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Thread: Condensing pressure control
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20-08-2015, 03:27 AM #1
Condensing pressure control
Typically, in North America we have 2 types of condensing pressure controls for industrial refrigeration plants.
1. Pressurestats. Each pump or fan controlled by its own pressurestat. This is not perfect control but it is cheap $1,000-2,000.
2. PLC. Condensing pressure control is part of the PLC, but this PLC is not cheap $30,000 - 100,000.
Does anybody use another approach to control condensing pressure which have costs $5,000-10,000?
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20-08-2015, 04:37 AM #2
Re: Condensing pressure control
So what do you want to have controlled? fan or pump? 1 kw or 300kw?
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20-08-2015, 04:50 AM #3
Re: Condensing pressure control
variable speed drive and pressure transducer, generally prefer Danfoss
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20-08-2015, 03:24 PM #4
Re: Condensing pressure control
Hi Segei
I totally agree with Magoo. Switching fans and pumps on & off causes pressure swings to the liquid supply line, this creates major instability to the whole system & costs a lot of money to try keep the system under control .
By the use of speed control (VSD's ) the system is stable, and runs more efficiently, the fans and pumps last longer along with the electrical components as they are no longer switched on/off causing electrical surges as one of the benefits of using VSD's is the soft starter plus with pumps and fans with the VSD the electrical savings can be huge as the power consumption works on the cube rule ie run at half speed with only 12.5% of the power consumed a total win win solution. Most supermarkets in the UK are using VSD technology on the lead compressor on packs , condenser fans, etc to reduce their power consumption. Floating the discharge pressure with the ambient using a VSD further reduces their payback time. Most system controllers these days give out a 0-10 volt signal for use with VSD technology
When upgrading to VSD usage especially on condensers where the head pressure is lowered or floated with the ambient it is necessary to make sure that the system control valves are compatible especially servo valves.
One system I was called to sort out was on a Flooded NH3 system, where they used a Danfoss SV float with a PMFL main valve for the level control. They service company had fitted VSD's to the condensers and to the Screw compressors, and had slowly reduced the discharge pressure to reduce their running costs to the max. But they reduced it to a point that the servo action of the SV & PMFL valve become compromised to the point that on the slightly colder days the system failed to work with the lower liquid pressure. To overcome this a Capacitive level rod was fitted with a Motorised ICM valve which solved the problem, so always look at the whole system to make sure that it will still work under all conditions , as mechanical valves have limitations with servo requirements whereas motorised valves just need electrical powerLast edited by Glenn Moore; 20-08-2015 at 03:42 PM.
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20-08-2015, 09:51 PM #5
Re: Condensing pressure control
Johnson controls have a Quantum LX condenser controller.
It would have to be at the price range your after
http://www.johnsoncontrols.com/conte...e_10-08-09.pdf
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21-08-2015, 01:31 AM #6
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21-08-2015, 01:29 AM #7
Re: Condensing pressure control
Hi, Glenn.
I agree with you except one issue. I will not put VFD(VSD) for water pump of evaporative condenser.
People usually invest money in something that they understand. For example, they invest in LED light. It is easy to understand, that this light use much less energy especially with motion sensors. Many people don'y understand energy savings in industrial refrigeration and they are very careful about investing in these savings. This is the reason I want to give a customer different options at different prices.
For example. He can save 400,000 kWh but $200,000 should be invested or he can invest $20,000 and save 100,000 kWh. Sometimes people invest $20,000 and when they see savings they will invest more.
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21-08-2015, 09:57 AM #8
Re: Condensing pressure control
Another possibility for controls
http://www.mmrefrigeration.com/secti...ment/controls/
http://www.mmsysinc.com/off-the-shelf-control-systems/Last edited by RANGER1; 21-08-2015 at 10:03 AM.
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22-08-2015, 05:25 PM #9
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22-08-2015, 10:49 PM #10
Re: Condensing pressure control
Is it worth finding out price & a few contacts from M&M.
Sounds like a big player in that region of USA.
If you know exactly what you want & approached a PLC controls company, they could make one as simple or as complex as you like.
We always stipulate that we pay them to develop it, so it belongs to us, no secrets, copy of programe etc.
Is there someone like that in your region?
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22-08-2015, 11:57 PM #11
Re: Condensing pressure control
I will get information about M&M.
Actually, I'd like to find simple PLC from the shelf. Usually, it is much cheaper than custom made PLC. It should have two set points of the condensing pressure. One for operation and one for defrosting. Additionally, sequence of the fans and pumps should be chosen. I ask one company in our region but their cheapest PLC is $30,000. We know how to ave energy but we need tools(not expensive) to implement that knowledge.
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23-08-2015, 10:14 AM #12
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Re: Condensing pressure control
That seems wildly overpriced, we deliver high end controlpanels for freezing and RSW systems for less than half that price, with integrated condenser pressure regulation through VFD and valve actuators or both, depending on the application.
Be it a fan or a pump you need to regulate, all you need is a VFD, danfoss, ABB or Vacon, doesn't matter.
the VFD can be set to maintain a setpoint through a pressure sensor.
If you require a higher, or different setpoint during defrosting, that is all available through a simple input on the VFD, where you set it to a different speed or a different setpoint.
you don't need expensive PLC solutions, it can all be done in the VFD.-Cheers-
Tycho
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22-08-2015, 08:24 PM #14
Re: Condensing pressure control
Pressure controlled frequency converter for fans and temperature controlled frequency converter for pumps.
I work with ABB products.
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22-08-2015, 09:08 PM #15
Re: Condensing pressure control
http://effbox.com/
This is a good product with proved savings on large brewery and dairy plants that I have worked with them on to deliver.I love the smell of Ammonia in the morning!
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23-08-2015, 01:40 AM #16
Re: Condensing pressure control
Hi Segei.
I fully understand your concern on costs of any improvements, but your client will understand any costs saving on energy outlays will involve spending money to achieve results. They will base spending on capital expenditure / improvements on recovery period of costs. Generally 24 months payback. Then savings going forward. Cheap options that may or may not achieve savings will reflect on yourself and put your reputation at for false advise. Put on the salesman hat.
cheers magoo.