Mobile air conditioning sucks

Published on
By Imre Jonk

With temperatures rising in the Netherlands and summer being just around the corner, most of us are looking for effective means to keep one's home or office (or home office) cool. The current heat record stands at 40,7 °C, measured on July 25th, 2019, near the city of Tilburg. There's no point in trying to get any work done in those temperatures. For me, the tipping point between "it's hot, but I'm coping" and "Jesus Christ who can work in this heat" is around 30 °C. That number might also be psychological.

Wind is also a huge factor. An example: the average high temperature while I was on a diving holiday in Egypt two years ago was around 40 °C, but this was okay as there was often a fresh breeze coming from the sea and I was in and around the water all day anyway. Then, one day I woke up and saw that the sea was completely flat. Not even a single ripple was to be seen. I walked into the restaurant where one of the Egyptian staff members was doing some live cooking. I asked him about the weather and he just responded, sweating excessively, "It's very hot today sir. Very hot."

To combat this heat, humanity has invented air conditioning. The ancient Egyptians already had passive air-conditioning techniques available to them, but nowadays the term 'air conditioning' is associated with A/C units that are powered by electricity. There are many types and sizes, but the thing they have in common is that they work by means of a heat pump and evaporative cooling. A compressor pumps the refrigirant, a substance that easily transitions between liquid and gaseous phases, between the evaporator coil and the condensing coil. The evaporative cooling takes place in the evaporator coil. Here, the refrigerant evaporates (transitions from liquid to gaseous), taking in a lot of heat. You'll want to have this side of the unit on the inside of the building. After this, the refrigerant passes the compressor where the pressure of the refrigirant is increased, allowing it to transition back to a liquid phase in the condensing coil, releasing a lot of heat in the process. This is the part that you want outside. The cycle repeats after an expansion valve which functions as a way to lower the refrigirant pressure before letting it pass through the evaporator coil again.

A type of air conditioning that is getting more popular is the mobile A/C. It is mobile in the sense that it has little wheels underneath and it can be installed somewhat temporarily. These units have a flexible hose that is used to transport hot air outside. There are, however, a number of issues with these units. First, the condensing coil, the part that is built to release energy in the form of heat, is inside the room. This part gets hot. In standard air condition units, the condensing coil is placed outside for precisely this reason. Second, there is the issue of transporting air outside. This lowers the air pressure in the room a tiny bit, causing it to suck air in from elsewhere, usually outside. On a sunny day this air is hot. Third, the air intake is in the same room, meaning that the mobile A/C unit basically takes in the air it just cooled, and throws it outside. And fourth, the exhaust hose is often long and badly insulated, causing it to lose heat to the same room you are trying to cool. It is also often hard to install the hose in such a way that outside air can't get in. I see many people just opening their windows in order to hang the hose outside. This vastly undermines the usefulness of powered air conditioning.

Mobile A/C units would be a lot more efficient if they had two hoses instead of one, so that outside air can be used to cool the condensing coil in a closed loop instead of sucking air in from outside. But alas, this would make mobile A/C units less attractive to consumers because you now have two bulky hoses to deal with.

If you are looking for some tips to keep it cool, here are my recommendations:

  1. Try keeping sunlight outside before it enters the room. See if you can have awnings installed above your windows. If that is not possible, try light-coloured curtains that don't let light through, or stick special sunblocking foil on the inside (but preferably, outside) of your windows.
  2. Open windows on both sides of the building in order to create a nice breeze. If that is not possible, open all windows and ventilation grates and put the mechanical ventilation system on max. Clean out your ventilation grates once a year.
  3. If you notice heat travelling through your walls or ceiling, see if something can be done about the bad insulation of the building.
  4. Keep it cool and drink a lot of water. Avoid consuming alcohol.
  5. If you long for a constant breeze on your body, get yourself a fan.
  6. If all else fails, have an air conditioning unit installed. Don't go with a mobile one.

A great video on the subject of mobile air conditioners is Portable Air Conditioners - Why you shouldn't like them from Technology Connections.