Compressor on ammonia refrig system 5

[drmigs]

I am trying to find a way to curb electrical cost and was wondering if there is such a device that would regulate the electrical spike upon start up of the compressors? or is it necessary for the compressors to have the spike to start up?
Thanks,
drmigs

 

[jraef]

There are certainly ways to reduce starting current surge, but just so you know, doing that is not likely going to save you any electrical costs. Starting peaks are not really seen by the vast majority of utilities, they use a Demand Meter with a sliding time window, usually 15 - 30 minutes, so anything that happens in less than that amount of time is not really recorded for billing purposes.

There are plenty of mechanical benefits to soft starting however and it may still be worth doing. But before you embark on any change to the starting system of that compressor, double check the validity of that with the compressor mfr first. Many ammonia compressors cannot be soft started without risking damage to the bearings because of lubrication issues.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[powerjunx]

drmig,

Main equipment to drive a compressor is a motor. Starting a motor surely induces a voltage spike or transient surges. And you can never deny or even stop it.
To cut down the electrical cost (energy consumption), one way
is to use a low current starting machine that is a NEMA Code Letter Rating. Secondly, use a device (control) that somehow reduce the current, while starting since starting a machine on peak load hours will soar high your electric bill as it adds up to the maximum load demand.
To reduce or regulate the spikes, it is is recommended to install a surge suppressor which are readily available in the market.

 

[davidbeach]

A surge suppressor will do nothing to the current spike known as motor starting inrush. Any voltage response that the motor starting will be a sag, not a swell and surge suppressors won't do anything about sags. One start in a demand window will have negligible impact on the kwhr or kwhrd metering, it could have an impact on the kvarh and kvarhd metering as the starting inrush has a very low power factor. It takes a certain amount of power to get a motor started and a soft starter won't change that, just spread it out over more time; so a soft starter won't won't help on the kwhr, but might make a negligible improvement on the kwhrd.

 

[drmigs]

Thanks for all you educated answers, they have certainly shed light on my situation.
I did have one more question to throw out there: Are there solar panel systems powerfull enough to power a large ammonia refrigeration system? The refrigeration system is used for an ice skating rink in Florida(plenty of sun)
Thank's once again,
drmigs

 

[itsmoked]

Solar panels to run heavy motor loads are generally a poor solution. The motors just take sooo much energy.

You understand that there are ammonia based domestic refrigerators? They run on natural gas. A small flame like a pilot light runs the refrigeration cycle. It is called an "absorption refrigeration cycle". Perhaps you can find someone who could utilize your FL sunshine instead of that motor running your "mechanical refrigeration". Or better yet a dual system so you have mechanical backup for night cooling. Then you could get onto your utility's "off peak hours" rate buy using mechanical from 6pm to 6am or something similar.

Another option; Modify your system to run the refrigeration only between 6pm and 6am. This could save you about half your refrigeration costs (typically). You change from chilling the ice to chilling a few thousand gallons of a non-freezable liquid in an insulated tank. Enough to carry your ice needs through the day. Here in CA a lot of big companies do this. They run large chillers all night to chill the coolant in a large tank then use the chilled coolant for air conditioning during the day. They save about 2/3 on their electrical power.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Just so you know, solar cell output is at best, around 1kW for every 11 sq.ft. of surface . So if you have a 200HP compressor, that's essentially 150kW steady state full load, so to start it even with an inverter drive you would probably need 150% of that. So 150kW x 1.5 = 225kW needed to start and run your compressor, x 11 sq. ft. = 2475 square feet of solar cells to power that compresor, at hih noon, no clodes.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[itsmoked]

Never-mind the clodes... Panels cost $8 per watt..

225kW = 225,000W

225,000W x $8 = 1.8 million dollars!!

Then you still night time to contend with. Heck it would be cheaper to use natural gas at the site then electrons..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

This is one of those things that, when you compare the savings with the cost of changes, it just isn't worth changing anything.
The exception is adjusting operating times. If you have off peak hours and are able to draw the ice temperature down during off peak and then let the ice temperature rise slowly during peak energy times, you may be able to save some money. It depends on your energy rates and how much you can vary the ice temperature. The controls should be less then the savings.
The less work the motor does the less energy it uses.
If your machine has or can be fitted with some kind of capacity control it may be possible to run at reduced capacity during the day and let the ice temperature rise a little. Then run full capacity during cheap power intervals to over cool the ice again.
There are various types of capacity controls and most large machines have some type fitted.
Re KVAR on starting. Where the power company is charging penalties based on monthly KVAR usage, it only takes a very small capacitor connected 24/7 to supply all the extra vars that a large motor will use during starting.
respectfully

 

[jraef]

Really, $8/watt? I had no idea it was so high. I read an article a few years ago that said new technology was going to bring the cost down to $0.20/watt (at the time it was about $4.00). Guess that hasn't happened yet. Still a good point though Keith. Even at .20/watt, that's $45,000.00 to be able to run a 200HP compressor.

Clouds not clodes... and high noon, not hih noon for that matter. Smart ass.

Bought a wireless keyboard / mouse combo and no matter where I put the transceiver I get intermittent connections. I had added that last statement after the Google spell checker and was too lazy to check again. Leave it to you to find my errors and drub me with them Keith.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[itsmoked]

It's my only hobby.. harassing you and waross's speeling.

There have been a few large solar projects in my absurdly 'politically correct' town. West Marine chandlery, the city sewer plant, a grocery store, the largest private solar system in the world, and Plantronics; the headset maker.

They of course have write-ups of these in the paper. The latest(Plantronics) stated that panels are so hard to get in large quantities, it's like a James Bond movie, to acquire them. They said it actually took 'international intrigue' to finally corral the number they needed.

All this, of course means, the price ain't never gonna come down.(appreciatively) I got that price from a quote for a 50W BP panel $354, add a buck for the install. That didn't include any engineering or equipment.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[powerjunx]

drmigs,
"..Are there solar panel systems powerfull enough to power a large ammonia refrigeration system?.."

I could say, it's impractical and are not feasible to power up your application.


If you dont mind, better to post this query to new thread rather than merging to this thread, for you to recieve lots of
reply - better do it next time.

 

[jraef]

Huh? He is the OP and it was still the same general subject. "I am trying to find a way to curb electrical cost..."

I don't agree that it needed a new thread.

 

[itsmoked]

Ah,, he has a point of sorts. Looking at the title I can imagine lots of people not reading further or after their first read because "solar" or "energy savings" is nowhere to be seen. But I agree, of course it's the OP's post to work.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com