Registered Public Utility Engineer - HVAC (China) cheat sheet

Design indoor conditions per GB 50736: winter heating 18–24 °C, summer cooling 24–28 °C, relative humidity 40–70 % (cooling) and 30–60 % (heating); design fresh-air rate per person depends on occupancy category.

Sensible heat equation: Q_s = 1.2 × L × Δt (W), with L in m³/s and 1.2 the volumetric heat capacity of moist air in kJ/(m³·K); latent heat Q_l = 2500 × 1.2 × L × Δd (W) with Δd in kg/kg.

Conduction load: Q = K·F·Δt, with K the overall heat-transfer coefficient in W/(m²·K); add solar correction factors for orientation and shading on external walls and roofs.

Sol-air temperature t_sa = t_out + ρ·I/α − ε·ΔR/α; for horizontal surfaces summer design uses the peak solar intensity at local solar time, not the peak air temperature.

Internal gains: occupants (sensible ~ 60–75 W/person light work, latent ~ 60–110 W), lighting (W/m² × area × 1.0), equipment; diversity factors applied to non-coincident loads.

Air infiltration and exfiltration: L = a·l·(Δp)^(2/3) for cracks (a, l empirical), or use the air-change method L = n·V/3600; stack and wind pressure combine as Δp = Δp_wind + Δp_stack.

Coil load = room sensible + room latent + fresh-air sensible + fresh-air latent + duct/fan gains; fan heat enters the airstream when the fan is downstream of the coil.

Sizing margin: total cooling capacity typically 1.05–1.15 × calculated block load; do not oversize because part-load humidity control degrades (low sensible heat ratio).

Design outdoor heating temperature: the winter dry-bulb value with 50 % cumulative frequency (not the extreme minimum); indoor design temperature 18–24 °C per GB 50736.

Hot-water supply/return design temperatures: 95/70 °C for conventional radiator systems, 85/60 °C or 75/50 °C for energy-efficient designs; low-temperature floor heating uses ≤ 60 °C supply with Δt ≤ 10 K.

Radiator output correction: Q = Q_std × (ΔT_m/ΔT_std)^n, where ΔT_m is the mean water-to-air temperature difference and n ≈ 1.3 for radiators; correction factors for flow rate and connection scheme apply.

Hydronic pipe sizing: velocity limits 0.25–1.0 m/s for small-diameter branches, ≤ 1.5 m/s for mains; friction per unit length typically 60–120 Pa/m to limit pump head.

Pump head = friction losses + local losses + static height difference + terminal pressure; for closed loops the static height cancels and only friction and terminal drop remain.

Expansion tank volume V_e = V_system × (v₂/v₁ − 1) × safety factor; pre-charge pressure set to static height plus 3–5 m water column.

Boiler efficiency: thermal efficiency = Q_absorbed/Q_fuel; condensing boilers achieve 95–108 % on higher heating value only with return water below the flue-gas dew point (~55–60 °C).

Two-pipe direct-return vs reverse-return: reverse-return equalizes path lengths so terminal flows stay near design without balancing valves; direct-return requires balancing valves on near terminals.

Minimum fresh air per person in offices: 30 m³/(h·person) per GB 50736; for high-density spaces use per-area values and check CO₂ concentration stays below 1000 ppm.

Natural ventilation driving pressure: Δp = h·(ρ_out − ρ_in)·g + 0.5·ρ·v²·C_p; effective opening area A_eff = A₁A₂/√(A₁²+A₂²) for two openings in series.

Mechanical exhaust hood capture velocity: 0.25–0.5 m/s for low-velocity enclosures, 0.5–1.0 m/s for side-draft slots; the required exhaust volume depends on hood geometry and distance from the source.

Duct friction: Δp = λ·(L/D_e)·(ρv²/2); rectangular duct equivalent diameter D_e = 2ab/(a+b) for equal friction; use the Darcy-Weisbach or the equal-friction chart method consistently.

Local exhaust duct velocity minimums: 10–12 m/s for dry dust, 14–18 m/s for metal dust, 18–23 m/s for moist or condensable contaminants to prevent deposition.

Stairwell pressurization: 25–30 Pa differential with all doors closed, ≥ 50 Pa across an open door to the fire floor; relief provisions must prevent door-opening force above 110 N.

Smoke exhaust in corridors: exhaust rate ≥ 60 m³/(h·m²) of floor area for corridors and 120 m³/(h·m²) for atria per GB 51251; make-up air at 50–80 % of exhaust volume.

Air cleaning for industrial exhaust: cyclone efficiency η = 1 − (particulate out)/(particulate in); fabric filters target 99 %+ for fine particulate and require pre-cooling below the bag temperature limit.

Refrigeration cycle COP = refrigerating effect / compressor work; Carnot COP_c = T_L/(T_H − T_L) in kelvin; real cycle COP is 40–60 % of Carnot for chillers.

Chiller efficiency metrics: kW/RT (1 RT = 3.517 kW); a 5.0 COP chiller equals 0.703 kW/RT; IPLV/NPLV weight part-load points (100 %, 75 %, 50 %, 25 %).

Air-side coil bypass factor BF = (t_out − t_ADP)/(t_in − t_ADP); contact factor CF = 1 − BF; number of rows and face velocity (typically 2.0–2.8 m/s) control BF.

Sensible heat ratio SHR = Q_s/(Q_s + Q_l); the coil apparatus dew point must lie below the room air dew point to remove latent load; low-load conditions raise SHR and risk high room humidity.

Air handling unit static pressure = filter + coil + duct + terminal + fan internal losses; fan power P = L·Δp/(3600·η_fan·η_transmission) with L in m³/h and Δp in Pa.

Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³; variable-speed drives give large part-load savings, but minimum speed is limited by motor cooling and duct static control.

Chilled-water design: supply 7 °C, return 12 °C for conventional coils; ΔT of 5 K is standard, low ΔT syndrome (ΔT < 3 K) indicates coil or valve problems and increases pump energy.

Refrigerant safety: A1 refrigerants (R410A, R134a) have low toxicity and no flame propagation; occupied-space concentration limit per GB 50736 and refrigerant charge limits per ASHRAE 15 principles.

Envelope thermal performance governed by GB 55015 (energy efficiency) and GB 50189 (public buildings): U-values for roofs, walls and windows vary by climate zone (severe cold, cold, hot summer/cold winter, hot summer/warm winter, mild).

Window-to-wall ratio limits: ≤ 0.70 for severe cold and cold zones, ≤ 0.60 for hot summer/cold winter, ≤ 0.40 for north-facing in cold zones; larger ratios require trade-off calculation.

Chiller part-load performance: centrifugal chillers must meet COP and IPLV thresholds in GB 19577; air-cooled units have lower thresholds than water-cooled.

Fan and pump specific power limits: GB 55015 sets maximum W_s per unit airflow (W/(m³/h)) and per unit water flow, encouraging high-efficiency motors and variable-speed drives.

Heat recovery: exhaust-air heat recovery required when fresh-air ratio is high and the climate zone warrants it; sensible effectiveness typically 50–70 %, enthalpy wheels 60–80 %.

Economizer (free cooling): allowed when outdoor air enthalpy or temperature is below the return-air value; air-side economizer with a changeover setpoint saves chiller energy in transitional seasons.

Lighting and plug-load power density caps: office lighting ≤ 9 W/m² (LPD), with automatic control requirements for large spaces; internal gains feed directly into cooling load.

Whole-building energy compliance uses the reference-building method: proposed design annual energy ≤ reference design; trade-offs among envelope, equipment and systems are permitted within the calculation.

PID control: output = K_p·e + K_i∫e dt + K_d·de/dt; proportional band PB = 100/K_p (%); integral time T_i and derivative time T_d set from process time constant and dead time.

Control valve authority β = Δp_valve/(Δp_valve + Δp_circuit); require β ≥ 0.3–0.5 for stable modulating control; equal-percentage valves suit coils with large turndown.

Sensor placement: temperature sensors ≥ 1.5 m above floor, away from direct sunlight and supply jets; averaging sensors across duct cross-sections for accurate mixed-air temperature.

Static pressure reset: duct static setpoint reset downward as VAV boxes open; supply fan controlled to keep the critical zone damper 80–90 % open, saving fan energy.

Commissioning sequence: pre-functional checks, functional performance tests, seasonal testing, and continuous commissioning; TAB (testing, adjusting, balancing) precedes functional tests.

Air balancing tolerance: supply airflow within ±10 % of design, room pressure differentials within ±5 Pa; duct leakage test pressure 1.5 × working pressure.

Chiller plant sequencing: stage chillers on leaving-water temperature and load; avoid short cycling with minimum run times and 10–15 min anti-recycle timers.

Fault detection: monitor approach temperatures (condenser and evaporator), superheat/subcooling, and chilled-water ΔT; rising condenser approach signals fouling and reduced efficiency.

Smoke control design basis: GB 51251 covers smoke exhaust and pressurization; design fire size for atria and large spaces typically 2.5–5 MW with steady burning, and smoke layer height kept above the safe egress height (≥ 2.0 m).

Pressurization systems: stairwell 25–30 Pa, elevator lobby 25–30 Pa, refuge floor 25–30 Pa relative to adjacent spaces; pressure relief dampers or barometric relief prevent overpressure.

Smoke exhaust rate for a corridor: 60 m³/(h·m²); for a room with fixed windows: 60 m³/(h·m²); for an atrium: 120 m³/(h·m²) or calculated by the plume/axisymmetric plume method.

Make-up air: 50 % of exhaust volume for natural make-up, 80 % for mechanical; make-up velocity at the fire floor ≤ 1.0 m/s to avoid disturbing the smoke layer.

Fire dampers required where ducts penetrate fire-rated walls and floors; smoke dampers at smoke compartment boundaries; combination dampers where both functions are needed.

Duct fire resistance: exhaust ducts in smoke control systems must maintain integrity at 280 °C for 30 min (or 1.0 h for certain occupancies); fans rated for 280 °C/30 min continuous operation.

Stair pressurization with open doors: the door-opening force must not exceed 110 N; check with the largest door open and the required pressure differential maintained.

Basement and windowless spaces: mechanical smoke exhaust required; smoke exhaust fans must be independent of normal ventilation and start automatically on fire signal.

Registered Public Utility Engineer (HVAC) practice scope: design, construction, supervision and consultation for heating, ventilation, air conditioning and smoke control systems within the licensed scope.

Stamp and seal: only the registered engineer may sign and seal design documents; signing documents not prepared or supervised by the engineer is a violation of the registration regulation.

Conflict of interest: disclose financial interests in suppliers or contractors; do not specify proprietary products without an approved equal clause unless justified by sole-source documentation.

Design liability: the designer is responsible for compliance with mandatory codes (GB 55015, GB 51251, GB 50736); deviations require formal review and approval by the authority.

Confidentiality: client data, drawings and reports are confidential; disclosure requires client consent except where required by law or safety.

Continuing education: registered engineers must complete the required continuing-education hours per registration cycle to maintain the license.

Ethical reporting: if a design or installation poses a public safety risk, the engineer must report to the responsible authority even if it conflicts with the employer's interest.

Record keeping: retain design calculations, load calculations, commissioning reports and as-built documentation for the period required by regulation to support audit and liability defense.

Design indoor conditions per GB 50736: winter heating 18–24 °C, summer cooling 24–28 °C, relative humidity 40–70 % (cooling) and 30–60 % (heating); fresh-air rate per person depends on occupancy category.

Sensible heat equation: Q_s = 1.2 × L × Δt (W), with L in m³/s and 1.2 the volumetric heat capacity of moist air in kJ/(m³·K); latent heat Q_l = 2500 × 1.2 × L × Δd (W) with Δd in kg/kg.

Conduction load: Q = K·F·Δt, with K the overall heat-transfer coefficient in W/(m²·K); add solar correction factors for orientation and shading on external walls and roofs.

Sol-air temperature t_sa = t_out + ρ·I/α − ε·ΔR/α; for horizontal surfaces summer design uses the peak solar intensity at local solar time, not the peak air temperature.

Internal gains: occupants (sensible ~60–75 W/person light work, latent ~60–110 W), lighting (W/m² × area), equipment; diversity factors applied to non-coincident loads.

Air infiltration: L = a·l·(Δp)^(2/3) for cracks, or the air-change method L = n·V/3600; stack and wind pressure combine as Δp = Δp_wind + Δp_stack.

Coil load = room sensible + room latent + fresh-air sensible + fresh-air latent + duct/fan gains; fan heat enters the airstream when the fan is downstream of the coil.

Sizing margin: total cooling capacity typically 1.05–1.15 × calculated block load; do not oversize because part-load humidity control degrades at low sensible heat ratio.

Design outdoor heating temperature: the winter dry-bulb value with 50 % cumulative frequency (not the extreme minimum); indoor design temperature 18–24 °C per GB 50736.

Hot-water supply/return design temperatures: 95/70 °C for conventional radiator systems, 85/60 °C or 75/50 °C for energy-efficient designs; low-temperature floor heating uses ≤60 °C supply with Δt ≤10 K.

Radiator output correction: Q = Q_std × (ΔT_m/ΔT_std)^n, where ΔT_m is the mean water-to-air temperature difference and n ≈ 1.3 for radiators; correction factors for flow rate and connection scheme apply.

Hydronic pipe sizing: velocity limits 0.25–1.0 m/s for small-diameter branches, ≤1.5 m/s for mains; friction per unit length typically 60–120 Pa/m to limit pump head.

Pump head = friction losses + local losses + static height difference + terminal pressure; for closed loops the static height cancels and only friction and terminal drop remain.

Expansion tank volume V_e = V_system × (v₂/v₁ − 1) × safety factor; pre-charge pressure set to static height plus 3–5 m water column.

Boiler efficiency: thermal efficiency = Q_absorbed/Q_fuel; condensing boilers achieve 95–108 % on higher heating value only with return water below the flue-gas dew point (~55–60 °C).

Two-pipe direct-return vs reverse-return: reverse-return equalizes path lengths so terminal flows stay near design without balancing valves; direct-return requires balancing valves on near terminals.

Minimum fresh air per person in offices: 30 m³/(h·person) per GB 50736; for high-density spaces use per-area values and check CO₂ concentration stays below 1000 ppm.

Natural ventilation driving pressure: Δp = h·(ρ_out − ρ_in)·g + 0.5·ρ·v²·C_p; effective opening area A_eff = A₁A₂/√(A₁²+A₂²) for two openings in series.

Mechanical exhaust hood capture velocity: 0.25–0.5 m/s for low-velocity enclosures, 0.5–1.0 m/s for side-draft slots; required exhaust volume depends on hood geometry and distance from the source.

Duct friction: Δp = λ·(L/D_e)·(ρv²/2); rectangular duct equivalent diameter D_e = 2ab/(a+b) for equal friction; use the Darcy-Weisbach or equal-friction chart method consistently.

Local exhaust duct velocity minimums: 10–12 m/s for dry dust, 14–18 m/s for metal dust, 18–23 m/s for moist or condensable contaminants to prevent deposition.

Stairwell pressurization: 25–30 Pa differential with all doors closed, ≥50 Pa across an open door to the fire floor; relief provisions must prevent door-opening force above 110 N.

Smoke exhaust in corridors: exhaust rate ≥60 m³/(h·m²) of floor area for corridors and 120 m³/(h·m²) for atria per GB 51251; make-up air at 50–80 % of exhaust volume.

Air cleaning for industrial exhaust: cyclone efficiency η = 1 − (particulate out)/(particulate in); fabric filters target 99 %+ for fine particulate and require pre-cooling below the bag temperature limit.

Refrigeration cycle COP = refrigerating effect / compressor work; Carnot COP_c = T_L/(T_H − T_L) in kelvin; real cycle COP is 40–60 % of Carnot for chillers.

Chiller efficiency metrics: kW/RT (1 RT = 3.517 kW); a 5.0 COP chiller equals 0.703 kW/RT; IPLV/NPLV weight part-load points (100 %, 75 %, 50 %, 25 %).

Air-side coil bypass factor BF = (t_out − t_ADP)/(t_in − t_ADP); contact factor CF = 1 − BF; number of rows and face velocity (typically 2.0–2.8 m/s) control BF.

Sensible heat ratio SHR = Q_s/(Q_s + Q_l); the coil apparatus dew point must lie below the room air dew point to remove latent load; low-load conditions raise SHR and risk high room humidity.

Air handling unit static pressure = filter + coil + duct + terminal + fan internal losses; fan power P = L·Δp/(3600·η_fan·η_transmission) with L in m³/h and Δp in Pa.

Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³; variable-speed drives give large part-load savings, but minimum speed is limited by motor cooling and duct static control.

Chilled-water design: supply 7 °C, return 12 °C for conventional coils; ΔT of 5 K is standard; low ΔT syndrome (ΔT < 3 K) indicates coil or valve problems and increases pump energy.

Refrigerant safety: A1 refrigerants (R410A, R134a) have low toxicity and no flame propagation; occupied-space concentration limits and refrigerant charge limits apply.

Envelope thermal performance governed by GB 55015 (energy efficiency) and GB 50189 (public buildings): U-values for roofs, walls and windows vary by climate zone (severe cold, cold, hot summer/cold winter, hot summer/warm winter, mild).

Window-to-wall ratio limits: ≤0.70 for severe cold and cold zones, ≤0.60 for hot summer/cold winter, ≤0.40 for north-facing in cold zones; larger ratios require trade-off calculation.

Chiller part-load performance: centrifugal chillers must meet COP and IPLV thresholds in GB 19577; air-cooled units have lower thresholds than water-cooled.

Fan and pump specific power limits: GB 55015 sets maximum W_s per unit airflow (W/(m³/h)) and per unit water flow, encouraging high-efficiency motors and variable-speed drives.

Heat recovery: exhaust-air heat recovery required when fresh-air ratio is high and the climate zone warrants it; sensible effectiveness typically 50–70 %, enthalpy wheels 60–80 %.

Economizer (free cooling): allowed when outdoor air enthalpy or temperature is below the return-air value; air-side economizer with a changeover setpoint saves chiller energy in transitional seasons.

Lighting and plug-load power density caps: office lighting ≤9 W/m² (LPD), with automatic control requirements for large spaces; internal gains feed directly into cooling load.

Whole-building energy compliance uses the reference-building method: proposed design annual energy ≤ reference design; trade-offs among envelope, equipment and systems are permitted within the calculation.

PID control: output = K_p·e + K_i∫e dt + K_d·de/dt; proportional band PB = 100/K_p (%); integral time T_i and derivative time T_d set from process time constant and dead time.

Control valve authority β = Δp_valve/(Δp_valve + Δp_circuit); require β ≥0.3–0.5 for stable modulating control; equal-percentage valves suit coils with large turndown.

Sensor placement: temperature sensors ≥1.5 m above floor, away from direct sunlight and supply jets; averaging sensors across duct cross-sections for accurate mixed-air temperature.

Static pressure reset: duct static setpoint reset downward as VAV boxes open; supply fan controlled to keep the critical zone damper 80–90 % open, saving fan energy.

Commissioning sequence: pre-functional checks, functional performance tests, seasonal testing, and continuous commissioning; TAB (testing, adjusting, balancing) precedes functional tests.

Air balancing tolerance: supply airflow within ±10 % of design, room pressure differentials within ±5 Pa; duct leakage test pressure 1.5 × working pressure.

Chiller plant sequencing: stage chillers on leaving-water temperature and load; avoid short cycling with minimum run times and 10–15 min anti-recycle timers.

Fault detection: monitor approach temperatures (condenser and evaporator), superheat/subcooling, and chilled-water ΔT; rising condenser approach signals fouling and reduced efficiency.

Smoke control design basis: GB 51251 covers smoke exhaust and pressurization; design fire size for atria and large spaces typically 2.5–5 MW with steady burning, and smoke layer height kept above the safe egress height (≥2.0 m).

Pressurization systems: stairwell 25–30 Pa, elevator lobby 25–30 Pa, refuge floor 25–30 Pa relative to adjacent spaces; pressure relief dampers or barometric relief prevent overpressure.

Smoke exhaust rate for a corridor: 60 m³/(h·m²); for a room with fixed windows: 60 m³/(h·m²); for an atrium: 120 m³/(h·m²) or calculated by the plume method.

Make-up air: 50 % of exhaust volume for natural make-up, 80 % for mechanical; make-up velocity at the fire floor ≤1.0 m/s to avoid disturbing the smoke layer.

Fire dampers required where ducts penetrate fire-rated walls and floors; smoke dampers at smoke compartment boundaries; combination dampers where both functions are needed.

Duct fire resistance: exhaust ducts in smoke control systems must maintain integrity at 280 °C for 30 min (or 1.0 h for certain occupancies); fans rated for 280 °C/30 min continuous operation.

Stair pressurization with open doors: the door-opening force must not exceed 110 N; check with the largest door open and the required pressure differential maintained.

Basement and windowless spaces: mechanical smoke exhaust required; smoke exhaust fans must be independent of normal ventilation and start automatically on fire signal.

Registered Public Utility Engineer (HVAC) practice scope: design, construction, supervision and consultation for heating, ventilation, air conditioning and smoke control systems within the licensed scope.

Stamp and seal: only the registered engineer may sign and seal design documents; signing documents not prepared or supervised by the engineer is a violation of the registration regulation.

Conflict of interest: disclose financial interests in suppliers or contractors; do not specify proprietary products without an approved equal clause unless justified by sole-source documentation.

Design liability: the designer is responsible for compliance with mandatory codes (GB 55015, GB 51251, GB 50736); deviations require formal review and approval by the authority.

Confidentiality: client data, drawings and reports are confidential; disclosure requires client consent except where required by law or safety.

Continuing education: registered engineers must complete the required continuing-education hours per registration cycle to maintain the license.

Ethical reporting: if a design or installation poses a public safety risk, the engineer must report to the responsible authority even if it conflicts with the employer's interest.

Record keeping: retain design calculations, load calculations, commissioning reports and as-built documentation for the period required by regulation to support audit and liability defense.

Design indoor conditions per GB 50736: winter heating 18–24 °C, summer cooling 24–28 °C, relative humidity 40–70 % (cooling) and 30–60 % (heating); fresh-air rate per person depends on occupancy category.

Sensible heat equation: Q_s = 1.2 × L × Δt (W), with L in m³/s and 1.2 the volumetric heat capacity of moist air in kJ/(m³·K); latent heat Q_l = 2500 × 1.2 × L × Δd (W) with Δd in kg/kg.

Conduction load: Q = K·F·Δt, with K the overall heat-transfer coefficient in W/(m²·K); add solar correction factors for orientation and shading on external walls and roofs.

Sol-air temperature t_sa = t_out + ρ·I/α − ε·ΔR/α; for horizontal surfaces summer design uses the peak solar intensity at local solar time, not the peak air temperature.

Internal gains: occupants (sensible ~60–75 W/person light work, latent ~60–110 W), lighting (W/m² × area), equipment; diversity factors applied to non-coincident loads.

Air infiltration: L = a·l·(Δp)^(2/3) for cracks, or the air-change method L = n·V/3600; stack and wind pressure combine as Δp = Δp_wind + Δp_stack.

Coil load = room sensible + room latent + fresh-air sensible + fresh-air latent + duct/fan gains; fan heat enters the airstream when the fan is downstream of the coil.

Sizing margin: total cooling capacity typically 1.05–1.15 × calculated block load; do not oversize because part-load humidity control degrades at low sensible heat ratio.

Design outdoor heating temperature: the winter dry-bulb value with 50 % cumulative frequency (not the extreme minimum); indoor design temperature 18–24 °C per GB 50736.

Hot-water supply/return design temperatures: 95/70 °C for conventional radiator systems, 85/60 °C or 75/50 °C for energy-efficient designs; low-temperature floor heating uses ≤60 °C supply with Δt ≤10 K.

Radiator output correction: Q = Q_std × (ΔT_m/ΔT_std)^n, where ΔT_m is the mean water-to-air temperature difference and n ≈ 1.3 for radiators; correction factors for flow rate and connection scheme apply.

Hydronic pipe sizing: velocity limits 0.25–1.0 m/s for small-diameter branches, ≤1.5 m/s for mains; friction per unit length typically 60–120 Pa/m to limit pump head.

Pump head = friction losses + local losses + static height difference + terminal pressure; for closed loops the static height cancels and only friction and terminal drop remain.

Expansion tank volume V_e = V_system × (v₂/v₁ − 1) × safety factor; pre-charge pressure set to static height plus 3–5 m water column.

Boiler efficiency: thermal efficiency = Q_absorbed/Q_fuel; condensing boilers achieve 95–108 % on higher heating value only with return water below the flue-gas dew point (~55–60 °C).

Two-pipe direct-return vs reverse-return: reverse-return equalizes path lengths so terminal flows stay near design without balancing valves; direct-return requires balancing valves on near terminals.

Minimum fresh air per person in offices: 30 m³/(h·person) per GB 50736; for high-density spaces use per-area values and check CO₂ concentration stays below 1000 ppm.

Natural ventilation driving pressure: Δp = h·(ρ_out − ρ_in)·g + 0.5·ρ·v²·C_p; effective opening area A_eff = A₁A₂/√(A₁²+A₂²) for two openings in series.

Mechanical exhaust hood capture velocity: 0.25–0.5 m/s for low-velocity enclosures, 0.5–1.0 m/s for side-draft slots; required exhaust volume depends on hood geometry and distance from the source.

Duct friction: Δp = λ·(L/D_e)·(ρv²/2); rectangular duct equivalent diameter D_e = 2ab/(a+b) for equal friction; use the Darcy-Weisbach or equal-friction chart method consistently.

Local exhaust duct velocity minimums: 10–12 m/s for dry dust, 14–18 m/s for metal dust, 18–23 m/s for moist or condensable contaminants to prevent deposition.

Stairwell pressurization: 25–30 Pa differential with all doors closed, ≥50 Pa across an open door to the fire floor; relief provisions must prevent door-opening force above 110 N.

Smoke exhaust in corridors: exhaust rate ≥60 m³/(h·m²) of floor area for corridors and 120 m³/(h·m²) for atria per GB 51251; make-up air at 50–80 % of exhaust volume.

Air cleaning for industrial exhaust: cyclone efficiency η = 1 − (particulate out)/(particulate in); fabric filters target 99 %+ for fine particulate and require pre-cooling below the bag temperature limit.

Refrigeration cycle COP = refrigerating effect / compressor work; Carnot COP_c = T_L/(T_H − T_L) in kelvin; real cycle COP is 40–60 % of Carnot for chillers.

Chiller efficiency metrics: kW/RT (1 RT = 3.517 kW); a 5.0 COP chiller equals 0.703 kW/RT; IPLV/NPLV weight part-load points (100 %, 75 %, 50 %, 25 %).

Air-side coil bypass factor BF = (t_out − t_ADP)/(t_in − t_ADP); contact factor CF = 1 − BF; number of rows and face velocity (typically 2.0–2.8 m/s) control BF.

Sensible heat ratio SHR = Q_s/(Q_s + Q_l); the coil apparatus dew point must lie below the room air dew point to remove latent load; low-load conditions raise SHR and risk high room humidity.

Air handling unit static pressure = filter + coil + duct + terminal + fan internal losses; fan power P = L·Δp/(3600·η_fan·η_transmission) with L in m³/h and Δp in Pa.

Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³; variable-speed drives give large part-load savings, but minimum speed is limited by motor cooling and duct static control.

Chilled-water design: supply 7 °C, return 12 °C for conventional coils; ΔT of 5 K is standard; low ΔT syndrome (ΔT < 3 K) indicates coil or valve problems and increases pump energy.

Refrigerant safety: A1 refrigerants (R410A, R134a) have low toxicity and no flame propagation; occupied-space concentration limits and refrigerant charge limits apply.

Envelope thermal performance governed by GB 55015 (energy efficiency) and GB 50189 (public buildings): U-values for roofs, walls and windows vary by climate zone (severe cold, cold, hot summer/cold winter, hot summer/warm winter, mild).

Window-to-wall ratio limits: ≤0.70 for severe cold and cold zones, ≤0.60 for hot summer/cold winter, ≤0.40 for north-facing in cold zones; larger ratios require trade-off calculation.

Chiller part-load performance: centrifugal chillers must meet COP and IPLV thresholds in GB 19577; air-cooled units have lower thresholds than water-cooled.

Fan and pump specific power limits: GB 55015 sets maximum W_s per unit airflow (W/(m³/h)) and per unit water flow, encouraging high-efficiency motors and variable-speed drives.

Heat recovery: exhaust-air heat recovery required when fresh-air ratio is high and the climate zone warrants it; sensible effectiveness typically 50–70 %, enthalpy wheels 60–80 %.

Economizer (free cooling): allowed when outdoor air enthalpy or temperature is below the return-air value; air-side economizer with a changeover setpoint saves chiller energy in transitional seasons.

Lighting and plug-load power density caps: office lighting ≤9 W/m² (LPD), with automatic control requirements for large spaces; internal gains feed directly into cooling load.

Whole-building energy compliance uses the reference-building method: proposed design annual energy ≤ reference design; trade-offs among envelope, equipment and systems are permitted within the calculation.

PID control: output = K_p·e + K_i∫e dt + K_d·de/dt; proportional band PB = 100/K_p (%); integral time T_i and derivative time T_d set from process time constant and dead time.

Control valve authority β = Δp_valve/(Δp_valve + Δp_circuit); require β ≥0.3–0.5 for stable modulating control; equal-percentage valves suit coils with large turndown.

Sensor placement: temperature sensors ≥1.5 m above floor, away from direct sunlight and supply jets; averaging sensors across duct cross-sections for accurate mixed-air temperature.

Static pressure reset: duct static setpoint reset downward as VAV boxes open; supply fan controlled to keep the critical zone damper 80–90 % open, saving fan energy.

Commissioning sequence: pre-functional checks, functional performance tests, seasonal testing, and continuous commissioning; TAB (testing, adjusting, balancing) precedes functional tests.

Air balancing tolerance: supply airflow within ±10 % of design, room pressure differentials within ±5 Pa; duct leakage test pressure 1.5 × working pressure.

Chiller plant sequencing: stage chillers on leaving-water temperature and load; avoid short cycling with minimum run times and 10–15 min anti-recycle timers.

Fault detection: monitor approach temperatures (condenser and evaporator), superheat/subcooling, and chilled-water ΔT; rising condenser approach signals fouling and reduced efficiency.

Smoke control design basis: GB 51251 covers smoke exhaust and pressurization; design fire size for atria and large spaces typically 2.5–5 MW with steady burning, and smoke layer height kept above the safe egress height (≥2.0 m).

Pressurization systems: stairwell 25–30 Pa, elevator lobby 25–30 Pa, refuge floor 25–30 Pa relative to adjacent spaces; pressure relief dampers or barometric relief prevent overpressure.

Smoke exhaust rate for a corridor: 60 m³/(h·m²); for a room with fixed windows: 60 m³/(h·m²); for an atrium: 120 m³/(h·m²) or calculated by the plume method.

Make-up air: 50 % of exhaust volume for natural make-up, 80 % for mechanical; make-up velocity at the fire floor ≤1.0 m/s to avoid disturbing the smoke layer.

Fire dampers required where ducts penetrate fire-rated walls and floors; smoke dampers at smoke compartment boundaries; combination dampers where both functions are needed.

Duct fire resistance: exhaust ducts in smoke control systems must maintain integrity at 280 °C for 30 min (or 1.0 h for certain occupancies); fans rated for 280 °C/30 min continuous operation.

Stair pressurization with open doors: the door-opening force must not exceed 110 N; check with the largest door open and the required pressure differential maintained.

Basement and windowless spaces: mechanical smoke exhaust required; smoke exhaust fans must be independent of normal ventilation and start automatically on fire signal.

Registered Public Utility Engineer (HVAC) practice scope: design, construction, supervision and consultation for heating, ventilation, air conditioning and smoke control systems within the licensed scope.

Stamp and seal: only the registered engineer may sign and seal design documents; signing documents not prepared or supervised by the engineer is a violation of the registration regulation.

Conflict of interest: disclose financial interests in suppliers or contractors; do not specify proprietary products without an approved equal clause unless justified by sole-source documentation.

Design liability: the designer is responsible for compliance with mandatory codes (GB 55015, GB 51251, GB 50736); deviations require formal review and approval by the authority.

Confidentiality: client data, drawings and reports are confidential; disclosure requires client consent except where required by law or safety.

Continuing education: registered engineers must complete the required continuing-education hours per registration cycle to maintain the license.

Ethical reporting: if a design or installation poses a public safety risk, the engineer must report to the responsible authority even if it conflicts with the employer's interest.

Record keeping: retain design calculations, load calculations, commissioning reports and as-built documentation for the period required by regulation to support audit and liability defense.

Design indoor conditions per GB 50736: winter heating 18–24 °C, summer cooling 24–28 °C, relative humidity 40–70 % (cooling) and 30–60 % (heating); fresh-air rate per person depends on occupancy category.

Sensible heat equation: Q_s = 1.2 × L × Δt (W), with L in m³/s and 1.2 the volumetric heat capacity of moist air in kJ/(m³·K); latent heat Q_l = 2500 × 1.2 × L × Δd (W) with Δd in kg/kg.

Conduction load: Q = K·F·Δt, with K the overall heat-transfer coefficient in W/(m²·K); add solar correction factors for orientation and shading on external walls and roofs.

Sol-air temperature t_sa = t_out + ρ·I/α − ε·ΔR/α; for horizontal surfaces summer design uses the peak solar intensity at local solar time, not the peak air temperature.

Internal gains: occupants (sensible ~60–75 W/person light work, latent ~60–110 W), lighting (W/m² × area), equipment; diversity factors applied to non-coincident loads.

Air infiltration: L = a·l·(Δp)^(2/3) for cracks, or the air-change method L = n·V/3600; stack and wind pressure combine as Δp = Δp_wind + Δp_stack.

Coil load = room sensible + room latent + fresh-air sensible + fresh-air latent + duct/fan gains; fan heat enters the airstream when the fan is downstream of the coil.

Sizing margin: total cooling capacity typically 1.05–1.15 × calculated block load; do not oversize because part-load humidity control degrades at low sensible heat ratio.

Design outdoor heating temperature: the winter dry-bulb value with 50 % cumulative frequency (not the extreme minimum); indoor design temperature 18–24 °C per GB 50736.

Hot-water supply/return design temperatures: 95/70 °C for conventional radiator systems, 85/60 °C or 75/50 °C for energy-efficient designs; low-temperature floor heating uses ≤60 °C supply with Δt ≤10 K.

Radiator output correction: Q = Q_std × (ΔT_m/ΔT_std)^n, where ΔT_m is the mean water-to-air temperature difference and n ≈ 1.3 for radiators; correction factors for flow rate and connection scheme apply.

Hydronic pipe sizing: velocity limits 0.25–1.0 m/s for small-diameter branches, ≤1.5 m/s for mains; friction per unit length typically 60–120 Pa/m to limit pump head.

Pump head = friction losses + local losses + static height difference + terminal pressure; for closed loops the static height cancels and only friction and terminal drop remain.

Expansion tank volume V_e = V_system × (v₂/v₁ − 1) × safety factor; pre-charge pressure set to static height plus 3–5 m water column.

Boiler efficiency: thermal efficiency = Q_absorbed/Q_fuel; condensing boilers achieve 95–108 % on higher heating value only with return water below the flue-gas dew point (~55–60 °C).

Two-pipe direct-return vs reverse-return: reverse-return equalizes path lengths so terminal flows stay near design without balancing valves; direct-return requires balancing valves on near terminals.

Minimum fresh air per person in offices: 30 m³/(h·person) per GB 50736; for high-density spaces use per-area values and check CO₂ concentration stays below 1000 ppm.

Natural ventilation driving pressure: Δp = h·(ρ_out − ρ_in)·g + 0.5·ρ·v²·C_p; effective opening area A_eff = A₁A₂/√(A₁²+A₂²) for two openings in series.

Mechanical exhaust hood capture velocity: 0.25–0.5 m/s for low-velocity enclosures, 0.5–1.0 m/s for side-draft slots; required exhaust volume depends on hood geometry and distance from the source.

Duct friction: Δp = λ·(L/D_e)·(ρv²/2); rectangular duct equivalent diameter D_e = 2ab/(a+b) for equal friction; use the Darcy-Weisbach or equal-friction chart method consistently.

Local exhaust duct velocity minimums: 10–12 m/s for dry dust, 14–18 m/s for metal dust, 18–23 m/s for moist or condensable contaminants to prevent deposition.

Stairwell pressurization: 25–30 Pa differential with all doors closed, ≥50 Pa across an open door to the fire floor; relief provisions must prevent door-opening force above 110 N.

Smoke exhaust in corridors: exhaust rate ≥60 m³/(h·m²) of floor area for corridors and 120 m³/(h·m²) for atria per GB 51251; make-up air at 50–80 % of exhaust volume.

Air cleaning for industrial exhaust: cyclone efficiency η = 1 − (particulate out)/(particulate in); fabric filters target 99 %+ for fine particulate and require pre-cooling below the bag temperature limit.

Refrigeration cycle COP = refrigerating effect / compressor work; Carnot COP_c = T_L/(T_H − T_L) in kelvin; real cycle COP is 40–60 % of Carnot for chillers.

Chiller efficiency metrics: kW/RT (1 RT = 3.517 kW); a 5.0 COP chiller equals 0.703 kW/RT; IPLV/NPLV weight part-load points (100 %, 75 %, 50 %, 25 %).

Air-side coil bypass factor BF = (t_out − t_ADP)/(t_in − t_ADP); contact factor CF = 1 − BF; number of rows and face velocity (typically 2.0–2.8 m/s) control BF.

Sensible heat ratio SHR = Q_s/(Q_s + Q_l); the coil apparatus dew point must lie below the room air dew point to remove latent load; low-load conditions raise SHR and risk high room humidity.

Air handling unit static pressure = filter + coil + duct + terminal + fan internal losses; fan power P = L·Δp/(3600·η_fan·η_transmission) with L in m³/h and Δp in Pa.

Fan laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³; variable-speed drives give large part-load savings, but minimum speed is limited by motor cooling and duct static control.

Chilled-water design: supply 7 °C, return 12 °C for conventional coils; ΔT of 5 K is standard; low ΔT syndrome (ΔT < 3 K) indicates coil or valve problems and increases pump energy.

Refrigerant safety: A1 refrigerants (R410A, R134a) have low toxicity and no flame propagation; occupied-space concentration limits and refrigerant charge limits apply.

Envelope thermal performance governed by GB 55015 (energy efficiency) and GB 50189 (public buildings): U-values for roofs, walls and windows vary by climate zone (severe cold, cold, hot summer/cold winter, hot summer/warm winter, mild).

Window-to-wall ratio limits: ≤0.70 for severe cold and cold zones, ≤0.60 for hot summer/cold winter, ≤0.40 for north-facing in cold zones; larger ratios require trade-off calculation.

Chiller part-load performance: centrifugal chillers must meet COP and IPLV thresholds in GB 19577; air-cooled units have lower thresholds than water-cooled.

Fan and pump specific power limits: GB 55015 sets maximum W_s per unit airflow (W/(m³/h)) and per unit water flow, encouraging high-efficiency motors and variable-speed drives.

Heat recovery: exhaust-air heat recovery required when fresh-air ratio is high and the climate zone warrants it; sensible effectiveness typically 50–70 %, enthalpy wheels 60–80 %.

Economizer (free cooling): allowed when outdoor air enthalpy or temperature is below the return-air value; air-side economizer with a changeover setpoint saves chiller energy in transitional seasons.

Lighting and plug-load power density caps: office lighting ≤9 W/m² (LPD), with automatic control requirements for large spaces; internal gains feed directly into cooling load.

Whole-building energy compliance uses the reference-building method: proposed design annual energy ≤ reference design; trade-offs among envelope, equipment and systems are permitted within the calculation.

PID control: output = K_p·e + K_i∫e dt + K_d·de/dt; proportional band PB = 100/K_p (%); integral time T_i and derivative time T_d set from process time constant and dead time.

Control valve authority β = Δp_valve/(Δp_valve + Δp_circuit); require β ≥0.3–0.5 for stable modulating control; equal-percentage valves suit coils with large turndown.

Sensor placement: temperature sensors ≥1.5 m above floor, away from direct sunlight and supply jets; averaging sensors across duct cross-sections for accurate mixed-air temperature.

Static pressure reset: duct static setpoint reset downward as VAV boxes open; supply fan controlled to keep the critical zone damper 80–90 % open, saving fan energy.

Commissioning sequence: pre-functional checks, functional performance tests, seasonal testing, and continuous commissioning; TAB (testing, adjusting, balancing) precedes functional tests.

Air balancing tolerance: supply airflow within ±10 % of design, room pressure differentials within ±5 Pa; duct leakage test pressure 1.5 × working pressure.

Chiller plant sequencing: stage chillers on leaving-water temperature and load; avoid short cycling with minimum run times and 10–15 min anti-recycle timers.

Fault detection: monitor approach temperatures (condenser and evaporator), superheat/subcooling, and chilled-water ΔT; rising condenser approach signals fouling and reduced efficiency.

Smoke control design basis: GB 51251 covers smoke exhaust and pressurization; design fire size for atria and large spaces typically 2.5–5 MW with steady burning, and smoke layer height kept above the safe egress height (≥2.0 m).

Pressurization systems: stairwell 25–30 Pa, elevator lobby 25–30 Pa, refuge floor 25–30 Pa relative to adjacent spaces; pressure relief dampers or barometric relief prevent overpressure.

Smoke exhaust rate for a corridor: 60 m³/(h·m²); for a room with fixed windows: 60 m³/(h·m²); for an atrium: 120 m³/(h·m²) or calculated by the plume method.

Make-up air: 50 % of exhaust volume for natural make-up, 80 % for mechanical; make-up velocity at the fire floor ≤1.0 m/s to avoid disturbing the smoke layer.

Fire dampers required where ducts penetrate fire-rated walls and floors; smoke dampers at smoke compartment boundaries; combination dampers where both functions are needed.

Duct fire resistance: exhaust ducts in smoke control systems must maintain integrity at 280 °C for 30 min (or 1.0 h for certain occupancies); fans rated for 280 °C/30 min continuous operation.

Stair pressurization with open doors: the door-opening force must not exceed 110 N; check with the largest door open and the required pressure differential maintained.

Basement and windowless spaces: mechanical smoke exhaust required; smoke exhaust fans must be independent of normal ventilation and start automatically on fire signal.

Registered Public Utility Engineer (HVAC) practice scope: design, construction, supervision and consultation for heating, ventilation, air conditioning and smoke control systems within the licensed scope.

Stamp and seal: only the registered engineer may sign and seal design documents; signing documents not prepared or supervised by the engineer is a violation of the registration regulation.

Conflict of interest: disclose financial interests in suppliers or contractors; do not specify proprietary products without an approved equal clause unless justified by sole-source documentation.

Design liability: the designer is responsible for compliance with mandatory codes (GB 55015, GB 51251, GB 50736); deviations require formal review and approval by the authority.

Confidentiality: client data, drawings and reports are confidential; disclosure requires client consent except where required by law or safety.

Continuing education: registered engineers must complete the required continuing-education hours per registration cycle to maintain the license.

Ethical reporting: if a design or installation poses a public safety risk, the engineer must report to the responsible authority even if it conflicts with the employer's interest.

Record keeping: retain design calculations, load calculations, commissioning reports and as-built documentation for the period required by regulation to support audit and liability defense.