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and (334), the (296), #heating (164), systems (105), for (99), #cooling (76), heat (69), with (66), floor (65), radiant (61), underfloor (58), air (55), energy (54), thermal (49), system (47), from (46), temperature (41), are (39), building (31), ashrae (31), water (30), based (30), edit (30), low (29), buildings (28), use (27), comfort (27), efficiency (26), used (26), archived (23), electric (23), can (23), temperatures (23), using (21), hydronic (21), fluid (21), 2010 (21), surface (21), pipes (20), floors (19), control (19), also (19), ventilation (18), design (18), part (18), heated (18), this (17), than (17), high (16), polyethylene (16), under (15), quality (15), pex (15), when (15), such (15), installation (14), pdf (14), history (14), ondol (14), retrieved (13), solar (13), heater (13), pump (13), materials (13), which (13), flooring (13), other (13), articles (12), wood (12), standards (12), surfaces (12), embedded (12), performance (12), original (12), between (12), more 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ble 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 storage areas domestic cold water lines air conditioning and ventilation ducts to control this the pipes cables and other building components must all be well insulated with underfloor cooling condensation may collect on the surface of the floor to prevent this air humidity is kept low below 50 and floor temperatures are maintained above the dew point 19 c 66f 64 building systems and materials edit heat losses to below grade the thermal conductivity of soil will influence the conductive heat transfer between the ground and heated or cooled slab on grade floors soils with moisture contents greater than 20 can be as much as 15 times more conductive than soils with less than 4 moisture content 65 water tables and general soil conditions should be evaluated suitable underslab insulation such as rigid extruded or expanded polystyrene is required by model national energy codes 66 67 heat losses at the exterior floor framing the heated or cooled sub floor increases the temperature difference between the outdoors and the conditioned floor the cavities created by the framing timbers such as headers trimmers and cantilevered sections must then be insulated with rigid batt or spray type insulations of suitable value based on climate and building techniques masonry and other hard flooring considerations concrete floors must accommodate shrinkage and expansion due to curing and changes in temperature curing times and temperatures for poured floors concrete lightweight toppings must follow industry standards control and expansion joints and crack suppression techniques are required for all masonry type floors including tile slate terrazzo stone marble concrete stained textured and stamped wood flooring the dimensional stability of wood is based primary on moisture content 68 however other factors can mitigate the changes to wood as it is heated or cooled including wood species milling techniques quarter sawn or plane sawn acclimation period relative humidity within the space piping standards notes 3 control system edit see also hydronics underfloor heating and cooling systems can have several control points including the management of fluid temperatures in the heating and cooling plant e g boilers chillers heat pumps influences the efficiency fluid temperatures in distribution network between the plant and the radiant manifolds influences the capital and operating costs fluid temperatures in the pe x piping systems which is based on 28 heating and cooling demands tube spacing upward and downward losses flooring characteristics operative temperature incorporates the mean radiant and dry bulb surface temperatures for 69 comfort health and safety material integrity dew point for floor cooling mechanical schematic edit example of a radiant based hvac schematic illustrated is a simplified mechanical schematic of an underfloor heating and cooling system for thermal comfort quality 69 with a separate air handling system for indoor air quality 70 71 in high performance residential homes of moderate size e g under 3000 ft 2 278 m 2 total conditioned floor area this system using manufactured hydronic control appliances would take up about the same space as a three or four piece bathroom modeling piping patterns with finite element analysis edit modeling radiant piping also tube or loop patterns with finite element analysis fea predicts the thermal diffusions and surface temperature quality or efficacy of various loop layouts the performance of the model left image below and image to the right are useful to gain an understanding in relationships between flooring resistances conductivities of surrounding mass tube spacings depths and fluid temperatures as with all fea simulations they depict a snap shot in time for a specific assembly and may not be representative of all floor assemblies nor for system that have been operative for considerable time in a steady state condition the practical application of fea for the engineer is being able to assess each design for fluid temperature back losses and surface temperature quality through several iterations it is possible to optimize the design for the lowest fluid temperature in heating and the highest fluid temperature in cooling which enables combustion and compression equipment to achieve its maximum rated efficiency performance thermal diffusions and surface temperature quality efficacy of various piping layouts typical fea output screen shots of wire mesh thermal isotherms and color coded mapping economics edit there is a wide range of pricing for underfloor systems based on regional differences materials application and project complexity it is widely adopted in the nordic asian and european communities consequently the market is more mature and systems relatively more affordable than less developed markets such as north america where market share for fluid based systems remains between 3 and 7 of hvac systems ref statistics canada and united states census bureau in energy efficiency buildings such as passive house r 2000 or net zero energy simple thermostatic radiator valves can be installed along with a single compact circulator and small condensing heater controlled without or with basic hot water reset 72 control economical electric resistance based systems also are useful in small zones such as bathrooms and kitchens but also for entire buildings where heating loads are very low larger structures will need more sophisticated systems to deal with cooling and heating needs and often require building management control systems to regulate the energy use and control the overall indoor environment low temperature radiant heating and high temperature radiant cooling systems lend themselves well to district energy systems community based systems due to the temperature differentials between the plant and the buildings which allow small diameter insulated distribution networks and low pumping power requirements the low return temperatures in heating and high return temperatures in cooling enable the district energy plant to achieve maximum efficiency the principles behind district energy with underfloor systems can also be applied to stand alone multi story buildings with the same benefits 73 additionally underfloor radiant systems are ideally suited to renewable energy sources including geothermal and solar thermal systems or any system where waste heat is recoverable in the global drive for sustainability long term economics supports the need to eliminate where possible compression for cooling and combustion for heating it will then be necessary to use low quality heat sources for which radiant underfloor heating and cooling is well suited clarification needed citation needed system efficiency edit system efficiency and energy use analysis takes into account building enclosure performance efficiency of the heating and cooling plant system controls and the conductivities surface characteristics tube element spacing and depth of the radiant panel operating fluid temperatures and wire to water efficiency of the circulators 74 the efficiency in electric systems is analyzed by similar processes and includes the efficiency of electricity generation though the efficiency of radiant systems is under constant debate with no shortage of anecdotal claims and scientific papers presenting both sides the low return fluid temperatures in heating and high return fluid temperatures in cooling enable condensing boilers 75 chillers 76 and heat pumps 77 to operate at or near their maximum engineered performance 78 79 the greater efficiency of wire to water versus wire to air flow due to water s significantly greater heat capacity favors fluid based systems over air based systems 80 both field application and simulation research have demonstrated significant electr...
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