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#1 2023-03-23 16:47:57

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Heat your House for Free with an LP Air Compressor

If we are able to make use of heat and cold resulting from adiabatic compression and expansion of air, we can literally get something for nothing.

I was interested in calculating the efficiency of compressed air energy storage at low pressures.  Because I am lazy, I decided to make use of these two online calculators, rather than crunch all the numbers myself.
https://tribology-abc.com/abc/thermodynamics.htm
https://www.omnicalculator.com/physics/ … -processes

My assumption is that outside air starts at a temperature of 10°C (283.2K), with a density of 1.2kg/m3.  Using the omnicalculator, I take 1.5m3 of air and compress it from 100KPa to 150KPa.  The calculator tells me that this will require 46.082KJ of work and the internal energy of the gas rises by the same amount.  Its temperature is now 318K (44.8°C) and its volume is 1.1228m3.  I pass it through a counterflow heat exchanger, with water entering the heat exchanger at 10°C and leaving at 44.8°C.  Air temperature returns to 10°C or 283.2K, its pressure is still 150KPa, but volume has reduced to 1m3.  The Cp of air at 1.5bar is 1.005KJ/kg.  Cooling the air back to 283.2K, reduces its internal energy by 62.84KJ.  We can use the water thus heated as wash water.  We now have 1m3 of air with pressure 1.5bar and temperature 283.2K.  We decide to expand it adiabatically through a turbine to produce work.  The tribology calculator tells me that with adiabatic expansion, we get 41.042KJ of work out (89% of what we put in).  The temperature of the air after expansion is 252.2K (-21.1°C).

For an input work energy cost of 46KJ, we get 41KJ of work back and 63KJ of free heat!  It hasn't come from nowhere of course.  The heat we are able to extract is balanced by the difference in internal energy of the air between the compressor inlet (T=283.2K) and the turbine outlet (252.2K).  Our air compressor has acted as a heat pump.  But because we can make use of both the compression heat and expansion cold, we are effectively getting about 4x as much energy as we put in.  The hot water from the compressor heat exchanger can be used for washwater heating.  The cold air from the expander can exhaust into a freezer.

Air compressors typically exhaust into a receiver tank, which maintains a pressure of 10bar(a).  This allows a compressor with fixed power output to meet varying short term loads which can exceed its steady state power output.  Without a receiver tank, the compressor would have to be rated to the peak power output of tools and would need to operate at full power 100% of time, which would waste energy.  Most receiver tanks are steel vessels.  These would be expensive were we to use them for a home based CAES system.  However, for air at very low pressure (1.5bar(a)) a pressure vessel is not needed.  Air can be stored in a gravity vessel.  This is essentially a pit dug into the ground, with a mound of rock and soil heaped over it, providing 5 tonnes/m2 of overburden to counteract internal pressure.  The only materials needed to build a low pressure air store like this are dirt, stone and wooden planks or sheets to hold up the roof against the weight ofbthe overburden.  Low pressure CAES like this can be done as a DIY home project.  The downside of low pressure CAES is that the energy density of LP air is very low.  From the example above, at 1.5 bar(a), or 0.5bar(g), air will store 41KJ of recoverable mechanical energy per cubic metre, if expansion is adiabatic.  To store 1kWh of mechanical power, our pit must have a volume of 88m3.  That is a cylindrical cavity, some 6m in diameter and 3m deep.  But if properly constructed, such a store could last for centuries, with hundreds of thousands of charge discharge cycles.  LP CAES there meets the criteria of the Permenance principle.  It will be relatively expensive to build, but once built it should last indefinitely.

Given that energy recovery from the low pressure compressed air is close to 90% efficient, the simplest arrangement would be to build a wind turbine that generates LP air directly, using a single cylinder piston compressor driven from the turbine shaft.  If the tower is made from stone or brick, it could be built over the air store, adding to the weight of the overburden.  The air turbine would be coupled to an AC generator.  The turbine would be equipped with a governor, which would open the valve from the air tank wider as the turbine slows, maintaining a constant speed as load on the generator varies.  A generator producing a time averaged power of 1kWe, would require a wind turbine producing 1.2kW mechanical power on average.  The wind turbine would produce 1.5kW of heat and the expansion turbine a comparable amount of cold.  The cold air can be used to supply a giant underground freezer, storing many months of food in case of zombie apocalypse.

Last edited by Calliban (2023-03-23 16:59:18)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#2 2023-03-23 18:03:36

tahanson43206
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Registered: 2018-04-27
Posts: 18,111

Re: Heat your House for Free with an LP Air Compressor

For those who might be curious about the title for this new topic, Google found this:

define lp air compressor

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About 10,400,000 results (0.60 seconds)
The abbreviation means LP = low pressure, MP = medium pressure, HP = high pressure, oc = outer chamber, ic = inner chamber, c = compression and, s = suction. Source publication. A novel double chamber rotary sleeve air compressor part I: design and thermodynamic model. Article.

Compression cycle of the DCRSC. The abbreviation means ...

ResearchGate
https://www.researchgate.net › figure › Compression-cyc...

The term in the title "for free" ** may ** mean (free if you have wind available).

The term "for free" might also mean "after you have paid off the investment to build the system" AND "have wind available"

(th)

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#3 2023-03-23 19:25:58

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

TH, when you store 10 units of electricity in a battery, you get 6-9 units back in the form of electricity.  Nothing more than that.  When you store 10 units of mechanical energy in LP compressed air, you get 9 units back as mechanical energy, plus 12 units of heat and 11 units of cold energy.  If you are using the air store as a kind of battery, then the heat that you get is a bonus.  If the battery and air store have about the same long term cost, then we can think of the heat as a free bonus.  Of course, the device has not created the heat as such.  It has pumped it out of the air and into the cooling water.  The cold (absence of heat) is another bonus that we don't have to pay for.

Not all areas of Earth are equally endowed with wind energy.  But for most places in the northern hemisphere, tapping the wind is a lot more energetically favourable that converting sunlight into electricity using PV.  Mechanical wind machines are technologically simple and could be built by anyone with the right tools and machine shop experience.

Last edited by Calliban (2023-03-23 19:35:17)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#4 2023-03-23 19:55:12

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,304

Re: Heat your House for Free with an LP Air Compressor

Not to mention we can also add in more energy from solar sources via concentration as well to the exchanger.

Since we might make the device for human energy input we can add it to a bike frame and get some exercise while we are at it without going to the gym.

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#5 2023-03-23 20:38:52

tahanson43206
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Registered: 2018-04-27
Posts: 18,111

Re: Heat your House for Free with an LP Air Compressor

For Calliban re new topic ... thanks for your reply about the potential benefits of storing mechanical energy in various forms.

The 'for free" part of your title invites comparison with other energy management procedures.

The output of the windmill could be used to heat a house by generating electricity.

The efficiency of that procedure is probably knowable, and you are someone who has shown the ability in the past to estimate efficiency with some reliability.

I'd be interested in knowing how much of the energy pulled from a store of gas molecules during compression can be made available for home heating, and how that thermal energy would be distributed in the home. 

I can see how the storage of mechanical energy in the spring-like conditions of a pressure tank has advantages over batteries.  The energy does not go anywhere while it is waiting to be used.  In that respect it is similar to a gravity energy store, which can take many forms but waits patiently until it is needed, and does not leak away.

The cooling effect when the gas is released to perform mechanical service is a nice benefit if it can be used.

Since no energy is created by any of these transformations, I am having difficulty with the word "free".

Energy storage systems have been the subject of your posts over several years now.  Each system has advantages and disadvantages, but this is the first time I can recall your use of the word "free" in the context of an energy storage system.

Every energy flow is used now or stored and used later, but ultimately every last bit is used, and none is created along the way.

I'd like to see the energy budget for your proposed scenario of gas compression, in comparison to other energy storage systems.

(th)

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#6 2023-03-24 07:54:58

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

TH, I will put a more detailed description onto the thread sometime today.

Another option to LP air, would be to store energy in vacuum.  We use a compressor to suck air out of a closed vessel.  If we reduce pressure from 100KPa to 50KPa, we have a stored potential energy of 27KJ/m3.  This is a very low energy density.  But the thing that this idea has in its favour, is that the vacuum tank is an entirely compressive structure and the pressure difference is only 50KPa.  We could use soil bricks, cob or loose rocks with mud binding, to make a hemispherical vacuum store.  The thick walls would actually be useful against buckling instability.

To store 1kWh, a hemispherical vacuum tank some 8m in diameter would be needed.  So this not something you do without a lot of space.  From the outside, the vacuum tank would appear as a small grassy hill.  You could graze sheep on it or landscape it with flowers.  As a compressive structure, there is no real definite limit to its lifespan.  It may be relatively expensive to build.  But you build it once and it lasts forever.  The only materials needed are mud, or mud and stone.  Damp sealing can be accomplished using few sheets of polythene or alternatively, layer flat stones to prevent damp from soaking up by capillary action or entering vertically as rainwater.  This is an energy store that you could build after the zombie apocalypse, without access to industrial materials.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#7 2023-03-24 13:06:46

tahanson43206
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Registered: 2018-04-27
Posts: 18,111

Re: Heat your House for Free with an LP Air Compressor

For Calliban re further development of your idea ...

Thanks for adding an additional view of your storage concept, but also, for adding the Zombie Apocalypse angle.

There are members of Dr. Dartnell's Knowledge Forum whose brains operate along those lines.  I have a correspondent there who might be interested. He lives in the far North and travels for long intervals, so it may be a while before I catch up with him, but I'm sure to remember to pass along your ideas.

You still haven't changed your topic title, so I'm very likely to be inspired by the word "free" to invite your further explanation.

In the mean time, vacuum storage would seem (to me at least) most useful where the atmosphere is dense.

For some reason, ** my ** mind just lept to Venus, where NASA's deep thinkers have been struggling for some time to think of a way to put a probe on the surface with any hope of survival.  Your idea of a vacuum is quite interesting in that context, and fortunately, your knowledge of thermal dynamics is (probably) up to the challenge I'm about to offer ...

If NASA (or anyone with the resources) were to place an instrument package inside a vacuum bottle and lower it gently to the surface of Venus, what temperature would the equipment inside the vacuum bottle experience?

"Heat your house for free" .... OK ... I'm asking for how to ** avoid ** heating the house, so I'm way off topic.

Perhaps this might be interesting enough to you so we could create an entirely new topic for a vacuum equipment chamber for Venus?

We have several members trying to deal with heating issues in their various situations.

SpaceNut has the modest challenge of heating a home in New Hampshire without spending any money.

Terraformer has a somewhat more ambitious vision of heating an entire town by stirring up collective effort to accomplish what no individual could achieve.

Calliban has an option of considering purchase of land in Northern England (assuming the family agrees to the venture) and creating an independent homestead.

All-in-all, this forum has a ** lot ** going on that is practical Real Universe activity, as a sidebar to the creative imagining about Mars that is the bread-and-butter of this forum.

(th)

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#8 2023-03-24 14:00:49

Terraformer
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From: The Fortunate Isles
Registered: 2007-08-27
Posts: 3,855
Website

Re: Heat your House for Free with an LP Air Compressor

Re. Compressing air, British air in particular is very humid. What happens to the water when you compress it? I asked this before but I'm not sure anyone understood what I was asking. If compressing it causes it to condense out, that's a *lot* of latent heat being released. More than you get from the air possibly.

Heat pumps move heat around. A heat pump that can tap *latent* heat rather than sensible heat could achieve a really high CoP. A solar collector using the entire sea as the collection area.


Use what is abundant and build to last

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#9 2023-03-24 15:16:55

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

Moisture is a big problem in air compressors.
https://www.quincycompressor.com/air-co … ure-guide/

The latent heat of condensation is a problem.  The increase in temperature of the air raises vapour pressure, but humid air will still result in condensation within the receiver tank, where the compressed air will cool to ambient.  Any moisture that condenses in the compressor results in corrosion of steel components.  Worse still, air cools as it expands.  Air tools can get extremely cold.  Any moisture in the compressed air can seize them with ice.  Some compressors incorporate dryers.  One way of removing moisture would be to pre-chill the air.  If the air is cooled to beneath 0°C, any moisture will freeze out onto cold surfaces.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#10 2023-03-24 16:23:22

Terraformer
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From: The Fortunate Isles
Registered: 2007-08-27
Posts: 3,855
Website

Re: Heat your House for Free with an LP Air Compressor

...and that condensing will release heat. The heat you gain from the compressed air as it cools should be more than expected based solely on sensible heat. Quite possibly a lot more.


Use what is abundant and build to last

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#11 2023-03-24 17:28:08

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

At 10°C, air with 100% humidity, will carry 9.39 grams of water vapour per cubic metre.
https://www.engineeringtoolbox.com/maxi … _1403.html

Latent heat of evaporation of water is 2.5MJ/kg at 0°C.
https://www.engineeringtoolbox.com/wate … _1573.html

Removing all of the water by cooling implies a heat energy flux of 23.5KJ.  That is a significant energy flux.  If we were using CAES on a large enough scale, then a heat pump could be used to achieve this cooling.  If we are cooling from 10°C to -20°C, the ideal COP would be 8.44.  Assuming a real heat pump can get 2/3 of carnot efficiency, real COP would be 5.6.  To remove 23.5KJ of heat would take 4.2KJ of work.  That is about 10% of the energy that we expect to get from expansion of air from 1.5 bar.  A significant expense.

But our system is small scale and we want design simplicity.  We could store some of the cold from the adiabatic air expansion and use it to chill and dry the air prior to compression.

Adiabatic expansion of dry air from 1.5bar(a) and 10°C, to 1.0bar(a), results in a temperature drop of 32K.  Even a small amount of residual water vapour could clog the expander with ice at this temperature.  So drying the air is important

Last edited by Calliban (2023-03-24 17:30:14)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#12 2023-03-24 17:43:54

Terraformer
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From: The Fortunate Isles
Registered: 2007-08-27
Posts: 3,855
Website

Re: Heat your House for Free with an LP Air Compressor

I have no idea why you're convinced this heat is a problem, rather than something to be taken and used.


Use what is abundant and build to last

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#13 2023-03-24 18:44:16

tahanson43206
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Registered: 2018-04-27
Posts: 18,111

Re: Heat your House for Free with an LP Air Compressor

For Terraformer .... the process the two of you are describing for removal of water from air sounds (to me at least) a ** lot ** like the method used to wring water out of the air in climates/regions with little (or no) ground water.

The question of heat has not come up in articles I have seen about that process, because the focus was production of water literally from thin air.

I'm not sure this observation helps Calliban get to the "free" part of the topic title, but I'm sure he'll get there eventually.

(th)

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#14 2023-03-24 20:07:01

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,304

Re: Heat your House for Free with an LP Air Compressor

The issue for water present in the air tank after compression is that under a quick pressure release the moisture will freeze the outlet is when know as this happened with submarines that were trying to quickly ascend to sea level surface from being deep. It is why the stored air requires drying before it is fully compressed to the higher pressure that we require.
I know that pressurizing a scuba sized tank to 5000 psi it does get quite hot and that it will become very cold under release.

Off the top of my head, I do not have a reference point for using the metric air pressure units that are kPa. So the calculator indicates approximate 14.5 psi going to just 21.8 psi.

https://en.wikipedia.org/wiki/Gas_laws

Calliban is attempting to get energy from the Combined and ideal gas laws that has temperature contained in the equation.

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#15 2023-03-26 15:23:41

kbd512
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Registered: 2015-01-02
Posts: 7,602

Re: Heat your House for Free with an LP Air Compressor

You have to get rid of the water vapor before you compress the air- pretty much all of it, or you corrode the parts of the machine you can't easily replace.  You could use some of the cold turbine exhaust to condense the water out of the incoming air, but again, that's a net loss.  Even if you don't remove the water, compressing humid air requires more work than compressing dry air, so it definitely IS a problem.

As near as I can tell, what we're doing here is as follows (Calliban, correct me if I'm wrong):

1. We're trying to devise a simpler mechanical system with lighter components that requires fewer technology metals to make and store energy.  Some of it will still be converted to electricity, but most of it is use and storage of sensible heat energy using a combination of temperature deltas and low pressure compressed air.

2. We recognize and accept that 75% of home and commercial business (office buildings, not manufacturing plants) energy use is direct heating and cooling applications.  By directly producing and consuming the thing we're actually using the most of, we avoid the need to create and use gigantic electric motor-generators perched atop wind turbine towers.  We're choosing to use thermal energy where all-electric solutions are poor in terms of cost, sheer weight of scarce materials required, and embodied emissions contained therein.  None of this wind turbine technology is produced using anything but hydrocarbon fuels.  It's an artifact of hydrocarbon fuels, not a way to stop using them, or at least to use less of them.  This change removes the weight / load of the electric generator from the very top of the wind turbine tower, where the tower structure is weakest, and puts it on the ground next to the compressed air tank, where structural concerns are trivial.  In its place we will add a much lighter low pressure air compressor.  The tower itself could be the low pressure compressed air tank.  It's already a high grade steel structure that has to resist extreme aero loads imparted to it by the blades, and maybe a lightly pressurized core would help resist those loads.

3. We're still going to use electricity, but less of it, and we're going to move our electric generator to the ground where servicing it is much easier.  If our grid can tolerate variable frequency AC power, then a much simpler alternator can be substituted for a potentially more efficient motor-generator that must be geared to run at a specific rpm- 3,000rpm / 50Hz for your grid or 3,600rpm / 60Hz for the American grid.  By accepting variable frequency power, most of the expensive frequency stabilizing equipment can be done away with.  Presumably, it can also be 1/4 of the size it previously was, which means using 1/4 of the materials it previously used.  We would also expect materials weight savings for the tower and nacelle, although much of that is related to the loads transmitted to the tower through the wind turbine blades.

3. We make and use simpler appliances which rely less upon electricity and more upon compressed air and hot water supplied by wind turbines or solar thermal arrays.  This pays off during manufacture, recycling, and maintenance / repair, which requires no sophisticated electronic tools to diagnose problems with computers and no scarce materials.  The appliances are already mostly steel to begin with.

We get rid of as much of the non-recyclable plastic and rubber nonsense as we can, so that we're left with machines that require very infrequent parts replacement, limited to seals and bearings.  If it costs a few dollars more to create buttons made from 7075 Aluminum billet, then we eat the cost, knowing that the buttons will still be fully functional a couple of centuries from now.  Temporary cheapness is illusory.  When the plastic buttons break every 5 to 10 years or so, replacing them will cost every bit as much as a high quality Aluminum billet in terms of money and energy.  When electronics break, it is completely non-economical to repair them and potentially impossible irrespective of cost, as is the case with most integrated circuits, because to do so involves disassembly and reassembly of major parts of the machine in addition to remanufacturing of the electronics, and replacements may be non-existent even if those first two problems were not an impediment.

4. For the limited number of applications that truly require electrical power with a stable frequency, which is limited to computers and LED lights, we can use smaller power inverters, again saving energy / materials / cost.  One potential way to handle the increasing costs of Copper and Aluminum is to stop wiring homes.  As LED lights have supplanted incandescent bulbs and miniature remotes for lights, sometimes incorporated into a cellphone or smart watch, these devices can be self-contained.  Instead of throwing away an entire light bulb and having lights wired into the home, it should be possible to use batteries.  Lights would essentially become flashlights tethered to strings and suspended from the ceiling.  If a flashlight LED quits working, then only the LED chip needs to be replaced.  The rest of the flashlight is still good to go.  The suspended flashlight can have its batteries recharged, as required.  The runtime on some of the LED flashlight is measured in hundreds to more than a thousand hours before recharging is required.  If the batteries could be recharged quickly, then a lot less expensive Copper wiring and installation labor is required.  A pretty spectacular EMP from the Sun or a nuclear weapon would have almost no effect on such devices, because they're not connected to anything.  If there's almost nothing for an electrical charge to conduct into, then there's no effect on the electronic device.  A lightning storm, high winds, power transformer explosion, power surge or dip, or similar event that takes down the grid has no effect on home lighting or computers, none of which are connected to any central electric grid.  An electric power company is then free to focus on hospitals and manufacturing plants.  This makes all of us less dependent upon centralized control and distribution of electrical power, which requires sufficient staffing, planning, and spare parts to maintain.

5. We can make our wind turbines blades from long-term sustainable materials like bamboo, balsa, and aircraft grade plywood, saving a great deal of energy cost and emissions.  This also helps support skilled trades, such as carpenters and welders, both of which pay well enough to support a family.  The 86 meter length bamboo blades in the design study I read represents a substantial cost and emissions reduction over both GFRP and CFRP, even if the blade weighs about 12t when made from bamboo vs 4t when made from CFRP vs 13t when made from GFRP.  Each CFRP blade costs the same as 4.5 bamboo blades, so the energy cost of a CFRP blade is equal to 1 complete wind turbine blade set, plus 1.5 spare blades.  Put another way, 3 sets of 3 bamboo blades for the price of 2 CFRP blades.  If we're going to make these giant aircraft wings by the millions, then they need to be very low cost, very low emissions, very easy to recycle by burning.  Each blade will last about the same length of time in operation.

All the added weight of the bamboo blade comes from not allowing it to flex to the point that it strikes the tower, meaning stiffness, not the tensile strength of the bamboo itself, so if we or our AI-enabled computerized mechanical engineering tools came up with a novel cantilever tower design which permitted more blade tip flex, then we could conceivably make the bamboo blades much lighter because they are not tensile strength or fatigue-limited, bamboo fiber is simply nowhere near as stiff as Carbon Fiber.  This property of bamboo is both a blessing and a curse.

For structures under 10m in length or so, there's not a dramatic stiffness difference between properly designed and fabricated structures made from CFRP / GFRP / bamboo / Aluminum alloy.  There is a dramatic weight per unit volume difference, though, which is why aircraft made from composites, natural or synthetic, resist aero loads so much better for a given weight.  AI has shown us a variety of clever parts geometry tricks that can make denser materials stiffer for a given weight and size, but most of those tricks come at the cost of manufacturing time and complexity, with many requiring 3D printers to achieve.

What I'm kinda hoping for is that we can use everything in our proverbial "bag of clever tricks" to reduce consumption of materials of all types except for air, water, steel, concrete, and natural materials that regenerate as we regrow them (cotton / hemp / bamboo / balsa / wood).  We have to increase consumption of something if we insist upon using low energy-density sources and technologies over liquid and solid hydrocarbon fuels.  That issue is baked-in to all actual solutions that don't involve extraction or synthesis of hydrocarbon fuels.  Energy density and materials availability was always a problem, it was simply ignored by people who knew better or not known to people who were too ignorant to know any better.

As this problem of materials usage relates to airframe design, very few airframes have had zero airworthiness directives issued against them.  All such airframes have either been steel tubing (built strong enough to remain below the steel's stress-strain limit) or properly fabricated composites (very difficult to actually do in a repeatable manner).  As GW had stated before, there's no such thing as an Aluminum airframe with infinite fatigue life.  No matter how strong an Aluminum structure is built, at some point it will crack and fail catastrophically.  This is not to say that Aluminum is not a good material for aircraft construction, but Aluminum wings are nowhere near as large or heavily stressed / loaded as wind turbine blades.  Aluminum propeller blades come with a set of operating limitations to prevent vibration from destroying them within seconds to hours, as well as lifetime fatigue limits, after which they must be replaced.

As blade length increases much beyond the diameter of a large aircraft propeller, wind turbine blades are stressed well beyond the limit of what a steel structure of acceptable weight could actually withstand, which leaves Aluminum and composites.  Aluminum requires very little energy input to recycle after it fatigues into uselessness, but a sky-high amount of energy input to make from scratch.  That's why Aluminum does its best work in other applications.  Aluminum blades also cost about 5X more than CFRP, which is why even most small wind turbine blades use CFRP or GFRP or natural composites.

In the business world, we have to justify the cost of every potential solution to a problem.  We tend to choose the lowest cost solutions that meet requirements because we recognize that the stream of problems coming at us is endless, so more money / energy / labor must also be devoted to solving all the other problems waiting in the wings.  We must pick and choose the degree to which a solution meets requirements.  If a seal can be made to last for 10 years, but an assembly has to come apart every 5 years for inspection and have its seals replaced, then spending the money to make the seals last for 10 years does little good for anyone.  The enhanced part will inevitably require more money and energy.  This is fine for something like a seal, which has very little monetary or energy cost.  This would definitely not be okay for an entire engine or electric motor, so whatever it costs to make the major parts of a machine reliable and durable, that is money which must be spent, or the end result is unsustainable.  The notion that we can completely replace our power generating infrastructure every 10 to 20 years is fantasy-based thinking.  If coal-fired power plants only lasted 10 to 20 years, then they would be unsustainable as well.

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#16 2023-03-26 17:18:54

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

Kbd512, yes.  The more we eliminate electrical and electronic systems the better.  I wanted a very simple system that a semi-skilled tinkerer like me could make in a workshop with hand operated machines and simple materials, like stone, brick, wood and carbon steel.  I know how to work those materials.  I know how to stick weld plain carbon steels, but have never welded aluminium.  I am not a skilled machinist or tool maker.  I cannot make an alternator and really complex mechanical devices would be beyond my skill or time to make.  But a single piston compressor is not beyond me.

Our houses and factories need heat and cold energy.  They also need electricity for lighting and some appliances and mechanical power for washers and various tools.  Wind power can produce mechanical power with very simple devices.  It can produce electric power with minimal storage if we are prepared to use it when it is there and cut back or eliminate use when it is not abundant.  But even in situations where we are prepared to adapt to intermittent energy, it is useful to store some energy to allow tasks to be finished and to have a reserve for high value, but low consumption appliances like lighting.

I wanted to investigate if a simple single-stage wind driven air compressor could generate enough hot and cold to be useful, whilst also generating mechanical and electrical power and storing enough energy to be useful.  It seems that very low pressure air could work very well, provided we had enough space to build the store.  If air pressure is <1 bar relative to ambient, we don't need steel pressure vessels.  We can store air in gravity vessels.  And at such low pressures, we don't need intercooling between compressor stages.  A single stage, single piston device does what is needed with adiabatic compression and expansion.

Drying the air is a significant diffulty.  One option would be to adopt a combined approach.  First chill it to 0°C, using some of the recycled cold from expansion.  Then pass the semi-dried air through a magnesium sulphate bed to remove the remaining moisture.  The sulphate can be regenerated by heating it to 150°C using concentrated summer heat.

I like the idea of eliminating wiring.  If all electrics can run on small rechargeable power cells, it eliminates a lot of copper usage.  Even things like washing machines could be designed to operate with the minimum of electric power.  If hydraulics or compressed air were used to turn the drum and hot water is drawn from a storage tank, then electricity is needed only to actuate valves.  Such small power demands could be met by batteries.  The same with fixed machine tools.  A wind turbine driving hydraulics can provide mechanical power, whilst electronics controls valves.

Last edited by Calliban (2023-03-26 17:22:31)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#17 2023-03-26 19:33:43

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,304

Re: Heat your House for Free with an LP Air Compressor

Here is WIND-POWERED AIR COMPRESSORS

Brainstorming a windmill air-compressor design


Compressed air energy storage systems could be the next big thing in managing green energy

so, taking an ordinary compressor head and direct driving it from the windmill itself could mean one needs to calculate the torque required for the rpm of the spin to make this work.

In fact, I have a junk compressor head that I could try this with...

energy-bags_1_vIbWf_69.jpg
This was sort of the concept for the mars fuel tank that collapsed when empty.

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#18 2023-03-26 20:38:23

kbd512
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Registered: 2015-01-02
Posts: 7,602

Re: Heat your House for Free with an LP Air Compressor

Calliban,

Washing machines don't even need electrical devices to operate valves.  A simple spring-driven timer and a few more springs can turn valves on and off using water pressure.  This is the same technology that makes sprinkler systems work.  An air turbine can drive the tumbler.

Most washing machines, in the United States, have a motor horsepower rating of one-half to three-quarter horsepower. For decades one-half horsepower was the industry standard, but with the advent of the larger capacity tubs, some manufacturer's have correspondingly increased the motor rating as well.

A 1hp air turbine for a power tool will fit in the palm of your hand.  The electric motor from one of the washing machines we had weighed about as much as a couple of bricks.  Perhaps smaller electric motors can be used, but that was a Kenmore washing machine that was nothing spectacular.

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#19 2023-03-27 10:58:23

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

I read through SpaceNut's links.  The Amish are already using wind-compressed air systems instead of electricity.  They use it to power kitchen appliances and tools.  It is popular to use 1000 gallon LNG tanks as receiver tanks.  They are rated to 10 bar(g), which bounds the 100psi working pressure of most air tools.  So this is a system that is already used by a lot of people.

I ran a search on the effective lifetime of steel pressure vessels.  Provided the vessels are kept in a dry and non-corrosive environment and wall stresses are nowhere near yield stress, the effective lifetime can be 10 million cycles.  That is effectively an infinite life expectancy.  Although steel vessels would be expensive to buy, you need only buy them once.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#20 2023-03-27 11:21:26

Terraformer
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From: The Fortunate Isles
Registered: 2007-08-27
Posts: 3,855
Website

Re: Heat your House for Free with an LP Air Compressor

A good candidate then for Ragnarok Proofing society? Sweep out the dust, make sure there aren't any nests in the equipment, and two thousand years after leaving your laundromat is back up and running in less than a day.


Use what is abundant and build to last

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#21 2023-03-27 13:22:09

kbd512
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Registered: 2015-01-02
Posts: 7,602

Re: Heat your House for Free with an LP Air Compressor

Nobody here is claiming that electricity isn't useful.  It's very useful.  If you want a society that is truly sustainable, then more electricity cannot be the only solution.  Owning a hammer doesn't make you a carpenter.  A hammer is only one of many tools required to be a carpenter.  The hammer works great for driving nails.  It's probably the absolute worst tool for cutting wood.  The fewer things that society throws away, the more sustainable the society eventually becomes.  It won't be an overnight transformation.  This change could easily take another human lifetime to achieve.  Material wealth in terms of durable goods is cumulative.  Unless we want to become trash heap owners, then we need to start making things we can pass down to our children, which they can then use to continue their lives.  We cannot keep throwing things away moments after they're used one time, or after a brief period of time.

An all-mechanical washing machine, run off of compressed air and water, should last for at least a human lifetime.  Bearings and seals should be the only parts which require periodic replacement.  We know how to make that work, but we choose to make things that will instead last through the duration of a warranty period, after which we don't seem to care at all about how much it costs to repair, nor if repairing it is even possible, because we expect the purchaser to replace it with a brand new model that is more complex / more difficult to make and repair / more expensive as a result.  We cannot replace every washing machine on the planet, every 5 to 10 years.  Doing that requires far too much energy, too much labor which could be used to do other useful things, and too much investment in time.

A barrel of oil contains the same amount of energy that a human could perform in terms of physical work, over 4 to 5 years.  Apart from nuclear energy, we don't have anything else to replace that.  This inconvenient little fact of life is why we need to start designing and making things intended to be semi-permanent solutions, even if it costs a little more up-front.  We have some options, but they're not unlimited and all of them come with marked changes in how we operate society.

If I had built a washing machine manufacturing company, it would be with the understanding that I will only see my customers once per lifetime.  After the washing machines are built, it's time to start making other things.  The machinery to stamp out the steel will be put in the corner of the factory.  If we have some catastrophe that destroys a bunch of washing machines, then we can dust it off to make some more, but it should be the result of a non-repeatable event like an earthquake or flood or war driving me to produce more washing machines.

General Motors made everything from machine guns to silverware to entire aircraft during WWII, despite the fact that the company was founded to make cars and trucks.  It made no difference what the company was founded to do.  When a task was set before them to ensure the continued survival of their people, the only questions that had to be answered were "how fast" and "how many".  The government asked all of our Captains of Industry to report to the White House, a list of contracts for things the government thought they needed to fight the war was laid out on the table, and then those men picked which ones they thought their companies could deliver on.  There were a myriad of problems to solve, but they solved each problem as it presented itself, because that was the only way to do it.  There was no disagreement about what the problem was, or that it needed to be solved as expeditiously as humanly possible.  There were numerous points of contention at all levels, but none of them approached the point of impeding prosecution of the war effort.  Lots of imperfect solutions were implemented, but at the end of the day they did the job as best they knew how.

Making things should be a checklist of what we think people need, not a way to endlessly keep selling all of the same products to them (and if you want to do that, then school teacher / health care practitioner / farmer / trash collector / soldier / undertaker should be your professions of choice; there's even a synergistic effect between the last two professions on the list, so watch out for that):

1. Protection from invaders (a military to prevent invasion) and the environment (places to live to prevent lethal exposure to the elements)

2. Food and water- these are mass-produced consumable items which must be frequently replaced with new stock

3. Medical care and sanitation services - these are also consuambles or involve lots of consumables

4. Durable goods which permit other useful work to be done- home appliances, furnishings, ships, cars, trucks, trains, and planes

5. Semi-durable goods like clothing and electronics or even spacecraft which allow scouting new places to live and extract resources from

Availability of on-demand energy underpins all of those other activities.  If the military doesn't have ships / tanks / artillery / combat jets, then you don't have protection from foreign invaders with the military hardware to come and take what you have.  If the construction industry can't build shelters, then you won't survive a winter in Canada for very long.  Plenty of people died in Texas where the temperatures are far more benign during winter.  Without food, everyone eventually starves.  Schools may not strictly require desks and paper and pencils, but for some reason all schools have them, even the ones in Africa, so that must be a requirement for education.  Offices seem to require typewriters or computers to function as they do.  Sure, we had offices without those tools, but doing paperwork took a lot longer to complete.

The luxury items that come from society, such as fancy clothes and personal electronics, must be consumed in moderation.  I have pairs of pants older than my children, and most cost about $20 to $30.  They still cover my rear end.  When they fail to do that, then it's time for a new pair, and yes I have worn a few pairs threadbare.  Maybe they could've been repaired, but they were falling apart in multiple places.  Nothing lasts forever.  The computer I type this from was made in 2010.  I'll buy a new one when the mother board finally croaks, assuming it cannot be repaired, which I've already done once.  I expect it to last another 10 years or so with RAM and hard drive replacements.  It's fast enough to get the job done, which is all that matters, and the parts to repair it have already been manufactured, so they may as well be pressed into service at some point.

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#22 2023-03-27 19:26:11

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 29,304

Re: Heat your House for Free with an LP Air Compressor

In man's efforts to create I find not much is made for a lifetime and manufacturing is always parading the next shiny unit out with statements of new and improved but is it really.
As for trade education add it the graduation so that many would not waste their time and money on a pipedream..

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#23 2023-03-28 11:03:22

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

A home based wind energy system looks much easier if we can use floating switches and demand control within the house.  The floating switch idea has certain energy consuming functions (like the freezer and water heating) on an automatic switch, which activates when your energy store is full and deactivates when it declines to say, 80%.  Thermal applications can have thermal inertia built into them, allowing them to absorb intermittent bursts of power.

Your energy store has a number of indicators and level switches on it.  If the store level is greater than 80%, then a green indicator is shown and you can add more loads.  If level is 50-80%, then an amber light shows.  This tells you that you can keep existing loads but shouldn't add more.  If level drops beneath 50%, a red indicator light shows.  This tells you that you need to shed loads.  If the store level drops to say, 20%, a small petrol or diesel powered generator starts and refills the energy store with water, air or whatever else you are using to store energy.

Ideally, we would manage loads to use all of the wind energy when it is available and never use the diesel generator.  But some processes have certain run times built into them.  We could make judgements about whether wind speed is going to rise, fall or remain stable based on weather reports.  It wouldn't be a disaster to get it wrong, but would cost more.  Overall, I think, this is a system that most people couod get used to.

Last edited by Calliban (2023-03-28 11:12:13)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#24 2023-03-28 16:40:46

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,568

Re: Heat your House for Free with an LP Air Compressor

Small scale, combined pumped and compressed gas energy storage.
https://www.osti.gov/biblio/1891390

Interesting.  This combines pumped storage with CAES.  This technology works well with wind turbines that replace the electric generator with a hydraulic water pump.  Water is incompressible, allowing a single stage hydraulic piston pump to achieve very high pressure without any need for intercooling.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#25 2023-03-28 18:55:06

tahanson43206
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Registered: 2018-04-27
Posts: 18,111

Re: Heat your House for Free with an LP Air Compressor

For Calliban re #24

Thanks for the link to the DOE study!   I only read the abstract, before remembering the numerous occasions when you have reminded us of the practice of compressing air using falling water (in England as I recall).

The abstract hints at using water to compress gas.  I'm wondering if a system to compress gas using gravity as a component is worth considering?

The wind crank would return water to the surface after it had done the useful work of compressing gas.

This implementation of the old (relatively speaking) technology would presumably eliminate the need for high pressure machinery.

Abstract
Energy storage is essential for cost-effective integration of variable renewable energy sources to support a low-carbon grid. It is also a key enabler of a modern grid infrastructure for demand management. However, several main challenges remain for different kind of energy storage technologies in grid scale deployment. Currently, the largest source of utility-scale storage and long-duration storage in the US is pumped storage hydropower (PSH). Prospect of growth in conventional PSH faces challenges that have limited its deployment over the last three decades, including high capital costs and long deployment timelines. Batteries have high energy densities and are the primary technology of choice for small-scale energy storage. Compressed air energy storage (CAES) is another large-scale energy storage technology, but there are few plants deployed worldwide. They suffer from their low round trip efficiency (RTE) due to the use of high-pressure air compressors. To address some of the challenges associated with these various storage technologies, the Ground-Level Integrated Diverse Energy Storage (GLIDES) is a modular PSH technology that was invented in 2015 at Oak Ridge National Laboratory. It utilizes gas compression to store electric energy. GLIDES stores energy by compressing gas using a liquid piston in high-pressure vessels. In doing ... »

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