Mostly the joy of designing, installing and starting-up a large refrigeration system and knowing that if these things are done properly my customers can prosper. After 23 yrs my favorite saying is the only reason someone called me is because someone else screwed it up. It's nice to know that your customers appreciate you as much as you appreciate them. Remember don't screw it up or if you do admit it.
Industrial side is all pressure. Refrigeration, process cooling, or MAU with direct fire heat, etc. when it don't work and the line stops money evaporates! Butts pucker!! And tempers flair!! I love it. If your good you are appreciated, for the most part, and will always have work. When you have big clients who haven't lost a minute of production in years to your equipment failing they know it. They will trust you and seek your opinion. When you tell them something needs to be done they will cut the PO. This is usually true till a new bean counter comes in and wants low bid everytime. It happens but the pay me now or pay me later, later costs more rule almost always comes into play in these situations.
Love the markets and the industrial refer. As Tommy said, pay me now or later. Either way, you get paid. Its hard work and long, odd hours but it is rewarding. Lately I have been enjoying refer wharehouses. They are so neglected and so easy to make money.
Yes, I have a lot of production cooling/refridgeration experience in industrial settings. As Thermofridge said hard work, long hours and I might add usually not the most desirable working conditions. My worst ?? I once had a trailer full of explosive chemicals in 55 gallon drums that had to be kept at a certain temp.. Another a cascade system that recovered butane from gas fumes in an explosion proof hut. Obviously im here now, so all went well. I like it because I get to see things the general public will never see or experience. Disadvantages are usually you WILL stay until things are running, and the danger involved.