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Help Calculating kW/H Usage on Compressor
2

Help Calculating kW/H Usage on Compressor

Help Calculating kW/H Usage on Compressor

(OP)
Good afternoon.

I'm trying to calculate the kW usage per hour for the following Ingersoll Rand Compressor. Does anyone know how I could find it based on the following plate stamped on the side? I know next to nothing on what these ratings even mean, I just have a strong suspicion our facility could be saving quite a bit of money if we shut them down daily when the facility is not running. If I can get their kW usage per hour I can easily run that against what DTE is charging us per kW. Even if it's not during peak time, I suspect those savings could add up.



Any help would be appreciated.

edit - grammar.

RE: Help Calculating kW/H Usage on Compressor

Depends on how the compressor operates.

Many of this size the motor and compressor doesn't stop but just stops pumping air and hence uses a lot less power.

Only by looking at the usage of air and pressure cycles can you see what is going on.

This guide might help you.

https://www.air-compressor-guide.com/articles/unlo...

So your compressor might already be shutting down if the is very little air usage.

The control system for the machine might need some adjustment.

Find the manual and read it first.

Stopping and starting the motor might not be the right thing to do. I'm all for saving energy but not at the expense of a new motor or compressor.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Help Calculating kW/H Usage on Compressor

(108 Amps x 480 Volts x 1.73) 0.8 = 90 KWHr per Hr. when actually loaded.
About 10% to 15% when unloaded.
If you shut down every time the compressor unloads, you may exceed the recommended starts per hour and damage the motor.
I was faced with a back-up compressor that only started when the main compressor could not hold the set pressure.
It was limited to three starts per hour.
During heavy air usage, the starts per hour may have been exceeded.
We fitted a timer so that once the standby compressor started, it would run for a minimum of 20 minutes. If the air was not needed, it would run unloaded.
20 minutes between starts meant a maximum of three starts per hour.

Beware of unintended consequences when making changes to a working system.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Help Calculating kW/H Usage on Compressor

According to LI's link, a screw compressor uses 33% power when unloaded.
Piston compressors often use less power when unloaded.
Fully loaded, a factor of 0.8 allows for power factor and efficiency.
with the motor unloaded the power factor will drop significantly and you cannot use Amps alone to judge power consumption.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Help Calculating kW/H Usage on Compressor

Typically compressors only output air on demand, but they may run unloaded when air is not needed. There will be a receiving tank with a pressure switch that will start and stop the compressor based on demand. If the facility is not running, the operation of the compressor would be based on the leakage with all of the piping and equipment. That can be significant in some cases. I worked on one plant where the CFM usage of air with the building shut down was about 1/3 of that with the building running.
A very rough rule of thumb is one kW per horsepower, so running that motor for one hour would be 75 kWH. It will be less than that, but you need a lot more information to know how much less.

RE: Help Calculating kW/H Usage on Compressor

I just checked, that is a screw compressor. Use 1/3 for unloaded power consumption.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Help Calculating kW/H Usage on Compressor

It's an IR R55i A125 compressor package which looks really quite neat.

I suso ect its already operating quite efficiently, but find the manual and look at how the unit is set up.

Or call IR and talk to them.

These units are >$30,0000
 

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Help Calculating kW/H Usage on Compressor

(OP)
Thank you all for your replies. You've certainly given me a lot to think about. I am going to reach out to IR and ask about whether or not it would be advantageous for us to attempt a nightly shutdown.

Quote (LittleInch)

Depends on how the compressor operates.

Many of this size the motor and compressor doesn't stop but just stops pumping air and hence uses a lot less power.

Only by looking at the usage of air and pressure cycles can you see what is going on.

This guide might help you.

https://www.air-compressor-guide.com/articles/unlo...

So your compressor might already be shutting down if the is very little air usage.

The control system for the machine might need some adjustment.

Find the manual and read it first.

Stopping and starting the motor might not be the right thing to do. I'm all for saving energy but not at the expense of a new motor or compressor.

- Thank you! I will be sure to check out that link. We have a manual somewhere around here I'll search for it and turn it over to my maintenance team.

Quote (Waross)

(108 Amps x 480 Volts x 1.73) 0.8 = 90 KWHr per Hr. when actually loaded.
About 10% to 15% when unloaded.
If you shut down every time the compressor unloads, you may exceed the recommended starts per hour and damage the motor.
I was faced with a back-up compressor that only started when the main compressor could not hold the set pressure.
It was limited to three starts per hour.
During heavy air usage, the starts per hour may have been exceeded.
We fitted a timer so that once the standby compressor started, it would run for a minimum of 20 minutes. If the air was not needed, it would run unloaded.
20 minutes between starts meant a maximum of three starts per hour.

Beware of unintended consequences when making changes to a working system.
- I am always reluctant to try anything new without collecting information from those smarter than me lol. When you say shutdown, what do you mean exactly? We fire these up on Sunday by simply pushing a button. We don't touch them again until the following Sunday (they automatically shut down sometime between Friday night and Sunday morning as we are down on Saturdays).

Quote (Waross)

According to LI's link, a screw compressor uses 33% power when unloaded.
Piston compressors often use less power when unloaded.
Fully loaded, a factor of 0.8 allows for power factor and efficiency.
with the motor unloaded the power factor will drop significantly and you cannot use Amps alone to judge power consumption.
- The only time this would be unloaded would be the time I'm proposing we shut them down.

Quote (LittleInch)

It's an IR R55i A125 compressor package which looks really quite neat.

I suso ect its already operating quite efficiently, but find the manual and look at how the unit is set up.

Or call IR and talk to them.

These units are >$30,0000
- Yes they are quite expensive and we're running two of them. At first I was excited about "double the savings" but this group has done a good job of snapping me back to reality.

Again, thank you all for your replies. I'll let you know what IR says.

RE: Help Calculating kW/H Usage on Compressor

Unless these units are base load or you somehow have air usage exactly equal to compressor output, they will unload at regular intervals. Watch to see if the air pressure in the receiver goes up to a certain value, down to a different one maybe 1 bar lower then back to the previous high level....

However the motor and compressor keeps running so it might not sound like it's not actually pumping air.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Help Calculating kW/H Usage on Compressor

Ingersol Rand R55i-A125, 75 HP Rotary Screw Air Compressor, 328 CFM @ 125 PSI,
I concur with most of the recommendations above. There is a variant of this compressor that has a variable speed drive. If that is your compressor, much of the time you would be running unloaded the compressor will be running at part speed, which is more efficient than unloading.

If your system has 2 or more compressors you need to think about operating strategy, and may benefit from a supervisory system that rotates the next to start, and next to unload.

If your load (compressor run time) does not drop when usage should be low look for leaks, fixing leaks saves $$$$.

If you eventually decide to turn off the compressors at night, expect unintended results. You could have something important that uses compressed air when the plant is otherwise idle.

RE: Help Calculating kW/H Usage on Compressor

Can you give us a list of equipment that uses air, and which equipment needs a lot of air?
Does your plant run 3 shifts?
Do you run both compressors all the time?

IR has some sophisticated control options available and we don't know which control package you have.
You may have a control package that is already giving you savings.

See if you can find a way to log the operations of the unloader.
How many hours per shift is the compressor pumping and how many hours is it unloaded.
Can your process stand a drop in pressure at times?
What may work well in one plant may be a disaster in another plant.

Do you need both compressors running all the time for three shifts?
How much air do you need at peak consumption, relative to the output from two compressors?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Help Calculating kW/H Usage on Compressor

Like Facengr says, the most cost effective and highest value thing you can do is go round and fix all the leaks and general hissing.

Everyone thinks "It's only a small leak / its only compressed air". Well yes, but they add up to a huge cost over the space of a year.

It costs money to create compressed air and then you just let it dribble away all over the factory.

Think if it like leaving incandescent lights on everywhere you go and leave them on all day, every day.

Compressed air systems tend to stay live for long periods getting topped up regularly.

Why do you have to "fire them up" on a sunday. Won't they come back to life as soon as you start using air?
IR as noted make a lot of control equipment and the newer systems in particular you can program to do lots of things - you just need to read the manual! It could be that it works at its most effective way now together with a set number of starts per hour to avoid damage to your machines.

You probably have a drier in there as well and they need regeneration / drying so don't interrupt that cycle by just turning the whole thing off

But if you haven't got notes now on how much power you use now, how are you going to know if you're successful or not?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Help Calculating kW/H Usage on Compressor

If you want to know power and energy consumption, put an appropriate power meter on the power circuit that can measure what you want to know. They are available with clamp-on leads to measure the current and can clip to voltage terminations. Yes, you can also look at all the compressed air data, but measuring the power and energy would be the first thing I'd do if that's what I wanted to know.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Help Calculating kW/H Usage on Compressor

We found this out many years ago (1985?).

We had sold a 2MW generating set, a spark ignition gas engine fuelled by mines gas - methane from a disused coal mine.

The sales guys (and one gal) had included the cost of a fuel gas compressor, but the customer woke up to the fact that we had sold a 2MW set (genset terminals), but a lot of the auxiliaries were electric motor driven...

He (quite rightly IMO) said "you cheating b*****s, you sold me a 2MW genset that produces (nett) less than 2MW...”

So we analysed all the electric driven auxiliaries.

First fun was with the engine manufacturer. For diesel engine drive he offered mechanically driven water and lube pumps. For gas engines, he removed them and suggested electric motor driven pumps. The engine kW did not change. When we queried this, the response was "the (pumps) do not consume much power."

My response was to ask them to go down to the factory stores and confirm that these wonderful pumps ran magically on their own...

The worst bit was the fuel gas compressor which was a reciprocating compressor. This (from memory) we found was to be fitted with a 100-kw compressor. Sorry: a compressor driven b= a 100kw electric motor.

So we asked the compressor manufacturer what the absorbed Kw was. Then the fun began. It became obvious that they knew what the required kw was, but not the kwh…

To our surprise the compressor came with a receiver, a gas storage chamber. The way the system operated was that the compressor ran all the time. When it met the required receiver pressure it ‘unloaded’ by opening a valve to recirculate gas to the inlet, via a cooler (radiator – with an electric motor driven fan…).

The efficiency of the then partly loaded compressor drive motor was very poor! The system efficiency was worse!
Long experience had shown them that stopping and starting the electric motor too often resulted in electric motor failures.

The compressor motor was selected for full charging power … plus 10% as petrochemical customers wanted that margin. We wanted efficiency and quickly realised that a smaller motor being overloaded during charging periods would have a lower average kWh.

We thought of variable speed drives, but time and technology (1985) were not on our side.
The compressor manufacturer found it difficult to calculate the average energy input to compress a flow of gas from one pressure to another.

No one had ever thought of an overall CBA – Cost Benefit Analysis.

This was all spurred by the English government requiring renewable projects to have a DNC – Declared Nett Capacity, i.e. power from power station terminals, not the old power station practice of using the generator terminal power.

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