This article describes how I created, with the help of one useful and several useless service professionals, a refrigerated box truck for my local foods brokering and distribution business. Any produce distribution that occurs in summertime needs to keep the goods cool to ensure longevity and food safety. The problem for young local food systems is that the cost of refrigerated vehicles in good condition can be very high. My hope is to show readers what I've learned so that if someone else tries this they won't do some of the things I did.
Basically, a refrigerated truck works by taking a refrigerant gas and compressing it, which makes it hot. This compressed gas is forced through a heat exchanger on the roof (the condenser), where heat is dissipated to the air. This causes the compressed gas to liquefy. Next, this liquid travels through an expansion valve where the liquid, which has really been wanting to expand and turn into a gas so badly, gets a chance to. Because the gas is really the product of a substance that boils at low temperature, the compression part of this cycle has reversed the act of boiling and turned the gas back into a liquid. Now, when the liquid is allowed to expand and turn back into gas, its temperature drops to its boiling point and when air is passed over the pipes containing the gas (the evaporater), the air is cooled. The reefer unit on my truck uses R134a, the most common vehicle air conditioning gas, which has a boiling point of -15.34 degrees Fahrenheit.
I didn't know all that when I built the truck so don't worry if it seems dense. What you need to build your own refrigerated box truck are these materials and tools. If you don't have them, consider making friends with people who do:
Spray foam insulation
Lumber to frame out and panel the interior
Screws, paint, brushes, nuts, bolts, glue, etc.
Discussion of Trucks
I won't go into the relative merits of Chevy, Ford, and Dodge. I bought a 1990 Ford because it was cheap (about $4000) and had a brand new re-manufactured diesel engine. As you peruse Craigslist and eBay, you'll see a lot of former rental fleet box trucks. Rental companies usually get rid of their trucks in the 80,000 - 100,000 mile range, meaning that they are still in good shape. A 12 to 14 foot box truck from any of these sources can run $7000 - $10,000, depending on your locale.
Things to consider when making your purchase include mechanical condition of the truck (Who was driving it? Who was maintaining it?), engine size and fuel economy (My 7.3L diesel gets about 10 mpg under load with the reefer running - consider a smaller engine or vehicle!), how far away the truck is (It will cost real money to retrieve it), how easy it will be to work on and get parts for, and some ease of use considerations (Does it have a pull-out ramp or lift gate? Is the box high enough so that when it's insulated with 4 inches of foam on floor and ceiling you will still be able to stand up?).
Remodeling the Box
One unfortunate task I needed to perform was scraping several layers of vinyl and paint off the truck box. Consider a truck that you can just paint over! My truck had a roll-up rear door, which I needed to replace since it would be impossible to insulate. These doors are very heavy and are under spring tension, so be careful when you are unbolting them. Once the door was removed, I proceeded with framing out the interior of the truck box and installing an insulated walk-in cooler door I found on Craigslist. See the photos for visual details.
The insulated door I used was about an inch too tall, so I cut off the bottom with a skill saw and steel cutting blade. Although this kind of foodservice door is rugged and good in many ways for this application, it is designed to be used indoors, and moves on urethane bushings. I've noticed that sand and dust collect in these bushings and that the grit is wearing them out after one season of use - the door is sagging by about 1/8 inch.
I framed the floor of the box with 2/4s on a fairly tight grid and 5/8" OSB board, figuring that the floor would get the most abuse. For the walls and ceiling, I used 1x4s on a 4' spacing and 3/8" plywood, thinking I could save structure and gain foam volume. This sort of worked, but it turned out to be difficult to align plywood joints on top of these skinny studs, and almost every piece of plywood paneling had to be custom cut several times. I would recommend 2x4 studs, and a closer spacing. The 3/8" plywood seems to be working fine, although it has bowed out or in in some places. I may try re-doing the ceiling with tongue-and-groove aspen, which is cheap around here.
After the box was framed out and the door installed, I had the reefer unit put in. In most cases, however,I think it would be best to put the reefer unit in last, after all the insulation and carpentry are finished. Most reefer units of this size will mount to the front of the box, above the cab of the truck, but since my truck is a former Uhaul truck with the over-cab extension, I chose to mount the condenser on the roof, so that the weight of the entire reefer unit could be borne by the vertical interior front wall of the box. A front-mount installation seems preferable to me for ease of access, better hose routing, and less loss of interior space. Just make sure to frame your front wall to bear the weight of a couple hundred of pounds of reefer unit.
The framing in the rear was covered with steel panels I found at our local junk yard. They are attached with rivets and screws to the framing and truck box.
The next step was to have a local spray foam business come and fill the spaces between all the studs with closed-cell spray foam. This material is about R6 per inch, and I used about 3.5 - 4" on the walls and floor, with a little more on the ceiling due to the curve of the roof. What you are insulating against is heat penetration, so it makes sense to have more insulation on the roof than on the floor. It's very effective insulation, and is the only practical solution to insulating a box truck. It's expensive, but not more so than foam board, and once cured, it's very structural, meaning that it's not going to separate or allow loose framing to rattle. Insulating my 12' box cost about $1000.
Make sure that the foam guys either don't spray a full depth of foam or that they pledge to trim their over spray to the depth of your studs. I spent many long angst-ridden hours with sub-par tools trimming back the foam to be flush with the studs. A little less foam is worth avoiding this aggravation. After the foam was trimmed flush, I added the flooring and wall and ceiling paneling. I had to cut a ramp at the rear door to transition from the height of the insulated floor to the level of the truck bed, about 4". I covered this ramp with scrap aluminium diamond plate material from the local junk yard, and laid linoleum as a floor surface.
The reefer unit I bought is a Carrier 30s, which is just barely powerful enough to cool this box. It produces 10,000 BTU and in the heat of the day takes about 2 hours to bring the box to 40 degrees. Since most of my distribution starts early in the morning, it generally takes less than an hour of running time to cool the box. If my unit had standby power, I could plug it in to a wall socket and cool the truck prior to driving. This is also a nice feature if you plan to hold produce overnight in the vehicle. This reefer unit is powered by a compressor on the engine of the truck ("direct drive"), but most larger units have their own small gas or diesel engines built in that power the compressor.
My reefer unit came with a compressor, but I didn't use it since there was already a beefy one on the truck engine that had been used for the vehicle's air conditioning. Compressors can be expensive to work on or replace so it's nice if you know whether it works before you use it for this project. I got lucky. Also, using the truck's AC compressor means you won't have air conditioning in the cab. Just make sure that your compressor is designed for whatever gas your reefer unit takes (134a is nice because most auto compressors are designed for it). I bought my reefer unit off eBay sight unseen for $800, not knowing if it worked. I eventually got lucky there, but I would recommend you see these things in person and determine whether they do work before you buy them.
I strongly recommend you buy new refrigerant hoses from a reputable auto parts store to connect your compressor with the condenser and evaporater on your reefer unit. This mistake cost me a lot of time and money - the person who installed the reefer unit for me used hydraulic hoses, which although they can take the pressure, are not formulated to resist the corrosive nature of refrigerant gas. I spent the first half of this season paying people to try and figure out where the gas was leaking out, and it turned out to be dozens of tiny pinholes in the hoses themselves, apparently caused by the gas eating through them. It cost $400 for new heavy-duty refrigerant-specific hoses at NAPA, but it solved the problem. In my town, NAPA also installs high-pressure hose fittings needed for refrigeration.
I suggest having an experienced refrigeration technician assist you with the installation of the reefer unit. It will probably save you lots of time and money, and there are a lot of hoses and wires that need to be connected in the right places. Additionally, a licensed person will have to pressure test and fill the system with coolant gas. A word to the wise: find a technician with a solid reputation who has experience working on vehicle-specific refrigeration systems. Just because someone knows how to fix household refrigeration doesn't mean they know everything about vehicle refrigeration. Once I followed this advice, my reefer system worked the rest of the season without fail.
The interior of my box is painted plywood with a stylin' moppable linoleum floor. This is in keeping with what my local health department recommended, although they do not regulate the construction of refrigerated vehicles. In fact, I have not been able to find a government agency interested in giving me advice on materials and construction. This is a nice, if unsettling, position for wholesale businesses to operate from, since it would appear that any liability for the condition and safety of the produce lies with the wholesale buyer, and not the broker and transporter. Therefore, although it will behoove you to make sure your customers know you have a safe, clean, and well-maintained refrigerated vehicle, it appears that regulations regarding construction materials don't exist. I suggest abiding as closely as you can to health department regulations for food preparation facilities.
In the past, I have used second-hand wax cardboard boxes to transport produce, with boxes labeled by customer account. Since I receive most produce in plastic bags, this system has worked and is fairly sanitary. However, used boxes are probably a potential disease vector, and they can't be bleached. One advantage of being a small local food distributor is that I can deliver the produce in plastic bags and keep my containers. Recently, our Department of Tourism gave me a grant to buy rectangular plastic milk crates [source = http://www.milkcratesdirect.com/], which will solve the sanitation issue, and they are of uniform size with mesh sides to allow ventilation. The only drawback is that they don't nest when empty.
Some future improvements I plan to make to the inside of the box include retractable cargo netting to stabilize higher stacks of crates, some bumper rails to keep crates away from the wall, LED strip lighting (solar powered?), and a coolbot-powered AC setup to accomplish standby cooling. I also hope to someday convert the diesel to burn vegetable oil, since there are considerable cost savings in that fuel.
$4250 Box truck
$1050 Spray foam installation
$285 Insulated door
$800 Reefer unit, used
$37 Metal materials
$271 Tools directly related to construction
$450 Retrieving truck, reefer unit, door from distant cities
$1413 Reefer unit install, subsequent refrigeration work
$445 Truck parts including starter, glow plugs, glow plug relay, some diagnostic work
$248 Carpentry supplies including screws, bolts, glue, paint, etc.
$1025 Six new tires
$10,759 Total Project Cost
Estimated hours: Unknown. I had to learn a lot as I went along. Someone with more advanced carpentry and auto repair skills could do it faster, by a lot. I'd say I have a couple hundred hours into the project, but probably more with the various problems discovered along the way. Commercially manufactured reefer trucks on eBay of comparable size and condition are selling for $15,000 to $20,000. You may decide that given the hours and troubles involved in a project like this that it's worth it to spend the extra $5000 or so and get a truck that's set up for this job. Unless you're a good carpenter, a decent mechanic, and live in an area with lots of technician services to choose from, I might agree that spending the extra money is worth it. However, if you have resources that I didn't, you might even be able to do the job for less. Either way, I hope this article helps you make the best choices. Good luck!