Ask Me Help Desk - Air con water pressure

Hi

I'm new to this forum and I hope you guys can help with my question.

I'm by no means an expert on air cons & I work in the hospitality industry but here goes.

I have a problem with a unit which is located on the 5fh floor of a hotel, this is a water cooled unit and is fed from chillers on the ground floor. The unit is not able to cool effectively & I have tried almost everything I know to correct it. The unit is operating fine & I have discovered that the return pressure is higher than the supply pressure although not by much and I suspect that is the reason for not cooling effectively and also suspect the supply pressure drop is due to a restriction in the pipes. Can any one tell me if this sounds feasible and if so what (if any) pressure differential there should be.
Also is there a standard for split air con units to determine the lowest cooling setting achievable, by that I mean is there a set mimimum temperature design by the manufactures, I know in the above case this is probably determined by the chilled water temperature.

Hope you guys can help

Thanks and regards

If the air handler you have doesnot give you the cooling capacity as stated by the manufacture... here are some of cause: dirty coil / fan, not enough water flow ( air bound,supply too small valves / piping), fan speed... assuming your supply ch.w temp.. is OK ( 42- 52F ?). What your temp S/ R?. returns' pressure higher than supply may indicating gauge not accurate or supply valve close...

I do not see how the return pressure can be higher than the supply unless you are measuring it at the bottom, and the supply on the 5th floor. Best way to find the correct pressure is to try checking the pressures of the other units on the same floor. You could try breaking the pipes and see if any junk in the line is flushed out. You can unscrew the guts of most gate valves, allowing water to flush out something restricting the line. After checking this, post back if it doesn't help.

Hi Guys

Thanks to you both for replying.

Labman & Caibuadday... I have checked the pressures on the gauges at the ground floor by the chillers and the supply pressure is approx, 450kpa and the return pressure is approx. 300kpa which I think is about right, I have not physically checked the pressures on the 5th floor by means of a pressure gauge, only by removing both the supply & the return line pipes and the return line seems higher. I did check the cooling on all units on that block and they all appear to be the same, which as far as I'm concerned is not enough cooling (only being able to cool to about 18deg.) The other thing I checked was to disconnect the return line from the unit and valve off the return to the chillers and connected a pipe from the return outlet of the unit and ran it into the bath and so now I have a constant flow through the unit, this now produces perfect cooling, which to me indicates that there is no correct flow through the unit when the return line is connected. Hence my question about the pressure, which would appear to be causing a poor flow situation and the water not being able to flow through the unit is not being able to supply cold air efficiently as the water is becoming static in the line or its getting return water which is warmer than the supply temp.
The fact that I tried the water into the bath removed the issue of air bound system unless there is an airlock in the whole system somewhere else, Fan, coils etc have been checked, I did check the valves and all appears o.k although we do have a automatic controller which governs the supply of chilled water depending on the demand required but this appears o.k also. The suggestion about not enough water flow could be a possibility and maybe a check on the pump impeller is a good idea but based on the pressures I'm assuming that's not the problem.

Thanks guys, I hope I explained it well enough for you to understand.

Look forward to your reply.
Regards Cremora

18 F is a good temp differential... what is the design flow... try increase flow with balancing valve? ( watchout for amp!)... check air eliminator?. does pipings have a lot of horizon run?. welllllll goood luck! How old is the system

It sounds to me like there could be a restriction in the return line. You could try a plumbers snake in it. Before you do that, look at where any debris you knock loose may go. You do not want hard scale getting into the pump. If the return line goes into a vented tank at the bottom it should actually have a strong suction unless it can draw air in.

Has it always been like that? Does each floor get a little worse? As you go from the ground floor up to the 5th floor, you will have less pressure losing about 200 kpa by the top. That is a big chunk of the 450 kpa at the chiller.

Quote:

Originally Posted by caibuadday

18 F is a good temp differential...... what is the design flow....try increase flow with balancing valve? ( watchout for amp!).... check air eliminator???...... does pipings have a lot of horizon run?.... welllllll goood luck! how old is the system

... base on the pump discharge your S.CH.W should be about 230kpa and R.CH.W about 170kpa at the coil ( assume each Fl total height of 3.7m)