New Isotherm energy use testing results

[booster]

We just got a new Isotherm Cruise 85 Elegance 3.0cf frig as our old Isotherm lost capacity on the last trip. I also got the ITC digital display and control for it as it appeared it would allow no more separate wireless thermometer as the temp sensor is in the frig instead of on the evaporator/freezer. It still comes with the mechanical thermostat in place so when I wired it all for the install I put it all on watertight plugs so I can switch from the ITC to the mechanical and back if I choose in about 2 minutes through the lower vent opening.

I tested 24hr energy use with frig in the van and ready for travel so exactly how it will be used in real life. It is in the very close to always same temp shop garage so ambient is constant with no sun to deal with. The ITC was tested in automatic ITC mode and in ECO mode which is lowest compressor speed (allegedly). Most of the testing was done at 37/38* or 35* frig temp on our old wireless which we know is where like to run based on that thermometer. There are 4 one quart oil bottles flat on the middle shelf for thermal ballast and airflow disruption like food would do. Measurements were made directly to watts hours accumulated on a Wattsup energy totalizer right at the power to the frig.

Here are the results of what I saw in the various tests run.

Test 1 35* ITC set on ECO setting 360 watt hours in 24 hours

Test 2 35* ITC set on ITC automatic setting 440 watt hours in 24 hours

Test 3 35* freezer door open a couple inches ITC set on ECO 360 watt hours in 24 hours

Test 4 38* ITC set on ECO 315 watt hours in 24 hours

Test 5 38* Mechanical thermostat 290 watt hours in 24 hours

Test 6 is currently running and is test 5 repeated but with the drip tray removed.

Of further interest was that on ECO the ITC controller says it runs at the slowest compressor speed and I wondered why it was higher at 2.7 amps than our old frig on lowest speed. I found out why when I tested the mechanical thermostat that ran at 2.1 amps. How does that happen if the ECO mode is on lowest speed. Also odd that the mechanical runs that slow or old one stock ran on 2nd or 3rd speed it appeared.

So the winner for energy use is the decades (century?) old mechanical thermostat. Go figger

Do the "convenience" features of the ITC make it worth the extra energy use? Questionable at the 25 watt hour difference in power use but that difference might be substantially larger in hot conditions where you might need higher than low speed compressor running. Yes you can get high recover rate when you have charging level voltage, but you need to put into that mode so not automatic and then switch back to ECO after that voltage is back to battery voltage, so might just as well have compressor speed control knob. The remote display is nice, but never dims and is so bright it will not be good at night in a small van. The temp sensor to display calculation doesn't seem to have any damping on it so shows wild swings of 6* or more on every run cycle. The digital wireless has the sensor in a light ziploc bag to prevent water damage gives more like 3-4* swing on the ITC, so you really have no idea where the fig is between 33* and 39* for instance. The mechanical thermostat swung about 2* only. The temp compensation has to be set 2* off to get the midpoint of the ITC swing to be the actual swing midpoint based on the wireless and that mucks up the displayed temp by 2*. So based on the big downsides of the features and probably less convenient, the system we had on our old frig was more repeatable and much more user friendly.

That system was as follows.

* Mechanical thermostat from Isotherm

* 6 position compressor speed control (3 or 4 speeds would be plenty)

* Wireless digital thermometer

Based on all of the above, the old school mechanical blew away the ITC, IMO.

Extremely surprised and disappointed in the performance and convenience of the ITC.

Questions, comments and suggested welcome as I think this really an odd thing to have happen.

We will be using the mechanical thermostat as is until this winter and then I will make a new compressor speed control and on/off switch for it and install them while removing the ITC.

 

[rowiebowie]

Interesting (and I agree disappointing) results. Especially Test 2 Auto setting was worse than Test 3 freezer door open.

EDIT: I originally assumed a two-door fridge meaning an exterior door open. My wife corrected me that you probably had the interior freezer flap open. I had always wondered it this would help my fridge by circulating cold air better, but now I guess it wouldn't based on your results.

 

[GeorgeRad]

Were your tests done at charge voltages? Did you test the overcooling mode?

Control response time with the capillary bulb is likely faster than with the temperature sensor inside the fridge. This could be the reason for lower energy use. The freezer plate could have larger temperature swings with electronic control.

 

[booster]

Interesting (and I agree disappointing) results. Especially Test 2 Auto setting was worse than Test 3 freezer door open.

EDIT: I originally assumed a two-door fridge meaning an exterior door open. My wife corrected me that you probably had the interior freezer flap open. I had always wondered it this would help my fridge by circulating cold air better, but now I guess it wouldn't based on your results.

Yep, internal door. The entire evaporator/freezer area is totally different than our old one. It has a slotted plastic box around it instead of the typical bare evaporator box and the drip tray underneath also has holes (baffled for no water leaks) through it for airflow. The freezer door on the old one fit very poorly so didn't really seal much at all which may have been intentional on that one as removing the solid drip tray made the frig run much cooler in the frig area. The new on only changes a few degrees colder on the mechanical thermostat.

 

[booster]

Were your tests done at charge voltages? Did you test the overcooling mode?

Control response time with the capillary bulb is likely faster than with the temperature sensor inside the fridge. This could be the reason for lower energy use. The freezer plate could have larger temperature swings with electronic control.

All ICT auto tests were run with the battery charger on set to 13 volts as that is what it is intended for to cool quicker when the power is available.


The ECO and mechanical tests were done on battery voltage, that range from 12.8 to about 12.6v over the testing until I would recharge if needed.


I actually expected the mechanical to have a bit higher than it did as it so hard to match the positioning to match the lag lag times for the cold to reach the frig section, so they have done a really good job on that part. I don't know if the setpoint will change as frost builds up on the evaprator at this point as we will need to in and out of it in use to really know. The old frig would always need a couple of degree adjustment after 3-5 days and if we defrosted we then had to go back to the original setting. Moving the bulb to a warmer area also totally changed the range we would see on the old one but had little effect on the power use.


I did not test the overcooling as we really would not want the frig that cold for extended times like long drives and many users stated they had trouble turning it off and t would do that even on ECO, although I think they may been just seeing the very wide on/off temp range which is really odd to watch on the display. It is not an easy on off of the overcooling feature as it is deep in the settings menus so I just didn't even try it at all.


Does anyone know if the new Secop compressors use the same resistor values as the older ones for speed control?

 

[GeorgeRad]

Is your new fridge rear view similar to mine which is 85l Isotherm Cruise from 2013. I replaced the factory fan with this quieter and more efficient fan.

 

[booster]

Is your new fridge rear view similar to mine which is 85l Isotherm Cruise from 2013. I replaced the factory fan with this quieter and more efficient fan.

Yep, I think the 85s have had that since at least 2010.


Did you check the actual amp draw on the old and new fan? I didn't change the fan but did check the old one that was rated at .24 amps but checked at nearer .12amps when I checked it. The .03 amp rating on the one you used is so low already, better wouldn't mean much. Saving .1 amp would be about 2.4ah so no very much, but certainly would be less.


Have you done a 24 hr use on yours?


I just ordered the parts to build a new speed control and on/off switch panel that I will try to mount in the ITC box on the kitchen side splash already. Bummer is that the wiring up it is already caulked up.


You must have the inconvenient center pull door like ours that DW can't pull hard enough with handle up to move so she has to use a second hand on the door edge. But maybe the thick door has been added since yours was made.

 

[dicktill]

<snip>
There are 4 one quart oil bottles flat on the middle shelf for thermal ballast and airflow disruption like food would do.
<snip>

Hey you got a new oil cooler!

 

[GeorgeRad]

Yep, I think the 85s have had that since at least 2010.


Did you check the actual amp draw on the old and new fan? I didn't change the fan but did check the old one that was rated at .24 amps but checked at nearer .12amps when I checked it. The .03 amp rating on the one you used is so low already, better wouldn't mean much. Saving .1 amp would be about 2.4ah so no very much, but certainly would be less.


Have you done a 24 hr use on yours?


I just ordered the parts to build a new speed control and on/off switch panel that I will try to mount in the ITC box on the kitchen side splash already. Bummer is that the wiring up it is already caulked up.


You must have the inconvenient center pull door like ours that DW can't pull hard enough with handle up to move so she has to use a second hand on the door edge. But maybe the thick door has been added since yours was made.

I didn’t check fans current actual draws, based on specs B12-3 fan drew 0.02A less, not much (0.17 vs 0.19A). https://www.blacknoise.com/datas/downloads/datasheets/TData_eloop120_122012_de.pdf.

I did measure sound reduction with the new fan by finding distance to fans at even noise levels, based on this measurement new fan is 50% quieter (4.25” vs 6”).

SEC reduced noise by elimination of annoying clicking of the mechanical thermostat relay, and maybe by soft start.

I never did a 24hr test, usually rely on getting batteries back to full charge by midday at a reasonable solar exposure. With the evening draw of 1.5hr. 100W projector (9Ah), water heater (3Ah), (it is diesel but it has coolant motor and 8A glow plug), heater (2Ah), lights (2Ah), misc. charges and the fridge I am at about 85% SOC in the morning, so it is about 35Ah total, minus (9+3+2+2=16) = 19 Ah for fridge-night, which is about 38 Ah per day.

I have side door opening latch, change the front to brushed aluminum.

Good luck with your control. Are you planning soft start as well?

 

[booster]

I had to go back and see where I got the .03amp for your fan. I had looked at your original post a while ago with an Amazon link and the box shown in the pic shows .03, but it is for a 12-1. Post modified. Yep not enough change at all even though the on you got would probably test under .1 amp.

 

[booster]

OK, I think I am done testing the frig as test #6 just finished this morning. This was a repeat of test 5 explained in earlier posts, but with with drip tray removed. Test 5 was our least energy use test at 290 watt hours per 24 hours.

It ran fine with nice close 2* temp range so all good that way.

I ran this test because when I originally tested our old Isotherm I did this test for a reason I don't recall actually and found a decrease in energy use big enough to get me to make a cold air passing drip tray that worked well but was to fragile for the road, it turned out. The new frig has a similar ventilated drip tray so I expected the increased efficiency to be much smaller or not there at all.

It did turn out to improve efficiency quite a bit and we aren't at the 41-43* temp or our old tests (that is what Isotherm rates them at) but at the 37-38* we run in the real world.

The power use dropped from the 290 of the last test to 265wh per 24hr which is only 22ah at the 12.4v we were at on batteries which is really quite good, I think.

I wondered what the freezer temp would do as it would have to go up for that kind of change to happen to the efficiency (warmer evaporator helps efficiency). The freezer ran at about 6* in the other tests and in test 6 and it only went up to 15* so that is also fine for us if we need to do this in real use. The freezer door on this frig fits much better than the old one did so the whole freezer was at 15* where the old one would be above freezing at the door end when the tray was out. I don't see us ever needing to this, but it is what saved our last trip by getting the old frig just cold enough to let us use it, even though it ran 24/7. We couldn't even get ice as the entire area was sold out because it was unseasonably warm there.

Bottom line is that the mechanical thermostat outperformed the ITC easily in both temp holding variations and energy use when forced to run in the lowest compressor speed like we did 98% of the time with the old frig. Speed control is easy to add on like we did on our old frig.

After all this testing and expense of the ITC we are going to wind up with essentially the same setup as we did on old frig. Mechanical thermostat and homemade speed control and on/off switch. Very disappointed in the ITC performance and even more with very, very, inaccurate information that Isotherm gives for the ITC. Maybe the ITC would get better energy use numbers if you use the overcooling, but lots of others have had issues with overcooling working correctly and with the horrible temp control the ITC has I wonder if it would be capable of cooling as cold as they say without freezing stuff because of the poor temp ranges.

With the extra insulation on the outside of the box, good ventilation, and compressor speed control it is easy to beat the Isotherm 24 hour spec of 380wh per day, but they were at different test points of 77* ambient and 41* box temps and at whatever speed the mechanical thermostat runs the compressor at.

 

[GeorgeRad]

OK, I think I am done testing the frig as test #6 just finished this morning. This was a repeat of test 5 explained in earlier posts, but with with drip tray removed. Test 5 was our least energy use test at 290 watt hours per 24 hours.

It ran fine with nice close 2* temp range so all good that way.

I ran this test because when I originally tested our old Isotherm I did this test for a reason I don't recall actually and found a decrease in energy use big enough to get me to make a cold air passing drip tray that worked well but was to fragile for the road, it turned out. The new frig has a similar ventilated drip tray so I expected the increased efficiency to be much smaller or not there at all.

It did turn out to improve efficiency quite a bit and we aren't at the 41-43* temp or our old tests (that is what Isotherm rates them at) but at the 37-38* we run in the real world.

The power use dropped from the 290 of the last test to 265wh per 24hr which is only 22ah at the 12.4v we were at on batteries which is really quite good, I think.

I wondered what the freezer temp would do as it would have to go up for that kind of change to happen to the efficiency (warmer evaporator helps efficiency). The freezer ran at about 6* in the other tests and in test 6 and it only went up to 15* so that is also fine for us if we need to do this in real use. The freezer door on this frig fits much better than the old one did so the whole freezer was at 15* where the old one would be above freezing at the door end when the tray was out. I don't see us ever needing to this, but it is what saved our last trip by getting the old frig just cold enough to let us use it, even though it ran 24/7. We couldn't even get ice as the entire area was sold out because it was unseasonably warm there.

Bottom line is that the mechanical thermostat outperformed the ITC easily in both temp holding variations and energy use when forced to run in the lowest compressor speed like we did 98% of the time with the old frig. Speed control is easy to add on like we did on our old frig.

After all this testing and expense of the ITC we are going to wind up with essentially the same setup as we did on old frig. Mechanical thermostat and homemade speed control and on/off switch. Very disappointed in the ITC performance and even more with very, very, inaccurate information that Isotherm gives for the ITC. Maybe the ITC would get better energy use numbers if you use the overcooling, but lots of others have had issues with overcooling working correctly and with the horrible temp control the ITC has I wonder if it would be capable of cooling as cold as they say without freezing stuff because of the poor temp ranges.

With the extra insulation on the outside of the box, good ventilation, and compressor speed control it is easy to beat the Isotherm 24 hour spec of 380wh per day, but they were at different test points of 77* ambient and 41* box temps and at whatever speed the mechanical thermostat runs the compressor at.

https://www.indelwebastomarine.com/...heets/ITC-Intelligent_Temperature_Control.pdf

Based on your test data I should run my 24 hrs. test. It seems as SEC and ITC use different algorithms and ITC is focused on energy savings. My capillary thermostat is gone so I can’t compare SEC to capillary but having more accurate numbers would be helpful.

 

[booster]

https://www.indelwebastomarine.com/...heets/ITC-Intelligent_Temperature_Control.pdf

Based on your test data I should run my 24 hrs. test. It seems as SEC and ITC use different algorithms and ITC is focused on energy savings. My capillary thermostat is gone so I can’t compare SEC to capillary but having more accurate numbers would be helpful.

Yep always nice to know where you are on use for future reference, also for knowing how much the frig is taking.


Do you have a digital thermometer in it all the time?


I just looked at the manual for the SEC and came to conclusion you would have be Italian to understand what it says. Maybe it lost some clarity in the translation. When it does what temps and what differentials was pretty confusing to say the least. It does look like some of the differentials are around the 6*F that I saw with ITC though and a lot of DIP switch functions are very similar to what is in the ITC. I wondered why a digital set controller had 2* increments and I think I know know because some of the DIP switches in the SEC change about that much, or maybe it is a calc from *C.


It will be interesting to see what you get for energy use in the different modes that you use when traveling and what the temps and swing is.

 

[GeorgeRad]

I don't have built in digital thermometer, rather low science - it is cold and not frozen.

I found Isotherm manual difficult to digest as well. I talked with them about their units in 2013 but got nowhere. https://www.indelwebastomarine.com/...-100-l/cruise-85-clean-touch-stainless-steel/

Energy consumed listed as 368[W/24hrs].

 

[booster]

I don't have built in digital thermometer, rather low science - it is cold and not frozen.

I found Isotherm manual difficult to digest as well. I talked with them about their units in 2013 but got nowhere. https://www.indelwebastomarine.com/...-100-l/cruise-85-clean-touch-stainless-steel/

Energy consumed listed as 368[W/24hrs].

Time to buy a cheap indoor/outdoor wireless thermometer?



I will expect you to do better than the 368 with the extra insulation it looks like you have.

 

[booster]

A little more on the drip tray test, which may or may not be of real world usefulness or not.


Here is what the drip tray in our new Cruise 85 Elegance looks like, and it is pretty odd to be sure.

Isotherm has apparently decided to come off of the old bare evaporator hanging in a box design model, although I do think their older frigs used the drip tray to restrain too much cold air dropping off the evaporator as it almost totally sealed the bottom area from airflow.


Here is how they changed the evaporator area. The left side and top are essentially tight to side and back of the box and not much room for airflow. Those areas don't have the plastic covers, and neither does the bottom. Most of cold air out would be coming down through the tray after entering as warmer air from the box. The drip tray is still used to close off the area under the evaporator and make the air go through the holes and slot.

This all makes it appear, based on our testing, that the freezer temp (and that also would be the big factor in efficiency changes) could be tuned by letting more air through to raise the freezer temp relative to the frig section. Like your ice cream rock hard reduce airflow. Want to get the freezer temp and high as possible to save energy use, increase the airflow. The airflow change could all be done with the tray, I think, on this frig.


I probably won't mess with it unless I get bored sometime with nothing better to do, as we have lots of batteries and plenty of charging capacity from 3 sources. The 2-3ah per day removing the tray in the latest test is pretty insignificant to us, unless we ran into a frig failure and capacity loss issue like we did on our last trip. Long term off grid, low power use, small battery bank folks might find it worth while to mess with.


It is likely pretty easy to be able to determine if messing with the airflow from the evaporator to frig would help or not. If the freezer is colder than you deem essential, you probably could do something to increase it with airflow and save some energy. Adding a small fan would probably work but use as much power as you save. Past testing on our old frig turned out that way both for a fan on the evaporator or on the condenser area (condenser area made no saving, only loss, as the ducted air works well. Ours without the tray stabilized a bit higher than initially and was in the 17* range at the end. I would be OK with 25* as we only do short term storage in it to keep it from spoiling and that should do that OK. If this frig was at 25* freezer and 38* frig it would probably go under 20ah per day at 12v or 240 watt hours/day.


It would be interesting to see if other compressor frigs increase efficiency by removing the tray, but it would depend on the design of the frig. A quick test can be done to see if a temp increase has helped efficiency by simply reading the running amps before and after the change, at the same compressor speed. If the amps go up (yes up because the higher efficiency comes with higher evaporator temp) it probably helped and the run time % would drop similarly.

 

[GallenH]

Booster: What exactly caused the loss of capacity in your old fridge and how old was it? thx.glenn

 

[booster]

Booster: What exactly caused the loss of capacity in your old fridge and how old was it? thx.glenn

Undetermined at this point, but in hindsight even the trip before we a few odd temps in the frig which we never did before, but then it went fine for long periods. We had one such "healing" on the last trip before it went bad and stayed there. Maybe some sort of checkvalve or something sticking because the compressor runs, cooling fan runs but doesn't cool well and compressor runs barely above ambient. No funny noises, either.


It is about 10 years old, so I would call that a bit early, I think.

 

[booster]

I figured I would bring this up again as I ran across something I missed in the midst of all the testing, while I was starting to put together our new speed control and on/off panel parts to install this winter.


The Isotherm description of the ECO function on the ITC says something like it "runs the compressor at the most efficient speed all the time, but might not always be able to keep up with the cooling load". To my engineer brain that means it runs at the most efficient speed for the compressor, which in the Danfoss compressors is the slowest spreed of 2000 rpm. At 2000 it has the highest watt removal of heat per watt of energy used and has the lowest heat removal capacity per the actual Danfoss compressor data sheets. As it turns out that was not the correct conclusion because the ECO mode runs the compressor at 2500 rpm, which is the 3rd speed out of the 6 listed in the Danfoss speed vs speed resistor value chart. 2500 is not as efficient as 2000 per all the Danfoss literature.


This explains why I saw the higher amps than expected on ECO mode in the testing.


The only thing I can think of is that the ITC seems to be able to be used for multiple frigs of different sizes, including ones with the bigger BD50 compressor, so they must have set the compressor speed higher so it would be able keep up most of the time in the larger ones. Our 85L on with extra insulation and good ventilation easily can run at 2000rpm 95+% of the time so 2500 just wastes energy.


All and all just another reason for us to change back to mechanical.


About all the ITC has over the mechanical thermostat with speed control, for us, is the soft start, built in display, and maybe some reliability. I does most everything else worse.

 

[avanti]

I have never gotten around to looking at this stuff carefully. Am I correct that if @Michael added the ability to control the compressor speed to his awesome project, he could do pretty much anything he wanted wrt efficiency/cooling tradeoffs?

The less ambitious of us could use a tiny microprocessor--just enough to flip the speed inputs, measure temperatures, and maybe a little display. It would essentially be an Isotherm that could be made to work exactly to one's taste.

Is this in any way harder than it looks?