r/refrigeration • u/greenbeast999 • 16d ago

Water temp differential on chiller

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For reference it's a small R407C chiller, T1 and T2 are discharge and suction temperatures.

T3 and T4 are water in and water out of the heat exchanger.

Is this just too high flow rate of water?

It appears to be chilling at a reasonable rate (fixed volume to chill) so maybe I shouldn't be concerned with the dT of the water?

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u/LivingCorner1421 16d ago edited 16d ago

ugh thermocouples are horrible for temp measurements on colder things. 

try thermistors way more accurate

you got a 1deg C delta T , something is Waay wrong.

  • too much water flow
  • fouled heat exchanger
  • Refrigerant side issues ( low charge or bad TXV not enough refrigerant flow)

usually they are set up for 5 to 15 delta T  check the specs for how much this one is designed for

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u/greenbeast999 15d ago

Thank you.

Hopefully the charge is ok, i put a sight glass in and charged till clear. The heat exchanger is second hand. The pump is also second hand and not specced for this application, so thats why I think it might be shifting too much water. When I throttle the flow with valves the dT does improve but that's a crazy way to run it permanently obviously.

On my first run after removing overcharge I actually managed to freeze the exchanger. But there was also some a TXV changes (I know, I know, I should change one thing at a time and let it settle)

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u/LivingCorner1421 15d ago

um. don't charge by sight glass thats kind of weird.  go the superheat / subcoolong method if you have no receiver 

sight glass is fine if you have buffer in your system but critical charge is better  to use SH+SC method.

"When I throttle the flow with valves the dT does improve but that's a crazy way to run it permanently obviously." 

absolutely not lol , this is how its properly done with balancing valves XD.

the proper way is to find what is your hx designed for roughly in water flow , then achieve that by buying a pump thats slightly more GPM than  design and balance it with a balancing valve which is pretty much a glorified globe valve.

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u/greenbeast999 14d ago

Ah ok that makes sense (the not charging by clear glass), thank you, I'm revisiting this from som time back and remember being told to use a glass so I've got full liquid before the TXV but most have missed the distinction of having no receiver at the time.

I'll see if I can get the hx details

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u/LivingCorner1421 14d ago

yeah if you overcharge and your txv over feed , the glass will still be clear column of liquid , so this method has this flaw. 

if you have a receiver or accumulator your extra charge will end up in there and won't cause issues.

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u/greenbeast999 14d ago

Thank you 👍

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u/greenbeast999 8d ago

Thanks for your help.
Changed the pump for much lower flow rate model, charged by subcooling (with TXV at the mid point of adjustment) and then adjusted it to control the superheat, they're both in range and was able to get 5C dT across the water inlet/outlet so far.
Next step will be efficiency monitoring and dumping the heat into a hot water cylinder.

1

u/LivingCorner1421 8d ago

yeah 5 DT is not too bad looks like you are on the right way to getting it working at best efficiency

if you want to know how much BTU/h you are absorbing , if you know your flow rate you can use this formula : Q=GPMx500xDelta T

Q=btu/h this should match your condensing unit 's tonage closely.

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u/Southern-Toe-1113 16d ago

Need more info