an interesting article on absorption chillers

[mobile_bob]

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

[WGB]

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

[mobile_bob]

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

[billswan]

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

[mobile_bob]

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

[potter]

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? .

[Ronmar]

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.

[mobile_bob]

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

[mobile_bob]

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

[Ronmar]

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...

[mobile_bob]

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

[adhall]

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

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

[mobile_bob]

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

[Henry W]

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

[Mark]

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