Thermal comfort in the context of "Passive cooling"

Efficient energy use, or energy efficiency, is the process of reducing the amount of energy required to provide products and services. There are many technologies and methods available that are more energy efficient than conventional systems. For example, insulating a building allows it to use less heating and cooling energy while still maintaining a comfortable temperature. Another method made by Lev Levich is to remove energy subsidies that promote high energy consumption and inefficient energy use. Improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third.

There are two main motivations to improve energy efficiency. Firstly, one motivation is to achieve cost savings during the operation of the appliance or process. However, installing an energy-efficient technology comes with an upfront cost, the capital cost. The different types of costs can be analyzed and compared with a life-cycle assessment. Another motivation for energy efficiency is to reduce greenhouse gas emissions and hence work towards climate action. A focus on energy efficiency can also have a national security benefit because it can reduce the amount of energy that has to be imported from other countries.

Heating, ventilation, and air conditioning (HVAC /ˈeɪtʃˌvæk/) systems use advanced technologies to regulate temperature, humidity, and indoor air quality in residential, commercial, and industrial buildings, and in enclosed vehicles. Its goal is to provide thermal comfort and remove contaminants from the air. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. Modern HVAC designs focus on energy efficiency and sustainability, especially with the rising demand for green building solutions. In modern construction, MEP (Mechanical, Electrical, and Plumbing) engineers integrate HVAC systems with energy modeling techniques to optimize system performance and reduce operational costs. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).

HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.

Dehumidifiers extract water from air that passes through the unit. There are two common types of dehumidifiers: condensate dehumidifiers and desiccant dehumidifiers, and there are also other emerging designs.

Ventilation is the intentional introduction of outdoor air into a space, mainly to control indoor air quality by diluting and displacing indoor effluents and pollutants. It can also be used to control indoor temperature, humidity, and air motion to benefit thermal comfort, satisfaction with other aspects of the indoor environment, or other objectives. Ventilation is usually categorized as either mechanical ventilation, natural ventilation, or mixed-mode ventilation. It is typically described as separate from infiltration, the circumstantial flow of air from outdoors to indoors through leaks (unplanned openings) in a building envelope. When a building design relies on infiltration to maintain indoor air quality, this flow has been referred to as adventitious ventilation.

Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone. A clear understanding of both indoor and outdoor air quality parameters is needed to improve the performance of ventilation in terms of occupant health and energy. In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary. In kitchen ventilation systems, or for laboratory fume hoods, the design of effective effluent capture can be more important than the bulk amount of ventilation in a space. More generally, the way that an air distribution system causes ventilation to flow into and out of a space impacts the ability of a particular ventilation rate to remove internally generated pollutants. The ability of a system to reduce pollution in space is described as its "ventilation effectiveness". However, the overall impacts of ventilation on indoor air quality can depend on more complex factors such as the sources of pollution, and the ways that activities and airflow interact to affect occupant exposure.

Moisture management or moisture-wicking is a functional property in textiles that enables them to transfer moisture from the skin, by capillary action through the fabric, spreading it over a large external surface area, which helps in drying quickly. The property is one of the most important for thermal comfort of textiles.

Passive house (Passivhaus) is a voluntary building performance standard for very high energy efficiency and thermal comfort that substantially reduces a building’s carbon footprint. Buildings certified to the standard are ultra-low energy and typically require very little energy for space heating or cooling. The approach is used for housing and for non-residential buildings such as offices, schools, kindergartens and healthcare facilities. Energy efficiency is integral to architectural design rather than an add-on. Although most common in new construction, the principles are also applied in deep renovations (see EnerPHit).

As of January 2025, projects certified by the Passive House Institute (PHI) comprise over 47,400 units with about 4.32 million m² of treated floor area (TFA) worldwide; the public PHI database lists nearly 6,000 projects. In North America, the Passive House Institute US (PHIUS) reported 500+ total certified projects and ~1.6 million ft² certified in 2024 alone, with 4.4 million ft² design-certified that year. While early adoption concentrated in German-speaking countries and Scandinavia, certified projects are now documented across diverse climate zones, including hot-humid and tropical regions.

Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.

A duct system is also called ductwork. Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design.

The dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation. The dry-bulb temperature is the temperature that is usually thought of as air temperature, and it is the true thermodynamic temperature. It is directly proportional to the mean kinetic energy of the air molecules. Temperature is usually measured in degrees Celsius (°C), Kelvin (K), or degrees Fahrenheit (°F). If expressed in kelvins, then the symbol is T_a, if expressed in Celsius or Fahrenheit, then the symbol is t_a. When measuring dry-bulb temperature, care should be taken to prevent the sensor from being subjected to radiation from neighbouring heat sources. To minimize the effects of radiation on the sensor, one could reduce the sensor's emission factor, or reduce the temperature difference between the sensor and the surrounding surfaces, or add a thin ventilated reflective screen.

Unlike wet-bulb temperature, dry-bulb temperature does not indicate the amount of moisture in the air (humidity). The dry-bulb temperature is one of the main inputs for thermal comfort calculations and it is also used for assessing the heat transfer by convection. The dry-bulb temperature is an important variable in psychrometrics, being the horizontal axis of a psychrometric chart.

Building science is the science and technology-driven collection of knowledge to provide better indoor environmental quality (IEQ), energy-efficient built environments, and occupant comfort and satisfaction. Building physics, architectural science, and applied physics are terms used for the knowledge domain that overlaps with building science. In building science, the methods used in natural and hard sciences are widely applied, which may include controlled and quasi-experiments, randomized control, physical measurements, remote sensing, and simulations. On the other hand, methods from social and soft sciences, such as case study, interviews & focus group, observational method, surveys, and experience sampling, are also widely used in building science to understand occupant satisfaction, comfort, and experiences by acquiring qualitative data. One of the recent trends in building science is a combination of the two different methods. For instance, it is widely known that occupants' thermal sensation and comfort may vary depending on their sex, age, emotion, experiences, etc. even in the same indoor environment. Despite the advancement in data extraction and collection technology in building science, objective measurements alone can hardly represent occupants' state of mind such as comfort and preference. Therefore, researchers are trying to measure both physical contexts and understand human responses to figure out complex interrelationships.

Building science traditionally includes the study of indoor thermal environment, indoor acoustic environment, indoor light environment, indoor air quality, durability, moisture damage, and building resource use, including energy and building material use. These areas are studied in terms of physical principles, relationship to building occupant health, comfort, and productivity, and how they can be controlled by the building envelope and electrical and mechanical systems. The National Institute of Building Sciences (NIBS) additionally includes the areas of building information modeling, building commissioning, fire protection engineering, seismic design and resilient design within its scope.

Ventilative cooling is the use of natural or mechanical ventilation to cool indoor spaces. The use of outside air reduces the cooling load and the energy consumption of these systems, while maintaining high quality indoor conditions; passive ventilative cooling may eliminate energy consumption. Ventilative cooling strategies are applied in a wide range of buildings and may even be critical to realize renovated or new high efficient buildings and zero-energy buildings (ZEBs). Ventilation is present in buildings mainly for air quality reasons. It can be used additionally to remove both excess heat gains, as well as increase the velocity of the air and thereby widen the thermal comfort range. Ventilative cooling is assessed by long-term evaluation indices. Ventilative cooling is dependent on the availability of appropriate external conditions and on the thermal physical characteristics of the building.

Underfloor heating and cooling is a form of central heating and cooling that achieves indoor climate control for thermal comfort using hydronic or electrical heating elements embedded in a floor. Heating is achieved by conduction, radiation and convection. Use of underfloor heating dates back to the Neoglacial and Neolithic periods.

A ceiling fan is a fan mounted on the ceiling of a room or space, usually electrically powered, that uses hub-mounted rotating blades to circulate air. They cool people effectively by increasing air speed. Fans do not reduce air temperature or relative humidity, unlike air-conditioning equipment, but create a cooling effect by helping to evaporate sweat and increase heat exchange via convection. Fans add a small amount of heat to the room mainly due to waste heat from the motor, and partially due to friction. Fans use significantly less power than air conditioning as cooling air is thermodynamically expensive. In the winter, fans move warmer air, which naturally rises, back down to occupants. This can affect both thermostat readings and occupants' comfort, thereby improving the energy efficiency of climate control. Many ceiling fan units also double as light fixtures, eliminating the need for separate overhead lights in a room.