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Comment by scottLobster | Hacker News Reader

I'm curious as to how much maintenance the desiccant would require under realistic loads. Does it need to be flushed/replaced periodically? Is is corrosive to its enclosure?

I really wish science journalism would pay more attention to stuff like this. I've been burned by all the Popular Science articles from 20 years ago about zero-emission coal plans with filtered exhaust and built-in carbon capture facilities. They all sound the same, and all leave out details necessary to determine viability. I'm convinced at this point that most science journalists have simply learned to not ask questions beyond a certain point.

But hey I'm happy to be surprised if this actually works.

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>I really wish science journalism would pay more attention to stuff like this.

I think the journalist did answer your questions and the answer is "no one knows how viable this is in the real-world, not even this company":

Blue Frontier is still in the very early stages of proving its technology and breaking into the massive global AC industry. The company will need to show in field tests that its units work as well as it says they have in the lab—without requiring more space or maintenance than the AC units already on the market.

That was my first question too. I found the following. Sadly, because journalisming is oh so hard, they omitted the actual innovations.

TLDR: Novel liquid desiccant functions as a "humidity battery" (my phrase). A salt solution which captures and releases moisture. It's closed loop and doesn't need to be replenished. Claimed OpEx $/hWh (for just the dehumidifier) is ~ $20/hWh, vs > $600 for Li-ion and ~ $400 for ice thermal based systems. It's safer and more durable.

Liquid Desiccants as Breakthrough Energy Storage [2021] https://www.youtube.com/watch?v=2SwMyGzXsuE

Liquid Desiccants and Our Cooling Process - Blue Frontier, LLC [2021] https://www.youtube.com/watch?v=r8B4LQTQ94g

https://bluefrontierac.com

"At Blue Frontier, our mission is to transform buildings into sustainable, comfortable, and interactive spaces. Our first step towards achieving this goal is the commercialization of a revolutionary air conditioning technology. Blue Frontier’s AC system combines dew-point-style sensible cooling with liquid desiccant dehumidification to reduce electricity use by up to 90% (non-fan). The desiccant is recharged and stored when electricity is the cleanest or lowest cost, and later used to deliver cooling when electricity is dirty or costly. These features enable our system to solve an array of today’s largest sustainability problems — from the Duck Curve to peak load management, from humidity control to integration of intermittent renewable resources."

Note the "Duck Curve" bit. Their "humidity battery" (my phrase) allows them to do load shifting. In the actual AC unit(s).

That's really bitchin'.

Okay, that's a shame. The most interesting part of the product is the part the article didn't even touch on!

Thank you for finding this!

Heat batteries were tried in furnaces a couple of decades ago, but they used some sort of high heat capacity bricks and forced the house air through them. As GP asks, the matter of maintenance was forgotten.

Recently I heard someone is trying this again with water heaters. The working fluid has roughly four times the heat capacity of water, so your “water” heater is substantially a fluid heater with either no water tank or a very small one. Incoming water is heated with the fluid, and the fluid is heated on demand. Only the heat exchanger has maintenance concerns.

Driving the whole thing with a heat pump makes the math a little more fiddly, since peak pump efficiency and peak power prices overlap some of the same parts of the day. You’re calculating BTUs per dollar, not watt hours per dollar.

It’s already cheap to just use a larger water heater as the thermal battery.

Few households use more than 80 gallons of hot water per day which is still within the normal range of hot water heaters. Just add a timer so it doesn’t kick on until powers cheap and you’ll be good to go. At least assuming your cheap electricity window is long enough to fully heat the water.

This is one of the reasons people overestimate the need for grid energy storage. People time shift electricity to the night because it’s cheap. If it was cheaper 10AM-4PM then significant demand would shift to that window.

> significant demand would shift to that window

Sounds like we would need “smart” water heaters that can query energy prices. That most likely means they would be online sharing all kinds of data most of us probably don’t want shared and would have a small monthly fee. The water heater might even be very inexpensive because of this.

I know it wouldn’t have to be implemented this way, but of course that’s how it would go.

Such things already exist: “ If applicable download the Time of Use schedule of your local electric utility to prioritize heating when the rates are most affordable” https://www.statewaterheaters.com/literature/spec-sheets/res...

Not necessarily smart. Here (France), most water heaters can be controlled with an extra "pilot" wire, or closing a circuit. It has been common practice since maybe the 60s to have multiple mettering rates, and a dry contact (relay) on the electricity meter to switch on/off some loads (mostly electric water heaters, though some electric space heaters can be connected as well).

These days, rates can be more flexible thanks to "smart" meters (communicating via PLC). Just after the russian invasion of Ukraine, there were plans in place to open the dry contacts of customers outside of the scheduled hours in case the electricity grid needed to shed extra load. Thankfully this didn't end up being necessary.

What I'm saying is that you don't really require smart end devices. Put the incentives in place (deep discounts) and the rest will follow. You probably need at least one smart device to control the others if a timer is not enough, and I think the electricity meter is a good fit for that role.

What liquid has 4x the specific heat of water? Water is 4.1 J/g°C

I dont think much else even comes close

so i put on my scientist hat and started to write a reply going through the mechanics of beating water's heat capacity, first pointing out that what you want for these types of systems is likely high volumetric heat capacity rather than gravimetric. then i went on to discuss the density of room temp ionic liquids (RTILs), only to find myself digging into their heat capacity numbers and man, you're right! I forgot how well water stores heat compared to other liquids. RTILs vol. heat capacity has trouble breaking 2 J/cm3-K![1]

[1] Table 4, https://www.researchgate.net/publication/231542196_Heat_Capa...

To beat water's specific heat, you have to cheat and use a phase change material (special wax) that melts near the desired water temp, or a bit higher if you use a cold water mixing value.

Wax

Paraffin is 2.1 Kj/whatever

https://www.researchgate.net/publication/336006577_Comparing...

That’s missing the phase change energy, which is in the zone we’re looking at here.

Not necessarily. If you're trying to heat water to 120º you may not want the paraffin to phase change at all. Because then you have a problem transferring heat from liquid->solid->pipe->liquid.

Phase change seems to work better for trying to maintain an ambient temperature. The input side is always going to be cold, and at some times of year far colder than others.

> some sort of high heat capacity bricks..., the matter of maintenance was forgotten.

Tangent: Startup Andora Energy claims to have solved the maintenance problem with some novel carbon bricks.

Further: Their next gen product plans to use thermophotovoltaics, converting heat into electricity, directly. That'd be spiffy.

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