Over the spring and part of the summer I have been working on building a walk-in cooler for my produce. Since I’m scooting about to half a dozen different yards I thought it would be keen to have a cooler that could scoot around with me, so following some directions on a couple blogs (EverGood Farm and Pack’N’Cool) and using my vast skills at “Riednering” things together I built a pretty handy cooler unit.

I took a light weight trailer (FeatherLite V-Nose 8ft trailer) on low-ride suspension with as high a roof line as I could find. Being over six feet tall I have a pretty strong loathing for concussion chambers. For me the extra couple inches in head room was worth the hit to the pocket book. Especially once the insulation went goes in and you lose 8″ in height.

Being a little bit of a greenie and always loving scope creep I decided I would also add in the ability for the trailer to run the cooling system while on the go using a combination of solar panels and shore-charged battery banks. In retrospect this tripled the build time, doubled the cost, and has been the main source of problems for the trailer (and by extension me). The solar component still does not work properly, and I am probably looking at a significant cost to get it up and running, so it has been put on the back burners.

For anyone planning to try adding battery banks and solar panels to their cooler unit on wheels I would highly suggest you think about getting a gas generator instead, it will cost less and serve you with more flexibility even though it will be obnoxiously noisy. Solar power and battery banks in conjunction with refrigeration are a real pain in the pocket book due to the piggish energy draw for cooling. That being said I’ll share all my mistakes on the solar side, so anyone who reads this doesn’t make them as well.

Here is my parts list and approximate costs (in Canadian Dollars) for the trailer:

  • Used 8ft FeatherLite Trailer – $2500.00
  • 32 Sheets of Foamular Rigid Insulation (Pink Polystyrene) – $1500.00
  • UberHaus 12,000 BTU Horizontal Window Air Conditioner (Danby Rebrand) – $420.00
  • CoolBot Controller (including shipping)- $350.00
  • 10 Sheets of 1/4″ OSB – $120.00
  • 10 Cans of Expanding Insulating Foam – $100.00
  • Miscellaneous Hardware (screws, nails, brackets) – $100.00
  • 8 Tubes of Polystyrene Glue – $100.00
  • 8 Tubes of Silicon Caulking (Outdoor) – $80.00
  • 200 6″ Robertson Wood Screws – $35.00
  • 25ft Heavy Duty Outdoor Extension Cord – $30.00
  • 6 8ft 2×4’s – $20.00
  • 2 Rolls Tuck Tape – $20.00
  • Power Bar – $10.00

I am going to leave the solar components list off, since the system I currently have is too small and does not support the above build in any way-shape-or-form. I will post an update on that and the pricing once I figure out a system that works.

You could do the whole build solo, but it is way easier to have at least one helper. I had a couple people help out; Sarah and Sam, my Father In-law Lonnie, and my little sister Tahiti von Riednerstein (aka: Tina).

Tools you need:

  • Drill with screw and bi-metal drill bits
  • 1″ bi-metal drill bit
  • Table Saw or Circular Saw
  • Compound Mitre Saw
  • Hand Wood Saw
  • Hand Hack Saw
  • Sawzall with wood and bi-metal blades (scroll and 4″ blades worked best)
  • Screwdriver
  • Hammer
  • Clamps of various sizes
  • Crowbar/Wrecking Bar

Step 1: Clean the trailer and remove any side rails. Leave the cladding, it will help later with attaching insulation.

Step 2: Find where the electrical lines run. I accidentally chopped into the cable casing while going a bit nuts with the sawzall. Thankfully I didn’t cut the wires, or I’d have had to redo the electrical for the trailer.

Step 3: Chop a hole out of the front of the trailer for your air conditioner. I made my hole too big and crooked, and suggest taking the time and having someone help you mark out the A/C by placing it against the cladding. If I were to build another trailer like this I would consider a split A/C and roof mount it for easier maintenance over time.

Step 4: If you plan to do solar or battery banks frame out a compartment for the components. Leave LOTS of extra space for airflow and ease of access, then mount in your electronics and cable lines. I used some scrap EMT conduit I found laying about and it worked nice, though thicker cables are a pain to pull. I would also recommend designing it for a proper lid instead of the ghetto lid I made. It works, but it isn’t pretty.

If you are just doing wall power cut a 1″ hole in the trailer wall and run the extension cord through, then rig up the power bar in prep for running the electronics.

Step 5: Frame supports for the A/C unit and balance it in place, DO NOT SCREW IT DOWN PERMANENTLY. If you can rig it up so the housing can be removed do so, our A/C you can’t.

Step 6:  TEST THE A/C AND COOLBOT SYSTEM!

Do NOT under any circumstances insulate the entire trailer before you test, or you get the fun of ripping everything apart because the A/C doesn’t work. You should be able to get the trailer down to 5-7ºC without any insulation.

Step 7: Seal any cracks and gaps in the cladding.

Step 8: Painstakingly piece in the first layer of insulation. I took a lot of time doing this because I couldn’t find any flexible high grade insulation material. The centre line of our trailer did not have anything to mount anything too, so I ran a 2×4 along the centre of the trailer and screwed it into the aluminum cross bracing along the ceiling. This part takes forever since nothing in the trailer is square or level, and nothing I build is square or level and you end up doing a lot of chopping and cutting of insulation. I tacked it all in place with glue, sprayed expanding foam in any gaps, and put Tuck Tap over the bigger joints to help stop airflow.

I did the front of the trailer first, then the walls, then the ceiling, then the floor.

Step 9: Put in the second layer of insulation. When you do try to rotate the pieces 90 decrees to help break any air flow through cracks. Spray foam and tuck tape again.

Step 10: Using a table saw or circular saw cut the OSB cladding to fit your now much smaller interior space. We did the floor first, since it was raining and we were tracking mud on to the insulation. Then we did the walls, and last we did the ceiling. To keep the OSB up on the ceiling we screwed into the 2×4 I mentioned above and used metal L brackets along the perimeter. 6″ screws on the walls and floor worked fine and did not punch the exterior cladding, but you might need to use different sizes based on your own trailer. The ceiling was 5″ screws into the 2×4, and 1″ screws through the L brackets.

Step 10: Caulk the inevitable gaps. I ran out, it’s not critical, but it does help break airflow and keep moisture where it should be. I will finish caulking in the autumn once the season is done.

Step 11: Insulate the doors, and make sure they are a TIGHT fit. Weatherstrip if needed. I secured the insulation to the doors using nails with plastic rings on them, then used the same plastic rings and shoved them on screws for a better hold.

Step 12: Mount the CoolBot properly, and secure the fin and room sensors. I used some tuck tape to help keep them from bouncing loose in transit.

Step 13: Fire it all up and see how it works.

Step 14: Possibly pat yourself on the back.

Over all the trailer is working good. It keeps things cool and fresh, and even on the days when I’m doing our CSA drops/pickups the produce stays nice and cool even in rubbermaid bins. I do double bin with ice packs on the bottom, and have backup coolers that I pre-chill the night before. If the solar/mobile cooling system worked I would have an epic win for keeping things cool on delivery day. I am considering getting a gas generator to help with that, but they are so obnoxious and loud that I hesitate. I am going to try putting in 5-6 5 gallon pails of water as cold-sinks and see if that helps.

I am still troubleshooting some issues with the cooler. On some hot or humid days it has a real problem icing up and swinging around in temperatures. I suspect it is a combination of too little mass in the trailer and being lax about cleaning the fins. I am also finding that opening and closing the doors hoovers cold air into the world. I am going to install some 5mm poly with slits cut in it and magnets to keep them closed as a way to help keep cold air inside. I know my biggest air leaks are at the back by the doors, so this should help with the icing as well.

Over all it works good, and I really recommend it to anyone doing urban or spin farming. It is portable infrastructure that you can move easily if you are renting, or if your cooler is in one of your borrowed yards. It can easily be parked in place long term or be used fully mobile like I do. Right now when I pull up to one of the yards I’m working I plug into the wall power to keep things cold inside. I am betting it is costing about $1-2/day to run here in Alberta with our power costs depending on if the door is opening a lot (harvest days) or if it is super warm.

 

Trailer
The trailer, from behind. Yup.
Solar panels on the trialier.
Solar panels on the trialier.
Inverter and batteries
Inverter and batteries, they are both inadequate for running the A/C due to the unspecified peak surge on the unit.
Electronics Box
I built a bench/box to hold the electronics. Works pretty good on CSA pickups where I build the bags as customers show up.
Another shot of the electronics.
Another shot of the electronics.
A/C Hole
Uh oh, someone chopped a hole in the front of my trailer…
Framing for A/C
Here’s the framing for supporting the A/C. It is over engineered and crooked like everything I build.
A/C in Place
The A/C in place, ready to test. Don’t forget to test…
Mmm, pink insulation...
Mmm, pink insulation…
OSB Cladding
The OSB cladding going up, you can see how great it is at hiding mistakes!

[UPDATE: 2015/01/08]

After two seasons of use I am loving the unit. Sadly, the solar system sucked. I couldn’t get it to work, it was an endless series of problems or break-downs due to the vibrating nature of the trailer and the variable draw from the A/C. Rather than sink more money into solving it, I am repurposing the electronics for lighting a Seacan and prospectors tent. The cubby is now an excellent storage space for farmer’s market equipment.

One thought to “Walk-In Cooler On Wheels”

  • Mark (Johnny) Schraefel

    I believe you are 95% done Marcus. The hard part. Maybe we can assist you on the last 5%. I’ll send you what we started.
    Johnny
    CBI Solar.
    Red Deer.

    Reply

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