water cooled units

[weidit]

hi guys been coming across water cooled units a lot recently i know daikin need 60 litres per minute per condensing unit.

i was wondering what the signs would be of the flow rate was say halfed? As this as the a/c service man i see as something we cant check onsite.

dont want to be checking units for hours and hours if its bad flow rate?

i have been told its can hold compressors out. is this correct?

Many thanks

[frank]

On water cooled condensers, the flow rate is set to match the heat rejection rate. If you know the duty of the condenser, it is very simple to measure the temperature difference to calculate the water flow rate - so it is something that should be done during the course of the service/mantenance visit.

If the flow rate is halved, the discharge pressure will increase leading to a reduction in refrigeration effect.

Most water cooled condensers have a 3 port bypass valve arrangement to regulate the water flow based on discharge temperature, thereby allowing for differing evap loads

[VRVIII]

hi guys been coming across water cooled units a lot recently i know daikin need 60 litres per minute per condensing unit.

i was wondering what the signs would be of the flow rate was say halfed? As this as the a/c service man i see as something we cant check onsite.

dont want to be checking units for hours and hours if its bad flow rate?

i have been told its can hold compressors out. is this correct?

Many thanks

Alec,

The nominal flow rate for a Daikin water cooled VRV is 90 L/min, a system should never be designed on the minimum flow of 60 L/min that you are referring to. This is the absolute minimum based on certain conditions (inlet water temp/indoor capacity), the unit will operate at reduced capacity due to the high head pressure limiting function reducing compressor speed.

I indicated the checks you could do for low water flow in reply to your previous post.


A liquid line pressure of 33 bar is excessively high, I suspect you have insufficient water flow through the condenser plate heat exchangers.
Have you checked the following:
1/ Head pressure (must be <30bar – limiting function will be active >29.5bar)
2/ Entering/leaving water temperatures (difference should be < 10 C)
3/ Water flow rate (nominal flow rate is around 90 l/min per unit)

Each unit should have an inlet water strainer and a flow switch connected across terminal Block X2 connections 3 & 4. I would suggest you check all water strainers and correct operation of the master unit flow switch this could also prevent the master unit operating.

[weidit]

The one I have seen recently has 30 degree in and when running in full cooling has 40 degrees return.

Sorry frank but how can you determine the flow rate without hooking into the drv valves? And taking proper flow readings?

[VRVIII]

The one I have seen recently has 30 degree in and when running in full cooling has 40 degrees return.
Yes but what was the head pressure? What was the compressor capacity?


Sorry frank but how can you determine the flow rate without hooking into the drv valves? And taking proper flow readings?

Frank,
It can be very difficult to calculate the duty of a water cooled VRV during normal operation, the compressor capacity, indoor EEV openings and air on temps are continually varying. If the water flow rate was low the duty would be further reduced due to the high press limiting function reducing compressor speed to prevent an HP trip.

You could calculate the flow rate by measuring the heat exchanger pressure drop then compare with pressure drop curve table (providing the heat exchanger is clean!) or measure the flow rate properly at binder points or metering station.

[frank]

Frank,
It can be very difficult to calculate the duty of a water cooled VRV during normal operation, the compressor capacity, indoor EEV openings and air on temps are continually varying. If the water flow rate was low the duty would be further reduced due to the high press limiting function reducing compressor speed to prevent an HP trip.

You could calculate the flow rate by measuring the heat exchanger pressure drop then compare with pressure drop curve table (providing the heat exchanger is clean!) or measure the flow rate properly at binder points or metering station.
I'm well aware of that :), but you can calculate flow rate by measuring temp difference with the unit at any point of it's cycle....preferably at full load conditions.

The OP seems to be struggling with the basics. My post was intended to point out that, by calculation, you can determine the flow rate without binder points, etc.

As this as the a/c service man i see as something we cant check onsite.

dont want to be checking units for hours and hours if its bad flow rate?

:)

[weidit]

So what would you news to take
measurements off to work this out then? Is it more a test that you can do to see if it's not correct?

You can't test and say it's gettings 41 litres per minute can you? Without checking the drv test ports?

Many thanks