Rome

Underfloor heating was first used by the Romans. Initially the preserve of the rich, underfloor heating became increasingly commonplace in public buildings and villas, particularly in the colder regions of the Roman Empire.

The Roman system was based on hypocausts, comprising ducts that underlay the floor (itself built on raised brick piles) and flues that were built into walls. Hot air or steam from fires circulated up through this system, warming the floor and walls, with heat passing into the rooms.

More specifically, the floor was laid out as series of concrete slabs supported by columns of layered tiles, with a furnace at the bottom of one exterior wall. By placing the fire here, the draught would take the heat under the floor, and up through the walls to chimneys located in the corners of the room. The height of the stack of tiles was about 2 ft (60 cm) as this was found to be the most efficient height for the air to travel through.

Once the air had passed under the floor, the air was drawn into the walls and up the flues by the action of the hot air already rising in the flues creating a partial vacuum and so pulling the air below into the walls. The walls were very often made of bricks with two holes horizontally through them. This had the effect of passing the air through the walls and into the flues, thereby warming the walls also.

In the Roman baths, the furnace was placed next to the hottest room caldarium in which three walls of this room were heated so that the room reached a temperature of up to 120 °F (50 °C). The warm room tepidarium only had one wall heated which made this room cooler than the caldarium.

The furnace was the heating source of the system and this was placed on the outside of the house, below the floor that ran under the room that was to be the hottest room in the house. One room was always hotter than the rest, as the air flowing under the floor would naturally lose some of its heat as it was traveling under the floor.

The Roman underfloor heating system was a labor intensive device that required constant attention to feed the fire and remove the ashes. (Again, it was originally only the wealthy that could afford to have it.) The fire would need regular attention from a household worker who would have to rake out the ashes with a long handled tool and, using the same tool, push new fuel into the fire.

The fuel was mainly small branches and twigs (up to about 3 in/76 mm in diameter and up to 2 ft/610 mmlong), which were placed 2–3 feet (610–910 mm) into the furnace opening. This would allow air to be drawn in and around the wood and so made sure the air flowed freely. Logs were not used as these burned too slowly to be effective, and too many would block the passage of air. The height of the fire was restricted to around half the height of the opening so that air could flow through the flames and so accelerate circulation and increase heat output. This was essential in the baths, where the maximum amount of heat had to be generated.

The hypocaust was recently voted the most important heating invention ever by the British HVAC industry.[1]

Korea

In contrast to the eventual disappearance of the Roman underfloor hypocausts, underfloor heating has remained in use for millennia in Korea, where it is known as ondol. It is thought that the ondol system dates back to the Koguryo or Three Kingdoms (37 BC-AD 668) period when excess heat from stoves were used to warm homes.

Ondol continues to be a typical feature of the South Korean home, and is widely credited with making possible distinctively Korean customs such as removing one's shoes upon entering a home and sitting on its floor. (The "sitting culture" brought about by ondol influenced the design of hanbok, the traditional Korean outfit; hanbok trousers are loose and have enough room for people to easily bend their knees and sit for long periods of time, and traditional shoes were also made to be easy to take off and put on compared to Western shoes.)

In fact, when Western forms of heating, such as blowers venting hot air, became more widely used in Korea, many families began to miss the ondol system that had long been an integral part of Korean life. As a result, developers in Korea during the 1990s began to discard Western forms of heating, and started to incorporate ondol in new housing developments. Even the most modern Korean hotels offer guests the option of selecting a traditional ondol room with no beds.

Korean ondol technology

Ondol, literally meaning "warm stone", comprised three main components: a fireplace or stove, which is also used for cooking and located below floor level; a heated floor underlayed by horizontal smoke passages; and a vertical chimney, located lower than the roofline, to provide a draft.

The heated floor comprised a network of underground flues that transported heat from the kitchen to each room. These flues were covered by thin, flat, wide stones two or three inches thick called kudul that lay underneath the floor. Kudul, literally meaning "fired stone", was covered with yellow earth, and the floor was leveled. To top it off, several layers of yellow paper sheets were pasted on the floor. This process was efficient since the heat and smoke generated during cooking would be transported automatically to each room in the house. Usually the kitchen would be built at a lower level (about one m), and the heated rooms would be in an elevated position to allow the flues to run underneath. Notably, with just one heating the floors would retain their warmth for extended periods, ranging from more than 30 days to three months depending on the design of the flue structure.

The traditional ondol rooms found in the northern part of the Korean Peninsula differed somewhat from those in the south. In the north the ondol- heated room and the kitchen were not separated by a wall. Heat from both the fireplace and the ondol floor kept the room warm. In the south, a wall separated the kitchen from the living room, preventing the smoke from disturbing people sitting there. Also, in a room heated by ondol, the floor at the far end of the room tended to be cool. (Elders such as grandparents or parents as well as guests were invited to sit in the warmer area as an expression of respect.)

The continuing legacy of ondol

In the early 1900's, when the American architect Frank Lloyd Wright was building the Imperial Hotel in Japan, he was invited to the home of a Japanese nobleman. There Wright found a room that was different from typical Japanese rooms, with a warm floor covered with yellow paper -- a Korean ondol room. The Japanese gentleman had experienced ondol in Korea and, once back in Japan, had an ondol room built in his house. "The indescribable comfort of being warmed from below" impressed Wright.

Wright decided then and there that ondol was the ideal heating system and began incorporating it in his buildings. Wright invented radiant floor heating, using hot water running through pipes instead of hot air through flues. In Korea, ondol has likewise been adapted to modern technologies and changes in fuel. Modern Korean homes and apartments are built with heating pipes embedded in floors that are typically concrete covered with vinyl or oiled papers. Heated water circulating through the pipes, warmed by a gas or oil boiler, has replaced heated air, minimizing the danger of carbon monoxide poisoning or burns.

With its modernization, ondol has received international recognition and has become increasingly popular abroad, particularly throughout Asia. Moreover, a new type of ondol product, to which Western living patterns have given birth, is increasing in sales outside of Korea. Tolchimdae, meaning stone bed, has emerged as a hot seller in the furniture market beginning in 1998. Tolchimdae, which first appeared in the market in the early 1990s, is a stone bed filled with either carbon film or copper coils that are electrically heated. Its development was based on the concept of the ondol system. The new product is especially popular among older customers who want to enjoy ondol, but on a Western-style bed.

                                                                                                                                                                        sursa : Wikipedia

HOME > Produse > Incalzirea in pardoseala > Istoria