Holding Plate Refrigeration

Dave Angelini
Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
in Energy Use & Conservation #1
I am new here but an old lurker. I once built a holding plate freezer and frige that was run by a 1/2 HP electric compressor. It ran for 1 or 2 hours a day depending on the temperature where the boat was.

I surface this old idea from time to time in hope that someone will start manufacturing one. For offgrid you could run the system in float during the afternoon. For grid tie this system could run off peak or get you away from the utility.

The plates are multi quart stainless serving trays but are also built by marine refrigeration companies. Copper coils inside the plates freeze the solution and have various ways cooling the box. There are dual coils that can be run by a large and small compressor for various design goals. The compressors can be quite far away or designed in to the box.

Technautics and Gruenert are two of the marine refrigeration dealers for reference.
The goal of using ever watt of power when the sun is out is at the heart of this system and the big payoff is not using energy for ice when the sun is down.

Dave

http://www.sierratel.com/offgridsolar/
"we go where power lines don't" Sierra Nevada mountain area
   htps://offgridsolar1.com/
E-mail offgridsolar@sti.net

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Holding Plate Refrigeration

    Welcome to the forum Dave! (gosh--I keep flashing on the movie 2001 "DAVE" :roll: )

    My question regarding efficiency--typically refrigeration efficiency drops as the differential temperature increases (over-cooling of the plate could be an energy hog)...

    So running a compressor to "over cool" a copper/steel plate during floating sounds somewhat interesting as this is otherwise "wasted/lost" energy. But, would the over costs/efficiency be better than just running a more efficient (energy star type) fridge/freezer with a bit more battery backup vs the added costs/complexity of a dual cooling system?

    Here is a link to one of your suggested manufacturers Technautics.

    Their pricing appears to be in the $2,000-$5,000+ range for their systems.

    Their 7 cuft fridge/freezer cooling assembly (does not include cabinet?) is rated at 24 amp*hours @ 12 volts... or [corrected to] ~288 watt*hours per day...

    A cheap ~15 cuft freezer is probably well less than $1,000 (I paid $500 or so for mine on clearance) and uses around 1,000 Watt*Hours per day (mine is using a bit less--but I was cheap and got a "frost-full" freezer that I have to defrost a couple times a year).

    And we have the Chest Freezer conversion thread that get down towards ~250 watt*hours per day for a 7cuft refrigerator conversion system (or [corrected to] a bit less than the above energy usage--if I recall correctly).

    Boats and such are special cases (size, packaging, marine requirements, etc.)--if you are running your engine--the additional loads applied by plate freezer subsystems are not going to be that noticeable--but the same load applied often on an off-grid solar system needs to be accounted for (more panels, possibly battery capacity).

    Over the years--we here have seen that a good Energy Star Fridge/Freezer is getting very close to the efficiency of a "dedicated" off-grid type device--plus the cost reductions of mass market white goods and the reliability/feature sets available (frost free, ice maker, etc.).

    And when working the dollars and cents comparisons--the cost differences between the "designed for off-grid" systems higher costs end up being more than the additional solar panels+batteries would cost that may be required to operate a typical Energy Start rated fridge/freezer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Holding Plate Refrigeration

    PS: Cleaned up the above post a bit--I was on hold with the IRS as I was typing it--obviously my mind was not 100% on the post when I was doing this... :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Holding Plate Refrigeration

    Also, to talk a bit about grid tied systems...

    I have a 3kW GT system just south of San Francisco CA--And I have PG&E's Time of Use / Net Metering plan for my system...

    So, I have a digital timer that "turns off" my freezer from noon-6pm (my peak rate charge times)... During the summer, my off-peak is $0.09 per kWhr and my peak rate is $0.27 per kWhr.

    If I save two hours of run time during the noon-6pm period (Mon-Fri)--I get "free power" for the rest of the day--and I do this by over cooling my freezer (set it to minimum thermostat temperature). Over cool during off-peak and no cooling during peak times.

    My only concern with this is that I may be freezer burning my food more because of this--typically cycling temperatures in a freezer tends to draw more moisture from frozen foods.

    I have not done any measurements / comparisons yet--just try to get my wife to use up food faster (less buying ahead) instead.

    Also, regarding optimum freezer temperatures--there was a neat thread where this was discussed before--Seems there is a good reason to keep the freezer at 0F for long term storage. Even keeping food at 5F seems to cause faster loss of nutrients.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #5
    Re: Holding Plate Refrigeration

    The freezer thread was good! I just read the Homepower review on the Steca 6 cu ft. Pretty amazing little box.

    Your comments on doing something with cold storage (holding plates) as opposed to conventional all make sense but I just like the idea of not having to even use a battery or more batteries for refrigeration. When you look at prices you can really not use Marine for reference as those people are use to the basic marine unit which is often thousand dollar bills. They do know what they are doing however.

    The other way to use surplus energy that I currently like is the Sanyo heat pump.
    To my way of thinking it is one of the wonders of the world right now. Service people often think the compressor is not running it is so quiet. The 3/4 ton units perform as 1 tons and seer 16 to 20 is amazing at 120VAC.

    I never got behind using electricity to heat water as solar water is way too efficient and easy to waste electricity on. Maybe someone can convince me....
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: Holding Plate Refrigeration

    We used to build walkin freezer/coolers using a large frost plates rather than an evaporator. ( I guess as an evaporator) Is this the kind of system this is. Is the idea that there is enough thermal mass such that you super cool it,,, and it warms slowly thereby allowing the duty cycle to be different?

    Tony
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #7
    Re: Holding Plate Refrigeration

    Yes Icarus it is kind of like an ice cream truck. They plug-in over night and freeze their plates and are good to go. There is either a brine solution or a eutectic that is mixed for freezer plates or reefer plates. There are probably even better ways these days but.......

    I always come back to this idea because I always liked the idea of adding a major appliance that replaced one that needed a battery. Like getting a bigger capacity battery and not having to lift it!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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