(a).

Predicted mean vote (PMV):

PMV is an index that represents the predicted mean vote (on the thermal sensation scale) of a large population exposed to a given environment, and is acknowledged as an international thermal environment indicator. This indicator has a range from -3 to +3, and it includes an air temperature, relative humidity, mean radiant temperature, air velocity, clothing thermal resistance and a metabolic rate. The range from -0.5 to +0.5 is a range for comfortableness, and this range has been used as a condition for the air conditioning or as an indicator for indoor environments in order to create a comfortable environment for people.

Predicted percentage of dissatisfied (PPD):

PPD index predicts the percentage of occupants that will be dissatisfied with the thermal conditions which determined from PMV index. It is a function of PMV, given that as PMV moves further from 0, or neutral, PPD increases. The maximum number of people dissatisfied with their comfort conditions is 100% and, as you can never please all of the people all of the time, the recommended acceptable PPD range for thermal comfort from ASHRAE 55 is less than 10% persons dissatisfied for an interior space.

(b).

Humans prefer to live within a certain range of temperatures. This is known as the human comfort zone, or alternatively, the thermal comfort zone. It is defined as the range of temperature, air movement, and humidity conditions that most people will find comfortable the majority of the time. Therefore to identify the key requirements and limits, they have developed ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy) which is able quantify and specify what is required to ensure human comfort.

ANSI/ASHRAE Standard 55 provides minimum requirements for acceptable thermal indoor environments. It establishes the ranges of indoor environmental conditions that are acceptable to achieve thermal comfort for occupants. The main factors that influence thermal comfort are those that determine heat gain and loss, namely metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed and relative humidity. These factors can be grouped in two categories: personal factors - because they are characteristics of the occupants - and environmental factors - which are conditions of the thermal environment. Psychological parameters such as individual expectations also affect thermal comfort.

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. Therefore laboratory and field data have been collected to define conditions that will be found comfortable for a specified percentage of occupants. It is to be noted that as

general requirement of this standard, this should be applied to a space where occupancies has a residency of more than 15 minutes within the space. The factors that state in above where the comfortabillity depends, are time dependent and however, this standard only addresses thermal comfort in a steady state. As a result, people entering a space that meets the requirements of this standard may not immediately find the conditions comfortable if they have experienced different environmental conditions just prior to entering the space.

Metabolic rate of a person is activity depend and clothing level which provides the thermal insulation to the body is also depends on occupancies likelihood. For example, person who perform office task has metabolic rate of1.0-1.7 met, 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. Similarly the level of clothing which give the insulation to heat loss from body is also activity depend and the person’s likelihood. According to that the limits of the parameters which define the comfort zone is depend on activity performed in the space and occupancies clothing as well. Therefore to define operative temperatures and other factors to define the comfort zone, whatever the value selected for parameters should be for 80% occupancy acceptability and 10% of allowable dissatisfaction criteria for general (whole body) thermal comfort based on the PMV-PPD index, plus 10% dissatisfaction that may occur on average from local (partial body) thermal discomfort.

(c).

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 to which the body is exposed, with respect to location and time. There is no such precise relationships between increased air speed and improved comfort established yet. However,

this standard allows increased air speed to be used to increase the maximum temperature for acceptability if the affected occupants are able to control the air speed. When the mean radiant temperature is low and the air temperature is high, elevated air speed is less effective at increasing heat loss. Conversely, elevated air speed is more effective at increasing heat loss when the mean radiant temperature is high and the air temperature is low.