AC_Hacker's Hasty Freezer Conversion

[AC_Hacker]

There has been talk in a thread in the Appliances and Gadgets section about State of the Art Refrigerators.

I have heard of the legendary performance of converted chest freezers and have been tempted to try one myself. The idea of reaching down into a chest of food has been a bit of a deterrent, also the knowledge that any flat surface in my kitchen will collect things... things like motors, and mail I don't want to read yet, and yard tool, the list goes on... But to clear all that stuff off to get at some food is really what stopped me.

My current refrigerator is a tiny 3 cubic foot freezer/refrigerator which does hold most of what I actually need and also has an admirably small energy foot print. But the freezer is absolutely useless, so the actual refrigerated storage is in the neighborhood of 2.5 cubic feet... pretty small even for me.

I looked for 'all refrigerators' to replace it with and saw several candidates, but their energy consumption was 2x to 3x higher than the one I have. So I started looking for a small vertical freezer to convert.

I saw several, the most attractive was a Haier ($291) with 4.8 cubic foot of space (707 watt-hr/day),

...and the least attractive was a Summit freezer ($350) with about 5 cubic foot of space (879 watt-hr/day).

The photo of the Summit doesn't show it, but the insulation is much thinner than on the Haier... not so thick, not so good.

A quick search through CraigsList turned up the energy hog (non Energy Star) Summit for $125. Being the tightwad that I am, I went for it just to see what kind of a refrigerator a crappy compact freezer would make.

I ordered a digital thermostat from ebay for about $16, free shipping... but then remembered that it might be a month before it arrives...

So I found a spare Arduino-clone 'Teensy++' and a LM355 analog temperature sensor and a Solid State Relay (AKA: 'SSR') laying about and set to work making a bare-bones thermostat while I wait for the unit from China to arrive.

Here's a photo of the Teensy Thermostat. The LM355 is visible at the back of the protoboard between the Teensy and the SSR.

Here's a photo of the hasty test setup, showing the expert use of red duct tape to secure everything.

This is a graph of the Summit performance (watt-hr/day) over a 24 hour period prior to the Thermostat. The yellow line indicates the EPA power use figure, converted to 879 watt-hr/day.

This is a graph of the Summit performance for a period of about 16 hours after the thermostat is being used. The spike is because I put a pot of warm soup into the refrigerator. The average energy use is about 340 watt-hr/day after the conversion. Not a miracle, but quite respectable, and it is a 61% reduction from the energy use of the unconverted freezer.

A refrigerator that uses only 340 watt-hr/day deserves more than casual consideration.

This is a page from my notebook where I wrote about various refrigerators that were being discussed. It is very satisfying that this miserable freezer, once converted (See Red Line In Photo) is able to out perform the $1900 German miracle Refrigerator, and for only $150, too!

[EDIT: A quick calculation suggests that if the Haier freezer had been converted instead of the wretched Summit, the energy use would be about 274 watt-hr/day, and that's before defeating auto-defrost.]

Best,

-AC

See Code Below:

(Of interest is that a 'smoothing' routine has been used to reduce false triggering of the compressor.)

/*
 * refrigerator_thermostat_smoothed.pde
 * -----------------
 * Sensor (LM335) input is converted
 * to Kelvin degrees, then to Fahrenheit.
 * When temperature exceeds the SetPointTemp, compressor goes on.
 * When temperature is below than SetPointTemp, compressor goes off.
 * Refrigerator temperature is changed by changing SetPointTemp value
 */
 
const int numReadings = 20;

int readings[numReadings];      // the readings from the analog input
int index = 0;                  // the index of the current reading
int total = 0;                  // the running total
int average = 0;                // the average
int inputPin = 38;              // Teensy++ input pin
 
const int CompressorPin =  7;      // Define Teensy++ output pin
const int SetPointTemp =  38;      // Temperature set-point (different value = different temperature)
const int TempVariance = 2;
float temp_in_kelvin=0, temp_in_fahrenheit=0;

void setup()
{
// set the analog pin as input:
  pinMode(inputPin, INPUT);  
// set the digital pin as output:
  pinMode(CompressorPin, OUTPUT);
  
// initialize serial communication with computer:
  Serial.begin(9600);                   
  // initialize all the readings to 0: 
  for (int thisReading = 0; thisReading < numReadings; thisReading++)
    readings[thisReading] = 0;          

// Variables will change:
  int CompressorPin = LOW;      // Set initial state. Teensy HIGH turns off the SSR
}

void loop()
{
  // subtract the last reading:
  total= total - readings[index];         
  // read from the sensor:  
  readings[index] = analogRead(inputPin); 
  // add the reading to the total:
  total= total + readings[index];       
  // advance to the next position in the array:  
  index = index + 1;                    

  // if we're at the end of the array...
  if (index >= numReadings)              
    // ...wrap around to the beginning: 
    index = 0;                           

  // calculate the average:
  average = total / numReadings;         
  // send it to the computer as ASCII digits
  //Serial.println(average);   
  delay(1);        // delay in between reads for stability  

  //Reads the input and convert to Kelvin degrees
  temp_in_kelvin = average * 0.004882812 * 100;
 
  //Convert Kelvin to Fahrenheit
  temp_in_fahrenheit = (temp_in_kelvin * 9 / 5) - 459.67;
           
  //Print the temperature in Fahrenheit to the serial port
  Serial.print("Fahrenheit: ");
  Serial.println(temp_in_fahrenheit);
  Serial.println();
  
  
  // if the temp_in_fahrenheit is >= SetPointTemp,++ turn on compressor and vice-versa:
  if (temp_in_fahrenheit >= SetPointTemp)
   digitalWrite(CompressorPin, HIGH);   // turn the Compressor on (Teensy HIGH turns on the SSR)
  else 
  if (temp_in_fahrenheit <= SetPointTemp - TempVariance)
   digitalWrite(CompressorPin, LOW);   // turn the Compressor off (Teensy LOW turns off the SSR)   
  else
   //digitalWrite(CompressorPin, LOW);    // turn the Compressor off (Teensy LOW turns off the SSR)

  delay(1000);                          //wait one sec

}

[AC_Hacker]

Everything is still working well.

The temperature of the refrigerator has been running a bit too cold, so I am tweaking the value of "SetPointTemp" upward to achieve close to an actual 38 degree F inside reading.

All of my digital 'wonder-thermometers' are producing different results, so I am using my fall back lab-grade mercury column thermometer as a standard.

After the first tweak, the temperature went from sub 30 degrees F (difficult to read a mercury column at night) up to 35 degrees F.

I just adjusted SetPointTemp up two more degrees, which should get me to 37 F which would be good enough.

The LM355 was not calibrated, so the temperatures it indicates are not reflective of actual temps. Therefore, the mercury column thermometer is being used as a standard.

-AC

[creeky]

Nice. I'm heading to Kijiji now (Candian Craigs list)

Of course the miracle fridge is 12 cuft and has a freezer ...

[stevehull]

I guess I don't understand. You are using the EPA estimate as the prior standard? I would suggest running the unit as is, without the modified thermostat, and NOT using the EPA estimate. Then you have a true baseline allowing an apples to apples comparison.

It could be that the new thermostat is better - but why? The insulation is the same, the compressor is the same - what is different?

Steve

[AC_Hacker]

Originally Posted by stevehull

I guess I don't understand. You are using the EPA estimate as the prior standard? I would suggest running the unit as is, without the modified thermostat, and NOT using the EPA estimate. Then you have a true baseline allowing an apples to apples comparison.

SH,

I supplied two graphs, the first one was used as a baseline. The yellow bar indicated to me that the asymptote would fall pretty close to the EPA number. That was close enough for me. There is a reason that I used 'hasty' in the title.

If you'd like greater certainty, please try the experiment yourself. That's the way science works.

Originally Posted by stevehull

It could be that the new thermostat is better - but why? The insulation is the same, the compressor is the same - what is different?

The difference is that I'm not demanding the unit to chill the box down to 0 degrees F, I'm only asking it to go to 38 degrees F.

It all has to do with Carnot's Efficiency Theorem.

It a matter of delta-T and the work required to achieve some delta-T.

As a freezer, asking a box to get 60 - 0 = 60 degrees colder is an act against nature. To perform this act, considerable work is required.

As a refrigerator, asking a box to get 60 - 38 = 22 degrees colder is a lesser act against nature. To perform this lesser act, less work is required.

Es claro?

Also, I've heard people wondering as to why a converted freezer was so much more efficient...

Some say that it is because you don't dump air every time you open the door. I doubt that this is such a great factor, because the energy to chill down a freezer full of air is not so much.

Some say it is because the insulation is thicker. This would be a pretty large factor. That was one of the reasons I jumped on this unit, because it didn't have much more insulation than a refrigerator.

Some say that it is because the freezer is built to be more efficient, else the cost of operation would deter people from owning one. I think that this actually might be true. At least comparing my conversion and what I estimate it's energy use to be, to a refrigerator of the same size. So with a converted freezer, you're taking a fairly high efficiency refrigeration system and lowering the physical demands on it.

Thicker insulation would be better...

Not dumping air would be better...

Not stooping over to get a cantaloupe is not so bad.

-AC

[AC_Hacker]

Originally Posted by creeky

...the miracle fridge is 12 cuft and has a freezer ...

If I had 12 cubic feet of space, rather than 5 cubic feet, I'd have 12 - 5 = 7 cubic feet of extra space for food to rot.

For my lifestyle, more space in a refrigerator is not more better... lower utility bill is much more better.

As to the freezer, I have a very small one down cellar. Don't need more.

If you're going to 'roll your own' thermostat, I'd suggest using a 1-wire temperature sensor... more accurate. An LED display would be nice too, but I was in a real hurry to prove or disprove the concept. The thermostat I ordered has a display, and I was able to use the Arduino serial monitor to see what was happening during testing.

Good luck with your search and conversion!

-AC

[AC_Hacker]

The waterproof 1-wire sensors I ordered from China for my Freezerator (newly coined term) arrived a couple of days ago. Cost per each was about $3. Time to receive the shipment was just about forever.

I made a header for one of them that would be compatible with my Multilogger that is shown below. Also shown is the 4.8v power supply from a cell phone charger:

The Multilogger already has a 1-wire compatible header, so my waterproof 1-wire sensor makes the second sensor that the Multilogger will be reading.

I plugged the logger in and put the sensor into the Freezerator, and this is the graph that was produced:

You can see the sensor inside the Freezerator get colder, until it reaches the inside temperature. Also visible are the undulations as the compressor kicks in periodically to maintain the temperature.

The 'blip' around the 37 minute mark was when I got some orange juice from the Freezerator.

The upper data line is the 1-wire sensor that in on-board the Multilogger. Interesting how it is out of phase with the inside sensor. This is because there are condenser coils on top of the Freezerator, as well as the back and both sides. So the compressor extracts heat from the inside and dumps the heat on the outside.

* * *

I have used the Freezerator for almost eleven days, and have something of an initial user report...

Over that time the watts per day has averaged 414 w-hr/day. More than the Bosch miracle fridge, but still quite respectable.

The idea of converting the freezer to function as a refrigerator has worked out well, as I had hoped it would... even better actually.

On hindsight, my initial comparison of the energy saved was an apples to oranges comparison after all, because I was comparing the same machine running in two different modes, freezer mode and refrigerator mode, so it's pretty much a no brainer that refrigerator mode would use less energy.

A better comparison is to compare the Freezerator with different units that are designed to function as a refrigerator.

If I compare the Freezerator to other refrigerators that are of the same size and are in the same order-of-magnitude price category, like the Danbury all-fridge which consumes 901 watts per day, the comparison remains very favorable.

* * *

On the user side, there are issues still to deal with because small upright freezers are designed to accommodate manufactured food packages. I have noticed that some agreement seems to have been made as to what the dimensions of manufactured freezer food packages would be.

So the door storage and to a lesser extent, shelf storage, do not easily accommodate food packaging that has been standardized for refrigeration. Therefore, food repackaging will be required. This is not all together a problem for me, because I would prefer that the contents of my refrigerator NOT be a battlefield of competing brand names. I would much rather open the refrig and just see food.

The door storage may present a special problem, and I may end up reconstructing the inside of the door all together.

* * *

There is also the whole idea of the way this refrigerator, and almost all currently available refrigerators are designed...

In older refrigerators, there was a condenser coil that was held away from the back of the refrigerator. This is where most of the heat from the compressor and the inside of the refrigerators was dumped.

Now refrigerators, which are after all, six-sided boxes, have heat being dumped into 4 of their six sides, which is in direct contact with the insulation. Most of the heat does go out, but placing the coils in direct contact means that on 4 out of 6 sides, some percentage of the waste heat goes back into the refrigerator, where it will need eventually need electrical power to be removed, etc., etc.

From the viewpoint of the user of the refrigerator, this is not good design because it means that power bills will be higher than they would be otherwise.

I can see that the manufacturer would like this idea, because the internal condenser coils are much less prone to damage in shipment.

I think that a motivated EcoRenovator can do much better in designing and building a high efficiency refrigerator.

Best,

-AC

[AC_Hacker]

The inscrutable thermostat (AKA: WH7016 Ultimate) arrived today. It only took 11 days, but it feels like that many months.

Here is a photo of the unit:

The appearance of build quality looks pretty good.

Here's a photo of the top of the unit:

The silk screen matches the terminals on the back... so far we're good to go (but what are terminals 5 & 6 all about?).


There are also instructions included:

...this is where it could get sticky.

I Googled the model number and found instructions in English that appear to jive.

So I have learned that the unit is intended for Peltier Junction control (may be a problem), uses a Sensor NTC 10K / 3435 thermister for the temperature sensor, and that the display is only in Celsius (not a deal breaker) and that there is a menu system that must be used to enter the desired set-point, and upper limit set-point, and lower limit set-point, and upper-limit alarm, and lower limit alarm, and hysterisis.

Sounds interesting so far. Could turn out to be a Chinese puzzle.

More later.

-AC

[AC_Hacker]

I worked on the thermostat this morning, the menu in particular, and I found that there were actually some aspects where the where the Chinese 'manual' and the downloaded 'manual' and the menu in the device that displays on the front of the thermostat, actually agree... but then sometimes not so much.

So here is what I found out...

This is a typical display, there are two LEDs that may or may not be lit, depending on their status on the left side of the display. Right now the display is showing the temperature and neither of the status LEDs are on.


The upper LED, 'WORK' comes on whenever the internal relay is active and off when the relay is inactive.


The lower LED, 'SET' comes on whenever the 'SET' mode is active, and goes off whenever the set mode is not active.


To set the temperature to the trigger point at which you want the thermostat to turn on (or off, depending on whether you want to use this device to control cooling or heating) you push the 'SET' control once and use the up and down arrows to set the 'trigger point'. The display will return to the usual display in a few seconds after sensing no activity from the buttons.


To enter 'MENU' mode, press the 'SET' button and hold for 3 or more seconds.


I found 6 menu items, and they were: HC, P7, CA, H5, L5, and d.

This is the 'HC' menu item. press 'SET' again and you will enter the HC menu, where you will be able to choose 'HC' (for chill) or 'HH' (for heat). HC will allow you to use the thermostat for a cooling device (turning on a cooler if the target temperature is exceeded). Likewise, HH will allow you to use the thermostat for a heating device (turning on a heater if the target temperature is too low).

This is the 'P7' menu item. It is supposed to be understood as 'PT'. The range of values available was 0 through 10.

This is the 'CA' menu item and it is used for calibration. You can use this to shift the displayed temperature to agree with the actual temperature. I found I needed to use this. The thermistor was accurate at room temperature, but at refrigerator temperature, it was off by 3 degrees C or more. I was able to adjust the displayed temp to very accurately agree with a more reliable thermometer.

This is the 'H5' menu item. It is supposed to be understood as 'HS'. The range is large. With this menu item, you can adjust the upper temperature range. Possibly this can be used for an alarm?

This is the 'L5' menu item. It is supposed to be understood as 'LS'. The range is large. With this menu item, you can adjust the lower temperature range. Possibly this can be used for an alarm?

This is the 'd' menu item. It is used to adjust the hysteresis of the system. Perhaps the 'd' means 'deviation', and so allows the user to set the deviation range before the thermostat triggers, thus preventing short cycling.

[NOTE: Both the Chinese instruction manual that came with the thermostat unit and the English on-line manual indicated that there were more choices available in the menu, specifically choices for setting alarms (which could be very useful), that did not appear in the menu of the unit I received. Possibly terminals #5 & #6 that have Chinese descriptors are for an alarm.]


This is what I have uncovered so far... not yet complete.

I am still running the Freezerator with the old Teensy thermostat, and I have the WH7016 running in parallel, monitoring its readout and the status of the output relay.

When they are pretty close to equivalent, I'll switch over.

Best,

-AC

[jeff5may]

Awesome! I've seen these controllers on ebay but have yet to pull the trigger on one. Let us know how it works and if not more trouble than it's worth, I may end up using one in the next monster project. The price seems too good to be true, but if the thing actually does its job well, that would be great! I look forward to your opinions on the unit.