New Method for Compressor Load Modulation

[Dreyfus]

I would be interested in comments relating to the potential pitfalls of this innovation and next steps.

Essentially the aim is to build a compressor with an efficiency similar to scroll compressors at a lower price point- something that could be attractive in price conscious developing markets.

The innovation basically alters the stroke length of a reciprocating piston compressor using a unique control connection driven by a brushless DC motor. The load can vary from 20% to 100%.

Naturally there are numerous disadvantages with recips such as vibration and noise, but equally they are very useful for high pressure needs.

At first this sounds expensive and complex however the price of brushless DC motors has collapsed due their use in drones and really, all that is needed is a 24v supply and sufficient logic to advance and reverse the motor according to a position sensor and temperature probe.

The mechanism is exact and easy to implement (unlike many forms of inlet valve modulation) and has the advantage of not only being able to track temp and humidity as closely as a 2 speed or even pulse width modulated scroll but the start up load of 20% is handy in lowering in-rush current. Naturally it would benefit from a VFD but the aim is to provide good efficiency at a low price.

The unit is larger than a standard recip. There may be issues in lubrication at low rpm.

I would welcome any comments based on people's experience. Where I live (Australia) the most common residential units are rotary compressors with inverters. Few people can afford scroll based compressors of any kind. I think emerging markets would be attracted to this new design based on build cost and relatively good efficiency.

My belief is that recips are easier to build cheaply since they don't require the machining tolerances of scrolls and the electronics of inverters. Hence rotaries are a good compromise but are not popular in very large units.

I have been involved in inventing (unsuccessfully) for a while. I built an alternating valve from polypipe (20 mins in the shed) Please google alternating valve and look for 2 youtube videos.

it has a single moving part and has been running in my garden for 2 years without a break.

That invention was a cheap alternative to the galcon alternator valve (google it too).

I approached 3 australian manufacturers about this valve. One just wanted to know how it worked but in the end offered a very frank understanding of the realities of bringing things to market. In retail u have to convince a chain store to take something off the shelf in order to put yours on. Of course people can market online and do, but without real demand it is just an ego exercise and not how inventors want to spend their time.

The second manufacturer signed an NDA and assessed it but viewed the demand as too low to bother with.

The third manufacturer would not sign an NDA since they claimed they had been sued in the past for things they saw but had been working on anyway.

I have also looked at applications in hydraulics and pneumatics but again see little need for a very neat, robust as a brick, cheap innovation that only met a need I had and which already exist but at a higher price point.

So I assume I will get similar treatment with this innovation. Many companies will not touch any external IP except on terms that are insane. For example, the Honda marine group has a web page that says you can send any innovation you like but (a) they don't have to acknowledge they received it (b) they can do whatever they like with it including making money. Rotax Bombardier- the engine maker- had similar conditions but in addition (up to 2 years ago) you sent paper copes of plans to a PO Box in Canada!

It is increasingly true that companies only want to know about their internal IP development and not that of others unless the conditions are extortionate. For example the innocentive people (google innocentive) set up competitions for prizes in the 30K range for innovations that would be worth millions if patented.

Anyway I would appreciate any practical comments/advice about this method of load modulation from people in the industry and also those who may have commercial experiences in bringing innovations to market.

Thank you.

[R600a]

Sounds like the new Infiniti variable compression motor turned compressor.

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[Dreyfus]

Sounds like the new Infiniti variable compression motor turned compressor.

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You have a good sense for the concept however u should note that most variable compression approaches in internal combustion engines vary the displacement by only small amounts since the range of compression ratios is very small e.g. maybe 8: 1 to 15:1. On the other hand this innovation varies from 10% to 100% displacement.

[R600a]

Agreed. All i can say is hurry up and produce it because i want to buy it.

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[R600a]

I volunteer to test your compressor in my system for free.

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[R600a]

You have a good sense for the concept however u should note that most variable compression approaches in internal combustion engines vary the displacement by only small amounts since the range of compression ratios is very small e.g. maybe 8: 1 to 15:1. On the other hand this innovation varies from 10% to 100% displacement.

It just got 10% better.

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[R600a]

Since I commented the other day I've been thinking about your question and your situation because I had a hard time understanding why you wouldn't use primarily Scrolls in your area.
I think I may have come up with one reason if I'm not mistaken it gets quite hot in the summer and rotary compressors are not vapor cooled. The reason I mention that is with a rotary compressor that is not vapor cooled you're able to make a higher efficiency unit for much cheaper. That is why they're quite common in window units. The condenser coil can be much smaller.

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[Juan Madera]

Rotary compressors are highly efficient. Only reason they were not used in larger systems is the vanes wear and leak too quickly. Now we are starting to see larger systems like the Bosch resi unit on a variable speed control. Apparently Mitsubishi has overcome the rotary's limitations... If so, we may start seeing these used in larger systems and refrigeration systems. All piston compressors suffer from adibatic losses. This is why scrolls and rotary's are taking over the market.

[Dreyfus]

Since I commented the other day I've been thinking about your question and your situation because I had a hard time understanding why you wouldn't use primarily Scrolls in your area.
I think I may have come up with one reason if I'm not mistaken it gets quite hot in the summer and rotary compressors are not vapor cooled. The reason I mention that is with a rotary compressor that is not vapor cooled you're able to make a higher efficiency unit for much cheaper. That is why they're quite common in window units. The condenser coil can be much smaller.

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Sorry I haven't been monitoring this forum. You could be right. I am a novice at the advantages and disadvantages of compressor mechanisms and only base my understanding on what I have read. My understanding is that scrolls require very exact machining to get the tolerances right and the machinery to do this is kind of custom made for each model. Factories find it hard to reconfigure to a different spec. That may be incorrect but it seems logical.

My intention is to see if there is a 2nd or third world market for this design. While it won't be as efficient as most other methods, it will certainly be more efficient than current recip models at a slightly higher price point. Certainly, most of the components could be sourced from existing factories- piston, motor etc. That is pretty cost effective.

Of course inverter technology is the future but this method would appear to be superior to the earlier solutions to load modulation such as gas bypass and valve control - both of which have issues.

Also it's temperature tracking should be more accurate than any 2 stage scroll compressor and would probably be as good digital scroll modulation- possibly better for reasons I can't mention here.

As an aside I have never understood why modulation below 50% for a large part of the duty cycle is seen as good. That would suggest to me that the unit was over specced.

Anyway, as with most of my inventions I don't create things with radical advantages- just stuff that works well enough and should be cheaper to make.

The issue is whether that cheapness is worth modifying factory to chase a price point that occupies maybe only a small part of the market. In the developed world I doubt this thing has merit but in the developing world where people are taking up a/c I am hoping that such price differentials matter.

[Dreyfus]

Thanks. In my area rotary split systems up to 11KW seem to be the only things offered by installers for residential a/c.
Here, humidity is very high in the wet (northern australia) and a/c is not used much during the dry season. It doesn't rain at all for 6 months.

I don't know the situation in other parts of Oz.

I'm sure the efficiencies of my innovation would not rival a rotary or scroll but would certainly be better than a current recip due to the ability to modulate load quite cheaply and accurately. So, I would not claim better efficiencies than other technologies other than recip. In certain 3rd world markets this efficiency gain for modest price increase might fit into their market. But I am guessing of course.

[R600a]

My understanding is that if you want to build a scroll you have to buy the compressor plates from Copeland because they are the only one that knows how to machine them properly.

Sorry I haven't been monitoring this forum. You could be right. I am a novice at the advantages and disadvantages of compressor mechanisms and only base my understanding on what I have read. My understanding is that scrolls require very exact machining to get the tolerances right and the machinery to do this is kind of custom made for each model. Factories find it hard to reconfigure to a different spec. That may be incorrect but it seems logical.

My intention is to see if there is a 2nd or third world market for this design. While it won't be as efficient as most other methods, it will certainly be more efficient than current recip models at a slightly higher price point. Certainly, most of the components could be sourced from existing factories- piston, motor etc. That is pretty cost effective.

Of course inverter technology is the future but this method would appear to be superior to the earlier solutions to load modulation such as gas bypass and valve control - both of which have issues.

Also it's temperature tracking should be more accurate than any 2 stage scroll compressor and would probably be as good digital scroll modulation- possibly better for reasons I can't mention here.

As an aside I have never understood why modulation below 50% for a large part of the duty cycle is seen as good. That would suggest to me that the unit was over specced.

Anyway, as with most of my inventions I don't create things with radical advantages- just stuff that works well enough and should be cheaper to make.

The issue is whether that cheapness is worth modifying factory to chase a price point that occupies maybe only a small part of the market. In the developed world I doubt this thing has merit but in the developing world where people are taking up a/c I am hoping that such price differentials matter.

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[R600a]

I think you would be better off with a good inverter drive reciprocating compressor. It should last longer and if the inverter goes bad you can replace it. Besides that your electrical efficiency goes way up with inverter drive.

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[R600a]

The other thing is that you can have one controller that runs any common voltage and frequency.

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[Dreyfus]

We all know that inverters are more efficient but that comes at a price. There may be markets where that price in unacceptable for many and where their usage patterns can't make up for the initial hit in price outlay.

My mini market survey suggests that an inverter a/c unit regardless of compressor type costs at least 50-60% more than a basic recip. Many people around the world want A/c but can't afford that difference. In addition, if they only use it for cooling at night to sleep (like I do) then the efficiency difference may never be realised in savings in electricity.

I'm hoping that my innovation will provide the efficiency gains of a 2 stage or digital scroll - not the gains of an inverter- but also be cheaper than everything except a basic recip.

So you are correct if talking about first world markets where inverters will dominate but there are very different price sensitivities on other markets.

[R600a]

I tend to think that most variable speed units are not so expensive just because of the inverter technology because minisplits are available for $400 - $800 up to 2 tons and they are decently reliable. I think that with an inverter drive reciprocating compressor you could achieve good efficiency and durability for a low price if that was your aim. I think most oems are not trying yet.
I think the current cost of variable speed equipment is driven by design cost and market placement not manufacturing cost.


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[Dreyfus]

I tend to think that most variable speed units are not so expensive just because of the inverter technology because minisplits are available for $400 - $800 up to 2 tons and they are decently reliable. I think that with an inverter drive reciprocating compressor you could achieve good efficiency and durability for a low price if that was your aim. I think most oems are not trying yet.
I think the current cost of variable speed equipment is driven by design cost and market placement not manufacturing cost.


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I think Danfoss have been selling inverter based recips for a long time-mostly for the RV, boat and off grid markets as fridge/freezers. They are widely regarded as expensive but that may be because of the size of the market i.e. lower volumes vs residential a/c.

I don't see a place for my own innovation with an inverter. They are really alternatives to each other and dialing down rpm as well as piston stroke would be overkill for most applications and probably too expensive.

I will beaver on with what I have and so how I go. Thanks for your insights.

[R600a]

I definitely agree I wouldn't think putting inverter tech on your design is a good idea.
Just curious without giving away too much information have you been able to build a working model?

I think Danfoss have been selling inverter based recips for a long time-mostly for the RV, boat and off grid markets as fridge/freezers. They are widely regarded as expensive but that may be because of the size of the market i.e. lower volumes vs residential a/c.

I don't see a place for my own innovation with an inverter. They are really alternatives to each other and dialing down rpm as well as piston stroke would be overkill for most applications and probably too expensive.

I will beaver on with what I have and so how I go. Thanks for your insights.

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[Dreyfus]

I definitely agree I wouldn't think putting inverter tech on your design is a good idea.
Just curious without giving away too much information have you been able to build a working model?

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I have built a large scale model of the crank system and powered it using 2 battery drills just to test the feasibility of control. Obviously one simulates the compressor motor and the other the controller. It works well enough although the level of vibration at large piston strokes is alarming. That is one reason I applied it to A/C compressors since these are typically damped using springs and noise suppression is more feasible with various materials and enclosures.

I haven't looked in detail at the infiniti variable compression engine design but its limited range of variation in vibration would I imagine be controlled with a flywheel. I think any internal combustion application of my concept would be very challenged by vibration due to the extreme variation in crank trajectory,

In a sense this concept is closer to variable displacement than variable compression due to the range of variation. Other methods of variable displacement such as turning off cylinders or skip firing or varying the combustion chamber volume structurally, don't involve this kind of variation in rotating mass.

I have yet to build anything that actually compresses gas in a cylinder but in practice that should be straightforward. The challenge is that most manufacturers will want to see something that looks like a compressor actually compressing. That probably means I will have to adapt parts from old units as best I can into something not too frankenstein.

Once again I don't see this as being worthwhile in the developed world where purchase price is less sensitive. However there are many parts of the world where the extra purchase price of an inverter will never be recouped in efficiencies because the units just aren't run long enough because people can't afford the power. For example, I rarely use an a/c in the day but rely on it at night for sleeping in humid conditions.

I imagine filipinos for example could afford a more efficient and slightly more expensive recip and maybe recoup that cost in their usage level, but an inverter is out of their reach just in intial purchase price and the difference will not be recouped due to limited run times. But I could be wrong.

Anyway, we shall see. Thanks again

[R600a]

While having no real idea what your system looks like I am sure it could be balanced at least to a degree. Sounds like an interesting idea.
Does the piston always come to the top of the cylinder or does the compression vary with capacity?

I have built a large scale model of the crank system and powered it using 2 battery drills just to test the feasibility of control. Obviously one simulates the compressor motor and the other the controller. It works well enough although the level of vibration at large piston strokes is alarming. That is one reason I applied it to A/C compressors since these are typically damped using springs and noise suppression is more feasible with various materials and enclosures.

I haven't looked in detail at the infiniti variable compression engine design but its limited range of variation in vibration would I imagine be controlled with a flywheel. I think any internal combustion application of my concept would be very challenged by vibration due to the extreme variation in crank trajectory,

In a sense this concept is closer to variable displacement than variable compression due to the range of variation. Other methods of variable displacement such as turning off cylinders or skip firing or varying the combustion chamber volume structurally, don't involve this kind of variation in rotating mass.

I have yet to build anything that actually compresses gas in a cylinder but in practice that should be straightforward. The challenge is that most manufacturers will want to see something that looks like a compressor actually compressing. That probably means I will have to adapt parts from old units as best I can into something not too frankenstein.

Once again I don't see this as being worthwhile in the developed world where purchase price is less sensitive. However there are many parts of the world where the extra purchase price of an inverter will never be recouped in efficiencies because the units just aren't run long enough because people can't afford the power. For example, I rarely use an a/c in the day but rely on it at night for sleeping in humid conditions.

I imagine filipinos for example could afford a more efficient and slightly more expensive recip and maybe recoup that cost in their usage level, but an inverter is out of their reach just in intial purchase price and the difference will not be recouped due to limited run times. But I could be wrong.

Anyway, we shall see. Thanks again

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