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Buying an Industrial

Air Compressor - Questions


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A I R - C O M P R E S S O R - G U I D E . C O M

Buying an industrial air compressor - questions

Air Compressor Guidehttp://www.air-compressor-guide.com

[email protected]

http://www.air-compressor-guide.com/http://www.air-compressor-guide.com/mailto:[email protected]:[email protected]:[email protected]://www.air-compressor-guide.com/


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Table of Contents

Questions to ask when buying an industrial air compressor ..... 1 Q1. Do you offer 24/7 (emergency) service and what is themaximum arrival time? ............................................................. 2 Q2. What is the rated capacity at full load operating pressure? 2 Q3. Let’s ta lk about power consumption. .................................. 3

3a. Total input power at rated capacity and full load operatingpressure? ........................................................................................ 4

3b. Total input power at zero flow (unloaded) ................................. 4

3c. Specific Input Power at Rated Capacity and Full Load OperatingPressure .......................................................................................... 4

Q4. Will my compressor run partly loaded most of the time? .... 5 Q5. Will my compressor make enough running hours (or, is mycompressor small enough). ...................................................... 6 Q6. What is the yearly expected cost of maintenance and spare

parts? ....................................................................................... 7 Q7. What are the ventilation / ambient air / installationrequirements? .......................................................................... 7 Q8. Can I use an energy recovery system?.............................. 8 Q9. Are there any energy incentives available? ....................... 8


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Questions to ask when buying anindustrial air compressor

Ask the right questions to get the right air compressor for your business

Here is my list of the most important questions to ask when buying anew industrial air compressor.

You should either ask these questions to the salesperson visiting yourbusiness or you should ask these questions to yourself when decidingon a new air compressor.

These are – by far- not all the things that you should think about whenbuying a new compressor. I also made a list of ‘all’ things to thinkabout, which you should also have received.

I won’t cover all the basic things like the required pressure andcapacity. Please read my online buying guide for an introduction tothose things.


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1. Do you offer 24/7 (emergency)service and what is the maximum

arrival time? Your compressor serves your business.. You NEEDcompressed air. A compressor failure can result inhuge production losses and plant downtime.

How long does it take your service provider to showup when you call them for help? Are they available 24 hours a day?Even during holidays?

2. What is the rated capacity at full load operatingpressure? Manufacturers or salespeople sometime try to trick you by make itseem that the compressor is bigger than it actually is.

They might specify the capacity at a lower pressure or at some other,for them favorable but now real-life conditions.

Or they might specify a larger capacity but at a lower pressure thanyou will use the compressor at.


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3. Let’s talk about power consumption. Energy costs will amount to more than 75% of total cost of ownershipof your air compressor.

The purchase price is only 10 - 15% of your total cost of ownershipover the lifetime of the compressor.

Your energy bill in the first year alone will be about equal of thepurchase price of your new air compressor!

This means it’s smart to spend a little more on an energy -efficientcompressor as it will pay back many times over in the coming years!


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3a. Total input power at rated capacity and full loadoperating pressure?

Ask for the power consumption at full power, when the compressor isrunning at maximum pressure and the corresponding maximumcapacity (air flow).

This value is given as kW.

You need this value if you want to calculate the expected yearly energycosts.

3b. Total input power at zero flow (unloaded)

Most compressors can run ‘loaded’ and ‘unloaded’. The power a compressor consumes when running unloaded can be ashigh as 30% of nominal power or more than 50% for smallercompressors.

This means that even if your compressor is not pumping air, it stillconsumes 30% - 50% of nominal power!

This value is given as kW.

You need this value if you want to calculate the expected yearly energycosts.

3c. Specific Input Power at Rated Capacity and FullLoad Operating Pressure

This is a good way to compare various air compressors.

This number gives you the amount of power required to pump 100

cfm when the compressor is running full load (full capacity and fullpressure).

The lower the number the better.

Because it power PER unit of capacity, you can compare compressorof various sizes and manufacturers.


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This value is given as kW/100 cfm.

In other words: how many kW’s does it take to pump 100 cfm (which

is flow rate).

4. Will my compressor run partly loaded most ofthe time? Ordinary industrial compressors can run either at full load or at no-load (loaded/unloaded).

For example when a compressor has a capacity of 400 cfm (cubic feet

per minute) and you use only 200 cfm (50%) the compressor willcontinuously switch between loaded and unloaded.

In this case, it’s better to buy a variable speed (VSD) compressor. These compressors can run at any capacity within its range.

So if you need only 50% of capacity, it runs slowly and only outputs50% capacity.

This is a huge energy saving each and every year!

But, if your compressor runs fully loaded (at or near 100% capacity) allthe time a variable speed compressor will actually consume more power than an ordinary compressor (this is because of the energylosses in the variable speed drive).

The ‘sweet -spot’ for a VSD compressor is between 50% and 80%. Ifyour compressor runs below 50% all the time, you’d be better off witha smaller compressor.

If your compressor runs above 80% all of the time, you are not saving,or even wasting, energy.

So, only buy a variable speed compressor when you will run it in thesweet-spot most of the time.


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5. Will my compressor make enough running hours(or, is my compressor small enough).

This might sound like a strange question at first, but let me explain.Don’t let the salesperson push you to get a bigger compressor thanyou actually need.

Ever.

Often they will give arguments like ‘buy it for future growth’ or ‘it’sbetter to have some extra spare capacity’, or whatever.

I have seen this so many times. A big, big, compressor that only runsfor 5 minutes every hour. Or a big variable speed compressor thannever runs above 20% capacity.

Why is this bad?

A compressor that never really runs will never really heat up. Water (fromthe air that is sucked-in) is yourcompressor number one enemy.

If your compressor never heats up,this water will collect in valves, bend,couplings, etc.

This will give you many maintenance problems with rust, water, valvesthat get stuck and what not.

A compressor that never really runs is a compressor full of

problems

A compressor that runs at full load each and every day is a happycompressor.


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Besides the maintenance issues, a too big compressor will consumemore energy than a smaller compressor. It will start and stop morefrequently and run a longer time unloaded than loaded.

6. What is the yearly expected cost ofmaintenance and spare parts?

Ask about the expected annual costs of maintenance and spareparts.

How expensive are spareparts? Can the compressor be serviced by athird party, or only by the manufacturer (to keep the warranty).

Maintenance and spares account for roughly 15% of costs over thelifetime of the air compressor.

The purchase price of your compressor only for 10%.

7. What are the ventilation / ambient air /installation requirements? Sometimes salesman, hunting for their sale, will ‘forget’ about whereyou want to install the compressor.

But if you want your compressor to have a long and happy life, youneed to carefully consider where you install the compressor.

The compressor should be installed in a place where clean, dust-freeand cool air is available. If this is not available anywhere, ductingshould be installed so the compressor can ‘breathe’ outside air.

In the long run, this will greatly reduce your maintenance costs, reduceyour energy bill and increase your compressors life.


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8. Can I use an energy recovery system? Although this cannot always be used, an energy recovery system canrecover up to 90 percent of the compressors input energy.

With energy costs typically running into the tens of thousands ofdollars per year, this can be a significant saving.

Energy is mostly recovered in the form of heat. There are systemsavailable that use the heat of compressor to heat your factory or (pre-)heat water (for showers, etc.).

9. Are there any energy incentives available?

In many countries and states the government has put energy incentiveprograms in place to encourage businesses to save energy and save theenvironment.

If you currently operate an old air compressor and you replace this with a new, more energy efficient system, chances are that you areeligible for these incentives.

This means you both save on your energy costs and you get moneyback!

But to be eligible you need to play by the rules and this often requiresan assessment for both the old and the new situation.

You can ask your compressor salesman, the local government or thelocal energy supplier for more information.

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