ice maker vs chest freezer for ice production?

Aloha Permies,

Not sure if this is in the most appropriate place so please feel free to relocate my post if there is a better sub-forum.

I am looking into the feasibility of doing a pastured poultry broiler operation on an off-grid property here in the beautiful subtropics of Hawaii. The property we're looking at currently has a small solar system which I'm guessing would need to be upgraded substantially in order to produce enough ice to cool down the meat after processing, and to keep it cool while transporting it to market. I'm thinking that we would probably need to use several coolers quite full of ice to progressively cool the carcasses off and then several coolers, say, half-full of ice, to transport them in. While I've been looking into the ISAAC (Intermittent Solar Ammonia-water Absorption Cycle) ice-makers, I'm afraid the $7000 price tag is prohibitive and alas I don't yet have the chemistry knowledge or the engineering skills to do it myself...

So, my question is: what would be the most energy efficient means of producing the necessary ice - a chest freezer or a purpose built ice maker? (or can you think of a climate-appropriate, outside-the-(ice)box solution to my conundrum?

I've noticed that most ice makers are rated according to how much ice they can produce in a 24-hour period. Obviously, if our electricity is produced by photovoltaics we would probably want to produce most of our ice while the sun is shining in order to avoid drawing down our batteries excessively. So, I'm guessing this would mean that an entry-level commercial ice maker that produces 100 lbs of ice in a 24 hour period would really only yield somewhat less than 1/2 of that figure the way we would want to use it. Then too, I'm not sure how to compare the energy consumption of an ice-maker with that of a chest freezer, since presumably the chest freezer works harder to make things frozen and then not so hard to keep them frozen, so that their energy consumption specs probably don't reflect the type of use we would subject it to on days when we needed a lot of ice all at once to process 100+ birds at a time.

I also came across a tip for making ice-packs for coolers that recommended using reusable bottles and dissolving a few spoonfuls of salt per bottle of water to be frozen, as this apparently reduces the time needed to freeze the water and also makes the ice last longer before it melts. Obviously it wouldn't be possible to utilize this energy-saving strategy when using an ice cube maker, but I'm also wondering if the ice makers aren't more energy efficient in the first place such that these gains would be irrelevant.

Does anyone have any experience or the knowledge necessary to teach me how to make an educated choice?

Many thanks!

Ice machines make ice quick but it is only 32 degree ice and melts quickly. They are also really picky about water quality.

Off grid deep freezes will work really hard for a day to freeze the ice, then cruise nicely. You will have to be careful not to overload them.

How often will you be processing?

The salt water bottles do work. Gatorade bottles are our favorite for longevity.

Thanks, R Scott. So, it is all theoretical at the moment, but I'd say our aim would be to process a fairly large number of birds (say 150-250) at least once per week. From what you're saying I'm thinking that we might be best to use both - an icemaker on the day of the processing supplemented by some large blocks made (with salt) in a chest freezer, say one per day in between processing days, or whenever the sun is shining. I'm thinking that on on processing days we would probably need to resort to running a generator anyway, especially if we are running an electric plucker and an electric scalder (I like the idea of using a more efficient heat source for this, but then the convenience of a thermostatically controlled unit when in the midst of chicken slaughtering and eviscerating is appealing). So, perhaps it would work to start the ice maker running on processing days as soon as the sun is shining on the solar panels, and then once we are ready to start processing to run it along with the plucker and scalder directly from the generator, presuming it could handle the load. Does this sound feasible?

And maybe some running the icemaker during the week when there is surplus power or generating for other reasons. Store that ice in the deep freeze. That is what we do on grid. The birds we keep go where the ice was.

You need to balance the peak draw of the icemaker vs capacity of your inverter and generator. You probably need to figure you can make a fourth of the rated capacity-cut the rating in half for solar hours and probably in half again for ambient temperature.

The electric scaler is nice, but a huge power hog. If could suck every watt from your generator. The whiz bang plucker guy (you can Google him) has plans for a gas scalder made from a water heater. Temp regulated no power, just a propane bottle.

Thanks a lot for the feedback, R Scott, I appreciate it and your suggestions seem very sensible and practical. I've had a brief look at the whizz bang websites, and may well throw down for them now that they've come recommended here

Hi Richard,

One thing no one has mentioned yet about commercial ice makers is that they break down. CONSTANTLY. Repairs often run $100+ just for labor. They are, as someone mentioned briefly upthread, highly selective about their water quality. What they didn't say is that air quality, power supply consistency, and the phase of the moon also affect their operations. My husband and I own a cafe, and he has spent 10+ years as a restaurant equipment sales & repairman. What's the #1 piece of equipment that would make our lives SO MUCH easier, but we don't have because it's such a PITA to maintain? An ice maker. We buy our ice by the bag from the local grocery, even in summer when we're using upwards of 100# daily.

You'll be much better off with several deep freezes, especially in an off grid environment. Even in Hawaii, there's no solar array on less than the most massive of scales that can power commercial restaurant equipment for any length of time. Commercial equipment is, it often seems to me, designed to use the maximum possible amount of electricity.

Have you looked in to the CoolBot system? I have a farmer friend here who uses one as a cool cellar and another one as a freezer - the freezer understandably takes a LONG time to freeze things, but with the superinsulated room she has it in, it doesn't matter so much and the power consumption is quite low for the area of cooled space. Were I facing your conundrum, I'd look seriously at a combination of large saltwater-ice blocks and a CoolBot room, powered by a combination of solar and generator, or solar and whatever else I could get my father in law (the family alt-energy guy, invents new battery materials for a living) to plug into the system - solar boiler turbines, solar thermoelectric generation, etc... (Look into some of the really cool solar stuff the French were doing in Algeria around the close of the 19th century, none of it generates a ton of power on its own, but if you have sun and space and several in sequence the trickle charge can add up nicely)

What about buying in a batch of dry ice when you process your carcasses?

I just looked are prices here and 50kg cost under £200. You can use standard cool boxes/old chest freezers then transfer them to an on grid system once processing is done - or sell them direct to customers over a 5 day window while you have ice.

A lot of energy has to be removed from water to change it from 32 degree liquid water to 32 degree solid water. For example, to freeze two and a half gallons (~10 liters) of water 3,340,000 Jules of energy has to be removed which is about a kilowatt hour. Based on your solar array and ice needs it seems likely that you'll need to be making ice for several days in advance so I'd probably go with the chest freezer since they tend to be better insulated. Using a chest freezer would also allow you to make blocks of ice which I find easier to work with.

Michael Cox wrote:What about buying in a batch of dry ice when you process your carcasses?
I just looked are prices here and 50kg cost under £200. You can use standard cool boxes/old chest freezers then transfer them to an on grid system once processing is done - or sell them direct to customers over a 5 day window while you have ice.

That may not provide enough cooling capacity for their needs. When a kilogram of dry ice sublimates it absorbs 571 KJ of energy and when a kilogram of water thaws it absorbs 334 KJ of energy. If you get liquid water and it is at -10 C and the final temp is +10C that kilogram of water absorbs another ~60 KJ of energy. In comparison, when you get dry ice, it is at -78 C, but it sublimates into a gas and would leave the tank without providing substantially more cooling.

So for the OP's purpose the 50 kg of dry ice would only have 40% more cooling capacity than 50 kg of water ice, but cost substantially more.

Buying ice from the local store or ice company may make more sense, depending on cost. It doesn't take much power to keep ice frozen. And gives back to a community.

Dry ice has the advantage of being clean - pretty important for food/meat preparation. Chilling a big batch of chickens with water ice sounds like a recipe for salmonella spread (think about the water draining out of your chiller as the ice melts), compared to the CO2 gas safely and cleanly venting to atmosphere. Once the meat is down to temperature it becomes a much more manageable problem - one of insulation primarily, to stop heat gain from the environment. It is a fairly simple retro-fit to add more insulation to most chest freezers such that your off grid solar/battery supply can maintain the temperature.