9, Jan 2020 / rebound

IcePoint: at last, a better way to cool

By: Kevin Davis

Eight years ago, in a Colorado garage, Russell Goldfarbmuren and I invented an innovative way of cooling, and Rebound Technologies was born. Now, as our startup morphs into a real company (with a new headquarters and nearly a dozen employees and millions of dollars invested) I figure it’s time to fill the world in on our revolutionary technology and the exciting future I see for us. Simply put, we are going to change the way the world cools itself…

The big picture

In trucks, homes, factories, and warehouses around the world, air conditioners, refrigerators and freezers remain pathetically antiquated, based on an inherently-flawed cooling cycle developed 170 years ago. We are, essentially, stuck with this obsolete technology – as if limited to telegraphs in the era of iPhones. Actually, the situation is worse than that – because the dominant cooling technology, called vapor compression, isn’t just inconvenient, but is energy-intensive, maintenance-prone (and hazardous), environmentally devastating, and functionally inept. As I’ll explain, vapor compression systems are the equivalent of one-speed Model Ts. That was our starting point: we aimed to build a cooling vehicle more suited to modern times.

Rebound’s patented cooling system, which was developed with support from the National Science Foundation, represents not just a drastic technological improvement over vapor compression, but a quantum leap forward for the trillion dollar cooling industry, and a massive opportunity for the world, which devotes a substantial portion of its energy to cooling. We call our system IcePoint.

IcePoint: a better way to cool

Producing heat is easy, but producing cold – unless you’re Zeus or Thor – is not. The best we mortals can do to stay cool is trap and move heat from one place to another. Since the 1850’s, the most obvious way to do this has entailed taking advantage of basic physics: as liquids vaporize, they absorb heat. By constructing just the right network of pipes, and constraining a fancy liquid – called a refrigerant – just so, and inducing it to undergo a phase change in the right time and place, it’s possible to capture heat and then shuffle it along. That’s more or less how vapor compression systems provide cooling: by moderating the pressure of refrigerants, inducing them to transform from liquid to gas and back.

Rebound’s IcePoint system provides cooling not by using pressure, but by moderating the chemical composition of its refrigerant. And the refrigerant is simple: it’s a mixture of plain old ice (water) and a salt called potassium acetate. Around the world, airports use potassium acetate to de-ice runways. It’s safe, and it works really well. By mixing up this saltwater, we produce a very cold (-40°F) brine… that can go suck up a lot of heat.

But that’s just the start of what IcePoint can do…

IcePoint’s 3-step cycle is simple

  1. charging: combine 32°F ice and liquid salt to create a -40°F liquid refrigerant
  2. discharging: pump liquid refrigerant to provide cooling by absorbing heat
  3. regeneration: separate refrigerant into salt and water… for refreezing and remixing.

In the broadest sense (because all we can do is move heat around), the thermodynamic principles of Rebound’s IcePoint system are nearly identical to those of a traditional vapor compression system. But IcePoint’s revolutionary architecture – which relies on mixing and separation, rather than expansion and compression – allows it to outperform traditional vapor compression systems on every practical front.

Common cooling scenarios

Before enumerating IcePoint’s various operational benefits, it’s useful to consider two common industrial cooling scenarios:

A) Sarah’s Super Strawberry Farm grows nothing but strawberries. During the August harvest, Sarah’s batch freezer is crammed full of pallets of berries, overtaxing her cooling system. The rest of the year, her expensive freezer is nearly empty.

B) Charlie’s Chicken Chompers produces processed (cooked) chicken tenders, which are continuously frozen at a steady rate on a conveyer belt as they emerge from Charlie’s oven. Charlie’s freezer is on 365 days a year – even, unfortunately, on those August days when electricity costs spike.

Where vapor compression disappoints

For Sarah and Charlie, traditional vapor compression cooling systems become unyielding at exactly the wrong times. Their cooling systems, in fact, behave like toddlers throwing temper tantrums. “I will not try harder!” Sarah’s freezer screams. “I will not take a nap!” Charlie’s freezer roars. Why won’t they cooperate? Because vapor compression cooling systems are fundamentally rigid. Each vapor compression system – its compressors and condensers and evaporators and pipes – is designed to accommodate a specific cooling load, and performs poorly when tasked with anything different.

Actually, that’s understating things, because “anything different” includes doing less work and doing more, and vapor compression systems respond uniquely to each case. When you ask a 1000TR vapor compression system (a system designed to cool one thousand tons of stuff) to do only 500TR of cooling, it responds awkwardly and lamely. It shuts off some portion of its compressors, and makes use of a slide valve – which comes with a significant efficiency penalty. This is half of the reason I compared vapor compression technology to an old clunker that only goes one speed. If your car only goes 30mph, and you want to go 15mph, you could, of course, stomp on the gas pedal and the brake pedal at the same time – sacrificing mileage and brake pads concurrently. (When you ask a smaller vapor compression system, like a home refrigerator, to do less work than it’s designed to do, it cycles on and off… which is a bit like driving 30, and then stopping, and then 30, and then stopping. The math works out, but not surprisingly, it’s also inefficient.) In this situation, your car’s limitations become apparent quickly.

But when you ask a 1000TR vapor compression system to do 1200 tons of cooling, it responds even worse, by slowing down. OK, the compressors don’t slow down, and neither does the flow of refrigerant – but the job at hand does. This is because traditional pressure-moderated refrigerants can only absorb so much heat – and once they do, they turn to gas, leaving less liquid refrigerant available to capture heat. The refrigerant, ironically enough, overheats! That’s the second half of the reason I compared vapor compression technology to an old clunker. Even with the pedal to the metal, when you drive up long, steep hills, you cannot hold speed. Though you yearn to peg it at 30mph, you’ll be lucky if you hold 20. This negative feedback loop illustrates a sad reality about vapor compression cooling systems: as they exceed capacity, they consume more energy while cooling more slowly.

So pause for a second, and consider the response you’d have if an automaker tried to sell you a car with these attributes. Imagine a salesman saying, “Well, this baby won’t go 60 miles an hour, or 20 miles an hour, but it gets pretty good gas mileage at 40, unless you’re going uphill, in which case you might need to ditch some cargo…” I suspect you’d walk out of the showroom.

And that’s why I said that, as far as cooling goes, we’re stuck: around the world, for the last century and a half, there’s only been one type of car on the market.

Enter IcePoint, the agile cooling system

With IcePoint, Sarah and Charlie can run their businesses more smartly, by accommodating real-world variability. How would that look in each scenario? Sarah could reliably maximize revenue during peak season, freezing as many strawberries as possible by continuously charging, discharging and regenerating daily in August. The rest of the year, she could eliminate peak-demand electrical expenses by charging only during daily off-peak hours, while discharging stored capacity during on-peak hours. Charlie could do the opposite, running full time 11 months of the year, while minimizing August’s high peak-demand electrical expenses by charging only during off-peak hours.

As such, IcePoint functions like a thermal battery – albeit a more efficient one. But IcePoint delivers more agility still. By accommodating an exceptionally wide range of cooling scenarios, IcePoint also gives Sarah and Charlie the freedom to expand. Sarah, for example, could freeze 55-gallon drums of strawberry juice at the same rate that she freezes packaged strawberries – even though the products have very different properties. Charlie, meanwhile, could run a new product using the same production line – and still meet output targets – something no rigid vapor compression system could handle.

I want to hone in on this, because it’s significant. Let’s say Charlie spent all the money he saved on peak-electrical charges developing a new variety of chicken tender, which, on account of its barbecue glaze, requires more energy to freeze than a plain chicken tender. Charlie could run that new product using his same continuous freezer – without slowing down production. Thanks to IcePoint, Charlie would not have to sacrifice line speed (and profit) for opportunity. At the rate already deemed optimal (and intertwined in downstream processes, like packaging and shipping), Charlie could continue running new chicken tenders one day, and old ones the next, and rely on IcePoint to keep up with cooling. Incredibly, the IcePoint system can maintain peak efficiency across a cooling capacity of X → 5X. Think of it this way: with a vapor compression system, the chicken would become the boss of Charlie. With IcePoint, Charlie can remain the boss of his chicken. Two cheers for Charlie! In this way, IcePoint’s agility – its ability to provide dynamic cooling – provides Charlie with previously unimaginable wiggle room, freeing him from the tyranny of a rigid cooling system.

IcePoint turns the cooling bottleneck into a cooling weapon

IcePoint’s unique design allows users to gain temperature control, something not possible with vapor compression systems. This becomes especially notable in continuous freezers, which are almost universally plagued by frost build-up. As frost accumulates on evaporator coils, their efficiency – their ability to absorb heat – plummets. The problem is so universal that most continuous freezers feature three parallel refrigerant loops (all of them oversized) where only two are needed, so that one may always be taken out of commission for thawing and defrosting. This is a little bit like building a six-wheeled car and putting six leaky tires on it, on the premise that it should be possible to run around with a pump and keep four of ‘em inflated at any given time. Car metaphors aside, moisture presents such a problem in continuous freezers that many operators go to great lengths to install desiccant systems. These systems gobble up a lot of energy, and often rely on ethylene glycol, a toxic chemical that I, for one, would prefer not to have around my food.

Rebound’s IcePoint system solves the moisture-control problem elegantly, by eliminating the moisture with unparalleled proficiency. How? By lending the evaporator coils a helpful hand through two simple air ducts. The first diverts hot, wet air to an exterior unit, where it passes through a mist of supercold brine. This air-mist heat exchanger works ultra-efficiently, concurrently cooling the air AND sucking out the moisture. What remains is cold, dry air, which is re-injected through the second air duct.

By eradicating the moisture-control problem from continuous freezers, IcePoint avoids frost build-up and delivers temperature control, which means faster cooling, and more reliable cooling, and less expensive (more efficient) cooling, which I’ll get to. As such, Russell and I often describe IcePoint as a supercharged cooling system – which, as I’ll explain, it literally is. As you can see, this new vehicle is a lot more appealing than our clunky old Model T.

Across the board, IcePoint is superior to vapor compression

Earlier, I described traditional vapor compression cooling systems as relying on “fancy” refrigerants. By “fancy” I meant able-to-absorb-lots-of-heat-when-they-vaporize, but I also meant nasty (toxic, or explosive, or ozone-destroying), because chemicals with the former trait by and large possess the second. The sad truth about traditional refrigerants is that their performance comes at the expense of other characteristics. The history of vapor compression technology, in fact, is little more than a series of bad trade-off followed by worse-trade off – first at the expense of the environment, and then at the expense of efficiency. Consider this sad irony: where physics dictates that optimum heat transfer in a vapor compression system would involve large number of small copper evaporator coils, economics dictates the practical impossibility of building such a design! What it all boils down to is this: there’s a performance ceiling above which vapor compression cooling technology cannot rise. Vapor compression technology can get (and has gotten) cheaper, but it can’t get better. The fundamental design is flawed.

Rebound’s IcePoint system, on the other hand, is not hamstrung by its own design, but freed by it. From a physics perspective, in which maximizing coolant surface area is the name of the game, IcePoint’s air-mist heat exchangers are ideal. From an operational perspective, IcePoint’s primary refrigerant is nontoxic, nonflammable, nonexplosive, non-ozone-depleting, easy-to-store, and not federally-regulated. The IcePoint system operates at ambient pressure, and has cycle stages that operate independently. Mechanically, this makes IcePoint resilient, easy to optimize, easy to maintain (No invisible leaks! No ammonia-certified technician necessary!), and simple to scale. More importantly, this drastically-improved cooling system is designed from top to bottom for efficiency.

IcePoint: designed for efficiency

Rebound’s freeze-point suppression architecture is optimized for efficiency in three ways:

* Extra-efficient Ice Generation: Where traditional systems generate ice by using refrigerants well below 0°F, Rebound’s proprietary system generates ice using a 23°F refrigerant. The icemaking system saves still more energy by self-harvesting ice. In other words, it does not require mechanical force or hot fluid to extract built-up ice. Consequently, Rebound is able to produce ice with smaller-than-typical condenser units. And, at night, the icemaker takes advantage of lower ambient temperatures, gaining up to a 30% efficiency boost.

* Thermal Recuperation: Where vapor-to-liquid heat exchange is prohibitively expensive and often yields a net performance reduction in traditional vapor compression systems, it’s a simple and ultra-efficient matter in the IcePoint system. Better still, thanks to efficient liquid-to-liquid heat exchangers, the more heat IcePoint’s refrigerant captures, the better, as this heat speeds up the regeneration leg of its cycle.

* Ultra-efficient Separation: We separate our brine the same way that Minute Maid makes orange juice concentrate, with a well-known process called mechanical vapor recompression (MVR). Since the large positive-displacement blowers in standard MVR units were too big, expensive, and unreliable for us, we developed our own centrifugal model, seals, impeller, high-speed motor and all. This system, essentially a custom supercharger, delivers unprecedented separation performance.

THE RESULT: IcePoint is up to 35% more efficient than traditional vapor compression.

IcePoint: comprehensively studied

I wouldn’t make such a bold claim if I weren’t sure of it, and if I couldn’t back it up. I’m sure because over the last eight years, with our proprietary thermodynamics modeling library, we’ve spent more than sixty thousand hours refining the IcePoint cycle. We’ve tested hundreds of components, and evaluated more than a dozen designs. We’ve gathered laboratory validation with a major utility company (Southern California Edison), and, more to the point, have successfully helped freeze a couple million strawberries in California. IcePoint works, and it works better than vapor compression. At long last, a modern cooling system is available.

IcePoint: cooling that’s innovative and superior

Vapor compression technology predates the light bulb, the telephone, and the car. It predates dynamite! Yet since vapor compression emerged as the dominant technology, the cooling industry has seen very little innovation of consequence. Take thermoelectric cooling: it’s nifty, but it’s terribly inefficient and expensive, making it impractical at scale. And while natural (rather than synthetic) refrigerants are nice, they’re still going into one-speed Model Ts! Who cares what fuel you’re putting into obsolete clunkers – you’re still stuck with obsolete clunkers!

IcePoint, which takes advantage of advances in controls, heat exchangers, and other thermal fluid components, represents the innovation long lacking in the cooling industry. It’s the totally new cooling vehicle the world needs.

Better cooling pays off

IcePoint delivers immediate and recurring financial benefits related to capital costs, operating costs, and revenue generation. If it pains business owners like Sarah and Charlie to purchase oversized capital assets, it pains them even more to have those expensive assets sit around and collect dust much of the time. By design, IcePoint is different. It’s a small but powerful system. Its nimbleness, in fact, makes it potent. IcePoint is the only cooling system that can sync with cooling demand AND significantly reduce regular and peak energy costs. On account of its independently-structured cycle stages, the IcePoint system also mitigates losses that result from maintenance-incurred downtime. All mechanical systems require maintenance, but few mechanical systems can be maintained without shutting down. Lastly, where IcePoint can help insure against quality-related losses (spoilage, bacterial spread, food-safety recalls) and even unpredictable grid reliability, it’s also ideal for forward-thinking businesses. Simply put, no other cooling system can immediately accommodate top-line, revenue-generating growth – which makes IcePoint a prudent business investment.

Compare: IcePoint vs. vapor compression

I could go on and on, but I think it’s clear by now that when I say that IcePoint is superior to vapor compression, I mean that it’s better in every way: in operations, economics, safety, reliability, and flexibility. A cooling system that’s drastically more efficient than the industry standard, and eliminates the number-one headache, and which can easily accommodate real-world variability, promises an immediate return on investment.

Rebound’s plan: retrofits –> standalone systems

Revolutionizing an industry is a process, and it takes time. To transform the cooling industry, we’re targeting food processors and refrigerated warehouses (cold-storage logistics companies), and we’re trying to make the technology transition palatable. As such, we aim to dedicate the next five years toward low-hassle, minimum-commitment system retrofits. For both batch and continuous systems, the integrations are simple:

Continuous: install two air ducts from the freezer to an air-mist heat exchanger. Then plumb heat exchanger to IcePoint’s exterior skids.

Batch: install heat exchanger in engine (compressor) room, and plumb to IcePoint’s exterior skids.

We’ve calculated that by delivering supplemental cooling power, such IcePoint retrofits offer the potential to boost annual earnings by $500k → $1.5M.

Once we have such validation, we’ll begin selling standalone IcePoint systems that provide 100% of the cooling needs for both types of freezers. The continuous IcePoint model will be nearly identical to the continuous retrofit system. The batch model, though, will look pretty different from the batch retrofit system. Instead of sub-cooling the existing refrigerant via an engine-room integration, it will directly feed proprietary “evaporators” incorporated in facility batch freezers (ie: blast cells) – obviating traditional evaporators, ammonia, and associated plumbing. We’re already working on this design, and I can’t wait to share more details about it.

And once we demonstrate what IcePoint technology can do in the low-temperature market, we’ll begin making medium-temperature systems (freezers and supermarket refrigerators) and high-temperature systems (air conditioners.) As you can imagine, it’s a thrilling time for Rebound Technologies, with a ton to anticipate – but I’ll leave it for now at this:

If 40% of the food processor, refrigerated warehouse, supermarkets and commercial air conditioner sectors deploy IcePoint by 2050, the net effect will be a carbon reduction of over 600MMT, or 1.7% of global emissions. Just for staying cool better! Let’s get going…


Kevin Davis is CEO and cofounder of Rebound Technologies, an advanced engineering firm that’s revolutionizing the global cooling industry with an economically and operationally superior cooling cycle called IcePoint.