Absorption vs Compressor 'fridge?

[booster]

Originally Posted by rowiebowie

I have only tested running consumption (41 watts/3.154 amps) on my battery monitor and I've not tried to test consumption over a 24 hr period.

I have constant readout temmometer with a probe behind the fridge and a 16CFM squirrel cage fan on a 100 degree on/ 80 degree off button thermostat that vents the cavity through a tube to the rear lounge area of the van. But since we camp in mild weather, it rarely runs. I have also improved lower venting since Airstream provided none in the initial build. Top ventilation (barely adequate) is supplemented by my fan.

The following is anecdotal:
The fridge runs very silently so I can only really hear it run at night while in the bathroom where the sound comes through the fiberglass shower wall. It's only when the compressor turns off that I notice the silence, because being off is that rare.

Don't know if our home fridge is comparable, but while it cycles more like 1/3 on 2/3 off, it never cycles off for more than 30 minutes. And during our February deep freeze power outage, the interior temp of our home fridge rose from 37 degrees to the low 40's in less than 2 hours with the doors remaining closed.

I would have thought an undisturbed home fridge could go 8 hours before losing more than 5-10 degrees so long as doors remain closed. But this has made me think that manufacturers decided that since their fridges run efficiently, that they decided to skimp on insulation and just run longer.

You run numbers, if you are an 66% run time would indicate a bit over 50ah at the 12.5v most of actually run at with lead acid batteries which is a comparison I can relate to easier. Your amps and watts would indicate you were running at 13v.


That said, with 41 watts and 66% run time you would use a bit over 650 watt hours per day which would be over 50ah at 12.5v for instance. That may or may not be on the high side based of frig size and the temp in the frig and temp of ambient in the area. For comparison, the test I just finished of our new frig ran at 360 watt hours over a 24 hour period. That is with frig temp reading 34*-35* and a room temp of 72* average. I am currently warming up the frig to run the next temp at 39*-40* to see what the difference is. The Isotherm ratings are at 41* frig temp and 77* ambient IIRC. I expect it to be quite a bit, but we will see, as this frig is designed differently in the evaporator/freezer area and it seems to make how it reacts different from the old on.


I like to get this testing done on a new frig so I have it not only for energy use predictions, but also so if the frig seems to be acting up in the future I can easily test it to see if it really is. The testing takes some time to run, but it is easy to as you just reset the AH/watt counter once the frig is at temp and let it run.


I haven't found good correlation with our home frig on our RV ones. It is probably that the home ones are designed to operate over a narrower range and have things like auto defrost. I think they also tend to put internal space as a higher priority than insulation as it sells better.

[booster]

I just noticed I got rowie's run time reversed. We are really looking at somewhere in the 330whr per 24hr period depending on what his actual voltage is with lithium, I used 13v. That would be in the 26-27ah per day range if it were lead acid batteries above 50% full.


Much more typical of what see in most compressor frig installs with decent ventilation in moderate temps.


My bad...

[ks@yvr]

I just ran a test on my Novakool 4.6 cu ft fridge for power consumption over a 24 hour period. The ambient temperature is very hot right now and has been 80-90’F. I filled the fridge 1/2 full of liquids that were at room temperature and turned on the fridge to cool to 36’F. My fridge draw was 3.5-4.3 amps at 13.2 V on a 200 a/hr lithium battery. Nothing else was running except the fridge. My fridge also has a cooling fan on the compressor and an extra layer of thinsulate insulation on the sides, top and bottom in addition to the insulation provided by Novakool. The 24 hour draw was 35.4 a/hrs (avg 1.475 amps/hr) which would lead me to believe around a 33% duty cycle over 24 hours. (467 watts/24 hours)

[booster]

Originally Posted by ks@yvr

I just ran a test on my Novakool 4.6 cu ft fridge for power consumption over a 24 hour period. The ambient temperature is very hot right now and has been 80-90’F. I filled the fridge 1/2 full of liquids that were at room temperature and turned on the fridge to cool to 36’F. My fridge draw was 3.5-4.3 amps at 13.2 V on a 200 a/hr lithium battery. Nothing else was running except the fridge. My fridge also has a cooling fan on the compressor and an extra layer of thinsulate insulation on the sides, top and bottom in addition to the insulation provided by Novakool. The 24 hour draw was 35.4 a/hrs (avg 1.475 amps/hr) which would lead me to believe around a 33% duty cycle over 24 hours. (467 watts/24 hours)

Did you let the liquids get to stabilized temperature before running the test time. If not, you readings are probably quite a bit higher than steady state would be. I have 4 one quart engine oil bottles lying down on the second shelf, so large heat capacity and help simulate air blockage by food. It probably takes close to 24 hrs before the liquids are at average inside temp, it appears, as that is when the energy use goes flat. This is during my current testing of our new Isotherm 3.1cf model. With 38-39* in the frig by our wireless thermometer we have used for years in old Isotherm also and a 75* no sun garage it is running about 310wh/24hr on the last test time.


I assume it was outside? If so how cool did it get overnight?

[ks@yvr]

I did not let the liquids get to a stabilized temperature first. They were room temperature and I let the fridge cool as it got to the correct temperature. The overnight local temperatures did not drop below 80 so the conditions were on the hot side. So you are correct that the energy use was probably higher than if I had started out with chilled items. The freezer had frozen a couple of water bottles overnight but I was trying to get a read on how much energy I would use in a hot zone. I was impressed with the consumption and thought the numbers were very reasonable given that I made the refrigerator/freezer cool and freeze the liquids.

This was with the van outside on my driveway in the sun during the day and only awning windows open and maxair open but turned off. Not sure what the inside van temperature was but with its insulation and awning windows open it doesn’t get too hot on the inside.

[booster]

Originally Posted by ks@yvr

I did not let the liquids get to a stabilized temperature first. They were room temperature and I let the fridge cool as it got to the correct temperature. The overnight local temperatures did not drop below 80 so the conditions were on the hot side. So you are correct that the energy use was probably higher than if I had started out with chilled items. The freezer had frozen a couple of water bottles overnight but I was trying to get a read on how much energy I would use in a hot zone. I was impressed with the consumption and thought the numbers were very reasonable given that I made the refrigerator/freezer cool and freeze the liquids.

This was with the van outside on my driveway in the sun during the day and only awning windows open and maxair open but turned off. Not sure what the inside van temperature was but with its insulation and awning windows open it doesn’t get too hot on the inside.

Those numbers are really quite good for a 4.6cf from what I recall seeing about others of similar size in Novakool. How thick is the Thinsulate?


Does your battery/power monitor allow you to set it for watt hours. Especially now with lithium and lead acid batteries both being used and talked about, watt hours get to be a better comparison unit because the running voltages are different and in lead acid can be quite different day to day.

[MsNomer]

I’m honestly surprised that absorption fridges are even made or being considered anymore now that compressor fridges have become so efficient.

[booster]

Originally Posted by MsNomer

I’m honestly surprised that absorption fridges are even made or being considered anymore now that compressor fridges have become so efficient.

Efficiency doesn't mean no more extra energy use, and that has to be able to be provided and then replaced, so there probably will be market for absorption for quite a while as more no generator and no idling rules go into affect. To replace the energy it means going for drive or solar and good sun which sometimes isn't possible or not wanted to do for whatever reasons. Probably will be mostly hardcore boondockers for the most part.

[ks@yvr]

I had no issues with the absorption fridges we have had - only you had to make sure you were more level than with a compressor fridge and they did take much longer to reach operating temperature but once there they were fine. They also need good airflow where the refrigeration coils are on the outside to cool properly. There are a number of things you can do to improve performance that some manufacturers now incorporate in their products that you can also add after the fact.

Boosters Question: our Thinsulite is 2” compressed to 1” on the sides, top and bottom. Our guage doesn’t give a watt/hr reading but it is easily converted as the voltage is 13.2 V

[booster]

Originally Posted by ks@yvr

I had no issues with the absorption fridges we have had - only you had to make sure you were more level than with a compressor fridge and they did take much longer to reach operating temperature but once there they were fine. They also need good airflow where the refrigeration coils are on the outside to cool properly. There are a number of things you can do to improve performance that some manufacturers now incorporate in their products that you can also add after the fact.

Boosters Question: our Thinsulite is 2” compressed to 1” on the sides, top and bottom. Our guage doesn’t give a watt/hr reading but it is easily converted as the voltage is 13.2 V

Does the lithium hold that 13.2v for the whole 24 hrs?

[ks@yvr]

Yes it holds 13.2 until it drops below about 20% SOC remaining then gradually drops in the 12V range. For my test it stayed at a steady 13.2V. Much more stable power with Lithium over AGM batteries in the summer at least.

We get about 3-4 days out of the Lithium before we must recharge them by driving or shore power. We don’t have solar at this point but I did prewire for it should I decide to add later. We run the fridge, led lights, an induction cooktop and very occasionally microwave off the Lithium batteries 2x100 ah and boil water for coffee/tea with a tabletop propane water turbo boiler. I will probably add another 100 ah battery before adding solar to get a couple more days power. We easily go 3 days and have gone 4 but we are around 10-15% SOC on day 4 the 2 times we have gone this long. The batteries recharge quickly while driving and are fully charged after 3-4 hours driving time.

[eric1514]

Originally Posted by MsNomer

I’m honestly surprised that absorption fridges are even made or being considered anymore now that compressor fridges have become so efficient.

What you see in other forums, specifically the Forest River forum of which I am a member, is a lot of resistance to compressor fridges. IMHO, this is because of several factors.

1) There is a lack of differentiation among users between true residential refrigerators, those that are built for stick homes that find their way into RVs and mobile refrigerators built for RVs like campers or boats. Every refrigerator with a compressor is a residential fridge regardless. Many refrigerators in large RVs are Whirlpools or GEs running on inverters and they suck juice. Many are also very cheaply made units like Everchill or Furrion because of cost savings and they are not reliable.

2) RV manufacturers give compressor fridges a bad rep because, especially now with supply chain issues, they are installing compressor fridges in place of harder to get absorption fridges without supporting them with the necessary electrical and shoddy ventilation. Many refrigerators are installed with 1 grp 24 marine battery and 100 watts of solar. When the fridges don't cool longer than a few hours, most owners blame the fridge because the absorption fridge running on propane would have been fine for a couple of days.

3) New owners are finding they need to spend more on batteries and charging after the purchase and they're not happy. Couple that with the general lack of knowledge among the huge base of new users about how to maintain those batteries and now they're really mad because their fridge that worked last year won't work this year because the batteries were neglected over the winter.

In general, most new RV owners prefer absorption refrigerators because they're easier to use even if they don't work as well and compressor refrigerators are difficult to use and don't work at all in many cases.

[GeorgeRa]

Originally Posted by eric1514

What you see in other forums, specifically the Forest River forum of which I am a member, is a lot of resistance to compressor fridges. IMHO, this is because of several factors.

1) There is a lack of differentiation among users between true residential refrigerators, those that are built for stick homes that find their way into RVs and mobile refrigerators built for RVs like campers or boats. Every refrigerator with a compressor is a residential fridge regardless. Many refrigerators in large RVs are Whirlpools or GEs running on inverters and they suck juice. Many are also very cheaply made units like Everchill or Furrion because of cost savings and they are not reliable.

2) RV manufacturers give compressor fridges a bad rep because, especially now with supply chain issues, they are installing compressor fridges in place of harder to get absorption fridges without supporting them with the necessary electrical and shoddy ventilation. Many refrigerators are installed with 1 grp 24 marine battery and 100 watts of solar. When the fridges don't cool longer than a few hours, most owners blame the fridge because the absorption fridge running on propane would have been fine for a couple of days.

3) New owners are finding they need to spend more on batteries and charging after the purchase and they're not happy. Couple that with the general lack of knowledge among the huge base of new users about how to maintain those batteries and now they're really mad because their fridge that worked last year won't work this year because the batteries were neglected over the winter.

In general, most new RV owners prefer absorption refrigerators because they're easier to use even if they don't work as well and compressor refrigerators are difficult to use and don't work at all in many cases.

Good summary, absorption fridges will prevail in majority RVs for years to come. A 10 CuFt fridge consumes about 1.5 lb. of LP per day so 13 days on one 20 lb. tank. With most of RV appliances running one LPG energy system which runs stove, oven, furnace, water heater, and a refrigerator, I believe LPG will stay in the RV world for a while.

B class is unique and very different than typical RV, most RV don’t have Li batteries, nor diesel water heaters, nor gasoline furnaces etc.

If I would do another conversion, I would reanalyze some of the tradeoffs such as electrical overhead for a compressor fridge vs van leveling with LP fridge, or simplicity of LPG vs maintenance hungry diesel appliances.

[Bud]

It seems as though Class B RV's provided the worst reputations for absorption vs C and A. I'm guessing because of venting being the worst vs C and A.

Bud

[booster]

Originally Posted by GeorgeRa

Good summary, absorption fridges will prevail in majority RVs for years to come. A 10 CuFt fridge consumes about 1.5 lb. of LP per day so 13 days on one 20 lb. tank. With most of RV appliances running one LPG energy system which runs stove, oven, furnace, water heater, and a refrigerator, I believe LPG will stay in the RV world for a while.

B class is unique and very different than typical RV, most RV don’t have Li batteries, nor diesel water heaters, nor gasoline furnaces etc.

If I would do another conversion, I would reanalyze some of the tradeoffs such as electrical overhead for a compressor fridge vs van leveling with LP fridge, or simplicity of LPG vs maintenance hungry diesel appliances.

I would certainly do the same analyzing of all the new stuff if we got another van (very unlikely I think). As all the newer components come out I always seem to wind up thinking they might be a good thing, but mostly there always seem to be downsides that overway the better parts, at least for us. One exception for us were the compressor frig as we so hated the absorption one, probably also related to how we travel, though, with lots of unlevel parking etc. A second was the ditching of the Onan generator and replacing with batteries as there was only one advantage with the Onan and that was off grid air conditioning that we almost never needed. The battery/inverter upgrade to handle the few higher power use things came with that change as we then had room for the batteries.


The only real failures we have had in traveling have been electronics with the Suburban furnace board and Fantastic fan being the most inconvenient. Having a fully multiplexed complex electrical system that controlled everything would increase the failure rate of that kind of issue be a lot, I think, and if it went down you lose everything not just one item.


Back to compressor frigs as I am near completion of my testing of our new Isotherm 3cf Cruise 85L frig. Most of the testing concerns the ITC control which is the latest of their energy saving electronic energy saving themostatic setups. I will be doing a thread on that testing shortly, but as it looks right now I think the results are going to be very surprising to me and maybe some others. I am very glad we were in a slack period in our schedule so I have had the time to do the testing thoroughly as it will make our using the frig easier with less surprises. Each test point takes more than a full day, so it has dragged out for a long time, but at least the time isn't lost as it is untended for the most part during 99% of the test.

[RT-NY]

Originally Posted by MsNomer

I’m honestly surprised that absorption fridges are even made or being considered anymore now that compressor fridges have become so efficient.

It depends on if you are talking about a new (very expensive!) class B or a vintage rig. And, as the OP mentioned, on how often you boondock. Adding (and maintaining) enough battery/solar to run even a very efficient compressor for a week to a vintage RV is a major project/expense. With propane, it is no problem at all. And, at least in my 1999 RT 170, I have never run into any issues with leveling.

As with all of the passionate debates on this forum, there is no right answer. It is just a matter of matching what you need with what is available and what the costs are. Obviously, the "best" option is going to look very different when approached with a budget of several thousand dollars as compared to a budget of a few hundred.

[Davydd]

Originally Posted by booster

Efficiency doesn't mean no more extra energy use, and that has to be able to be provided and then replaced, so there probably will be market for absorption for quite a while as more no generator and no idling rules go into affect. To replace the energy it means going for drive or solar and good sun which sometimes isn't possible or not wanted to do for whatever reasons. Probably will be mostly hardcore boondockers for the most part.

Anyone with lithium batteries and experience will tell you you idling for charging them is not a normal routine if you have a second alternator. You have fallen for the old Roadtrek Etrek promo garbage which I guess lives to this day. I just spent three days in the Minnesota north woods boondocking and had my batteries fully charged in under an hour coming home—no idling, no driving, no solar and an Isotherm compressor 115 liter refrigerator in our stay.

If you invest in lithium you should have over 200ah, preferably over 400ah and when you get over 400ah then a second alternator instead of a propane generator to efficiently charge them and many times an excursion to a restaurant, trail head, etc. will do. Experienced Class B RVers quickly learn that idling is just an emergency last resort and not a normal activity. If more idling rules go in effect in campgrounds the propane generator users with low amp hour battery systems will be affected more regardless of refrigerator type.

The compressor refrigerator is the key to dumping propane altogether. If you boondock you will encounter more un-level sites which make a compressor refrigerator better for that situation.

Placement of a compressor refrigerator does not rely on an outside wall and the tell tell placement of vents cut into the van walls up and down. They aren’t three-way requiring change over in driving, boondocking or shore power and constant adjustment to control temperatures with the varying power efficiencies. In a month on the road, I haven’t touched the controls of my Isotherm compressor refrigerator.

With better batteries and more amp hours the compressor refrigerator will be the norm in Class B’s, IMO. Boondocking is becoming more prevalent as the idea of Harvest Host and Boondockers Welcome fast taking hold for what Class Bs do—touring and remote locations. The best way to achieve that is higher amp capacity and in Class Bs that means lighter batteries than lead-acid.

[Bud]

"With better batteries and more amp hours the compressor refrigerator will be the norm in Class B’s, IMO"

Isn't that true Now?

[booster]

Originally Posted by Davydd

Anyone with lithium batteries and experience will tell you you idling for charging them is not a normal routine if you have a second alternator. You have fallen for the old Roadtrek Etrek promo garbage which I guess lives to this day.

IMO, this is not correct. What you have given as reason/example is based on how YOU use YOUR system and is necessarily representative of anyone else's use pattern and system. If you are sitting without some stationery replacement charging like solar and don't drive you will run out of power and lithium has nothing to do with it. If you are a heavy user of power like the amounts you have stated in the past about usage in your previous van in the 300ah per day, you will run out in however many days it takes to deplete the batteries, which in your previous van would have been under 3 days IIRC. You would need to have shore power, drive, or use idling to recharge. That is just how it works, energy out/energy in most balance.


I have not fallen for anyone's promo or lies on this IMO. You now have 600ah of lithium, I think, so how many days can you sit without driving or idling? Does everyone drive that often?

[Davydd]

Originally Posted by booster

I have not fallen for anyone's promo or lies on this IMO. You now have 600ah of lithium, I think, so how many days can you sit without driving or idling? Does everyone drive that often?

Have you any experience with lithium ion batteries, second alternators, or auto generation of them?

I just told you of my 3 days parked experience. I have 460ah or 80% of 576ah available to use and I used 300ah over 3 days. I have a newer extremely efficient van with newer lithium ion technology in many ways where I no longer need to have an inverter on to operate electric articulating beds and the Isotherm refrigerator is proving way more efficient that my previous Nova Kool. I still have to turn on the inverter temporarily to use the microwave, induction cooktop and Kuerig coffee maker but that is for a very short time. I get over the air and cable TV via cell phones and tablets sans 120v TV. So, no built-in TV.

Three days seems to be my impatience to get moving and have settled for less amp hours than my previous van as I seldom used air conditioning which would have required a 3500 chassis instead of a 2500 to get the proverbial overnight. As a tourer and not sit camper the Class B is more ideal than any other RV. If you want to sit and just drive to destinations, then a more spacious RV will be desirable especially for families. Seems many of the so called “YouTube influencers” have moved up to Class Cs.

Battery technology is improving rapidly and getting cheaper and more desirable that engine and fossil fuel technology. They have a distinct advantage for space and weight savings. Lead-acid will be relegated to low use power old school, old vans and will be looked at as an arm tied behind your back with anyone wanting to buy a new Class B of seemingly over $150,000 now.

Propane adds weight and space where batteries could be of better use or in my case since batteries are inside the van now I get more fresh, gray and black tank capacity than any other 2500 short Sprinter van on the road that I am aware of. Onan generators add weight and especially space in otherwise better use of that space. I’ve had vans with Onan generators, wet-cell lead-acid and AGMs. I would never go back. I also desired to go non-dually and could not do all that without lithium ion batteries. I still wanted a Class B van where I didn’t have to take a shower or poop and pee in the living space. I also didn’t want a van where you had to make either/or conversion of space decision of sleeping or staying up.