Micro CoGen.

while looking for info on rock salt absorption chillers i came across this pdf
found it interesting, maybe a use for waste exhaust heat?

http://www.johnsoncontrols.com/publish/etc/medialib/jci/be/integrated_hvac_systems/hvac_equipment/chiller_products/absorption_single.Par.6762.File.dat/Absorption%20Single%20Stage%20Application%20Guide%20PDF.pdf

we need to find a refrigeration guy or three to join the forum
sure would be nice to have someone with a lister/oid or other small diesel engine working on using the waste heat
from the exhaust system to drive an absorption chiller, even if only to chill beer it would be very interesting.

bob g

I'm an old refrigeration man, never did do much absorption.
Look at this concept could be utilized.

aha!!!

i knew we had a refrigeration guy in here somewhere!

now that we got you down here in the refer section, we gotta put a chain on your ankle

you'll understand, its for your own good you see.

:)

btw, thanks for the link

something like this would be a good use for the excess heat off the exhaust of an engine that is run intermittently
each day, and would likely provide a significant portion of one refrigeration needs.

bob g

Got to hand it to you mobil bob this section will be a great asset to this forum now that you found WGB!

WGB the pdf you posted is great stuff, thanks.

Billswan

amen to that one, i figured the odds were pretty good out of over a hundred members there
would be at least on refrigeration guy in the house, and we found him!

:)

something i have given alot of thought to was mounting a front opening freezer box above the cogen unit
and drive the absorption unit in tandem with an exhaust heat exchanger, via a gate valve in the exhaust
much like a one of those header dump gates they used to sell for our old hotrods years ago

gate one way and you can drive a water exchanger for heat capture, switch the gate the other way
and you can drive the absorption unit. maybe set on a timer or some sort of pressure switch that trips the
gate should the system pressure get to high and divert the exhaust back to the water exchanger.

i just can't think of a more elegant and useful use for the waste heat from the exhaust system.

on my changfa, under full load operation i could run my water exchanger and use the exit heat to run the
absorption unit as my exchanger inlet temp is ~640F and outlet is ~240F. i think 240 is high enough to drive
the absorption process and would increase the overall system efficiency to a very high level.

so the unit would be a stacked affair, trigen on the bottom and a freezer cabinet on the top, for backup freezer storage
that is not opened several times a day, my bet is it would do quite well.

i am thinking now of going out and getting some of that warehouse extra hd shelf units, like you see at the box stores
and use a setup as the framework for a complete system.

or get me a 20ft shipping container and build  a power room within it? as long as it doesn't get to heavy it could be picked up
and moved half way across the country when i am ready to make my exodus from here.

bob g

Anyone know for sure what temp will drive one of these,I have a donor apartment size ide like to try. If set high enough think I could thermo syphon off of the exhaust with tubing? .

That is interesting.  The unit shown appears to have a fairly high heat input threshold.  I have seen a plans add for a small "icy ball" type that talked about input temps of around 255F.  That might be hot enough to be really compatible with a diesel exhaust and not soot up too badly.  The interesting thing about the cycle is that as you drive/boil off the final part of the amonia, the collector unit could probably be allowed to become quite hot, which might promote self cleaning.  What is the melting point of Calcium Chloride?

The drawback is that the condensed amonia is still at room temp+.  Not something I would want to put in quantity into a cold freezer box.  The heat absorbtion at evaporation will occur at the surface of the amonia, so a collector tank and some valve control would be required to make it evaporate inside a chiller box and not in the collector tank.  Perhaps something like the below pic.  

During a charge cycle, the exhaust is diverted to the generator portion to drive the amonia out of the calcium chloride.  The amonia passes to the condenser and collects in the header tank.  Once all the amonia is cooked off of the generator section, which could probably be determined by a float switch in the collector tank, the exhaust is sent elswhere and the valves at top and bottom of system are opened.  Oops, forgot a valve at the top of the collector tank, that valve would have to be closed.  The liquid amonia could only escape out the bottom and into the evaporator.  A restricted orifice would allow the amonia to enter the evap only fast enough so that it is completely evaporated by the time it reaches the end of the evap piping.  Too fast and it might still be evaporating and absorbing heat in the return pipe instead of the chiller box...  Once the header tank is empty, all the valve positions are reversed and the exhaust gas is again sent to the generator portion to cook off the amonia.

(http://i270.photobucket.com/albums/jj85/rmarlett/reefer.jpg)

salt has a fairly high melting point of around 1100 degree F iirc,
basically far above what most of our engines are able to stuff out the exhaust pipe.

finding that out a few years ago, really opened up the possibility of using salt as the
absorption medium to me.

i just assumed that the salt would melt from the heat of exhaust and become a solid mass
which surface area would be dramatically reduced to the point of making the process unworkable.

the absorption chiller seems to be a natural fit for the high quality heat from the exhaust in my opinion

the icyball ran on a small kerosene burner for about an hour to drive the ammonia, and would then chill
for about 24hours and make two small icecube trays of ice as well.

i have to believe that a 6hp or in my case 12hp engine could drive several times the capacity of a keroburner
in the same one hour timeframe.

there is probably a relationship between what the kerosene burner consumed in btu's to what the icyball
produced in ice, if we knew this ratio it would take but a few calculations to determine pretty close what
a 6 or 12 hp ( or more) could produce in an hours runtime to drive the system over the next 24 hours.

it might be quite surprising indeed, maybe one could make 5lbs ice per engine hp?

only one way to find out i guess, one of us has got to build one!

i can't imagine a more useful and groundbreaking project for the DIY'er community.

everyone needs ice or at least refrigeration, and refrigeration is about the largest and most difficult to provide
for load in an offgrid installation in my opinion.

bob g

from a couple of articles,

large scale chiller driven from the waste heat of gensets

1 megawatt of genset can drive a 250ton chiller

that works out to 4kwatts of generator capacity per ton of chiller

so maybe a micro scale unit can attain something like a ton of chiller driven by a 5kwatt generator?

thats a substantial amount of cooling capacity from a waste heat source, 1 ton refer = 12000 btu's iirc

still reading, ...

bob g

SO you build an icy ball and weld fins to the collector/generator tank and put that into an insulated can that the exhaust is run into...  SOunds like a pretty simple experiment rig to me 


With this sort of setup, you run the reefers and freezers with AC from the generator as well as top off your batteries when it is running, and store liquid amonia generated via exhaust heat to drip thru a secondary evap in those devices to help maintain temperature when the generator is offline.  This would take the reefer loads off of the inverter using waste heat? sounds like a good deal to me.

The amonia condensation could also be done with water via a heatex and that heat reclaimed.  I think my brazed flat plate heatex is rated to 400 PSI...

i am stalling folks with my heat exchanger for a couple reasons i haven't mentioned
one has to do with timeing for this forum and the other...

is an easy adaptation of it for use as a driven element of an absorption chiller.

i am working on the switchover exhaust changergear, where i can select either to drive
the absorption unit or the water exchanger.

i really like the salt based system, because once the ammonia is driven out, there is no further pressurization of the system
unlike a water based system where overheat would boil the water and make of  the need of a pressure release valve
very necessary to keep from having a bomb on my hands,
i figure if you have a pressure relief sure as heck it will operate with some frequency and then have ammonia released as well
which is anything from very unpleasant to deadly as well.

at least with salt the ammonia is driven off and the worst that can happen from that point on is the salt gets hotter.

just trying to guage how many pounds of salt is needed to make a system sufficiently large to do an average refrigeration system.
not the sort of thing one wants to build blindly and be undersized and have to start over again, bleeding off ammonia
and reworking the whole system.

it sure is a project screaming out to be done though.

my problem is not so much building such a system, but then be faced with trying to ship it 2000 miles to its final installation.
this part may well have to wait to be built and charged in place after i get moved, although getting all the engineering done
now would be nice.

bob g

Bob,

I've had some interest in this subject ever since I learned that my conventional heat pump is dying and needs a total replacement--to the tune of $7000 - $12000 USD.

So, here is a link to an interesting article describing several methods that use relatively low temperature heat sources to drive chillers:

http://www.solair-project.eu/114.0.html (http://www.solair-project.eu/114.0.html)

You will note that some of these systems operate at temperatures as low as 50 C.

Unfortunately, there doesn't seem to be much on the market right now in small sizes. The smallest I have found so far is a 5 Ton unit, which seems a little big for my needs. I'm still looking, though.

Best regards,
Andy Hall

welcome aboard our little forum!

i had hoped you would find your way here.

thanks for the link, it will give me something to read up on tonight

bob g

Quote from: WGB on October 02, 2009, 06:10:39 AM
I'm an old refrigeration man, never did do much absorption.
Look at this concept could be utilized.

I missed this! Looks almost too easy to make!

Thanks for posting this WGB.

Henry

Hi Bob,

I see some safety issues in the system you plan on using.

First, you need alot more ammonia, an explosive in its self.  It also becomes deadly to breath if it goes through the engine.

Because of this reason, most absorption units use a water chiller to transfer cold for air conditioning applications.

Certification is of concern as well as the BATFE storage regs on large farm type storages.  The one cylinder I have in stock ran almost $500.00 and I was required to sign docs, show HVAC certification and was then limited to amount allowed to purchase as of 9-11-01.

The easiest unit to build for experiment looks like a boomerang.  One end you heat and the other dips into a water storage.  Problem; unit is batch fired.


In my opinion, a water absortion system would work the best.  This type of system recirculates while operating, no batch, uses less NH4 and you can regain the heat off the water cooling coils for domestic uses.

I will need help posting a written plan but I will write it up for you to post for me.

Thanks for reading, Mark

Thanks Mark for your comments, here are my concerns or rather questions

i don't see how or rather why you would need more ammonia in a salt/ammonia system than you would with a water/ammonia system
it is the return of the ammonia to the absorption material that sets the amount of btu's of the system?

i would concur that combusting the ammonia might not be a good idea, however i have reference to a diesel engine being fueled with ammonia,  but,, i see no reason to use it as a fuel, and would take precautions to keep any leaks from being ingested.

water transfer of the cold seems like a more than reasonable approach for air conditioning, but not sure how effective it would be for
refrigeration much less a freezer application, perhaps you can address that one for me?

as for certification for its use, i figured it most appropriate to hire someone such as yourself to charge the system, not at all sure i would
want to mess with that.

as for a water based system driven by exhaust heat of an engine, that i have issues with, in that water once the ammonia is driven off
if continued to be heated will pressurize the system to dangerous levels, however
a salt based system will just run as hot as the exhaust after the ammonia is driven off without further pressurization, as far as i can tell
that seems to be a safer system. All i would have to have is a thermostatically controlled exhaust diverter to allow the exhaust to bypass
the absorption unit so that the refrigeration cycle could begin, and then divert back again when the cycle is complete with the ammonia all being reabsorbed by the salt.

maybe i am missing something here? which is likely i certainly am no expert on absorption chillers or cooling.

go ahead and write up your plan, and we will see what we can do to get it posted here on the board

thanks
bob g

Hi Bob,

I was assuming that you would be cooling a medium to store the cold and slowly release and not use the ammonia to slowly feed back to the absorbant.

For refrigeration in its easiest form one could make ice to release over a period that could be monitored for the next firing needed.  If your condenser coil is liquid cooled as well as the absorbant then your complete cycle time wouldnt be much slower than a pump system.

Your concern about the overpressure of water is over come by using a medium to transfer heat as in the design of the Faraday systems of the 1930's.  They used Trichloromonofluoromethane for the heat transfer and not direct heating of any absorbant directly.

The addition of Hydrogen to the system will also drop total system pressure to work at or below 200 PSI, which is about 250 PSI lower than our current R134a systems.  See Electrolux air cooled systems of 1935.

I feel that the system could be moved outside of the building structure, affording a higher level of safety.  Less refrigerant in a recirculatory system with an absorbant medium would put the cold in place for storage with a safer compound rather than large amounts of ammonia sitting in suspension over the cold box suspended in hydrogen or pooled up in the freezer box.

I would also consider, would a valid company come to your house to fill a homemade unit with a potentially deadly gas.  Are you going to pull the permits on this system?  Have it engineered?  Inspectors check system?  Install required "safety items"?  Subject to annual inspections?  Install fire code compliant items?  BATFE inspections?  Keep product records?  Aquire zoning rulings?

Maybe these wont be an issue in the Midwest but in Washington these are!  As owner of a repair service would you allow for the liability of charging a homemade system with any type of .... that could be life threatening?  Would an insurance company cover such an action?  I would be the one who would hate to find out first hand!

On a positive note I think your system has alot of potential and would work favorably.  I look forward to your final system.  I have always liked hvac systems and have alot of reference material on hand and would be honored to help with any system you move forward with.

  I think that their could be safer ways of skinning this cat.  I would like to be able to say that I atleast pointed out some options.  I know you have the skill to design a sound system, but in an open forum, I'd hate to see someone not qualified get hurt. 

Just looking out for you, Mark

first of all i would not build such a system to be placed within a dwelling that was habitated by man or beast
however i would have no such problem placing it in a detached engine room.

my thinking was a refrigerator or bulk freezer compartment above the engine drive, basically for bulk cold storage
of food, or even for makeing ice for other uses elsewhere.

as for homebuilt, i have little doubt that one could build to as high a standard as any commercial product, and could
certainly pressure test to whatever level one saw fit.

and for the right amount of money i can find just about anyone that will do just about anything, so getting the unit charged
buy a refer guy is not likely to be a problem.

then there is this, ammonia is but one absorption refrigerant, there ought to be other compounds that could be used in a heat driven
system?  seems like i have read of others. Even if not as efficient if the heat source is a waste product anyway, why not use a less
efficient compound?

i don't know if i would ever build such a system, but there is a certain appeal to useing the waste heat for something productive
and i cannot think of a better use for it, at least after making domestic hot water or space heating. of course in the summer the need
for one is less and none for the other, but ice is nice at that time of year.

as you know i already have the sanden compressor and it will be used to drive the refer box via a cold plate, so my need for an absorption
system would be more of an experiment rather than i have to have it to function.

Good points though, thanks for the input

bob g

Bob,

One of the interresting ice box conversions upon the introduction of freon type systems was the Calcium Chloride [CaCl] ice systems.  The absorption drive was put in place outside the house structure in a small housing.  Most access doors for ice boxes were designed for north wall of structure.  The Calcium Chloride was cooled to below freezing [melt point at 0 degree F] and pumped through a cooling plate inside the ice box door.  This sytem allowed the direct use inside the structure without any of the ammonia entering the dwelling.  Safe but effective.

Mark

   Some good info ----------- Crosbey Ice Ball