Chinook RV

How about a long reply to a short question (my specialty ).

So you absolutely do need ventilation for a compressor refrigerator, BUT you don't need the exact same thing. After all, you are no longer burning a fire back there, and the byproducts of combustion aren't being vented. Instead you are just supply cool air for intake and then exhausting heat. For the BD35, according to Danfoss, I believe they are looking for 25 square inches on both the in and out side (if you are using screening or a louvered vent there is a subtraction factor; in other words, a 5" x 5" hole with screening over it is not 25 square inches of ventilation). I think the DP2600 has the larger BD50 compressor, and that will have a spec for ventilation area in/out (the compressor is made by Danfoss).

The Vitrifrigo manual does give some guidance and specs. Most of these are for interior venting, since more of these go in boats (and you can't have a vent along the side of a boat in the same way that you can on an RV). They do essentially say that exterior venting is great if you can get it. In case you don't have this document, here is the page, copied. The dimensions are metric (since they are made in Italy).
Reviewing the DP2600, I see that the compressor is at the very bottom. So in some ways the original Chinook venting scheme is perfect. Air in at the bottom, chimney effect, air out at the top. It looks like they want about 4" of depth to the vent plenum, and I think the original one is deeper, so you might be able to make a "false wall" at the back and fit both some insulation (against the fridge back) plus the plenum. I don't have a measurement to hand, but the original one must have been deeper than that (for all the "pachinko machine" guts of the cooling unit). I think we put around 5-6" of insulation in my buddy's rig where the original propane fridge was (he elected to eliminate the vent chimney).

On the other hand, that lower vent on our Chinooks can sometimes have issues. There is no way to positively keep all water out, and at least on my generation of Chinook, there wasn't a good outcome when water would get in. Basically the bottom of the compartment was lower than the lowest drain-to-the-outside area. Boo. When I still had the propane fridge, I used flashing to make a sort of self-draining vent door, but knew that I would want to eliminate that vent when I went compressor. On the other hand, I've never had any water come in the roof vent. So I felt that keeping that was an option.

You'll want to decide about that for your own rig, of course.

For my smaller unit (Vitrifrigo C130, BD 35 remote compressor), I need to provide at least 25 square inches of intake and exhaust. That's after taking off any deductions for screening, slats or whatever. I haven't decided for sure whether to go for all inside venting, or all outside venting. The "easiest" thing would be inside intake and roof exhaust, but I'm not super keen on mixing the two. I am not enough of an expert to know for sure whether or not it would be a problem, but I can imagine possible bad scenarios and just don't feel totally comfortable with a "mixed" venting scenario. I'm more comfortable with all out or all in. Considering that I have had a BD 35 running inside all the time now for two years (small "cooler shaped" refrigerator with BD 35 compressor which is a pre-cursor to the "real" refrigerator), I'm less worried about the potential heat gain with all-inside venting than I was at first (thinking it might heat up the rig in summer). But on the other hand if I go with all exterior venting then I should be able to hear the compressor/fan less (it's pretty quiet, but I like sensory deprivation levels of silence ). With all exterior venting, I should be able to isolate the sound more (vs. having 50 square inches of "sound ventilation" into the interior).

I won't go into all the specifics for my various design ideas, because they are different given that the C130 has an external compressor (I can put it in another place because it's not attached to the refrigerator).

For the DP 2600 I would probably choose one of two options. But, like with my friend's installation of the DP150, we had to assess once we had it in hand and then make a decision.

1) Use original "chimney" venting scheme from the propane refrigerator. If there is extra depth, then perhaps put some rigid extruded polystyrene insulation behind the refrigerator, then a thin ply "wall" then the chimney area. In this case you'd want to exclude interior air from this exchange.

2) Go to all interior venting as shown in some of the Vitrifrigo diagrams. Basically, a path for air to come in at the bottom front of the refrigerator (if there is room over the generator box), slide up the rear, and then come out to the inside over the top of the refrigerator. This eliminates all complications of exterior vents/leakage/etc. And perhaps allows for more insulation. Just have to look at the space and the options. One potential use for the roof vent "flat" is to fit a "real" stove vent hood, if that's a priority.

If the refrigerator doesn't get enough venting, I think the compressor will run warm and increase the duty cycle (boo). It's important that the "intake" of the compressor NOT be able to take in pre-warmed air (from the exhaust). Sometimes you can make a hood type thing (like the intake on a car) or etc. The supplied fan (at least on BD35) sucks air in.

The Danfoss compressor has a few nifty goodies you can tap into, optionally. There are some very good youtube videos by "Penguin Refrigeration Limited" that explain and show it all.

1) If you put a fan across two specific terminals on the compressor, it will come on when the compressor comes on. Not saying this would have been my exact choice, but my buddy elected to keep only the lower vent opening from the propane setup, and he mounted a second fan that comes on when the compressor comes on and exhausts air (the fan that's included with the compressor sucks air in).

2) If you put an LED light across two terminals it will flash codes if there are errors.

3) There is a resistor on the compressor terminals. I forget the exact numbers/terms at the moment, but they set it up with a sort of middle ground one that runs things at a certain speed and duty cycle. I think the refrigerator is actually more efficient at a slightly higher (but lower speed) duty cycle, which you can achieve by changing the resistor (this is official, not an off the books hack). But they figure some people might be worried by thinking it is running "too much." And besides, just like anything else pre-made, they have to pick something as the stock setting.

Another important thing is the the electronics of the compressor DO NOT want to see voltage drop. They are sensitive to that. IIRC they say to run straight to the battery, but then everyone says that and if you complied you'd have a hundred ring terminals on your battery. Basically, they don't want a breaker shared with a bunch of other things, and no long/thin wire run. It could lead to early demise of the (expensive) compressor. On my rig, the original 8AWG run for the propane refrigerator was just okay, and that's with much larger (refit) cables going from the fuse block to the batteries. I'm thinking I may run a new wire across under the coach, or possibly re-purpose the generator start wire (6AWG). The trouble with a new inside wire is that it's a just about equally long run "around the horn" either way (forward or aft) to the refrigerator. No good way to "cut across" inside. Going around, it's hard to get behind the shower, and a 6AWG over the overcab is kinda big. I guess all of the ways have their plusses and minuses, and too, maybe the 8AWG would be okay. It could certainly be worse.

I'm far from an expert on this, so if anything sounds "off," do double check me. I also have not yet installed my C130. Only planned I have been running a cooler shaped refrigerator with the same compressor (easy way to see how much energy I'd need since this was my first "can't be stopped" demand back when I set up my test solar charging system). And my buddy whose DP150 we installed really likes it. In fact, he's getting a different RV and is planning to get the same one again (I think he'd upsize to the DP2600 if he regularly traveled with 2-3 people).

Thanks for the tips. I'll probably do something to prevent leaks in the original outside wall vent - previous leaks caused the cabinet door below the fridge to rot at the frame so I know that water can get in there.

Got a call from the installer and the fridge is actually slightly shorter than the Dometic so they're putting in a piece of wood to fill the gap. If I close off the outside vent panel completely I'll probably use install vents above the fridge to allow for more circulation. I plan on leaving the roof fridge vent in place for now. Looks like around 6 hours of labor to get the window out, install the fridge and put the window back in (The patented "Blu-Method" of chain-sawing the fridge in half only works for removal...).

Next week - off to the upholstery guy to have the springs cut out of the jack knife sofa and installing "flat" cushions to make a more level bed when folded down. As part of this project all the dinette cushions will be re-stuffed with the same memory foam combo (firm foam with a memory foam layer on top) that will be used for the jackknife sofa.

After that, I'm looking into suspension mods. Those scholastic devices look interesting for the rear but I keep seeing people on here that have gone to the 08 and later front suspension. Is that a easy swap for the mechanic?

Paul

Lots of great info in there, BG. I know the compressor-fridge crew is made of just a handful of us, but I thought I'd add some experience/opinion on vents. I had problematic water intrusion at the lower vent. It felt great to blank that off. My upper vent remains stock, but is now open to the coach. It has never leaked. To make it bug proof, I covered the coarse aluminum wire mesh with fine mesh nylon screen. I also used the front vertical face of the vent body for an entry point for the solar line. I have deflectors on the cab windows, so with those windows open an inch or so, I have fairly decent full-coach ventilation in any weather. And I don't have to use vent covers, or worry about a night time rain storm rolling in after falling asleep with an open side window or roof vent. I treasure fresh air and this system has been great on many warm rainy nights. It's also great ventilation for when the coach is parked for extended periods. All of this is very positive for me, but maybe not for others. The drawbacks are that it's less efficient when heating/cooling the space (which I almost never do), and it's a point of entry for dust. I travel a lot of dry/dusty roads, and my fridge is black, so I have a good idea of what's getting in. If all windows are shut tight while I'm on dirt roads, not too much more dust gets in compared to before. Occasional interior dusting of windows and cabinets is always a fact of life for me when camping, so I really don't notice much more work or mess. I admit that I've cleaned out the interior of my coach with a leaf blower once, but that was right after I ripped out the carpet .

Now after all that, I'll say that if I can eat my cake too, I'd like to close off the upper vent with a sheet of PVC, then install a vent that I can open/close at will, preferably from a couple feet away using a lever or cable. I've briefly looked at boat ventilators, but haven't seen anything that will work. I might have to make something. Or just leave alone.

Oh that's interesting, Scott. So you essentially have interior intake, and exterior exhaust. I know that there's nothing "dangerous" about back flow in a non-combustion-byproducts setting (i.e. compressor refrigerator vs. actually exhausting from a small fire as in an absorption refrigerator), but I still wondered about, say, running the Fantastic fan and unintentionally "reversing" the venting scheme. Maybe that's a non-issue in real life.

I do hate dust, so also wouldn't want negative pressure when driving -- and maybe that would happen with the interior intake/exterior vent? I run my dash fan on medium or high when on dusty roads as it is to try to create some positive pressure.

I, too have had the refrigerator vent somewhat open to the rig since I removed the original refrigerator. I did enclose it with a mockup cabinet though. Since I have a remote compressor my latest possible idea was to put it in that cabinet and use the roof vent for both intake and exhaust (maybe with a septum?). But that's just noodling. Like you, I have never seen evidence of any water leakage through the stock refrigerator roof vent. (And I have closed off the lower wall vent, also like you.)

Guess I'll noodle it a bit more.

On your vent, I can mention a few marine possibilities. The trouble is most of them don't have 25 square inches of ventilation (but maybe you are not looking for that much). One thing I don't know how to calculate (but it seems it must be true?) is how that changes if you have a fan. Like, say, if you have 12.5 square inches of open area for the exhaust (vs. 25) but you have a 42cfm fan pushing that air. Is there some calculation for how much "equivalent" square inches of ventilation that is? I have found some really complicated things on Google, but nothing I could get a solid grip on as an amateur. Or maybe it's so obvious that no-one feels the need to explain

So, here are some possibilities if you haven't already considered them. These are things I'd picture sitting on top of the "flat" in the roof where the current refrigerator vent is. I made a flat fiberglass board panel for a potential new base, but just have it set aside until I come up with my plan. But since it doesn't really show, it doesn't need to be artwork (for me), just tidy and strong.

1) Good old mushroom vent. Can be manually opened and closed although not typically remotely.
Example: Vetus Athos 1, about 7 square inches of free area. Or Vetus Dartagn1, Just under 11 square inches. These don't gush water in when open, but are not as "waterproof" as an overlapping design (but more free area).

2) Vetus UFO vent. The UFO has an even more overlapping design, such that it can be "always open" without leaking. It's about 5 square inches of free area.

3) The UFO2 is actively closable. It's around 4-1/2" square inches of free area.

4) The Vetus FAN12 is a very low draw ventilation fan (.19 amp) with a 50,000 hour life expectancy. Two speeds, 42 cfm (I would guess that's on the higher speed). But, darnit, I don't know how this corresponds to "25 square inches" of passive free area ventilation. (And of course nicer not to have a fan.) The FAN12 can be fitted to the underside of a UFO vent, but not the UFO2.

5) Nicro 4" Day/Night Plus. Nicro vents have been used on boats for decades, with mixed results. Everyone loves their functioning, but sometimes they last longer than others (and they are not cheap). They are essentially a round roof vent, self-draining, with a built in fan (switchable on some models) and a built in mini-solar panel and built in batteries to power it (so it runs at night too). Nice that it is self-contained, but on the other hand something like the FAN12 runs on your more robust batteries vs. little ones that might fail and are semi-proprietary.
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BTW Vetus also has some engine intake vents with fittable inside diverters that might work very nicely set into the lower ventilation panel blanker; but for me I don't have the depth for the diverter since I want the new refrigerator there and also want a wide hallway (but I can put the compressor elsewhere since it's on a tether).

Blue~Go wrote:On your vent, I can mention a few marine possibilities. The trouble is most of them don't have 25 square inches of ventilation (but maybe you are not looking for that much). One thing I don't know how to calculate (but it seems it must be true?) is how that changes if you have a fan. Like, say, if you have 12.5 square inches of open area for the exhaust (vs. 25) but you have a 42cfm fan pushing that air. Is there some calculation for how much "equivalent" square inches of ventilation that is? I have found some really complicated things on Google, but nothing I could get a solid grip on as an amateur. Or maybe it's so obvious that no-one feels the need to explain

As for a convenient "equivalence" conversion, I don't know. I also don't know how they come up with the 25 sq in of ventilation area. There are so many factors involved. Heat transfer coefficient, heat transfer area, log mean temp difference, cleanliness of condenser fins, ambient temp versus fridge temp setting = load on compressor, humidity, etc. As you know, a fridge just removes heat from inside the box, so that's the amount of heat you need to reject, plus heat created by the compressor and other inefficiencies. But rather than knowing the suggested area of ventilation, I think my preference would be to know the manufacturer's suggested temperature at the compressor/condenser for optimum efficiency. Then I would just monitor the temp under varying conditions. From your experience with your Danfoss cooler, you probably have a close approximation of what's going on. Even with minimal interior static ventilation area, you can always set up a core-mounted pusher fan on a thermoswitch, or even a couple fans (maybe one pusher, one puller) set to activate at two different temperatures; this way if you only need to move a small amount of air to maintain optimum operating temperature, you run one small fan to reduce short-cycling. Same for compressor duty. I'd rather have it lope along at lower flow for longer periods versus having it crank hard for short bursts, but that too would "depend." Oh, and keep the temp inside the box as consistent as possible by never opening the door . Digital PID controllers are plentiful and inexpensive, and many come with temp probes that would be perfect for this type of experimentation. You're lucky because you have complete control over this stuff by having a remote compressor, which is definitely the best design thermodynamically. I have a mass-produced 110V fridge, and the condenser coils are in the sidewalls, which is common practice even in the world of Energy Star approval. So my ventilation needs are primitive and simple to accommodate. A couple inches of clearance to the left/right of the fridge and we're clear for takeoff. I mounted the fridge on a frame (there's no floor), so the upward flow across the sides is ample; it just goes up and out of the stock upper fridge vent. If I had a remote compressor, I'd possibly duct in-and-out from the roof vent (as you mentioned). You'd want to separate them as much as is convenient, but even if they do communicate slightly, I'd be surprised if efficiency would be affected in a measurable manner, but it's possible. As I'm sure you know, flow characteristics will be unpredictable once you start down the road.

Thanks so much for the recommendations on the vents. I'll check 'em out ...

I've now had my new Vitrifrigo fridge installed for about ten days running on battery only. During that time the rig was indoors for the first 4 days and then has been through 4 rainy days and only a few sunny ones. The battery charge level as of yesterday as at 88% - not bad considering it was down to 68% after being inside for the first 4 days. My rig is over at an upholstery shop for modifications to the jack knife sofa and dinette cushions and is not plugged in so we'll see how well the solar power system keeps up with the fridge. The owner of the shop was concerned because the rig is not level right now but I reminded him that with compressor fridge that's not a concern. Looking forward to being able to park anywhere without having to level the rig.

Well, the fridge has been running for over two weeks now on battery power; battery status is 100% by about noon but now I'm having some trouble with getting the freezer colder. At a high thermostat setting the fridge got down to 30 degrees but the freezer was only down to 10 degrees. Backed off the setting and now the fridge is at 40 degrees and the freezer is at 20 degrees. I'm worried since the ambient temperature inside the rig was no more than 80 degrees. I was not around when the installation was done but it appears that I have about an inch of air space on either side of the unit. I have the original outside fridge vent but I had installed some Camco screens on the louvers. I'm now wondering if I'm letting enough air in through those screens to meet the 25 square inch venting requirements. I would like to avoid adding fans if possible. Any recommendations?

Well, this weekend I put my new 110/12 volt fridge to the test. Temperatures where we camp got to 105 degrees during the day and only dropped down to 80 degrees at night. The fridge struggled to maintain temperatures in both the fridge and freezer compartments but I did learn several things and now want to do some modifications.

1. The compressor is small so it takes a long time to recover from any heat load. Loading in some room temperature items the day before we left caused the temperature to rise almost 10 degrees. It took 24 hours to get back to a safe fridge temperature.

2. Parked at our marina with the fridge side exposed to direct sun all day. This drove fridge and freezer temps up 20 degrees. While the old chimney from the LP fridge provides venting it also provides no insulation for that area. I'll probably add a fan to pull the hot air up the chimney and will insulate better. Unfortunately this will involve pulling the fridge out but that will also give me a chance to "Dynamat" the whole inside of the cabinet around the fridge and will hopefully also reduce generator noise.

3. Have contacted Sure Marine - who sold me the fridge - and Vitrifrigo to find out if I can adjust something to get the freezer temp down lower without getting fridge temperatures too low.

4. Overall I would have to say the Vitrifrigo is a pretty nice unit. The shelves slide out smoothly, doors close securely and I love the fact that after some bad moves on my part the unit was able to perform pretty well given the extreme heat. A few more tweaks and it should be great.

Sounds like you're headed in the right direction, Paul. Thanks for the update.

I would definitely get some rigid foam insulation between the inside wall and the back of the fridge. That's of big importance.

Another thing I try to avoid as much as possible is loading room-temperature stuff into the fridge, especially massive stuff like beverages/glass/etc. I try to buy everything pre-chilled. If there's something that I must have, and it's not refrigerated at the store, I grab that first when shopping, stick it in the frozen food section, then finish my shopping. Every bit helps. And open the door as infrequently as possible. One other thing I do before short trips; I sometimes freeze bottles of drinking water at home, then put them in the Chinook fridge just before taking off. They're ready to drink the next day and can help reduce compressor load.

I'm glad you posted back. As I've mentioned before (probably ad nauseam), a buddy (different brand Class C) removed the same basic size/model of absorption refrigerator from the same basic hole. He was between the DP2600, which you got (fits hole, is larger inside due to no chimney etc. in the back), and the DP 150, which is a bit smaller.

He went DP 150, because he just wasn't sure, and didn't want to worry about power (confirmed boondocker, tries not to run generator). When we installed it, we were able to add 1-1/2" inches of extruded polystyrene to each side (there was 1/2" of expanded polystyrene there already), something like 4" to the top (plus we made a "pan locker" about 11" high), and 6-1/2" to the back (!)

Reason I'm mentioning this is because we debated what to do with the back (outside wall). It had the chimney of course. My first choice would have been to add around 4" of insulation and then have something like a 2" chimney (2" deep by 24" wide), then maintain the side and roof vents (on his rig the side vent never ever leaks, unlike our slanted Chinooks). I thought that would have been the best of both worlds: Great insulation, plus good heat removal from the compressor.

My friend decided to go another way, also fine just different, and we filled in the entire back and just kept the lower side wall vent for the compressor. Danfoss has a terminal on the compressor where you can add another fan that comes on when the compressor does, so he has a second fan (stock one pulls air in on one side of the compressor unit, his fan pushes it out on the other (both from the wall vent. We also installed a foam septum on the intake fan shroud/wall grate.

So those are a couple of options.

He keeps ice cream in the freezer and lettuce in the fridge, no issues (the fridge might be at 36 and the freezer at say, 7, so the fridge is on the cooler side to be sure but doesn't freeze things). He doesn't tend to put a lot of warm stuff in it (transports groceries in a cold space on the way to the RV), but other than that doesn't baby it. We were camped in 100º heat last week and his fridge was doing fine - afternoon sun did hit that wall all afternoon. He did say he had to turn the thermostat a little bit colder, but those were brutal conditions.

So what's my point? Well, just that (as you mentioned already), you might want to partially or fully insulate the rear (chimney) area. And just to mention that easy to use fan terminal on the compressor (can add a fan that comes on only when compressor does). And that the smaller refrigerator, more insulation, and not putting in massive quantities of warm stuff equal a unit that works great, so maybe you can tweak, as you say.

(BTW, he does wish the freezer on the DP 150 was larger, so for that the DP2600 is great. He's now waffling a bit as he's changing RV's and going to make the decision again (leaning DP 150, but still wishing for the larger freezer )