I've been looking for an off grid solution to powering an icebox ever since an extended grid power outage taught me that all that we would really need is some way to keep food cool. For permanently off grid, an obvious choice is absorbtion cycle refrigerators powered by propane gas. The probems there are; 1) propane is a non-renewable fossil fuel and 2) such refrigerators are complex and somewhat more dangerous than an electric refrigerator. As a form of temporary grid-down refrigeration, it leaves much to be desired. As a refrigeration solution for an intentionally off-grid home, it exposes the household to price spikes and supply interuptions, as it's (practially) impossible for a homesteading household to produce it themselves.
That's not quite as true with carbon dioxide, however. Of course, we are all aware of the usefulness of dry ice, but that is not what I'm talking about here. I'm talking about compressed & liquified CO2. Apparently, CO2 was a commonly used refrigerant prior to the commercial availability of flurocarbons as closed cycle refrigerants. The main problem with CO2 as a refigerant is that it's vapor pressure is very high, around 1000 PSI as it approaches it's 'critical temp' of 87 degrees F. Because of this, closed cycle CO2 compressors are entirely a industrial product, but they do exist. I'm not talking about a closed system using a huge compressor, however. I'm talking about simply taking a used, perhaps broken, chest freezer and installing a high-pressure expansion valve rated for R-744, and simply having liquified CO2 delivered in industrial tanks with a 'siphon tube' installed so that, once properly connected to the expansion valve inside the chest freezer, liquid CO2 is permitted to expand inside the valve. This is similar to how the old fashioned refrigerators maintained the design temp without electronic controls. The downside is that the industrial bottles would have to be maintained below 87 degrees F. for safety reasons, which means that the industrial bottles would have to be inside the chest freezer space. And even then, I wouldn't want the setup inside my kitchen, in the event that the expansion valve failed. The level of force that an industrial bottle of CO2 can produce would be very dangerous.
Still, it's an idea. If any of the enginners around here might take up the task of designing such a refrigerator, hopefully minimizing the boom-squish potential, I'd love to see the results.
Having liquified CO2 delivered is "off-grid"?? I'm going to quote that great philosopher Inigo Montoya, "I do not that means what you think it means". In fact, I can't think of a better way to create a link to the network of modern industrial society than relying on deliveries from Praxair or AirLiquide.
Instead, I would invite you to consider joining our discussion on rocket stove and solar powered closed-cycle absorption systems here. There are many cycles that are not "somewhat more dangerous", because they have avoided compressed ammonia gas in the design. The absorption chillers that run on propane do so simply out of laziness; they could be redesigned to run off of biomass or focused solar or some other heat source other than propane. Propane was used because most of the absorption refrigerator market is RVs, and RVs need propane for a cookstove, so it's right there.
posted 7 years ago
John Elliott wrote:Having liquified CO2 delivered is "off-grid"?? I'm going to quote that great philosopher Inigo Montoya, "I do not that means what you think it means". In fact, I can't think of a better way to create a link to the network of modern industrial society than relying on deliveries from Praxair or AirLiquide.
Certainly not more than regular propane deliveries, but yes. I'm referring to the electrical grid. Sure, I'd still be tied to a supplier with CO2 just as with propane. However, it's possible for an individual household, or a co-op, to compress CO2 from either the air or from a more pure source, such as the exhaust of a rocket mass heater. It's not possible, as far as I know, to create propane; whether or not you can compress it for storage. An absorbtion cycle, pressurized or otherwise, would be overkill for the average refrigerator using a RMH, and a RMH requires ongoing attention while it's in use. I'm looking for a refrigeration method that 1) does not require a connection to the national electrical grid (i.e. the very definition of off-grid), 2) is cost effective and 3) of an appropiate scale.
However, I can see how a RMH could be used to great effect for an off-grid co-op to freeze large amounts of block water-ice, and then deliver that to the member homes. So I guess it depends.
People in rural China manage biogas systems for cooking and for running refrigerators. Most have no technical training beyond having watched and helped set their systems up with the help of government supplied technicians. The byproduct is liquid fertilizer. These problems have been solved thousands of times all over the world. The big winner on a numerical basis seems to be gas, when reliable electricity is unavailable. I think solar electric is also quite viable for many.
posted 7 years ago
It has come to my attention that biopropane is possible, and that such a commericialized process is being investigated by Brazil for conversion of their excess glycerin from biodiesel production. So my complaints about the sustainablility of a propane powered off-grid home have been overcome by advances in chemistry.