Field of the Invention
One of the primary needs for the disclosed invention stems from the desire to reduce energy consumption of buildings, which is a major contributor to global energy consumptions and thus indirectly to CO2 emissions.
The world's energy demand and consumption is rapidly growing, in particular in developing countries. The finite amount of ultimately recoverable fossil fuels (primarily coal, oil, gas), but more importantly the associated environmental pollutions and CO2 emissions—unsustainable at current rates,—as well as expected future price increases of energy from fossil resources make global energy supply one of the biggest challenge man kind faces.
Currently, the resources used for heating or cooling of buildings constitutes a major part of the total global energy (40%) and water (25%) consumption. Buildings are the source of nearly one third of the greenhouse gas emission. Further details on this topic can be found, for example, at UNEP. Sustainable buildings & climate initiative, building and climate change, United Nations Environment Program (2009), the entirety of which is incorporated herein by reference. During the period of 1973-2010, the CO2 emission was doubled (from 15.637 to 30,326 million tons CO2)
Further details on this topic can be found, for example, at International Energy Agency. Key world energy statistics. OECD/IEA (2012). http://www.iea.org/publications/freepublications/publication/kwes.pdf, the entirety of which is incorporated herein by reference. Therefore, buildings provide a substantial potential for reducing CO2 emission (and operating expenses) at relatively low cost, which is a concern primarily in developed counties such as the USA or Europe. Simultaneously, advances in building materials, designs and system operations related to energy consumption, if implemented on a large enough scale in developing countries, can be a major contributor to at least slow down the currently occurring and often environmentally unacceptable (e.g. China) or even technically unsustainable (e.g. India) rate of required energy supply, in particular of electric energy, resulting from an constantly increasing standard of living for large portions of said populations.
The International Energy Agency (IEA) has published data on energy consumption trends. While the total primary energy supply (TPES) was doubled from 1973 to 2010 (from 6107 to 12,717 million tons of oil equivalent, MTOE) and crude oil production increased almost 40% (from 2869 to 4011 million tons), the total final energy consumption showed 31% increase (from 2815 to 3691 MTOE).
The European Union's Energy Efficiency Directive (passed on 25 Oct. 2012) ‘ . . . recognizes that the rate of building renovation needs to be increased, as the existing building stock represents the single biggest potential sector for energy savings. Moreover, buildings are crucial to achieving the Union's objective of reducing greenhouse gas emissions by 80-95% by 2050 compared to 1990’. Further details on this topic can be found, for example, at Directive 2012/27/EU of the European Parliament and of the Council of 25 Oct. 2012 on energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC http://eur-lex. europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:315:0001:0056:EN:PDF, the entirety of which is incorporated herein by reference.
A related problematic aspect is the relative cost of energy. In most of the equatorial regions, where developing countries are predominantly located, the price for electricity compared to the average income is too high to permit 24/7 active air conditioning (AC) of most residential or office building. Therefore, any material, design, or systems control improvements to buildings, which will noticeably lower indoor temperatures and/or reduce required energy consumption of air conditioning, especially during dry seasons—i.e., during high solar radiation input, will considerably contribute to well-being and efficiency of its occupants.
Henceforth the term ‘supplied energy’ shall be understood to refer to the energy delivered or supplied to a building (or similar space) on purpose, typically produced elsewhere, and typically in form of electrical energy (regardless how it was generated, including but not limited to being derived from chemical energy (typically fossil fuels), nuclear energy, mechanical kinetic energy (wind, water), or electromagnetic (EM) wave energy in form of optical and/or IR solar irradiance, but explicitly also including electricity generated in photo-voltaic cells mounted at least partially on the surface and/or in the vicinity of said building). In some instances said supplied energy may at least in part be delivered to a building in form of chemical energy, in such cases typically as fossil fuels, but also e.g. in form of previously generated hydrogen or other generated chemicals, and the electricity required to operate said air conditioning system is generated from said supplied chemical energy inside said building.
Thus, the term ‘supplied energy’ shall serve to distinguish it from sources and types of energy involved in the discussed problem, namely from solar energy in from of electromagnetic irradiance arriving at a building, thermal energy of the ambient air, thermal energy stored in the structure of said building, it's components or dedicated energy storage systems, as well as in the air contained in said building etc.
Thus one of the primary need for the disclosed invention stems more specifically from the desire to reduce the amount of supplied energy required to keep certain portions of buildings within certain temperature ranges.
On of the secondary benefits of the disclosed invention is that in some embodiments it helps to reduce the consumption of other resources, namely building materials and labor. By at least approximating certain physical and/or chemical target values within at least portion of said predominantly enclosed space, in some embodiments on average more favorable conditions in terms of average temperature, humidity, and air throughput (volume per time) can be achieved, which result in a higher lifetime of at least some components from which said predominantly enclosed space is built. For example, in some such embodiments the lifetime of components made from wood or other organic materials can be increased, and thus the time between repairs increased or the need for repairs entirely eliminated.
One of the tertiary benefits of the disclosed invention is that it provides means to supersede antiquated and unscientific building codes concerning air flow in buildings, which are not based or derived from optimization or at least approximation of specific physical target values.
Description of the Related Art
As explained in more technical detail further down, the thermal behavior of a building is a classic example of a highly complex multiphysics-problem, i.e. various physical effects determine—in a coupled manner—the energy budget (and thus temperature) as well as airflow inside and within the direct vicinity of a building. Specifically, actively driven and/or permitted or suppressed passive air flow within a building has a considerable effect on the energy budget of a building. However, air flow in (at least parts of) buildings is typically not a primary design point, at least not with respect to resulting impact on the thermal budget of buildings, and if considered at all overly simplifying approximations are frequently used, i.e. it is not considered a fluid dynamic and aerodynamic problem.
Thus, there is a need for innovation to address aspects of air flow in at least parts of a building specifically targeted at reducing the average supplied energy expenditure for any one or any combination of a) keeping at least one primary compartment of a building within a desired temperature range by means of active air conditioning or heating, or b) reducing temperature variations during a typical 24-hour cycle within said at least one primary compartment of said building, or c) reducing one or both of the average temperature or the peak temperature of said at least one primary compartment of said building.
Secondly, throughout the most parts of the world, regulations and rules have been established, which govern certain technical aspects building constructions, commonly referred to as building standards or building codes. Clearly, the primary purpose is to ensure safety of occupants. Furthermore, such codes also govern requirements directly or indirectly related to energy consumption, including but not limited to insulation, wall thicknesses, ventilation etc. In addition, some such codes concern requirements related to esthetic aspects, i.e. the visual appearance of buildings.
It is noteworthy that within the United States of America, building codes and standards adopted in numerous US states can all be traced back to a set of publications developed by at least one non-government for-profit organization. Further details on this topic can be found, for example, at “A Guide to California Housing Construction Codes”, State of California, 2014 Department of Housing and Community Development, Division of Codes and Standards; “2013 California Building Code”, California Code of Regulations, Title 24, Part 2, Volume 1, California Building Standards Commission, Sacramento, Calif. 95833-2936, ISBN: 978-1-60983-457-9; “2013 California Building Code”, California Code of Regulations, Title 24, Part 2, Volume 2, California Building Standards Commission, Sacramento, Calif. 95833-2936, ISBN: 978-1-60983-457-9; “2013 California Residential Code”, California Code of Regulations, Title 24, Part 2.5, California Building Standards Commission, Sacramento, Calif. 95833-2936, ISBN: 978-1-60983-458-6; and Douglas W. Thornburg, John R. Henry: “2012 International Building Code Handbook” McGraw-Hill Education, LLC, New York 2012, ISBN 978-0-07-180131-7, the entirety of which are incorporated herein by reference.
While some aspects of these standards and codes are obviously independent of geographic location—and thus climatic conditions—certain other aspects do considerably depend on typical environmental and climatic conditions (temperatures, solar input, humidity, wind etc.) and thus these environmental aspects should be considered for establishing meaningful and effective guidelines and codes for a given geographic region. Yet this critical process of adjusting said standards and codes has thus far not or only insufficiently occurred with respect to some specific technical aspect. (In future, a better way how standards should be defined is to make the definition independent of said environmental and climatic conditions by not specifying specific shapes or sized, but by specifying specific desirable results.)
One specific such aspect expressed in these standards and codes relates to ventilation, and more specifically one peculiar subsections concerns the concept of a “net free vent area”, which will henceforth be discussed in more detail.
For example, in the 2013 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 1, California Building Standards Commission, the following formulation can be found: “Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space by ventilation openings protected against the entrance of rain and snow. Blocking and bridging shall be arranged so as not to interfere with the movement of air. An airspace of not less than . . . 25 mm shall be provided between the insulation and the roof sheathing. The net free ventilating area shall not be less than 1/150th of the area of the space ventilated”.
And furthermore: “Exterior openings into the attic space of any building intended for human occupancy shall be protected to prevent the entry of birds, squirrels, rodents, snakes and other similar creatures. Openings for ventilation having a least dimension of not less than . . . 1.6 mm and not more than . . . 6.4 mm shall be permitted. Openings for ventilation having a least dimension larger than . . . 6.4 mm shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of not less than . . . 1.6 mm) and not more than . . . 6.4 mm.”
Comparable statements are made about under-floor ventilation. “Openings for under-floor ventilation: The net area of ventilation openings shall not be less than . . . 0.67 m2 for each 100 m2 of crawl-space area. Ventilation openings shall be covered for their height and width with any of the following materials, provided that the least dimension of the covering shall be not greater than . . . 6 mm.”
Thus, the seemingly magic ratio of 1:150 appears again. (In a few instances that ratio is inexplicably changed to 1:300, but the associated fundamental problem remains.) This concept of a fixed “net free vent area” (more accurately it should be call “vent area ratio”) is questionable in terms of its technical utility based on at least 3 major arguments:
1.) It lacks fundamental technical or scientific rationale. In order to be meaningful, any recommendations or standards expressed in respect to required ventilation, or more accurately required air flow, an actual physical (or chemical) objective has to be defined, which by implementation of said requirements one attempts to at least approximate. Ideally, specific minimal or maximal target values of specific physical or chemical quantities should be given. However, before mentioned concept of a “net free vent area” fails address any fundamental physical objective. One may image, for example, that a possible target might be to maintain (or at least not to exceed) a certain level of humidity, a certain level of temperature, a certain amount of replaced air volume within a certain time frame, a certain air flow velocity, etc. all of which is entirely impossible to ensure in a consistent manner for variably shaped buildings under hugely varying climatic conditions only with said trivial definition of a “net free vent area”.
2.) It illustrated fundamental lack of understanding fluid dynamics and aerodynamic phenomena.
The manner in which requirements are expressed in the 2013 California Building Code are effectively non-physical. First of all, based on the given definition, the term “net free ventilating area” is a misnomer, since it is the ratio of two areas, i.e. a dimensionless quantity and—if used at all—should e.g. better be referred to as “ventilation area ratio”. Another ambiguity arises from the term “area of the space ventilated”. It is not clear if this refers to the horizontal floor area of the “space ventilated” or to the area of the roof (ceiling) above said space (i.e., if it is indeed supposed to be a “ventilation inlet area to floor area ratio” or a “ventilation inlet area to roof area ratio”)
Secondly, either way, what is required is simply to surpass a certain ratio (1:150) of two areas, presumably the sum of the area openings for ventilation divided by presumably floor area. It is physically entirely impossible to make any meaningful predictions about the resulting air flow speed, spatial distribution, and throughput volume (i.e., a three-dimensional vector field) in an arbitrarily shaped attic with arbitrarily shaped and located openings solely based on such a single ratio. It is physically impossible that such a single simplistic rule can ensure any specific physical target for different buildings and under varying conditions. Without specifying at least the shape of the building (including the attic, including any sub-spaces and divisions), thus also its volume, the number of openings, their cross section of all ventilation openings, their shape, and size, the location where the openings are placed, any (typically occurring) external air flow, the spatial orientation of the building with respect to such typical external air flow, and furthermore any knowledge of thermally induces flows (i.e. temperature profiles resulting in buoyancy and thus convection) the actually occurring throughput of air can easily differ several orders of magnitude, thus rendering the requirements such as those expressed in the California Building Code, or other references, such as the 2012 International Building Code Handbook (Thornburg) physically and technically meaningless.
Such hugely simplified specification completely ignore the considerable physical complexity of the underlying phenomena, in particular related the fluid dynamics and thermal effects. More comments regarding the difficulties of air flow predictions based (at least) on the governing Navier-Stokes equations (a system of nonlinear second order differential equations of vector and scalar fields in three dimensions) will be given further down.
3.) It suffers from lack of consideration of geographic and thus meteorological variations.
Literally the same requirements to fulfill the “net free vent area” standards are being stated for California, District of Columbia, Puerto Rico, New York (state), and Washington (state), to name a few. The corresponding phrases have been verbatim copied from [8], likely without any further technical review, which in some instances leads to incongruous requirements. For example, all standards, including the ones for Florida and Puerto Rico, specify that “ventilation openings shall be protected against rain and snow”. We believe that there is not a single event in recorded human history of naturally occurring snow in Puerto Rico.
Thus, there is also a need for innovation to address aspects of air flow in buildings in a technically meaningful manner, which also provides an opportunity to achieve savings of various resources, namely in some instances energy and/or materials, at least for certain building designs and under certain climatic conditions.