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f the home based flue gas system to a central water based heating plants oxygen permeation becomes corrosion issue in europe leading to the development of barriered pipe and oxygen permeation standards 1980 the first standards for floor heating are developed in europe water based ondol system is applied to almost all of residential buildings in korea 1985 floor heating becomes a traditional heating systems in residential buildings in middle europe and nordic countries and increasing applications in non residential buildings 1995 the application of floor cooling and thermal active building systems tabs in residential and commercial buildings are widely introduced into the market 22 2000 the use of embedded radiant cooling systems in the middle of europe becomes a standard system with many parts of the world applying radiant based hvac systems as means of using low temperatures for heating and high temperatures for cooling 2010 radiant conditioned pearl river tower in guangzhou china topped out at 71 stories description edit modern underfloor heating systems use either electrical resistance elements electric systems or fluid flowing in pipes hydronic systems to heat the floor either type can be installed as the primary whole building heating system or as localized floor heating for thermal comfort some systems allow for single rooms to be heated when they are a part of a larger multi room system avoiding any wasted heat electrical resistance can only be used for heating when space cooling is also required hydronic systems must be used other applications for which either electric or hydronic systems are suited include snow ice melting for walks driveways and landing pads turf conditioning of football and soccer fields and frost prevention in freezers and skating rinks a range of underfloor heating systems and designs are available to suit different types of flooring 23 some underfloor heating systems are designed to be laid within the floor construction with the pipework embedded within a screed beneath the floor covering typically used in extensions or new builds meanwhile other underfloor heating systems can be fitted directly on top of an existing floor providing it is level and stable using self adhesive panels into which the pipework is laid and a self levelling screed is poured a popular solution for retrofit projects 24 electric heating elements or hydronic piping can be cast in a concrete floor slab poured floor system or wet system under the floor covering dry system or attached directly to a wood sub floor sub floor system or dry system underfloor heating can also be installed in suspended timber joisted floors both ground and upper floors either between the joists using a metal plate to transfer the heat across the floor above or by incorporating the pipework within a specially designed structural floor deck 25 some commercial buildings are designed to take advantage of thermal mass which is heated or cooled during off peak hours when utility rates are lower with the heating cooling system turned off during the day the concrete mass and room temperature drift up or down within the desired comfort range such systems are known as thermally activated building systems or tabs 26 27 the terms radiant heating and radiant cooling are commonly used to describe this approach because radiation is responsible for a significant portion of the resulting thermal comfort but this usage is technically correct only when radiation composes more than 50 of the heat exchange between the floor and the rest of the space 28 hydronic systems edit hydronic systems use water or a mix of water and anti freeze such as propylene glycol 29 as the heat transfer fluid in a closed loop that is recirculated between the floor and the boiler various types of pipes are available specifically for hydronic underfloor heating and cooling systems and are generally made from polyethylene including pex pex al pex and pert older materials such as polybutylene pb and copper or steel pipe are still used in some locales or for specialized applications hydronic systems require skilled designers and tradespeople familiar with boilers circulators controls fluid pressures and temperature the use of modern factory assembled sub stations used primarily in district heating and cooling can greatly simplify design requirements and reduce the installation and commissioning time of hydronic systems hydronic systems can use a single source or combination of energy sources to help manage energy costs hydronic system energy source options are boilers heaters including combined heat and power plants notes 1 heated by natural gas or methane industry wide is considered the cleanest and most efficient method of heating water depending on availability costs about 7 million b t u propane mainly made from oil less efficient than natural gas by volume and generally much more expensive on a b t u basis produces more carbon dioxide than methane on a b t u basis costs about 25 million b t u coal oil or waste oil electricity solar thermal wood or other biomass bio fuels heat pumps and chillers powered by electricity natural gas geothermal heat pump underfloor heating is particularly suitable when the energy source is a heat pump because underfloor heating uses lower water temperatures than systems using radiators which improves the efficiency of the heat pump 30 underfloor heating pipes before they are covered by the screed underfloor heating pipes before they are covered by a concrete garage slab radiant tubing layout project bcit aerospace hangar vancouver british columbia canada manifold assembly modern factory assembled hydronic control appliances for underfloor heating and cooling shown with covers on modern factory assembled hydronic control appliances for underfloor heating and cooling shown with covers off wax actuators electric systems edit electric floor heating installation cement being applied electric systems are used only for heating and employ non corrosive flexible heating elements including cables pre formed cable mats bronze mesh and carbon films due to their low profile they can be installed in a thermal mass or directly under floor finishes electric systems can also take advantage of time of use electricity metering and are frequently used as carpet heaters portable under area rug heaters under laminate floor heaters under tile heating under wood floor heating and floor warming systems including under shower floor and seat heating large electric systems also require skilled designers and tradespeople but this is less so for small floor warming systems electric systems use fewer components and are simpler to install and commission than hydronic systems some electric systems use line voltage technology while others use low voltage technology the power consumption of an electric system is not based on voltage but rather wattage output produced by the heating element features edit airflow from vertical temperature gradients edit vertical temperature gradient caused by stable stratification of air inside a room without underfloor heating the floor is over three degrees celsius colder than the ceiling thermal comfort quality edit as defined by ansi ashrae standard 55 thermal environmental conditions for human occupancy thermal comfort is that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation relating specifically to underfloor heating thermal comfort is influenced by floor surface temperature and associated elements such as radiant asymmetry mean radiant temperature and operative temperature research by nevins rohles gagge p ole fanger et al show that humans at rest with clothing typical of light office and home wear exchange over 50 of their sensible heat via radiation underfloor heating influences the radiant exchange by warming the interior surfaces the heating of the surfaces suppresses body heat loss resulting in a perception of heating comfort this general sensation of comfort is further enhanced through conduction feet on floor and through convection by the surface s influence on air density underfloor cooling works by absorbing both short wave and long wave radiation resulting in cool interior surfaces these cool surfaces encourage the loss of body heat resulting in a perception of cooling comfort localized discomfort due to cold and warm floors wearing normal footwear and stocking feet is addressed in the iso 7730 and ashrae 55 standards and ashrae fundamentals handbooks and can be corrected or regulated with floor heating and cooling systems indoor air quality edit underfloor heating can have a positive effect on the quality of indoor air by facilitating the choice of otherwise perceived cold flooring materials such as tile slate terrazzo and concrete these masonry surfaces typically have very low voc emissions volatile organic compounds in comparison to other flooring options in conjunction with moisture control floor heating also establishes temperature conditions that are less favorable in supporting mold bacteria viruses and dust mites 31 32 by removing the sensible heating load from the total hvac heating ventilating and air conditioning load ventilation filtration and dehumidification of incoming air can be accomplished with dedicated outdoor air systems having less volumetric turnover to mitigate distribution of airborne contaminates there is recognition from the medical community relating to the benefits of floor heating especially as it relates to allergens 33 34 energy edit under floor radiant systems are evaluated for sustainability through the principles of efficiency entropy exergy 35 and efficacy when combined with high performance buildings underfloor systems operate with low temperatures in heating and high temperatures in cooling 36 in the ranges found typically in geothermal 37 and solar thermal systems when coupled with these non combustible renewable energy sources the sustainability benefits include reduction or elimination of combustion and greenhouse gases produced by boilers and power generation for heat pumps 38 and chillers as well as reduced demands for non renewables and greater inventories for future generations this has been supported through simulation evaluations 39 40 41 42 and through research funded by the u s department of energy 43 44 canada mortgage and housing corporation 45 fraunhofer institute ise 46 as well as ashrae 47 safety and health edit low temperature underfloor heating is embedded in the floor or placed under the floor covering as such it occupies no wall space and creates no burn hazards nor is it a hazard for physical injuries due to accidental contact leading to tripping and falling this has been referenced as a positive feature in healthcare facilities including those serving elderly clients and those with dementia 48 49 50 anecdotally under similar environmental conditions heated floors will speed evaporation of wetted floors showering cleaning and spills additionally underfloor heating with fluid filled pipes is useful in heating and cooling explosion proof environments where combustion and electrical equipment can be located remotely from the explosive environment there is a likelihood that underfloor heating may add to offgassing and sick building syndrome in an environment particularly when the carpet is used as flooring citation needed electric underfloor heating systems cause low frequency magnetic fields in the 50 60 hz range old 1 wire systems much more so than modern 2 wire systems 51 52 the international agency for research on cancer iarc has classified static and low frequency magnetic fields as possibly carcinogenic group 2b 53 longevity maintenance and repair edit equipment maintenance and repair is the same as for other water or electrical based hvac systems except when pipes cables or mats are embedded in the floor early trials for example homes built by levitt and eichler c 1940 1970s experienced failures in embedded copper and steel piping systems as well as failures assigned by the courts to shell goodyear and others for polybutylene and epdm materials 54 55 there also have been a few publicized claims of failed electric heated gypsum panels from the mid 1990s 56 failures associated with most installations are attributable to job site neglect installation errors and product mishandling such as exposure to ultraviolet radiation pre pour pressure tests required by concrete installation standards 57 and good practice guidelines 58 for the design construction operation and repair of radiant heating and cooling systems mitigate problems resulting from improper installation and operation fluid based systems using cross linked polyethylene pex a product developed in the 1930s and its various derivatives such as pe rt have demonstrated reliable long term performance in harsh cold climate applications such as bridge decks aircraft hangar aprons and landing pads pex has become a popular and reliable option in home use for new concrete slab construction and new underfloor joist construction as well as joist retrofit since the materials are produced from polyethylene and its bonds are cross linked it is highly resistant to corrosion or the temperature and pressure stresses associated with typical fluid based hvac systems 59 for pex reliability installation procedures must be precise especially at joints and manufacturers specifications for a maximum temperature of water or fluid etc must be carefully followed design and installation edit general considerations for placing radiant heating and cooling pipes in flooring assemblies where other hvac and plumbing components may be present typical underfloor heating and cooling assemblies local practices codes standards best practices and fire regulations will determine actual materials and methods the engineering of underfloor cooling and heating systems is governed by industry standards and guidelines 60 61 notes 2 technical design edit the amount of heat exchanged from or to an underfloor system is based on the combined radiant and convective heat transfer coefficients radiant heat transfer is constant based on the stefan boltzmann constant convective heat transfer changes over time depending on the air s density and thus its buoyancy air buoyancy changes according to surface temperatures and forced air movement due to fans and the motion of people and objects in the space convective heat transfer with underfloor systems is much greater when the system is operating in a heating rather than cooling mode 62 typically with underfloor heating the convective component is almost 50 of the total heat transfer and in underfloor cooling the convective component is less than 10 63 heat and moisture considerations edit when heated and cooled pipes or heating cables share the same spaces as other building components parasitic heat transfer can occur between refrigeration appliances cold stor...
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