Misplaced Pages

#778221

55-400: Today, while some older hogans are still used as dwellings and others are maintained for ceremonial purposes, new hogans are rarely intended as family dwellings. Hogans are also considered pioneers of energy efficient homes. Using packed mud against the wooden walls, the home was kept cool in summer by natural ventilation and water sprinkled on the packed dirt floor. In winter the fireplace kept

110-418: A i } , { A j } ) {\displaystyle F(\{a_{i}\},\{A_{j}\})} . If the size of the system is changed by some scaling factor, λ {\displaystyle \lambda } , only the extensive properties will change, since intensive properties are independent of the size of the system. The scaled system, then, can be represented as F ( {

165-578: A i } , { λ A j } ) {\displaystyle F(\{a_{i}\},\{\lambda A_{j}\})} . Intensive properties are independent of the size of the system, so the property F is an intensive property if for all values of the scaling factor, λ {\displaystyle \lambda } , (This is equivalent to saying that intensive composite properties are homogeneous functions of degree 0 with respect to { A j } {\displaystyle \{A_{j}\}} .) It follows, for example, that

220-583: A building's thermal conductivity , allowing it to be heated or cooled relatively separately from the outside, or even just retain the occupants' thermal energy longer. Scientifically, thermal mass is equivalent to thermal capacity or heat capacity , the ability of a body to store thermal energy . It is typically referred to by the symbol C th , and its SI unit is J/K or J/°C (which are equivalent). Thermal mass may also be used for bodies of water, machines or machine parts, living things, or any other structure or body in engineering or biology. In those contexts,

275-407: A community – in preference for HUD -standardized construction. With government and lender requirements requiring low costs, as well as bathrooms and kitchens, the hogan as a person's home was dwindling away, save for those who could build their own. That began to officially change in the late 1990s with various small projects to find ways to bring the hogan back. In 2001, a joint venture involving

330-455: A component i {\displaystyle i} in a mixture. For the characterization of substances or reactions, tables usually report the molar properties referred to a standard state . In that case a superscript ∘ {\displaystyle ^{\circ }} is added to the symbol. Examples: The general validity of the division of physical properties into extensive and intensive kinds has been addressed in

385-418: A flow of heat in order for it to change temperature. In scientific writing the term " heat capacity " is preferred. It is sometimes known as the thermal flywheel effect . The thermal mass of heavy structural elements can be designed to work alongside a construction's lighter thermal resistance components to create energy efficient buildings . For example, when outside temperatures are fluctuating throughout

440-580: A general rule, additional solar-exposed thermal mass needs to be applied in a ratio from 6:1 to 8:1 for any area of sun-facing (north-facing in Southern Hemisphere or south-facing in Northern Hemisphere) glazing above 7% of the total floor area. For example, a 200 m house with 20 m of sun-facing glazing has 10% of glazing by total floor area; 6 m of that glazing will require additional thermal mass. Therefore, using

495-469: A homogeneous material with sufficiently known physical properties, the thermal mass is simply the mass of material present times the specific heat capacity of that material. For bodies made of many materials, the sum of heat capacities for their pure components may be used in the calculation, or in some cases (as for a whole animal, for example) the number may simply be measured for the entire body in question, directly. As an extensive property , heat capacity

550-710: A maximum PAHS/STES. It has also been used successfully in the UK at Hockerton Housing Project . Extensive property Physical or chemical properties of materials and systems can often be categorized as being either intensive or extensive , according to how the property changes when the size (or extent) of the system changes. The terms "intensive and extensive quantities" were introduced into physics by German mathematician Georg Helm in 1898, and by American physicist and chemist Richard C. Tolman in 1917. According to International Union of Pure and Applied Chemistry (IUPAC), an intensive property or intensive quantity

605-424: A more exhaustive list specifically pertaining to materials. An extensive property is a physical quantity whose value is proportional to the size of the system it describes, or to the quantity of matter in the system. For example, the mass of a sample is an extensive quantity; it depends on the amount of substance. The related intensive quantity is the density which is independent of the amount. The density of water

SECTION 10

#1732771739779

660-455: A subscript "m" to the corresponding extensive property. For example, molar enthalpy is H m {\displaystyle H_{\mathrm {m} }} . Molar Gibbs free energy is commonly referred to as chemical potential , symbolized by μ {\displaystyle \mu } , particularly when discussing a partial molar Gibbs free energy μ i {\displaystyle \mu _{i}} for

715-475: A substance is an intensive property. For example, the boiling temperature of water is 100 °C at a pressure of one atmosphere , regardless of the quantity of water remaining as liquid. Any extensive quantity E for a sample can be divided by the sample's volume, to become the "E density" for the sample; similarly, any extensive quantity "E" can be divided by the sample's mass, to become the sample's "specific E"; extensive quantities "E" which have been divided by

770-412: A thermodynamic process of transfer. They are transferred across a wall between two thermodynamic systems or subsystems. For example, species of matter may be transferred through a semipermeable membrane. Likewise, volume may be thought of as transferred in a process in which there is a motion of the wall between two systems, increasing the volume of one and decreasing that of the other by equal amounts. On

825-452: A thermodynamic system. Conjugate setups are associated by Legendre transformations . The ratio of two extensive properties of the same object or system is an intensive property. For example, the ratio of an object's mass and volume, which are two extensive properties, is density, which is an intensive property. More generally properties can be combined to give new properties, which may be called derived or composite properties. For example,

880-404: Is additive for subsystems. Examples include mass , volume and entropy . Not all properties of matter fall into these two categories. For example, the square root of the volume is neither intensive nor extensive. If a system is doubled in size by juxtaposing a second identical system, the value of an intensive property equals the value for each subsystem and the value of an extensive property

935-594: Is an extensive property if for all λ {\displaystyle \lambda } , (This is equivalent to saying that extensive composite properties are homogeneous functions of degree 1 with respect to { A j } {\displaystyle \{A_{j}\}} .) It follows from Euler's homogeneous function theorem that where the partial derivative is taken with all parameters constant except A j {\displaystyle A_{j}} . This last equation can be used to derive thermodynamic relations. A specific property

990-447: Is approximately 1g/mL whether you consider a drop of water or a swimming pool, but the mass is different in the two cases. Dividing one extensive property by another extensive property generally gives an intensive value—for example: mass (extensive) divided by volume (extensive) gives density (intensive). Examples of extensive properties include: In thermodynamics, some extensive quantities measure amounts that are conserved in

1045-457: Is associated with a temperature change. A change in the amount of electric polarization is associated with an electric field change. The transferred extensive quantities and their associated respective intensive quantities have dimensions that multiply to give the dimensions of energy. The two members of such respective specific pairs are mutually conjugate. Either one, but not both, of a conjugate pair may be set up as an independent state variable of

1100-426: Is characteristic of an object; its corresponding intensive property is specific heat capacity, expressed in terms of a measure of the amount of material such as mass or number of moles, which must be multiplied by similar units to give the heat capacity of the entire body of material. Thus the heat capacity can be equivalently calculated as the product of the mass m of the body and the specific heat capacity c for

1155-484: Is most advantageous where there is a big difference in outdoor temperatures from day to night (or, where nighttime temperatures are at least 10 degrees cooler than the thermostat set point). The terms heavy-weight and light-weight are often used to describe buildings with different thermal mass strategies, and affects the choice of numerical factors used in subsequent calculations to describe their thermal response to heating and cooling. In building services engineering ,

SECTION 20

#1732771739779

1210-534: Is one easy solution. Another novel method is to place the masonry facade of a timber-framed house on the inside ('reverse-brick veneer'). Thermal mass in this situation is best applied over a large area rather than in large volumes or thicknesses. 7.5–10 cm (3″–4″) is often adequate. Since the most important source of thermal energy is the Sun, the ratio of glazing to thermal mass is an important factor to consider. Various formulas have been devised to determine this. As

1265-418: Is one whose magnitude is independent of the size of the system. An intensive property is not necessarily homogeneously distributed in space; it can vary from place to place in a body of matter and radiation. Examples of intensive properties include temperature , T ; refractive index , n ; density , ρ ; and hardness , η . By contrast, an extensive property or extensive quantity is one whose magnitude

1320-432: Is operated at night to carry away the heat from the slab. In naturally ventilated buildings it is normal to provide automated window openings to facilitate this process automatically. This is a classical use of thermal mass. Examples include adobe , rammed earth , or limestone block houses. Its function is highly dependent on marked diurnal temperature variations . The wall predominantly acts to retard heat transfer from

1375-425: Is primarily as a temporary heat sink. However, it needs to be strategically located to prevent overheating. It should be placed in an area that is not directly exposed to solar gain and also allows adequate ventilation at night to carry away stored energy without increasing internal temperatures any further. If to be used at all it should be used in judicious amounts and again not in large thicknesses. If enough mass

1430-415: Is slightly different. The correct use and application of thermal mass is dependent on the prevailing climate in a district. Thermal mass is ideally placed within the building and situated where it still can be exposed to low-angle winter sunlight (via windows) but insulated from heat loss. In summer the same thermal mass should be obscured from higher-angle summer sunlight in order to prevent overheating of

1485-410: Is the intensive property obtained by dividing an extensive property of a system by its mass. For example, heat capacity is an extensive property of a system. Dividing heat capacity, C p {\displaystyle C_{p}} , by the mass of the system gives the specific heat capacity, c p {\displaystyle c_{p}} , which is an intensive property. When

1540-718: Is the mass of the body and c p {\displaystyle c_{\mathrm {p} }} is the isobaric specific heat capacity of the material averaged over temperature range in question. For bodies composed of numerous different materials, the thermal masses for the different components can just be added together. Thermal mass is effective in improving building comfort in any place that experiences these types of daily temperature fluctuations—both in winter as well as in summer. When used well and combined with passive solar design , thermal mass can play an important role in major reductions to energy use in active heating and cooling systems . The use of materials with thermal mass

1595-475: Is twice the value for each subsystem. However the property √V is instead multiplied by √2 . An intensive property is a physical quantity whose value does not depend on the amount of substance which was measured. The most obvious intensive quantities are ratios of extensive quantities. In a homogeneous system divided into two halves, all its extensive properties, in particular its volume and its mass, are divided into two halves. All its intensive properties, such as

1650-515: Is used it can create a seasonal advantage. That is, it can heat in the winter and cool in the summer. This is sometimes called passive annual heat storage or PAHS. The PAHS system has been successfully used at 7000 ft. in Colorado and in a number of homes in Montana. The Earthships of New Mexico utilize passive heating and cooling as well as using recycled tires for foundation wall yielding

1705-677: The Navajo Nation , Northern Arizona University , and the US Forest Service began building log hogans with materials from a Navajo-owned log home factory in Cameron, Arizona , next to the Cameron Chapter House, using surplus wood culled from Northern Arizona forests to prevent wildfires. Through cooperation among elders, medicine men, and project leaders, this ancient Navajo tradition is reviving. While providing

Hogan - Misplaced Pages Continue

1760-462: The ratio of two extensive properties is an intensive property. To illustrate, consider a system having a certain mass, m {\displaystyle m} , and volume, V {\displaystyle V} . The density, ρ {\displaystyle \rho } is equal to mass (extensive) divided by volume (extensive): ρ = m V {\displaystyle \rho ={\frac {m}{V}}} . If

1815-438: The 6:1 to 8:1 ratio above, an additional 36–48 m of solar-exposed thermal mass is required. The exact requirements vary from climate to climate. Thermal mass is ideally placed within a building where it is shielded from direct solar gain but exposed to the building occupants. It is therefore most commonly associated with solid concrete floor slabs in naturally ventilated or low-energy mechanically ventilated buildings where

1870-536: The base quantities mass and volume can be combined to give the derived quantity density. These composite properties can sometimes also be classified as intensive or extensive. Suppose a composite property F {\displaystyle F} is a function of a set of intensive properties { a i } {\displaystyle \{a_{i}\}} and a set of extensive properties { A j } {\displaystyle \{A_{j}\}} , which can be shown as F ( {

1925-421: The concrete soffit is left exposed to the occupied space. During the day heat is gained from the sun, the occupants of the building, and any electrical lighting and equipment, causing the air temperatures within the space to increase, but this heat is absorbed by the exposed concrete slab above, thus limiting the temperature rise within the space to be within acceptable levels for human thermal comfort. In addition

1980-418: The course of science. Redlich noted that, although physical properties and especially thermodynamic properties are most conveniently defined as either intensive or extensive, these two categories are not all-inclusive and some well-defined concepts like the square-root of a volume conform to neither definition. Other systems, for which standard definitions do not provide a simple answer, are systems in which

2035-417: The day, a large thermal mass within the insulated portion of a house can serve to "flatten out" the daily temperature fluctuations, since the thermal mass will absorb thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy back when the surroundings are cooler, without reaching thermal equilibrium . This is distinct from a material's insulative value, which reduces

2090-562: The extensive property is represented by an upper-case letter, the symbol for the corresponding intensive property is usually represented by a lower-case letter. Common examples are given in the table below. If the amount of substance in moles can be determined, then each of these thermodynamic properties may be expressed on a molar basis, and their name may be qualified with the adjective molar , yielding terms such as molar volume, molar internal energy, molar enthalpy, and molar entropy. The symbol for molar quantities may be indicated by adding

2145-478: The exterior to the interior during the day. The high volumetric heat capacity and thickness prevents thermal energy from reaching the inner surface. When temperatures fall at night, the walls re-radiate the thermal energy back into the night sky. In this application it is important for such walls to be massive to prevent heat transfer into the interior. The use of thermal mass is the most challenging in this environment where night temperatures remain elevated. Its use

2200-478: The inside warm well into the night, due to the high thermal mass of earth in the construction. The preference of hogan construction and use is still very popular among the Navajos, although the use of it as a home shelter dwindled through the 1900s, due mainly to the requirement by many Navajos to acquire homes built through government and lender funding – which largely ignored the hogan-style and cultural needs of

2255-421: The lower surface temperature of the concrete slab also absorbs radiant heat directly from the occupants, also benefiting their thermal comfort. By the end of the day the slab has in turn warmed up, and now, as external temperatures decrease, the heat can be released and the slab cooled down, ready for the start of the next day. However this "regeneration" process is only effective if the building ventilation system

Hogan - Misplaced Pages Continue

2310-419: The mass per volume (mass density) or volume per mass ( specific volume ), must remain the same in each half. The temperature of a system in thermal equilibrium is the same as the temperature of any part of it, so temperature is an intensive quantity. If the system is divided by a wall that is permeable to heat or to matter, the temperature of each subsystem is identical. Additionally, the boiling temperature of

2365-522: The material, or the product of the number of moles of molecules present n and the molar specific heat capacity c ¯ {\displaystyle {\bar {c}}} . For discussion of why the thermal energy storage abilities of pure substances vary, see factors that affect specific heat capacity . For a body of uniform composition, C t h {\displaystyle C_{\mathrm {th} }} can be approximated by where m {\displaystyle m}

2420-410: The need for such systems altogether. Ideal materials for thermal mass are those materials that have: Any solid, liquid, or gas will have some thermal mass. A common misconception is that only concrete or earth soil has thermal mass; even air has thermal mass (although very little). A table of volumetric heat capacity for building materials is available, but note that their definition of thermal mass

2475-506: The number of moles in their sample are referred to as "molar E". The distinction between intensive and extensive properties has some theoretical uses. For example, in thermodynamics, the state of a simple compressible system is completely specified by two independent, intensive properties, along with one extensive property, such as mass. Other intensive properties are derived from those two intensive variables. Examples of intensive properties include: See List of materials properties for

2530-418: The other hand, some extensive quantities measure amounts that are not conserved in a thermodynamic process of transfer between a system and its surroundings. In a thermodynamic process in which a quantity of energy is transferred from the surroundings into or out of a system as heat, a corresponding quantity of entropy in the system respectively increases or decreases, but, in general, not in the same amount as in

2585-436: The same cells are connected in series , the charge becomes intensive and the voltage extensive. The IUPAC definitions do not consider such cases. Some intensive properties do not apply at very small sizes. For example, viscosity is a macroscopic quantity and is not relevant for extremely small systems. Likewise, at a very small scale color is not independent of size, as shown by quantum dots , whose color depends on

2640-456: The structure. The thermal mass is warmed passively by the sun or additionally by internal heating systems during the day. Thermal energy stored in the mass is then released back into the interior during the night. It is essential that it be used in conjunction with the standard principles of passive solar design . Any form of thermal mass can be used. A concrete slab foundation either left exposed or covered with conductive materials, e.g. tiles,

2695-406: The subsystems interact when combined. Redlich pointed out that the assignment of some properties as intensive or extensive may depend on the way subsystems are arranged. For example, if two identical galvanic cells are connected in parallel , the voltage of the system is equal to the voltage of each cell, while the electric charge transferred (or the electric current ) is extensive. However, if

2750-412: The surroundings. Likewise, a change in the amount of electric polarization in a system is not necessarily matched by a corresponding change in electric polarization in the surroundings. In a thermodynamic system, transfers of extensive quantities are associated with changes in respective specific intensive quantities. For example, a volume transfer is associated with a change in pressure. An entropy change

2805-438: The system is scaled by the factor λ {\displaystyle \lambda } , then the mass and volume become λ m {\displaystyle \lambda m} and λ V {\displaystyle \lambda V} , and the density becomes ρ = λ m λ V {\displaystyle \rho ={\frac {\lambda m}{\lambda V}}} ;

SECTION 50

#1732771739779

2860-416: The term "heat capacity" is typically used instead. The equation relating thermal energy to thermal mass is: where Q is the thermal energy transferred, C th is the thermal mass of the body, and Δ T is the change in temperature. For example, if 250 J of heat energy is added to a copper gear with a thermal mass of 38.46 J/°C, its temperature will rise by 6.50 °C. If the body consists of

2915-458: The traditional sacred space of the hogan, new construction also meets requirements for modern amenities. The project has also provided jobs, summer school construction experience for Navajo teens, and new public buildings. Possible Native American sources of the English word hogan : Thermal mass In building design, thermal mass is a property of the matter of a building that requires

2970-451: The two λ {\displaystyle \lambda } s cancel, so this could be written mathematically as ρ ( λ m , λ V ) = ρ ( m , V ) {\displaystyle \rho (\lambda m,\lambda V)=\rho (m,V)} , which is analogous to the equation for F {\displaystyle F} above. The property F {\displaystyle F}

3025-480: The use of dynamic simulation computational modelling software has allowed for the accurate calculation of the environmental performance within buildings with different constructions and for different annual climate data sets. This allows the architect or engineer to explore in detail the relationship between heavy-weight and light-weight constructions, as well as insulation levels, in reducing energy consumption for mechanical heating or cooling systems , or even removing

#778221