Sunday, 14 July 2013

I am in Gujarat with new energy....

this blog i am writing with immense sense of satisfaction. after my services were abruptly ended at particular institute in mumbai, i was forcefully put on introspection period. also meanwhile my services at other institutes were continuing i became more or less passive almost to minimal intervention when other teachers were horribly off mark. and during that period i was thankful of all other teachers who put up with my this hibernation period. i said to myself, i can always return to build buildings, the skills i learnt so meticulously in last 22 years of my experience (if you do not count 4 years of teaching). i always have advantage over other teachers, some of whom have never designed or built a single building in their lifetime and are desperately in need of one or other teaching jobs. and also they are the teachers who are always hiding behind syllabus and university rules and requirements of external vivas (which is again taken by teachers who have never built a building) for taking up new technology and methodology of designing buildings.    

so students, majority of whom have no idea whats going on, suffer endlessly boring classes, boring teachers who have no clear pedagogy, and also fear of victimizing & failing in internal markings if they do not follow irrational course of teaching handed out day in day out by so called self-styled "expert" teachers. i have developed strongest empathy with students. Also while practicing architecture & designing buildings there is so much comfort available to architects. non of these comforts are passed on to students. take for example designing buildings in single line in initial concept stage till it is approved by clients. this is fairly good practice also accepting by clients. in this method only external walls are drawn in double lines because they involve elevations and also window openings. but internal partition walls are drawn in single line facilitating faster re-drafting in case of any revisions, internal or on suggestions of client.    

my view is that students should find the architectural course very enjoyable. the student should look forward to come to architectural institute with a relaxed attitude and with eagerness to enjoy the process of putting up the building. if designing and constructing the building is a rational engineering process, don't you think then every step of above should look logical to students. instead the student is put through all the tortures of endless requirements to be fulfilled whether the student is able to grasp the basic design parameters or not. whether the student is happy or unhappy with the design solution s/he has come up with; s/he is required to submit all the drawings, models and perspective views. now somebody can argue should teachers wait endlessly for a student to put up a decent design. my argument has teacher deconstructed the whole process of design process and spilled techniques of design in class appropriately in proper way during design class. 
even though design is creative process it has same system of strategies and tactics employed say like in football game. so all coaches are ready with strategies & tactics employed world wide to counter the opposite team. similarly in my view it is predominantly design teachers role to spell out design strategies and tactics to negotiate every possible parameter as expected by client or any other requirement of site conditions or technology or time and cost of building. 

Monday, 8 October 2012

i am cool on students' complaints

my dear students (June 4th '12 to Sept  3rd '12 semester Vth yr WD group)

i am getting messages from many students to the effect that did i leave your institute due to your behavior. to put all speculation to rest, let me tell you that i left your institute because i was asked to leave. and for this i will not blame anybody. i will not blame the students who complained against me nor the principal who asked me to leave. i am cool. 

but i had something of a special relationship with you all. i always experiment in every institute and also sometimes in the same institute with different classes, by different ways of interaction with students. so i had adopted a model of interaction with you whereby i wanted to show complete empathy with your issues. i was okay if you entered late in my class, i was okay even if when i did not see the required progress of work. i was depending on virtue of self guilt that you will feel when you were forgiven so many times and a day will come when you will like to pay back with good work, may be late, but of some value. 

(with some other students i happen to be strict and i cannot put up with  certain type of in-discipline. so may be then, my interaction with this student will involve some harsh treatment. but here again in long run, when the student will pass in all my subjects then the smile returns back to his/her face. i am sure we all are always expecting some rebukes from our loved ones for our laziness or nasty behaviors). 

and i did see progress in some of the students' WD work. also we had developed some comfort zone whereby we knew what to expect from each other. and the reason i am getting so many messages (its only coming from your group mates), is that it was the delivery time of our heightened expectations, and suddenly the arrangements were disturbed. the question is could it have been avoided? an honest answer would be yes. all this could have been avoided. 

for that we need to understand from which position we can review this. if we consider the institutes as behavior correction and mind training centers (apart from learning centers), then probably it is not only for students. but it is for everybody associated with the institutes. right from office boys, to administrative staff, to faculty members (including principals, vice chairman and chairman) and even to canteen managers, security and lift operating staff. so in case if there is problem or complaint for anybody's behavior, then institute is obliged to give sufficient chances for correction of behavior and may be at least one (if not more) warning before dismissing anybody. why any institute is obliged to do that. because that is the primary role of institute. otherwise it will be termed as commercial venture. even commercial ventures are nowadays improving and have certain measures in place for corrective behaviors. even if i accept that i had committed some mistake, i was not given any warning before sacking. nor my side of story was heard. this is saddest part. 

so it could have been avoided. so in that case, somebody has goofed up in assessing the situation and applying proper measures. yes i would say, if we respect the above position. but again institutes are reflection of what is happening in outside world. and outside world is sometimes unjust with all of us sometimes. also this same world  is a larger institute where mind's of people are trained for achieving higher pleasures and founding out TRUTH. so we have to allow for some mistakes when some people will judge us wrongly and may be we are removed from that place. in that case it is always better to move on, by lesson so learned you are always wiser and better off.

we can always meet. lets keep it after you are free from all your submissions in current final year. it will be some time in november 1st week. send me message or e-mail deciding time, day and venue of meet. i will be there...

with best wishes for all your submissions....

prof. atule kedia

Thursday, 28 June 2012

Vth-yr-working drawing-nbc-application-to-stairs.

dear all,

in our last class we solved a few cases by taking occupant load for any user and arriving at total number of people using it. then with the help of tables 20, 21 & 22 we arrived at proper widths and number of stairs required for cinema. 

i would like to make a passing observation that in most public buildings like cinema, theaters, etc it will be more convenient to use a few stairs of more width then more stairs of minimum  width of 2000 mm. so in case we need to give stairs width of 5200 mm by calculation, then instead of providing 3 stairs of 2000 mm, it will be perfectly acceptable by standards to give 2 stairs of 2600 mm width, whereby you will get economy of stairs in relation to structural and space criteria or even a single stair of width 5200 mm if all exit doors linked by common corridor lead to this stair. 

so please be imaginative and pragmatic while applying principals of nbc. 

you see that in your design of cinema (case study of bhusan, i am trying to recall by memory), we required 2 stairs of 3600 mm or 4 stairs of 2000 mm whereas he had provided only one stair of 1350 mm width which is also not acceptable as minimum stairs as per nbc norms. so you can see that your design is completely un-done if we check it against stringent application of nbc. 

so please as discussed in our class, if you find that applying nbc will involve lot of re-design work, then i would expect it to leave it as it is and proceed to work more on grid-lines, dimensions, levels, door - window schedules indicators, room user number, etc.  please bring your up dated drawings in class on tuesday morning. plotted or cad reviews, i will leave it entirely to your judgement. 

with best regards,

prof. atule kedia

Sunday, 24 June 2012


dear all,

please hit the link below for a pdf presentation on above topic:

also read the following article taken from

Air-conditioning Basics

Air conditioners use refrigeration to chill indoor air, taking advantage of a remarkable physical law: When a liquid converts to a gas (in a process called phase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds to evaporate and condense over and over again in a closed system of coils.
The compounds involved are refrigerants that have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these serpentine, air-chilling coils.
When hot air flows over the cold, low-pressure evaporator coils, the refrigerant inside absorbs heat as it changes from a liquid to a gaseous state. To keep cooling efficiently, the air conditioner has to convert the refrigerant gas back to a liquid again. To do that, a compressor puts the gas under high pressure, a process that creates unwanted heat. All the extra heat created by compressing the gas is then evacuated to the outdoors with the help of a second set of coils called condenser coils, and a second fan. As the gas cools, it changes back to a liquid, and the process starts all over again. Think of it as an endless, elegant cycle: liquid refrigerant, phase conversion to a gas/ heat absorption, compression and phase transition back to a liquid again.
It's easy to see that there are two distinct things going on in an air conditioner. Refrigerant is chilling the indoor air, and the resulting gas is being continually compressed and cooled for conversion back to a liquid again. On the next page, we'll look at how the different parts of an air conditioner work to make all that possible.

The Parts of an Air Conditioner

Let's get some housekeeping topics out of the way before we tackle the unique components that make up a standard air conditioner. The biggest job an air conditioner has to do is to cool the indoor air. That's not all it does, though. Air conditioners monitor and regulate the air temperature via a thermostat. They also have an onboard filter that removes airborne particulates from the circulating air. Air conditioners function as dehumidifiers. Because temperature is a key component of relative humidity, reducing the temperature of a volume of humid air causes it to release a portion of its moisture. That's why there are drains and moisture-collecting pans near or attached to air conditioners, and why air conditioners discharge water when they operate on humid days.
Still, the major parts of an air conditioner manage refrigerant and move air in two directions: indoors and outside:
  • Evaporator - Receives the liquid refrigerant
  • Condenser - Facilitates heat transfer
  • Expansion valve - regulates refrigerant flow into the evaporator
  • Compressor - A pump that pressurizes refrigerant
The cold side of an air conditioner contains the evaporator and a fan that blows air over the chilled coils and into the room. The hot side contains the compressor, condenser and another fan to vent hot air coming off the compressed refrigerant to the outdoors. In between the two sets of coils, there's an expansion valve. It regulates the amount of compressed liquid refrigerant moving into the evaporator. Once in the evaporator, the refrigerant experiences a pressure drop, expands and changes back into a gas. The compressor is actually a large electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a liquid. There are some additional sensors, timers and valves, but the evaporator, compressor, condenser and expansion valve are the main components of an air conditioner.
Although this is a conventional setup for an air conditioner, there are a couple of variations you should know about. Window air conditioners have all these components mounted into a relatively small metal box that installs into a window opening. The hot air vents from the back of the unit, while the condenser coils and a fan cool and re-circulate indoor air. Bigger air conditioners work a little differently: Central air conditioners share a control thermostat with a home's heating system, and the compressor and condenser, the hot side of the unit, isn't even in the house. It's in a separate all-weather housing outdoors. In very large buildings, like hotels and hospitals, the exterior condensing unit is often mounted somewhere on the roof.

Window and Split-system AC Units

A window air conditioner unit implements a complete air conditioner in a small space. The units are made small enough to fit into a standard window frame. You close the window down on the unit, plug it in and turn it on to get cool air. If you take the cover off of an unplugged window unit, you'll find that it contains:
  • A compressor
  • An expansion valve
  • A hot coil (on the outside)
  • A chilled coil (on the inside)
  • Two fans
  • A control unit
The fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled).
When you get into larger air-conditioning applications, its time to start looking at split-system units. A split-system air conditioner splits the hot side from the cold side of the system, as in the diagram below.
The cold side, consisting of the expansion valve and the cold coil, is generally placed into a furnace or some other air handler. The air handler blows air through the coil and routes the air throughout the building using a series of ducts. The hot side, known as the condensing unit, lives outside the building.
The unit consists of a long, spiral coil shaped like a cylinder. Inside the coil is a fan, to blow air through the coil, along with a weather-resistant compressor and some control logic. This approach has evolved over the years because it's low-cost, and also because it normally results in reduced noise inside the house (at the expense of increased noise outside the house). Other than the fact that the hot and cold sides are split apart and the capacity is higher (making the coils and compressor larger), there's no difference between a split-system and a window air conditioner.
In warehouses, large business offices, malls, big department stores and other sizeable buildings, the condensing unit normally lives on the roof and can be quite massive. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building.
In larger buildings and particularly in multi-story buildings, the split-system approach begins to run into problems. Either running the pipe between the condenser and the air handler exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor), or the amount of duct work and the length of ducts becomes unmanageable. At this point, it's time to think about a chilled-water system.

Chilled-water and Cooling-tower AC Units

Although standard air conditioners are very popular, they can use a lot of energy and generate quite a bit of heat. For large installations like office buildings, air handling and conditioning is sometimes managed a little differently.
Some systems use water as part of the cooling process. The two most well-known are chilled water systems and cooling tower air conditioners.
  • Chilled water systems - In a chilled-water system, the entire air conditioner is installed on the roof or behind the building. It cools water to between 40 and 45 degrees Fahrenheit (4.4 and 7.2 degrees Celsius). The chilled water is then piped throughout the building and connected to air handlers. This can be a versatile system where the water pipes work like the evaporator coils in a standard air conditioner. If it's well-insulated, there's no practical distance limitation to the length of a chilled-water pipe.
  • Cooling tower technology - In all of the air conditioning systems we've described so far, air is used to dissipate heat from the compressor coils. In some large systems, a cooling tower is used instead. The tower creates a stream of cold water that runs through a heat exchanger, cooling the hot condenser coils. The tower blows air through a stream of water causing some of it to evaporate, and the evaporation cools the water stream. One of the disadvantages of this type of system is that water has to be added regularly to make up for liquid lost through evaporation. The actual amount of cooling that an air conditioning system gets from a cooling tower depends on the relative humidity of the air and the barometric pressure.
Because of rising electrical costs and environmental concerns, some other air cooling methods are being explored, too. One is off-peak or ice-cooling technology. An off-peak cooling system uses ice frozen during the evening hours to chill interior air during the hottest part of the day. Although the system does use energy, the largest energy drain is when community demand for power is at its lowest. Energy is less expensive during off-peak hours, and the lowered consumption during peak times eases the demand on the power grid.
Another option is geo-thermal heating. It varies, but at around 6 feet (1.8 meters) underground, the earth's temperature ranges from 45 to 75 degrees Fahrenheit (7.2 to 23.8 degrees Celsius). The basic idea behindgeo-thermal cooling is to use this constant temperature as a heat or cold source instead of using electricity to generate heat or cold. The most common type of geo-thermal unit for the home is a closed-loop system. Polyethylene pipes filled with a liquid mixture are buried underground. During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat through the pipes to deposit it underground [source: Geo Heating].
For real energy efficiency, solar powered air conditioners are also making their debut. There may still be some kinks to work out, but around 5 percent of all electricity consumed in the U.S. is used to power air conditioning of one type or another, so there's a big market for energy-friendly air conditioning options [source: ACEEE].


Most air conditioners have their capacity rated in British thermal units (Btu). A Btu is the amount of heat necessary to raise the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). One Btu equals 1,055 joules. In heating and cooling terms, one ton equals 12,000 Btu.
A typical window air conditioner might be rated at 10,000 Btu. For comparison, a typical 2,000-square-foot (185.8 square meters) house might have a 5-ton (60,000-Btu) air conditioning system, implying that you might need perhaps 30 Btu per square foot. These are rough estimates. To size an air conditioner accurately for your specific application, you should contact an HVAC contractor.
The energy efficiency rating (EER) of an air conditioner is its Btu rating over its wattage. As an example, if a 10,000-Btu air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 Btu/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.
Let's say you have a choice between two 10,000-Btu units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let's also say that the price difference is $100. To determine the payback period on the more expensive unit, you need to know approximately how many hours per year you will be operating the air conditioner and how much a kilowatt-hour (kWh) costs in your area.
Assuming you plan to use the air conditioner six hours a day for four months of the year, at a cost of $0.10/kWh. The difference in energy consumption between the two units is 200 watts. This means that every five hours the less expensive unit will consume one additional kWh (or $0.10) more than the more expensive unit.
Let's do the math: With roughly 30 days in a month, you're operating the air conditioner:
4 months x 30 days per month x 6 hours per day = 720 hours
[(720 hours x 200 watts) / (1000 watts/kilowatt)] x $0.10/kilowatt hours = $14.40
The more expensive air conditioning unit costs $100 more to purchase but less money to operate. In our example, it'll take seven years for the higher priced unit to break even.

Energy Efficient Cooling Systems

Because of the rising costs of electricity and a growing trend to "go green," more people are turning to alternative cooling methods to spare their pocketbooks and the environment. Big businesses are even jumping on board in an effort to improve their public image and lower their overhead.
Ice cooling systems are one way that businesses are combating high electricity costs during the summer. Ice cooling is as simple as it sounds. Large tanks of water freeze into ice at night, when energy demands are lower. The next day, a system much like a conventional air conditioner pumps the cool air from the ice into the building. Ice cooling saves money, cuts pollution, eases the strain on the power grid and can be used alongside traditional systems. The downside of ice cooling is that the systems are expensive to install and require a lot of space. Even with the high startup costs, more than 3,000 systems are in use worldwide [source: CNN]. You can read more about ice cooling in Are Ice Blocks Better than Air Conditioning?
An ice cooling system is a great way to save money and conserve energy, but its price tag and space requirements limit it to large buildings. One way that homeowners can save on energy costs is by installing geo-thermal heating and cooling systems, also known as ground source heat pumps (GSHP). The Environmental Protection Agency recently named geo-thermal units "the most energy-efficient and environmentally sensitive of all space conditioning systems" [source: EPA].
Although it varies, at six feet underground the Earth's temperatures range from 45 to 75 degrees Fahrenheit. The basic principle behind geo-thermal cooling is to use this constant temperature as a heat source instead of generating heat with electricity.
The most common type of geo-thermal unit for homes is the closed-loop system. Polyethylene pipes are buried under the ground, either vertically like a well or horizontally in three- to six-foot trenches. They can also be buried under ponds. Water or an anti-freeze/water mixture is pumped through the pipes. During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat from the building, carrying it through the system and placing it in the ground [source: Geo Heating].
Homeowners can save 30 to 50 percent on their cooling bills by replacing their traditional HVAC systems with ground source heat pumps. The initial costs can be up to 30 percent more, but that money can be recouped in three to five years, and most states offer financial purchase incentives. Another benefit is that the system lasts longer than traditional units because it's protected from the elements and immune to theft [source: Geo Exchange].

Vth-yr-working drawing-cibse/nbc/bye-laws: application to all parts....

dear all,

with reference to above i have received many answers for application of CIBSE guidelines. 

i would request you to bring a print out of above (all) and also of my e-mails on nbc application for lifts, basements, stairs,corridors, doors, and ramps (anyone student who present in wd class). 

now you guys are working at two levels. at one level u r correcting the design errors in  design of different parts of building as stated above. it goes without saying that before issuing final WDD's it is ur last chance to correct such mistakes. so normally all architects undergo this process during design and they check it one more time before issuing the WDD's. 

at second level u r reqd to put ur carpet dimensions, end to end dimensions for all building parts, after placing structural columns, u r reqd to put grid lines which may pass through centre of columns. i have already brought some reference drawings last time and given you fairly good idea how they are structured. so that should not be a difficulty. as also i mentioned to you, i am serious about giving soft copies of my 2d, 3d cad library, reference drawings, complete package including services and structural drawings to a few deserving students who will be able to produce substantial work by end of july. so again with help of such cadding tools you will be able to produce professional level of working drawings efficiently in less time then others.   

so please revise your drawings in both the levels as above and bring to class. taking out hard copy of above is entirely up to you. for soft copies to be checked on laptop, it must be your own personal laptop. borrowing laptop from others will waste time of owner of laptop.  

so for 1st level, regarding application of nbc, i want you all to work for higher floors for stairways, doors and corridors (minimum). if you do not have time to revise your drawings, then at least i want you to work it out on a4 paper or send me e-mail like last time as sent for cibse. 

hoping to see some progress. 

prof. atule kedia

Thursday, 21 June 2012

Vth-yr-working drawing-NBC-application-to-parts

dear all,

it is heartening to know u r keen to learn more and work hard to apply it in current WD package.

i m talking to other institutes hod's and they too agree w/me  that it is reqd by students to learn these matters (application of nbc, cibse,etc).

so for different parts i will tell u how it is done. 

basic rule to apply in design of facility is as follows:

1). if u r designing say for example a 5 hotel project, and you have banquet halls, it is always better to put such facilities like banquet hall etc, which are high people density on ground floor leading to safety.

because for exits you are only required to provide doors wide and sufficient in numbers leading to outside or to corridor which will lead to outside. again corridor width and numbers should be sufficient as per nbc (national building code). but u r saved the cost of stairways.

2). Municipal bye-laws will always insist to give minimum width of stairs, corridors, (passage ways) and door exits. but u must always add extra over minimum required as per occupant load as given in NBC. so for example if i have 1000 seats assembly facility like conferencing on second floor, then as per occupant load per exit unit i will get 1000/40 = 25. one exit unit = 500 mm. so total exit unit for stairway reqd is 25x 500 mm = 12500. now minimum width of stair for assembly building is 2000. so i will require 12500/2000 = 6.25 staircases to give quick exit time for 1000 ppl to go out to safety on ground level. 6.25 (below 0.5) can be rounded to 6 stairs. 

3). for same 1000 ppl doors reqd will be 1000/60 = 16.66 units of exits. so total door width reqd is 16.66 x 500 mm = 8333 mm. so u can give 4 doors of 2100 mm width on two sides of hall or on one side at sufficient intervals to avoid overcrowding near doors. please exit for assembly building shall not be less than 2000 mm width. for other facilities no door will be less than 1000 mm. 

4). for ramp for same 1000 ppl width reqd will be 1000/50 = 20 x 500 mm = 10000 mm. so u can give single ramp of above width or 2 ramps of 5000 mm width or 4 ramps of 2500 mm width.

5). for corridors: please keep this in mind: 
      NBC states as follows: Exit corridors and passage ways shall be of width not less than the aggregate required width of exit doorways leading from them in the direction of travel to exterior. 

the interpretation of above statement in our case of 1000 ppl assembly building will be as follows:

total aggregate width of doors = 8333 mm. so width of corridor will be 4200mm if 2 doors of 2100mm size open into it. it will be 2100 mm if one door open into it. it will be 6300 mm if 3 doors of 2100 mm open into it. 

hence i told u in the beginning that for high occupant load areas which ask for wider exits, please put them on ground floor. so u will at least save money on stairways. so stairs are always provided for less occupant facilities like residences / offices on upper floors.

please remind me to give you a copy of all necessary nbc tables like 20 for occupant load, 21 for occupants per unit exit width for stairways, ramps and doors for various group of occupancy like residential, educational, assembly, etc. also travel distance for the same. 

with best regards,

atule kedia 

Saturday, 16 June 2012

IV th-yr-building-services-comfort-conditions

dear students,

human beings give off heat, around an average of 100 kcal (kilo-calories) or 400 BTU (british thermal unit) per hour per person, due to what is known as 'metabolism'. the temperature mechanism within the human body maintains a body temperature of around 36.9 degree C (celsius) or 98.4 degree F (fahrenheit). but the skin temperature varies according to the surrounding temperature and relative humidity. to dissipate the heat  generated by metabolism in order to maintain the body temperature at the normal level, there must be a flow of heat from the skin to the surrounding air. if the surrounding temperature is slightly less than that of the body, there will be a steady flow of heat from the skin. 

but if the surrounding temperature is very low, as on a cold winter day, the rate of heat flow from the body will be quite rapid, thus the person feels cold. that is why we wear woolen winter clothing, which impede the rapid flow of heat from the body. on the other hand on a hot summer day, the surrounding temperature is higher than that of the body, and so there cannot be flow of heat from the skin to the surroundings; thus the person feels hot. in such a situation water from the body evaporates at the skin surface dissipating the heat due to metabolism. this helps in maintaining normal body temperature. but if the surrounding air is not only hot but highly humid as well, very little evaporation of water can take place from the skin surface, and so the person feels hot and uncomfortable. 

a movement of air (such as by a fan) over the body helps in slightly improving the rate of evaporation of water at the skin surface, thereby giving some relief. too high a level of relative humidity causes a damp unpleasant feeling because of the accumulation of moisture in clothing and also leads to emanation of body odours. while too low a level of relative humidity causes the skin, mouth and nose to become dry and parched. so to obtain comfort, the temperature, relative humidity and air movement within the room are maintained by air conditioning. this is done so that the heat dissipation from the body is steady to maintain a normal body temperature resulting in a sensation of comfort. 

in addition to maintaining proper temperature and relative humidity, it is evident that there must also be certain amount of air movement in the room. here again, too much of air movement (or draft) can cause discomfort. so the movement of air within the room should be gentle and uniform. the body odours emanating from people can become unbearable and for this, sufficient ventilation has to be provided. this can be done by taking in a certain amount of fresh air for dilution of the body odours. removal of dirt/dust particles is important from the health point of view, and also to maintain a neat environment.

since the combination of temperature, relative humidity and air motion influence the rate of heat dissipation from the body, these three can be considered interrelated for creating the sensation of comfort. therefore different combinations of temperature, relative humidity and air motion will give the same sense of comfort. again the sense of comfort can vary from person to person and also depends on the nature of their activities. for example, persons involved in heavy manual labour in a factory may need a different temperature, humidity and air motion combination from those seated in an auditorium. 

in general, the range of temperature and humidity conditions maintained in the air conditioned space during summer are 23.5 to 25.5 degree C (74 to 78 degree F) and 55 to 65 RH with an air movement of 4.5 to 12 m/min. (15 to 40 ft/min.).

please heat the link below for more discussion on above topic:

prof. atule kedia