Can you have too much storage?

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muleman51

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Feb 18, 2008
246
SE Minnesota
My new boiler seems to be having trouble keeping up, maybe. First of all the empyre elite is non pressure so I have to use a plate exchanger, so the warmest I have been able to get the storage is about 160*, I would really like to be in the 170-180* range. The boiler only operates at a high of 180*. The dealer says the problem is that I have too much storage. I have had another "expert" tell me the same thing. What is the best way to tell how much heat you do have stored? I only have temp gauge's on the incoming line from the plate exchanger and on the outgoing line to the house and they run very close to the same temps. hopefully I can get to the bottom of this. Jim
 
I have an eko 40 with 1150 gal storage and i'm charging it right now and cant get above 176 °F could be pipe insulation ,controller settings ,thermocouple. I know others on here are getting close to 190 °F . Your boilers output is fairly close .
 
If you have 8,000 pounds of water in your tank, then every 8,000 Btu into that tank will raise the temperature 1°F. If it is well insulated and you are not drawing water for heat, your boiler should raise the temperature 10 degrees per hour.

Perhaps the heat exchanger needs a look. What are the four temperatures at the heat exchanger to/from boiler and to/from tank?
 
You can go to www.flatplate.com and use a free HX sizer.

If you have 180F on at A side of the HX you should be able to get to 170- 175F on the tank side. You need enough boiler output to cover any load while you are trying to charge the tank. On a low, or no load day, all the boiler output will be able to go to charging the tank.

The closer you want the tank temperature to the boiler temperature, called close approach, or the faster you want to exchange, the larger the heat exchanger required. And you need enough pump capacity to move the GPM through the HX.

hr
 

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If every thing posted checks out then you could look at the possibility of the HX getting some debris in it ? Are there strainers in system ? You mentioned new system maybe there was left over debris from factory or assembly.
You should be able to heat 1000G.
 
I would guess you have a bit of heatloss or excessive load on your battery. The other option could be a pump problem and flow than is not matched properly. HX is definately a concern as well. yes you can have too much storage. I would want to know the temps at the HX. Could you have too big of pump on the Elite ? And velocity is too high ? Temp readings would tell you how much your doing.
 
Pressurized boilers can be run that high but my temp control will only go to 180* since it is non pressure. Then going through the plate exchanger you don't get all the temp. The temps on the plate exchanger are: in from boiler 162* back to boiler 148*, storage side in 142*, out 156*. The boiler readout said 165* and the gauge in the storage side right above the PE was 160*. these temps are hard to tell just using an infrared gun. I guess you can't put in enough temp gauges or valves.
 
Your Empyre is rated at a maximum or peak output of 125,000btu/hour and 66,000 over an 8 hour burn. That's not a lot of oompah if you're trying to heat 1100 gallons of water. The math is pretty simple. Let's say you want to bring the storage from 140 up to 180 or a 40* rise. 40* x 1100 x 8.33 = 366,520 btu's. So, if you take the average output listed on Empyre's website you are looking at about 5 hours to get the storage up to temp. Deduct the heating power going to your house loads simultaneously and you could probably double the time frame needed to top off your tank. You could probably up the "horsepower" a bit by loading frequently instead of letting a load burn most or all of the way down.

That's one issue.
The other one is probably related to heat exchanger sizing. When I size a plate HX in the situation you find yourself in, I pretty much ignore the btu ratings on the hx. Usually they are based on a 20* split from side A to side B and your system, or any other like it demands what is called a close "approach temperature". A close approach is a function of nothing more than the amount of transfer area in the HX and flow rate. You want to get Side B as close to side A as possible to effect maximum heat going to your storage.. You will find that generally speaking you may need to upsize the hx by 50% to get the temps tight. Without getting into all the math (which you can easily do on Flat Plates website) I find that in a situation where a 40 plate might do the trick for straight btu transfer, a 60 plate may be needed to get the temps really tight.

I'd look at that first and see how close your two sides are running. You want to get them within a degree or two with enough flow to stay ahead of the actual demand going to your heating load. If the boiler doesn't have enough grunt to keep up that will become apparent very quickly once you get the HX where it needs to be.
 
muleman51 said:
My new boiler seems to be having trouble keeping up, maybe. First of all the empyre elite is non pressure so I have to use a plate exchanger, so the warmest I have been able to get the storage is about 160*, I would really like to be in the 170-180* range. The boiler only operates at a high of 180*. The dealer says the problem is that I have too much storage. I have had another "expert" tell me the same thing. What is the best way to tell how much heat you do have stored? I only have temp gauge's on the incoming line from the plate exchanger and on the outgoing line to the house and they run very close to the same temps. hopefully I can get to the bottom of this. Jim


With the Jetstream boiler I had a very similar problem.
The 1000 gal storage tank and the boiler were to share the same water with a vented expansion tank a floor above giving 3 psi at the boiler. Kerr, the maker of the boiler, felt there would be a corrosion problem at this low pressure. Recommended using a coil of 120' of 1" copper in the bottom of the storage tank for a heat exchanger. This arrangement did not work as I could not get the storage above 170 degrees. The heat exchange was just not fast enough. Your Elite and the Jetstream are similar in output at 120,000 BTUs per hour. The water between boiler and storage now circulate directly, using a pump moving 35 gpm and now I have no problem getting storage to 195 F.


Heaterman's and In hot Water advice, I believe, are in the right direction for boiler.
 
That would be open, and that would also be static head, obviously the pressure at your expansion is zero.

On the plate, if you paint it flat black the laser reading will be more accurate , by increasing the emissivity. Always read on the same type of material when comparing. Always shoot the same spot on each surface, prefferably a flat one on a fitting if possible. Always take reading at the same distance away from the surface as well. From your temp readings if accurate the storage side might have too much velocity, I would also say the boiler side is too. If possible reduce flow until you have a 20* DT on both sides. The easy one would be the storage, if you dont have multispeed pumps you can throttle a valve down a bit temporarily to test this, don't worry if it appears to be almost shut before you see a change. On the boiler side you can however speed up the pump to see if that will raise the temp to the plate. And it is ok if you have less than 20* DT on the boiler side as long as velocity isn't way above 4fps.
 
What your describing sounds reasonable in my opinion. One of the benefits of a pressurized system is you are typically able to acheive higher storage temps since there is no HX involved.

Any heat exchanger is going to become less efficient as you approach peak temps on both sides. The smaller the difference between input and output the slower you're going to add heat to the storage side of your system. I don't think it's reasonable to assume you could ever get 1,000 gallons of storage up to 170+ with a boiler output of 180. If your boiler idles at 180 that means it probably lets it drop to 175 +/- before it kicks on again? If that is the case your actual average max output is probably in the 170's. Add to that a few degrees of error in consumer grade thermometers and I really don't think you can get much better than what you have now.

And for what it's worth your two experts are not providing you with a satisfactory response if they simply say "you have too much storage". I'd be willing to bet you couldn't get 500 gallons of storage much higher than you currently get 1000 gallons.
 
There is a type of system which is termed semi open which I have heard of in my travels but I am not sure what the design parameters for such a beast are exactly. I think it has to to do with amount of make up water in that any liquid that evaporates is returned to the system. I think many of the "open" wood burners out there would fall into that category.
 
Any updates muleman? I was considering an Elite, but the main thing that concerns me is max output temp of 180°, that has yet to pass through a heat exchanger. I really like being able to feed 180° water to my baseboards, I'm thinking that with the Elite plus an exhanger it would be lucky to get over 165 - unless it would be possible to safely trick a temp probe to get output temps up another 10° or so, or something of the like. That's likely risky though...
 
Strange, most Jetstreams with storage had a hx with four 1/2" 25 ft coils, designed to give a delta T of 40 F at 10 gpm when dumping the full output of the Jetstream. 120 ft of 1" should be as good but the original did use stratified charging.

With the Jetstream boiler I had a very similar problem. Kerr, the maker of the boiler, felt there would be a corrosion problem at this low pressure. Recommended using a coil of 120' of 1" copper in the bottom of the storage tank for a heat exchanger.
 
Strange, most Jetstreams with storage had a hx with four 1/2" 25 ft coils, designed to give a delta T of 40 F at 10 gpm when dumping the full output of the Jetstream. 120 ft of 1" should be as good but the original did use stratified charging.


The storage tank is an ex-Steam Boiler with its flame tubes removed. 56" diameter and 106" long. The heat exchanger was a flat grid made of 1" rigid copper running the full length of the tank at 8" from the bottom of the tank. The spacing between each pipe section was whatever 180 degree 1" copper elbow would give and all the pipes were at the same level. With the boiler aquastat set to shut the blower off at 190 degrees, I was unable to get the tank over 170 without cycling.
The previous boiler had heated the tank as a gravity system and had no problem getting storage to 195, so I went back to circulating the water between the boiler and tank directly. If the storage and boiler water were pressurized, I could likely use a much smaller circulator.
If solar ever becomes a useful alternative, I have a ready and waiting heat exchanger in the bottom of the tank.
 

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The storage tank is an ex-Steam Boiler with its flame tubes removed. 56" diameter and 106" long. The heat exchanger was a flat grid made of 1" rigid copper running the full length of the tank at 8" from the bottom of the tank. The spacing between each pipe section was whatever 180 degree 1" copper elbow would give and all the pipes were at the same level. With the boiler aquastat set to shut the blower off at 190 degrees, I was unable to get the tank over 170 without cycling.
The previous boiler had heated the tank as a gravity system and had no problem getting storage to 195, so I went back to circulating the water between the boiler and tank directly. If the storage and boiler water were pressurized, I could likely use a much smaller circulator.
If solar ever becomes a useful alternative, I have a ready and waiting heat exchanger in the bottom of the tank.

I don't have this new web system down yet so maybe this is messy , we'll see. Before I shut down a couple of weeks ago the highest I could ever get was 160-5* on the storage side. I have not even thought about replumbing as the ProFab people want me to. I think I will eliminate the whole exchanger system and storage and go to nonpressure. This will eliminate 2 extra pumps that are running now. The ProFab people tell me this will fix all my problems, I think I've heard this before but it isn't working to my satisfaction now, so I don't have alot to lose. None of this will probably get done until I should have had the boiler going for a couple of weeks next fall. You no the extreme procastination deal. Right now I need to work on the wood pile. Jim
 
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