Heating with Portable Air Conditioners – a Reversal

Heating with Portable Air Conditioners a Reversal

Certain models of portable air conditioner have a heating function as well as cooling. People often ask how this function works, or if it is just a space heater sandwiched into the unit. The answer is no, the heat function is based on reversing the same heat pump used to cool.

Portable air conditioners cool air with a heat pump, not unlike central air conditioners. Indrawn air from the room contains heat energy. The heat pump uses compression and expansion of a coolant to remove the heat from some of the indrawn air and concentrate it into a smaller volume of the indrawn air. The majority of the air is cooled by the loss of heat energy. So the indrawn of air is split into a 'hot side' and a 'cold side'. Air in the hot side is blown out the window, and that on the cold side is blown back into the room. During this process, moisture in the air returns to liquid form, or condensates. This is how portable ac's dehumidify. Much of the condensate water is used to cool the unit itself. Unlike window or central ac's, portable air conditioners are located within the room, only connected to the outside by a duct, so the remaining condensate tends to accumulate in a drain pan within the unit. Older styles had to have the pan emptied as often as daily, but most modern units get rid of the liquid by evaporating it and exhausting it out the window, eliminating the need to empty the pan.

Now back to the question at hand. The heat function is a reversal of the above process. This is done by reversing the flow of refrigerant, so that what was the 'cold side' is now the 'hot side', and vice-verse. In heat mode then, the air returned to the room is the portion into which the heat energy has been concentrated, and the cooler portion is blown out the window. Since this is a reversal of the normal function, it is often less efficient than the cooling function, and many units have considerably lower BTU ratings for heating than for cooling. This is why one will often see a statement that the heat mode is generally recommended as supplementation when room temperatures are above 50 degrees, and not as the sole source of warm air in a cold room . This is not always the case though, since some units have been designed to be equally efficient in both modes. One can get the BTU ratings of both functions from the model's spec sheet, an important piece of information when evaluating which unit is best for a given application. In either functional mode, since some of the indrawn air has been blown outside, less air is returned to the room than is originally drawn in the unit. This explains the loss of pressure in the room, which sometimes is enough to move doors, etc. Dual-hose units offset this by supplementing the intake with air from out side the room, so the amount of air returned to the room is closer to the amount originally drawn from the room.

I hope this brief non-technical explanation will help give readers a basic understanding of how portable air conditioners with heat actually heat. These are not toys or cheap gadgets but pretty sophisticated pieces of equipment applying old technology in a new way to make a versatile, mobile, effective, and relatively inexpensive room air conditioning option.

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