How to run AC units efficiently at home or office? PART 4

(For the time being we are ignoring the existence of Inverter type units)

The heat loads are normally estimated for the worst ambient conditions and units are selected. However the actual load seldom remains the same because the ambient temperature keeps varying. However once a unit is selected and installed, it always tries to produce its full capacity possible at that ambient condition, irrespective of the actual cooling required. Though there is a thermostat, the room goes through a cyclic cooling, which makes the occupant feel uncomfortable. The cyclic process is unavoidable for a few reasons. First, the rate at which cooling is produced is never equal to the rate which heat enters the room. Hence the unbalance always produces un-comfortableness. Second, the thermostat being a mechanical device requires two end points to cut off the compressor and restart it a little latter. When the cutting off takes place, say at 24 ˚ C, then the next minute theoretically it would have to restart because the temperature would have risen. But in practice it is allowed to do so, as otherwise the compressor starts cycling, or repeatedly starts and stops. This not only disturbs the power supply systems characteristics, but also the life of the compressor itself! Also practically it is impossible to produce a device that does two opposing functions at a single point, namely cutting off and restarting. Hence a gap is given in the device to function, which is referred to as ‘differential’. Either it is allowed to overcool and restart at the set point or cuts off at the set point but restarts at a slightly higher temperature!

In addition the human body is so sensitive to temperature, that at the same indoor temperature, it feels differently during summer and winter. (i.e) You may feel very comfortable at 22 ˚ C during summer, but during winter a slightly higher temperature will feel more comfortable. The poor combination of your compressor and thermostat do not understand this.

So as long as you have installed an equipments that produces constant cooling irrespective of the load, you have to set your preferred temperature in the thermostat and accept a cyclic nature of indoor temperature and be comfortable with that!

Now enter the new variety of, not only ENERGY EFFICIENT AC units, but also units that can think like you!