Help! - Need startup override solution for Carrier twin screw chiller.

[NorCape]

Hi All,

Have installed a Carrier 30HXC155AH chiller in North-West Australia which, on commissioning, failed to start because the water in the CHW loop entering the evaporator was above 25degC (supposedly a set point to protect the compressor motors from over current).

We were able to eventually bring the Carrier unit online due to the fact that we still have two old Trane chillers on site that were used to bring the CHW loop below 25degC. These old Tranes don't seem to care what temperature the CHW loop is at. They just turn on and start cooling.

With the old Tranes destined to be replaced by two more identical Carrier units, and ambient temperatures in excess of 30degC most of the year (even at night), we may shortly be faced with an unrecoverable situation whereby we are unable to start any chiller because the CHW loop temperature is above 25degC (eg from a prolonged power outage).

Is anyone on the forum aware of a control based override or 'battle-short' that would permit us to start one of the Carrier units under a high CHW inlet temperature situation? Any other way we might 'trick' the system into starting?

Thanks.

Ian

[HVACRsaurus]

Hi Buddy,

1) Remove chilled water sensor from pipe & put it in a cup of cool (less than 25°C) water to get the chiller underway..

Or

2) Take various resistance readings (unless you have access to a resistance chart) of the temperature sensor at known temperatures. Substitute a resistor with equivalent resistance to 20°C water at the terminal strip..

Or

3) Buy a spare temperature sensor, when needed, plug onto harness & give a squirt of that freeze spray stuff (or just use rexona)

[HVACRsaurus]

Further,

Whilst I'm not sure, the sensor could be the 10K Type II

If so;

40°C = 5,325 ohms
35°C = 6,530 ohms
30°C = 8,056 ohms
25°C =10,000 ohms
20°C = 12,494 ohms
15°C = 15,714 ohms
10°C = 19.903 ohms
5°C = 25,395 ohms

Say you have chilled water at 30°C, connecting a 2K ohm resistor in series with the temperature sensor would bluff the controller to 25°C.

An adjustable potentiometer could be fitted as a permanent feature, obviously it would always need to be rotated to zero position as quickly as possible.

Perhaps others could confirm the resistance table.

Happy tinkering.

[Brian_UK]

Not sure of your exact model version but have read that some versions can be load limited.

Is this something that can be done with yours in conjunction with fooling the controls as suggested above.

[NorCape]

Thank you all for your responses. The answers align with what we were thinking was the easy answer but the supplier was trying to sell us cooling towers and thermal storage storage systems at a course a nice price tag.

Shall give your suggestions a try and see what comes of them.


Cheers

Ian.

[Magoo]

Probably limit the loading until water temp gets into safe zone, no point tripping breakers and overloading compressors. Would not look good on a warranty claim for a failure.