refrigeration for off grid

[almac]

this thread has been done b4 but couldnt find it. some have asked before about running the fridge in a stand alone system, gas vs electric , i have found one solution to this, using a chest freezer on a timer for about 4-6hrs a day, keeping some water filled bottles frozen at the bottom. with mine i have 9 x 2L bottles of ice at the bottom of the freezer, this setup keeps food frozen on the lower section and very cold in the upper section 24hrs.DSCN0004.JPG

[sensij]

This setup doesn't really do anything to reduce the overall energy requirement of the freezer (and has a large energy cost during the initial freeze)... but it can let you time shift the load to daylight hours to reduce the amount of discharge required from the battery.

https://www.solarpaneltalk.com/forum/off-grid-solar/solar-living/17632-reducing-overnight-loads-for-freezers

[J.P.M.]

This setup doesn't really do anything to reduce the overall energy requirement of the freezer (and has a large energy cost during the initial freeze)... but it can let you time shift the load to daylight hours to reduce the amount of discharge required from the battery.


https://www.solarpaneltalk.com/forum...s-for-freezers

Provided the ice does not change the internal average operating temp. of what the freezer would operate at without the ice, it will not change the heat transfer (heat gain) over time, or the rate of heat transfer. Added thermal mass can perhaps improve (reduce) the amount of energy needed to maintain a temp. difference if it enables the equipment to cycle less. Such considerations have little to do with heat transfer however.

The increased thermal mass will increase the thermal time constant - roughly f(thermal mass /heat loss rate) of the freezer and slow the rate of temperature change between the inside and the outside of the freezer boundary (the freezer walls) - note, not heat loss rate, which is why the cooling equipment will cycle less (and, BTW, run longer when it does cycle) if it is thermostatically controlled as is common.

So, if the goal is to maintain an adequate freezer temp. while minimizing battery discharge for that purpose, and some temp. swings can be accommodated, with a bit of experimentation, some H2O jugs and a timer for the freezer, it is quite possible that a freezer can maintain an adequate temp. between times when solar generated power stops in late afternoon to when it becomes available the next morning, without any power input, based on good insulation on the freezer envelope and a lot of added thermal mass inside the freezer - basically, increasing the thermal time constant of the freezer. Maintaining adequate temps. longer than 24 hrs. or so might take some finessing however. Also, the added thermal mass will, of course, reduce freezer available volume. There ain't no free lunch.

BTW, the referenced post was mostly about a similar but different subject and seemed to be mostly dealing with the merits and possible ways of adjusting (lowering) the phase change temperature - the freeze/melt point of water, usually called the eutectic point for other mixtures and materials, and some discussion of eutectic salts, etc.

Add: More BTW, the idea of adding thermal mass can work the same way to time shift A/C loads in a dwelling, sort of like a DIY T.O.U. scheme. Think of it as a thermal storage battery. It's also one of the common tactics used in passive solar design for several end purposes, but primarily to help minimize internal temp. swings, get a higher solar fraction, and help minimize aux. fuel used for space heating/cooling.

[hammick]

I am buying this fridge for $299 next time it goes on sale: http://www.homedepot.com/p/Vissani-9...g&gclsrc=aw.ds

It has the least energy use I can find without spending twice as much. My system will be an SW4048 inverter, 325ah Trojan L16RE-As, and 1720 watts of solar power.

This is the route I'm going unless somebody convinces me otherwise.

[Logan005]

there are a number of chest refrig/freezers that run directly from DC voltage, namely 24volts. These units have 4 to 4 1/2 inch thick walls and use 1/4 the power of AC chest unit's. EcoSolarCool ESCFR250N

makes a 2 door unit

[hammick]

there are a number of chest refrig/freezers that run directly from DC voltage, namely 24volts. These units have 4 to 4 1/2 inch thick walls and use 1/4 the power of AC chest unit's. EcoSolarCool ESCFR250N

makes a 2 door unit

Those look nice but very pricey. Not sure the wife can get by with 7.1 cu ft which appears to be their biggest upright model.

[Logan005]

I do not recommend an upright model for off grid battery use. every time you open the door it looses 90% of it's internal cold air. causing it to cycle batteries. they make a double door 8.8cu.chest but I have to admit it takes some getting used to stacking, rather than shelves. Much easier if you already store egg's at room temp. In the long run I believe the high initial cost is more than made up for in reduced cycling of expensive batteries.

[hammick]

The unit I am looking at is estimated to use 329kwh per year. I calculate that to .9kwh per day. Isn't that doable with a 325ah 48v system? This is a vacation place and the fridge will be turned off when vacant. I really don't want to run the batteries below 80% SOC on a regular basis.

At $299 it's a relative inexpensive fridge and I'm willing to take the chance but I will look at the EcoSolarCools if I really have to.

If I have to go the high dollar route I'm probably going to look at the propane absorption fridges. Those are super expensive.

[hammick]

I have calculated .9 kwh per day for the fridge to 19ah at 48v. A good part of the 19ah will be during the day when the sun is nice and bright in the summer. Am I calculating this correctly?

When we are up there during the winter we can keep food cold using other means if necessary.

I figure if I want to keep my 325ah bank at 80% SOC I have 65ah per night to play with. My only other major load is a 230v well pump that won't be running much.

[almac]

I do not recommend an upright model for off grid battery use. every time you open the door it looses 90% of it's internal cold air. causing it to cycle batteries. they make a double door 8.8cu.chest but I have to admit it takes some getting used to stacking, rather than shelves. Much easier if you already store egg's at room temp. In the long run I believe the high initial cost is more than made up for in reduced cycling of expensive batteries.

yes i found that at 1st i had an upright fridge with frozen bottles in the top compartment. it didnt take long to realize every time i opened the door the cold air would flow out the bottom of the fridge to the floor. thats why the chest freezer is better. it holds the cold air like a cup holds water.

[almac]

I am buying this fridge for $299 next time it goes on sale: http://www.homedepot.com/p/Vissani-9...g&gclsrc=aw.ds

It has the least energy use I can find without spending twice as much. My system will be an SW4048 inverter, 325ah Trojan L16RE-As, and 1720 watts of solar power.

This is the route I'm going unless somebody convinces me otherwise.

my chest freezer in the pic cost $20au. works fine, the lid was rusty but covered it with a coat of wall paintDSCN0008.JPG