Floor Heating: Achieving Thermal Comfort in Artificial Environments  Modern man demands high levels of thermal comfort in artificial environments. Linked to this international pressure grows to reduce demand on the earth’s energy reserves. Modern technology
has made great strides forward in developing new innovative heat sources but probably the greatest advance in combined thermal comfort and energy conservation is the modern wet floor heating system. The advent of high quality plastics pipes has made possible the utilization of low temperature water in floor heating systems perfectly compatible with the new heat source technology. Fully developed for all types of floor construction, U.F.H. combines all types of heat, conduction, radiation and convection, matching the ideal temperature gradient throughout an entire building. The safe, invisible, space saving, vandal and tamper proof system is both responsive and energy conscious offering passive self regulation.
 Thermal comfort can be defined as the state of mind where satisfaction is felt with the thermal environment. Research shows that people feel most comfortable when their feet are a little warmer than their heads. Independent tests reveal that the most acceptable indoor climate is one in which the floor temperature ranges between 19！29? and the air temperature at head level ranges
between 20 and 24?.
 However, since individuality is integral to all human activity it is not possible to specify one set of environmental conditions which will meet all cases. The best results we are likely to achieve depend on a 5% dissatisfaction factor. There is to temperature that will please everyone, but we can aim to establish a comfort zone that will satisfy the highest possible percentage of those using the area.
 With radiator or convector heating systems a vertical temperature gradient is produced; colder at foot level than at the head. A modern indoor climate surely demands a heating system which will match the required conditions for human thermal comfort with the principal heating effect being evenly distributed at ground level and not above head level. We have seen that warm feet create good sensations, so let us examine the effect upon the door climate if we warm the whole floor to just the right temperature.
 We have touched on improvements in building standards but no amount of insulation can change the laws of physics—heat sill rises. Efficient insulation will, however, serve to trap heat above head level in an area where it can make no contribution to human comfort. Solving this problem involves a close study of the three types of heat available to us. Radiant heat provides the most pleasurable sensation of comfort. It contributes to the exhilaration of a walk in the spring sunshine even though the ambient air temperature may be only a few degrees above freezing. We humans also respond well to conducted heat—the cat-like pleasure that comes from the warmth of
a hot water bottle or just cuddling up to another person. Lastly, there is convected heat caused by the effects of the radiation and conduction warming the air and causing it to rise. By using all three types of heat in association we can achieve very high levels of thermal comfort. The normal criterion for heating design is to achieve a specified air temperature against the given heat loss of the building at a specified outside ambient temperature. When designing a floor heating system, however, lower air temperatures may be acceptable because of the higher level of overall radiation and the added benefit of conduction from warm, friendly floors.
 In modern, well insulated buildings the temperature of the floor surface need be only just above air temperature in order to achieve the required comfort factor. These low temperature differentials result in gentle, low velocity convection throughout the entire building. Low velocity
convection reduces the amount of dust in the air in comparison with other types of heating. There are no inaccessible areas behind radiators or convectors where dust or dirt can collect. It is also cost efficient to operate. Eliminating high velocity convection means there will be no stack of high temperature air above head level.
 A heated floor is a radiant plane: subjects standing on it will therefore receive the benefit of all round radiation.
 A high level of radiant comfort means that air temperatures can actually be slightly lower with an infloor heating system than those usually required for other methods of heating. Radiation, conduction and convection combine to create the ideal thermal environment for health and comfort.
New words and expressions
vandal  n. 破坏者 a. 破坏性的
convector n. 对流散热器
gradient [greidi] n. 梯度
exhilaration n. 高兴
cat-like a. 像猫一样
cuddle v. 卷缩着身子躺