In the late 19th century, and first half of the 20th, ice refrigerators were a common feature in American households. Blocks of ice could be purchased every few days and placed in an insulated box to slow the decay of foodstuffs. The length of time between new blocks varied according to the size of the block, ambient conditions, condition and effectiveness of the refrigerator, and the economic access afforded to the household. By and large, production of ice was first accomplished through the natural winter freezing of lakes and ponds in the northern latitudes, where it would then be scored, cut, and hauled into insulated warehouses and then distributed to customers. This practice would continue well into the 20th century, but would eventually be supplanted by the mechanical production of ice with vapor compression or absorption machines, then altogether with the advent of affordable domestic mechanical refrigerators. Very few individuals still utilize ice to for everyday home refrigeration needs.
Advantages to Living in a Cold Climate
As a means to provide home refrigeration without the assistance of industry, harvesting naturally produced ice in the winter, and using it throughout the year is certainly an option, but the region of southwestern Pennsylvania I am from doesn’t typically get cold enough, or for long enough, to freeze bodies of water to a thickness where sizable blocks could be cut. An insulated storeroom would have to be of a size to hold a years worth of ice. Also, there is the potential issue of refrigerator temperatures peaking higher than the target temperature of 4 degrees C. Ice typically melts around 0 degrees, so such a small temperature difference would have to be maintained with ample refrigerator insulation, and well designed air circulation.
Nonetheless, some of these problems are solvable by looking at the problem with fresh eyes. I believe there are great opportunities that come with low outdoor temperatures for a few months out of the year. Dissipating latent heat from a substance like water, and in large enough quantities, then storing the “charged” phase change material, can have the effect of caching cold wintry conditions where food keeps longer, for use in high ambient conditions when it doesn’t. Furthermore, this “ice bank” could drastically improve the performance of mechanical refrigeration systems as the discharge heat of these machines would be very effectively cooled by ice, only to later be dissipated to cold winter air. Essentially, we’re talking about temporal heat displacement for refrigeration.
Examples of Prior Work
Natural ice harvesting was described above, and represents the best (and most developed) example of this, but we’re going to move beyond that.
Various studies, and actual installations have been performed to establish effective ways to offset annual heating and cooling loads on homes and commercial buildings. These typically include a reversible heat pump which extracts latent heat from water to make ice and heat the building in the winter, then dump heat into the ice bank in the summer for better overall energy economy. One of the first such studies I read was done by the Oak Ridge National Laboratory in the late 70s. This is one of the papers produced. Several large commercial buildings produce ice during night-time hours when outdoor temperatures are lower and electric rates are cheaper, in order to provide lower cost air conditioning during the day. These systems are not passive, although there may be some that incorporate passive features.
A very simple example of domestic refrigeration was done in Essex Vermont. I know of two such installations: one was a refrigerated store room, and the other a freezer. These are largely passive systems in that they do not actively pump heat, but instead freeze a large ice bank of plastic bottles with the frigid New England winter air. The bottles distribute the total volume of ice into many small pieces, and increase the surface area of the water substantially, helping both to freeze them, and to maintain cold temperatures throughout the year. Some use of small electric fans were the only active components, but also passive air ventilation. I know of no recent updates on the effectiveness of the systems. One of these systems is found here. These examples could be great if you live in an environment where winter temperatures are low enough to freeze plastic bottles of water, without excessive amounts of active ventilation. Of course, passive ventilation could be improved by catching prevailing winds, dumping cold air in the bottom of the ice bunker while removing warm air from the top. Maybe a solar chimney or greenhouse could be coupled to it to pull cold winter air through. Automatic temperature controlled or manual shutters would be a must. With sufficient ventilation, a system like this could be made to work in environments that are slightly warmer, but it would be tricky. Fewer bottles might be needed for a small domestic refrigerator, but these bottles take up more space than a solid block of ice. Still though, I appreciate the simplicity.
Over at Sunfrost Refrigerators, Larry did some experiments with counterflow two-phase thermosiphons (called them heat pipes) to see how much passive refrigeration could reduce compressor runs, by dissipating heat to the outdoor envrionment in cold winter climates. He did demonstrate energy savings. A paper about the study can be found here. Sunfrost has unfortunately closed their doors, but the website is still up. Many interesting products and projects relating to DC refrigeration, composting, and thermal water heating. Check em out here.
My final example is by far my favorite. First built by Scott Nielsen, Vermont, in the late 1970’s, it is quite simply a well insulated ice refrigerator, using a very large block. The clever thing about it, is the use of a two-phase thermosiphon (he uses the term “heat pipe”, but we’ll get into that later) filled with r12 refrigerant to carry heat in the water to the cold outdoor winter air. With enough sufficiently cold days, the 1550 pounds of water is frozen solid, keeping the adjacent food storage compartment cold throughout the year. A shut off valve was installed between the indoor and outdoor heat exchangers to prevent the ice from subcooling too much, and freezing the food in the refrigerator.
Last year, I was doing a lot of work with two-phase thermosiphons in a thermoelectric refrigerator refrigerator design. I generally lost interest in Peltiers, but have been captivated by thermosiphons ever since. I quickly decided a sensible option for domestic refrigeration in the climate I grew up in would be this very design I just described. Granted, I later found out I was 40 years too late to be the first one, but hey, at least I know it works!
From Bob English’s Four Mile Island Website clone.
Before I found out about the details of the Scott Nielsen refrigerator, I found Bob English’s refrigerator on his website, with a design similar Scott, but scaled up. Unfortunately, Bob took the website down, but you can still view it using the Way Back Machine on The Internet Archive. This link should get you there. I have had the pleasure of talking a bit to Bob, and he has told me the refrigerator still works well after all these years, although it doesn’t freeze completely every year. It starts to move the r134a refrigerant significanlty at about 25 degrees F, but I’m sure would take many days at that temperature to completely freeze the block. Colder is better.
Bob sent me the article from “Home Power” where the Scott Nielsen refrigerator is described. It’s a little grainy, but worth sharing, so that will be the next post. After that, we’ll get into two phase thermosiphons, and some of the design considerations for building a a passive ice refrigerator.