Choice of Design Conditions 2 December 2015choise of design condition1

At the end of the lecture the student should be able to: Select suitable outdoor design conditions based on weather data and applications Find the supply conditions based on the psychrometry of air conditioning systems, and Analyze various summer air conditioning systems

Choice of Inside Design Conditions 2 December 2015choise of design condition3

Comfort Zone According to ASHRAE (approximately) Dry bulb temperature from 20 o C to 26 o C Dew point temperature from 1.7 to 16.7 o C Relative Humidity between 30% and 80% at 20 o C and between 26 and 72 at 22 o C Air movement: is related to air temperature for lightly clothed people Air velocity(m/s) Dry Bulb T December 20154choise of design condition

Thermal comfort depends on creating an environment of dry-bulb temperature, humidity, and air motion, that is appropriate for the activity level of the people in the space. This environment allows the body’s rate of heat generation to balance with the body’s rate of heat loss. 2 December 2015choise of design condition5

Using Psychometric Chart ASHRAE comfort zone can be shown using the s.chart 2 December 20156choise of design condition

Choice of Inside Design Conditions For a person to feel comfortable the following conditions are desirable 1. The air temp should be higher than the mean radiant temperature in summer, but lower in winter 2. Average air velocity should not exceed 0.15m/s 3. Relative humidity should lie between 20% and 60% and should not exceed 70%( >60 % > smell) 4. The temperature difference between the feet and the head should be as small as possible (<1.5 o C) 5. Thermal radiation is best not directed on the tops of the heads 6. CO 2 concentration should not exceed about 0.1% 2 December 20157choise of design condition

Selection of Outdoor Design Conditions The ambient temperature & moisture content vary from hour to hour and day to day & from place to place For most of the major locations of the world, meteorological data are available in the form of mean daily or monthly maximum and minimum temperatures and corresponding relative humidity or wet bulb temperature Selection of worst possible condition leads to excessively large cooling/heating equipment as worst conditions prevail for a few hours in an a year

Choice of Out side Design Conditions There are three ways to decide outside summer design states 1. Follow the technique described below i.choose the highest mean monthly maximum temperature as the design dry bulb temperature ii.For the same month used in (i) couple the mean daily maximum temperature and the afternoon record of relative humidity iii.With the temperature and humidity coupled in (ii) determine the corresponding moisture content from psychometric chart 2 December 20159choise of design condition

Cont… iv. Use the moisture content in (iii) with the mean monthly maximum temperature to establish the corresponding wet bulb temperature v. Select the mean monthly maximum temperature (i) and wet bulb obtained in (iv) as the outside design state 2. Choose the outside dry and wet bulb temperatures in terms of their frequency of occurrence in the summer months 3. Adopt what is chosen by common custom, locally 2 December choise of design condition