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arkay
16-03-2006, 12:02 PM
Hi Friends!

To our brewery, where we have three J&E Hall monoscrew chillers, we have added a new chiller recently. The previous ones were all water cooled, with cooling towers. The new chiller installed has an evaporative condenser and is fitted with VFD. The system works to provide chilled glycolated water at -6 deg.C. Propylene glycol is used.
We have an automatic control whereby the last chiller does the modulation while the other three work on full capacity only. This is all as per recommendations of J&E Hall.
Since the installation has been made we are consuming much less electricity now and we are quite happy with the new installation.
But still I would like to know whether there are further steps to be taken for more energy savings. I am actually looking into moving from -6 deg to -4 deg.C.
Are there any other areas where savings can be made?
I have a 5-yr old chiller, water cooled with a cooling tower which can be converted to take an evaporative condenser. Do you think it's worthwhile?
I'll be pleased to have your views.

US Iceman
16-03-2006, 02:06 PM
Hi arkay,

The compressors operating with cooling towers are typically designed to operate with a higher discharge pressure. The new compressor with the evaporative condenser is normally designed for a lower discharge pressure.

One of the first items to check is; "What is the discharge pressure you are operating with now?" I would recommend you lower the discharge pressure control settings a small amount. Check the motor amps and monitor the system operation.

If the systems seems to be OK after a few days or a week, lower the discharge pressure control setting again.

Depending on the system and controls you may be able to gain significant savings by just lowering the discharge pressure control set points.

Your idea of raising the supply glycol temperature is a very good one. I suggest you raise the set point in small increments over a period of several weeks. This allows the system to stabilize.

As the compressor suction pressure increases, the compressor capacity will increase. The motor amps will also. You may find that one compressor is operating at part load, after the suction pressure has been increased.

The end result is that you want to increase the suction pressure as much as possible AND still maintain the temperatures required. You also would want to decrease the discharge pressure as low as possible and still maintain adequate liquid refrigerant supply pressure to the control valves to the chillers.

As part of the trial control adjustments you want to find the lowest energy use.

One word of caution... You can lower the discharge pressure too much, or increase the suction pressure to high.

If the discharge pressure is reduced too low, the oil separator velocity can increase due to a higher specific vapor volume. Additional oil carry over can result.

The same applies for higher suction pressures. If the suction pressure increases too high, the compressor mass flow increases. The higher mass flow can also result in higher oil separator velocities.

The combination of higher suction pressure and lower discharge pressure results in the highest oil separator velocity.

It may be more cost effective to use VFD's on the cooling tower fans and simply change the control set points.

kasperDK
16-03-2006, 04:07 PM
Hi

York koleteknik in denmark have developed a cond.press. optimeser for use on chillers with evap cond. using a calcutation for optimersing the energi use
bye temp and humid


kasper

Andy
16-03-2006, 09:37 PM
Hi

York koleteknik in denmark have developed a cond.press. optimeser for use on chillers with evap cond. using a calcutation for optimersing the energi use
bye temp and humid


kasper

That I think is an add on to the Unisab-multisab

We have developed a complete system optomiser, which will rise the suction set point on the compressors, if the plant is acheiving the required media temperature too quickly or too often. On an industrial site we would use Danfoss AK2 control combined with PLC's and our own control.
To be honest it is quite simple to do, we would do something similar with the condenser, using either danfoss or something even simplier. On the condenser side an oversized evaporative condenser helps acheive good energy savings, coupled with an inverter drive on the fan.

Kind Regards. Andy:)

Andy
16-03-2006, 09:39 PM
Hi

York koleteknik in denmark have developed a cond.press. optimeser for use on chillers with evap cond. using a calcutation for optimersing the energi use
bye temp and humid


kasper

Kasper, York Koletenik have supplied R744 systems to Denmans, would you be able to find out about these, I would love to see one in action, somewhere away from the UK.

Kind Regards. Andy:)

arkay
17-03-2006, 10:11 AM
Hi US Iceman,

Thanks for your feedback.
I like the idea of raising the suction pressure and reducing the discharge pressure to the optimal value. This reduces the load on the compressor to a minimum. We are talking here about a maximum cooling capacity of 1.4 MW, so a few percentage savings is a lot!!
Okay we'll increase the glycol temp slowly as you recommend.
I was also thinking to do something about the cooling towers - we have three of them, one for each chiller. Our ambient temp varies from 35 deg C to 15 deg C between summer and winter, and it is obvious we are losing money by running them all the time. VFD on the fan is a good option.
I was thinking of 'centralising' them in some way so that they could start one by one depending on the return water temperature. Do you think it's a good idea? If so, is there a way how this can be done? First I thought about having a primary and a secondary circuit. then I realised I will have to duplicate the pumps...???

US Iceman
17-03-2006, 01:36 PM
I have heard of several strange problems when cooling towers are connected together. The different towers can be thought of as cells of a larger tower.

When multiple cells are connected together you can have water level control problems. The variations in the drain/return line pressure, and/or lack of balance line can result in water level control problems.

The piping is one area to consider and the pumps will require some thought to prevent any new issues.

New evaporative condensers would help you in the summer as the condensing temperature would normally be lower in the most humid time (lower than the cooling tower).

Depending on how many hours of the year you have high wet bulb temperatures the use of the evaporative condensers might be worthwhile. It depends on the energy savings and the new condenser costs.