Living Comfort

The comfort of a home, an office, is a key requirement in designing places and environments, because it aims to improve the quality of living and ensure high levels of well-being for all users.
It is our task as designers to know, evaluate, and design the best solutions that take into account the many parameters that affect environmental well-being.
To know means to gather all the information about the features of the location (climate, dominant winds, irradiation …), the destination of the premises, the building materials, the habits of the users. Based on these indications, the positive aspects to be used and the negative aspects to be addressed through an integrated design are subsequently evaluated.
In order to evaluate the levels of optimal comfort refer to the following welfare classes:

physical-thermo-hygrometric well-being: the state in which the individual within an environment expresses a state of thermal neutrality
acoustic Well Being: a psychophysical condition in which an individual, in the presence of a noise field, declares to be in a state of well-being, taking into account also the particular activity he is doing
visual well-being: sthe state in which the individual can best perform the various tasks he is called upon to fulfill
respiratory well-being and air quality: an individual’s satisfaction state in relation to the breathing air, where there are no pollutants at concentrations considered to be harmful to human health

Physical well-being

The feeling of environmental well-being depends on parameters related to the individual and on factors related to the environment itself. The welfare state can be expressed as a state of thermal neutrality in which the person is not affected by cold or hot feelings and can be obtained through certain environmental parameters including:

average ambient air temperature detectable at the center of the environment at a height of 1.5 m using a dry bulb thermometer shielded by solar and infrared radiation.
average radiant temperature defined as the average of the temperatures of the individual surrounding surfaces, weighted according to their area
air velocity, defined as the average relative air velocity respect to a person still in the environment. It produces an increase or decrease in evaporative and convective cooling of the human body resulting in heat dissipation.
air humidity, defined as the relationship between the partial pressure of the water steam contained in ambient air and the saturation pressure at the same dry bulb temperature of the air
clothing (1 clo = 0.155 m2 ° C / W) defined by the overall thermal resistance of the clothing to heat transfer through them
Kind of activity performed (1 met = 58.2 W / m2) defined as the energy produced by body mass metabolism during each activity

The human body continuously exchanges heat with the surrounding environment by convection, radiation and evapotranspiration. In particular, heat exchange by radiation takes on important importance for environmental well-being as small differences in temperature between the body surface and the surfaces of the environment involve considerable quantities of exchanged energy that can cause discomfort (remember that the Physics law describing heat exchanges by irradiation Qirr = ε * σ * (T14 – T24), temperature differences are elevated to fourth power). Consequently, in order to ensure levels of comfort it is essential to avoid phenomena related to local discomfort such as:

asymmetric radiative exchanges
localized air currents (draughts)
high vertical temperature gradient (warm head and cold feet)
contact with cold surfaces (uninsulated wall)

Results from some surveys conducted on a number of people, revealed that a 3 ° C difference in air temperature between the head and the feet causes a percentage of 5% of dissatisfied persons. UNI-EN-ISO 7730 rates as a level of acceptability for a sedentary person performing a sedentary activity, a vertical air temperature difference of 3 ° C between 1.1 and 0.1 m from the floor (head to ankle level). Direct contact with a floor with a temperature that is too high or too low causes a localized discomfort.
Among the welfare requirements, for a sedentary activity in winter conditions, the standard recommends a surface temperature of 19 ° C to 26 ° C, with the possibility of designing floor heating systems at 29 ° C. Indeed surface temperatures limit of the floor for barefoot people is slightly different: in a bathroom the optimum temperature is 29 ° C for a marble floor and 26 ° C for a wooden floor.
The asymmetry of radiant temperature due to windows or cold vertical surfaces should be less than 10 ° C and the relative humidity between 30% and 70%. To avoid one of the most common causes of local discomfort such as air draughts, it is advisable to keep the air speed within certain values depending on the air temperature.
The UNI EN ISO 7730 standard defines a method for assessing the thermal sensations experienced by a sample of people under certain environmental conditions and their degree of discomfort (thermal dissatisfaction).
By combining the various parameters (temperature, humidity, …), it is possible to assess the comfort level of an environment according to the judgment expressed by a number of people by computing two indices: the PMV index ( “Predicted Mean Vote”), which represents the average value of the votes of the sample of people who express, according to a seven-point scale ranging from +3 = very hot to -3 = cold, their own thermal sensation inside of a certain environment , and the PPD index (“Predicted Percentage of Dissatisfied”) that provides information on thermal discomfort or on heat mood, predicting the percentage of people who would feel too hot or too cold in a certain environment.
The PMV index can be determined when are estimated the clothing (thermal resistance), the activity performed and are measured the environmental parameters (air temperature, average radiant temperature, air velocity, partial water vapor pressure) . The PPD index provides a quantitative forecast of the number of people who are insensitive from the thermal point of view. The relationship between the PMV and PPD indexes is based on a research conducted on the thermal sensation expressed by a sample of 1300 subjects dressed in lightweight clothes exposed for three consecutive hours in an environment

From the relationship between PMV and PPD described in the graph it is shown that at a PMV = 0 there is still a 5% unsatisfied person and that the PMV range of tolerance between 0.5 and +0.5 corresponds to a value of PPD of 10%. ASHRAE 55 accepts a 20% for PPD, that is a PMV between +0.85 and -0.85.
The regulations describe variations of the PMV index based on parameters such as activity level, hygrometric degree, and clothing resistance index.

Acoustic well-being

The protection of environments from outside noise or from adjacent environments is becoming more and more important either for the requirement of a regulatory certification added to the current law (DPCM 5/12/97) and for the increasing sensitivity of people to noise pollution issue.

Once the external or internal noise sources are defined, the sound waves propagation modes are then evaluated within the various environments of a building that can be divided into:

aerial noise generated by an external source (traffic, airplanes, …)
aerial noise generated by the interior source of the building (technical spaces, elevators, commercial activities, recreational …)
rumore di tipo impattivo (calpestio solaio)
impact noise (floor clomping)
noise generated by plants or people’s activities

Aerial noise propagates in two ways: by direct air, where the sound source is in the same environment as the listener who is reached directly by the sound waves without them undergoing any attenuation (with the exception of the absorption and reflection phenomena depending on the geometry and surface coatings of the environment) due to the presence of obstacles such as walls, floors.
By indirect air when the sound wave undergoes attenuation by the presence of obstacles (partition walls) in its propagation path. The type of air noise is closely related to the acoustic performance of the building structures that make up the housing, building skin (vertical walls, roofs, floors). Another mode of propagation is the structural one where sound waves are generated by vibrations of impacted structures (floor clomping noise). This type of noise depends on the acoustic characteristics of the structures (floors, partition walls), and of finishes (plaster, floors) inside the building. The acoustic welfare is evaluated in terms of acoustic quantities such as:

sound pressure level
level of sound intensity
sound power level

Air propagation occurs conventionally in two ways: by direct air, that is when the sound source is contained in the room where the listener is present. In this case the sound waves that developed from the source reaches the listener without encountering obstacles and do not encounter walls to cross but only surfaces from which they are reflected. The phenomena involved are therefore substantially reflection and absorption. By air, but through partition walls, that is, when the sound wave, in its propagation path, encounters a wall to cross so that, before reaching the listener, it attenuates the amplitude according to the specific modes that we will see below.
With reference to the physical laws regulating aerial noise transmission, a shell of the building made up of different sub-systems is the element with the worst acoustic performance to affect overall acoustic behavior, so on a facade the window system and the wall attachment node represent the weaknesses to which more attention is to be given.

Classificazione degli ambienti abitativi e relativi valori limite

Classification of living environments and their limit values

The existing Italian legislation regulates noise pollution through DPCM 14/11/97 which establishes noise limit values and with DPCM 5/12/97 defining the acoustic passive requirements of buildings that are divided into seven categories according to their use. For each category the decree sets the limit values for the acoustic performance of the building and its components with reference to the following measured values:

the assessment index of the apparent sound-isolating power of separation elements between environments R’w It defines the insulating properties of a dividing wall between two real estate units. The apparent term means “detected in work”
standardized façade acoustic evaluation index (D2m, nT, w) defines the sound insulation properties of a wall that delimits an indoor environment from an outside. The measurement is carried out at 2m from the façade (2m) and the normalized value compared to the reverberation time of the indoor environment
standardized solitary floor level noise assessment index (L’n, w) defines the noise level transmitted through the structure of the floor
continuous equivalent sound pressure level, weighted A (LA, eq) due to continuously-working plants, it defines the average value of the pressure level produced by a continuous cycle system
the maximum sound pressure level weighted A measured with slow time constant (LA, S, max), due to systems with discontinuous operation defines the maximum sound pressure level measured during the sound event caused by a discontinuous cycle system.

Insulation Evaluation Index

The acoustic behavior of a building element is described through a graph in which the values reported are derived from a frequency range between 100 and 3150 Hz (measurements in operation) The acoustic performance of buildings and their components is defined by UNI EN ISO 717-1-2-3 through a single number parameter, called “ rating index” that is obtained by superimposing the reference curve defined by ISO, with the experimental curve so that the average of unfavorable deviations calculated on the whole frequency band is less than 2 dB. Once checked, the rating index on the reference curve corresponding to the frequency of 500 Hz will be read.


Determination of assessment index for aerial noise insulation (UNI EN ISO 717-1)	Determination of impact index for impact isolation (UNI EN ISO 717-2)

Psychoacoustic parameters

Physical parameters so far described represent the various physical phenomena that affect environmental acoustics without providing any indication of subjective perception of sounds, subjective intensity, and the effects of disturbance that certain noises produce.
The sound as perceived with psychosensory features is defined by:

the tone that is related to the frequency; deep tones are characterized by low frequencies, soothing tones by high frequencies
the intensity of hearing sensation linked to the sound pressure level and the spectral composition of the sound
the timbre cthat indicates the ability of the ear to distinguish identical sounds for intensity and tone but emitted from different sources: eg. from different musical instruments, man’s voice from that of the woman, etc.

The human ear auditory range varies according to sound pressure levels and to frequencies ranging between 20 and 20000 Hz; This behavior is described through a diagram called “normal audiogram” where isofonic curves are represented, delimited by a lower one representing the ‘threshold of hearing’ and an upper one representing the ‘threshold of pain’.
The isophonic curves (phon) represent, as the frequency changes, the sound pressure levels (Hz) that produce the same sound sensation. So, by observing the graph, it can be seen that a pure sound having a sound pressure level of 35 DB at 200 Hz produces the same sensation of subjective intensity of a sound of 50 dB to 70 Hz; In turn, both sounds have the same level of subjective intensity equal to 30 Phon (30 dB to 1000 Hz).
The evaluation of problems or even damages caused by noise is performed through simplified methods that employ 4 frequency weighting curves (A, B, C, D) each of which specific for certain applications. The assessment of the effects of noise on people is carried out using the weighting curve A.

Normal audiogram – Each curve is characterized by a sensing level value expressed in phon indicating the sound pressure level (dB) corresponding to a frequency of 1000 Hz. The lower curve represents the audible threshold, the upper curve the pain tolerance level

Visual well-being

Visual well-being represents the optimum level of light that allows our eyes the best visual perception of the environment, intended as the highlight of contrasts of colors and brightness, the distinction of objects even the most distant ones …
Visual well-being is a highly articulated subject, and still under debate today, due essentially to the multiplicity of affecting factors that influence the performance; among which we remember:

luminous flux (lm = lumen)
Represents the amount of light energy emitted in the time unit from a source
light intensity (cd = candle)
Represents the amount of luminous flux emitted by a source within the solid angle (steradiant) in a given direction. A point light source emits radiation of the same intensity in all directions, so its luminous flux propagates uniformly as it is generated by the center of a sphere.
Artificial light sources do not emit light uniformly in all directions in the space, so depending on the direction considered those may have a different intensity. A practical system for visualizing the distribution of light emitted by a source in space is to represent luminous intensities as vectors applied at the same point as rays out of the center of a sphere.
Catalogs of lighting devices often carry photometric curves, ie the photometric solid sections on the two main planes, orthogonal to each other, intersected by the axis of symmetry and rotation.
illumination (lux= lumen / m²)
It represents the amount of light that affects a unit surface. In other words the ratio between the incident light flux on a surface and the area of the illuminated surface. A good planning must first of all aim at ensuring the right level of illumination in every environment. The lighting values to be taken are related to the type of activity performed in the environment and are influenced by the absorption and reflection power of the luminous flux from the materials present in the environment and their color.
luminance (cd / m²)
It represents the intensity of the light reflected or emitted by a surface towards the person looking at, or, in other words, the relationship between the luminous intensity emitted by a surface in a given direction and the apparent area of that surface. It is important to have clear the difference between enlightening and luminance. If the first magnitude indicates the amount of light emitted by a source that strikes a certain surface, the second indicates the sensation of luminosity we receive from this surface: this means that on two surfaces, a white and a black one, we can have the same enlightening value, for example 300 lux, but the sensation of luminance received, and therefore the luminance, will be completely different since the two surfaces have different reflection coefficients.
The effectiveness of a lighting project is the result of the execution of two different quantitative analyzes, by determining the number of light sources and their positioning, and qualitative, given by the choice of the light type most suitable to carry out a certain activity and by its distribution in space

To these are to be added the physiological factors of the eye:

– adaptability
Indicates the ability of the eye to adapt to different brightness conditions
contrast
Indicates the luminance ratio between the object to be visualized and its background. IE it represents the ability of the eye to distinguish objects based on their luminosity
visual acuity
Represents the ability of the eye to recognize objects and details. Increases with increasing contrast and luminance.
perception speed
indicates the time it takes for an object to be recognized
light shade
The light shadeis evaluated through the color temperature. Hot tones are preferable for low illumination values, while for the higher ones cold tones are preferable.
direction of light
a direct and intense light generates dazzling phenomena
dazzle
It is a disturbance to optical vision generally caused by direct light or reflected from surfaces and as a consequence it results in a worsening of perception of the image. It is one of the main causes of discomfort
illuminance
The illuminance is inversely proportional to the distance of the illuminated surface; in other words, the luminance of the surface by the light source is the smaller the greater the distance of the source from the surface.
chromatic rendering index
It indicates the effect produced by a light source on the chromatic scale of an object compared to that obtained by the effect of a sample black body having the same color temperature. The color rendering index should not be confused with the color temperature, since the latter indicates the color of the light emitted but does not tell us anything about its ability to render colors.