R Scott wrote:I gotta see this!!! No, really. Do you have pictures or video?
They also mention having multiple units staged so one could be cooling while the other is regenerating. It wouldn't be hard to make two and alternate which one gets fired.
I wonder if you can scale this to the point you can use it as AC in a small cabin? It is easy to stay cool in the desert with a swamp cooler, but swamp coolers don't work IN the swamp. I see this as a potential solution for hot humid off-grid!!!
Marcos Buenijo wrote: The heat transfer rates through this kind of insulation is listed as 20 times lower than polyurethane foam.
Dale Hodgins wrote:This seems awfully high ! Is this an R value rating ? This would indicate R 120 per inch. I wonder if it reflects just radiant or just conductive or some other measure. If an inch of this equals 20 inches of polyurethane, I want it in the attic.
Abe Connally wrote:why would perlite in a vacuum be more effective than just a vacuum?
dry perlite has excellent insulation value, but more on the lines of R2-3 per inch.
Marcos Buenijo wrote:I don't expect perlite under vacuum is better than a vacuum. I suspect perlite is used as a filler to help resist the forces. Otherwise, perhaps the costs involved would be higher. Of course, I am speculating here.
Abe Connally wrote:oh, I see. Yeah, that makes sense. Use something like perlite as an internal structure. That should be pretty easy to make. Just take a plastic bag, fill with perlite, and suck the air out.
I was thinking a lot about this concept last night. Some evacuated tubes for the solar collector and a well insulated chest freezer would make a good test system. Do you have any links to data for what is needed in terms of temperatures to get down to -10C with zeolite/water?
As part of a wood gas CHP system, it might be really good, too.
Marcos Buenijo wrote:
I do a lot of brainstorming on this forum. Some of my ideas could be practical in some settings, but most are not. I don't have a problem with this as it can be educational to think without such constraints. However, I will emphasize practicality at times, and I think this is important.
With respect to a freezer (which I also consider a must in an off grid setting), I take the position that a conventional unit is the most practical option. I do like the idea of powering the unit with a PV array using opportunity loading and the phase change thermal mass that you noted. This combined with a large array seems a practical possibility. The idea there is to use the thermal mass to carry the system over night, and use a large array to get some cooling even during inclement weather. This makes sense if you plan to be away for long periods as a larger array normally used to support systems in addition to the freezer can be dedicated solely to the freezer during these times. Augmenting insulation might also be done.
Salt water (that is, aqueous NaCl) is probably not the best option, but it would work. Other solutions would probably be better like a glycol solution or other aqueous salts like calcium chloride.
The idea there is of course to minimize the demands on a battery system which I consider the Achilles heel of off grid power systems. It may be possible to do away with the battery by using a capacitor in its place as a voltage buffer for the inverter - if PV panels of the right voltage can be found, then this might work well - but you can manipulate the voltage with a simple circuit if necessary.
A modest capacitor pack will start large motors, and I made a post recently where a 2 pound pack is used to start a car several times with a single charge... you don't get a lot of energy, but it delivers it quickly with little voltage droop - perfect for starting motors. https://permies.com/t/30468/energy/Super-capacitors
I will consider the details of an ammonia absorption freezer if you are set on this, but I don't consider it a practical alternative. I DO consider an absorption/adsorption chiller to be a good prospect for off grid air conditioning, and I prefer the prospect of using a solid adsorbent with water refrigerant.
Another possibility is to use a wood gas engine system to intermittently power a vapor compression cycle for freezing a thermal mass. The most efficient system would use the engine to drive the compressor mechanically. However, I still don't consider this to be terribly practical.
Marcos Buenijo wrote: A modest capacitor pack will start large motors, and I made a post recently where a 2 pound pack is used to start a car several times with a single charge... you don't get a lot of energy, but it delivers it quickly with little voltage droop - perfect for starting motors. https://permies.com/t/30468/energy/Super-capacitors
Nick Raaum wrote:Marcos,
Have you ever considered running a stirling engine as a cooler or even simpler an open loop single piston expansion cooler with air as working medium? I've not looked into the realities of it, but seems conceptually simple enough. Probably need to run multiple stages to achieve desired cooling temp, but don't see why it couldn't be done with a slow speed high volume simple to construct approach. Any thoughts on the idea?
Marcos Buenijo wrote:Len, just a few thoughts. I'm speculating, but a suitable mechanical compressor might be had in automotive a/c compressors. These are available as piston or scroll units. Using a dc electric motor as an opportunity load on a PV array seems interesting, and this would eliminate the inverter. Optimizing the life of these units can be done by running at lower speeds and ensuring good lubrication. A piston unit tends to run most efficiently at low speed, and I expect the lower speed there will allow a piston unit to last longer than the scroll - but again, I'm speculating.
Since I'll be finally locating to the east Texas region, then a/c is a special consideration.
Len Ovens wrote:Well that answers some of my questions There is leakage. This not a huge problem as it seems as they are still able to give lots of current. I understand a bit more what you mean by "manipulate the voltage"... most inverters are made for batteries which do not like going below a certain voltage and so they are designed to drop out relatively early to protect the battery. The caps could give useful power much lower because current draw could increase for constant power use. This would balance out some of the lower capacity of the caps compared to batteries. His use of a "small" solar panel for trickling the booster to keep it topped shows that while there is leakage, it is not much. It is just that the booster doesn't have that much over all capacity to begin with and in the case of the starter motor it can only get enough starting power down to 10v or so. Unfortunately, some of the other electronics in the car are even less forgiving... things like injectors and fuel pumps seem to have a higher voltage dropout... the spark is not so hot either as some of the newer circuits don't run the coil at double as they did in days past... gotta sell the new battery sooner and all.
All in all, I think that all of our battery sizing is based on the quirks and failures of the flooded lead acid battery:
- at half of their life, they have half the life... or half the charge
- they don't like being over charged
- each cell has an innate voltage
- they don't like being under charged, even deep cycle batteries don't do well if drained beyond 50%. So even brand new, a 100 amp hour battery can only supply 50 amps for an hour before needing to be recharged.
Considering these things, I think super caps could be considered as only needing 1/4 the storage of a flooded lead acid battery to be equivalent. Perhaps even less with an inverter designed to work with a wider range of input voltage. The same inverter techniques could be used do provide various DC voltages as well.
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