Air Conditioning and Air Handling Systems

Chapter Introduction

This chapter covers the fundamental principles of air conditioning and air handling systems as assessed on the Red Seal exam for the refrigeration and air conditioning mechanic trade. You must master not only thermodynamic cycles, but also duct sizing, heat load calculations, applied psychrometrics, and Canadian regulatory requirements. This chapter is structured to follow the logical progression of a system analysis: from heat load to equipment selection, then to air distribution and commissioning.

1. Fundamental Principles of Air Conditioning

1.1 Definition and Objectives of Air Conditioning

Air conditioning is the process of treating air to simultaneously control its temperature, humidity, cleanliness, and distribution, in order to maintain specific comfort conditions or process conditions. For the exam, remember that air conditioning is not limited to cooling: it encompasses heating, ventilation, filtration, humidification, and dehumidification.

The four fundamental psychrometric quantities you must know:

Quantity	Symbol	Unit	Definition
Dry-bulb temperature	DBT	°C	Temperature measured by an ordinary thermometer
Wet-bulb temperature	WBT	°C	Temperature measured by a thermometer whose bulb is wrapped in a wet wick
Relative humidity	RH	%	Ratio of the partial pressure of water vapor to the saturation pressure at the same temperature
Absolute humidity	ω	g/kg of dry air	Mass of water vapor per kilogram of dry air

1.2 Thermal Comfort

Thermal comfort is defined by ASHRAE Standard 55 as the state of mind that expresses satisfaction with the thermal environment. The factors influencing comfort are:

Dry-bulb temperature (recommended: 22 to 26 °C in summer)

Relative humidity (recommended: 30 to 60 %)

Air velocity (recommended: 0.15 to 0.25 m/s in occupied zones)

Mean radiant temperature of surfaces

Metabolic activity level (in met)

Clothing insulation (in clo)

For the exam, remember the typical summer comfort zone: 24 °C ± 2 °C and 50 % RH ± 10 %. In winter, the recommended temperature is 21 °C ± 2 °C.

1.3 The Air Conditioning Cycle — Thermodynamic Review

The mechanical refrigeration cycle used in air conditioning is the vapor compression cycle. The four main components are:

21.The compressor: draws in low-pressure vapor and compresses it to high pressure

22.The condenser: rejects heat from the refrigerant to the outdoors

23.The expansion device (TXV or capillary tube): lowers the pressure and temperature of the refrigerant

24.The evaporator: absorbs heat from the air or water being cooled

In a direct expansion (DX) air conditioning system, the evaporator is placed directly in the air handling unit. In a chilled water system, the evaporator cools water (typically to 6.7 °C) which then circulates to the coils of air handling units.

Sensible heat calculation for an air flow rate:

Q sensible = 1.23 × flow rate (L/s) × ΔT (K)

Where 1.23 is the product of air density (1.2 kg/m³) and specific heat (1.026 kJ/kg·K), converted for flow rate units in L/s. This factor must be memorized.

Latent heat calculation:

Q latent = 3.0 × flow rate (L/s) × Δω (g/kg)

Where 3.0 is the latent heat of vaporization factor for water at room temperature (≈ 2500 kJ/kg) converted.

2. Applied Psychrometrics

2.1 The Psychrometric Chart

The psychrometric chart is the essential graphical tool for the air conditioning mechanic. It represents the thermodynamic properties of moist air at a given atmospheric pressure (typically 101.325 kPa at sea level). The main lines:

Dry-bulb temperature lines (vertical)

Wet-bulb temperature lines (diagonal, descending)

Relative humidity lines (curved)

Humidity ratio lines (horizontal)

Specific volume lines (diagonal)

Enthalpy lines (diagonal, parallel to WBT lines)

2.2 Fundamental Psychrometric Processes

Process	Line on the Chart	Application
Sensible heating	Horizontal to the right	Heating coil
Sensible cooling	Horizontal to the left	Cooling coil (dry air)
Adiabatic humidification	Constant enthalpy line	Air washer, steam humidifier
Dehumidification by cooling	Curve downward and to the left	Cold coil with condensation
Mixing of two air streams	Straight line between the two points	Return air/outdoor air mixing

Dew point: the temperature at which air becomes saturated (RH = 100 %) if cooled at constant pressure. It is the coil surface temperature below which condensation will occur.

Sensible Heat Factor (SHF):

SHF = Q sensible / (Q sensible + Q latent)

An SHF of 0.75 means that 75 % of the total heat load is sensible. This factor determines the slope of the condition line (or sensible heat factor line) on the psychrometric chart, which connects the return air point to the supply air point.

2.3 Typical Psychrometric Calculations for the Exam

Example 1 — Air Mixing:

You mix 600 L/s of return air at 24 °C DBT, 50 % RH with 200 L/s of outdoor air at 32 °C DBT, 60 % RH. The mixture temperature is:

DBT mixture = (600 × 24 + 200 × 32) / (600 + 200) = (14,400 + 6,400) / 800 = 26 °C

Example 2 — Dehumidification:

A coil cools 1,000 L/s of air from 26 °C DBT, 21 °C WBT to 12 °C DBT, 11 °C WBT. The amount of condensed water is:

Δω = ω₁ − ω₂ = 13.5 g/kg − 8.0 g/kg = 5.5 g/kg

Mass flow rate of air = 1,000 L/s × 1.2 kg/m³ / 1,000 = 1.2 kg/s

Condensed water = 1.2 kg/s × 5.5 g/kg = 6.6 g/s = 23.8 kg/h

Common trap: do not confuse the 1.23 factor (sensible heat) with the 3.0 factor (latent heat). Always check the units of the air flow rate.

3. Heat Load Calculations

3.1 Calculation Methodology

Heat load calculations follow the method from the ASHRAE Handbook — Fundamentals (RTS — Radiant Time Series method for cooling loads). For the exam, you must know the components of the load:

External sensible loads:

Solar gains through glazing (function of orientation, glazing type, shading)

Transmission through opaque walls (walls, roof): Q = U × A × ΔT equivalent

Outdoor air infiltration

Ventilation (required outdoor air)

Internal sensible loads:

Occupants: approximately 75 W sensible per person (sedentary activity)

Lighting: installed power × utilization factor × diversity factor

Electrical equipment and motors

Cooking appliances and processes

Latent loads:

Occupants: approximately 55 W latent per person (sedentary activity)

Infiltration and ventilation (humidity difference)

Processes producing water vapor

3.2 Typical Thermal Transmission Coefficients (U)

Element	Typical U value (W/m²·K)
Insulated exterior wall (R-20)	0.30
Insulated roof (R-30)	0.20
Double sealed glazing	2.8
Triple glazing with low-emissivity coating	1.6
Solid wood door	2.2

Golden rule: the lower the U value, the better the insulation. Thermal resistance R = 1/U.

3.3 Ventilation and Indoor Air Quality

Standard ASHRAE 62.1 (Ventilation for Acceptable Indoor Air Quality) is the reference. For commercial buildings, the required outdoor air flow rate is calculated using the zone ventilation method:

Vbz = Rp × Pz + Ra × Az

Where:

Rp = air flow rate per person (L/s·person)

Pz = number of people in the zone

Ra = air flow rate per unit area (L/s·m²)

Az = zone area (m²)

Typical values for an office: Rp = 2.5 L/s·person, Ra = 0.3 L/s·m².

Minimum requirement: the National Building Code of Canada (NBC) requires a minimum of 8 L/s per person for spaces where occupants are sedentary, or 0.35 air changes per hour, whichever is greater.

4. Air Handling Systems

4.1 System Classification

System Type	Distribution Fluid	Advantages	Disadvantages
All-air (constant volume)	Air	Good humidity control, centralized maintenance	Large ductwork
All-air (variable volume — VAV)	Air	Energy savings, individual control	Risk of stratification, need for reheat
Air-water (fan coils)	Air + water	Reduced ductwork, local control	Possible condensation, multiple maintenance points
All-water (fan coils)	Water	Very compact	No mechanical ventilation, freeze risk
Direct expansion (DX)	Refrigerant	Efficient, compact	Limited line lengths, limited humidity control

4.2 The Air Handling Unit (AHU)

The air handling unit is the heart of the system. Its components, in air flow order:

97.Mixing section: outdoor air, return air, and exhaust air dampers

98.Filters: pre-filters (MERV 8) and final filters (MERV 13 or higher)

99.Cooling coil: chilled water or direct expansion

100.Heating coil: hot water, electric, or steam

101.Humidifier: steam, evaporative, or atomizing

102.Supply fan: centrifugal or axial

103.Silencer sections and acoustic attenuation

Exam trap: the order of components is crucial. The cooling coil must be placed before the heating coil and after the filters. The humidifier is generally placed after the coils.

4.3 Fans

The two main families of fans:

Centrifugal fans:

Forward-curved blades: high flow rate, moderate static pressure, low efficiency

Backward-curved blades: high efficiency, high static pressure, non-overloading

Radial blades: for high-pressure applications and abrasive materials

Axial fans:

Propeller: low pressure, high flow rate

Tubular: medium pressure

Variable pitch: for large flow rates at variable pressure

Fan Laws (at constant density):

Flow rate Q ∝ rotational speed N

Pressure P ∝ N²

Power W ∝ N³

Example: If the rotational speed increases by 10 %, the flow rate increases by 10 %, the pressure increases by 21 % (1.1² = 1.21), and the power increases by 33 % (1.1³ = 1.331). This is a classic exam trap.

4.4 Air Ducts

Sizing methods:

122.Constant velocity method: you set a maximum velocity in each section (e.g., 5 m/s in the main duct, 3 m/s in branches). Simple but can unbalance the system.

123.Constant pressure loss method (or constant friction method): ducts are sized to maintain a constant pressure loss per metre (typically 0.8 Pa/m). This is the most commonly used method.

124.Static regain method: ducts are sized so that static pressure is the same at each outlet. More accurate but more complex.

Pressure loss in ducts:

ΔP = f × (L/D) × (ρ × V² / 2)

Where f is the friction factor (dependent on Reynolds number and roughness), L the length, D the hydraulic diameter, ρ the density, and V the velocity.

Equivalent diameter for a rectangular duct:

De = 1.30 × [(a × b)⁵ / (a + b)²]^(1/8)

Where a and b are the dimensions of the rectangular duct in mm. This formula is used to use the pressure loss charts for circular ducts.

Recommended duct velocities:

Application	Main duct (m/s)	Branch (m/s)
Residential	3 to 4	2 to 3
Commercial (quiet)	5 to 6	3 to 4
Commercial (standard)	7 to 9	5 to 6
Industrial	10 to 13	7 to 10

5. Air Conditioning Equipment

5.1 Chilled Water Chillers

Chilled water chillers produce cold water (typically at 6.7 °C) to supply the coils of AHUs and fan coils. Two main types:

Air-cooled chillers:

Condenser cooled by ambient air

Installed outdoors

Lower energy efficiency (typical EER of 9 to 11)

No cooling tower required

Water-cooled chillers:

Condenser cooled by water from a cooling tower

Installed indoors

Higher efficiency (typical EER of 12 to 16)

Requires a cooling tower and pump

Coefficient of Performance (COP):

COP = Cooling capacity (kW) / Power input (kW)

EER (Energy Efficiency Ratio) = COP × 3.412 (in BTU/h per watt)

Exam trap: COP is dimensionless (kW/kW), while EER is in BTU/(h·W). Never confuse them.

5.2 Cooling Towers

The cooling tower rejects condenser heat to the atmosphere through evaporation. Types:

Natural draft: large chimney, air flow by natural convection

Mechanical draft: axial or centrifugal fan (most common)

Cross-flow: air flows horizontally through the falling water

Counter-flow: air rises vertically against the downward-flowing water

Operating parameters:

Approach: difference between the leaving cold water temperature and the ambient wet-bulb temperature (typically 3 to 5 °C)

Range: difference between the entering hot water temperature and the leaving cold water temperature (typically 5 to 10 °C)

Example: Outdoor air at 28 °C DBT, 22 °C WBT. A tower with an approach of 4 °C will produce water at 26 °C. If the range is 6 °C, the hot water will enter at 32 °C.

Freeze consideration: in northern climates, cooling towers must be protected against freezing. Measures include: water bypass, basin heating, fan speed control, and automatic drain.

5.3 Evaporative Condensers

The evaporative condenser combines the condenser and cooling tower into a single unit. The refrigerant circulates directly through coils that are sprayed with water and swept by air. The evaporated water absorbs heat from the refrigerant. Advantages: compactness, high efficiency. Disadvantages: water quality maintenance, corrosion risk.

5.4 Rooftop Units (RTU)

Rooftop units (RTUs) are self-contained systems installed on the roof, containing the compressor, condenser, evaporator, fans, and filters in a single enclosure. They are factory-fabricated and only require electrical connection and ductwork. Typical capacities: from 3 to 100 tons of refrigeration.

1 ton of refrigeration = 12,000 BTU/h = 3.517 kW

6. Control and Regulation

6.1 Control Strategies

Temperature control in a chilled water system is achieved by:

172.Chilled water valve control: the valve modulates the water flow through the coil based on the supply air temperature or zone temperature

173.Bypass damper control: a portion of the air bypasses the coil

174.Fan speed variation control: for VAV systems

Typical AHU control sequence:

Heating: hot water valve modulates from 0 to 100 %

Cooling: chilled water valve modulates from 0 to 100 %

The two never operate simultaneously (except during dehumidification)

6.2 Sensors

Sensor	Measurement	Typical Accuracy
Thermistor	Temperature	± 0.2 °C
RTD (Pt100)	Temperature	± 0.1 °C
Capacitive humidity sensor	Relative humidity	± 2 %
Differential pressure sensor	Pressure	± 0.5 % of scale
Hot wire anemometer	Air velocity	± 2 %

6.3 Free Cooling Sequence

Free cooling (economizer) uses outdoor air to cool the building when its temperature is lower than the return air temperature. Two strategies:

Dry-bulb economizer: compares outdoor DBT to a threshold (e.g., 18 °C)

Enthalpy economizer: compares the enthalpy of outdoor air to that of return air

The enthalpy economizer is more accurate because it accounts for humidity. The National Energy Code of Canada for Buildings (NECB) requires economizers on systems over 35 kW (10 tons) in most Canadian climates.

7. Commissioning and Troubleshooting

7.1 Commissioning Procedure

Commissioning is the process of verifying that all systems operate in accordance with specifications. Steps:

190.Pre-verification: visual inspection, verification of electrical and mechanical connections

191.Operational tests: start-up of each piece of equipment individually

192.Air balancing (TAB — Testing, Adjusting and Balancing): measurement of air flow rates at each diffuser and damper

193.Water balancing: measurement of water flow rates in each coil

194.Control adjustment: sensor calibration, verification of sequences

195.Performance measurements: verification of temperatures, pressures, humidities

196.Documentation: commissioning report, operation manuals

7.2 Common Troubleshooting

Symptom: insufficient air flow

Dirty filters (excessive pressure drop)

Loose or worn fan belt

Obstructed ducts or closed dampers

Incorrect fan speed

System static pressure too high

Symptom: supply air temperature too high

Insufficient refrigerant charge (undercharge)

Chilled water valve stuck or faulty

Chilled water too warm (undersized chiller)

Dirty or frozen coil

Symptom: excessive humidity

Undersized cooling coil

Chilled water temperature too high

Air flow rate too high through the coil

System SHF too high relative to the load

7.3 Heat Balances

Cooling coil balance:

Q total = Q sensible + Q latent

Q total = mass flow rate of air × (h₁ − h₂)

Where h₁ and h₂ are the enthalpies of the air entering and leaving the coil.

Condenser balance:

Q condenser = Q evaporator + W compressor

This relationship is fundamental. If the compressor consumes 10 kW and the evaporator absorbs 40 kW, the condenser must reject 50 kW.

8. Applicable Canadian Codes and Standards

8.1 The Canadian Electrical Code (CE Code)

The Canadian Electrical Code, Part I (C22.1) applies to all electrical installations. Key points for air conditioning systems:

Rule 8-200: calculation of electrical demand for motors — the demand is based on the highest rated power plus 25 % of the largest motor added to the sum of the other motors

Rule 26-250: motor overload protection — the protective device must be set at 125 % of the full-load current for continuous duty motors

Rule 26-252: short-circuit protection — the fuse or circuit breaker must be sized according to Table 29 of the CE Code

Exam trap: the CE Code requires an accessible disconnecting means within 3 m of the equipment for motors and air conditioning appliances (Rule 28-600).

8.2 The National Building Code of Canada (NBC)

The NBC (National Building Code of Canada) contains ventilation, fire safety, and energy efficiency requirements. Relevant sections:

Section 3.2: fire safety — ducts must be made of non-combustible materials in high-rise buildings

Section 6.2: ventilation — minimum outdoor air flow requirements

Section 9.32: ventilation of small buildings

8.3 The National Energy Code of Canada for Buildings (NECB)

The NECB (National Energy Code of Canada for Buildings) imposes energy efficiency requirements:

Minimum chiller efficiency based on capacity (minimum COP)

Economizer requirement for systems over 35 kW

Duct and pipe insulation

Lighting control and heat recovery

8.4 CSA Standard B52

Standard CSA B52 (Mechanical Refrigeration Code) governs the installation of refrigeration systems. Key points:

Refrigerant classification based on toxicity and flammability (Groups A1, A2, A3, B1, etc.)

Refrigerant charge limits based on occupancy classification

Ventilation requirements for machinery rooms

Mandatory safety devices (pressure switches, relief valves, etc.)

8.5 CSA Standard B149.1

Standard CSA B149.1 (Natural Gas and Propane Installation Code) applies to gas-fired heating systems that are part of air handling. Key points:

Article 5.4: ventilation of gas appliances — appliances must have adequate combustion air supply

Article 8.2: venting of combustion products

Minimum clearance requirements around appliances

9. Energy Efficiency and Sustainability

9.1 Performance Indicators

Indicator	Definition	Application
EER	BTU/h of cooling per watt consumed	DX units
COP	kW of cooling per kW consumed	Chillers, heat pumps
IPLV	Integrated Part Load Value — weighted efficiency at part load	Chillers
kW/ton	Power consumed per ton of refrigeration	Quick comparison
SCOP	Seasonal COP — seasonal efficiency	Heat pumps

Typical values for the exam:

Air-cooled chiller: COP of 2.8 to 3.2

Water-cooled chiller: COP of 4.5 to 6.5

Residential DX unit: SEER of 13 to 22

Geothermal heat pump: COP of 3.5 to 5.0

9.2 Heat Recovery

Heat recovery systems transfer energy from exhaust air to incoming outdoor air. Types:

Thermal wheel (enthalpy wheel): transfers heat and humidity, efficiency of 60 to 80 %

Plate heat exchanger: transfers sensible heat only, efficiency of 50 to 70 %

Heat pipe: passive transfer through phase change, efficiency of 40 to 60 %

Run-around loop (glycol loop): flexible, efficiency of 40 to 50 %

Heat exchanger efficiency calculation:

ε = (T outdoor outlet − T outdoor inlet) / (T exhaust inlet − T outdoor inlet) × 100 %

Example: Outdoor air at −10 °C, exhaust air at 22 °C. The outdoor air leaves at 12 °C. Efficiency = (12 − (−10)) / (22 − (−10)) × 100 % = 22 / 32 × 100 % = 68.75 %.

10. Safety and Environment

10.1 Refrigerants and the Environment

Refrigerants are classified according to their GWP (Global Warming Potential) and ODP (Ozone Depletion Potential):

Refrigerant	Type	GWP (100 years)	ODP	Status
R-22	HCFC	1,810	0.055	Phase-out
R-410A	HFC	2,088	0	In transition
R-134a	HFC	1,430	0	In transition
R-32	HFC	675	0	Accepted
R-454B	HFO	466	0	New
R-290 (propane)	HC	3	0	Flammable A3
R-717 (ammonia)	Natural	0	0	Toxic B2

The Ozone-depleting Substances and Halocarbon Alternatives Regulations (Government of Canada) requires:

Mandatory technician certification (Section 3 exam of the Regulations)

Record keeping of refrigerant quantities used

Mandatory recovery before opening any circuit

Prohibition of intentional refrigerant release

10.2 Risks Related to Air Handling Systems

Legionnaires' disease: cooling towers and humidifiers can promote the growth of Legionella bacteria. Maintenance: chemical water treatment, regular cleaning, water temperature control (maintain < 20 °C or > 60 °C)

Indoor air quality: adequate filtration, humidity control (avoid > 60 % RH to prevent mold)

Mechanical safety: guards on pulleys and belts, lockout/tagout before intervention

Electrical safety: compliance with the CE Code, grounding verification, use of personal protective equipment

10.3 Lockout/Tagout

Lockout/tagout is mandatory before any intervention on an air conditioning system. Procedure:

287.Identify all energy sources (electrical, mechanical, pneumatic, hydraulic)

288.Notify affected persons

289.Shut down the equipment

290.Isolate all energy sources

291.Apply locks and tags

292.Dissipate residual energy (capacitors, springs, pressure)

293.Verify absence of voltage with a voltmeter

294.Perform the intervention

295.Remove locks and return to service

Traps to Avoid

298.Confusing the 1.23 and 3.0 factors in load calculations — the first is for sensible heat, the second for latent heat

299.Forgetting that COP is dimensionless while EER is in BTU/(h·W)

300.Applying fan laws without checking air density — the laws only apply at constant density

301.Confusing wet-bulb temperature and dew point — WBT is always greater than or equal to the dew point

302.Neglecting the latent load of occupants — it represents approximately 40 % of the total occupant load

303.Placing the humidifier before the cooling coil — the correct order is: filters → cooling coil → heating coil → humidifier → fan

304.Sizing a duct with the constant velocity method without checking pressure losses — this can create imbalances

305.Forgetting the diversity factor in electrical load calculations — not all equipment operates simultaneously

306.Confusing the requirements of the CE Code and the NBC — the CE Code deals with electricity, the NBC with construction

307.Not checking refrigerant and oil compatibility — R-410A requires POE oil, not mineral oil

308.Ignoring external static pressure when selecting a fan — it must include ducts, coils, filters, and diffusers

309.Calculating air mixing with wet-bulb temperatures instead of dry-bulb temperatures — mixing is done on DBT and absolute humidity, not WBT

Summary

This chapter has presented the essential knowledge to pass the "Air Conditioning and Air Handling Systems" section of the Red Seal exam. Here are the key points to remember:

313.Psychrometrics: master the psychrometric chart, the four fundamental processes (heating, cooling, humidification, dehumidification) and the calculation factors 1.23 and 3.0.

314.Heat loads: know the sensible and latent components, internal and external, and the calculation method according to ASHRAE.

315.Systems: distinguish all-air, air-water, all-water, and DX systems, and know the advantages and disadvantages of each.

316.Fans: correctly apply the fan laws (Q ∝ N, P ∝ N², W ∝ N³) and select the appropriate type.

317.Ducts: use the constant friction method for sizing and check recommended velocities.

318.Equipment: know chillers, cooling towers, evaporative condensers, and rooftop units, as well as their operating parameters (approach, range).

319.Control: understand control sequences, sensors, and economizer strategies.

320.Codes: the CE Code (Rules 8-200, 26-250, 28-600), the NBC (Section 6.2), the NECB, CSA B52, and CSA B149.1 are the key regulatory references.

321.Energy efficiency: know how to calculate and interpret COP, EER, IPLV, and kW/ton.

322.Safety: lockout/tagout, refrigerant management, and Legionella prevention are professional responsibilities.

For the exam, practice solving air mixing problems, coil heat balance calculations, and duct sizing. Speed and accuracy in these calculations make the difference between a passing grade and an excellent one.

Air Conditioning and Air Handling Systems