PE Exam Exam > PE Exam Notes > Mechanical Engineering for PE > Cheatsheet: HVAC Systems
Cheatsheet: HVAC Systems
1. Psychrometrics
1.1 Fundamental Properties
| Property | Definition & Formula |
|---|---|
| Dry Bulb Temperature (DBT) | Air temperature measured by standard thermometer, °F or °C |
| Wet Bulb Temperature (WBT) | Temperature measured with wet wick over thermometer bulb; measures evaporative cooling effect |
| Dew Point Temperature (DPT) | Temperature at which water vapor begins to condense at constant pressure |
| Humidity Ratio (W) | Mass of water vapor per mass of dry air, W = 0.622(Pv/(P - Pv)), lb water/lb dry air |
| Relative Humidity (φ) | φ = (Pv/Psat) × 100%, ratio of actual vapor pressure to saturation vapor pressure |
| Specific Volume (v) | Volume per unit mass of dry air, v = 0.754(T + 460)/P, ft³/lb dry air |
| Enthalpy (h) | h = 0.240T + W(1061 + 0.444T), Btu/lb dry air; T in °F |
1.2 Psychrometric Chart
- DBT lines: vertical lines
- WBT lines: diagonal lines sloping down from left to right
- Relative humidity curves: curved lines, 100% RH at saturation line
- Humidity ratio lines: horizontal lines
- Enthalpy lines: diagonal lines nearly parallel to WBT lines
- Specific volume lines: diagonal lines sloping down from right to left
- Standard sea level pressure: 14.696 psia (101.325 kPa)
1.3 Psychrometric Processes
| Process | Description |
|---|---|
| Sensible Heating | Horizontal line to right; increases DBT, constant W |
| Sensible Cooling | Horizontal line to left; decreases DBT, constant W |
| Humidification | Vertical line upward; increases W, constant DBT (adiabatic adds moisture and heat) |
| Dehumidification | Line toward saturation curve then along it; cooling below dew point removes moisture |
| Evaporative Cooling | Line along constant WBT toward saturation; decreases DBT, increases W |
| Heating & Humidifying | Diagonal line upward to right; increases DBT and W |
| Cooling & Dehumidifying | Line toward and along saturation curve; decreases DBT and W |
1.4 Key Calculations
| Parameter | Formula |
|---|---|
| Sensible Heat (qs) | qs = 1.08 × CFM × ΔT, Btu/hr; or qs = 60 × ṁ × cp × ΔT |
| Latent Heat (ql) | ql = 0.68 × CFM × ΔW, Btu/hr; or ql = 60 × ṁ × hfg × ΔW |
| Total Heat (qt) | qt = 4.5 × CFM × Δh, Btu/hr; or qt = qs + ql |
| Sensible Heat Ratio (SHR) | SHR = qs/qt |
| Mixing of Air Streams | Weighted average: T3 = (ṁ1×T1 + ṁ2×T2)/(ṁ1 + ṁ2); same for W, h |
2. HVAC Load Calculations
2.1 Cooling Load Components
| Component | Description |
|---|---|
| External Sensible | Solar radiation through windows, conduction through walls/roof/floors |
| Internal Sensible | People, lights, equipment, appliances |
| Latent Load | Moisture from people, infiltration, ventilation, equipment |
| Ventilation Load | Outdoor air for IAQ requirements (sensible + latent) |
2.2 Heat Transfer Formulas
| Type | Formula |
|---|---|
| Conduction | Q = U × A × ΔT, Btu/hr; U = overall heat transfer coefficient, Btu/(hr·ft²·°F) |
| Solar Heat Gain | Q = A × SHGC × SC × CLF, where SHGC = solar heat gain coefficient, SC = shading coefficient, CLF = cooling load factor |
| People Load (Sensible) | qs = N × qs,person × CLF, qs,person = 250 Btu/hr (seated, light work) |
| People Load (Latent) | ql = N × ql,person, ql,person = 200 Btu/hr (seated, light work) |
| Lighting Load | Q = 3.41 × W × Fut × Fsb × CLF, W in watts |
| Equipment Load | Q = 3.41 × W × Fload × Frad × CLF (electric); Q = Fu × Qinput (gas) |
| Infiltration | qs = 1.08 × CFM × ΔT; ql = 0.68 × CFM × ΔW |
2.3 Heating Load Components
- Conduction losses through building envelope: Q = U × A × ΔT
- Infiltration: qs = 1.08 × CFM × ΔT
- Ventilation outdoor air load
- Design temperature difference: indoor setpoint minus outdoor design temperature
- No solar gains or internal gains credited for heating load
2.4 Design Conditions
- Indoor design: 75°F DBT, 50% RH (cooling); 70°F (heating)
- Outdoor design: 0.4%, 1%, 2% ASHRAE design conditions for summer and winter
- Ventilation rates: ASHRAE 62.1 for commercial, 62.2 for residential
- Safety factor: 10-20% for equipment sizing
3. HVAC System Types
3.1 All-Air Systems
| System Type | Characteristics |
|---|---|
| Single Zone Constant Volume | One thermostat controls entire system; simple, low cost; suited for single space |
| Multi-Zone | Central unit with hot and cold decks; mixing dampers for each zone; limited to 12-15 zones |
| Variable Air Volume (VAV) | Varies airflow to maintain temperature; terminal boxes with dampers; energy efficient |
| Dual Duct | Separate hot and cold air ducts; mixing boxes at zones; high energy use, flexible |
| Reheat | Cool air to all zones, reheat coils for individual control; poor energy efficiency |
3.2 All-Water Systems
| System Type | Characteristics |
|---|---|
| Two-Pipe | One supply, one return; heating or cooling only at one time |
| Three-Pipe | Hot supply, cold supply, common return; simultaneous heating/cooling; energy waste in return |
| Four-Pipe | Separate hot/cold supply and return; most flexible, highest cost, best energy performance |
| Fan Coil Units | Individual room units with fan and coil; simple control, local maintenance |
3.3 Air-Water Systems
- Induction units: high-velocity primary air induces room air over coil
- Fan coil with supplementary air: central air plus local fan coils
- Radiant panels with ventilation air: water piping in ceiling/floor, separate ventilation
3.4 Refrigerant-Based Systems
| System Type | Characteristics |
|---|---|
| Split System | Outdoor condensing unit, indoor evaporator; residential and light commercial |
| Package Unit | All components in single cabinet; rooftop or ground-mounted |
| Variable Refrigerant Flow (VRF) | One outdoor unit, multiple indoor units; variable capacity compressor; heat recovery option |
| Heat Pump | Reversible refrigeration cycle; heating and cooling from one unit |
3.5 Dedicated Outdoor Air Systems (DOAS)
- Separate system handles ventilation air only
- Decouples ventilation from space conditioning
- Reduces latent load on primary system
- Energy recovery ventilator (ERV) transfers heat and moisture
- Heat recovery ventilator (HRV) transfers sensible heat only
4. Air Distribution
4.1 Duct Design Methods
| Method | Description |
|---|---|
| Equal Friction | Constant pressure drop per unit length throughout system; simplest method |
| Static Regain | Velocity reduction in downstream sections regains static pressure; self-balancing |
| Total Pressure | Optimizes total pressure at each section; most complex, best for long runs |
4.2 Duct Sizing Fundamentals
| Parameter | Formula/Value |
|---|---|
| Velocity (V) | V = Q/A, Q = volumetric flow (CFM), A = area (ft²), V in ft/min (FPM) |
| Pressure Drop | ΔP = f × (L/D) × (V²/2g) × (ρ/12), in. w.g.; simplified: ΔP = C × L, C = friction rate |
| Velocity Pressure (VP) | VP = (V/4005)², in. w.g.; V in FPM |
| Total Pressure (TP) | TP = SP + VP, SP = static pressure |
| Equivalent Diameter (De) | De = 1.30 × [(a × b)^0.625] / [(a + b)^0.25], rectangular duct, a and b in inches |
4.3 Recommended Duct Velocities
| Application | Main Ducts (FPM) |
|---|---|
| Residential | 700-900 |
| Commercial Low Velocity | 1000-1800 |
| Commercial High Velocity | 2000-3000 |
| Industrial | 1800-3000 |
4.4 Fitting Losses
- Local losses expressed as dynamic loss coefficient (C) or equivalent length (Leq)
- ΔP = C × VP, VP at fitting velocity
- Elbow losses: 90° smooth radius R/D = 1.5, C ≈ 0.2; square elbow C ≈ 1.2
- Branch takeoff: C = 0.1 to 0.5 depending on geometry
- Sudden expansion: C = (1 - A1/A2)²
- Sudden contraction: C = 0.5(1 - A2/A1)²
4.5 Air Distribution Devices
| Device | Application |
|---|---|
| Diffusers (Ceiling) | Supply air; circular, square, or linear; low velocity for comfort |
| Grilles | Return or exhaust air; fixed or adjustable vanes |
| Registers | Supply air; adjustable vanes for directional control |
| Slot Diffusers | Linear supply; architectural integration; perimeter heating |
4.6 Air Distribution Performance
- Throw: horizontal distance air travels at terminal velocity (50 FPM)
- Drop: vertical distance from outlet to 50 FPM
- ADPI (Air Diffusion Performance Index): percentage of points meeting comfort criteria; target >80%
- Induction ratio: ratio of total airflow in occupied zone to primary supply
5. Heating Systems
5.1 Boiler Types
| Type | Characteristics |
|---|---|
| Fire-Tube | Hot gases pass through tubes surrounded by water; lower pressure (<300 psig);="" smaller=""> |
| Water-Tube | Water flows through tubes heated externally; higher pressure (>300 psig); larger capacity |
| Condensing | Extracts latent heat from flue gas; efficiency >90%; requires corrosion-resistant materials |
| Non-Condensing | Standard efficiency 75-85%; flue gas above dew point |
5.2 Boiler Efficiency
| Term | Definition |
|---|---|
| Thermal Efficiency | η = Qout/Qin = (ṁ × cp × ΔT) / (ṁfuel × HHV) |
| Combustion Efficiency | Based on flue gas temperature and composition; 80-85% typical |
| Annual Fuel Utilization Efficiency (AFUE) | Accounts for cycling losses; seasonal average; residential rating |
5.3 Hydronic System Components
| Component | Function |
|---|---|
| Expansion Tank | Accommodates water volume change with temperature; diaphragm or compression type |
| Circulating Pump | Moves water through system; head (ft) = pressure drop; centrifugal type |
| Air Separator | Removes entrained air to prevent corrosion and noise |
| Pressure Relief Valve | Safety device; set at 30 psig for low-pressure systems |
| Mixing Valve | Blends supply and return water for temperature control |
5.4 Hydronic Piping Arrangements
| Type | Description |
|---|---|
| Series Loop | Single continuous pipe through all terminals; simplest, no individual control |
| One-Pipe | Supply main with diverting tees to terminals; poor balance |
| Two-Pipe Direct Return | Separate supply and return; first terminal has shortest circuit; balancing required |
| Two-Pipe Reverse Return | All circuits equal length; self-balancing; more piping |
| Primary-Secondary | Decouples production from distribution; separate pumps; allows variable flow |
5.5 Terminal Units
- Radiators: cast iron or steel; freestanding; convection and radiation heat transfer
- Baseboard: fin-tube convectors; installed along perimeter walls
- Unit heaters: fan and coil assembly; suspended or wall-mounted; high airflow
- Radiant panels: embedded piping in floor or ceiling; low temperature, high comfort
5.6 Furnace Types
| Type | Characteristics |
|---|---|
| Gas-Fired | Natural gas or propane; AFUE 80-97%; atmospheric or forced draft burner |
| Oil-Fired | Fuel oil atomization; AFUE 80-90%; pressure burner |
| Electric Resistance | 100% efficient at point of use; high operating cost; no combustion |
| Heat Pump | COP = 2-4; electric backup; economical in mild climates |
6. Cooling Systems
6.1 Refrigeration Cycle
| Process | Component & Description |
|---|---|
| 1-2: Compression | Compressor; isentropic compression of superheated vapor; work input |
| 2-3: Condensation | Condenser; rejects heat to cooling medium; high-pressure vapor to liquid |
| 3-4: Expansion | Expansion valve; isenthalpic throttling; pressure and temperature drop |
| 4-1: Evaporation | Evaporator; absorbs heat from space; low-pressure liquid to vapor |
6.2 Refrigeration Performance
| Term | Formula |
|---|---|
| Coefficient of Performance (COP) | COP = Qevap / Wcomp = (h1 - h4) / (h2 - h1) |
| Energy Efficiency Ratio (EER) | EER = Cooling capacity (Btu/hr) / Power input (W); steady-state rating |
| Seasonal Energy Efficiency Ratio (SEER) | Seasonal average cooling output / electrical input; accounts for cycling; minimum 13-14 for residential |
| Integrated Part Load Value (IPLV) | Weighted efficiency at 100%, 75%, 50%, 25% load; commercial chiller rating |
| Tons of Refrigeration | 1 ton = 12,000 Btu/hr = 3.517 kW |
6.3 Compressor Types
| Type | Characteristics |
|---|---|
| Reciprocating | Positive displacement; piston and cylinder; 5-200 tons; capacity control via cylinder unloading |
| Scroll | Positive displacement; two spiral scrolls; 1-20 tons; quiet, efficient, few moving parts |
| Screw | Positive displacement; twin helical rotors; 20-750 tons; continuous capacity modulation |
| Centrifugal | Dynamic; impeller imparts velocity; 100-10,000 tons; variable speed, efficient at full load |
6.4 Chiller Types
| Type | Description |
|---|---|
| Air-Cooled | Air-cooled condenser; no cooling tower; lower efficiency; less maintenance |
| Water-Cooled | Water-cooled condenser; requires cooling tower; higher efficiency; more maintenance |
| Evaporatively-Cooled | Spray water on condenser; intermediate efficiency; lower water use than cooling tower |
| Absorption | Heat-driven cycle; LiBr-H2O or NH3-H2O; COP 0.6-1.2; uses waste heat or gas |
6.5 Refrigerants
| Refrigerant | Characteristics |
|---|---|
| R-22 (HCFC) | Phased out; ODP = 0.055; residential and commercial legacy systems |
| R-410A (HFC) | Replacement for R-22; ODP = 0, GWP = 2088; higher pressure; not drop-in replacement |
| R-134a (HFC) | Automotive and chillers; ODP = 0, GWP = 1430; lower pressure |
| R-32 (HFC) | Lower GWP = 675; higher efficiency; mildly flammable (A2L) |
| R-717 (NH3) | Ammonia; natural refrigerant; ODP = 0, GWP = 0; toxic, industrial use |
| R-744 (CO2) | Natural refrigerant; ODP = 0, GWP = 1; transcritical cycle; high pressure |
6.6 Cooling Towers
| Type | Description |
|---|---|
| Induced Draft | Fan at top pulls air through; counterflow or crossflow; most common |
| Forced Draft | Fan at bottom pushes air through; lower height; higher recirculation risk |
| Natural Draft | Hyperbolic shape; no fan; very large; power plants |
| Open Circuit | Direct water-air contact; evaporative cooling; high efficiency |
| Closed Circuit | Coil separates process water from spray water; less evaporation; protects process fluid |
6.7 Cooling Tower Performance
- Approach: difference between cold water temperature and wet bulb temperature; 5-10°F
- Range: difference between hot and cold water temperature; 10-20°F
- Effectiveness: (Range) / (Range + Approach)
- Cycles of concentration: TDS ratio of blowdown to makeup; 3-5 cycles
- Makeup water = Evaporation + Blowdown + Drift
- Evaporation ≈ 0.001 × GPM × Range
7. Ventilation and Indoor Air Quality
7.1 Outdoor Air Requirements
| Space Type | CFM per Person |
|---|---|
| Office Space | 5 |
| Conference Room | 5 |
| Classroom | 10 |
| Retail | 7.5 |
| Restaurant Dining | 7.5 |
| Gymnasium | 20 |
7.2 Ventilation Standards
- ASHRAE 62.1: Ventilation for Acceptable Indoor Air Quality (commercial buildings)
- ASHRAE 62.2: Ventilation for Acceptable Indoor Air Quality (residential buildings)
- Ventilation Rate Procedure: prescriptive outdoor air rates based on occupancy and floor area
- Indoor Air Quality Procedure: performance-based; maintain contaminant concentrations below limits
- Zone outdoor air: Voz = Rp × Pz + Ra × Az, Rp = people outdoor air rate, Ra = area outdoor air rate
7.3 Indoor Air Contaminants
| Contaminant | Source & Control |
|---|---|
| CO2 | Occupant respiration; indicator of ventilation adequacy; <1000 ppm=""> |
| CO | Combustion; garage exhaust; <9 ppm="" 8-hr=""> |
| Particulate Matter | Outdoor air, activities; filtration MERV 8-13 |
| VOCs | Building materials, furnishings, cleaning; source control, ventilation |
| Radon | Soil gas; sub-slab depressurization; <4> |
| Biological | Moisture, HVAC systems; humidity control <60% rh,=""> |
7.4 Air Filtration
| MERV Rating | Application |
|---|---|
| 1-4 | Residential; removes particles >10 μm |
| 5-8 | Commercial buildings; removes particles 3-10 μm |
| 9-12 | Superior commercial, hospital; removes particles 1-3 μm |
| 13-16 | Hospital, general surgery; removes particles 0.3-1 μm |
| 17-20 | HEPA; cleanrooms; removes particles <0.3 μm;="" 99.97%="" efficient="" at="" 0.3=""> |
7.5 Energy Recovery
| Device | Description |
|---|---|
| Heat Recovery Ventilator (HRV) | Sensible heat transfer only; air-to-air heat exchanger; heating climates |
| Energy Recovery Ventilator (ERV) | Sensible and latent heat transfer; enthalpy wheel or membrane; humid climates |
| Run-Around Loop | Coils in exhaust and outdoor air streams; pumped glycol loop; separated airstreams |
| Heat Pipe | Passive refrigerant transfer; no moving parts; limited capacity |
7.6 Economizer Operation
- Dry bulb economizer: compares outdoor and return air DBT; use outdoor air when cooler
- Enthalpy economizer: compares outdoor and return air enthalpy; more accurate in humid climates
- Differential enthalpy: outdoor air used when ho <>
- Lockout: high limit on outdoor air temperature or enthalpy; 75°F DBT or 28 Btu/lb enthalpy
- Integrated economizer: modulates cooling with mechanical refrigeration
8. HVAC Controls
8.1 Control System Types
| Type | Characteristics |
|---|---|
| Pneumatic | Compressed air 15-20 psig; reliable, simple; legacy systems |
| Electric | 24V AC or 120V AC; two-position or modulating; low cost |
| Electronic (Analog) | 0-10V DC or 4-20 mA signals; modulating control; accurate |
| Direct Digital Control (DDC) | Microprocessor-based; communication networks; complex sequences; remote monitoring |
8.2 Control Modes
| Mode | Description |
|---|---|
| On-Off (Two-Position) | Binary control; simple, low cost; temperature swings; residential thermostats |
| Proportional (P) | Output proportional to error; offset remains; throttling range (TR) = change in controlled variable for full actuator stroke |
| Proportional-Integral (PI) | Eliminates offset; integral time Ti; most common HVAC control |
| Proportional-Integral-Derivative (PID) | Adds derivative (rate) action; faster response; complex tuning; less common in HVAC |
8.3 Control Strategies
| Strategy | Description |
|---|---|
| Discharge Air Temperature Reset | Increase supply air temperature as load decreases; reduces reheat, improves efficiency |
| Static Pressure Reset | Reduce fan speed as VAV dampers open; saves fan energy |
| Chilled Water Temperature Reset | Increase CHW supply temperature at part load; improves chiller efficiency |
| Hot Water Temperature Reset | Outdoor air temperature reset; lower HW temperature in mild weather; reduces losses |
| Demand-Controlled Ventilation | Modulate outdoor air based on CO2 sensors; reduces ventilation energy at low occupancy |
| Optimal Start/Stop | Adaptive algorithm learns building thermal mass; starts equipment at latest time to meet setpoint |
| Night Setback | Raise cooling setpoint or lower heating setpoint during unoccupied periods |
8.4 Sensors and Actuators
| Device | Type & Application |
|---|---|
| Temperature Sensor | Thermistor, RTD, thermocouple; accuracy ±0.5-2°F |
| Humidity Sensor | Capacitive, resistive; accuracy ±3-5% RH |
| Pressure Sensor | Diaphragm, piezoelectric; static pressure, differential pressure |
| Flow Sensor | Differential pressure, thermal, ultrasonic; air or water flow measurement |
| CO2 Sensor | NDIR (non-dispersive infrared); demand-controlled ventilation; accuracy ±50 ppm |
| Control Valve | Two-way or three-way; modulating; hydronic systems; equal percentage or linear characteristic |
| Damper Actuator | Spring return or non-spring return; modulating or two-position; air systems |
| Variable Frequency Drive (VFD) | Modulates motor speed; fans and pumps; affinity laws apply |
8.5 Valve Authority
- Authority (N) = ΔPvalve / (ΔPvalve + ΔPsystem) at design flow
- Target N = 0.5 for good control; minimum N = 0.25
- Low authority causes poor control, nonlinear response
- Two-way valves: variable flow, simpler control
- Three-way valves: constant flow, mixing or diverting
9. Pumps and Fans
9.1 Pump Fundamentals
| Parameter | Formula |
|---|---|
| Head (H) | H = (P2 - P1) / (ρ × g) + z2 - z1 + hL, ft; P = pressure, z = elevation, hL = losses |
| Pump Power (Water) | BHP = (GPM × H × SG) / (3960 × ηp), BHP in hp; ηp = pump efficiency |
| System Curve | H = Hstatic + K × Q², K depends on pipe friction |
| Affinity Laws (Speed) | Q2/Q1 = N2/N1; H2/H1 = (N2/N1)²; P2/P1 = (N2/N1)³ |
| Affinity Laws (Impeller Diameter) | Q2/Q1 = D2/D1; H2/H1 = (D2/D1)²; P2/P1 = (D2/D1)³ |
| Net Positive Suction Head (NPSH) | NPSH available > NPSH required to prevent cavitation |
9.2 Pump Types
| Type | Characteristics |
|---|---|
| End Suction Centrifugal | Single inlet; horizontal or vertical; 10-5000 GPM; most common HVAC pump |
| Inline Centrifugal | Suction and discharge in line; space-saving; 10-1000 GPM |
| Split Case | Horizontal split casing; double suction; 500-10,000 GPM; high efficiency, low NPSH |
| Vertical Turbine | Multistage; sump or tank mounting; high head applications |
9.3 Fan Fundamentals
| Parameter | Formula |
|---|---|
| Fan Total Pressure (FTP) | FTP = TP_discharge - TP_inlet, in. w.g. |
| Fan Static Pressure (FSP) | FSP = FTP - VP_discharge |
| Fan Power | BHP = (CFM × FTP) / (6356 × ηf), BHP in hp; ηf = fan efficiency |
| Affinity Laws (Speed) | Q2/Q1 = N2/N1; P2/P1 = (N2/N1)²; BHP2/BHP1 = (N2/N1)³ |
| Affinity Laws (Density) | Q2/Q1 = 1; P2/P1 = ρ2/ρ1; BHP2/BHP1 = ρ2/ρ1 |
9.4 Fan Types
| Type | Characteristics |
|---|---|
| Forward Curved Centrifugal | Low speed, quiet; low efficiency 60-65%; space constraints; overloading power curve |
| Backward Inclined Centrifugal | High efficiency 75-80%; non-overloading; general HVAC; moderate noise |
| Airfoil Centrifugal | Highest efficiency 80-85%; low noise; premium cost; clean air only |
| Radial Blade Centrifugal | Material handling; erosion resistant; low efficiency; industrial |
| Vane Axial | Guide vanes; medium efficiency 65-75%; high pressure; compact |
| Tube Axial | Propeller in cylinder; efficiency 60-70%; low-medium pressure; inline installation |
| Propeller | No housing; low pressure; high volume; exhaust applications |
9.5 Variable Flow Systems
- VFD control: most efficient; soft start; affinity laws apply
- Inlet vanes: less efficient than VFD; quick response; no harmonics
- Discharge dampers: least efficient; simple; emergency use only
- Minimum flow required: 30-50% design flow for VAV systems
- Pump: minimum flow to prevent overheating; bypass valve if needed
- Energy savings proportional to cube of speed reduction
9.6 System Effect
- Poor inlet conditions: elbows, obstructions within 2-3 duct diameters of fan inlet reduce performance
- Blast area: insufficient discharge duct causes recirculation, reduces capacity
- System effect factor added to calculated system pressure drop: 0.1-0.5 in. w.g.
- Proper installation: straight inlet run, uniform velocity profile, turning vanes in elbows
10. Energy Efficiency and Codes
10.1 Energy Codes and Standards
| Standard | Scope |
|---|---|
| ASHRAE 90.1 | Energy Standard for Buildings Except Low-Rise Residential; prescriptive and performance paths |
| IECC | International Energy Conservation Code; adopted by most states; residential and commercial |
| Title 24 (California) | State energy code; stricter than ASHRAE 90.1; mandatory compliance |
| ASHRAE 189.1 | Standard for High-Performance Green Buildings; voluntary; beyond 90.1 |
10.2 ASHRAE 90.1 Requirements
- Envelope: insulation R-values, fenestration U-factor and SHGC by climate zone
- HVAC efficiency: minimum EER, COP, AFUE, IEER for equipment
- Economizers: mandatory in most climate zones for systems >54,000 Btu/hr cooling
- Ventilation: comply with ASHRAE 62.1; energy recovery for >40% outdoor air
- Controls: automatic shutoff, setback, zone control, demand-controlled ventilation
- Duct and pipe insulation: minimum R-values based on location and temperature
- Fan power limits: W/CFM based on system type and pressure class
10.3 Energy Modeling
| Method | Description |
|---|---|
| Simplified (Bin Method) | Weather data in temperature bins; steady-state calculations; quick estimates |
| Detailed Simulation | Hourly time-step; dynamic thermal response; EnergyPlus, eQUEST, TRACE; accurate predictions |
| Performance Rating Method | ASHRAE 90.1 Appendix G; proposed design vs. baseline; % better than code |
10.4 Energy Conservation Measures
| Measure | Typical Savings |
|---|---|
| Economizer | 10-30% cooling energy |
| VFD on Fans/Pumps | 30-50% fan/pump energy |
| Demand-Controlled Ventilation | 10-25% ventilation energy |
| Heat Recovery | 30-50% heating/cooling of ventilation air |
| High-Efficiency Equipment | 10-30% depending on baseline |
| Improved Controls | 5-15% overall HVAC energy |
| Duct Sealing | 10-30% distribution losses |
| Night Setback | 5-15% heating energy |
10.5 Fan Power Limitations (ASHRAE 90.1)
- System power: Pfan = CFMs × Ps + CFMr × Pr, CFMs = supply, CFMr = return/exhaust, Ps and Pr = fan power allowance
- Pressure budget: based on system type, filters, heat recovery, altitude
- Constant volume single zone: 0.5 W/CFM
- VAV: 0.6-1.3 W/CFM depending on complexity
- Credits: sound attenuation, MERV filters >13, exhaust systems
10.6 LEED and Green Building
- LEED: Leadership in Energy and Environmental Design; point-based rating system
- Energy & Atmosphere category: commissioning, energy performance, renewable energy, refrigerant management
- Minimum energy performance: 5% better than ASHRAE 90.1 baseline
- Optimize energy performance: up to 18 points for 50% improvement
- Enhanced commissioning: additional 6 points; Cx authority, systems manual, training
- Indoor Environmental Quality: increased ventilation, CO2 monitoring, thermal comfort, low-emitting materials
10.7 Commissioning
| Phase | Activities |
|---|---|
| Pre-Design | Owner's project requirements (OPR); basis of design (BOD) |
| Design | Review submittals; design intent verification; update BOD |
| Construction | Equipment verification; functional performance tests (FPT); issues log |
| Acceptance | Systems manual; operator training; final report |
| Warranty/Post-Occupancy | Seasonal testing; review operation; re-training |
The document Cheatsheet: HVAC Systems is a part of the PE Exam Course Mechanical Engineering for PE.
All you need of PE Exam at this link: PE Exam
About this Document
Apr 20, 2026
Last updated
Related Exams
Document Description: Cheatsheet: HVAC Systems for PE Exam 2026 is part of Mechanical Engineering for PE preparation.
The notes and questions for Cheatsheet: HVAC Systems have been prepared according to the PE Exam exam syllabus. Information about Cheatsheet: HVAC Systems covers topics
like and Cheatsheet: HVAC Systems Example, for PE Exam 2026 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Cheatsheet: HVAC Systems.
Introduction of Cheatsheet: HVAC Systems in English is available as part of our Mechanical Engineering for PE
for PE Exam & Cheatsheet: HVAC Systems in Hindi for Mechanical Engineering for PE course.
Download more important topics related with notes, lectures and mock test series for PE Exam
Exam by signing up for free. PE Exam: Cheatsheet: HVAC Systems
Description
Cheatsheet: HVAC Systems of Mechanical Engineering to help you remember important concepts with short tricks. Start learning for PE Exam exam & improve retention with EduRev.
Information about Cheatsheet: HVAC Systems
In this doc you can find the meaning of Cheatsheet: HVAC Systems defined & explained in the simplest way possible. Besides explaining types of
Cheatsheet: HVAC Systems theory, EduRev gives you an ample number of questions to practice Cheatsheet: HVAC Systems tests, examples and also practice PE Exam
tests
Related Searches
Cheatsheet: HVAC Systems, video lectures, Exam, ppt, Free, Sample Paper, pdf , study material, Summary, Cheatsheet: HVAC Systems, shortcuts and tricks, Viva Questions, practice quizzes, Extra Questions, Semester Notes, Previous Year Questions with Solutions, Objective type Questions, mock tests for examination, Important questions, Cheatsheet: HVAC Systems, MCQs, past year papers;