If the rate at which we radiate heat is correct, we feel comfortable. When the temperature difference between our body and the surrounding cool surfaces becomes too great, we have to put on a sweater to slow down the rate at which we are radiating. When the sun beats down on us through the window, we receive heat instead, and off comes the sweater. Our normal state is to lose heat at a constant and regulated rate. We are also designed to lose heat in other ways as well.
Air coming in contact with our skin conducts away heat.
Our skin is moist and moving air also causes evaporative cooling. A truly comfortable environment is one designed to draw heat away from our bodies at precisely the correct rate. This type of system heats water instead of heating air, the way most traditional systems do. Not only is it inherently comfortable and efficient, but the fact that it requires water temperatures as low as 90 degrees makes it a good match with lower-temperature heat sources like heat pumps and solar. The warm water is then carried to surfaces in rooms that can best store and slowly give off the heat to you while you are in there, reading Gone With The Wind.