Energy Matters Forums

[AlanJsStuff]

Hi Gordon

The point is you have to make the conversion to ice at some stage during the running of the refrigerator. Yes refrigerators are not efficient, but neither are batteries. There is a loss from electricity to battery back to electricity.
Here I go from electricity to ice one step.

I have designed a microprocessor circuit from inexpensive bits to control the running of the 240V ice banks compressor directly from the panel.

Once the refrigerator has reached the ice banks holding capacity, the any excess energy is diverted to a 200Ah truck battery to supply my LED lighting and washing machine occasionally, thus reducing the need for a large battery bank.

I understand it is not easy to make ice. However ice is excellent energy storage medium, if you want cold. After heating, and hot water, running the refrigerator is the next in line for reducing home energy demand.

Thanks for the tip re the NaCl solution; it may help with the temperature reduction. Keeping the temperature of the fridge regulated is best done with mechanical device, or manually with hand flap control.

One good thing about using ice in place is I do not have to cart it about as they did back in the days of grandpa. Those old boxes would keep stuff cold for up to 5 days, I read.

The next trick is powering the fan at night, so I can sleep in this heat.

Cheers AlanJ

[AlanJsStuff]

PS Hi Gordon
love your web site especially the
Comet Lovejoy & crescent moon picture thats a classic.
cheers alanj

[Gordon-Loomberah]

Thanks Alan

Recharging and using energy from a LiFePO4 is very efficient, up around 95%, see my thread here:
solar-wind-gear/topic5108.html

Lead-acid cycling, such as with your truck battery is much less efficient.

A freezer is a lot less efficient than a fridge, due to the greater temperature differential required - room temp to 5C is a lot more efficient than room temp to -30C. Using LiFePO4 batteries and a well insulated DC or even AC powered fridge will be much more energy efficient than making ice to use for keeping a fridge cold.

The main user of energy with a refrigerator is the heat gain through the walls and door, if you can insulate them very well, then the fridge becomes very efficient. Unfortunately newer fridges have the condenser coils built into the walls, right next to the bit you are trying to keep cold- a step backwards IMO. I once saw a fridge with the coils out the back with added extra insulation made from ~50mm polystyrene covered with hessian and it used about 0.5kWh/day. I don't think you could get anywhere near that efficiency by making ice blocks for use in a regular fridge.

I think your plan is doable on a small scale, but impractical for larger scales. I've certainly done it in the past when I had minimal battery capacity and no generator- freezing as much as I can when the sun shines, and turn the fridge off overnight. The question is, even if you can automate the ice making and fridge cooling, what happens when you are away for a cloudy week, how does the fridge stay cold?

Also, it does rule out keeping frozen food for any length of time- right now I have about 40 home grown trout in my freezer, which I hope to keep me going for a fair part of this year- and to ensure they are still good to eat in say October, they need to be kept colder than about -25C the whole time.

[Warpspeed]

One idea that comes to mind would be the application of the heat pipe principle between the mass ice storage and the refrigerator.
This works similarly to a normal refrigeration system, but without the compressor.

Basically its a closed loop system containing a refrigerant gas, with two heat exhangers.
Pressure in the system is pretty much equal everywhere, but the gas boils at the hot heat exchanger (the refrigerator) and condenses at cold heat exchanger (ice storage).
This can transfer quite a lot of heat fairly efficiently, and you may only need drill two fairly small holes for pipe entry into the refrigerator.

The evaporator heat exchanger in the refrigerator would be flooded with liquid refrigerant and mounted low.
The condensing heat exchanger in the ice storage mounted higher, so liquid refigerant has a gravity return.

Once the ice has all melted, heat transfer automatically stops with no loss of "cold" through the external heat exchanger system. It should be simple, with no controls or moving parts, and therefore pretty reliable.

If you are worried about the refrigerant gas, low cost and readily obtainable propane should work pretty well, and the working pressures for propane are realistic..

[AlanJsStuff]

Hi Gordon & WarpSpeed

Thanks for the tip, Certainly Li is actually more abundant than Pb, so would go this route in future, since it looks quite certain Li will replace lead in the long run. I looked at the link thanks, lots of useful stuff there.

Gordon, you to hit on the Achilles heel of the ice storage insulation. Really need lots to be able to compete with Li battery loss rate. I need to do some engineering on this before I finalise the design of the Ice bank. It may be possible to add it around the outside of the refrigerator.

Leaving the refrigerator alone for on cloudy days for a week would need more well insulated ice bank space. Does your motor generator set, turn itself on, when it is required? Personal I am trying to not have a motor generator, one good thing about the ice system, is there is usually more sunshine when its hot, a nice symbiotic relationship. Just go to make it work well.

With respect to keeping those trout frozen, perhaps some well sealed slots into the ice bank might do the trick; especially if I can get the temperature down to -25C.


Hi WarpSpeed
Indeed heat pipes are capable of 100’s of times more heat transfer time wise. I wonder how much effort to make them, and/or is there a local manufacturer?

Thanks to you both for the input
Cheers
AlanJ

[Gordon-Loomberah]

Does your motor generator set, turn itself on, when it is required?

I have not needed to use a generator since I went to Lithium in late 2012, and I did average around 12kWh/day for much of winter (details in the thread I linked I think) but when I did use one in the past with Lead-acids, it was manually started. It is just a 24V alternator driven by a small motor.

Here fridges and freezers are a significant, but not huge load in summer, especially when loaded with eggs and fresh cherries or apricots to preserve or sell at the weekly organic market, and not so much in winter. However, the aquaponics system water + air pumps generally use more energy than the fridges and freezers all year round. I can usually cut back on the the AP and fridge energy use when needed in extended periods of cloudy weather, to avoid the need for fossil fuel powered electricity generation. I even ocassionally use gas for cooking instead of the induction cooktop

[Warpspeed]

Hi WarpSpeed
Indeed heat pipes are capable of 100’s of times more heat transfer time wise. I wonder how much effort to make them, and/or is there a local manufacturer?

Heat pipes have been used for all kinds of things, and they are certainly made commercially, but why bother ?

Pretty easy to adapt a pair of suitable heat exchangers, hook them up together with some copper pipe, and flush out all the air with propane.
The ice heat exchanger could just be an open copper coil in a big plastic drum, the refrigerator could use a normal salvaged plate heat exchanger from another fridge.
If you included a decent capacity liquid reservoir tank in the plumbing, the filling quantity of liquid propane then becomes non critical.

[ssingh1945]

Sorry for being off topic, but I was intrigued by Tracker's comment that the carbon-tax killed off compressor repair in Australia. Please explain. Thanks.

[Tracker]

.... the carbon-tax killed off compressor repair in Australia. Please explain. Thanks.

The stupid Gillard Govt. classed refrigerants as one of the MOST damaging as far as Global Warming is concerned.
The result was that the price of the gas rose DRAMATICALLY.. To the point where to repair a blown compressor and replace the gas (which you virtually must do) , pushes the repair cost to the point where a NEW fridge is more acceptable.
The NEW fridge from China, is exempt from Carbon Tax.
The repaired fridge cost, is far more because of the tax.

So - if the compressor is blown, then it just goes to the tip, and a pipe gets broken along the way, so that someone does not have to pay to recycle the gas..

Net Result - In order to save the world, FAR MORE refrigerant is released into the atmosphere..

The practical proof... Back some years, I would replace a compressor every few weeks.
Now - I have not replaced one since the Carbon Tax was introduced..
AND - don't expect the Chinese product to last... I am seeing them unrepairable at 3yo..

A friend has a small cool-room (Meat Processing).. He said that the repair cost for gas replacement, was $3000.. plus the compressor etc.

BTW - I suspect that there will be no warranty repairs, either.. Just replacements..
The replacement would have NO environmental tax...
The repaired unit certainly would have an unrecoverable environmental tax
Repair of new models is more difficult - the pipe-work is SOoooo thin, it is easily destroyed..

PS - and the other is the insurance companies -- -- they offer you a discount for increasing your excess and you think that is an acceptable RISK..
Problem is that it wipes out MANY of the things you insure for.. like fused motors and broken glass..
( Too late once you have the problem )
..
.

[Smurf1976]

The stupid Gillard Govt. classed refrigerants as one of the MOST damaging as far as Global Warming is concerned.

This is essentially the point made by many opponents of the carbon tax. That it would simply relocate emissions, and actually increase them in the process, rather than actually reducing them.

For example, if we stop smelting aluminium, making steel or whatever in Australia then the world as a whole is still going to use just as much metal. We'll just ship the ore and coal / gas overseas and someone else will burn the coal / gas to process that ore rather than doing it here in Australia. The end result, once you take emissions from the increased volume of shipping into account (and ships use quite a lot of fuel), is that emissions go up rather than down. So we're exporting emissions rather than reducing them, meanwhile we're also exporting the local employment that would come with processing here in Australia too. Australia loses, someone else wins, no gain for the environment.

It is essentially the same outcome with refrigeration repair. Emissions go up rather than down, all we're doing is losing the local employment that would otherwise come with repairing these systems.

Much as I'm in favour of renewable energy, I am opposed to the carbon tax for this reason. If we're going to have it, then it should not apply to any business that competes internationally and where energy or other emissions are a significant cost. Apply it to the power bills of households and restaurants etc maybe, but not to a factory etc - all that ends up doing is forcing them offshore.

As for insurance, that comes down to risk management. Personally I have no need financially to insure against a small loss. If my fridge breaks or I accidentally break a window then I can afford to pay for that myself rather than paying someone else, who will on average make a profit, to take the risk for me. Hence I choose to have a significant excess. I need insurance in case the house burns down etc but not for a broken glass table top or if the fan motor in the oven stops working.