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Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 10:08 AM

I would like to size a solar panel or panels and battery to power an ammonia type refrigerator. The refrigerator would be the size of one used in a moderately sized travel trailer--say 7 cubic feet. I can't find the amount of electrical power required for the heat source. I don't want to use propane.

Any suggestions?

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#1

Re: Heat required for expansive type (ammonia) refrigerator

01/03/2017 10:51 AM
  • Take the electrical load drawn by similar or identical refrigerators and use that figure. The solar array needs to be sized to that figure, multiplied by the mark-space ratio of the equipment (which is a function of its size, the ambient temperature, the starting temperature, mass, and thermal capacity of the contents), multiplied by some figure to allow for conversion losses and battery size.
  • The battery size should be sufficient to sustain the refrigerator overnight given the above, allowing also for dreary days where the input power to the charging pack will be less than the bright sunshine power, which is a function of climate.
  • The final answers are likely to be the result of an iterative calculation.

Without knowing some of these numbers, there's nothing much more to go on.

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#2

Re: Heat required for expansive type (ammonia) refrigerator

01/03/2017 10:51 AM
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#3

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 12:19 PM

You're working too hard:

http://www.sundanzer.com/

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#4

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 2:34 PM

For an absorption type ammonia/water system, you would need some concentrating collectors for heat and photo-voltaic for electric power for pumps....

What you want are BTUs....

http://www.solaripedia.com/files/1113.pdf

...so, if you have tested a water collector, and measured the following:

Flow Rate = 1.2 gpm

Tinlet = 80F

Toutlet = 100F

Then the heat output is:

Qout = (Flow Rate gallons/min)*(8.2 lb/gallon)*(Toutlet - Tinlet)*(1.0 BTU/lb-F)

Qout = (1.2 gallons/min)*(8.2 lb/gallon)* (100F - 80F)*(1.0 BTU/lb-F)

Qout = 197 BUT/min or 11,800 BTU/hr,

the best way to measure the flow through the collector is to divert the collector flow into a container of known size, and time how long it takes to fill. This method is accurate and cheap. If the simple approach is not workable, then a flow meter can be used to measure the flow. Taking water flow measurements is discussed here.

http://www.builditsolar.com/References/Measurements/CollectorPerformance.htm

Be sure to make note of the materials compatibility...!

https://diyscience2015.wordpress.com/2015/10/26/final-project-solar-refrigerator/comment-page-1/

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#5
In reply to #4

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 2:37 PM

The orange Home Despot bucket is de rigueur for such installations, btw. "Let's do this."

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#11
In reply to #4

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 5:37 PM

I had an absorption fridge when I lived in the Caribbean. There was no electricity (ergo, no pumps), just a propane flame. It took a day or two to get cold but once it was working, it worked quite well. The flame was pretty small, about the size of a pilot light.

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#12
In reply to #11

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 8:58 PM
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#17
In reply to #11

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 1:00 PM

In the textbook, the Continuous Cycle Absorption System looks like this. Per the text;

The continuous absorption type of cooling unit is operated by the application of a limited amount of heat furnished by gas, electricity or kerosene. No moving parts are employed. The operation of the refrigerating mechanism is based on Dalton's Law.

Dalton's Law:

The total pressure of a confined mixture of gasses is the sum of the pressures of each of the gasses in the mixture.

To illustrate ; A refrigerator uses two gasses, ammonia and hydrogen. The ammonia at room temperature is absorbed by the water in the closed system. Heating this system drives out the ammonia. ( The hydrogen is not absorbed by the water and remains as a gas.) Due to the pressure it is under, the ammonia condenses into a liquid In the condenser. The pressure is uniform throughout the system. Total pressure in the system is the sum of the vapor pressure of the ammonia plus the hydrogen pressure. When the pressure of the ammonia vapor is below the pressure corresponding to the vapor pressure for ammonia alone, the ammonia continues to evaporate as it tries to reach a vapor pressure corresponding to the temperature in the absorber.

That's quite a mouthful.

If I was going to put together a solar to electric, refrigerator heating system, here are a few things I would consider.

1. How much wattage of power could my solar panels develop on average.

2. How much would be my total electrical loss be from my electric heating element, convey and control system and storage media.

3. How often would my refrigeration system cycle.

4. How much extra capacity would be required to account for loss such as convection or thermal radiation.

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#16
In reply to #4

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 9:57 AM

What would you suggest as a practical way to deal with the fact that you may need refrigeration at night or when the sun is not working? Honestly solar, do you really believe that contraption in the drawing will work? It will be absurdly expensive, rarely work, and require constant tinkering. You are not helping improve our reputation.

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#18
In reply to #16

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 1:00 PM

The drawing illustrates the principle involved...The OP is encouraged to flesh out his design so we may contribute...

..."You are not helping improve our reputation."...

I wasn't aware "our reputation" needed improvement...

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#21
In reply to #18

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 2:40 PM

I can see that. That is why it needs improvement. When you are oblivious, life is good.

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#6

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 3:17 PM

Make one of these, and no ammonia, then back with us, and tell about the experience.

It seems like a fancy tuning fork.

Title:

Quantum Absorption Refrigerator

Authors:

Levy, Amikam; Kosloff, Ronnie

Affiliation:

AA(Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel), AB(Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel)

Publication:

Physical Review Letters, vol. 108, Issue 7, id. 070604 (

PhRvL Homepage)

Publication Date:

02/2012

Origin:

APS

PACS Keywords:

Nonequilibrium and irreversible thermodynamics, Decoherence, open systems, quantum statistical methods, Quantum statistical mechanics, Heat engines, heat pumps, heat pipes

DOI:

10.1103/PhysRevLett.108.070604

Bibliographic Code:

2012PhRvL.108g0604L

Abstract

A quantum absorption refrigerator driven by noise is studied with the purpose of determining the limitations of cooling to absolute zero. The model consists of a working medium coupled simultaneously to hot, cold, and noise baths. Explicit expressions for the cooling power are obtained for Gaussian and Poisson white noise. The quantum model is consistent with the first and second laws of thermodynamics. The third law is quantified; the cooling power Jc vanishes as Jc∝Tcα, when Tc→0, where α=d+1 for dissipation by emission and absorption of quanta described by a linear coupling to a thermal bosonic field, where d is the dimension of the bath.

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#19
In reply to #6

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 1:15 PM

Until someone invented it, I doubt many people believed that you could inject compressed air in one side and get hot or cold air coming out the others.

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#27
In reply to #19

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 11:31 AM

Until someone invented it, ...

That future is now.

Its called a Vortex tube, it was invented in the 1940's and have been used in manufacturing especially welding for quite some time now.

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#29
In reply to #27

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 12:06 PM

It seems to take a lot of air, and really good skills to make a good vortex tube. I tried making several, and got weak results, but my compressor does not have the output required to sustain it.

Now if someone could make one that only takes 0.1 scfm air at 20 psig, that would be excellent!

Another cooling possibility is the nested clay pots they use in Africa. They can apparently keep perishable foods for a significant amount of time.

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#30
In reply to #29

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 12:14 PM

You definitely need the CFM's, I've used it for cooling parts as its being welded, But precision machining is required. At least the geometry anyways.

My post was to directed that the technology is already here and being applied, not so much the efficiency.

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#31
In reply to #30

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 12:36 PM

Yep, I will be continuing to experiment with cutting widening spirals (on the faces) in aluminum round pieces of stock, to make two halves of the air accelerator for a vortex tube. At least, now I have gears I can use to affect ratios of rotation to tool translation.

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#7

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 3:33 PM

21 cu. ft. model uses 1750 BTU/24 hours = 0.513 kWh (daily). Thus, the average power level for the electric heater is 21.4 watt. That should not take much; just a couple of 50 W, 10 Ohm resistors in parallel will get you that on a car battery. If you want to plug it into a 120 VAC outlet, then you need larger resistance. 21.4 R=V2, so that R = 672.9 Ohms. It could be a bit less (or more); also, I calculated for 21 cu. ft., so for a 7 cu. ft. it's probably less than half of the heat required but more than 1/3. Probably 10-13 Watt would do nicely.

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#8
In reply to #7

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 4:00 PM

That seems improbably low.

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#9
In reply to #8

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 4:34 PM

Let me go over it again:

One 21 cu.ft. model of the Crystal Cold: 1825 BTU/hr = 534.9 W, so there you are right, I was wrong by a factor of about 24 (probably picked up the wrong value, or applied it wrong.)

For that power level: 0.037 Ohms heater. OR whatever 500-600 Watt electric heater you can shove into the former burner panel? Or two 250 W light bulbs might work. OR one really powerful heat lamp, with special bulb socket for high temperature, and better than normal wiring. If that current (4.45 A) calls for 16 gauge wire, I would raise that 2 gauges to 12 gauge, and shield the leads from heat somehow (insulation).

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#15
In reply to #9

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 6:58 AM

Something aint right. 534.9=0.5349 kwh per hour. I use 3 kwh per hour for my entire house in the summertime. So, the .5349 kwh would be .5349(100)/3=17.8% of my total usage. 534.9 watts seems way high.

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#23
In reply to #15

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/05/2017 9:05 AM

I give up trying to convince anyone of anything here. If I calculate using one website's data, I get chided for low answer, and if I use a different website's answer, I get chided for the high answer. I suspect ammonia refrigeration might be that inefficient, so why not just use electric small refrigerator with known power demand on the sticker, and quit being a forking cheap skate.

There are more efficient cycles. If you are going off-grid, use the African clay pots evaporative refrigerator. Solar input drives the thing, and it does protect perishables.

Or bite the bullet and buy a real refrigerator and get over it. Stop re-inventing the wheel?

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#10
In reply to #7

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/03/2017 4:39 PM

Hey dummy, that is per hour, not 24 hours, nitwit!

Everyone just ignore #7, too bad, we cannot offer a bad answer rating, sorry.

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#14
In reply to #7

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 6:45 AM

Thanks. If I use 20 watts to be on the safe side, that would be 24x20=480watt-hrs. for 24 hour period.

480wh/6hr=80watts. So, I would need solar panels that would produce 80 watts. And, I would need a battery that would have a 20 hour rating of (80/12)(24/20)=160 Ah.

Is this correct?

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#20
In reply to #14

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 2:03 PM

If you're looking at peak output, you might want to consider that is not always the case....I would triple that...

Solar panel kit

http://www.defender.com/product.jsp?path=-1|2276204|2276226|2276235&id=1770670

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#13

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 3:14 AM

Why do you want to use teh ammonia type? It works well but quite inefficiently with a thermal source, but classical compressor type refrigerators are more efficient if you have an electrical power source.

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#22

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/04/2017 3:28 PM

These link may assist, in your electrical power from solar

http://homeguides.sfgate.com/run-refrigerator-inverter-49672.html

or you could build a simple hydrogen cell.

http://www.instructables.com/id/How-to-Convert-Water-into-Fuel-by-Building-a-DIY-O/

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#24
In reply to #22

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/05/2017 9:12 AM

right. If he were to blow himself up, it would definitely eliminate the need for him to own a refrigerator.

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#25

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 10:28 AM

I have been following this because if I can't get to the moon I will want to be able to make my retirement boat capable of living off the grid for periods of time. I have always liked the idea of these fridges because they seem to be mature designs and have been used in caravans for decades(?).

I already plan on using solar hot water for heating and hot water, i would love it if I could do cooling by solar as well. I am toying with a rube goldberg wave powered mechanical device that will pull a buoy towards an anchor on the bottom then spin a gear to drive the compressor on an air conditioner as it rises back to the surface.

Drew K

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#26
In reply to #25

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 11:11 AM

Have you seen those all motion to rotation devices? They work well with waves.

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#32
In reply to #26

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 1:28 PM

No, have not seen those. I do enjoy simple clockwork machines so my first thought is kind-of a reverse clock weight where the boat's movement ratchets a buoy down to the bottom then triggers a release that would allow the buoy to float back up and turn the crank on a compressor. If it could be timed right you could get it to cycle quite often; perhaps often enough to cool the boat?

My other thought was just to have a float on a chain that cranked up a large spring that could be tapped whenever needed. But spring steel and salt water may not mix so well even if I seal and oil it really well.

My plan is to keep coming up with ideas to try so I don't get bored in retirement!

too bad i have so many years yet till retirement :-/

Drew K

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#33
In reply to #32

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 2:27 PM

Here's you another idea: Seawater gets cooler typically away from the surface. Drop an intake tube into a better temperature (how far depends on temperature profile and local currents, I suppose), then simply heat exchange the cool water with hotter water (at or near surface) so that cool water keeps rising up and warmer water exits the tube at the top, and put a heat exchanger below the solar one to cool the boat's cabin, but you will need some pump energy, so I guess solar panels.

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#28
In reply to #25

Re: Heat Required for Expansive Type (Ammonia) Refrigerator

01/11/2017 11:40 AM

I will join James in his dismay and add this. Engineering a system that is theoretically sound is something to play with in your spare time. It is fun, and is a good way to learn new things. Having the ability to create novel solutions that reduce costs, energy requiremments and complexity while increasing reliability and assembly speed are the hallmarks of quality engineering. I think this is the strength of CR4, that forum that occasionally (not every post, like some seem to think) asks a question that you have the skill and experience to offfer a novel or practical solution that the OP has overlooked. I have worked on an ammonia refrigerator out of a caboose for a lot of years, It runs and cools well on a surprisingly small amount of propane. The secret is that it is a concentrated high temp source, even though it is low BTU's. Solar thermal production built to satisfy this requirement is like trying to power a tricycle with a sail.

Drew is only interested in amonia refrigrators, even though a far superior solution is being described. Let him tinker. A single 300Watt PV panel, a single charge controller, a single 220AH AGM battery will be a rock solid system for 10 years. On a boat, he probably already has the battery bank. He can buy a good DC fridge new or used on EBAY easily for far less money than it will take him to build an ammonia cycle fridge.

The reason these have been used in RV's for years is that they could not source cheap PV, which made offgrid DC refridgeration far less feasible. It recently quit working, we can't figure out why. The flame cycle seems to peter out and stop at the most inopertune times. We now have a small AC powered fridge that runs on our existing offgrid pv powered system, which is inverted and very small. It is fantastic, but we still cook with propane. Good luck, Drew!

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