energy-efficient walk-in cooler?

Yeah, I see people with these little machines that control an air conditioner to cool a sealed room. Someone told me theirs cost them 150 a month. It costs less if you don't open it much right? What if it was mostly underground, then wouldn't it be mostly insulated?
What if it was down in a cool basement?

Another thread mentioned modifying a chest freezer to be a hyper-efficient refrigerator. The same physics apply here.

It would definitely be more efficient with a small floor hatch & a ladder, rather than a full-size vertical door that exchanges all the air in the room every few seconds that the door is open.

Insulation design would also be important for efficiency. Maybe a few feet of rice husks? It's tough not to build in easy paths for heat to travel! Maybe mixing in a tiny amount of Portland cement would give the husks enough structure that the builder would not be so tempted to bridge the gap, without making them much more conductive.

I might also light the room with LEDs, not least because it will mean smaller wires piercing the insulation. They could even be set up to run inductively (cf. electric toothbrush charging stations, RF inventory control tags, etc.), with no physical connection across the insulation at all.

I don't know enough to say what proportion of that $150 went toward pulling heat out of warm air from an open door, and what proportion went toward pulling heat through the insulation while the door was closed.

Insulation is a decoupling of thermal mass, to prevent the transmission of heat energy. Underground is not insulated, but rather, buffered by a large thermal mass. The ground temperature below the frost line is usually the average of your year-round temperatures. About 55 degrees F where I live. So if you wanted to lower the temperature down to 35 degrees F you need to pump out 20 degrees of heat from the ground. Thermal mass is inertia. You can add thermal mass to the interior of the cooler by adding large storage containers of water, which will make it more efficient.

I think underground is better than above ground, unless it's 35 degrees out, of course. Cold air flows downwards, so opening a door wouldn't lose as much.

frankenstoen wrote:I think underground is better than above ground, unless it's 35 degrees out, of course. Cold air flows downwards, so opening a door wouldn't lose as much.

My thoughts exactly!

I came across this interesting article recently, and it reminded me of the underground freezer idea:

http://www.burlingtonfreepress.com/article/20100816/NEWS02/100815019/Essex-project-builds-backyard-passive-freezer

They appear to be using soda bottles filled with salt water for their thermal mass. Of course, this is just a modern take on the ice houses of years past, but for those living far enough to the North it might just make sense, especially if built underground.

The old cottages in Wales were often build 'cut in' to the slope of a hill, which was usually damp, and the room they stored food in would be a dark little place with no windows set right into the bank.  They would use slate floors and the shelves would be of thick slate slabs which would be kept wet so that the evaporation would keep the slabs, and the room, cool.  Milk would be in sealed containers placed in large bowls of water stood on the cold slabs, with a damp cloth draped over which dipped in the water in the bowl so that more water would be sucked up and evaporate, keeping the milk cool.

Of course, Wales isn't exactly the warmest of countries, but some of the principles might apply.

The similar subject was already observed somewhere at this thread

Just read the post on the Essex Project.

Anyone know what the ideal salt concentration (water: salt ratio) would be?

Anyone know what the ideal salt concentration (water: salt ratio) would be?

Good question! I haven't found out any more info on the Essex project, but some quick internet research suggests that the more salt added, the lower the freezing point gets. (So I assume that means keep adding salt until no more will dissolve.) When fully saturated, the freezing point of water can be lowered to -21 degrees Celsius. (about -6 Fahrenheit.)

I am assuming that the reason salt water is used in the bottles is to prevent ice from forming and damaging the flimsy plastic bottles.

I did a Google search on "University of Vermont " passive freezer and came up with this web site: http://www.uvm.edu/~cems/?Page=News&storyID=17191 .  At the bottom of this page is a local TV new report with pictures of the whole project and interview with the people building it. 

1. At about 51 seconds, the professor says "200 grams of salt in 2 liters of water, which gives us a 10% solution."

2. This ain't some tiny proof-of-concept project.  As the TV reports says, this is community sized.  It is two stories tall, with the first story (the one that's supposed to be the refrigerator) half-built into a hill.  The size explains to me why they need 3,000 of the 2-liter bottles.

I don't see how it can be easily scaled down to a single-family system; and unless you're dedicated to living entirely off the grid it might just be worthwhile to use a chest freezer as a fridge.

I have heard that before refrigeration they used to store ice in sawdust.
It is said that the ice kept solid all summer long.
http://en.wikipedia.org/wiki/Ice_house_(building) 


Perhaps a few Internet searches would surface some plans?

I did a Google search for "How to build your own ice house" and came up with several promising hits.  Unfortunately, they all seemed to be lifted straight from [url=http://www.gardenhistoryinfo.com/gardenpages/icehouse.html]How to Build an Ice House , from Charles McIntosh, The Practical Gardener, 1828.  You need a LOT of sawdust: you need at least 1 or 2 feet of sawdust on the floor.  After cutting the ice off your lake or stream, you pack each block with a couple of inches of sawdust on all sides before putting another block in place (and packing THAT with sawdust).  However, the source does say that in a well constructed ice house, ice can last two and sometimes three years.

Off-grid.net has an article on building and stocking an ice house that takes its start from this article, and goes into a lot more detail.  http://www.off-grid.net/2006/01/04/building-an-ice-house/   One thing both articles mention is the importance of also packing the ice house with snow, as the snow (when compacted) also turns into ice.

I know the shakers used a technique where they filled what i think they called ice silo with ice over the winter.  It was connected to a smaller building.  The bottom of a silo had a vent, allowing a flow of cold air into the smaller space. 
here is a picture of something similar

Muzhik:

Thank you so much for finding that University of Vermont video! That video answers a lot of the questions I had. (I had no idea that soda bottles were that strong!)

Were ice-houses ever used historically in single family systems? My impression was that there were businesses that provided this service for a community.

I think a LARGE family, or a small farm could make great use of a freezer/walk-in cooler of that size. My mother puts up TWO deep-freezes of vegetables each summer (much quicker than canning) and still much of the garden goes to waste (not really, it gets fed to the chickens and goats, but you know what I mean.) My family used to raise summer cattle and summer swine - just a few animals will quickly fill up a deep freeze. (We shared the animals with suburb-dwelling relatives who also had deep-freezes.)

I think the brilliance of the soda bottle concept is that you don't have to do all of the physical work of hauling blocks of ice into the house each year, and you don't need to live near a frozen lake either.

Frankenstoen, if you'll do a search you'll find a discussion earlier this year where someone was promoting an idea she had seen at some conference.  Instead of pop bottles filled with salt water, it used beer cans.  (Using cheap beer, of course.)  The cans would be embedded in cob around a central core.  The cob is about 12 inches thick; there's an evaporation pit in the bottom with burlap dipped into water, and a chimney up the top.  The cooler is painted white and the chimney is black.  It's something that if I ever am able to buy some land I'd like to experiment with.

We went dumpster diving yesterday to harvest plastic bottles from our towns transfer station.  I used a 10% salt solution like they folks in essex.  I'm hoping to build a makeshift walk in cooler in the next few weeks and get it filled with the frozen bottles.

Thomas Jefferson had an brick lined ice house in the ground at Monticello.  I am not sure but I think it was about 30 feet deep.  Ice was cut from local lakes ,  streams etc and layered with saw dust as insulation.  I believe they said he had ice in his drinks until sometime in July.  He liked to entertain alot,  so he gave alot of parties there.  He of course had a cheap labor force to make this all happen for him.  Doing all that work yourself is a whole different thing.

We are almost done with our walk in.  I ended up buying 2000 bottles from the local depository and filled them with water.  I was to late in the season to do the salt mix.  Its to early to tell but the digital thermometer has stayed at 32 during the day.  We haven't had to many warm days yet to really challenge it and we still need to blow in some more insulation to finish the job.  I havn't done the finishing work for it so its an ugly devil.  You can see a few pictures on out blog and on our flickr account http://breezymeadowsorchards.com/blog/

How about this idea for an in-ground ice house. The box size is 8'x8'x3'. This design would be more appropriate for an urban homestead on a flat lot. Seems like it could be done cheap.

I was thinking it would be more efficient than a walk-in cooler because the cool air stays in the pit. Of course a walk-in would give you more space. This could be made into a walk-in if it was deeper. I would worry about water seeping in. Maybe a plastic liner could be added on the outside to prevent that or a plastic covering extending 1-2' on the surface around the pit would shed the water away. Any thoughts? Tried something similar?

Franklin Stone wrote:Insulation is a decoupling of thermal mass, to prevent the transmission of heat energy. Underground is not insulated, but rather, buffered by a large thermal mass. The ground temperature below the frost line is usually the average of your year-round temperatures.

I'm just reading the book "Passive Annual Heat Storage". (The author's son is getting ready to release an updated and revised version soon.) Franklin's statement is the whole basis of this book. Except, they instruct you to take control of the "year-round temperatures" by way of insulation and using the house as the control mechanism, thereby establishing what average temperature the soil will hold.

After wading through all the intricate technical details all the way through the book, the author makes a nice application of his principles by showing this concept of making an underground freezer on one page near the end. The point being, you must lower the temperature of the ground around your cold room to the freezing point. The whole book is about SETTING an average temperature into the dirt that surrounds your building. So, SET that temperature really low!

Basically, he suggests using upside down earth tubes to an underground room. BUT, as the whole book discusses, you MUST have the "umbrella" (waterproof and insulated) over the house and 20' of soil in all directions in order to control that average temperature. The earth for 20' out in all directions then becomes your thermal mass and you have no need to add mass inside your cold room.

The idea is that you have earth tubes going UP from the room (you need two so that it can "breathe" - cold air coming in must move warmer air out). So, you have a room underground with tubes up through the earth. The tubes are open all winter, allowing cold air to fall into the room and warm air to escape. The soil releases its heat into the room all winter, the warm air escaping and new cold air dropping in, drawing the temperature of the surrounding soil down to the freezing point (heat always moves to cold). After sucking the heat out of the soil all winter long, you now have 20' of frozen thermal mass to keep your stuff cold all summer long. After a year or two, your storage room will set an average annual temperature somewhere in the frozen range. This should create a passive freezer that keeps frozen all year around, with zero operating cost and no moving parts!

Of course, this requires winter temperatures that drop below freezing...

As Mike Oehler has pointed out for over 40 years, DO NOT insulate your underground structures from the surrounding soil! And the next step, as shown in Passive Annual Heat Storage, is to use a waterproof umbrella 20' out and insulate that soil from the atmosphere.

We built something similar along these lines with our butcher shop. It is six structural shells of concrete nested one within the other each enclosed by insulation. Think like the Russian Matryoshka dolls. Our building is isolated from the ground since in our case the ground is the wrong temperature for what we're doing. The total is about 1.6 million pounds of stone and each shell of the building floats at a different temperature. Up above our reefer section there is room for a future cold attic where we'll have brine tanks that I can charge up in about two weeks of winter to give us enough coolth to get through 46 weeks of our hottest summer weather. The building also never freezes even during our cold northern Vermont winters. This all works passively - no electricity needed.

We also have mechanical refrigeration that augments it but the system is capable of working passively. The mechanical refrigeration lets us go down to -45°F in our blast freezer which I can't maintain with the passive system: that only goes down to about -20°F for the low during the winter.

See: http://SugarMtnFarm.com/butchershop

Cheers,

-Walter

Walter Jeffries : Have you seen this discussion in the earthen floor discussion ? The "other link'' would not open for me !

https://permies.com/t/20556/earthen-floor/harvesting-ice-building-ice-house#413947

I've seen that article. Very interesting. There are quite a few similar projects out there on the web, some here in Vermont.

The coolth attic that I referred to above is something that is quite similar in its principles but on a bit larger scale for our on-farm butcher shop. In the butcher shop attic there is a space I've reserved for four very large fluid tanks. Each will be able to hold about 7,500 gallons of coolant. I have not decided yet what fluid (e.g., brine concentration, etc) we'll use. Different tanks may hold different fluids to store different ideal temperature points - thus why we have four tank spaces.

Cold from the tanks will be able to both passively and actively drop down to the refrigerated rooms below. Or conversely you might say that heat from those rooms will rise up to the cold tanks. Heat from the tanks will rise up to lunar panels on the roof where the heat will dump to the night sky. This can be done both with passive fluid loops as well as pumps. Electricity is unreliable so I use thermal mass as primary to any mechanical refrigeration and design systems that can run passively, without any pumps, but can be augmented by electric power when available. The passive designs can achieve -20°F but not the -45°F of the blast freezer nor the -121°F of our SoLow shipping freezer that gets down colder than dry ice.

Based on my small scale tests and scaling up math I should be able to charge the system up in two weeks of our normal winter weather and then store enough 'coolth' to get our cold rooms through 46 weeks of our hottest summer months. This is another reason why the system is broken up into four tanks rather than one large tank. That and simple safety.

That won't drive us down to the -45°F for the blast freezer but it does get it close enough that a small amount of mechanical refrigeration will give us the blast freezer. Now that we've finished the first part of our on-farm butcher shop and are up and running we'll soon turn our attention to finishing off the walk-in coolers that are part of that natural coolth system. Since our building already stays cool we'll be one step ahead.

Someday I want to do something similar for our cottage as well as a cooling cave for the farm.

-Walter