Minimum discharge pressure for ammonia systems

[US Iceman]

Sergei,

I don't disagree with you. The points you mention are valid and as long as everyone understands there might be some limitations, then they know what they have to design for.

Personally, I prefer to use liquid overfeed systems instead of DX systems. A liquid overfeed system has very few limitations and no requirement for minimum discharge pressure (unless it is a gas powered recirculation system, with pumper drums).

Secondly, by the time you add the transfer system to the cost of the accumulator, you are getting close to the cost of a vessel and pumps. I don't think there is a lot of difference in cost between the two systems.

At least not enough to justify selling DX, but I recognize I may be in the minority on this viewpoint.

[Sergei]

Sergei,

I don't disagree with you. The points you mention are valid and as long as everyone understands there might be some limitations, then they know what they have to design for.

Personally, I prefer to use liquid overfeed systems instead of DX systems. A liquid overfeed system has very few limitations and no requirement for minimum discharge pressure (unless it is a gas powered recirculation system, with pumper drums).

Secondly, by the time you add the transfer system to the cost of the accumulator, you are getting close to the cost of a vessel and pumps. I don't think there is a lot of difference in cost between the two systems.

At least not enough to justify selling DX, but I recognize I may be in the minority on this viewpoint.

Hi, US Iceman.
Reduction of condensing pressure has several barriers. Liquid overfeed will eliminate one of them. Good design is a base for potential energy saving. However, I found that over 50% of potential energy savings can be saved by improving operating set points(one of them is minimum allowable condensing pressure) and operating strategies. This approach doesn't require significant investment and has payback just a few months. As far as know food companies in North America will invest in energy efficiency only if payback is shorter than 2 years.

Sergei

[US Iceman]

Hi Sergei,

It seems we are on the same page.

Reduction of condensing pressure has several barriers.

Indeed. The task is to find those and minimize their effect. The same applies to raising the suction pressure as much as possible.

However, I found that over 50% of potential energy savings can be saved by improving operating set points(one of them is minimum allowable condensing pressure) and operating strategies. This approach doesn't require significant investment and has payback just a few months. As far as know food companies in North America will invest in energy efficiency only if payback is shorter than 2 years.

I believe the 50% savings. There are a lot of systems that just don't run properly. Part of the problem is the initial design, the other part is how the system is operated.

This is where it pays to carefully review the system and electrical tariffs. Significant improvments can be accomplished in almost any system.

You are correct about the 2 year payback. This is something that everyone sticks to. However, I prefer to look at this as 50% ROI.

It seems the thought process with a 2 year payback stops after 2 years. By this I mean, people do not pay too much attention to what happens in the third year.

Putting it into an ROI perspective, they acheive a 50% return every year (based on the original costs). If energy costs increase, the ROI improves. This is something they get each year.

This argument has some semantics, since the above both mean the same thing. The important idea is how to present the data in terms that are meaningful.

[US Iceman]

I also wanted to add some other thoughts. I feel the system should be designed to work efficiently under all of the operating conditons; summer/winter & full load/part load.

All too often I see systems designed for the worse case (summer & full load) with little regard for the other conditions.

The way I see it, the systems should be designed for efficient operation all of the time, not just at one point.

Any control system used should simply provide the means to sustain the optimum operating conditions during those periods, and as loads change.

[Sergei]

Sorry, I don't agree with raising suction pressure as high as possible. I believe in optimum suction pressure.

[US Iceman]

Sorry, I don't agree with raising suction pressure as high as possible. I believe in optimum suction pressure.

OK, I suppose I should ask about your concerns or perhaps clarify my statement.

To me, the optimum suction pressure would be the highest pressure that still meets the temperature requirements of the load.

With this in mind I would attempt to find the temperature requirements for the loads attached to a common suction line. If we know the temperatures required by the load, and the performance of the evaporators, we can find the optimum suction pressure.

In a lot of cases we see back-pressure regulators set to maintain the evaporating temperatures, but the suction pressures are usually less than what the lowest evaporating temperature needs to be.

So if we can increase the operating suction pressure high enough to keep the back-pressure regulators open all of the time, we have reached our optimum suction pressure.

This is the essence of what I meant about getting the suction pressures as high as possible.

[Andy P]

Hello all - interesting debate going on here! Getting back to the head pressure "optimiser" I'm a big fan of keeping things as simple as possible, and it occurs to me that the difference between wet and dry bulb temps in a temperate climate is on average very small. For example in the UK the difference is usually less than 2 deg C, and we only see significant differences for prolonged periods when the dry bulb gets above 15C. Why not save the cost of a fancy black box "optimiser" and use a simple dry bulb measurement offset by 2 deg C when it reads less than 15C (and revert to standard head pressure control when it is higher than 15C - not often round here!)

...or maybe that doesn't sound simple at all!

btw the Australian Fridge Institute (AIRAH) used to provide ambient temperature charts where the frequency of wet/dry bulb combinations was printed on a psychrometric chart, and you could see the effect I'm trying to describe very clearly. Excellent data presentation, but I have never seen it anywhere else - anybody know of the same for other countries?

cheers

Andy P

[US Iceman]

...the Australian Fridge Institute (AIRAH) used to provide ambient temperature charts where the frequency of wet/dry bulb combinations was printed on a psychrometric chart,...

Is this similar to the revised ASHRAE data Andy, or the TMY2 data?

Can't say I have seen this printed on a psych chart.

[Andy P]

If I can find a page I will scan and post so you can see the idea - it is a very compact way of delivering a large amount of useful info: anybody using evap condensers should have it.

cheers

Andy P

[Mark Sanchez]

Andy,

Great point. I would like to see the chart as well. I'm sure someone has one for the States.

We have installed a few systems with the wetbulb sensors.
It would really only seem to matter if you're operating a large system with a low disch. press. setting, and it was set below the actual saturation corresponding to WB. Mainly in the middle of summer.
Chicago has a design of 95/78 (not if you refer to the latest ASHRAE, but the NH3 guys still use it) so a corresponding saturation = approx 132# Disch.

If you did not have the WB feature, the system would try and run more condenser fans/ pumps w/ no avail. as the saturated Disch press. setting was not attainable. Or you can stop a VFD on a condenser fan from driving higher if in fact you have already achieved the WB/ Saturation.

I'll have to look into the Sabroe system.
This sounds very interesting.
I'll forward the link for this site to Greg @ M&M to see if he knows anything about it.

It's great too see so many technicians & engineers involved with this site!!

Cheers
Mark.

I'll introduce myself if I see you at IIAR

[Sergei]

Hi, all.
Regarding to optimum suction pressure. Don't forget about evaporator fans. Their use energy and release this energy in refrigerated space. We have to spend additional energy for refrigeration plant to remove the heat from evaporator fans. Usually, for every 2HP(horse power) of fan energy we have to spend additional 1 HP for refrigeration plant to remove the parasitic heat from evaporator fans. Increasing suction pressure we save energy for compressors,but we use more energy for evaporator fans. At certain conditions, we will save less than we spend. Major criterion of optimum suction pressure is coefficient of evaporator coil HP(fan power) per TR(ton refrigeration) per degF(temperature difference).
Regarding to wet bulb approach. Idea of wet bulb approach is to balance capacities of compressors and evaporator condensers keeping total power(compressors + condensers) at minimum level. This feature is useful when outside temperature over 10C. If ambient temperature is lower than 10C, we usually run the plant at minimum allowable condensing pressure. It is very important to keep wet bulb approach at optimum level. Assume that optimum wet bulb approach is 10F. If we try to keep 6F( 4F or 2C difference), our condenser capacity should double. We can spend additional 200HP for condensers and we save just 50HP for compressors. We overspent 150HP.

Sergei

[US Iceman]

Regarding to wet bulb approach. Idea of wet bulb approach is to balance capacities of compressors and evaporator condensers keeping total power(compressors + condensers) at minimum level. This feature is useful when outside temperature over 10C. If ambient temperature is lower than 10C, we usually run the plant at minimum allowable condensing pressure. It is very important to keep wet bulb approach at optimum level. Assume that optimum wet bulb approach is 10F. If we try to keep 6F( 4F or 2C difference), our condenser capacity should double. We can spend additional 200HP for condensers and we save just 50HP for compressors. We overspent 150HP.

That's the very point I'm talking about with clients right now. In a similar thought as the optimum suction pressure we were discussing, the optimum discharge pressure is not the lowest discharge pressure you can achieve.

It is the lowest discharge pressure which uses the least amount of total energy (condenser fans + compressor motors).

You raise a very good point that all should consider Sergei. Energy savings should be based on the total use, not the individual components.

[PHANANHTUAN]

Re: What's PM3 valve? i can't understand it, help me ! please.
thanks !

[Josip]

Hi, PHANANHTUAN

Welcome to RE,

Re: What's PM3 valve? i can't understand it, help me ! please.
thanks !

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but you can search complete site to learn something more
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under Refrigeration and A/C
Hope this will help.

Best regards, Josip

[Andy P]

If I can find a page I will scan and post so you can see the idea - it is a very compact way of delivering a large amount of useful info: anybody using evap condensers should have it.

cheers

Andy P

Here is the chart for Adelaide, Australia. The figures in the middle of the chart are the number of hours that the combination of wet & dry bulb temp is achieved. The figures at the bottom of each column are the number of hours per year for that dry bulb temperature and the figures on the left hand side are the number of hours per year that the wet bulb temperature is exceeded. Charts are also available for 6am-6pm and for 6pm-6am in each location. I hope that this is clear enough to give the general idea - the 6 and 8 digits look very similar, so it is a bit difficult to read the detail.

cheers

Andy P

[US Iceman]

Hi Andy,

Thanks for taking the time to scan and post this information. I have never seen the data listed in this manner, but as you stated, the data is a very good source for those using evaporative condensers (or other evaporative processes, such as cooling towers, etc).

Unfortunately, I suspect this format is localized to Adelaide, Australia. Other charts would need to be generated for specific locales with the pertinent weather observations.

In 1997 ASHRAE revised their weather data, which trys to emulate a similar data set. The listed the dry bulb temperatures and mean coincident wet bulb temperatures in various percentages. The percentages are based on the percentage of annual hours in the following format; 0.4%, 1%, & 2%.

This translates into 35 hours, 87.6 hours, & 175 hours. The data provided for each percentage value, would provide a similar, but not as complete, set of values.

The flip side to the ASHRAE data is that there is also another set of data listed in the same format, except, this data lists the wet bulb temperature and mean coincident dry bulb temperature.

In this data set, the wet bulb temperatures are considerably higher for the same frequency values. For evaporative processes I would recommend using the values of wet bulb temperature and mean coincident dry bulb temperature.

I also like to use the TMY2 data for all of the annual hours to develop curves of the maximum, minimum, and average wet bulb temperatures to illustrate a graphical method of displaying the weather data. They end up looking like bell curves.

It's also a good idea to add some safety factor for the wet bulb temperatures and condenser capacity, because as we know, "things happen.".

[Sergei]

Hi, all.
I still believe in wet bulb approach, because it is major function to determine capacity of condensers relatively to capacity of compressors. Wet bulb approach is not complicated as it looks.
Measure wet bulb temperature by wet bulb sensor(for example 65F). Set the optimum wet bulb approach(for example 10F). Add these two numbers( 75F). Corresponding pressure to 75F is 126psig(ammonia). This is our set point for head pressure. If wet bulb temperature change to 70F, our set point will change to 138 psig( 80F). This is floating condensing pressure. This feature is working very well for refrigeration plant with fluctuating refrigeration load( up and down). For refrigeration plants with steady refrigeration load we can balance capacities of compressors and condensers just switching on(off) some condensers.
I have question to US Iceman. Why do you think that hot gas lines are undersized?

Sergei

[US Iceman]

I have question to US Iceman. Why do you think that hot gas lines are undersized?

A fair question...

Most of the systems I see usually take at least 30 minutes to defrost a coil (that's an average value for the entire cycle). My question is why does it take 30 minutes to defrost a coil? I have seen other systems where a coil was defrosted in under 10 minutes.

My thought on this is the speed of defrost is determined by the volume of hot gas that can be supplied to the evaporator in question. And, the ability to drain the condensate as fast as it forms.

In the past I have seen large evaporators that also take much longer to defrost (up to one hour).

This got me to thinking... Why does it take so long?

Obviously, the defrost ability is determiend by how much gas you can supply to the evaporator for defrosting.

The capacity of the hot gas header is determined by the available potential, i.e., pressure differential from the engine room to the coil.

In the summer the discharge pressure is much higher, so the available potential is much greater as there will be a greater differential pressure to allow higher mass flows.

In the winter with reduced or floating discharge pressure, the potential is much less, hence you see lower mass flow and potentially longer defrost times.

If the hot gas header is sized sufficiently large for low pressure drop (e.g., larger pipes) the ability to implement fast defrosts is provided.

In other words, the capacity of the hot as header is determined by the pressure loss across the pipe. Higher pressure losses in this pipe will require higher discharge pressures to maintain the same flow capacity.

This is one of those barriers to implementing low discharge pressure operation.

[US Iceman]

It is my belief the use of floating discharge pressure is a good method.

The weather data Andy P presented is a reference tool for use during the design process.

I think it's important to distinguish between operational and design parameters.

The floating discharge pressure method would simply be a function of the data Andy P posted and the capacity of the condensers and the load on the refrigeration system.

[Sergei]

I have a different opinion. I think that major reason of poor(slow) defrosting is under supply of hot gas due restriction in balancing valve. We don't have this problem at high condensing pressure, because we have higher pressure difference to supply hot gas to the coil and density of hot gas is higher at higher condensing pressure. Due to these 2 factors the mass flow of ammonia to the coil significantly greater at higher condensing pressure.
Pressure drop in main hot gas header. This header usually designed for defrosting from 25% to 50% of all coils. For example. We have cold storage with 6 penthouses and 4 coils in each penthouse. Total is 24 coils. Main hot gas header designed to defrost 6 coils simuntaniously. Most likely we defrost not more than 2 coils at the same time. Hot gas flow in main line will be 3 times less than design flow and pressure drop will be just 1-2 psig. Lower density of hot gas is another factor to reduce pressure drop.

Sergei

[US Iceman]

We don't have this problem at high condensing pressure, because we have higher pressure difference to supply hot gas to the coil and density of hot gas is higher at higher condensing pressure. Due to these 2 factors the mass flow of ammonia to the coil significantly greater at higher condensing pressure.

I think we saying essentially the same thing. Hot gas systems seem to work better at higher condensing pressures. However, I think they do so because the systems are designed for the summer time, and not quite for the conditions that result in winter operation.

[Sergei]

I think we saying essentially the same thing. Hot gas systems seem to work better at higher condensing pressures. However, I think they do so because the systems are designed for the summer time, and not quite for the conditions that result in winter operation.

Do you have any idea about winter design of hot gas supply?

[US Iceman]

Well let's see about this...

The defrost headers need to be able to be drained of condensate. Liquid drainers work well for this purpose. In the winter time, the colder ambient temperatures tend to condense a lot more gas.

The defrost headers need good DRY insulation. I have seen a fair amount with bad insulation jobs, or others that are not maintained properly. This causes more condensation also. All of the condensate has to flow through the coils (unless drainers are used), which increases the defrost time.

The hot gas header needs to be large enough to supply sufficient hot gas to the coils (at a low pressure drop, since we hopefully will be running low discharge pressures). All too often I see hot gas headers of about 2" or so, which is just too small in my opinion. This is probably the biggest problem.

The headers need to be pitched for gravity drainage. I see some occasionally that have the headers trapped between two different elevations.

Come to think of it, the design process is about the same for summer, except the colder air temperatures increase the condensation in the hot gas headers.

[Sergei]

Drainers are essential to hot gas lines. Certainly, they improve defrosting. These drainers should be installed for the safety reasons as well. They will prevent the coil damage during initial stage of defrosting.
In winter time we loose the superheat of ammonia in hot gas header. This is the major reason of poor defrosting for the farthest coils.

Sergei

[NH3LVR]

Most of the systems I see usually take at least 30 minutes to defrost a coil (that's an average value for the entire cycle). My question is why does it take 30 minutes to defrost a coil? I have seen other systems where a coil was defrosted in under 10 minutes. My thought on this is the speed of defrost is determined by the volume of hot gas that can be supplied to the evaporator in question. And, the ability to drain the condensate as fast as it forms.
This got me to thinking... Why does it take so long?

I have been watching this thread with some interest.
I am speaking mostly of Nh3 (Flooded) Evaps as they are what I have the most recent experience with.
Many Cold Storage Evaps we install today are put in a Penthouse, with the Valving outside. This works well and is easy to service, compared to inside mounting. However many of this Evaps have the Coil Outlet behind panels where it cannot be observed easily. Any buildup on this side of the coil is hidden until it restricts the Airflow. Then it becomes a problem to remove as it can be two inches thick, and embedded in the Coil.

Our Defrost Cycle commonly consists of;

3-5 Minutes: Pumpdown (Not very effective with Ammonia)
(?) Minutes: Fans stopped, and Hot Gas on (May use Soft Gas at first to to avoid Shocking Coil thermally or Mechanically?)
3 Minutes: Equalizing time (Bleed Down)
2-5 Minutes: Liquid back on, Fans off.
Fans on, normal operation

With proper drainage of the Hot Gas Line a Coil operating at -20F (-29C) can be defrosted in 25-30 Minutes. But 8-10 Minutes of that are not in the Hot Gas mode.
I have seen many Operators shorten these times, and pay for it later.

[Sergei]

I have been watching this thread with some interest.
I am speaking mostly of Nh3 (Flooded) Evaps as they are what I have the most recent experience with.
Many Cold Storage Evaps we install today are put in a Penthouse, with the Valving outside. This works well and is easy to service, compared to inside mounting. However many of this Evaps have the Coil Outlet behind panels where it cannot be observed easily. Any buildup on this side of the coil is hidden until it restricts the Airflow. Then it becomes a problem to remove as it can be two inches thick, and embedded in the Coil.

Our Defrost Cycle commonly consists of;

3-5 Minutes: Pumpdown (Not very effective with Ammonia)
(?) Minutes: Fans stopped, and Hot Gas on (May use Soft Gas at first to to avoid Shocking Coil thermally or Mechanically?)
3 Minutes: Equalizing time (Bleed Down)
2-5 Minutes: Liquid back on, Fans off.
Fans on, normal operation

With proper drainage of the Hot Gas Line a Coil operating at -20F (-29C) can be defrosted in 25-30 Minutes. But 8-10 Minutes of that are not in the Hot Gas mode.
I have seen many Operators shorten these times, and pay for it later.

I prefer at least 10 min. pumpdown to evaporate all liquid in the coil. Hot gas supply is in the same range 25-30 min. Hot gas supply should be optimal. Undersupply will lead to poor defrosting. Oversupply will lead to significant parasitic load on compressors, because only certain portion of the gas will condense and the rest will go through the coil, BPR to the suction line. This supply depends of coil size, refrigerated space temperature, amount of frost on the coil and etc.

Sergei

[NH3LVR]

I prefer at least 10 min. pumpdown to evaporate all liquid in the coil. Hot gas supply is in the same range 25-30 min. Hot gas supply should be optimal. Undersupply will lead to poor defrosting. Oversupply will lead to significant parasitic load on compressors, because only certain portion of the gas will condense and the rest will go through the coil, BPR to the suction line. This supply depends of coil size, refrigerated space temperature, amount of frost on the coil and etc.Sergei

I agree, although I have never ran across a situation with an oversupply of Hot Gas to an Evaporator.
I do question pumping out all the Liquid in Evaps (In the case of NH3). Due to the high Latent Heat of Ammonia that could take a very long time. Pump recirculated Coils are the worst in my experience. We now return the condensed Liquid to the Intercooler if possible.

[US Iceman]

Oversupply will lead to significant parasitic load on compressors, because only certain portion of the gas will condense and the rest will go through the coil, BPR to the suction line. This supply depends of coil size, refrigerated space temperature, amount of frost on the coil and etc.

NH3LVR, What Sergei is describing is the samething as the coil being in defrost (with the hot gas still on) after the coil has been defrosted. Once the frost is melted off, additional hot gas continues to heat the coil resulting in steaming and a lot of gas flowing out of the coil.

The gas flowing out of the defrost regulator adds to the compressor load (booster if the hot gas returns to the booster suction, or to the high stage if the condensate line is piped back to the intercooler).

Since the defrost pressure is around 75 to 90 psig ( 5.2 to 6.2 bar g), it would make sense to have the condensate piped back to either, a separate vessel with a separate recip. compressor, or a controlled pressure receiver. Whatever is close enough to work.

Pumping out ammonia evaporators is a pain for the reason stated. It's the same problem with trying to get a flooded out screw started. A little bit of ammonia takes a lot of heat.

[NH3LVR]

it would make sense to have the condensate piped back to either, a separate vessel with a separate recip. compressor, or a controlled pressure receiver. Whatever is close enough to work. Pumping out ammonia evaporators is a pain for the reason stated. It's the same problem with trying to get a flooded out screw started. A little bit of ammonia takes a lot of heat.

US Iceman;
I had never thought about the concept of using a separate Compressor. Has this been done before, could you elaborate?
On the subject of Flooded Screws, one of our Customers managed to fill up a Screw Booster with NH3 the other day. It took 3 days to get it going again. They now believe in the safety Shutdown on the LPR we wanted to install.

[US Iceman]

HI NH3LVR,

What I'm thinking about is to use a separate vessel (accumulator if you will) to collect the gas and liquid from the defrost regulators. If the suction pressure on the compressor attached to this vessel is running higher than any other house suction pressure, it just means the penalties for hot gas defrost would be much less.

In other words, we are taking the condensate up to as high as pressure as we possibily can. From that point, a separate compressor could run the suction pressure with no problem (especially a recip).

I've seen controlled pressure receivers run this way, so it should not be any big jump in logic to say try this for defrost.

The trick would be to size the compressor to handle the defrost loads accurately. This is just me thinking out loud. I have not done this for defrost, but I can't see why it wouldn't work.

On the subject of Flooded Screws, one of our Customers managed to fill up a Screw Booster with NH3 the other day. It took 3 days to get it going again. They now believe in the safety Shutdown on the LPR we wanted to install.

Ohhh, those are always fun jobs to get.

[Sergei]

Frequency of defrosting is another important factor of refrigeration plant optimization. Right now, here in Ontario, one cold storage has defrosting once per week, but another one has defrosting twice per day. I found that overdefrosting is common problem for many refrigeration plants. It is difficult to justify additional compressor installation, if you have defrosting once per week.

Sergei

[US Iceman]

I found that overdefrosting is common problem for many refrigeration plants. It is difficult to justify additional compressor installation, if you have defrosting once per week.

I would agree. Each facility has it's own personality in how it operates and what it needs. This also changes with the seasons (summer, winter, etc).

The concept I posted earlier is just one way of dealing with an issue. Just like in troubleshooting, there is always a cause and effect we need to account for in any instance.

[Bradford]

Frequency of defrosting is another important factor of refrigeration plant optimization. Right now, here in Ontario, one cold storage has defrosting once per week, but another one has defrosting twice per day. I found that overdefrosting is common problem for many refrigeration plants. It is difficult to justify additional compressor installation, if you have defrosting once per week.

I’ve been reading this post with great interest. What started out as a discussion on lowering head pressure and it’s implications has become a discussion on total system optimization! And it seems to be a topic that a lot of people are interested in. With the ever rising costs of energy and the push for a greener planet, I wonder if this would make a good topic for a forum or sub-forum.

What Sergei mentions about defrosts going from twice per day to once per week has become quite typical in plants that incorporate smarter controls and/or keener operators. Evaporators that require 2 defrosts per day during that one hot week in august can often get away with one or two defrosts during the winter months. This gets back to the problem of fixed setpoints often being the “worst case” setpoint. If two or three defrosts are needed in the summer, that’s where the pins are left in the time clock. If -25 suction kept the rooms cold in August, that’s where the suction is left all year. If one evaporator requires 145# for defrost, that’s where the pressure switches are set. It’s obvious that a lot of systems have a lot of room for energy usage improvements

Another great up-side to long durations between defrosts is you can float the head pressure lower for a longer period of time thus enhancing energy savings.

Brad

[US Iceman]

a discussion on total system optimization! ... I wonder if this would make a good topic for a forum or sub-forum.

That's good idea. Let me run it past the boss of RE for his comments.

[US Iceman]

It’s obvious that a lot of systems have a lot of room for energy usage improvements

That was my idea for starting this thread. Refrigeration systems waste too much energy doing something that can be done for less.

I continue to believe the system can be designed better and more flexible. The control systems actually provide the ability to sustain the original design concepts with the capability of smarter operation.

One other important criteria is the utility bills, i.e., how much energy and demand cost, the various time of use charges, and ratchet clauses can also present some challenges.

[stan1488]

recip plant on vfd ( im giving my tricks away) :P

[TXiceman]

recip plant on vfd ( im giving my tricks away) :P

This is nothing new, I did this years ago and it worked like a champ on lowering energy demand and smoothing out plant operation.

You have to think outside the box all of the time now.

Ken