Advancing Alvar

[avanti]

Booster,
Remind us what fridge you have. Do you have outdoor vents?

 

[Bud-ClassB]

Booster,
Remind us what fridge you have. Do you have outdoor vents?

It must be a booster system.

Bud

 

[booster]

Booster,
Remind us what fridge you have. Do you have outdoor vents?

We have an Isotherm approx 3 cubic foot model. The Isotherm frigs are a bit different than most other ones in that they have small rectangle that is the compressor and condenser coils, with a built in small fan that cools the compressor and coils together. Most other models are gravity off normal, back of the frig, condenser coils, with maybe a fan on the compressor only. There are shortcomings to both systems all related to airflow over the coils, compressor, and out of the area of the frig. The problem with ours was air looping back into the fan inlet after it had already been heated up from going past the compressor and coils. At times it would run continuously. Careful ducting of air in and out was needed to fix it, and now it has been very good for years, in lots of condtions.

The big thing is getting the coolest air available to the compressor and coils, and then getting rid of it after it is heated up. Hot air contains a lot of energy, so moving it by gravity is often not too hard to do, so fans aren't needed in those cases, which was true in our case.

We are different from most of the factory installs of compressor frigs in that we replaced a 3 way frig and chose to use the existing outdoor vents in our 07 C190P Roadtrek. In hindsight, it was the right choice, I think. The in and out vents have several feet of vertical height difference between them, so proper ducting allows for good thermal airflow generation to feed in the cooler air and discharge the hot air. The more "chimney" height you have the better. Intake and outlet air separation is essential.

I am a huge fan of compressor frigs, but they have to be installed very well to give their maximum benefit, and the power systems have to be matched with them. If not done right, even the absorption frigs start to look good by comparison.

 

[booster]

It must be a booster system.

Bud

Yep, with a big boost also from gravity:thumbup:

 

[avanti]

We have an Isotherm approx 3 cubic foot model.

That explains our different experiences. Our NovaKool is three times that size in capacity, and with no external venting (and ARV is the same). You certainly can't beat a pair of big outdoor vents for efficiency, but I do SO like the look of a van with a minimum of RV penetrations. Absent such vents (or the equivalent large internal venting bottom and top), you really need an extra fan or two to keep the back of the cabinet cool. If you do that correctly, though, it works very well. Ours has a big "in" vent below the fridge (doubles as the access hatch for the plumbing). The fans exhaust invisibly into an adjacent hanging closet, which leaks enough to be adequate. Looks and works great.

 

[booster]

Yours is 9 cubic feet? That is very large, most "big" frigs are more like 5-6 cubic feet, that I have seen. The numbers I have seen would seem to indicate a .3-.5 multiplier for size, assuming you are not going in and out of it a lot. So a 3cf to a 9cf would be .9 to 1.5 times more energy. Of course this is all guesses. That would put your 9cf unit at 1.9 to 2.5 times the amp hour use of ours.

Given the choice, I would opt for a very low side inlet, or even under floor inlet, vent and a roof outlet. It would give the best vertical height differential, and would also be less susceptible to wind influences that can affect both vents on one side installs. A venturi type top vent would allow any wind to help the frig ventilation instead of hurting it. With good, tight, airflow baffling to put the air on the compressor and coils instead of bypassing them, you could get an excellent, no booster fan, system on a compressor frig.

 

[mojoman]

Our Isotherm 7' exterior is all sheetmetal. By covering the exterior with 1/4" neoprene including the compressor area and the exhaust routing area , quieted it significantly and added a bit to its insulation.

 

[avanti]

Yours is 9 cubic feet? That is very large, most "big" frigs are more like 5-6 cubic feet, that I have seen. The numbers I have seen would seem to indicate a .3-.5 multiplier for size, assuming you are not going in and out of it a lot. So a 3cf to a 9cf would be .9 to 1.5 times more energy. Of course this is all guesses. That would put your 9cf unit at 1.9 to 2.5 times the amp hour use of ours.

Given the choice, I would opt for a very low side inlet, or even under floor inlet, vent and a roof outlet. It would give the best vertical height differential, and would also be less susceptible to wind influences that can affect both vents on one side installs. A venturi type top vent would allow any wind to help the frig ventilation instead of hurting it. With good, tight, airflow baffling to put the air on the compressor and coils instead of bypassing them, you could get an excellent, no booster fan, system on a compressor frig.

It is the NovaKool RFU6800. It is spec'd at 6.8CuFt fridge and 2.5CuFt freezer.

As I said, no penetrations for me. Well, maybe underneath...
Hmm, wouldn't it be cool to build a split unit, with the condenser underneath the van? If only I could solder well enough...

 

[booster]

Our Isotherm 7' exterior is all sheetmetal. By covering the exterior with 1/4" neoprene including the compressor area and the exhaust routing area , quieted it significantly and added a bit to its insulation.

Ours was the same, and we needed to space it out to fit the opening anyway, so we used 3/4" urethane foamboard insulation to do it. We used the same foamboard to build the inlet and exit air ducting parts. More and better insulation and sound deadening is never a bad thing!!

 

[Davydd]

Avanti, I was under the impression the 6.8 cf of the NovaKool was refrigerator and freezer combined. Still it is about the biggest installed in a Class B and they have the freezer in the right location at the bottom with a more energy efficient 2 door setup.

 

[avanti]

Avanti, I was under the impression the 6.8 cf of the NovaKool was refrigerator and freezer combined. Still it is about the biggest installed in a Class B and they have the freezer in the right location at the bottom with a more energy efficient 2 door setup.

I guess you may be right. The column labels on the NovaKool spec sheet are "Interior Volume" and "Freezer Volume". I read that as fridge and freezer volumes, but I guess that may just be gee-whiz marketing copy at the expense of clarity. As you say, still pretty big.

 

[booster]

I am a bit surprised that the inside vented units are requiring extra fans, and seem to be using quite a bit more than rated power. When I went out researching the "good" frigs, they essentially all appeared to be designed for boats which don't have outside venting available, making the frigs inside venting. It very well may be the units are not getting to rated efficiency in the boats either.

I know we certainly learned a lot about what works and what doesn't work in our installation. The airflow had to be reversed in every direction except the up and down movement. Of course all the changes require removing the frig, every time, it is a bit of work. In all the testing and in and out, I did put a fan blowing out of the top, exit, vent. It was put in early in the process, and is still there, with a variable speed controller. Once the ducting was right, the fan provided no measurable improvement in cooling, but did increase power use. We have never had the fan on when camping, up to 98*, and I will remove it if we ever have the frig out.

If anyone does look at their airflow in detail to try to understand it and maybe make it better, there are a few things that are kind of counter intuitive.

Big vents, big ducts, lots of airflow can often make the cooling worse.

Gravity is your friend, and the chimney effect works, but it is important to have the air volume as small as possible so the velocity stays up and you aren't trying to move a bunch of air that isn't getting heated.

The heat transfer from the air happens within a very small distance from the condenser or compressor, so any ducts or air deflectors should be quite close to the hot surfaces and as vertical as possible to keep the the heat rising quickly. The actual volume of air needed to remove the amount of heat from these frigs is really small, so if you can get to using that little bit of air by putting it where it belongs, life gets a lot better for gravity effectiveness and if you do need some fan, a very small one will be very effective in improving cooling.

The units that have the more conventional condenser on the back of the frig covering much of the entire back would get the least benefit from a fan because the area covered is so large. The fan would have to be very big to get much additional air over the coils themselves. I would guess this is why some the manufacturers don't add fans to the coil area, and if a fan is added as an option it blows on the compressor only. Unfortunately, the hot often blows out right at the bottom of the coils heating the air they see.

The Isotherm we have does use a very small fan from the factory with no option of not having it. The compressor and coils all get air from it in a very small and controller way with very little of the air wasted. This is a pic of a similar unit they use for the remote installs.

If Avanti were to go to a remote system, and assembly like this might be a good choice. It runs a BD35 compressor that can be made to be speed selectable. It think the same compressor is used in his frig. It could even be placed in a more airflow favorable place inside the van.

Here is a drawing that another Isotherm user drew up after having lots of problems and getting referred to the discussions we had on ours on the Yahoo board a few years earlier.

This is very similar to our setup, except we do not have a ducted outlet vent or fan(that we use). We have an open vent at about the level of the compressor. To keep the exit air going to the vent, we tightly sealed the area between the top and bottom vents so the small fan and gravity are enough to move the air out just fine. We run the compressor at it's lowest speed all the time and it keeps up easily, so we know it is running about as thermally efficiently as it can. Factory setting was the the third speed.

I believe these kinds of improvements could be done to varying degrees on most of the compressor frigs, if the time and effort were put into it. The Isotherm, turns out to react to improvement extremely well do to it's design, but was horrible in stock form.

 

[mojoman]

I ducted mine to exhaust where my wife normally sits, she's always cold.

 

[booster]

There is a note on the complete posting that the guy who made the drawing has on his website that says the setup was not a success and is saying ambient temps were just too high for outside air. He says that the compressors are made to run at the lower temps in boats, but I am not sure about that. Yeah they sit in water, but they also spend a lot of time in the tropics where it can be really hot and humid. I need to see if I can find an recommended operating temp for them.

More likely, I think, is that he was not super picky (which you need to be) about getting the inlet duct sealed to the inlet of the fan. If there are any gaps the fan will suck hot air back into it's inlet, and that is what the original problem is, so you just reduce it some. It appears his frig slides in to the duct, without the duct preattached and sealed, so that could be the issue. Our foamboard box duct goes right up to the inlet of the fan and is sealed to it.

on edit
The Danfoss literature says 55 degrees C as max ambient, so 131 degrees F. I do believe he had some other issue going on.

edit again
This is what Isotherm has in the newer manual, our old manual doesn't have this. I think it may just be a compressor speed change, but don't know for sure.

That would get you to 110 degrees F, so might be getting close to having and issue in the desert, but inside air might be just as bad unless you are plugged in all the time. I don't know if driving AC would even keep up. If his was rated at 32 degrees C, that is only 100 degrees F, so way easy to go beyond. We were close to 100*F and the frig did keep up on the slowest compressor speed.

This has to do with maximum cooling capacity, but of course that also is influenced by how good the system is to get to the factory rated level.

Using their new thermostat with variable speed control built in might be a very good idea if you are going to the very hot conditions.

 

[avanti]

I am a bit surprised that the inside vented units are requiring extra fans, and seem to be using quite a bit more than rated power.

The fans are needed because space and aesthetic considerations make it difficult to provide for proper convective chimneys without external venting. As a consequence, the back of the cabinet containing the fridge just gets too hot for lack of airflow. A couple of muffin fans fix the problem easily. Mine are thermally modulated, so they only run when necessary, and often very slowly.

You clearly have much more experience than I do on this issue, but it is a little hard for me to understand how larger vents or air volume can do harm. Yes, air velocity is your friend, but in thermodynamics temperature differentials rule. More air volume means greater heat carrying capacity and thus lower temperatures. Would not a fridge sitting in an open field (even w/o breeze) be the best possible configuration? I could be wrong, though.

 

[booster]

The fans are needed because space and aesthetic considerations make it difficult to provide for proper convective chimneys without external venting. As a consequence, the back of the cabinet containing the fridge just gets too hot for lack of airflow. A couple of muffin fans fix the problem easily. Mine are thermally modulated, so they only run when necessary, and often very slowly.

You clearly have much more experience than I do on this issue, but it is a little hard for me to understand how larger vents or air volume can do harm. Yes, air velocity is your friend, but in thermodynamics temperature differentials rule. More air volume means greater heat carrying capacity and thus lower temperatures. Would not a fridge sitting in an open field (even w/o breeze) be the best possible configuration? I could be wrong, though.

What I have seen on many of the factory setup in pix and what folks have done themselves is that the big vent openings, be it to outside or inside is not all that critical, but you want the airflow around the hot stuff to get all the air that will come in to the area of the coils and compressor. If you have big vents and they typical setup of 5-6" in back of the rear cooling coils, there is a lot space for any air you are extracting with the fan or gravity to just bypass the hot stuff. Once you are more than a very small distance from the hot stuff, extra air is moving but not getting any heat transfer. If the hot stuff is in a much smaller area any air you get in will be put in a place where it will get heat, and contribute to heat removal. So, yes, more air will be better but it has to get to the heat, and not contribute to heat looping in the area.

The field example is excellent and for a frig will give a decent result. It is the way the frigs are specified, it appears. As soon as you are moving air to and away from the hot stuff it can all change. For instance if heat could generate enough energy to gravity move X amount of air and the area of the hot parts is Y you would get a lot more over the hot parts if the area is small as opposed to large. It is even more true if you have a fan as they are less susceptible to airflow resistance. Why have a fan that is 10 times bigger than needed to cool things because 90% of the air is not picking up any of the heat, just bypassing. I think we have all also seen how much self generated draft a small chimney will make than a huge one or no chimney.

A good example of the tiny fan deal is what Snyder did in his kits for the absorption frigs. He put an entrance duct on the condenser that covered the entire bottom of it so quite a few square inches (20+ maybe). He fed the air to it through a 2" miniature fan in the inlet. We found that when we had one, it cooled better even when the fan was not running do to the smoother airflow and chimney through the heat exchanger. The fan moved tiny air amounts and did improve performance a bunch if the exit air could get out with going back to the inlet (good baffling). Compare that to 1-5 larger fans you often see on the absorption setups trying to get better cooling. They likely move 50 times the air of the Snyder fan, but probably don't help as much.

I think the give away on lack of airflow where is needed usually shows up and hot air in the area of the condenser and compressor. If the heat were getting picked up and carried out, you wouldn't have all that hot air volume getting heated, and the air coming out at the fan would be carrying it all if on the outlet side. It is likely once that air starts to warm up, it will make a convective loop and just keep going around through the hot parts and getting diluted a bit by whatever finds it's way in and out of the area. If the area is fed by a fan of any sort, the air could be delivered in a duct sealed to the area of hot things, so the would see only cool air (that is what ours system does). If the fan is on the exit side, it could pull of the air from a cover over the hot parts, only open at the bottom of area to let in air from wherever the inlet is. The big thing is to get the freshly heated up air out of the area before heating up the area itself, and not let it leak back into the area and inlet to hot things.

If you look at the current home frigs, I think all of them no longer use the backside gravity coil cooling, which would seem to be better because of all the air they are in. The new frigs carefully control air in and out of smaller condensers that are right along the floor with in and out at the same height. No outlet air can get back to the inlet of the coils, and though the move low amounts of air, essentially all of it is available to pick up heat in the condenser and compressor.

I find this a very interesting topic, as compressor frigs are going to be the future. Of course it may all be mute when better batteries and/or power cells come along, but we will see. For right now, a lot of the older units would be hard pressed to switch to a compressor frig unless it was very efficient. Using 60+ah per day wouldn't be feasible in many cases without severe amounts of other changes.

 

[Davydd]

Alvar has found a new home. We bought into an HOA townhome (twinhomes) concept and can no longer store our RV on premise. We accomplished three things -- one level living after living in a 6 level house, no exterior maintenance, and no loss of nature we enjoyed trading our 1-1/2 acre woods and marsh for a backyard 3,700 acre park reserve and a regional bike trail.

Alvar will now be protected from snow, cold, hail, rain, falling leaves, branches, sap, and bird poop. Alvar will now reside in a heated garage. Along with our new home, but separately, we bought a garage condo storage unit 18' x 45' with a 60 amp electrical service and a 45,000 BTU gas furnace. We are having an overhead fan install along with a 30a electrical outlet. This was the smallest size unit in a 270 garage complex with gated fence, restrooms, dump station and a huge enclosed RV wash bay with a portable ladder.

The checker flag epoxy floor was put in custom by a previous owner. This for Speedway, Indiana native and Indy race car fan felt like it was karma for me to have this space, the only space available for sale in the complex. The garage is 9 miles from our new Victoria, MN home and is located in Minnetrista, MN and an easy drive. It is a lot bigger than I thought I wanted as there was another unit at another complex about 20 miles away that was 14' x 30' and about the size I would have built for myself if we stayed where we previously lived. Rental for that smaller size would have been about $400 per month if one had become available. I have to look at this as an investment that hopefully will appreciate. In a brief talk with the guy in the garage next door, who was on his second unit, it appears it may pay off but that will be most likely for my inheritors. It will be a storage unit for all the stuff that will not fit in our new home (a lot) and man cave as well with a shop setup. At 18' x 45' this thing is a 4 car garage. Condo storage garages seem to be a big thing mainly for classic car collectors in our area. There was a big complex closer to our home but too rich for my blood. This company has several complexes around the Twin Cities.

Park Place Storage | Large storage garages you own

 

[BBQ-ClassB]

.

Looking good, both the home and the storage

+1

 

[Arlo-ClassB]

As a Hoosier, I appreciate the karmic boost from the floor. When I bought my E-Trek in 2013 I decided to build a 32x24x14 garage for it with heat, hot water, and 30 amp electric. It has been great to have, but If I'd skipped the garage I could have (almost) afforded an ARV! Hope to meet you at Advanced Fest in 3 weeks.

 

[gregmchugh]

For the car enthusiasts there is a new facility with private garages/man caves, an onsite racetrack, and a driving school that just opened on Woodward Avenue (the street for the Woodward Dream Cruise every year), just north of Detroit.

M1 Concourse