Minimizing Air Leaks During Mobile Home HVAC Installation

Minimizing Air Leaks During Mobile Home HVAC Installation

Importance of Selecting the Right Units for Upgrades

When it comes to mobile homes, the importance of a well-functioning HVAC system cannot be overstated. Ensuring that these systems are installed correctly is crucial for maintaining energy efficiency and comfort within these small, yet complex living spaces. One of the most common issues faced during HVAC installations in mobile homes is air leaks. Mobile homes require specialized HVAC systems due to their unique design hvac for mobile home air handler. Understanding the causes of these leaks is essential for minimizing their occurrence and ensuring optimal performance.


Air leaks can occur for a variety of reasons during the installation process. One prevalent cause is poor sealing around ductwork connections. Mobile homes often have unique structural constraints that make it challenging to install ductwork without gaps or misalignments. If ducts are not properly sealed at connections, air can escape, reducing efficiency and forcing the system to work harder than necessary.


Another common source of air leaks is inadequate sealing around windows and doors. During HVAC installation, technicians may need to make adjustments or updates to these parts of the home to accommodate new equipment or ductwork. If these areas are not resealed effectively after modifications, they can allow outside air to infiltrate the home or conditioned air to escape.


Improper insulation can also contribute significantly to air leakage in mobile homes. These structures often have less space for insulation compared to traditional homes, making any gaps or thin spots more impactful on energy efficiency. Inadequate insulation around walls, ceilings, and floors can lead to significant heat loss in winter months or heat gain during summer months.


Finally, poor workmanship during installation can lead to various minor issues that collectively result in substantial air leakage over time. Whether it's failing to seal joints correctly or neglecting regular maintenance tasks like checking for wear and tear on seals and gaskets, human error plays a significant role in potential inefficiencies.


To minimize air leaks during HVAC installation in mobile homes, attention must be paid at each stage of the process-from planning through execution and post-installation checks. Ensuring all components fit together snugly with appropriate materials like mastic sealant or foil tape at every joint can go a long way in preventing future problems.


Moreover, choosing high-quality materials designed specifically for mobile home applications will help address unique challenges posed by these dwellings' designs. Regular inspections should also be scheduled post-installation; this allows homeowners not only peace-of-mind but an opportunity for early detection before small issues become costly repairs down-the-line.


In conclusion, while installing an efficient HVAC system into a mobile home presents its own set-of-challenges due mostly-to-space limitations inherent-within-these-structures; understanding-and-addressing-common-causes-behind-air-leaks-can-help-ensure-homeowners enjoy-comfortable-living-environments-without-unnecessary-energy-expense-or-wear-on-equipment-over-time.-By-focusing-on-proper-sealing-techniques,-utilizing-appropriate-materials,-and-conducting-regular-maintenance-checks,-both-professionals-and-DIY-enthusiasts-alike-can-contribute-toward-more-efficient-mobile-home-HVAC-systems-that-benefit-not-only-their-pocketbooks-but-also-the-environment-at-large-through-reduced-energy-consumption-and-emissions-associated-with-heating-and-cooling-demand-in-residential-settings.-

When it comes to the installation of HVAC systems in mobile homes, minimizing air leaks is paramount for ensuring energy efficiency and maintaining a comfortable indoor environment. One critical step in this process is the pre-installation inspection and preparation, which aims to identify potential leak points before they become problematic. This proactive approach not only enhances the performance of the HVAC system but also contributes to long-term cost savings and environmental sustainability.


The first step in pre-installation inspection involves a thorough examination of the mobile home's structure. Mobile homes, due to their unique construction, often present different challenges compared to conventional houses. Inspectors must pay close attention to areas around windows, doors, and any existing ductwork. These are common sites for air leaks due to gaps or inadequate sealing that can develop over time or during transportation. By identifying these points early on, measures can be taken to seal them effectively before HVAC components are installed.


Another critical aspect of this inspection involves checking the integrity of insulation materials. Inadequate or deteriorated insulation can significantly contribute to air leakage and reduce the overall efficiency of an HVAC system. Inspectors should ensure that all walls, ceilings, and floors have sufficient insulation and that there are no gaps or compressed areas where heat transfer could occur unchecked. If issues are found, upgrading insulation materials or adding additional layers may be necessary.


Following this structural assessment, attention shifts to the planned layout for ducts and vents. Improperly designed ductwork is a notorious culprit for causing air leaks in mobile home installations. The inspection team should evaluate whether proposed routes for ducts avoid unnecessary bends or sharp turns which can increase resistance and lead to leaks at joints or connections. Ensuring that ducts will fit snugly within allotted spaces without being compressed or stretched is vital for maintaining airflow efficiency once the system is operational.


In addition to physical inspections, using technology such as thermal imaging cameras can provide valuable insights into potential problem areas that might not be immediately visible to the naked eye. These tools can detect temperature variations along surfaces indicating possible leaks where warm air escapes or cold air infiltrates into living spaces.


Once potential leak points have been identified through these various methods, preparation efforts focus on implementing solutions such as caulking around window frames, installing weather-stripping on doors, sealing joints in ductwork with mastic sealant rather than traditional tape which tends to deteriorate quickly under pressure changes common in HVAC systems operation.


By investing time in comprehensive pre-installation inspections and preparations focused on identifying potential leak points within mobile homes before commencing with HVAC installation processes ensures both immediate benefits like improved indoor comfort levels alongside longer-term advantages including reduced utility bills due largely decreased energy wastage associated with escaping conditioned air through otherwise overlooked gaps throughout structures involved thereby achieving significant strides towards sustainable living practices overall too!

Retrofitted Mobile Home AC Units Show Significant Reductions in Electric Bills

Retrofitted Mobile Home AC Units Show Significant Reductions in Electric Bills

When considering the long-term financial implications of retrofitting mobile home air conditioning units, it's essential to weigh the initial costs against the potential savings in electric bills.. Mobile homes, often designed with affordability in mind, may not always prioritize energy efficiency.

Posted by on 2024-12-29

Community Clinics Educate Residents on Proper Sizing for Mobile Home HVAC Systems

Community Clinics Educate Residents on Proper Sizing for Mobile Home HVAC Systems

In the heart of many mobile home communities, there exists a common challenge that often goes unnoticed: the sizing of HVAC systems.. As these communities strive for comfort and efficiency, the importance of having properly sized heating, ventilation, and air conditioning (HVAC) systems cannot be overstated.

Posted by on 2024-12-29

Emerging Technology Simplifies Air Handler Upgrades in Aging Mobile Homes

Emerging Technology Simplifies Air Handler Upgrades in Aging Mobile Homes

In recent years, the mobile home industry has undergone a quiet revolution, driven by advancements in HVAC technology that promise to transform how we approach air handler upgrades in aging mobile homes.. As these homes continue to age, maintaining a comfortable and energy-efficient environment becomes increasingly challenging.

Posted by on 2024-12-29

Pilot Program Explores Cost-Effective Retrofits for Electric-Only Mobile Home Furnaces

Pilot Program Explores Cost-Effective Retrofits for Electric-Only Mobile Home Furnaces

As the world continues to grapple with the dual challenges of energy efficiency and sustainability, innovative solutions in housing are gaining increasing attention.. One such initiative that stands out is the pilot program exploring cost-effective retrofits for electric-only mobile home furnaces.

Posted by on 2024-12-29

Energy Efficiency and Environmental Impact

Minimizing air leaks during mobile home HVAC installation is crucial for ensuring energy efficiency and maintaining indoor comfort. The process involves a meticulous approach to sealing ducts and vents, which are the primary culprits of air leakage in HVAC systems. Adopting best practices for this task not only enhances the system's performance but also extends its lifespan while reducing utility costs.


The first step in sealing ducts and vents effectively is to conduct a thorough inspection. This assessment helps identify areas prone to leaks, such as joints, seams, and connections within the ductwork. Often, these vulnerable points are located where ducts meet registers or at transitions between different segments. In mobile homes, where space constraints can lead to more complex duct paths, it is especially important to address these areas meticulously.


Once potential leak points have been identified, the next step is cleaning. Dust, debris, and moisture can hinder sealant adhesion; therefore, it's vital that surfaces are clean and dry before applying any sealing materials. A clean surface ensures maximum contact and bonding of sealants.


Selecting appropriate sealing materials is another critical aspect of minimizing air leaks. Mastic sealant or metal-backed (foil) tape are typically recommended over cloth-backed duct tape due to their durability and long-lasting adhesive properties. Mastic sealant provides a flexible yet robust barrier against air leaks when applied correctly around seams and joints. It should be spread generously with a brush or applicator tool to cover all gaps thoroughly.


For areas difficult to access with mastic sealant, foil tape offers an excellent alternative. Its pressure-sensitive adhesive makes it easy to apply even in tight spaces common in mobile home installations. However, it's essential that the tape is smoothed down firmly across seams to prevent any future peeling or detachment.


Additionally, insulating ductwork can significantly reduce thermal losses alongside preventing air leakage. Insulation wraps around ducts help maintain consistent temperatures within them by minimizing heat exchange with surrounding environments-this means less strain on the HVAC system itself.


Beyond technical measures lies the importance of professional installation expertise. Hiring certified technicians who understand mobile home specifics ensures that all components are installed according to code requirements and industry standards-further safeguarding against potential issues like improper fitment leading inadvertently towards leaks.


Regular maintenance checks post-installation cannot be overstated either-they're imperative for ongoing efficiency optimization within HVAC systems installed inside mobile homes! Scheduling periodic inspections allows homeowners timely identification/rectification opportunities concerning wear-and-tear effects inevitably encountered over time despite initial top-tier craftsmanship efforts undertaken during original deployment phases themselves!


In conclusion: Following best practices related specifically towards securing/sealing both ducts/vents remains essential strategy-wise whenever seeking minimize unwanted/uncontrolled airflow occurrences ultimately compromising overall operational effectiveness/economical considerations alike regarding one's cherished abode residing atop wheels! Through diligent inspection routines coupled alongside suitable material selection/application methods joined together harmoniously forming cohesive whole-it becomes feasible preserving desired climate conditions therein without undue burden imposed financially/environmentally either way simultaneously achieved thereby enhancing quality living experiences afforded therein indefinitely moving forward apace modern progressive society demands nowadays ubiquitously evident everywhere today universally acknowledged accordingly worldwide comprehensively speaking altogether succinctly put succinctly indeed!

Energy Efficiency and Environmental Impact

Cost-Effectiveness and Budget Considerations

In the realm of mobile home HVAC installation, one cannot overstate the importance of proper insulation when it comes to minimizing air leaks and enhancing overall efficiency. Mobile homes, by their very nature, are more susceptible to issues with temperature regulation due to their lightweight construction and sometimes limited design flexibility. As such, ensuring that these dwellings are adequately insulated is not merely an afterthought but a crucial step in the installation process.


Firstly, let's consider what happens when there is inadequate insulation during the HVAC installation process. Without proper insulation, mobile homes become vulnerable to significant air leaks. These leaks can lead to a loss of conditioned air, whether it's warm or cool depending on the season. This loss not only makes it difficult for the HVAC system to maintain a consistent indoor temperature but also forces it to work harder than necessary. Consequently, this can lead to increased energy consumption and higher utility bills-an unwelcome situation for any homeowner striving for efficiency and cost-effectiveness.


Proper insulation acts as a barrier that helps keep conditioned air inside while preventing outdoor air from infiltrating the living space. By effectively sealing off potential pathways for air leakage, high-quality insulation ensures that the HVAC system operates at its optimal level. This translates into better thermal comfort within the home, as well as improved energy efficiency.


Moreover, reducing air leaks through proper insulation contributes significantly to prolonging the lifespan of HVAC systems in mobile homes. Systems burdened by constant fluctuations due to leaks often experience wear and tear much faster than those operating under stable conditions. By maintaining a steady environment with minimal fluctuations in workload, properly insulated systems endure less stress and thus enjoy an extended operational life.


Additionally, environmental considerations come into play when discussing insulation's role in reducing air leaks during HVAC installations in mobile homes. Energy-efficient systems mean lower carbon footprints-a crucial factor in today's climate-conscious world. Properly insulating these homes not only benefits individual homeowners financially but also contributes positively towards broader ecological goals by conserving energy resources.


In conclusion, while mobile home HVAC installations may present unique challenges compared to traditional housing setups, addressing these challenges with proper insulation is key to minimizing air leaks and maximizing both performance and efficiency. It represents a wise investment that pays dividends not just in terms of immediate comfort and savings but also long-term durability and sustainability. Emphasizing robust insulation practices during installation ensures that mobile homes remain havens of comfort regardless of external weather conditions-making them truly efficient sanctuaries on wheels.

Sizing and Compatibility with Mobile Home Structures

Minimizing air leaks during mobile home HVAC installation is crucial for ensuring efficiency, maintaining indoor air quality, and reducing energy costs. Once an HVAC system is installed, it's important to verify its airtightness to confirm that it operates optimally. Various techniques can be employed to test and verify the airtightness of an HVAC system post-installation.


One of the most common methods for testing airtightness is the blower door test. This technique involves mounting a powerful fan in the frame of an exterior door. The fan pulls air out of the home, lowering the air pressure inside. The higher outside air pressure then flows into the house through all unsealed cracks and openings. A technician can use smoke pencils or infrared cameras to detect these leaks visibly, thereby assessing how well-sealed the HVAC system and ductwork are.


Duct leakage tests are another essential method specifically targeting the ductwork's integrity within an HVAC system. These tests typically involve sealing all vents and registers, then pressurizing the ducts with a calibrated fan connected to a duct blower. By measuring the amount of air needed to maintain specific pressures within the ducts, technicians can identify leakage rates and pinpoint areas needing sealing or repairs.


Tracer gas testing is a more sophisticated technique used in some cases where accurate measurements are critical. This method involves introducing a non-toxic tracer gas into the ductwork and using detectors to measure its concentration at various points throughout the system. Any significant decrease in concentration indicates potential leaks that need addressing.


Smoke testing offers another practical approach for visual leak detection post-installation. Similar to utilizing smoke pencils during a blower door test, this method introduces non-toxic smoke into sections of ductwork while observing for any visible escape routes that would signify leaks.


For those seeking high-tech solutions, thermal imaging cameras provide a non-invasive means of detecting temperature differences along duct surfaces and around HVAC components that may indicate poor insulation or leaks affecting performance.


In addition to these technical methods, visual inspections by experienced professionals remain invaluable for catching obvious installation errors such as improperly sealed joints or disconnected ducts which could contribute significantly to overall leakage.


In conclusion, verifying the airtightness of an HVAC system after installation in a mobile home is vital for ensuring energy efficiency and comfort while minimizing potential operational costs over time. Whether employing basic techniques like blower door tests or advanced methods such as tracer gas testing, each approach plays an integral role in identifying weaknesses within systems so they can be rectified promptly-thereby safeguarding both economic investments made by homeowners as well as environmental sustainability efforts through reduced energy consumption.

Installation Challenges and Solutions

Minimizing air leaks during mobile home HVAC installation is crucial for ensuring energy efficiency, maintaining indoor comfort, and reducing utility bills. Air leaks can lead to significant energy losses, as the conditioned air escapes through unsealed areas, forcing the HVAC system to work harder to maintain the desired temperature. This not only increases energy consumption but also shortens the lifespan of the HVAC system due to overuse. Therefore, implementing effective maintenance tips is vital for long-term success in minimizing air leaks.


One of the primary maintenance strategies is conducting regular inspections of your mobile home's HVAC system. This involves checking all ducts, vents, and seals for signs of wear and tear. Over time, seals can degrade or become loose due to various factors such as temperature fluctuations or physical damage. It is essential to repair or replace any damaged parts promptly to prevent air from escaping.


Another important tip is utilizing high-quality sealing materials. Silicone caulk or specialized HVAC sealants are excellent choices for sealing gaps around ductwork and vents. These materials are designed to withstand extreme temperatures and provide a durable seal that prevents air leakage effectively. Applying these sealants correctly can significantly enhance your home's energy efficiency by maintaining a tight seal around all potential leak points.


It is also advisable to insulate ductwork properly. Insulation helps maintain the temperature of the air traveling through ducts and prevents it from losing heat or cold as it moves through unconditioned spaces like attics or crawlspaces. Adding insulation sleeves or wraps around ducts can reduce thermal loss and minimize any potential leaks that might develop over time.


Regularly cleaning and maintaining your HVAC system also plays a pivotal role in preventing air leaks. Dust and debris accumulation can put extra strain on your system's components, potentially causing them to misalign or break down prematurely. Ensure that filters are replaced regularly and that all moving parts are lubricated according to manufacturer specifications.


Moreover, professional assessments should not be overlooked. Hiring an HVAC professional at least once a year for a thorough inspection ensures that any hidden issues are addressed before they escalate into major problems. Professionals have specialized tools that can detect even minor leaks which may go unnoticed during routine checks.


Finally, educating yourself about your specific HVAC model's requirements and limitations will enable you to implement more tailored maintenance practices effectively. Each model may have unique features needing particular attention; understanding these nuances allows you to optimize its performance while minimizing risks associated with air leaks.


In conclusion, maintaining an airtight mobile home requires dedication and regular upkeep of its HVAC systems. By conducting routine inspections, using quality sealing materials, insulating ductwork adequately, keeping systems clean, seeking professional advice periodically, and staying informed about your equipment's needs-homeowners can ensure their homes remain energy-efficient sanctuaries free from troublesome air leaks over time.

Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located. Some researchers refer it to “various materials joined together to form a component of the final installation procedure“.

The most commonly cited definition is by Goodier and Gibb in 2007, which described the process of manufacturing and preassembly of a certain number of building components, modules, and elements before their shipment and installation on construction sites.[1]

The term prefabrication also applies to the manufacturing of things other than structures at a fixed site. It is frequently used when fabrication of a section of a machine or any movable structure is shifted from the main manufacturing site to another location, and the section is supplied assembled and ready to fit. It is not generally used to refer to electrical or electronic components of a machine, or mechanical parts such as pumps, gearboxes and compressors which are usually supplied as separate items, but to sections of the body of the machine which in the past were fabricated with the whole machine. Prefabricated parts of the body of the machine may be called 'sub-assemblies' to distinguish them from the other components.

Process and theory

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Levittown, Puerto Rico

An example from house-building illustrates the process of prefabrication. The conventional method of building a house is to transport bricks, timber, cement, sand, steel and construction aggregate, etc. to the site, and to construct the house on site from these materials. In prefabricated construction, only the foundations are constructed in this way, while sections of walls, floors and roof are prefabricated (assembled) in a factory (possibly with window and door frames included), transported to the site, lifted into place by a crane and bolted together.

Prefabrication is used in the manufacture of ships, aircraft and all kinds of vehicles and machines where sections previously assembled at the final point of manufacture are assembled elsewhere instead, before being delivered for final assembly.

The theory behind the method is that time and cost is saved if similar construction tasks can be grouped, and assembly line techniques can be employed in prefabrication at a location where skilled labour is available, while congestion at the assembly site, which wastes time, can be reduced. The method finds application particularly where the structure is composed of repeating units or forms, or where multiple copies of the same basic structure are being constructed. Prefabrication avoids the need to transport so many skilled workers to the construction site, and other restricting conditions such as a lack of power, lack of water, exposure to harsh weather or a hazardous environment are avoided. Against these advantages must be weighed the cost of transporting prefabricated sections and lifting them into position as they will usually be larger, more fragile and more difficult to handle than the materials and components of which they are made.

History

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"Loren" Iron House, at Old Gippstown in Moe, Australia

Prefabrication has been used since ancient times. For example, it is claimed that the world's oldest known engineered roadway, the Sweet Track constructed in England around 3800 BC, employed prefabricated timber sections brought to the site rather than assembled on-site.[citation needed]

Sinhalese kings of ancient Sri Lanka have used prefabricated buildings technology to erect giant structures, which dates back as far as 2000 years, where some sections were prepared separately and then fitted together, specially in the Kingdom of Anuradhapura and Polonnaruwa.

After the great Lisbon earthquake of 1755, the Portuguese capital, especially the Baixa district, was rebuilt by using prefabrication on an unprecedented scale. Under the guidance of Sebastião José de Carvalho e Melo, popularly known as the Marquis de Pombal, the most powerful royal minister of D. Jose I, a new Pombaline style of architecture and urban planning arose, which introduced early anti-seismic design features and innovative prefabricated construction methods, according to which large multistory buildings were entirely manufactured outside the city, transported in pieces and then assembled on site. The process, which lasted into the nineteenth century, lodged the city's residents in safe new structures unheard-of before the quake.

Also in Portugal, the town of Vila Real de Santo António in the Algarve, founded on 30 December 1773, was quickly erected through the use of prefabricated materials en masse. The first of the prefabricated stones was laid in March 1774. By 13 May 1776, the centre of the town had been finished and was officially opened.

In 19th century Australia a large number of prefabricated houses were imported from the United Kingdom.

The method was widely used in the construction of prefabricated housing in the 20th century, such as in the United Kingdom as temporary housing for thousands of urban families "bombed out" during World War II. Assembling sections in factories saved time on-site and the lightness of the panels reduced the cost of foundations and assembly on site. Coloured concrete grey and with flat roofs, prefab houses were uninsulated and cold and life in a prefab acquired a certain stigma, but some London prefabs were occupied for much longer than the projected 10 years.[2]

The Crystal Palace, erected in London in 1851, was a highly visible example of iron and glass prefabricated construction; it was followed on a smaller scale by Oxford Rewley Road railway station.

During World War II, prefabricated Cargo ships, designed to quickly replace ships sunk by Nazi U-boats became increasingly common. The most ubiquitous of these ships was the American Liberty ship, which reached production of over 2,000 units, averaging 3 per day.

Current uses

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A house being built with prefabricated concrete panels.

The most widely used form of prefabrication in building and civil engineering is the use of prefabricated concrete and prefabricated steel sections in structures where a particular part or form is repeated many times. It can be difficult to construct the formwork required to mould concrete components on site, and delivering wet concrete to the site before it starts to set requires precise time management. Pouring concrete sections in a factory brings the advantages of being able to re-use moulds and the concrete can be mixed on the spot without having to be transported to and pumped wet on a congested construction site. Prefabricating steel sections reduces on-site cutting and welding costs as well as the associated hazards.

Prefabrication techniques are used in the construction of apartment blocks, and housing developments with repeated housing units. Prefabrication is an essential part of the industrialization of construction.[3] The quality of prefabricated housing units had increased to the point that they may not be distinguishable from traditionally built units to those that live in them. The technique is also used in office blocks, warehouses and factory buildings. Prefabricated steel and glass sections are widely used for the exterior of large buildings.

Detached houses, cottages, log cabin, saunas, etc. are also sold with prefabricated elements. Prefabrication of modular wall elements allows building of complex thermal insulation, window frame components, etc. on an assembly line, which tends to improve quality over on-site construction of each individual wall or frame. Wood construction in particular benefits from the improved quality. However, tradition often favors building by hand in many countries, and the image of prefab as a "cheap" method only slows its adoption. However, current practice already allows the modifying the floor plan according to the customer's requirements and selecting the surfacing material, e.g. a personalized brick facade can be masoned even if the load-supporting elements are timber.

Today, prefabrication is used in various industries and construction sectors such as healthcare, retail, hospitality, education, and public administration, due to its many advantages and benefits over traditional on-site construction, such as reduced installation time and cost savings.[4] Being used in single-story buildings as well as in multi-story projects and constructions. Providing the possibility of applying it to a specific part of the project or to the whole of it.

The efficiency and speed in the execution times of these works offer that, for example, in the case of the educational sector, it is possible to execute the projects without the cessation of the operations of the educational facilities during the development of the same.

Transportation of prefabricated Airbus wing assembly

Prefabrication saves engineering time on the construction site in civil engineering projects. This can be vital to the success of projects such as bridges and avalanche galleries, where weather conditions may only allow brief periods of construction. Prefabricated bridge elements and systems offer bridge designers and contractors significant advantages in terms of construction time, safety, environmental impact, constructibility, and cost. Prefabrication can also help minimize the impact on traffic from bridge building. Additionally, small, commonly used structures such as concrete pylons are in most cases prefabricated.

Radio towers for mobile phone and other services often consist of multiple prefabricated sections. Modern lattice towers and guyed masts are also commonly assembled of prefabricated elements.

Prefabrication has become widely used in the assembly of aircraft and spacecraft, with components such as wings and fuselage sections often being manufactured in different countries or states from the final assembly site. However, this is sometimes for political rather than commercial reasons, such as for Airbus.

Advantages

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  • Moving partial assemblies from a factory often costs less than moving pre-production resources to each site
  • Deploying resources on-site can add costs; prefabricating assemblies can save costs by reducing on-site work
  • Factory tools - jigs, cranes, conveyors, etc. - can make production faster and more precise
  • Factory tools - shake tables, hydraulic testers, etc. - can offer added quality assurance
  • Consistent indoor environments of factories eliminate most impacts of weather on production
  • Cranes and reusable factory supports can allow shapes and sequences without expensive on-site falsework
  • Higher-precision factory tools can aid more controlled movement of building heat and air, for lower energy consumption and healthier buildings
  • Factory production can facilitate more optimal materials usage, recycling, noise capture, dust capture, etc.
  • Machine-mediated parts movement, and freedom from wind and rain can improve construction safety
  • Homogeneous manufacturing allows high standardization and quality control, ensuring quality requirements subject to performance and resistance tests, which also facilitate high scalability of construction projects. [5]
  • The specific production processes in industrial assembly lines allow high sustainability, which enables savings of up to 20% of the total final cost, as well as considerable savings in indirect costs. [6]

Disadvantages

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  • Transportation costs may be higher for voluminous prefabricated sections (especially sections so big that they constitute oversize loads requiring special signage, escort vehicles, and temporary road closures) than for their constituent materials, which can often be packed more densely and are more likely to fit onto standard-sized vehicles.
  • Large prefabricated sections may require heavy-duty cranes and precision measurement and handling to place in position.

Off-site fabrication

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Off-site fabrication is a process that incorporates prefabrication and pre-assembly. The process involves the design and manufacture of units or modules, usually remote from the work site, and the installation at the site to form the permanent works at the site. In its fullest sense, off-site fabrication requires a project strategy that will change the orientation of the project process from construction to manufacture to installation. Examples of off-site fabrication are wall panels for homes, wooden truss bridge spans, airport control stations.

There are four main categories of off-site fabrication, which is often also referred to as off-site construction. These can be described as component (or sub-assembly) systems, panelised systems, volumetric systems, and modular systems. Below these categories different branches, or technologies are being developed. There are a vast number of different systems on the market which fall into these categories and with recent advances in digital design such as building information modeling (BIM), the task of integrating these different systems into a construction project is becoming increasingly a "digital" management proposition.

The prefabricated construction market is booming. It is growing at an accelerated pace both in more established markets such as North America and Europe and in emerging economies such as the Asia-Pacific region (mainly China and India). Considerable growth is expected in the coming years, with the prefabricated modular construction market expected to grow at a CAGR (compound annual growth rate) of 8% between 2022 and 2030. It is expected to reach USD 271 billion by 2030. [7]

See also

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  • Prefabricated home
  • Prefabricated buildings
  • Concrete perpend
  • Panelák
  • Tower block
  • St Crispin's School — an example of a prefabricated school building
  • Nonsuch House, first prefabricated building
  • Agile construction
  • Intermediate good

References

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  1. ^ (2022) Modularity clustering of economic development and ESG attributes in prefabricated building research. Frontiers in Environmental Science, 10. Retrieved from https://www.frontiersin.org/articles/10.3389/fenvs.2022.977887
  2. ^ Sargeant, Tony Anthony J. (11 November 2016) [2016-09-10]. "'Prefabs' in South London – built as emergency housing just after WW2 and meant to last for just 10 years". Tonyjsargeant.wordpress.com. Archived from the original on 14 October 2016. Retrieved 19 July 2018.
  3. ^ Goh, Edward; Loosemore, Martin (4 May 2017). "The impacts of industrialization on construction subcontractors: a resource based view". Construction Management and Economics. 35 (5): 288–304. doi:10.1080/01446193.2016.1253856. ISSN 0144-6193.
  4. ^ Details about the modular construction market. Hydrodiseno.com. 2022-08-17. Retrieved 2023-01-05
  5. ^ Zhou, Jingyang; Li, Yonghan; Ren, Dandan (November 2022). "Quantitative study on external benefits of prefabricated buildings: From perspectives of economy, environment, and society". Sustainable Cities and Society. 86. Bibcode:2022SusCS..8604132Z. doi:10.1016/j.scs.2022.104132.
  6. ^ Why Choose Modular Construction? Hydrodiseno.com. 2021-07-29. Retrieved 2023-03-07
  7. ^ Modular Construction Market Size is projected to reach USD 271 Billion by 2030, growing at a CAGR of 8%: Straits Research. Globenewswire.com. 2022-06-18. Retrieved 2023-02-16

Sources

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"Prefabricated Building Construction Systems Adopted in Hong Kong" (PDF). Retrieved 20 August 2013.

 

A thermal image of human

Thermal comfort is the condition of mind that expresses subjective satisfaction with the thermal environment.[1] The human body can be viewed as a heat engine where food is the input energy. The human body will release excess heat into the environment, so the body can continue to operate. The heat transfer is proportional to temperature difference. In cold environments, the body loses more heat to the environment and in hot environments the body does not release enough heat. Both the hot and cold scenarios lead to discomfort.[2] Maintaining this standard of thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC (heating, ventilation, and air conditioning) design engineers.

Thermal neutrality is maintained when the heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with the surroundings. The main factors that influence thermal neutrality are those that determine heat gain and loss, namely metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed and relative humidity. Psychological parameters, such as individual expectations, and physiological parameters also affect thermal neutrality.[3] Neutral temperature is the temperature that can lead to thermal neutrality and it may vary greatly between individuals and depending on factors such as activity level, clothing, and humidity. People are highly sensitive to even small differences in environmental temperature. At 24 °C, a difference of 0.38 °C can be detected between the temperature of two rooms.[4]

The Predicted Mean Vote (PMV) model stands among the most recognized thermal comfort models. It was developed using principles of heat balance and experimental data collected in a controlled climate chamber under steady state conditions.[5] The adaptive model, on the other hand, was developed based on hundreds of field studies with the idea that occupants dynamically interact with their environment. Occupants control their thermal environment by means of clothing, operable windows, fans, personal heaters, and sun shades.[3][6] The PMV model can be applied to air-conditioned buildings, while the adaptive model can be applied only to buildings where no mechanical systems have been installed.[1] There is no consensus about which comfort model should be applied for buildings that are partially air-conditioned spatially or temporally.

Thermal comfort calculations in accordance with the ANSI/ASHRAE Standard 55,[1] the ISO 7730 Standard[7] and the EN 16798-1 Standard[8] can be freely performed with either the CBE Thermal Comfort Tool for ASHRAE 55,[9] with the Python package pythermalcomfort[10] or with the R package comf.

Significance

[edit]

Satisfaction with the thermal environment is important because thermal conditions are potentially life-threatening for humans if the core body temperature reaches conditions of hyperthermia, above 37.5–38.3 °C (99.5–100.9 °F),[11][12] or hypothermia, below 35.0 °C (95.0 °F).[13] Buildings modify the conditions of the external environment and reduce the effort that the human body needs to do in order to stay stable at a normal human body temperature, important for the correct functioning of human physiological processes.

The Roman writer Vitruvius actually linked this purpose to the birth of architecture.[14] David Linden also suggests that the reason why we associate tropical beaches with paradise is because in those environments is where human bodies need to do less metabolic effort to maintain their core temperature.[15] Temperature not only supports human life; coolness and warmth have also become in different cultures a symbol of protection, community and even the sacred.[16]

In building science studies, thermal comfort has been related to productivity and health. Office workers who are satisfied with their thermal environment are more productive.[17][18] The combination of high temperature and high relative humidity reduces thermal comfort and indoor air quality.[19]

Although a single static temperature can be comfortable, people are attracted by thermal changes, such as campfires and cool pools. Thermal pleasure is caused by varying thermal sensations from a state of unpleasantness to a state of pleasantness, and the scientific term for it is positive thermal alliesthesia.[20] From a state of thermal neutrality or comfort any change will be perceived as unpleasant.[21] This challenges the assumption that mechanically controlled buildings should deliver uniform temperatures and comfort, if it is at the cost of excluding thermal pleasure.[22]

Influencing factors

[edit]

Since there are large variations from person to person in terms of physiological and psychological satisfaction, it is hard to find an optimal temperature for everyone in a given space. Laboratory and field data have been collected to define conditions that will be found comfortable for a specified percentage of occupants.[1]

There are numerous factors that directly affect thermal comfort that can be grouped in two categories:

  1. Personal factors – characteristics of the occupants such as metabolic rate and clothing level
  2. Environmental factors – which are conditions of the thermal environment, specifically air temperature, mean radiant temperature, air speed and humidity

Even if all these factors may vary with time, standards usually refer to a steady state to study thermal comfort, just allowing limited temperature variations.

Personal factors

[edit]

Metabolic rate

[edit]

People have different metabolic rates that can fluctuate due to activity level and environmental conditions.[23][24][25] ASHRAE 55-2017 defines metabolic rate as the rate of transformation of chemical energy into heat and mechanical work by metabolic activities of an individual, per unit of skin surface area.[1]: 3 

Metabolic rate is expressed in units of met, equal to 58.2 W/m² (18.4 Btu/h·ft²). One met is equal to the energy produced per unit surface area of an average person seated at rest.

ASHRAE 55 provides a table of metabolic rates for a variety of activities. Some common values are 0.7 met for sleeping, 1.0 met for a seated and quiet position, 1.2–1.4 met for light activities standing, 2.0 met or more for activities that involve movement, walking, lifting heavy loads or operating machinery. For intermittent activity, the standard states that it is permissible to use a time-weighted average metabolic rate if individuals are performing activities that vary over a period of one hour or less. For longer periods, different metabolic rates must be considered.[1]

According to ASHRAE Handbook of Fundamentals, estimating metabolic rates is complex, and for levels above 2 or 3 met – especially if there are various ways of performing such activities – the accuracy is low. Therefore, the standard is not applicable for activities with an average level higher than 2 met. Met values can also be determined more accurately than the tabulated ones, using an empirical equation that takes into account the rate of respiratory oxygen consumption and carbon dioxide production. Another physiological yet less accurate method is related to the heart rate, since there is a relationship between the latter and oxygen consumption.[26]

The Compendium of Physical Activities is used by physicians to record physical activities. It has a different definition of met that is the ratio of the metabolic rate of the activity in question to a resting metabolic rate.[27] As the formulation of the concept is different from the one that ASHRAE uses, these met values cannot be used directly in PMV calculations, but it opens up a new way of quantifying physical activities.

Food and drink habits may have an influence on metabolic rates, which indirectly influences thermal preferences. These effects may change depending on food and drink intake.[28]

Body shape is another factor that affects metabolic rate and hence thermal comfort. Heat dissipation depends on body surface area. The surface area of an average person is 1.8 m2 (19 ft2).[1] A tall and skinny person has a larger surface-to-volume ratio, can dissipate heat more easily, and can tolerate higher temperatures more than a person with a rounded body shape.[28]

Clothing insulation

[edit]

The amount of thermal insulation worn by a person has a substantial impact on thermal comfort, because it influences the heat loss and consequently the thermal balance. Layers of insulating clothing prevent heat loss and can either help keep a person warm or lead to overheating. Generally, the thicker the garment is, the greater insulating ability it has. Depending on the type of material the clothing is made out of, air movement and relative humidity can decrease the insulating ability of the material.[29][30]

1 clo is equal to 0.155 m2·K/W (0.88 °F·ft2·h/Btu). This corresponds to trousers, a long sleeved shirt, and a jacket. Clothing insulation values for other common ensembles or single garments can be found in ASHRAE 55.[1]

Skin wetness
[edit]

Skin wetness is defined as "the proportion of the total skin surface area of the body covered with sweat".[31] The wetness of skin in different areas also affects perceived thermal comfort. Humidity can increase wetness in different areas of the body, leading to a perception of discomfort. This is usually localized in different parts of the body, and local thermal comfort limits for skin wetness differ by locations of the body.[32] The extremities are much more sensitive to thermal discomfort from wetness than the trunk of the body. Although local thermal discomfort can be caused by wetness, the thermal comfort of the whole body will not be affected by the wetness of certain parts.

Environmental factors

[edit]

Air temperature

[edit]

The air temperature is the average temperature of the air surrounding the occupant, with respect to location and time. According to ASHRAE 55 standard, the spatial average takes into account the ankle, waist and head levels, which vary for seated or standing occupants. The temporal average is based on three-minutes intervals with at least 18 equally spaced points in time. Air temperature is measured with a dry-bulb thermometer and for this reason it is also known as dry-bulb temperature.

Mean radiant temperature

[edit]

The radiant temperature is related to the amount of radiant heat transferred from a surface, and it depends on the material's ability to absorb or emit heat, or its emissivity. The mean radiant temperature depends on the temperatures and emissivities of the surrounding surfaces as well as the view factor, or the amount of the surface that is “seen” by the object. So the mean radiant temperature experienced by a person in a room with the sunlight streaming in varies based on how much of their body is in the sun.

Air speed

[edit]

Air speed is defined as the rate of air movement at a point, without regard to direction. According to ANSI/ASHRAE Standard 55, it is the average speed of the air surrounding a representative occupant, with respect to location and time. The spatial average is for three heights as defined for average air temperature. For an occupant moving in a space the sensors shall follow the movements of the occupant. The air speed is averaged over an interval not less than one and not greater than three minutes. Variations that occur over a period greater than three minutes shall be treated as multiple different air speeds.[33]

Relative humidity

[edit]

Relative humidity (RH) is the ratio of the amount of water vapor in the air to the amount of water vapor that the air could hold at the specific temperature and pressure. While the human body has thermoreceptors in the skin that enable perception of temperature, relative humidity is detected indirectly. Sweating is an effective heat loss mechanism that relies on evaporation from the skin. However at high RH, the air has close to the maximum water vapor that it can hold, so evaporation, and therefore heat loss, is decreased. On the other hand, very dry environments (RH < 20–30%) are also uncomfortable because of their effect on the mucous membranes. The recommended level of indoor humidity is in the range of 30–60% in air conditioned buildings,[34][35] but new standards such as the adaptive model allow lower and higher humidity, depending on the other factors involved in thermal comfort.

Recently, the effects of low relative humidity and high air velocity were tested on humans after bathing. Researchers found that low relative humidity engendered thermal discomfort as well as the sensation of dryness and itching. It is recommended to keep relative humidity levels higher in a bathroom than other rooms in the house for optimal conditions.[36]

Various types of apparent temperature have been developed to combine air temperature and air humidity. For higher temperatures, there are quantitative scales, such as the heat index. For lower temperatures, a related interplay was identified only qualitatively:

  • High humidity and low temperatures cause the air to feel chilly.[37]
  • Cold air with high relative humidity "feels" colder than dry air of the same temperature because high humidity in cold weather increases the conduction of heat from the body.[38]

There has been controversy over why damp cold air feels colder than dry cold air. Some believe it is because when the humidity is high, our skin and clothing become moist and are better conductors of heat, so there is more cooling by conduction.[39]

The influence of humidity can be exacerbated with the combined use of fans (forced convection cooling).[40]

Natural ventilation

[edit]

Many buildings use an HVAC unit to control their thermal environment. Other buildings are naturally ventilated (or would have cross ventilation) and do not rely on mechanical systems to provide thermal comfort. Depending on the climate, this can drastically reduce energy consumption. It is sometimes seen as a risk, though, since indoor temperatures can be too extreme if the building is poorly designed. Properly designed, naturally ventilated buildings keep indoor conditions within the range where opening windows and using fans in the summer, and wearing extra clothing in the winter, can keep people thermally comfortable.[41]

Models and indices

[edit]

There are several different models or indices that can be used to assess thermal comfort conditions indoors as described below.

PMV/PPD method

[edit]
Psychrometric Chart
Temperature-relative humidity chart
Two alternative representations of thermal comfort for the PMV/PPD method

The PMV/PPD model was developed by P.O. Fanger using heat-balance equations and empirical studies about skin temperature to define comfort. Standard thermal comfort surveys ask subjects about their thermal sensation on a seven-point scale from cold (−3) to hot (+3). Fanger's equations are used to calculate the predicted mean vote (PMV) of a group of subjects for a particular combination of air temperature, mean radiant temperature, relative humidity, air speed, metabolic rate, and clothing insulation.[5] PMV equal to zero is representing thermal neutrality, and the comfort zone is defined by the combinations of the six parameters for which the PMV is within the recommended limits (−0.5 < PMV < +0.5).[1] Although predicting the thermal sensation of a population is an important step in determining what conditions are comfortable, it is more useful to consider whether or not people will be satisfied. Fanger developed another equation to relate the PMV to the Predicted Percentage of Dissatisfied (PPD). This relation was based on studies that surveyed subjects in a chamber where the indoor conditions could be precisely controlled.[5]

The PMV/PPD model is applied globally but does not directly take into account the adaptation mechanisms and outdoor thermal conditions.[3][42][43]

ASHRAE Standard 55-2017 uses the PMV model to set the requirements for indoor thermal conditions. It requires that at least 80% of the occupants be satisfied.[1]

The CBE Thermal Comfort Tool for ASHRAE 55[9] allows users to input the six comfort parameters to determine whether a certain combination complies with ASHRAE 55. The results are displayed on a psychrometric or a temperature-relative humidity chart and indicate the ranges of temperature and relative humidity that will be comfortable with the given the values input for the remaining four parameters.[44]

The PMV/PPD model has a low prediction accuracy.[45] Using the world largest thermal comfort field survey database,[46] the accuracy of PMV in predicting occupant's thermal sensation was only 34%, meaning that the thermal sensation is correctly predicted one out of three times. The PPD was overestimating subject's thermal unacceptability outside the thermal neutrality ranges (-1≤PMV≤1). The PMV/PPD accuracy varies strongly between ventilation strategies, building types and climates.[45]

Elevated air speed method

[edit]

ASHRAE 55 2013 accounts for air speeds above 0.2 metres per second (0.66 ft/s) separately than the baseline model. Because air movement can provide direct cooling to people, particularly if they are not wearing much clothing, higher temperatures can be more comfortable than the PMV model predicts. Air speeds up to 0.8 m/s (2.6 ft/s) are allowed without local control, and 1.2 m/s is possible with local control. This elevated air movement increases the maximum temperature for an office space in the summer to 30 °C from 27.5 °C (86.0–81.5 °F).[1]

Virtual Energy for Thermal Comfort

[edit]

"Virtual Energy for Thermal Comfort" is the amount of energy that will be required to make a non-air-conditioned building relatively as comfortable as one with air-conditioning. This is based on the assumption that the home will eventually install air-conditioning or heating.[47] Passive design improves thermal comfort in a building, thus reducing demand for heating or cooling. In many developing countries, however, most occupants do not currently heat or cool, due to economic constraints, as well as climate conditions which border lines comfort conditions such as cold winter nights in Johannesburg (South Africa) or warm summer days in San Jose, Costa Rica. At the same time, as incomes rise, there is a strong tendency to introduce cooling and heating systems. If we recognize and reward passive design features that improve thermal comfort today, we diminish the risk of having to install HVAC systems in the future, or we at least ensure that such systems will be smaller and less frequently used. Or in case the heating or cooling system is not installed due to high cost, at least people should not suffer from discomfort indoors. To provide an example, in San Jose, Costa Rica, if a house were being designed with high level of glazing and small opening sizes, the internal temperature would easily rise above 30 °C (86 °F) and natural ventilation would not be enough to remove the internal heat gains and solar gains. This is why Virtual Energy for Comfort is important.

World Bank's assessment tool the EDGE software (Excellence in Design for Greater Efficiencies) illustrates the potential issues with discomfort in buildings and has created the concept of Virtual Energy for Comfort which provides for a way to present potential thermal discomfort. This approach is used to award for design solutions which improves thermal comfort even in a fully free running building. Despite the inclusion of requirements for overheating in CIBSE, overcooling has not been assessed. However, overcooling can be an issue, mainly in the developing world, for example in cities such as Lima (Peru), Bogota, and Delhi, where cooler indoor temperatures can occur frequently. This may be a new area for research and design guidance for reduction of discomfort.

Cooling Effect

[edit]

ASHRAE 55-2017 defines the Cooling Effect (CE) at elevated air speed (above 0.2 metres per second (0.66 ft/s)) as the value that, when subtracted from both the air temperature and the mean radiant temperature, yields the same SET value under still air (0.1 m/s) as in the first SET calculation under elevated air speed.[1]

The CE can be used to determine the PMV adjusted for an environment with elevated air speed using the adjusted temperature, the adjusted radiant temperature and still air (0.2 metres per second (0.66 ft/s)). Where the adjusted temperatures are equal to the original air and mean radiant temperatures minus the CE.

Local thermal discomfort

[edit]

Avoiding local thermal discomfort, whether caused by a vertical air temperature difference between the feet and the head, by an asymmetric radiant field, by local convective cooling (draft), or by contact with a hot or cold floor, is essential to providing acceptable thermal comfort. People are generally more sensitive to local discomfort when their thermal sensation is cooler than neutral, while they are less sensitive to it when their body is warmer than neutral.[33]

Radiant temperature asymmetry

[edit]

Large differences in the thermal radiation of the surfaces surrounding a person may cause local discomfort or reduce acceptance of the thermal conditions. ASHRAE Standard 55 sets limits on the allowable temperature differences between various surfaces. Because people are more sensitive to some asymmetries than others, for example that of a warm ceiling versus that of hot and cold vertical surfaces, the limits depend on which surfaces are involved. The ceiling is not allowed to be more than +5 °C (9.0 °F) warmer, whereas a wall may be up to +23 °C (41 °F) warmer than the other surfaces.[1]

Draft

[edit]

While air movement can be pleasant and provide comfort in some circumstances, it is sometimes unwanted and causes discomfort. This unwanted air movement is called "draft" and is most prevalent when the thermal sensation of the whole body is cool. People are most likely to feel a draft on uncovered body parts such as their head, neck, shoulders, ankles, feet, and legs, but the sensation also depends on the air speed, air temperature, activity, and clothing.[1]

Floor surface temperature

[edit]

Floors that are too warm or too cool may cause discomfort, depending on footwear. ASHRAE 55 recommends that floor temperatures stay in the range of 19–29 °C (66–84 °F) in spaces where occupants will be wearing lightweight shoes.[1]

Standard effective temperature

[edit]

Standard effective temperature (SET) is a model of human response to the thermal environment. Developed by A.P. Gagge and accepted by ASHRAE in 1986,[48] it is also referred to as the Pierce Two-Node model.[49] Its calculation is similar to PMV because it is a comprehensive comfort index based on heat-balance equations that incorporates the personal factors of clothing and metabolic rate. Its fundamental difference is it takes a two-node method to represent human physiology in measuring skin temperature and skin wettedness.[48]

The SET index is defined as the equivalent dry bulb temperature of an isothermal environment at 50% relative humidity in which a subject, while wearing clothing standardized for activity concerned, would have the same heat stress (skin temperature) and thermoregulatory strain (skin wettedness) as in the actual test environment.[48]

Research has tested the model against experimental data and found it tends to overestimate skin temperature and underestimate skin wettedness.[49][50] Fountain and Huizenga (1997) developed a thermal sensation prediction tool that computes SET.[51] The SET index can also be calculated using either the CBE Thermal Comfort Tool for ASHRAE 55,[9] the Python package pythermalcomfort,[10] or the R package comf.

Adaptive comfort model

[edit]
Adaptive chart according to ASHRAE Standard 55-2010

The adaptive model is based on the idea that outdoor climate might be used as a proxy of indoor comfort because of a statistically significant correlation between them. The adaptive hypothesis predicts that contextual factors, such as having access to environmental controls, and past thermal history can influence building occupants' thermal expectations and preferences.[3] Numerous researchers have conducted field studies worldwide in which they survey building occupants about their thermal comfort while taking simultaneous environmental measurements. Analyzing a database of results from 160 of these buildings revealed that occupants of naturally ventilated buildings accept and even prefer a wider range of temperatures than their counterparts in sealed, air-conditioned buildings because their preferred temperature depends on outdoor conditions.[3] These results were incorporated in the ASHRAE 55-2004 standard as the adaptive comfort model. The adaptive chart relates indoor comfort temperature to prevailing outdoor temperature and defines zones of 80% and 90% satisfaction.[1]

The ASHRAE-55 2010 Standard introduced the prevailing mean outdoor temperature as the input variable for the adaptive model. It is based on the arithmetic average of the mean daily outdoor temperatures over no fewer than 7 and no more than 30 sequential days prior to the day in question.[1] It can also be calculated by weighting the temperatures with different coefficients, assigning increasing importance to the most recent temperatures. In case this weighting is used, there is no need to respect the upper limit for the subsequent days. In order to apply the adaptive model, there should be no mechanical cooling system for the space, occupants should be engaged in sedentary activities with metabolic rates of 1–1.3 met, and a prevailing mean temperature of 10–33.5 °C (50.0–92.3 °F).[1]

This model applies especially to occupant-controlled, natural-conditioned spaces, where the outdoor climate can actually affect the indoor conditions and so the comfort zone. In fact, studies by de Dear and Brager showed that occupants in naturally ventilated buildings were tolerant of a wider range of temperatures.[3] This is due to both behavioral and physiological adjustments, since there are different types of adaptive processes.[52] ASHRAE Standard 55-2010 states that differences in recent thermal experiences, changes in clothing, availability of control options, and shifts in occupant expectations can change people's thermal responses.[1]

Adaptive models of thermal comfort are implemented in other standards, such as European EN 15251 and ISO 7730 standard. While the exact derivation methods and results are slightly different from the ASHRAE 55 adaptive standard, they are substantially the same. A larger difference is in applicability. The ASHRAE adaptive standard only applies to buildings without mechanical cooling installed, while EN15251 can be applied to mixed-mode buildings, provided the system is not running.[53]

There are basically three categories of thermal adaptation, namely: behavioral, physiological, and psychological.

Psychological adaptation

[edit]

An individual's comfort level in a given environment may change and adapt over time due to psychological factors. Subjective perception of thermal comfort may be influenced by the memory of previous experiences. Habituation takes place when repeated exposure moderates future expectations, and responses to sensory input. This is an important factor in explaining the difference between field observations and PMV predictions (based on the static model) in naturally ventilated buildings. In these buildings, the relationship with the outdoor temperatures has been twice as strong as predicted.[3]

Psychological adaptation is subtly different in the static and adaptive models. Laboratory tests of the static model can identify and quantify non-heat transfer (psychological) factors that affect reported comfort. The adaptive model is limited to reporting differences (called psychological) between modeled and reported comfort.[citation needed]

Thermal comfort as a "condition of mind" is defined in psychological terms. Among the factors that affect the condition of mind (in the laboratory) are a sense of control over the temperature, knowledge of the temperature and the appearance of the (test) environment. A thermal test chamber that appeared residential "felt" warmer than one which looked like the inside of a refrigerator.[54]

Physiological adaptation

[edit]

The body has several thermal adjustment mechanisms to survive in drastic temperature environments. In a cold environment the body utilizes vasoconstriction; which reduces blood flow to the skin, skin temperature and heat dissipation. In a warm environment, vasodilation will increase blood flow to the skin, heat transport, and skin temperature and heat dissipation.[55] If there is an imbalance despite the vasomotor adjustments listed above, in a warm environment sweat production will start and provide evaporative cooling. If this is insufficient, hyperthermia will set in, body temperature may reach 40 °C (104 °F), and heat stroke may occur. In a cold environment, shivering will start, involuntarily forcing the muscles to work and increasing the heat production by up to a factor of 10. If equilibrium is not restored, hypothermia can set in, which can be fatal.[55] Long-term adjustments to extreme temperatures, of a few days to six months, may result in cardiovascular and endocrine adjustments. A hot climate may create increased blood volume, improving the effectiveness of vasodilation, enhanced performance of the sweat mechanism, and the readjustment of thermal preferences. In cold or underheated conditions, vasoconstriction can become permanent, resulting in decreased blood volume and increased body metabolic rate.[55]

Behavioral adaptation

[edit]

In naturally ventilated buildings, occupants take numerous actions to keep themselves comfortable when the indoor conditions drift towards discomfort. Operating windows and fans, adjusting blinds/shades, changing clothing, and consuming food and drinks are some of the common adaptive strategies. Among these, adjusting windows is the most common.[56] Those occupants who take these sorts of actions tend to feel cooler at warmer temperatures than those who do not.[57]

The behavioral actions significantly influence energy simulation inputs, and researchers are developing behavior models to improve the accuracy of simulation results. For example, there are many window-opening models that have been developed to date, but there is no consensus over the factors that trigger window opening.[56]

People might adapt to seasonal heat by becoming more nocturnal, doing physical activity and even conducting business at night.

Specificity and sensitivity

[edit]

Individual differences

[edit]

The thermal sensitivity of an individual is quantified by the descriptor FS, which takes on higher values for individuals with lower tolerance to non-ideal thermal conditions.[58] This group includes pregnant women, the disabled, as well as individuals whose age is below fourteen or above sixty, which is considered the adult range. Existing literature provides consistent evidence that sensitivity to hot and cold surfaces usually declines with age. There is also some evidence of a gradual reduction in the effectiveness of the body in thermo-regulation after the age of sixty.[58] This is mainly due to a more sluggish response of the counteraction mechanisms in lower parts of the body that are used to maintain the core temperature of the body at ideal values.[58] Seniors prefer warmer temperatures than young adults (76 vs 72 degrees F or 24.4 vs 22.2 Celsius).[54]

Situational factors include the health, psychological, sociological, and vocational activities of the persons.

Biological sex differences

[edit]

While thermal comfort preferences between sexes seem to be small, there are some average differences. Studies have found males on average report discomfort due to rises in temperature much earlier than females. Males on average also estimate higher levels of their sensation of discomfort than females. One recent study tested males and females in the same cotton clothing, performing mental jobs while using a dial vote to report their thermal comfort to the changing temperature.[59] Many times, females preferred higher temperatures than males. But while females tend to be more sensitive to temperatures, males tend to be more sensitive to relative-humidity levels.[60][61]

An extensive field study was carried out in naturally ventilated residential buildings in Kota Kinabalu, Sabah, Malaysia. This investigation explored the sexes thermal sensitivity to the indoor environment in non-air-conditioned residential buildings. Multiple hierarchical regression for categorical moderator was selected for data analysis; the result showed that as a group females were slightly more sensitive than males to the indoor air temperatures, whereas, under thermal neutrality, it was found that males and females have similar thermal sensation.[62]

Regional differences

[edit]

In different areas of the world, thermal comfort needs may vary based on climate. In China[where?] the climate has hot humid summers and cold winters, causing a need for efficient thermal comfort. Energy conservation in relation to thermal comfort has become a large issue in China in the last several decades due to rapid economic and population growth.[63] Researchers are now looking into ways to heat and cool buildings in China for lower costs and also with less harm to the environment.

In tropical areas of Brazil, urbanization is creating urban heat islands (UHI). These are urban areas that have risen over the thermal comfort limits due to a large influx of people and only drop within the comfortable range during the rainy season.[64] Urban heat islands can occur over any urban city or built-up area with the correct conditions.[65][66]

In the hot, humid region of Saudi Arabia, the issue of thermal comfort has been important in mosques, because they are very large open buildings that are used only intermittently (very busy for the noon prayer on Fridays) it is hard to ventilate them properly. The large size requires a large amount of ventilation, which requires a lot of energy since the buildings are used only for short periods of time. Temperature regulation in mosques is a challenge due to the intermittent demand, leading to many mosques being either too hot or too cold. The stack effect also comes into play due to their large size and creates a large layer of hot air above the people in the mosque. New designs have placed the ventilation systems lower in the buildings to provide more temperature control at ground level.[67] New monitoring steps are also being taken to improve efficiency.[68]

Thermal stress

[edit]

The concept of thermal comfort is closely related to thermal stress. This attempts to predict the impact of solar radiation, air movement, and humidity for military personnel undergoing training exercises or athletes during competitive events. Several thermal stress indices have been proposed, such as the Predicted Heat Strain (PHS) or the humidex.[69] Generally, humans do not perform well under thermal stress. People's performances under thermal stress is about 11% lower than their performance at normal thermal wet conditions. Also, human performance in relation to thermal stress varies greatly by the type of task which the individual is completing. Some of the physiological effects of thermal heat stress include increased blood flow to the skin, sweating, and increased ventilation.[70][71]

Predicted Heat Strain (PHS)

[edit]

The PHS model, developed by the International Organization for Standardization (ISO) committee, allows the analytical evaluation of the thermal stress experienced by a working subject in a hot environment.[72] It describes a method for predicting the sweat rate and the internal core temperature that the human body will develop in response to the working conditions. The PHS is calculated as a function of several physical parameters, consequently it makes it possible to determine which parameter or group of parameters should be modified, and to what extent, in order to reduce the risk of physiological strains. The PHS model does not predict the physiological response of an individual subject, but only considers standard subjects in good health and fit for the work they perform. The PHS can be determined using either the Python package pythermalcomfort[10] or the R package comf.

American Conference on Governmental Industrial Hygienists (ACGIH) Action Limits and Threshold Limit Values

[edit]

ACGIH has established Action Limits and Threshold Limit Values for heat stress based upon the estimated metabolic rate of a worker and the environmental conditions the worker is subjected to.

This methodology has been adopted by the Occupational Safety and Health Administration (OSHA) as an effective method of assesing heat stress within workplaces.[73]

Research

[edit]

The factors affecting thermal comfort were explored experimentally in the 1970s. Many of these studies led to the development and refinement of ASHRAE Standard 55 and were performed at Kansas State University by Ole Fanger and others. Perceived comfort was found to be a complex interaction of these variables. It was found that the majority of individuals would be satisfied by an ideal set of values. As the range of values deviated progressively from the ideal, fewer and fewer people were satisfied. This observation could be expressed statistically as the percent of individuals who expressed satisfaction by comfort conditions and the predicted mean vote (PMV). This approach was challenged by the adaptive comfort model, developed from the ASHRAE 884 project, which revealed that occupants were comfortable in a broader range of temperatures.[3]

This research is applied to create Building Energy Simulation (BES) programs for residential buildings. Residential buildings in particular can vary much more in thermal comfort than public and commercial buildings. This is due to their smaller size, the variations in clothing worn, and different uses of each room. The main rooms of concern are bathrooms and bedrooms. Bathrooms need to be at a temperature comfortable for a human with or without clothing. Bedrooms are of importance because they need to accommodate different levels of clothing and also different metabolic rates of people asleep or awake.[74] Discomfort hours is a common metric used to evaluate the thermal performance of a space.

Thermal comfort research in clothing is currently being done by the military. New air-ventilated garments are being researched to improve evaporative cooling in military settings. Some models are being created and tested based on the amount of cooling they provide.[75]

In the last twenty years, researchers have also developed advanced thermal comfort models that divide the human body into many segments, and predict local thermal discomfort by considering heat balance.[76][77][78] This has opened up a new arena of thermal comfort modeling that aims at heating/cooling selected body parts.

Another area of study is the hue-heat hypothesis that states that an environment with warm colors (red, orange yellow hues) will feel warmer in terms of temperature and comfort, while an environment with cold colors (blue, green hues) will feel cooler.[79][80][81] The hue-heat hypothesis has both been investigated scientifically[82] and ingrained in popular culture in the terms warm and cold colors [83]

Medical environments

[edit]

Whenever the studies referenced tried to discuss the thermal conditions for different groups of occupants in one room, the studies ended up simply presenting comparisons of thermal comfort satisfaction based on the subjective studies. No study tried to reconcile the different thermal comfort requirements of different types of occupants who compulsorily must stay in one room. Therefore, it looks to be necessary to investigate the different thermal conditions required by different groups of occupants in hospitals to reconcile their different requirements in this concept. To reconcile the differences in the required thermal comfort conditions it is recommended to test the possibility of using different ranges of local radiant temperature in one room via a suitable mechanical system.

Although different researches are undertaken on thermal comfort for patients in hospitals, it is also necessary to study the effects of thermal comfort conditions on the quality and the quantity of healing for patients in hospitals. There are also original researches that show the link between thermal comfort for staff and their levels of productivity, but no studies have been produced individually in hospitals in this field. Therefore, research for coverage and methods individually for this subject is recommended. Also research in terms of cooling and heating delivery systems for patients with low levels of immune-system protection (such as HIV patients, burned patients, etc.) are recommended. There are important areas, which still need to be focused on including thermal comfort for staff and its relation with their productivity, using different heating systems to prevent hypothermia in the patient and to improve the thermal comfort for hospital staff simultaneously.

Finally, the interaction between people, systems and architectural design in hospitals is a field in which require further work needed to improve the knowledge of how to design buildings and systems to reconcile many conflicting factors for the people occupying these buildings.[84]

Personal comfort systems

[edit]

Personal comfort systems (PCS) refer to devices or systems which heat or cool a building occupant personally.[85] This concept is best appreciated in contrast to central HVAC systems which have uniform temperature settings for extensive areas. Personal comfort systems include fans and air diffusers of various kinds (e.g. desk fans, nozzles and slot diffusers, overhead fans, high-volume low-speed fans etc.) and personalized sources of radiant or conductive heat (footwarmers, legwarmers, hot water bottles etc.). PCS has the potential to satisfy individual comfort requirements much better than current HVAC systems, as interpersonal differences in thermal sensation due to age, sex, body mass, metabolic rate, clothing and thermal adaptation can amount to an equivalent temperature variation of 2–5 °C (3,6–9 °F), which is impossible for a central, uniform HVAC system to cater to.[85] Besides, research has shown that the perceived ability to control one's thermal environment tends to widen one's range of tolerable temperatures.[3] Traditionally, PCS devices have been used in isolation from one another. However, it has been proposed by Andersen et al. (2016) that a network of PCS devices which generate well-connected microzones of thermal comfort, and report real-time occupant information and respond to programmatic actuation requests (e.g. a party, a conference, a concert etc.) can combine with occupant-aware building applications to enable new methods of comfort maximization.[86]

See also

[edit]
  • ASHRAE
  • ANSI/ASHRAE Standard 55
  • Air conditioning
  • Building insulation
  • Cold and heat adaptations in humans
  • Heat stress
  • Mean radiant temperature
  • Mahoney tables
  • Povl Ole Fanger
  • Psychrometrics
  • Ralph G. Nevins
  • Room air distribution
  • Room temperature
  • Ventilative cooling

References

[edit]
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  7. ^ ISO, 2005. ISO 7730 - Ergonomics of the thermal environment — Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria.
  8. ^ CEN, 2019. EN 16798-1 - Energy performance of buildings - Ventilation for buildings. Part 1: Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics.
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Further reading

[edit]
  • Thermal Comfort, Fanger, P. O, Danish Technical Press, 1970 (Republished by McGraw-Hill, New York, 1973).
  • Thermal Comfort chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005.
  • Weiss, Hal (1998). Secrets of Warmth: For Comfort or Survival. Seattle, WA: Mountaineers Books. ISBN 978-0-89886-643-8. OCLC 40999076.
  • Godish, T. Indoor Environmental Quality. Boca Raton: CRC Press, 2001.
  • Bessoudo, M. Building Facades and Thermal Comfort: The impacts of climate, solar shading, and glazing on the indoor thermal environment. VDM Verlag, 2008
  • Nicol, Fergus (2012). Adaptive thermal comfort : principles and practice. London New York: Routledge. ISBN 978-0415691598.
  • Humphreys, Michael (2016). Adaptive thermal comfort : foundations and analysis. Abingdon, U.K. New York, NY: Routledge. ISBN 978-0415691611.
  • Communications in development and assembly of textile products, Open Access Journal, ISSN 2701-939X
  • Heat Stress, National Institute for Occupational Safety and Health.
  • Cold Stress, National Institute for Occupational Safety and Health.

 

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Frequently Asked Questions

The best materials for sealing air leaks during mobile home HVAC installation include high-quality duct sealant (mastic), foil-backed butyl tape, and closed-cell foam insulation. These materials help ensure airtight seals around ducts, vents, and other potential leak points in the system.
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