How to Build a Mobile Walk-In Cooler with a CoolBot

A refrigerated mobile cooler can really expand your opportunities and business. With a standard air conditioner and a CoolBot in your truck or trailer, a mobile cooler becomes an affordable option! A few common uses of a mobile cooler using the CoolBot include:

• Stands at distant farmers markets
• Direct harvest into a cooler for cooling in the field
• Mobile coolers for hunting trips
• Deliveries to restaurants and customers
• Food trucks
• Vending at events

On this page, we will walk you through the different steps of building a mobile walk-in cooler with a cooler. These steps are:

Mobile Cooler Construction

Shell

Our customers have created their mobile coolers in so many ways! It’s hard to name them all, but here are a few:

• Built on an existing trailer bed
• Built into the cab of a truck
• Converting old reefer units
• Using old buses

The Floor

Insulating the floors in mobile coolers is even more important than in stationary ones. Not only is there an additional side exposed to the elements and ambient air, but it is generally rolling over hot paved roads. Since cold air sinks and road heat rises, it is even more important to take preventative measures.

How to insulate the floor:

1. Lay 2 inches of polyurethane or polyisocyanurate rigid foam on the floor.
2. Put the next 2 inches of rigid foam down so the seams go in the opposite direction of the first layer.
3. Lay 3/8 inch plywood painted with outdoor paint on top.

The Door (and Sealing)

Some vans have sliding or rolling doors, which are not ideal for two main reasons: 1) it is incredibly hard to get a tight seal, and 2) there is nowhere to add insulation (we don’t recommend spraying foam in the body since this can cause the metal to pop out).

What works well is to put a wall inside, so you would have a door inside the van which would provide the tight seal we need. Plus. you would have space to store boxes and tables.

Insulation

For mobile applications, we only recommend Polyisocyanurate rigid foam insulation which is:

• Available in Lowes and Home Depot
• Yellowish/ gray in color
• Highest R-value at 6-7 R per inch; shoot for at least R25 if you are going down to 38°F

For Polyisocyanurate rigid foam insulation, note that there is a foil side that has to always face the “hot” side.

You can use spray adhesive to hold rigid foam insulation in place. We use “3M high strength 90” adhesive because it is very strong and readily available. Some of the adhesives can melt the styrofoam, so do a test first.

Spray foam – Some people hire a spray foam installer. Spray foam has just under R7 per inch at best, so make sure they do at least 3 inches if you go that route. We recommend the spray foam kits which you can buy from our friends at Energy Efficient Solutions. Use the coupon code COOLBOT_FOAM for 3% off your spray foam kit purchase (~$17 off per spray foam kit)!

DO use urethane spray foam like  “Great Stuff,” not the latex version. That way you can cut the pieces and then patch the gaps with “Great Stuff.”

Air Conditioner

Window Unit

The best type of A/C to use for mobile applications has been proven to be the durable and efficient window unit.

Our favorite brand is LG – we have the most experience and best results working with their window units.

Protect your A/C!  Unlike stationary coolers, your mobile cooler needs some additional care when it comes to the installation of the A/C.  To protect from bumps in the road, use some sort of shock absorber between the brackets and A/C to absorb impact. The last thing we want is the shock from hitting a pothole to jolt the coolant tubes hard enough to damage them.

Mini-Split Units

Another option that our customers have used in a mobile application is a Mini-Split air conditioner.

The reasons people use this option are:

1. It is much cheaper than conventional mobile refrigeration.
2. The “Soft start” compressors are very easy to run off of inverters directly on the engine.
3. The compressor is separate from the evaporator so they can be installed without cutting a hole in the side of the vehicle. The evaporator is very light and hangs on the wall inside truck. The compressor can be mounted somewhere else.
4. Because only about a 3″ hole has to be cut into the truck body, you don’t have to worry about bad seals.
5. In most cases you can get away with slightly less BTU’s when you use a mini-split unit versus a window unit. For example: if you were thinking of buying an 18,000 BTU window unit, the equivalent mini-split unit would be 15,000 BTUs.

Mini-splits are more expensive, but have a lot of advantages. Check out our Air Conditioner Selection Guide for a list of brands that we have had experience with.

RV Roof Top Units

Many of our customers want to use RV air conditioners, which we don’t recommend for the following reasons:

1. They are very expensive per BTU — especially when you try to find one with a digital display. 
2. They are difficult to set up and maintain due to the confined space in which the sensors are installed.
3. There is BTU-transfer penalty of almost 30% due to the limited surface area of the intake/output.
4. They use twice as much power as a window unit.
5. Overall the RV A/C is just more difficult to work with and less efficient than the window unit.

Power

Depending on the size of the cooler, there are a couple ways of going about powering your mobile unit:

Alternator

• You can run off the alternator of your vehicle only if you buy a 12,000 BTU air conditioner or smaller and use an inverter. Note that this can limit the size of your application or how cold you can get. For spaces up to 8’x6′ that are VERY well insulated, you should be able to hold 38°F.
• If your A/C is over 12,000 BTU’s (even on larger vehicles), you have to upsize your alternator and upsize your inverter into non-commodity items, both of which are very expensive.
• A more cost-effective alternative is to use a generator.

Inverters

• We recommend the TRIPPLITE heavy duty inverters. They are a bit more expensive than some other brands, but we think they worth it.
• In general, you want an inverter that can surge to *at least* 3X the running watts that are listed on the air conditioner.

Generators

• Customers running their coolers in big box trucks or on larger trailers (we have people running 20 foot trailers on CoolBots) generally run on generators and a 24,000 BTU air conditioner.
• To Determine What Size Generator You Need:
  1. Search for the window air conditioner you plan to use on Google. If you can’t find your exact model, find a similar air conditioner with the same BTU output*
  2. Find how many Cooling Amps the A/C uses (on a 15,000 BTU air conditioner, they say it’s 12 amps of cooling power).
  3. That’s what the A/C unit is drawing when the compressor is running (which is obviously not all the time; sometimes just the fan is running, and the A/C would draw less than 12 amps at those times).
  4. Generators and inverters are sold by WATTS which are determined by this equation: Watts = Amps*Volts
  5. There are 120 and 240 volt air conditioners. 15,000 BTUs and below are 120 volts. 18,000 and 24,000 BTU units are 240 volts. (When we say “120 volts and 240 volts” we actually mean “110-130 volts” and “220-250 volts”)
  6. Now… back to the equation.
  7. Watts = 12 Amps * 120 Volts…that’s 1,440 Watts!
  8. When the compressor is starting up, it can draw 2x to 5x the listed running watts for a few seconds (long enough to trip the circuit breaker on the inverter or generator). We’ve found that 3 times is safe enough, as no modern air conditioner seems to be drawing 5 times the wattage.
  9. That’s about 4,500 watts.
  10. Add on the continuous power output of 1,500 watts and a bit more as a buffer.

Notes

• If the generator and A/C are too closely matched, and there is barely enough power for the initial surge, you can get a hard start capacitor. We recently had a florist in Tampa report back on his experience and he said it worked great, was easy to install, and highly recommended being certain you are connecting the wires to the compressor and not the fan. Follow the wires back if you have to. Once installed, he said it was running just fine. His unit was picked up from a local home repair store for just over $20.

**Most window air conditioners of the same size are basically all the same power draw. Mini-splits are the same (about 30% less power draw than window units)

Plug In Cooler

Another option is to use your trailer as a “plug in” cooler. The concept is to run an extension cord from your A/C to a fixed outlet while the cooler is stationary, and leave the A/C unplugged while the trailer is in motion. You will need to use a larger air conditioner to go well below the target temperature. Then with R25 insulation you should be able to average 6 hours before gaining 1 degree C of temperature.

You wouldn’t be able to power the A/C while in motion, but if you keep the doors shut and aren’t far from the next outlet, this could be a good route if buying an inverter or generator are out of the question. When driving with the A/C off, you can build a cover out of solid styrofoam insulation to slide over the outside of your A/C to prevent 55mph warm air from being blown through the A/C.

Mobile Cooler Plans

We built a mobile walk-in cooler here at our office!  Watch our step by set video and download the construction guide here.