Where are we with freeze alarms?

softdown
softdown Solar Expert Posts: 3,915 ✭✭✭✭
edited September 2019 in Off Grid Solar & Battery Systems #1
Not looking for a phone call. Just a noise and the ability to set the temperature for the alarm. Seems that calling you when the temp hits 45F might be standard procedure with freeze alarms. Perhaps I am using the wrong search words. 

Being a prepper I store food and drinks in several rooms. Nothing else matters if we don't have food. Glass bottles and aluminum cans can't handle a "hard freeze" of course. I'd guess that 24F may produce a hard enough freeze to fracture the glass and aluminum containers. That guess is as wild as it can be. Plastic is likely safe for quite awhile longer.

This area can easily see -30F. So a storage unit could witness a "hard freeze" with the right weather conditions. 

I only heat 800 sq. ft. Or 10% of the entire building. The temperature of the rest varies  depending on passive solar heating. 

Generally the cooler the food and beverage the better. Just need to avoid the hard freeze. 
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #2
    I did some quick searches, and the only statement I could find was don't go below 40F.

    The point at which items freeze is usually dependent on the amount of sugars and other ingredients in the specific item (for example, sea water freezes at ~-4C or 24.8F)... But It appears that the "raw" food only may go a couple degrees F below 32F before crystallization (freezing) begins.

    Not exactly an answer to your canned good question, but I did run into this neat chart about the optimum storage conditions for a whole bunch of fruits and vegetables:

    https://www.engineeringtoolbox.com/fruits-vegetables-storage-conditions-d_710.html

    Proper storage conditions - temperature and humidity - are required to maximize storage life and maintain quality of harvested fruits and vegetables.

    Fresh fruit need low temperature and high relative humidity to reduce the respiration and slow down the metabolic processes. The table below indicates optimal temperatures and moisture conditions for some common fruits and vegetables (here is an example of the first few entries).


    ProductOptimal Storage TemperatureChill PointFreezing PointOptimal HumidityTop Ice Accepted
    1)    		Water Sprinkle Accepted
    2)    		Ethylene ProductionSensitive to Ethylene 3)Approximate Storage LifeComments
    (oF)(oC)(oF)(oC)(oF)%
    Apples30-40-1-429.390-95NoNoHighYes1-12 monthsChill sensitive stored at 35-40 F (2-4 C)
    Apricots31-32-1-030.190-95NoNoHighYes1-3 weeks
    Artichokes32-350-290-95YesYesNoNo
    Artichokes, Jerusalem31-320-228.090-95NoNoNoNo4-5 months

    The major issue, of course, with canning/glass jars is the damage to the container once freezing begins (damage to container, failure of lid seal). And then the issue of changes to texture of what is frozen (some may be OK, others may turn to mush).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    As Bill says, it depends on sugar content, etc, but freshwater ice is at minimum density near 0°C/32°F.  It's most dense at~4°C, drops slightly as it cools to just above freezing, then drops a lot as it freezes (density drop = ~8-9% increase in volume IIRC).  Once frozen, density increases (volume shrinks) a bit as temps get colder.

    https://www.engineeringtoolbox.com/ice-thermal-properties-d_576.html

    So it's not just temp, but also time that matters.  Eventually water will "hard freeze" in freezing temps, doing so more quickly in lower temps.

    If I wanted to be sure to avoid freezing, I'd keep the prepper supplies buried below the frost line with a rigid insulation access hatch.  Ground temp around here is ~7°C year-round.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • softdown
    softdown Solar Expert Posts: 3,915 ✭✭✭✭
    #4
    Estragon said:
    As Bill says, it depends on sugar content, etc, but freshwater ice is at minimum density near 0°C/32°F.  It's most dense at~4°C, drops slightly as it cools to just above freezing, then drops a lot as it freezes (density drop = ~8-9% increase in volume IIRC).  Once frozen, density increases (volume shrinks) a bit as temps get colder.

    https://www.engineeringtoolbox.com/ice-thermal-properties-d_576.html

    So it's not just temp, but also time that matters.  Eventually water will "hard freeze" in freezing temps, doing so more quickly in lower temps.

    If I wanted to be sure to avoid freezing, I'd keep the prepper supplies buried below the frost line with a rigid insulation access hatch.  Ground temp around here is ~7°C year-round.  
    That would work but digging through concrete floors would be tedious at best. I'm not sure if my supply rooms ever get below 40F. I want an alarm if they get to freezing. I get pretty energetic if an alarm sounds. Energy is nice when in their 60's. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    How about a cheap thermostat, wired to trigger an alarm instead of (or as well as) starting a furnace/heater?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    I use a kerosene lantern in my greenhouse and plumbing sheds to keep frost out.  Might work for food storage too.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • softdown
    softdown Solar Expert Posts: 3,915 ✭✭✭✭
    #7
    Estragon said:
    How about a cheap thermostat, wired to trigger an alarm instead of (or as well as) starting a furnace/heater?
    Pretty much describes what I am looking for. Have yet to find the ideal solution. As opposed to 'lost power' alarms? Those are easy to find. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • softdown
    softdown Solar Expert Posts: 3,915 ✭✭✭✭
    #8
    mike95490 said:
    I use a kerosene lantern in my greenhouse and plumbing sheds to keep frost out.  Might work for food storage too.
    The 1890s went that way>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

    The plan is to either use small propane heaters or simply move the endangered liquids. I think it takes a really hard freeze to damage canned foods as a rule. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
    softdown said:
    .........The plan is to either use small propane heaters.....


    I'd found the propane heaters were too hot, and pilot only, not warm enough, got tired of lugging propane tanks up and down frosted hills.  Kero seems to be just right

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • softdown
    softdown Solar Expert Posts: 3,915 ✭✭✭✭
    #10
    This is what I came up with: https://www.ebay.com/itm/Wireless-Digital-2-Sensor-Refrigerator-Freezer-Thermometer-Alarm-Low-Temperature/352707984328?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

    Just started using it yesterday. Have not set the audible alarms so don't know the efficacy of those. So far, so good though they do not transmit through several walls involving steel and ~60 feet - no surprise there.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #11
    Looks like it should do the trick. 

    I used some similar ones, but had to stop as the rf signals were triggering some remote controlled lights on or off, apparently at  random.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
    · Share on Twitter

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