Absorbtion chillers

[acrh502]

Ran across a building with a york absorbtion chiller. I am questioning the fact that all the air handling equipment has two way CW valves. Only bypass I could find is a small 3/4 inch bypass line on the end of the loop. Can absorbtion chillers tolerate low water flow? This is a primary system with only one CW pump.

[bradysmill]

What size is the main runs?
This is a cheap way of doing it, but they maybe banking on the fact that a load may exist pretty much all of the time.
Should be three way valves though.

[acrh502]

The mains are 6 inch,just can't believe this installation.The pump has a vfd but it doesnt work. The chilled water is only used for comfort cooling and they are running the chiller year round.

[bradysmill]

Sounds a little hairy doesn't it. You may be missing something like a pressure differential controller somewhere else on another bypass line?
Maybe the 2 way valves are fixed open and air of AHU's are controlled by face and bypass dampers only.....Just saying that maybe there is something else...

[gsxrsquid]

it has been a long time since I ran absorbers though I liked them a lot. most of them were 500 ton plus in size and used steam rather than direct fired. they didnt have much in the way of safety controls then and you could salt em up good if you werent paying attention.
The important thing with absorbers is low flow isn't a problem if you "throttle" them back. Since the building is cool and the absorber hasnt turned into a pillar of salt (I am assuming lithium bromide) I would assume the controls back off the heat when the load drops.
I would guess when all the CW valves start closing the VFD was designed to back off. The chiller should then back off too. one of the things I liked about absorbers was that you could "run" it without applying heat to the unit no problem. On the opposite end though if you put the fire to it you BETTER have a load or you will be putting a torch to it at least. I have seen 800 ton absorbers freeze up in a couple hours and rupture the tubes because the load dropped and the engineer didnt throttle back. I dindt do it. :-) I am assuming it is a direct fired unit?

[acrh502]

This unit is steam fired and modulated. It seems to run ok but I noticed at full load it is only doing about 6 degrees. Going to start checking flows this week and check out the vfd. Thanks for your input. I'll see if I can info from york on min and max water flows. No face and bypass on anything. All the valves are modulated 2 ways to control temperature. I walked the plant many times thinking I missed something also, But if I did I havent found it yet.Thanks again.

[Edited by acrh502 on 06-04-2006 at 07:37 PM]

[nun]

Does it have a chilled water bypass. When the 2-way valves close down it will open and the chiller will have flow. Whats wrong with the VFD? BAS?

[absrbrtek]

Unlike a centrifugal where you can unload it pretty quickly, an absorber holds alot of potential cooling capacity and does not unload quickly. Ive seen some machines take close to an hour to go thru a dilution cycle. The entire time your still chilling the water to some extent. I would look into the sequence of operation further.