Under-floor heating and cooling is a central heating and cooling feature that achieves indoor climate control for thermal comfort using conduction, radiation, and convection. The terms radiant heating and radiant cooling are commonly used to describe this approach because radiation is responsible for a significant portion of thermal comfort generated but this use is technically true only when radiation composes more than 50% heat exchange between the floor and the remaining space.
Video Underfloor heating
History
Under-floor heating has a long history back to Neoglacial and Neolithic periods. Archaeological excavations in Asia and the Alaska Aleutian islands reveal how residents construct smoke from fire through covered trenches of rocks dug on the floor of their underground homes. Hot smoke heats up the floor rocks that then radiate into the living spaces. These early forms have evolved into modern systems using fluid-filled pipes or wires and electric mats. Below is a chronological picture of under-floor heating from around the world.
Maps Underfloor heating
Description
Modern under-floor heating systems use either an element of electrical resistance ("electrical system") or the flow of liquid in a pipe ("hydronic system") to heat the floor. One of its kind can be installed as main heating system, whole building or as local floor heater for thermal comfort. Electrical resistance can only be used for heating; when cooling space is also needed, a hydronic system should be used. Other applications for suitable electrical or hydronic systems include melting snow/ice for walks, driveways and landing strips, football and soccer field support as well as ice prevention in freezers and skating rinks. Various under floor heating systems and designs are available for different types of flooring.
Electrical heating elements or hydronic pipes can be thrown on the concrete floor ("poured floor system" or "wet system"). They can also be placed under floor coverings ("dry systems") or installed directly onto sub-wood floor ("under floor system" or "dry system").
Some commercial buildings are designed to utilize thermal masses that are heated or cooled during peak hours when utility tariffs 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 thermal-activated building systems or TABs.
hydronic system
The hydronic system uses water or a mixture of water and anti-freeze such as propylene glycol as a heat transfer fluid in a "closed loop" that is recirculated between the floor and the boiler.
Various types of pipes are available specifically for under-floor heating and hydraulic cooling systems and are generally made of polyethylene including PEX, PEX-Al-PEX and PERT. Older materials such as Polybutylene (PB) and copper or steel pipes are still used in some locally or for specialized applications.
The hydronic system requires skilled designers and traders who are familiar with boilers, circulators, controls, fluid pressure and temperature. The use of modern factory assembled sub-stations, which are used primarily in heating and cooling districts, can greatly simplify design requirements and reduce installation and commissioning time of hydronic systems.
The hydronic system can use a single source or combination of energy sources to help manage energy costs. The Hydronic system energy source option is:
- Boilers (heaters) include combined heat and power plants heated by:
- Natural gas or "methane" throughout the industry is considered the cleanest and most efficient method of water heating, depending on availability. It costs about $ 7/million b.t.u.
- Propane is primarily made from oil, less efficient than natural gas by volume, and is generally much more expensive on b.t.u. basic. Produce more carbon dioxide than "methane" on b.t.u. basic. It costs about $ 25/million b.t.u.
- Coal, oil, or waste oil
- Electricity
- Hot sun
- Wood or other biomass
- bio fuel
- Heat pumps and chillers are supported by:
- Electricity
- Natural gas
- Geothermal heat pump
Electrical system
Electrical systems are only used for heating and using non-corrosive, flexible heating elements including cables, preformed cable mats, bronze mesh, and carbon films. Due to their low profile, they can be installed in thermal mass or directly below the floor surface. Electrical systems can also utilize electrical time measurements and are often used as carpet heater, portable under carpet heater, under laminated floor heating, under tile heating, under wood floor heating, and floor heating systems, including under heating and floor heating seat. Large electrical systems also require skilled designers and traders, but this is less so for small floor heating systems. Electrical systems use fewer components and are easier to install and command than hydrone systems. Some electrical systems use line voltage technology while others use low voltage technology. The power consumption of the electrical system is not based on the voltage but the output of the watt generated by the heating element.
Features
Quality thermal comfort
As defined by ANSI/ASHRAE Standard 55 - Thermal Environmental Condition for Human Occupancy, thermal comfort is, "a state of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation." Relating specifically to under floor heating, thermal comfort is affected by floor surface temperature and associated elements such as radiant asymmetry, radiant average temperature and operating temperature. Research by Nevins, Rohles, Gagge, P. Ole Fanger et al. showed that humans rested with the typical clothing of light offices and house clothing, exchanging more than 50% of the radiation-sensitive heat.
Under-floor heating affects luminous exchange by thermally conditioning the interior surface with low temperature long-wave radiation. Heating the surface suppresses the loss of body heat which results in the perception of warming comfort. This general comfort sensation is further enhanced through conduction (feet on the floor) and through convection by surface influences on air density. Underfloor cooling works by absorbing short waves and long wave radiation that results in a cold interior surface. This cold surface promotes loss of body heat which results in a perception of cooling comfort. Discomfort is localized because the cold and warm floor with normal foot and legs are covered in ISO 7730 and ASHRAE 55 and ASHRAE Fundamentals Handbooks and can be corrected or adjusted with heating and floor cooling systems.
Indoor air quality
Under-floor heating can have a positive effect on indoor air quality by facilitating the choice of perceived cold floor materials such as tiles, slate, terrazzo and concrete. These rock surfaces typically have very low VOC emissions (volatile organic compounds) compared to other flooring options. In conjunction with moisture control, floor heating also establishes conditions of less favorable temperatures in favor of mold, bacteria, viruses and dust mites. By removing a reasonable heating load from the total HVAC load (Heating, Ventilation and Air Conditioning), ventilation, filtration and dehumidification of incoming air can be achieved with a special outdoor air system that has less volumetric turnover to reduce air pollution distribution. There is recognition from the medical community with regard to the benefits of floor heating especially related to allergens.
Energy
Under the floor the luminous system is evaluated for sustainability through the principles of efficiency, entropy, exergy and efficacy. When combined with high-performance buildings, under floor systems operate with low temperatures in heating and high temperatures in cooling within the ranges found commonly in geothermal and geothermal systems. When combined with this non-combustible renewable energy source, sustainability benefits include the reduction or elimination of combustion and greenhouse gases generated by boilers and power plants for heat and cooling pumps, as well as reducing demand for renewable non-renewable and larger supplies for future generations. This has been supported through simulated evaluations and through research funded by the US Department of Energy, the Canadian Mortgage and Housing Corporation, the Fraunhofer Institute and ASHRAE.
Safety and health
Heating under low temperatures is embedded in the floor or placed under a floor covering. Thus it does not occupy the wall space and does not create a fire hazard, nor is it a danger to physical injury due to accidental contact that causes tripping and falling. These have been referenced as positive features in health care facilities including those serving elderly clients and those with dementia. Anecdotally, under the same environmental conditions, the heated floor will speed up the evaporation of the wet floor (bath, cleaning, and spillage). In addition, underfloor heating with fluid-filled pipes is useful in heating and cooling explosion-proof environments where combustion and electrical equipment can be placed remotely from an explosive environment.
It is possible that underfloor heating can add to offgassing and sick building syndromes in the environment, especially when the carpet is used as a floor.
Under-floor heating systems cause low frequency magnetic fields (in the 50-60 Hz range), the old 1-wire system is much more than the modern 2-wire system. The International Agency for Research on Cancer (IARC) has classified static and low frequency magnetic fields as probably carcinogenic (Group 2B).
Long term, maintenance and repair
Equipment maintenance and repairs are the same as other water or electrical HVAC systems except when pipes, cables or mats are embedded in the floor. Initial trials (eg houses built by Levitt and Eichler, c 1940-70's) experienced failures in copper and steel piping systems as well as court-determined failures for Shell, Goodyear and others for polybutylene and EPDM materials. There have also been several published claims about the failure of electrically heated gypsum panels from the mid-90s.
Failures associated with most installations are caused by work site neglect, incorrect installation errors and product handling such as exposure to ultraviolet radiation. The initial pressure tests required by concrete installation standards and good practice guidelines for the design, construction, operation and repair of radiant heating and cooling systems reduce the problems resulting from improper installation and operation.
The fluid-based system using crosslinked polyethylene (PEX), a product developed in the 1930s and its derivatives such as PE-rt, has demonstrated reliable long-term performance in harsh cold climatic applications such as bridge decks, aircraft hangar aprons and landing pads. PEX has become a popular and reliable choice in home use for new concrete slab construction, and the construction of new under-floor beams as well as retrofit (cross beams). Because the material produced from polyethylene and its bonds are interconnected, it is highly resistant to corrosion or pressure and temperature pressure associated with a typical fluid-based HVAC system. For PEX reliability, the mounting procedure should be appropriate (especially on the connection) and the manufacturer's specifications for maximum water or liquid temperature, etc. Must be followed carefully.
Design and installation
Engineering under-floor cooling and heating systems is governed by industry standards and guidelines.
Technical design
The amount of heat exchanged from or to the system under the floor is based on a combination of radiation and convective heat transfer coefficients.
- The radiant heat transfer is constant based on the Stefan-Boltzmann constant.
- Changes in convection heat transfer over time depend
- the air density and thus the buoyancy. The buoyancy of the air changes according to the surface temperature and
- forced air movement due to fan and movement of people and objects in space.
Convective heat transfer with under floor systems is much greater when the system operates in the heating rather than cooling mode. Usually with under-floor heating convective components nearly 50% of total heat transfer and under floor cooling of convective components is less than 10%.
Considerations of heat and humidity
When heated and cooled pipes or heating cables share the same space with other building components, parasitic heat transfer may occur between cooling equipment, cold storage areas, domestic cold water channels, air conditioning and ventilation ducts. To control this, pipes, cables and other building components must be well insulated.
With cooling under the floor, condensation can accumulate on the floor surface. To prevent this, the air humidity remains low, below 50%, and the floor temperature is maintained above the dew point, 19 Ã, Â ° C (66F).
Building systems and materials
- Heat loss to below level
- The thermal conductivity of the soil will affect conductive heat transfer between hot and cooled or cooled ground and floor floors.
- Soils with moisture content of more than 20% can be as much as 15 times more conductive than soils with a moisture content of less than 4%.
- The water table and general soil conditions should be evaluated.
- Suitable underslab isolation such as extruded or expanded polystyrene is rigidly required by the National Energy Code Model.
- Heat loss on exterior floor framing
- Heated or cooled sub-floor increases the temperature difference between the outside and the air-conditioned floor.
- Cavities made by framing woods such as headers, trimmers and cantilevered parts should be insulated with rigid, batt or spray type insulations with appropriate values ​​based on climate and building techniques.
- Masonry and other hard floor considerations
- Concrete floors should accommodate shrinkage and expansion due to curing and temperature changes.
- The pickling time and temperature for the poured floor (concrete, light topping) should follow industry standards.
- Expansion controls and connections and crack suppression techniques are required for all types of stone flooring including;
- Tiles
- Slate
- Terrazzo
- Stone
- Marble
- Concrete, stained, textured, and stamped
- Wooden floor
- Wood dimensional stability is based primarily on moisture content; however, other factors can reduce changes in wood when heated or cooled, including;
- Wood species
- Milling technique, quarter sawn or sawmill
- Acclimatization time
- Relative humidity in space
- Wood dimensional stability is based primarily on moisture content; however, other factors can reduce changes in wood when heated or cooled, including;
- Standard piping
System control
Under-floor heating and cooling systems can have multiple control points including management:
- Fluid temperatures in heating and cooling plants (eg boilers, coolers, heat pumps).
- Effect efficiency
- Liquid temperatures in the distribution network between plants and luminous manifolds.
- Affects capital and operating costs
- Liquid temperatures in PE-x piping systems, which are based on:
- Heating and cooling requests
- Tubing distance
- Upward and downward losses
- Floor characteristics
- Operating temperature
- Combine pointy and average dry bulb
- The surface temperature for;
- Convenience
- Health and safety
- Material integrity
- Dew point (for floor cooling).
Mechanical scheme
Illustrations are simplified mechanical schemes of under floor heating and cooling systems for thermal comfort qualities with separate air handling systems for indoor air quality. In medium-sized high-performance residential homes (eg under 3000Ã, ft 2 ) total air-conditioned floor area), the system uses a hydronic control device that produced will take about the same space with three or four bathrooms.
Model a piping pattern with finite element analysis
Modeling of transmitter pipe (also tube or loop) patterns with finite element analysis (FEA) predicts thermal diffusion and surface temperature quality or the efficacy of various layout loops. Model performance (left image above) and image to the right are useful for gaining insight in the relationship between floor resistance, surrounding mass conductivity, tube distance, depth and fluid temperature. Like all FEA simulations, they describe snap shots at times for certain assemblies and may not represent all floor assemblies or for systems that have been operating for a long time under steady state conditions. FEA's practical application for engineers is able to assess each of these designs for liquid temperature, back loss and surface temperature quality. Through multiple iterations it is possible to optimize the design for the lowest fluid temperature in the heating and the highest fluid temperature in the cooling that allows combustion and compression equipment to achieve maximum rated efficiency performance.
Economy
There are various pricing for under floor systems based on regional differences, materials, applications and project complexity. It is widely adopted in the Nordic, Asian and European communities. As a result, the market is more mature and the system is relatively more affordable than North America where market share for liquid-based systems stays between 3% to 7% of the HVAC system (refs Canadian Statistics and US Census Bureau).
In energy efficiency buildings such as Passive Homes, R-2000 or Clean Zero Energy, simple thermostatic radiator valves can be fitted together with one compact circulator and a small condensed heater that is controlled without or with basic thermal rearrangement controls. An economical electrical resistance-based system is also useful in small zones such as bathrooms and kitchens, but also for entire buildings where heating loads are very low. Larger structures will require more sophisticated systems to handle cooling and heating requirements, and often require building management control systems to regulate energy use and control the overall indoor environment.
The low-beam radiant heating and high-temperature beaming cooling systems allow the district's energy system (community-based system) due to the temperature difference between the plant and the building allowing small diameter distribution networks and low pump power requirements. The low back temperature in the heating and high temperature returns in cooling allows the district power plant to achieve maximum efficiency. The principles behind district energy with under floor systems can also be applied to stand-alone multi-storey buildings with the same benefits. In addition, under-floor jet systems are ideal for renewable energy sources including geothermal and solar systems or systems where waste heat can be recovered.
In a global push for sustainability, the long-term economy supports the need to eliminate where possible, compression for cooling and burning for heating. It will then be necessary to use low-quality heat sources that emit underfloor heating and cooling very well.
System efficiency
Analysis of system efficiency and energy use takes into account the performance of the building cage, the efficiency of the heating and cooling plant, the system control and conductivity, surface characteristics, tube distance/element and radiant panel depth, operating fluid temperature and wire efficiency to water. circulator. Efficiency in the electrical system is analyzed by a similar process and includes the efficiency of electricity generation.
Although the efficiency of a luminous system is constantly being debated in the absence of a lack of anecdotal claims and scientific papers presenting both sides, low temperature return fluids in heating and high fluid temperatures in cooling allow condensation of boilers, coolers and heat pumps to operate at or near performance their maximum engineering. Greater efficiency of the 'wire to water' flow than 'stream to air' because of the much greater heat capacity significantly supports liquid-based systems over air-based systems. Both field applications and simulated research have demonstrated significant electrical energy savings with air conditioning systems and special open air systems that are based in part on previously recorded principles.
At Passive Homes, R-2000 homes or the Clean Zero Energy building, the low temperature of the heating and cooling systems of the series provides a significant opportunity to exploit the allergy.
Efficiency considerations for floor surface materials
System efficiency is also influenced by floor coverings that serve as a radiographic boundary layer between floor masses and occupants and other content of conditioned space. For example, carpets have greater resistance or lower conductance than tiles. So carpeted floors need to operate at higher internal temperatures than tiles that can create lower efficiency for boilers and heat pumps. However, when the floor covering is known when the system is installed, the internal floor temperature required for a certain cover can be achieved through the correct tube distance without compromising plant efficiency (although higher internal floor temperatures may cause increased heat loss from non-floor floor surfaces ).
The emissivity, reflectivity and absorptivity of the floor surface is an important determinant of heat exchange with occupants and space. Non-scrubbed flooring and treatment materials have very high emissivity (0.85 to 0.95) and therefore produce a good heat radiator.
With underfloor heating and cooling ("reversible floor") floor surfaces with high absorption and emissivity and low reflectivity are the most desirable.
Thermographic evaluation
Thermography is a useful tool for viewing the actual thermal effectiveness of under floor systems from start up (as shown) in the operating conditions. In startup, it is easy to identify the tube location but less so the system moves to steady state conditions. It is important to interpret thermographic images correctly. As with finite element analysis (FEA), what is seen, reflects the conditions at the time of picture and may not represent stable conditions. For example, the surface seen in the displayed image may appear 'hot', but the reality is actually below the nominal temperature of the skin and the core temperature of the human body and the ability to 'see' the pipe is not the same as the 'feel' of the pipes. Thermography can also show defects in building cages (left image, angular junction details), thermal bridging (right picture, buttons) and heat loss associated with exterior doors (center drawing).
Global examples of large modern buildings using radiant heating and cooling
- 41 Cooper Square, United States
- Akron Art Museum, United States
- BMW Welt, Germany
- California Academy of Sciences, United States
- Copenhagen Opera House, Denmark
- Ewha Womans University, South Korea
- Hearst Tower, New York City, United States
- Manitoba Hydro Place, Canada
- The National Renewable Energy Laboratory Research Support Facility, United States
- Pearl River Tower, China
- Post Tower, Germany
- Suvarnabhumi Airport, Bangkok
See also
References
Note
External links
- American Society of Heating, Cooling and Air-Conditioning Engineers (ASHRAE)
- ASHRAE Technical Committee TC 6.5, Warming Up and Cooling Space and Convection (ASHRAE T.C. 6.5)
- ASHRAE Technical Committee TC 6.1, Hydronic & amp; Steam & amp; System (ASHRAE T.C. 6.1)
- The American Institute of Architects (AIA)
- American Society of Interior Designers (ASID)
- Canada Mortgage and Housing Corporation (CMHC)
- Canadian Institute of Plumbing & amp; Heating (CIPH)
- Netherlands Building Services Center (ISSO)
- Housing Resource Assessment Procedure - Ireland (DEAP)
- Federation of European Heating and Air Conditioning Associations (REHVA)
- Canadian Heating, Cooling and Air Conditioning Unit (HRAI)
- International Energy Agency, Energy Conservation in Building and Community Systems (IEA/ECBCS)
- International Organization for Standardization, TC 205/WG 8, Heating radiant and cooling system (ISO TC205/WG8)
- National Research Council Canada/NRC Institute for Research in Construction, Heating Acrylic Radiation Floor (NRC/IRC)
- Radiant Panel Association (RPA)
- Thermal Environmental Comfort Association (TECA)
- German Heating and Cooling Association (BVF)
- British Underfloor Producers Association (UHMA)
Source of the article : Wikipedia
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