Introduction to Architectural Technology Third Edition

Pete Silver, Will McLean

• Editore: Laurence King Publishing
• Anno: 2021
• ISBN:
  9781529423211
• Argomento: Architecture
• Categoria: Architecture Methods & Materials

Understanding the relationship between design and technology is critical to the understanding of architecture. This book clearly explains the core aspects of architectural technology: structural physics, structural elements and forms, heating, lighting, environmental control and computer modelling. The third edition includes six new case studies, more on structural types, new information on construction detailing, passive building principles and designing for different climatic conditions. This essential introduction to architecture will help students to integrate their design thinking with the appropriate structural and environmental solutions.

Climate and Shelter

A psychrometric chart is a complex graph of the thermodynamic parameters of (moist) air at a constant pressure. The key properties represented are wet bulb temperature (the lowest temperature at which any fluid can be cooled); dry bulb temperature (the typical measure of air temperature recorded by a thermometer exposed to the air, but shielded from radiation and moisture); and absolute and relative humidity and enthalpy (the energy content of air). The chart can therefore be used in relation to a specific site location in order to assess local requirements for climate control in buildings. The yellow box outlined on the chart indicates the area that humans perceive to be ‘comfortable’; however, this box (or comfort envelope) can be expanded in various ways by applying certain types of local climate control. For example, rather than heating or cooling the air inside a building for it to be within the normally accepted temperature range, air temperature can stray beyond this range if local shading protects inhabitants from direct sunlight or, in a humid climate, if mechanical fans perceivably ‘cool’ the air by increasing its velocity. John Farrell of XCO2 Energy describes this low-energy alternative to air-conditioning as ‘extending the comfort envelope’. It is important to note that atmospheric pressure varies with altitude; however, for altitudes lower than 600 m (1,969 ft) the sea-level psychrometric chart is considered adequate.

Human Comfort

Generally speaking, in architecture human comfort is dependent upon a number of factors:

Thermal Comfort

Maintaining the body at an acceptable temperature.

Air Quality

Ensuring the provision of clean air within enclosed spaces.

Illumination

Provision of adequate light levels.

Sound Quality

Clarity of communication and protection from noise pollution.

Sanitation

Providing for water distribution and waste disposal.

Subjective Perception and Adaptation

Human comfort is considered to be partially subjective, in that humans may perceive a room to be warmer or cooler than it actually is – because of its colour and materials, for example. Variation in human comfort levels also results from evolutionary adaptations, i.e. where a body has adapted its specific physiology as a response to local environmental conditions.

Of these factors, however, it is a structure’s ability to provide the body with good air quality that is the most important of its functions. Therefore, this section will focus on the principles of thermal comfort and its provider, the sun.

Thermal Comfort

Human comfort depends chiefly upon thermal comfort. Our core body temperature must remain at a constant 37.5°C (98.6°F): we must lose heat at the same rate as it is produced or gain heat at the same rate it is lost – a process known as thermoregulation. Long-term exposure to temperatures above approx. 55°C (130°F) is likely to result in hyperthermia, which can often be lethal. Similarly, when body temperature decreases below normal levels it results in hypothermia.

Body heat is transferred through convection, conduction, radiation and evaporation. When the ambient temperature is higher than skin temperature, the heat gained by radiation and conduction must be dispersed mainly through the evaporation of perspiration (see Passive Control/Evaporative Cooling, here).

The body generates heat even while at rest. Indeed, the body must always be losing heat to maintain comfort because it produces more heat than it needs. When internal body temperature is insufficient the body starts to shiver, which in turn increases the production of body heat. In animals covered with fur or hair, ‘goose pimples’ are created when muscles at the base of each hair contract and pull the hair erect as a response to cold. The erect hairs trap air to create a layer of insulation. As humans have lost most of their body hair, the reflex now serves little purpose.

The main factors influencing thermal comfort are:

Air Temperature

Air temperature is governed ultimately by solar radiation (see Solar Geometry, here).

Mean Radiant Temperature

Radiant temperature is governed both by the temperature of an object and its emissivity – its propensity to emit long-wave radiation. Mean radiant temperature (MRT) is the average radiant temperature of all objects within view of the subject, and can vary significantly from air temperature (for example, even a tightly sealed single-pane window feels ‘draughty’ on a cold winter day because its radiant temperature is much lower than other interior surfaces}. Because we lose a substantial amount of heat via radiation, MRT is as important a determinant of comfort as air temperature.

Air Movement

Air movement (a breeze or draught) is governed by air pressure. A breeze of around 50 cm (20 in) per second provides an equivalent temperature reduction of around 3°C (5.4°F).

Humidity

High humidity levels reduce evaporation rates. For human comfort, relative humidity should be between 40 per cent and 70 per cent. However, when relative humidity exceeds 60 per cent, our ability to cool is greatly reduced.* Exposure to radiant heat or cool sources will affect thermal comfort: radiating surfaces are related to our perception of comfort.

*Relative humidity is an indication of the water content of air. It is measured as the percentage of the actual water vapour density to the saturation vapour density (both are measured as mass per unit volume). Saturation vapour density is the amount of water vapour needed to saturate the air, and varies according to temperature. For example, if the actual vapour density is 9 g/m³ at 20°C (¹/₁₀₀ oz/ft3 at 68°F) compared with the saturation vapour density (at that temperature) of 17.5 g/m3 (¹/...