Micro CoGen.

My cogen system is on it's 4th year and has been working well. Cleaning the exhaust heatex is a PITA but that's how it is. I can provide enough hot water to meet all my heating and domestic hot water needs down to about 20°F.  The biggest problems I have is that by morning the water is just luke warm and in the summer I have to dump millions of BTUs to waste.

I scrounged 2, 165 gallon barrels. They will be hooked together with a 1" hose on top and bottom for temperature equalization. The hot water from the engine will heat the water in the barrels on it's own loop. When I need hot water for a shower, laundry, etc. I'll turn on a second loop that will heat the 10-12 gallons in the furnace. That's enough water for most jobs. If I need more I'll just leave the pump on. If it's not hot enough I can top it off with the furnace. If I need to I can bypass the storage barrels and bring it back to today's configuration. One barrel has 2, 1125 watt, hot water heater elements. I often have watts to spare. Heat exchangers are automobile heater cores. There will be 2 in the bottom (parallel) to heat the water in the barrels and one on top to move it to the furnace. They have about 315 sq. inches of surface area each. The heater cores will go in from the existing hole in the top and I'll use heater hose there instead of pex because of its curl.

I'll build a wood frame with a heavy duty bottom insulated to about R-18. The sides and top will be a light duty wood frame with walls made of 2.5" fiberglass insulation board. I have a bunch of cellulose insulation laying around and that will go around the barrels. The sides and top will have a minimum of 12" insulation, which gets me R-45 minimum and the average will be even higher.

I'll need a tube on the outside to check water level and top it off when needed.
I'll need a drain on the outside in case something goes wrong or it needs maintenance.
I have a thermometer on a wire, which will be close to the top.
I'm going to put a 2nd pump on the loop that goes to the engine room. There is close to 200' of  ¾" pex with a number of elbows, T's, valves and heat exchangers in it.

12/6/10 The barrels are going through an overnight leak test and are looking good. I hope it still passes when the water is hot.

Questions:
1, If I put thermal chimneys on the heater cores how much more efficient will they be?
2, I don't want to spend the $ on an expansion tank for the loop that goes to the furnace. It has less than a gallon. Do I need one? What's an easy DIY fix?
3, Additional thoughts or suggestions are welcome.

Thanks, Geno

Corrosion control ?
Cast iron block,  steel drums, aluminum heater core, SS hose clamps ?  Will drums be 50/50 anti-freeze w/corrosion inhibitor ?    Maybe add some outboard motor zinc's ?

+1 for corrosion protection.  If using antifreeze, be carefull that leaks cannot pass antifreeze to the domestic system.  What pressure is your domestic water system at?  Heater cores are not really pressure rated, and only designed for cooling system pressures of less than 30 PSI or so...  What temperature are you trying to store at?  The higher the temp the greater the heat transfer/loss.  I would say add another layer of high density foam underneath to up that R-18.  If I were doing it like that, I would try and put the barrels in a tray with a small drain line outside the enclosure to alert me to any leaks before the insulation got saturated.  A small chimney on the bottom heat exchangers should help with the thermosiphon thru them when heating.  What is your backup heat dissipation scheme?
   

I was wondering about whether or not the heater cores were lead soldered but likely the heating fluid here is well separated from potable water.

For expansion tank for small circuits I have heard of tapping on to a small trailer tire wheel assembly.

I obviously should have explained my current setup in detail. Most of your completely legitimate concerns have already been addressed. Currently the system has 3 loops. Loop 1 in the engine room to cool the engine. Loop 2 to move the hot coolant into the house and loop 3 which gets me domestic hot water. Loops 1 and 2 have poisonous antifreeze. Loop 3 is water with two levels of physical protection and one level of pressure protection before hot water comes out of the faucet (town water pressure is higher than loop 2 pressure). Loops 1 and 2 are at atmospheric pressure and loop 2 has an additional 15' of head on it. All loops are connected with heat exchangers. Loop 2 to 3 is a flat plate rated at way more pressure than it will ever see

Crappy hand drawn diagram one shows the engine room and garage side. Crappy hand drawn diagram two shows the house side. The engine room is attached to the garage and the garage is attached to the house. Once you understand what I have, imagine this. Cut loop 2 in the basement, put a heatex on each side and create another loop. Put the engine side heatex in the bottom of the barrel and the furnace side heatex in the top of the barrel. The water in the barrels doesn't go anywhere, it just stores the BTU's. I "think" I read that the barrels are rated up to 160°F, their very thick and I doubt the water will ever exceed 160°F. My current excess heat dissipation schemes are 2, 5" boxer fans on the rad on loop 1, an automotive heater core with a fan on loop 2 (which also serves as a garage heater in the winter) and my last resort is to run domestic hot water for a while. A thermal chimney on the heatex's in the barrel is now on the list as well as ss hose clamps.

Thanks, Geno

Another Pic or 2

Quote from: Crofter on December 07, 2010, 08:58:41 AM
For expansion tank for small circuits I have heard of tapping on to a small trailer tire wheel assembly.

I got some of those laying around. Good idea! Thanks

Quote from: Ronmar on December 07, 2010, 08:08:53 AM
I would say add another layer of high density foam underneath to up that R-18.   

That's pretty easy at this stage and will increase the BTU value by around 10.

Interesting setup.    Thanks for the pics.   The diagrams help a lot.   Great work!

The pics pretty well show what I did. One improvement I did to prevent leaks was to cut a hole in the top big enough for me to get in so I could seal the fittings from the inside. I used some flexible silicone and smeared it on heavy. The epoxy I used on the outside worked well but will crack if you flex the fittings.

Thanks, Geno

More pics. The barrel on the left shows the top being glued back on.

Thanks, Geno

Quote from: Jens on December 16, 2010, 02:31:45 PM
A sort of related thought .... has anyone explored heat storage in molten salt ? Is there a readily available affordable salt that changes for solid to liquid in the 60C to 80C range ? How much additional heat can you store in a given volume of liquid salt compared to the same volume of water ? 

Well, I am exploring heat storage using sodium acetate that changes from an ambient temp liquid to a 54C (130F) solid.

http://www.microcogen.info/index.php?topic=1492.msg17694#msg17694

You can't really store additional heat energy in sodium acetate than same volume water, but you can store this heat energy forever in sodium acetate without using any additional energy, and you can release it when needed via the exothermic reaction.  If the energy is surplus and/or free (e.g., from surplus hydro/solar power), the efficiency of "putting it into storage" becomes less significant.

Hi Jens,

These links explain the sodium acetate approach fairly well:

http://en.wikipedia.org/wiki/Sodium_acetate

http://www.howstuffworks.com/question290.htm

You would start with solid sodium acetate (at ambient temp) and heat it up to 100C at which point it would become a liquid.  It could then be stored in this liquid state (without insulating the storage container and without using any additional energy to maintain some temp) at ambient temp indefinitely.  This "supercooled" sodium acetate liquid is very stable and will stay a liquid at ambient temp indefinitely until you mechanically initiate the exothermic reaction as desribed in the first link.  The exothermic reaction will then create solid sodium acetate at 54C (130F).  This cycle can then be repeated indefinitely.

The process in inefficient in that you have to heat the sodium acetate solid to 100C in order to only obtain a future 54C solid. However, the storage requirements are easy and the heat can be released when needed.  Not all that different from storing electrical energy in a typical battery...hence my term "heat battery".

Bob B.

now isn't that the coolest stuff ever!

one question though, how would you do it so that you can be assured the stuff is fully melted, so that it can be on hold until you are ready
for it to go back to 130 degree's?

is there a link to this salts use as a large thermal battery, large enough to be useful in our applications?

bob g

Hi Bob G.,

I'm not aware of anyone having built a practical "heat battery" like this.  I don't see a big market for it either.  The patent app was submitted couple years ago, about same time we submitted this one which only published last month, so IP has been covered.

http://www.freepatentsonline.com/y2010/0292869.html

You would ensure fully melting the sodium acetate modules by continuing to heat the primary battery core fluid at 100C for a pre-determined sufficient time (which is a function of the sodium acetate module volume) pretty much like one does for small store bought heat pad.  The exothermic reaction is initiated remote from the battery electromechanically.  The sodium acetate modules then heat the central battery core which also contains the typical heat exchanger plumbing for transferring the heat to wherever it is desired.

Bob B.

I read up on Sodium Acetate the other day and it sounds like neat stuff. Even found a video of "hot ice"

I don't know how many of you freeze jugs of water for coolers (I do it a lot) but the problem I've had is that after a while you get an insulating layer of water around the block of ice and your beer gets warm. If you add about cup of salt to a gallon of water the ice melts evenly throughout the block and also gives up its BTUs faster. I built this highly insulated cooler out of a box someone was going to throw away and some scrap insulation I had laying around.

Thanks, Geno

Where most people see a dust bin I see a thermal chimney. This is the second one I built and it's a bit better than the first.

Thanks, Geno

Geno, if you don't mind my asking, what are those heater cores from?
Ron

I don't know what car there from but here's the link. 20 bucks. Can't beat that.
# on the box: Ready-Aire 399022
http://shop.advanceautoparts.com/1/1/539396-heater-core-by-ready-aire-part-399022.html

Thanks, Geno

Well, I got all excited seeing that price, thinking, "hey, why am I using copper coils instead of heater cores?"  Then I remembered: heater cores are not pressure rated for 50-60 psi.   I'd probably pop some soldered joint.   But it does make me wonder how well a heater core or radiator would work for water-water heat transfer instead of its designed use of water-air.

I would like to pressure test one to see what it will really handle but I'll never get around to that.

I can't see any reason why they wouldn't work well for liquid-to-liquid heat transfer. They have all that folded aluminum in there and the chimney will increase flow. Total surface area is about 4.3 sq. ft. I should have things ready for a real test in a week or two.

Thanks, Geno

Quote from: Geno on December 18, 2010, 04:05:53 PM
I don't know what car there from but here's the link. 20 bucks. Can't beat that.
# on the box: Ready-Aire 399022
http://shop.advanceautoparts.com/1/1/539396-heater-core-by-ready-aire-part-399022.html

Thanks, Geno

Thanks Geno!! That's cheaper than dirt.
Ron

if you want a relatively high pressure core, look for a gm A/C evaporator core

the too are aluminum construction and should handle 50-60 psi without problems,

new they are probably expensive, but used they don't bring much.

bob g

Hey All,

Alum. doesn't survive very well in an anaerobic environment, unless it's one of the marine grades. Just a thought.

Lloyd

Gotta be some additive or anode material or combination of the two that would stop the electrolysis. I would have thought that a fresh water
anaerobic environment would  be just peachy! However salt water would have been a disaster.
What happens Lloyd?
Ron

Looks like a proper PH level is the key.

http://www.floodbreak.com/default/Maintenance%20Ops/Aluminum%20corrosion%20paper.pdf

http://www.corrosion-doctors.org/MatSelect/corraluminalloys.htm

Thanks, Geno

(addition)  Based on some reading, unless my tap water is way out PH wise I should be fine in fresh water. I could get a magnesium anode for added protection. They're cheap enough. Anaerobic environments prevent the protective layer on aluminum from regenerating if it's damaged. In my application, with the materials I'm using, I don't believe there exists any way to damage this coating.

The hot loop from the engine room is all plumbed. The loop is refilled and bled. I had a leak at the heat ex's but double hose clamps on all the fittings fixed that. Once the loop was hot I put the heat exchangers in pic 1 in 5 gallon buckets and the results were good. I put small pieces of magnesium on the heat ex's. Second time around I did an unexpected pressure test by forgetting to open the valve to the vent/expansion/fill tank. No leaks.

Pic 2 shows the first test in the barrel. They need some weight, I don't want to take a chance of them shifting around. Should've thought of that. Good news is they're removing every BTU the engine can throw at them in this very cold water.

There is no insulation on the barrels or the new plumbing and the tops of the barrels are open. Engine load, 2400-2700 watts.
Startup temp. 0630, 9.9°c at the top of both barrels.
0730, main barrel 17.5°c, t-siphon barrel 11.2°c
0830, 23.5°c,  17°c
1045, 32.3°c, 27.8°c   Uh oh, the heat-ex barrel is warm from top to bottom but the t-siphon barrel is only warm to about 10" below the top cross connect. Hopefully it will find its groove with some more heat.

Thanks, Geno

Missing from first post. It's about 12.8°c in the basement. All temp readings are at the top of the barrels unless otherwise noted.
1200, Top of barrels covered.
1230, 37.5°c, 33.9°c  The t-siphon barrel is warm several inches further down and the temperature spread between them is declining.
1245, I turned on one of the heating elements. 1000 watts.
1345, 40.5°c, 37.5°c  T-siphon barrel is warm of 1/2 the way down.
1500, 44.2°c, 41.5°c  Temperature increases are decreasing, likely due to lack of insulation. T-siphon barrel is warm 2/3 of the way down.
1645, 47.4°c, 44.7c
1830, 50.1°c, 47.2°c The t-siphon barrel is somewhat warm near the bottom. 20" down it's 39°c. The heat-ex barrel is the same temp down to 20" and that's as far as my probe reaches. I thought thermosiphon would work better that this. Perhaps a small pump is in order. I'll wait and see for now and check temps in the morning to see if things equalize better. A lack of insulation skews this test quite a bit I'm sure, but all in all it was a success. It's time to shutdown and eat some leftovers.

Thanks, Geno

I don't know how long it took but 11 hours after I shut down the temps in the barrels were pretty much equalized. They cooled off to about 35°c and there was a .5°c difference where the temp probe could reach and I could feel by hand it was pretty close the rest of the way down. I'll have to do some more testing but I am now leaning towards a small pump to be used only while I'm adding heat. A second option would be to put one heat-ex in the t-siphon barrel. That would mean draining the system and putting longer hoses on. Draining, refilling and bleeding the system is a PITA. It would however increase efficiency due to the greater delta.

(addition) Before the t-siphon barrel warmed up there was a very distinct  boundary between the warm and cold water. It doesn't seem to make sense but I wonder if this thermocline did something to inhibit the t-siphon. My engine t-siphons just fine.

Thanks, Geno

Tha barrels are at the same height right?  One of the biggest things that powers thermosiphon is gravity.  the difference in potential from heated barrel to cool barrel is probably mostly used up in pumping the fluid across horizontally from one barrel to the other and back.    The flow is slow enough that the water gets to stratify, and that boundry layer just slowly moves downward as the barrels ultimatly equalize...

I would say yuour assessment is correct, either a small circ pump to equalize faster, or move one cooling tower to each tank.  I guess a third option would be to raise the secondary barrel up higher to improve thermosiphon flow, but that sounds like a bigger PITA than the other 2 options:(

Thanks Ron, I've been waiting to hear from you. Only problem is you didn't have an easy solution  ;)  Damn gravity. Works great on the engine loop though. The barrels are the same height.

I rather not have another pump. I've got enough stuff to turn on and off as it is. I've built in many options depending on what I need at the time and they're all manual. I'll soon need a clipboard to carry around with me. I'll just drain the system and do it right. Besides, I forgot to put in a couple valves for the next option. A hot water heat-ex off the wood stove in the basement.

Thanks, Geno

I'm done splitting the heat-ex's into each barrel. Temp spread between the barrels is only a couple degrees off now, top to bottom. The next hot water loop that goes to domestic hot water is complete. I don't get much domestic hot water yet since I can't get the barrels above 105°f without insulation but the basement is 15°f warmer because of that. No leaks yet. Some more testing and I'm ready to insulate everything.

Thanks, Geno

I've got the project to the next level and did some more testing today. The container is insulated with cellulose up to the top of the rigid fiberglass. The water temp in the barrels leveled out at about 135°f after 8 hours and there is still quite a bit of insulation to add. I keep getting small bubbles attaching themselves to the heat-ex's in the barrels and they must lower the efficiency. When I shake them a shower of bubbles surfaces. I believe its just the air trapped in the water and will go away with some time. Any other ideas on that?

Thanks, Geno

you might try adding a little liquid dish soap to the system, it will reduce the waters surface tension
and the air bubbles should work their way out of the system.

it shouldn't take very much to do so, certainly not enough to make suds, it only takes a few drop per gallon to
make water flow out on a glass plate, that is what you are looking to happen

so maybe a couple oz per 500 gallons?

start with very little and add more if you need it.

whatever the case, soap is cheap and it won't hurt anything, unless you plan on drinking that water?

bob g

bob g

That is the exact type of simple solution I was looking for. There might be a little Dawn in the kitchen. I won't be drinking the water in the barrels.

Thanks, Geno

i hope it works for you Geno, i am thinking that is should

i remember several years ago an associate of mine started a window washing business, he explained that
just a few drops of dish detergent along with some ammonia made the water layout and cover the glass better.

he told me he learned that from an old timer glass cleaner,

i really never thought about it but afterward i remember spraying some water from an atomizer bottle on a window and it would
sort of bead up and not lay out, i added a couple  drops of dawn, and wow it made the water lay out like automotive paint

then i remembered back in lab class, with microscope slides, when mounting specimens to view, water surface tension made for all sorts
of grief, i don't think we used soap, i think we cleaned the glass slide with alcohol, which then allowed the water surface tension to break
and layout,, but   i can't remember for sure.

it just seems like a little dawn ought to work for your application, please report back how it works out for you.

also another option is diesel engine DCA additive, while its primary use is to ph balance the coolant it also cuts corrosion and it must
also reduce the coolants surface tension and keeps down the formation of bubbles that eat holes in liners on some engine's.
i probably would not use it though if you have a coolant loop interfacing with potable water, the stuff probably if not poisonous is likely
not good for you to consume.

fwiw

bob g

You will need to add something to the water to control growth of alge...  Quick check if you can reach into a barrel, wipe your finger around on the inside surface below the water level.  If it feels slimy, it has started...

one used to be able to get the algicide at any water bed store, however they are not as common as they were 25 years ago.

where do you get a suitable algicide these days.

bob g

http://www.redlineoil.com/Products.aspx?pcid=10 (http://www.redlineoil.com/Products.aspx?pcid=10)

http://www.redlineoil.com/product.aspx?pid=74&pcid=10

techinfo http://www.redlineoil.com/content/files/tech/WaterWetter%20Tech%20Info.pdf (http://www.redlineoil.com/content/files/tech/WaterWetter%20Tech%20Info.pdf)

(http://www.redlineoil.com/content/images/products/74.png)

Water has twice the heat transfer capability when
compared to 50% glycol antifreeze/coolant in water.
Most passenger automobiles have a cooling system
designed to reject sufficient heat under normal operating
conditions using a 50/50 glycol solution in
water. However, in racing applications, the use of
water and WaterWetter® will enable the use of smaller
radiator systems, which means less frontal drag,
and it will also reduce cylinder head temperatures,
even when compared to water alone, which means
more spark advance may be used to improve engine
torque.

Bob, I put 4-5 ounces of Dawn in each barrel and it does help. I can now see a steady stream of bubbles coming to the surface all the time but there is still a bit of a shower when I shake the heat-ex's. Time and/or more Dawn should eliminate this.

Ron, I read where Marcus put some bleach in his tank. I think I'll try that and look for some algaecide.  However, this water will be in complete darkness and all the entrained?/entrapped?/dissolved? air should go out through the vent tubes given enough time......I hope. There will be no water added other than some make up for evap out the vent tubes. Won't this dark, anaerobic environment prevent the growth of algae?

Lloyd, that Redline product sounds like it's exactly what I need. I just need 10 gallons of it. What's the secret ingredient ;)

I'm probably going to drain the barrels before the final fill up, spray some bleach in them and wash them down. I'll then fill using the ingredients you good folks suggested.

Thanks, Geno

Quote from: Geno on January 09, 2011, 04:35:49 PM


Lloyd, that Redline product sounds like it's exactly what I need. I just need 10 gallons of it. What's the secret ingredient ;)



Thanks, Geno

Hi Geno,

This from the MSDS http://www.redlineoil.com/content/files/tech/WaterWetter%20MSDS.pdf

SECTION 1 INGREDIENTS  ______________________________________________________________________________

DiIsopropyl Alcohol Ether            1-40% CAS       #25265-71-8
Tri Isopropyl Alcohol DiEther       1-40% CAS        #24800-44-0
Sodium Molybdate                     2-10% CAS       #10102-40-6
Tolyltriazole                             1-3% CAS         #29385-43-1
PolySiloxane Polymer
This material is not known to contain greater than 0.1% of any carcinogen required to be listed under the OSHA
____________H_a_z_a_r_d_ C__o_m_m__u_n_ic_a_t_io_n_ S__ta_n_d_a_r_d_ (_2_9_C_F_R_1_9_1_0_._1_2_0_0_)____




Now just just need to put on your mad scientist hat a come up with the recipie.

Lloyd

Umm, uhh, hmm.........I think I'll just use Dawn, I'm already to close to blowing something up or burning something down.

Thanks, Geno

Pretty big mistake

1/15/11 One of the barrels had WVO in it before I repurposed it. I scrubbed it out real well but there was still some skin on the sides. All the soaking in hot water caused this skin to begin to flake off. It would eventually clog the heat-ex. I put a bunch of dawn in the barrels, let it soak in for a few days and began to drain them. I'd go in there with a brush every 10 minutes and scrub the sides. The water got cloudy. I hooked the tip of a heater element and it popped out. The elements are pretty long so leverage is easy to come by. Big leak, big mess, big clean up. The basement sump and pump are right next to it and it's a concrete floor so no harm done there but the whole thing has to be taken down to get rid of the wet insulation.

1/20/11 All taken apart. 3, 5 gallon buckets of wet cellulose insulation and a little bit of fiberglass as well. Not as bad as I thought it would be. I got the barrels really clean on the inside. I'll start putting it back together this weekend. Live and learn.

1/25/11 Mostly put back together. I'm at about the stage I was in post 33.

2/22/11 Been real busy at work. The project is all put back together and insulated. I just have to clean up and insulate the water lines that run to and from the tanks. At this point I can get the water up to about 135°f and then the heat ex's fall flat on their face. That's when the delta drops below 20°f. I know there is still a lot of air in the water and there are probable lots of bubbles on the heat ex's (see post 34) so this may improve when the air is gone. At this time things will work as planned but the water is not getting as hot as I expected.

Thanks, Geno

If that's how it is than so be it. It will still work. Another thing I didn't count on was how even the temp spread in the barrels is. I was expecting much cooler water at the bottom but it didn't turn out that way.

It's time to move on to the next project.

Thanks, Geno