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Saturday, 3 January 2015

HEATING VENTILATING AND AIR CONDITIONING (HVAC)


HVAC System

HVAC referred as heating ventilating & air conditioning system that provides human comfort by supplying conditioned air so that work men or persons, working inside building or office may feel comfort during work and they can increase productivity and also may maintain safety and green environment.

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I am posting this blog for understanding the overview of designing concept behind HVAC system.
We will study the basic concept of HVAC system and the design consideration for this system. Finally at the end of this post we will draw one floor plan of our selected site.

We will also discuss the following points in my next post
  1. Heating load calculations
  2. Cooling load calculations
  3. Heating Equipment selection
  4. Cooling equipment selection 
So let us start to understand the design procedure for HVAC system.

Let us consider we have to design a HVAC system for a building. Before going to design HVAC system for a building we must determine areas such as sleeping areas, living areas etc.

Before starting the designing, we will have information about the following points
  1. Building length and width
  2. No. of rooms and specifications
  3. No. of window and specifications
  4. No. of doors and specifications
  5. Floor and roof specifications
  6. Material of constructions for each component
Once we will have information about above mentioned points, we may draw a floor plan to understand easily about the sizing and layout of duct.

Let we have to design a HVAC for a residential family home.

Let, the specifications of building for which we are going to design HVAC system are as mentioned below and also mentioned in following figure.

Length and width of building

Length = 74 ft
Width = 36 ft
There are two windows on east walls and two windows for west walls also.
There are 6 nos. of windows for north walls and 9 nos. of windows for south wall.


Length
Width
Height
Qty



Building
74 ft
36 ft
8 ft




East
Window
4 ft
4 ft

3



Window
3 ft
3 ft

1



Door

3 ft
7 ft
1



West
Window
4 ft
6 ft

1



Window
3 ft
3 ft

1



Window
6 ft
8 ft

1



Door

3 ft
7 ft
1



North
Window







Door







South
Window
4 ft
4 ft

1



Door








Floor
74 ft
36 ft





Roof
74 ft
36 ft






Let us consider the materials of construction for each component of building

Roof -Construction

Conventional roof-attic-ceiling combination and it is also vented in order to withdraw the moisture with 6 inches. Insulation of fibrous batt & vapour retarder and value of U is as mentioned as U=0.05 BTU/h ft2 F.

Wall-construction

Construction of wall is as following
Frame= 4 inch face brick
Insulation of fibrous batt = 3.5 in
Sheathing of Polystyrene = 0.75 in
Gypsum Board for wall= 0.5 in
U= 0.06 BTU/h ft2 F

Construction of floor

Floor is constructed with concrete slab of 4 in.

Fenestration

0.125 In of thickness inner and outer with clear double –glass
There is overhanging of window–glass of 2 ft at the top of window

Doors (construction Plan is provided in attached image)

Doors are made of material whose value of U= 0.32 BTU/h ft2 F

Design Conditions or restrictions

 
Dry bulb temperature

Inside
75
50 %Relative humidity
Outside
96°F With 24°F daily range
74.6 F dew point

Occupancy

Let there are four persons are assigned to live in that house.

U-factor

U factor for every external surface are taken by assuming the wind velocity is equal to 7.5 m/h

Occupancy

Let there are four persons, one in each bedroom and two are living in master bedroom

Lights & Appliances

Let these are as following
Kitchen = 1600 Btu/h
Living room = 50 % appliance load of kitchen is taken in living room
Utility Room = 1600 Btu/h
Allow 25 % for storage room and 25 % for kitchen

Location of conditioning instrument 

We have located our conditioning device or system in garage

Category of construction

Let construction of selected site i.e. house is medium.
Now we will draw a floor plan of our selected site as mentioned below.

Do you have any suggestion? Please write in comment box