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US Iceman
19-02-2008, 02:04 AM
Here is an article some of you may find interesting if you are working on energy savings for industrial refrigeration systems.

http://www.hpac.com/Issue/Article/24472/24472

Core4 Guy
19-02-2008, 02:42 AM
Iceman,

I'm glad you sent this article. Floating heads (Reduced Compression TM) can be very tricky. Every facility is different and this article is good. (although way to much info for free).

I have a chicken processing plant with ice and storage that I designed and rerofit that runs SDT as low as 40F.

On another plant I acually run my heads lower than some of the common suctions. Then when the heads are low enough I thermosyphon the load right to the condersers... Anyways good article. A little tricky...

Core4 Guy

US Iceman
19-02-2008, 03:02 AM
I have a chicken processing plant with ice and storage that I designed and retrofit that runs SDT as low as 40F.


And, I had a supermarket running like this also. The big issue with this is not to exceed the design limits of the compressors. The manufacturers tend to get nervous when you mention very low condensing temperatures.:rolleyes:

Yes, these can be tricky but... it's just good engineering applied to real world conditions. What a thought, heh?

Core4 Guy
19-02-2008, 03:58 AM
Iceman,

Compressor manufactures have to be queasy. Imagine if everyone tried this! There are alot of issues to overcome. We hold the warrenties on the compressors we use, just so manufactures will sell us compressors.

As far as the halocarbon industry I'm using carlyle and wanting to use turbocor machines. I find with a carlyle if don't exceed the mass flow rate of the machine and they will last. I have carlyles running with a 15# differentials with discharge HA backpressure valves holding back to allow me to lower my cond temp below suction for compressor free cooling. I call this MTS Cooling (TM) Modified Thermosyphon Cooling. It's not that easy but its worth it to have a compressor free load for 3600 hours a year in CA.

Sergei
19-02-2008, 04:18 AM
Hi, Mike.
I'd like to discuss one sentence from your article. "Minimum (head)pressure may be determined by operator preference...."?
Several years ago I read manual from one PLC manufacturer. I remember one sentence from this manual. "Every experienced operator with basic refrigeration knowledge can set up(tune up) this PLC"??? I was really shocked.
What is the goal in energy saving process? The goal to operate the refrigeration plant at optimum set points and at optimum operating strategies. Determination and implementation of these set points and strategies is the most important part of energy savings. Without these points and strategies every PLC is almost useless. Why every experienced operator should tune up the plant?

US Iceman
19-02-2008, 05:46 AM
Hi Sergei,



Determination and implementation of these set points and strategies is the most important part of energy savings.


I would agree with one caveat. The system should be designed for the best performance capability at all conditions. Then the control strategies and implementation of them allow the system to operate at it's optimum under all conditions.



Without these points and strategies every PLC is almost useless.


Agreed. Control systems just turn things on or off. It is the control algorithms that provide the benefits.



Why every experienced operator should tune up the plant?


Well, if the control system does not do what it is supposed to do (or sold to do:rolleyes:) then it becomes the operators task/problem to sort it out. In some cases, the systems are operating as the operators were trained (right or wrongly) and as such they may think they need to maintain a certain discharge pressure (sometimes around 125 or 150 psig). These artificial limits are a function of the system design, not practical limitations of the equipment. I'm sure you have seen this before also.

Then, you see someone selling control systems as manna from heaven promising all sorts of wonderful things. I think your example of the PLC was one of those. I would be shocked too. There is certainly more to a system operation than setting several control points.

The sentence you question was directed to those facilities where they think the minimum discharge pressure is what they have been operating at. When you see systems running with 180 psig discharge in the winter and you ask, why? The usual answer is the system needs to run at this pressure to operate properly. So, the situation becomes one of operator preference. It's what they think they need versus what the system capability actually is.

Perhaps...but it might be required because the system was designed so poorly. Even on a conventionally designed system you can get to 125 psig discharge with little problems. Less is certainly possible, but it does create issues when you try to convince people that it is possible.

After all, if it is a good idea... the system would have been designed to operate like that!

US Iceman
19-02-2008, 05:53 AM
...if don't exceed the mass flow rate of the machine and they will last.


You know you have migh mass flows when the valves start to whistle! The valves and the valve port areas are the biggest concerns. Then the connecting rod loads as far as I can tell. Most of the manufacturers will say they want a minimum of a 2:1 pressure ratio on the machine.

What is a "discharge HA backpressure valve"? That's a new term I have not heard before.

Core4 Guy
19-02-2008, 02:58 PM
Iceman, I'm using Hansen HA4AB NO differential valves. Very tricky to size to to from chatering under varing conditions.

Imagine if the world were running on a 2:1 C Ratio, oh it is we have alot of work to do...

I've had a copeland recip running alot like this at a small supermarket VFD controlled. That unit is now 14 years old, no problems. Had to replace the VFD, the PID controller, but not the compressor.

Sergei
19-02-2008, 05:35 PM
I think that 3 steps should be done to maximize the energy savings:
1. Determination of optimum set points and operating strategies. If you don't know the goal, how you are going to reach it? Sometimes our goal is moving target(head pressure). It isn't simple as suction pressure up and head pressure down. Condenser sequence and compressor sequence can be changed, based on refrigeration load and ambient conditions.
2. Adjustment of the plant for these set points and operating strategies. I found that very often the problem with hot gas defrosting due to poor adjustment.
3. Implementation of optimum set points and optimum operating strategies. PLC will be helpful at this step. Unfortunately, PLC can't choose these set points and strategies. Someone should do that.
I think that the most important parts of this process are steps 1,2. This is the most complicated part of energy savings. Who should do that? Certainly, not operator regardless of his training.

Core4 Guy
19-02-2008, 06:26 PM
Sergei, I definitely agree... Thanks for bing easy on me.

US Iceman
20-02-2008, 04:10 PM
I think it is safe to say each system has it's own unique set of issues. No two systems are designed or operate the same way so it becomes imperative for someone who understands how system operate to investigate the proper control set points.

I have seen some system which operate reasonably well at 120 psig discharge for normal cooling, but then when defrost is required the system will not defrost properly.

Hot gas defrost systems are often not designed properly to operate with low discharge pressures, so yes I agree with you... hot gas defrost systems can be difficult to adjust, but then if they were designed properly they would defrost much better.;)

This system optimization process is a lot more complicated than a lot of people think. It is more than control systems and fancy graphics.

I look at it like this... If the system is designed properly to operate in all conditions (full load, part load, summer and winter) then a "good" control system can provide sustainability for the design to operate efficiently.

Sergei
20-02-2008, 05:16 PM
Sergei, I definitely agree... Thanks for bing easy on me.
I just share my vision of energy savings in industrial refrigeration. There are several misconceptions regarding to this issue.
1. Energy savings are expensive. I don't think so. What is our goal? It is optimum operation of refrigeration plant. First several steps of optimization aren't expensive, because they require just new setpoints and readjustment of the plant. No capital investment at this stage and more that 50% of potential energy savings can be achieved. Initial capital investment should be done to the points where you can get better payback.
2. PLCs save energy. PLC can help you to save energy, but it isn't saving itself. Better set points and operating strategies save energy. Sometimes, to achieve these points we need PLC. PLC is our tools to save energy, but this tools can be used differently. I know the company that invested more than $100,000 in sophisticated PLC. They didn't change settings and they were very surprised when they didn't get promised energy savings.

US Iceman
20-02-2008, 05:32 PM
First several steps of optimization aren't expensive, because they require just new setpoints and readjustment of the plant. No capital investment at this stage and more that 50% of potential energy savings can be achieved.


I fully agree. This falls into a category I call recommissioning. It is essentially a complete adjust of the operating parameters and set points to achieve energy savings. This is where the low-hanging fruit is and the easiest to establish if you know what to look for.

Your point 2 is also very valid. Control systems just turn things on or off. It is the strategies (algorithms) that affect the savings and benefits.

Core4 Guy
21-02-2008, 02:19 AM
Hot gas defrost systems are often not designed properly to operate with low discharge pressures, so yes I agree with you... hot gas defrost systems can be difficult to adjust, but then if they were designed properly they would defrost much better.;)


Guys, Has anybody ever tried to ensure the volume and quality of the hot gas by installing a backpressure regulator on the discharge of a compressor (equal or better to the volume of gas you need for defrost) and taking the hot gas supply off of that compressor (upstream of the valve) while the other compressors operate at all conditions floating or not. You would only need to energize this valve before you need a defrost and de-energize after. This has worked very well is certain projects. Has gas defrost is a pain...By the way install another valve in parrell to the main to ensure that when that first valve fails to open your compressor doesn't get hammered and you still defrost. Sizing if the main valve is critical and it will create a pressure drop at all times.

US Iceman
21-02-2008, 02:45 AM
...Has anybody ever tried to ensure the volume and quality of the hot gas...


Quality has nothing to do with. It's gas, not two phase.



...installing a backpressure regulator on the discharge of a compressor (equal or better to the volume of gas you need for defrost) and taking the hot gas supply off of that compressor (upstream of the valve) while the other compressors operate at all conditions floating or not.


This is one of those things you have to do to keep a hot gas defrost system working when you try to float the discharge pressure low. Why????

Because you need to keep the pressure up to overcome lines losses when the high flows occur during defrost.

Core4 Guy
21-02-2008, 06:04 AM
Iceman, your right again. I'm kind of found of Hussmans Cool Gas Defrost too. It's all about latent heat. You know, I haven't thought this much in years. Thanks.

US Iceman
21-02-2008, 07:57 PM
You know, I haven't thought this much in years.


I think a fitting analogy is: Exercise makes muscles stonger!:cool:

Oregon Jim
05-03-2008, 05:05 AM
I have found that my system operates well at condensing pressure as low as 100 psi, with no problems during hot gas defrosts. I have operated the system during cold weather and low heat load conditions with condensing pressure as low as 90 degrees without problems, but it just didn't "feel right" to me. Every system and every operator are different, and there are a gazillion variables in heat loads, but for me a pressure near 100 psi is just perfect.....

Kh1971
05-03-2008, 08:35 AM
Hi,

Thanks man, I was looking for this

Regards

US Iceman
05-03-2008, 05:39 PM
I have found that my system operates well at condensing pressure as low as 100 psi, with no problems during hot gas defrosts. I have operated the system during cold weather and low heat load conditions with condensing pressure as low as 90 degrees without problems, but it just didn't "feel right" to me.


I understand. Most of us are use to seeing systems operate the way they have for the last 75 years or so. To start doing things differently does not feel comfortable until you have done several.

As you say, each system is different and some operators get really excited when you mention these concepts. It just takes some time and innovation to get something new accomplished.

Oregon Jim
06-03-2008, 03:36 AM
My main concern with operating at low condensing temperature is due to worry about oil foaming within the compressors. I have an old Frick rotary booster compressor that is very prone to oil foaming and oil loss when the oil temperature gets too low. Of course foaming is not such a problem in my second stage compressors due to increased pressure, but because I am not an expert in oil behavior I become a tad nervous when my compressor temps begin to drop below their "normal" parameters.

As you said, adapting to change is difficult sometimes...