Ammonia refrigerator control by inverter

[torranin]

As my previous question about Ammonia refrigerator package "MYCOM" "N8B".
After I went to confirm customer application.
Their application is Temp control.
The control system will control numbers of solenoid valve to On/Off operation. Compressor motor run at full speed.

Our idea to apply inverter for this application,
We will open all solenoid valve.
And apply inverter to control motor speed.
Motor speed will be command from controller as multi-step (Speed range 800-1200 RPM as MYCOM advice).
The speed command signal are dry contacts which were connected to solenoid valves.
We expected this application will help customer to save energy.

Do you think It is OK?
If you have any, Please kindly advise?

[Tycho]

You should take the signal for inc/dec speed from the suction pressure.

1. start the compressor unloaded at minimum speed

2. increase the solenoids for cap step by step

3.when compressor is in 100% on the solenoids start inc speed step by step.

reverse for decreasing cap.

This will save many start stop and give you a very smooth operation, plus at minimum cap the compressor load would be next to nothing.

[Josip]

Hi, Torranin

It will be much better to remain within your previous thread, but here is also OK...

Our idea to apply inverter for this application,
We will open all solenoid valve.
And apply inverter to control motor speed.
Motor speed will be command from controller as multi-step (Speed range 800-1200 RPM as MYCOM advice).
The speed command signal are dry contacts which were connected to solenoid valves.
We expected this application will help customer to save energy.

Do you think It is OK?
If you have any, Please kindly advise?

It is possible to make it as you described, but for me suggestion given by Tycho seems better....

....start compressor unloaded until come to minimum speed (800rpm)....to obtain oil pressure...

then switch on one by one solenoid coming to 100% capacity....then speed up..... and the same way back......

....only what you have to change is to control capacity by evaporating pressure i.e. in real time..temperature control is maybe too inert...

but maybe I am not right...because we do not know how you control capacity now

Best regards, Josip

[torranin]

Hello, Tycho & Josip,

Thank you very much for your advise.
I just come back from Chinese New Year Holiday.

About your advise for start/stop peroids,
I still do not understand clearly.
May I confirm my understanding.

- Close all solenoid valves when we start compressor
- Run compressor at min speed until oil pressure up to normal operation level.
-open solenoid valve one by one until all open.
- motor speed control by temp control loop.

Is it correct?

By the way, I still do not understand clearly about the reason why.
I guess because of energy saving purpose. is it correct?

[Tycho]

Hello, Tycho & Josip,

- Close all solenoid valves when we start compressor
- Run compressor at min speed until oil pressure up to normal operation level.
-open solenoid valve one by one until all open.
- motor speed control by temp control loop.

Is it correct?

By the way, I still do not understand clearly about the reason why.
I guess because of energy saving purpose. is it correct?

When you start the compressor, start it in 0% capacity, when the compressor has minimum speed and has oil pressure, start increasing capacity step by step.

when the compressor has 100% capacity, start increasing speed, step by step.

this should be controlled by a pressure sensor connected to the low pressure liquid tank)

with this system, you can have the suction pressure at 0.1 bar, and you wont get any jumps in suction pressure when the compressor goes down in capacity.

when the compressor is at low speed and minimum capacity, the performance is so low that even a small load on the system can keep the compressor running.
This helps you keep a very stable low temp, compared to if the compressor stop on low pressure and you have to wait for the pressure to go up before it starts again.

How is the weather in Thailand now? I'm going to Phayakkhaphum Phisai in one and a half week

[torranin]

Hi, Tycho,

About Phayakkhaphum Phisai (Maha Sarakham Province) weather,
I found temp. around 14-33 Deg C and cloudy.
It may raining soon as Bangkok which raining everyday.
The 21st of this month, Thailand will have Makha Bucha holiday. a day relate to buddhism.
At North-earthern of Thailand (Rural area), they will has some activities like carnival. people will go to temple to pray the buddha and monk.

TKs
Torranin K.

[kelvin_27_84]

I would rather recommend Danfoss VSD soft starter. It is different from a Y/delta starting, uses less power to start and uses less power to maintain. Very cost effiecent. Check out danfoss asean site, let me know if you need help i can recommend people from Danfoss to help to

[Tycho]

I would rather recommend Danfoss VSD soft starter. It is different from a Y/delta starting, uses less power to start and uses less power to maintain. Very cost effiecent. Check out danfoss asean site, let me know if you need help i can recommend people from Danfoss to help to

A soft starter only saves power during startup, a inverter saves power during running