Problems in r22 chiller design

[umeshpradhan]

Hi
I have designed a chiller and I am facing problems with low suction pressure
The design conditions are
Medium - Water
Refrigerant - R-22
Water inlet temp - +11ºC
Water outlet temp - +6ºC
Evaporating temp - +1ºC

Chiller design: Type DX Chiller, Double circuit
Tube OD: 3/4", 20 Gauge plain copper tubes
Tube Length: 12 Ft
No of tubes:380 Nos
No of pass (refrigerant side):6 Pass (per Circuit)
No of Pass (Water side):22 Pass
No of tubes per pass:

1st pass: 9+9
2nd pass: 14+14
3rd pass: 28+28
4th pass: 31+31
5th pass: 52+52
6th pass: 56+56

The above chiller is designed for 135 TR Capacity, but I am unable to get the desired capacity.
The suction pressure is very low (Between 2.8 to 3 Kg/Sq Cm) at 6ºC chiller outlet

The chilled water flow through chiller is 90 Cu mtrs/hr
Temp diff across the chiller is not more than 3.5ºC

I request somebody to comment on this and suggest the remedy

Umesh

[Andy]

Hi umesh:)

what pressures and temperatures are you measuring?

Full log please.

Kind Regards Andy:)

[chemi-cool]

You also have to check the water flow and water pressure drop on the heat exchanger.

You might have a too small pump.

[fridgy]

You also have to check the water flow and water pressure drop on the heat exchanger.

You might have a too small pump.

it could also be the flow rate is too high. not enough dwell time in the evaporator will affect the heat absorbtion, i.e lowering the suction pressure and not achieving a good split. try slowing the CHW pump or restricting the flow to see if it makes a difference. good luck

[HallsEngineer]

Is it me or does that sound like a lot of passes for a chiller? Your expansion valve would have to be very good to cope with all conditions on a 6 pass chiller circuit. I would suggest a 2 or 3 pass circuit and check your valve sizing.

[Magoo]

'What is the TX valve superheat?
magoo

[D.D.KORANNE]

Calculated flow on the 135 tr is 83.7 m cub per hour .

1) probably flow appears to be high v/s design i.e. 90 m cub per hr .

2) chiller pump heat load is accounted in the design load calculations ?
3) liquid temp aproaching tex ?
4) temp at tex bulb ?
5) temp at comp suction ? High suction superheat .
6) pr drop in tex valve distributor ?
7) what is condensing temp ?

[moideen]

very intresting subject,but this first poster do not react!no manners.

Moideen-Dubai
:(

[TitanioMan]

Hello Umesh
from my point of vew
you do have a lot potential to do your needs with the chiller units, lot of area and tube arrange is OK, on DX chillers the unit is really 1 pass only on water side with maybe 22 buffles (looks a lot for me), this can cause a lot of pressure drop and reduce water velocity contact on tube face (the heat exchange rate is proportional to this velocity), you need to increase suction pressure with more liquid thrue TXV valve and set to 0 °, if you are using pure water do not operate chiller below -1 (3.5 to 3.8 BarG), revise the actual superheat and with temperature you can find if some ice is building inside or need more refrigerant, the ice cause heat transfer deficience

[umeshpradhan]

Hello everybody

First of all I am very sorry for not replying to your posts, as I was unwell and hospatilized, sorry Mr Moideen.

Firstly as replied by Hall engineer UK, pl clarify why I have to go for 2 to 3 pass, instead of 6 pass, will it not cause reduction in the per tube velicity and accumulation of oil?

As mentioned by Mr. DD Koranne, the recommended flow rate by him, of 83.7 cu m /Hr, will cause the temperature difference across of the chiller will increase, the total capacity will not change.

I have tried setting the expansion valve as suggested by titanio man but there is no change in the suction pressure.

My problem is the temperature difference is only upto 3.5ºC across the chiller and the suction pressure is not increasing, it goes upto 2.5ºC

I am unable to understand the proble, as I am not getting the required capacity

Regards

Umesh Pradhan