Absorption chillers - low load performance

[russmech]

Hello, I'm getting involved in the design of a chilled water plant (approximately 3000 tons)for HVAC cooling. Our location has a load profile with ALOT of cool temperatures 55F to 64F), so part load performance (of the total calcualated plant load) will be important. Because the chiller plant may coincide with a cogen plant, we're looking at steam absorption chillers. We've been advised to make it a "combined" plant, i.e. absorption + electric because aborptions chillers do not like part load operations and do not "trim" well. The question becomes how to mix relative sizes of electric vs absorption. I was told absorption chillers don't like part load operations (below 50% capacity), but other charts indicate a COP that gets better as the machine is unloaded, right down to the Mfr's low of 30%. Does anyone have any advise and/or literature/sources that can help me with low load ops on absorption machines and how best to pick sizes? Thanks.

 

[imok2]

russech, Check this out:

http://www.newbuildings.org/downloads/guidelines/AbsorptionChillerGuideline.pdf

 

[absrbrtek]

I don't understand what they mean by "trim" well at low loads. IMO trimming a machine at less than full load conditions is usually undesirable. Once the machine is trimmed at full load the low loads fall into place, and no trimming is nessasary.

 

[russmech]

Thanks imok2, I'll review that info again.

Maybe I should've just asked "Does anyone have any experience with the unloading characteristics of lithium bromide absorption chillers?"

 

[stanlsimon]

My limited experience with these machines is that they are more labor intensive than freon compression machines. If flow rates are too low they will "rock up" and mechanics will spend hours with blow torches blasting on the piping, trying to get the thing going. Maybe the new ones are better.

 

[MedicineEng]

If you have part loads, for electrical I would suggest a chiller with VSD. It can save you a lot of energy. We installed one for brine with very nice results.