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Chill water make up tank over flow
Hello hydronic cooling gurus, I have a chill water system with two make up water/ expansion tanks, there is an over flow piped to tanks and is dumping very frequently and consuming chill water and treatment. The refrigeration capacity serving water system is roughly 1800 Tons absorption machines. Water system capacity, best guess is about 40k gallons. Three chill water pumps at 2250 GPM each. What I have noticed about make up lines from City Water feed is piped directly with no regulation, only gate valves to stop and isolate, and make up water trickling into tanks, gate valves fully open, which makes no sense to me.
Also have issue with chill water pressure differential, barely have 7 pound diff at absorbers with two pumps running with drives at 100%, any less rate and differential is nearly equal at machines. Pump strainers clean. There was an issue with strainers dirty recently and differential pressure improved after cleaning.
Can anyone advise on this? Thanks Boys!
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Originally Posted by
Coolthings107
Hello hydronic cooling gurus, I have a chill water system with two make up water/ expansion tanks, there is an over flow piped to tanks and is dumping very frequently and consuming chill water and treatment. So, what controls the overflow dump. is it water pressure? The refrigeration capacity serving water system is roughly 1800 Tons absorption machines. Water system capacity, best guess is about 40k gallons. Three chill water pumps at 2250 GPM each. What I have noticed about make up lines from City Water feed is piped directly with no regulation, only gate valves to stop and isolate, and make up water trickling into tanks, gate valves fully open, which makes no sense to me. Closed circuit water systems that I have worked on a dual valve on the makeup water. One valve regulates the system water pressure (typically set at 15# for the pump suction side of the system). the other valve is a pressure relief valve to release pressure (typically set at 30#)
Also have issue with chill water pressure differential, barely have 7 pound diff at absorbers Two absorption units? with two pumps running with drives at 100%, on a single water circuit? any less rate and differential is nearly equal at machines What is the differential are you speaking of, and why is being equal bad?. Pump strainers clean. There was an issue with strainers dirty recently and differential pressure improved after cleaning. What differential do you want to have?
I take it the third pump is a backup pump for a single water circuit.
"I have never let my schooling interfere with my education."
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NEVER STOP LEARNING.
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I hope you don't have a steam bundle leaking. I'd check whatever means you have to see if you have excessive boiler feed makeup.
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To start with if you don't have a pressure regulating make-up valve the make-up was designed to be done manually. In that case close the make-up valves and add a regulator or make-up the system manually. Second assuming your system is full of water and the head tanks are overflowing you need to drain them down enough for an air cushion on top of the water. Then the tank pressure needs checked to make sure the system charge pressure is correct. When all this is done check the system pressure drops and verify they are within design.
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Safety concern:
With the makeup valve setup that you describe, there also must be a check valve in each makeup to prevent system water from ever backflowing and contaminating the domestic water supply
"I have never let my schooling interfere with my education."
Mark Twain
NEVER STOP LEARNING.
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I agree with the other guys. You should have a dual valve on the makeup. Pressure reducing valve set at 12# and pressure relief valve set at 30#. If you don't have the pressure reducing valve and the make up water is open, you'll have city water pressure (about 60#) on the system and that's why the pressure relief valve (30#) is blowing down.
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PRV and relief settings should be specific to the building. It's based off standing head pressure (height) of system.
There should be a PRV and a backflow preventer before it in the city water line. It is typically plumbed in on the suction side of the pumps.
It sounds like your expansion tanks are water logged (full with water and not much air). You can isolate the tanks and drain out much of the water.
When there are temperature swings in the system, there is nowhere for the water to go when it warms up (expands). This could be a lot of water depending on how large the system is. All it takes is a couple degrees of change.
As for the differential across the absorber chilled water bundles, are you using one gauge?
Last edited by BennyD; 06-20-2017 at 06:39 PM.
Reason: Hit send before finishing...
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Ran a quick calculation. Based off 40,000 gallons and a rise from 42° to 44°, it will grow by approx. 56 gallons!
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Originally Posted by
BennyD
Ran a quick calculation. Based off 40,000 gallons and a rise from 42° to 44°, it will grow by approx. 56 gallons!
That is around 10 cubic feet. The size of the expansion tanks and their air cushion should be considered. Mistakes and shortcuts happen.
"I have never let my schooling interfere with my education."
Mark Twain
NEVER STOP LEARNING.
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Originally Posted by
lynn comstock
That is around 10 cubic feet. The size of the expansion tanks and their air cushion should be considered. Mistakes and shortcuts happen.
Speaking of mistakes, one common one is automatic vents on a normal expansion tank. Water likes air and over time, it will pull the air out of the tank.
Auto vents are fine with bladder style expansion tanks.
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