Waste Heat Refrigeration

[macmet]

Where I work we provide heating for systems such as industrial heating, process heating, greenhouses, etc. Often times our clients burn fuel (such as wood) to minimize disposal costs. However, when the heat load is small, like in the summer, they cannot simply burn it, as they have no means of 'getting rid' of the heat. I was instructed to look at absorption refrigeration to use this potential waste heat to cool their buildings to 22degC in the summer.

The heat output of a typical system is ~15mmbtu/hr. 1 ton of refrigeration is 12,000btu/hr. Does that mean that we can provide 1000 refrigeration tonnes?

This is not my area so can anyone tell me if I am over looking something(s) in this calculation I would really appreciate it.

 

[MintJulep]

No, those pesky laws of thermodynamics get in the way.

Something about no process being 100% efficient.

 

[willard3]

The first law of thermodynamics: the best you can do is break even

The second law of thermodynamics: you can't even break even

I think the paydown for absorption systems running on recovered heat will be way more than 10 years.....return is better on T-bonds.

 

[macmet]

ok, I ignored efficiency because I was wondering if I could approach this project this way not so much my exact numbers.

The reason I ended up posting was I got a budget quote and the price was so high I couldn't believe it. Which goes along with what willard3 said, so I guess it was acceptable.

Thanks for the help though

 

[sterl]

Your 15,000 BTU per hour to produce 1- TR is about right for single effect type absorption units. 1000 Tons of refrigeration would then require about 15 million BTU/Hr of net input and that scale of equipment is certainly available, though if you have that big a load at steady state, you will almost certainly be able to rationalize double effect absorption unit.

The operation of absorption may be a different topic. There is a long ramp up and a long ramp down for a lot of this euqipment...it suits a campus-central system arrangement but the delivery of waste fuel may not follow any pattern that would yield continuity to the process. And the fuel prepping and processing itself will be a considerable investment.

 

[macmet]

Thank you Sterl. Long ramp times would not work well for our application as we still may need to use our heat for heating at night time, but were hoping to cool during the day.

Everyone I have talked to has given me the impression that absorption cooling is not a practical option for us.

Thanx for everyone's help.

 

[imok2]

Have you given some thought about a waste heat boiler the generate steam for electric turbines? you could ombine this with your existing electrical for driving your chillers in the summer.

 

[macmet]

This heat is provided as hot water. Steam is not a good option in this case because of the regulations requiring operating engineers.

In this particular case elec. generation has not been mentioned (b/c of the hot water). We do have some potential projects where staffing is available to meet the regulations to produce steam. Often times producing elec. power from is not feasible because we have no heat load for 6 months of the year. We are starting to look at condensing turbines/cooling towers to overcome this but capital cost is too high...but with energy costs increasing this is option is looking better.

If we could use the heat for cooling(or else?) we would have a use for the heat year round and the system would become more economically practical.

 

[mauner]

You can do both with your waste heat. The dual unit can produce electricity or airconditioning.

Check out this website:

http://www.energy-concepts.com/

 

[freefallingbody]

macmet,

I have two gas engine driven power plant of 1.4 MW each generating 4.0 TPH of 8.0 bar steam and 300 TR of chilling from engine jacket cooling water at 80 deg.C.

This system can be called a trigeneration system as it generates electricity, steam and cooling.

Absorption chiller can make very good economic sense if your power cost is high. In India, many plants are coming up with trigeneration system.

Regards

Dinesh

 

[cme]

Absorbers are bad news ...... I have all these horror stories from hospital facilities managers

 

[imok2]

I recall at a major L.A. County Hospital where we spent many weeks retubing two 1600 ton Trane absorbers only to have them both go belly up within six months. So there we were with this major delema. We went to various large Contractore to see how fast we could back on line, the fastest was over two months. We decided to do the job ourselves, so we poured a large cement pad outside the power plant and ordered 12-160 ton air cooled Trane Chillers with new chilled water pumps and we series-parelleled them, installed new MCC panels, controls and were on line in 27 days of course we worked 24/7. All this was done by the County of Los Angeles Employees Craft people. We eventually had a contractor remove the old absorbers and replace them with 3 York centrifugals as for the existing air ooled chillers we used them to replace older equipment in other County buildings. We had to do this twice so we had a good supply of 26 fairly new chillers. Ahh, those were fun times. :>)

 

[willard3]

Best chiller/boiler with absorption operation I have seen was in a hospital. Never froze, load-followed very well and never broke down. Everything worked, everything was painted and everything was clean.

The dude who ran the room was ex-german submarine capt.

 

[HVAC68]

Burning fuel to save on disposal costs ??? Did somebody look at the "environment angle" at all ???

HVAC68

 

[MedicineEng]

Is it possible to use the hot water for production processes, in the toilets to heat up shower's water or in your canteen (if any)?