Packaged terminal air conditioner (PTAC) systems are also known as wall-split air conditioning systems.They are ductless systems. PTACs, which are frequently used in hotels, have two separate units (terminal packages), the evaporative unit on the interior and the condensing unit on the exterior, with an opening passing through the wall and connecting them. This minimizes the interior system footprint and allows each room to be adjusted independently.
"Countercurrent" heat exchangers occur naturally in the circulation system of fish, whales and other marine mammals. Arteries to the skin carrying warm blood are intertwined with veins from the skin carrying cold blood, causing the warm arterial blood to exchange heat with the cold venous blood.
Estimated at US$42.7 billion in 2012, the global demand of heat exchangers will experience robust growth of about 7.8% annually over the next years. The market value is expected to reach US$57.9 billion by 2016 and to approach US$78.16 billion by 2020. Tubular heat exchangers and plate heat exchangers are still the most widely applied product types.
In the United States, 87 percent of the homes use air conditioning and 65 percent of those homes having central air conditioning. Most of the homes with central air conditioning have programmable thermostats, but approximately two-thirds of the homes with central air do not use the features of them to make their homes more energy efficient.