Introduction
When designing a building it is important to not only select the correct materials for building components but to also consider the basic factors that will affect human comforts in the internal built environment. Every human has different comfort levels and building design will be influenced by personal factors. Designers should also consider what the building is to be used for as this will dictate the internal environment conditions. It is important to achieve the correct internal environment conditions as the occupant’s health may be affected and Designers will need to consider the following;

Air Temperature
The air temperature indicates the degree of how hot or how cold the internal environment is and is measured in °C or °F using a thermometer. The air temperature of the internal environment will be influenced by the occupant’s activities, for example a room measuring 19°C may be comfortable for someone who is sitting reading a book but someone who is using an exercise machine will soon begin to overheat in a room at this temperature which may have a negative effect on their health.

The Buildings use therefore needs to be considered at design stage, for example if it is to be used as a gymnasium the internal environment will need to be cooler as the occupants will be more active and produce more body heat. As occupants will be less active in hotels they will produce less body heat and therefore the temperature of the internal environment will need to be warmer to ensure comfort levels are adequate. Personal factors will also dictate comfort levels such as size, age and gender. Clothing worn by occupants will also contribute to their comfort levels and how the air temperature affects them. This is measured on a scale expressed as clo value which ranges from 1 to 4 where 1 clo equals 0.155m² k/W of insulation to the body. [46, 47, 48]

Humidity
The amount of water or moisture vapour that is present in the air can be described as humidity or relative humidity. Humidity is measured using a hygrometer and is expressed in grams per cubic metres (g/m³). Relative humidity is also measured using a hygrometer and is expressed as a percentage. This percentage indicates the amount of water that is present in the air where 0% indicates the air is completely dry and 100% indicates the air is saturated. Humans will be most comfortable when the humidity is between 40% to 60% and when levels rise above 60% the air is described as being humid. This causes sensitivity to the human body as it uses evaporative cooling through perspiration to cool down and this becomes difficult in a humid environment making them feel hotter and uncomfortable. When humidity levels fall below 40% the air becomes dryer and humans may experience problems with dryness on the skin, eyes or throat. [46, 47, 48]

Although the relative humidity percentage level is 40% to 60% to provide adequate levels of comfort to the occupants it is sometimes necessary to create an internal environment that is outside this range. For example, plastic manufacturing plants needs to have a relative humidity of 5% to 30% to prevent damage being caused to products and to achieve proper process conditions. In this case, personal protective equipment may be provided to the occupants to improve their comfort while working in this environment. [49, 50]
Ventilation
Replacing stale air with fresh air is known as ventilation and is recorded as air changes per hour which is abbreviated as ACH. Ventilation may be provided to the building naturally through trickle vents in windows or it can occur as a result of the natural pressures between different rooms. Mechanical ventilation may also be implemented using fans. This option is more expensive than natural ventilation but it may be required if the air quality outside the building is of a poor standard or when the building cannot be ventilated from the perimeter due to its size.

It is important that a building has adequate air changes to ensure there is a sufficient supply of oxygen for the occupants to enable them to breathe in comfort. Good ventilation will also help to remove any odours or airborne bacteria that can accumulate when the building is occupied and prevent the occupants from becoming ill. Hospitals and care homes should be designed to have a greater level of ventilation to help ensure that any airborne bacteria is replaced with fresh air and to prevent the spread the illness or disease. [47, 48]

Light
Light refers to the visible energy that is produced through electromagnetic radiation transmitted by a substance at high temperature. Light that has a wavelength of between 380 to 760 nanometres is visible to the human eye. These wavelengths can produce various colours and will appear blue when the wavelengths are short and red when the wavelengths are long. Light travels in rays and when they touch an object some of the light is absorbed. The rest of the light is then reflected away from the object which enables the human eye to see objects and colours. Light can be measured using a light meter and is expressed as lux and the illumination a light source creates is known as luminous flux and is expressed as lumen or abbreviated as lm.

Light can be supplied to a building naturally by the sun and can enter through windows or other openings. It can also be provided artificially via electricity and emitted through lamps or bulbs as they are more commonly known. Light can also help to create an internal ambience and in places like restaurants or bars the light levels can be controlled by using low wattage bulbs or dimmer switches to enhance the occupant’s experience, but buildings such as offices or schools will require more light to ensure the occupants are able to conduct their work or studies efficiently. It is important to ensure the correct light intensity is achieved as human comforts can be negatively affected. Occupants in buildings that are inadequately lit may experience difficulties trying to see and this can cause their eyes to strain inducing headaches or raising stress levels. Internal environments that have too much light can also be of concern to occupants because if it is too bright occupants may be temporarily unable to see which will be a health and safety concern. [47, 48, 51]

Sound Activity Levels
Sound is a form of energy that vibrates and travels through the air that can be heard by the human ear. It can be measured on a sound level meter and is recorded as decibels and when it travels it is measured in metres per second and recorded as m/s. Sound can be produced naturally by the wind or it can be man made through speech. When sound travels through the air it is known as airborne sound. Airborne sounds are made by speech, radios or televisions and musical instruments. Sound can also travel through structures or solids and this known as impact sound. Impact sounds can be produced by footsteps or by slamming doors. There are different measure that can be implemented to control airborne and impact sounds. Thick partitions can reduce airborne sounds and using vibration pads or soft coverings on floors and walls will help to reduce impact sounds.

It is important to consider sound levels when designing buildings to ensure human comfort levels are not affected. If a building has a high sound level it can make it difficult for the occupants to hear and this can cause them to experience discomfort. It will make listening to others more difficult and prolonged exposure can lead to hearing problems. It can also affect concentration and occupants may become distracted by high levels of sound. For this reason offices should have the thick partitions or soft coverings on floors on walls to prevent airborne and impact sound from traveling. This will ensure the occupants can conduct their work efficiently without losing concentration. When designing concert halls or nightclubs the opposite design principles should be applied and floors and walls should have harder coverings which will enable the sound to travel which will help to enhance the entertainment experience of the occupant’s. [48, 52]

Health
The health of the occupants must also be considered when buildings are at the design stage. When humans are suffering from an illness it will be harder for their bodies to retain heat and therefore air temperature levels will need to be increased. Heating levels in buildings can be zoned to allow for better occupant control. In Hospital wards where sick patients recover the heat levels can be raised to improve human comfort. Working stations and corridors can then be set at a lower temperature to allow staff to conduct their work in comfort without their bodies overheating. Age of the occupants also needs to be considered as older people need higher levels of air temperature as they produce less body heat than younger people. With this in mind care homes should be designed with a higher air temperature to ensure the occupants comfort levels are adequate and their health is not affected by the internal environment. [48]