L8: HVAC

Question 1

What does HVAC stand for?

Answer 1

Heating and humidification
Ventilation
Air conditioning and dehumidification

Question 2

Is HVAC required?

Answer 2

Heating - yes

Cooling - no

Question 3

What does HVAC achieve?

Answer 3

Temperature control
Humidity control
Air movement
Air filtration

Question 4

What are the three categories that determine comfort?

Answer 4

Personal/physical
Measurable environment (RH, temp)
Psychological (air movement, noise)

Question 5

What is relative humidity?

Answer 5

The ratio of moisture in the air compared with the maximum (100% means air cannot contain any more moisture at that temp - higher temp = more moisture)

Question 6

What is the comfort envelope temperature and relative humidity?

Answer 6

Temperature 68-79ºF

RH targeted at 50%

Question 7

What other factor is considered in the comfort envelope?

Answer 7

Clothing coefficient

Question 8

What are the two thermal loading types?

Answer 8

Skin load dominated (outside - 55%)

Internal load dominated (outside - 20%; energy from people/lights/equipment dominate)

Question 9

What are the three different sources of heat flow/gain through a building envelope?

Answer 9

Temperature difference
Solar radiation
Air infiltration

Question 10

What is the R value?

Answer 10

Resistance to heat exchange = 1/k (1/conductivity)

Question 11

What is the U value?

Answer 11

Thermal transmittance = 1/R1+R2+R3+…

Question 12

What is the thermal gradient?

Answer 12

The gradual temperature change through the materials in the building envelope

Question 13

How is the heat flow through building envelope calculated?

Answer 13

As the hourly conductive heat loss through the envelope based on area, temperature difference and U value

Question 14

How is heat fain due to solar radiation calculated?

Answer 14

With complex calculations depending on type, shading, sunlight

Question 15

How does angle of incidence affect light reflected?

Answer 15

Shallower angle = higher % reflected

Question 16

What is heat flow by infiltration and what are the three most common causes?

Answer 16

Accidental influx of outdoor air

Floors, walls and ceilings, ducts, fireplaces

Question 17

What are zones?

Answer 17

Area divisions within a building that operate separately

Question 18

What are zones commonly based on?

Answer 18

Thermal loads - perimeter (changes with weather) vs core (always cold)

Use of space - tenants, different aromas, different operating hours

Quality of space - high quality gives independent control eg. hotel room, labs

Question 19

What are the 4 types of HVAC systems?

Answer 19

All-air
All-water
Air-water
Packaged

Question 20

What are the 4 types of all-air HVAC systems?

Answer 20

Single duct, constant air volume
Multi-zone, constant air volume
Single duct, variable air volume
Double (dual) duct

Question 21

What is single-duct CAV?

Answer 21

Constant temperature (cooled/chilled by water from chiller/boiler)
Low-velocity duct system
Master thermostat sets temp for whole building

Question 22

What is multi-zone CAV?

Answer 22

Allows separate temperature control (cannot change between hot/cold mode but can change how hot/cold with device that lets in small amounts of heat/coolth to adjust temp)
Separate ducts from AHU

Question 23

What is single-duct VAV?

Answer 23

Dampers at terminal outlets adjust air flow

More common/efficient than CAV

Question 24

What is double-duct?

Answer 24

Separate ducts for hot and cold air go to a mixing box where it is blended to reach the desired temperature providing unmatched comfort control
High velocity system to reduce duct size (less space)

Question 25

What is an all-water system and what are the two types?

Answer 25

Pipes carry hot/cold water to fan coil units; take air from room, heat/cool, replace 2 pipe and 4 pipe

Question 26

What is a 2 pipe system?

Answer 26

One supply and one exit pipe; whole building is either in heating or cooling mode

Question 27

What is a 4 pipe system?

Answer 27

Two supply and two exit (one hot, one cold); more variance as each fan coil can either be in heating or cooling mode irrespective of the others

Question 28

What do all water systems require and why?

Answer 28

Separate ventilation systems to change air because air is not being changed (just heated/cooled and replaced)

Question 29

What are air-water systems?

Answer 29

Air gets heated/cooled at fan room and then further heated/cooled when mixing with room air by fan coil unit

Question 30

What are packaged systems?

Answer 30

Self-contained systems for smaller scale buildings (rooftop units) Split units - outside compressor and condenser, inside coils and fan

Question 31

What are 8 components in an HVAC system?

Answer 31

Chilled water plant (evaporator/chiller, compressor, condenser) Cooling tower Air handling unit (supply fan, air filters) Boiler Ducts Diffusers/registers Grills

Question 32

What do the components in the chilled water plant do?

Answer 32

Evaporator/chiller - liquid expands, cools, becomes vapour (Boyle's Law) and cools water for AHU Compressor - increases pressure Condenser - cool condensing water turns vapour to liquid (warms condensing water)

Question 33

What does the cooling tower do?

Answer 33

Warmed water from condenser sprayed through air where it cools and returns to the condenser

Question 34

What does the air handling unit do in cooling/heating mode?

Answer 34

``` Cooling mode: Unconditioned air (used/outside) enters --> filtered --> passes over cooling coil (with chilled water from evaporator) and condensation drained --> conditioned air (lower temp and humidity) ``` Heating mode: Unconditioned air --> filtered --> preheated --> passes over cooling coil (turned off) --> reheated --> conditioned air through ductwork --> humidifier sprays mist to add moisture if necessary

Question 35

What does the supply fan do and what are the two types?

Answer 35

Provides moderate air pressure to blow air through ductwork Serial (propeller) Centrifugal (offset and easier to access)

Question 36

What do air filters do and what are the three types?

Answer 36

Remove odours, irritants and pollutants Arrestance - gauze/mesh traps particles; needs regular changing and can reduce air flow when clogged Washing - incoming air sprayed so particles wash into collection tray; increases humidity and can cause bacteria Electrostatic - particles magnetically drawn out; most effective

Question 37

What does the boiler do?

Answer 37

Produces hot water/steam used in air handling unit

Question 38

What are ducts typically made of and the two classifications?

Answer 38

Sheet metal | Low-velocity or high-velocity (>10ms-1)

Question 39

What do diffusers and registers do?

Answer 39

Supply air to spaces; diffusers have angled slates to distribute in various directions and registers have a grill and blades so supply air can be controlled

Question 40

What are grills?

Answer 40

An opening for air to return to the system

Question 41

How can ductwork be placed?

Answer 41

Vertically (core, structure, edges) | Horizontally (circulation paths, structure edges, plenum)

Question 42

What is the plenum and how does HVAC work there?

Answer 42

Space between ceiling and above floor deck | No ductwork; air pressurises in plenum space and displaced through openings in the ceiling

Question 43

What is typical cooling capacity and size of boiler/chiller room, cooling tower and fan room for a 15,000m2 high-rise?

Answer 43

Cooling capacity - 450tons Boiler/chiller room - 300m2 Cooling tower - 60m2 Fan room - reaches max 25 floors

Question 44

What is heat flow measured in?

Answer 44

British Thermal Unit / hour or Watts