Capacity Control Head

[abbasi]

Please can anybody tell me in detail about capacity control head of semihermetic compressors and

how the electrical wiring is done (example wud be worthwhile)


REgards


Ali

[frank]

Hi Ali

On large semi hermetic compressors some of the cylinders are unloaded during start up to reduce the inrush current.

After that the unloaders are energised to apply capacity control. The unloader is just a solenoid operated valve that causes the cylinder to be open so that compression cannot take place.

As far as wiring diagrams go it's just a case of supplying the solenoid valve with a live and neutral at whatever voltage you are using

[abbasi]

Actually we have 40 HP frascold compressor and there are 2 wires live and neutral the compressor runs on 33% 66% and 100% CCH(capacity control head). my query is that If there are only two connections then how come three steps are involved.

and thanks for your advice

[rbartlett]

I may be missing something here but

no wire energised 100%
1st or 2nd wire energised 66%
1st+2nd wire energised 33%
http://www.xpedio.carrier.com/idc/gr...control+&hl=en

cheers

richard

[chemi-cool]

Hi Richard,

You did not miss anything, Ali did.

Capacity control will be best achieved with a controller that control the whole unit or only the condensing unit.

These controllers start the compressor on 33% and increase the capacity if the suction pressure is above the required .


Here is a link to one manufacturer, but there are many, personaly, I prefer the Danfoss one.
http://www.cdk.co.uk/products.html
Or/and,
www.danfoss.com

Chemi

[Peter_1]

The Xpedio link was usefull I see but the link you gave us Richard seems not working.
Abbasi, the wiring is rather simple: as soon you need less capacity, you energise an SV on the compressorhead, so a change from 100 to 66% (for a 3 or 6 cilinder) and if stll too high capacity, energise the second SV so you can reduce to 33%.
You can do it also with a simple dead band pressure switch and a time delay between the steps, without fancy and expensive electronic controllers.
Eliwell, Carel, Dixell have rather cheap and very small step controllers, the same size as their thermostat range.

[abbasi]

Thanks Pete

Can u also tell me the basic principle of Capacity control head meaning what parameter does influence it to change its capacity from 33% to 100%

As in LAC(low ambient control) the discharge pressure is detrimental factor.

so in case of capacity control head i know its a solenoid valve but it is actuated on which parameter change.

REgards

Abbasi

[Peter_1]

Abassi,

The word says it almost it selves: when the evaporator capacity doesn’t match any longer the compressor capacity – mostly in a multi-evaporator setup – for a given evaporating pressure, then you need a capacity control.
So, solely the Low Pressure is responsible for this.
If the LP level doesn’t matter, then at reduced evaporator capacity, the suction pressure of the compressor will decrease so that the compressor capacity matches again the actual evaporator capacity. So, you can say then that lower the suction compressor is adapting the capacity in this case.

[abbasi]

Thanks Maite


Got it and thanks to u all wiring is done and unit with three 40HP semi hermetic air cooled chiller is complete.


again thank u all

[chemi-cool]

Hi Ali,

Nice to here all went well.

Can you post some pictures of that unit??

Chemi

[abbasi]

well unit has departed i got pics of 1 of our water cooled water chiller but attachment space is limited give me ur email and i will mail them

[chemi-cool]

here are 2 pictures of that chiller.

Thank you Ali.

Chemi