HVAC TYPES OF HVAC SYSTEMS

1. Based on method used to convey energy

HVAC types

2. Based on type of air- conditioner used1. Window Air Conditioning System2. Split Air Conditioner System3. Packaged Air Conditioners4. Central Air Conditioning

1. All- air systems2. Air-and-water systems3. All-water systems

Window AC

Packaged AC

Split AC

Window air conditioner is the most commonly used air conditioner for single rooms. In this air conditioner all the components, namely the compressor, condenser, expansion valve or coil, evaporator and cooling coil are enclosed in a single box. This unit is fitted in a slot made in the wall of the room, or more commonly a window sill.

The split air conditioner comprises of two parts: the outdoor unit and the indoor unit. The outdoor unit, fitted outside the room, houses components like the compressor, condenser and expansion valve. The indoor unit comprises the evaporator or cooling coil and the cooling fan.  For this unit you don’t have to make any slot in the wall of the room. Further, the present day split units have aesthetic looks and add to the beauty of the room. The split air conditioner can be used to cool one or two rooms.

The central air conditioning plants or the systems are used when large buildings, hotels, theaters, airports, shopping malls etc are to be air conditioned completely. The window and split air conditioners are used for single rooms or small office spaces. If the whole building is to be cooled it is not economically viable to put window or split air conditioner in each and every room. Further, these small units cannot satisfactorily cool the large halls, auditoriums, receptions areas etc.

Central air conditioning is used for cooling big buildings, houses, offices, entire hotels, gyms, movie theaters, factories etc. If the whole building is to be air conditioned, HVAC engineers find that putting individual units in each of the rooms is very expensive making this a better option. A central air conditioning system is comprised of a huge compressor that has the capacity to produce hundreds of tons of air conditioning. Cooling big halls, malls, huge spaces, galleries etc is usually only feasible with central conditioning units.

THERMAL COMFORT

1999 ASHRAE Applications Handbook (SI)

General Design Criteria

General Category Specific Category Inside Design Conditions Air Movement Circulation,air changes per hourWinter Summer

Dining andEntertainment Centers

Cafeterias and Luncheonettes

21 to 23°C 26°C e

20 to 30% rh 50% rh0.25 m/s at 1.8 m above floor

12 to 15

Restaurants 21 to 23°C 23 to 26°C20 to 30% rh 55 to 60% rh

0.13 to 0.15 m/s 8 to 12

Bars 21 to 23°C 23 to 26°C20 to 30% rh 50 to 60% rh

0.15 m/s at 1.8 m above floor

15 to 20

Nightclubs and Casinos

21 to 23°C 23 to 26°C20 to 30% rh 50 to 60% rh

below 0.13 m/s at1.5 m above floor

20 to 30

Kitchens 21 to 23°C 29 to 31°C 0.15 to 0.25 m/s 12 to 15h

Office Buildings 21 to 23°C 23 to 26°C20 to 30% rh 50 to 60% rh

0.13 to 0.23 m/s 4 to 10 L/(s·m2)

4 to 10

Museums, Libraries, and Archives(Also see Chapter 20.)

Average 20 to 22°C40 to 55% rh below 0.13 m/s

8 to 12

Archival See Chapter 20, Museums, Libraries, and Archives

below 0.13 m/s 8 to 12

Bowling Centers

21 to 23°C 24 to 26°C20 to 30% rh 50 to 55% rh

0.25 m/s at 1.8 m above floor

10 to 15

Communication Centers

Telephone Terminal Rooms

22 to 26°C 22 to 26°C40 to 50% rh 40 to 50% rh

0.13 to 0.15 m/s 8 to 20

Radio and Television Studios

21 to 23°C 23 to 26°C40 to 50% rh 45 to 55% rh

0.13 to 0.15 m/s 15 to 40

Transportation Centers

Airport Terminals

23 to 26°C 23 to 26°C30 to 40% rh 40 to 55% rh

below 0.13 m/s at3.7 m above floor

8 to 12

Ship Docks

21 to 23°C 23 to 26°C20 to 30% rh 50 to 60% rh

0.13 to 0.15 m/s at1.8 m above floor

8 to 12

Bus Terminals

21 to 23°C 23 to 26°C20 to 30% rh 50 to 60% rh

0.13 to 0.15 m/s at1.8 m above floor

8 to 12

Garagesl 4 to 13°C 27 to 38°C 0.15 to 0.38 m/s 4 to 6

Warehouses Inside design temperatures for warehouses often depend on the materials stored.

1 to 4

HVAC SYSTEM TYPE SELECTION

Commercial buildings commonly choose several types of systems based on the space conditioning needs of different systems.

1. A constant-volume system might cool the interior, which has relatively uniform cooling requirements

2. A VAV system conditions perimeter areas, which have variable requirements.

3. Where precision control is required (e.g., laboratories, precision electronic industry or hospital operating rooms), custom single-zone air handlers may be used.

In large facilities, which have widely varying requirements, flexibility is extremely important.

The window and split air conditioners are usually used for the small air conditioning capacities up to 5 tons.

The packaged air conditioners are available in the fixed rated capacities of 3, 5,7,10 and 15 tons. These units are used commonly in places like restaurants, telephone exchange, homes, small halls, etc.

The central air conditioning system are used for where the cooling loads extend beyond 20 tons.

Table showing some typical applications for various types of systems.

HVAC system selection

HVAC LOAD CALCULATIONS

Internal LoadsLightingOccupantsEquipmentHumidification anddehumidification

TYPES OF LOADS IN HVAC

External loads Fenestration Infiltration Building envelope

Ventilation LoadsThe air flow rates for ventilation purposes

There are many factors which effect the hvac loads calculation.

Climate

Orientation•Latitude

For the classification purpose these can be categorized as follows

HVAC LOAD CALCULATION METHODS

1. Can not be generalized, varies according to climatic conditions, site location etc

2. Rule-of-thumb sizing “does not account for orientation of the walls and windows,

3. The difference in surface area between a one-story and a two-story home of the same floor area,

4. The differences in insulation and air leakage between different buildings, the number of occupants, and many other factors.”

Rule-of-thumb sizing One ton of cooling equipment for every 400 square feet of conditioned space. In a concession to recent improvements in insulation levels and window specifications, some HVAC contractors have adjusted their rule of thumb, and now size air conditions at one ton per 600 square feet.

One ton of cooling per 1,000 square feet. According to Blasnik, “Sizing an air conditioner using tons per square foot actually works pretty well, as long as you choose the right rule of thumb.”

ADVANTAGESDISVANTAGES

1. Easy to calculate HVAC loads

2. Used for initial design stages

3. Takes into account similar types of building categories around the given site location

4. Usually these rules of thumb may result in gross oversizing of cooling equipment.

1. Rule of thumb to size an air conditioner is no substitute for performing a room-by-room cooling load calculation.

2. Room-by-room calculations are necessary for many reasons: to properly size ductwork, for example, and to address unusual architectural features like rooms with large west-facing windows. 

NOTES

HVAC LOAD CALCULATION METHODS

Software Programs

The physics involved in the transfer of heat and energy between buildings, occupants, and the environment is quite complex. The most current and best math models of this problem require significant input data and thousands of calculations in an iterative process.

ASHRAE has TETD (Total Equivalent Temperature Difference), CLTD (Cooling Load Temperature Difference), TFM (Transfer Function Method), HB (Heat Balance) and RTS (Radiant Time Series).

Building block Phase 1Population

Phase 2Pop.

Phase 3Pop.

Total Population

Area (sq. ft.)

Software development block 7500 12000 10500 30000 3900000

Food Court 2000 3200 2800 8000 360000

Education & Research Block 0 0 3000 3000 300000

Employee Care Centre 150 0 150 300 162000

Support Staff 100 160 140 400  Parking- Cars 1575 2520 2205 6300 (no.)  Parking- Two Wheelers 675 1080 945 2700 (no.)  

Surface Parking- Bus Bay (45 No) 39 62 54 154 (no.)

   

INITIAL HVAC LOAD CALCULATION URBAN DESIGN PROBLEM MAHINDRA SEZ

DESIGN BRIEF

HVAC LOAD CALCULATION : Using Rule-of-thumb sizing method PHASE-1

DESIGN BRIEF

Total Population

30000

8000

3000

300

4006300 (no.)

2700 (no.)

154 (no.) 

Area (sq. ft.)

3900000

360000

300000

162000

  

 

 

Building block

Software development block

Food Court

Education & Research Block

Employee Care CentreSupport StaffParking- CarsParking- Two Wheelers

Surface Parking- Bus Bay (45 No)

÷

÷÷

÷

=

=

==

Density (area/person)

130 sq.ft./person

45 sq.ft./person

100 sq.ft./person

540 sq.ft./person

 

PHASE-1

Phase 1Population

7500

2000

0

150

1001575

675

39

Phase 1Area (sq. ft.)

975000

90000

0

81000

xxxx

TOTAL BUILT UP AREA INPHASE-11146000 sq. ft.

106466.9 sq. mtr.=EXCLUDING 15 % CIRCULATION AREA AND ASSUMING THAT 60 % OF THE TOTAL BUILT UP AREA TO BE AIR CONDITIONED, THE TOTAL AREA TO BE AIR CONDITIONED WILL BE = 54298.1 sq. mtr

Applying rule of thumb : one ton of cooling per 1,000 square feetTotal HVAC cooling Load = 584.46 ton= 85 kwhr ( 1 ton=3.5kw )

=

=

==

was one ton of cooling equipment for every 400 square feet of conditioned space. In a concession to recent improvements in insulation levels and window specifications, some HVAC contractors have adjusted their rule of thumb, and now size air conditions at one ton per 600 square feet.

one ton of cooling per 1,000 square feet. According to Blasnik, “Sizing an air conditioner using tons per square foot actually works pretty well, as long as you choose the right rule of thumb.”

rule-of-thumb sizing “does not account for orientation of the walls and windows, the difference in surface area between a one-story and a two-story home of the same floor area, the differences in insulation and air leakage between different buildings, the number of occupants, and many other factors.”