealed it, and there was no visible jetting at all. As a matter of fact there was no sign in the tank water was moving. The only sign it was actually working was the sound of the water moving through pipes. I even double checked this by opening the purge valve to see that it was working and what the flow rate was like. (of course then I had to re-prime the lines) I would think that enough jetting to cause this kind of mixing would have been visible, but I could be wrong.

I will try Jebatty's suggestion of checking the temps on the lines instead. That should at least give me a better indication of the temp differential, but the temps may be lower than in the tank.

I was thinking of the CPVC to copper to minimize heating of the well pipe as well. Do others think that would work better? Any other ideas?

The tank is 4x4x12 so it is fairly short and long. With that perhaps some mixing and less stratification is inevitable. However, my hottest layer of water is larger than in a taller narrower tank, so perhaps it is somewhat proportional.

I am just glad it actually charged and I am off of oil for DHW. I will gladly take a few problems to work out for that benefit!

 

[WoodNotOil]

Siphoning is the culprit! I noticed that the lines were hot to the touch and decided to close the ball valve to see if the heat was siphoning from top to bottom. The lines are now cool to the touch. This means I will have to add something in the lines to close them when the pumps aren't running. I will have to research this a bit, as I don't want to introduce head resistence. Perhaps an acuated ball valve would be best. Suggestions would be welcome.

 

[pybyr]

Siphoning is the culprit! .... Suggestions would be welcome.

WoodNotOil- I am not quite getting it. If the lines both go into the top of the tank, and since hot water rises, how or why would siphoning through the pumps mess with the stratification. I am not disagreeing with your observations or conclusions, but am not quite getting how that could be occurring. I would most definitely like to understand/ follow/ help, as I want to do a system that is pretty similar to yours

 

[jebatty]

How about a diagram showing relative elevations, bends, etc. so that we can a better idea as to your thermo-siphoning theory. I too doubt that this is the cause. Unless your pipes are very large and there is a clear loop, there can be siphoning, but for that to cause the even heat distribution just doesn't seem possible.

What I think is possible is a direct flow loop developing inside the tank between the tank inlet and outlet. Someone who knows a lot about fluid dynamics could say more.