Symbols and units

Every symbol used in the Engineering library, with its meaning, unit and the notes that use it: 129 symbols with 196 meanings, from all 29 notes. Many symbols have more than one meaning; each note's own table gives the one it uses.

Symbol	Meaning, unit and notes
A	Area m²HVAC-04 Internal area m²HVAC-21 Plan area of water m²PHE-03 Room area m²ELEC-12
AF	Acceptance factor 0–1PHE-09
c_p	Air specific heat kJ/kg·KHVAC-08 HVAC-10 Water specific heat kJ/kg·KHVAC-09 HVAC-17 PHE-11 PHE-13
D	Outside diameter mmHVAC-18
d	Inside diameter mmHVAC-18 HVAC-21 Layer thickness mHVAC-04 Required internal diameter mmHVAC-15
E	Target average illuminance luxELEC-12
E_av	Resulting average illuminance luxELEC-12
f_ph	Peak-hour factorPHE-10
g	Gravity (blank = 9.80665) m/s²PHE-07
H	Room height (to the ceiling grid) mCLEAN-03 Total dynamic head mHVAC-13 PHE-07
h	Effective water depth mPHE-03 Moist-air enthalpy kJ/kg dry airHVAC-01 Selected water depth mPHE-03
h₁	Stream 1 enthalpy kJ/kg dry airHVAC-03
h₂	Stream 2 enthalpy kJ/kg dry airHVAC-03
h₃	Mixed enthalpy kJ/kg dry airHVAC-03
H_eq	Equipment head (coils, heat exchangers, chillers) mHVAC-13
H_f	Pipe friction head mHVAC-13
H_fit	Fittings head mHVAC-13
H_o	Other head mHVAC-13
H_st	Static head mHVAC-13
H_t	Terminal head (control valves, terminals) mHVAC-13
I	Load current AELEC-03
I_FL	Full-load current AELEC-08
k	Circuit factorELEC-03 Phase factorELEC-08
k_d	Demand factorELEC-01
k_v	Diversity factorELEC-01
L	Length mHVAC-18 HVAC-21 PHE-03 Room length mELEC-12 CLEAN-03 Route length (one way) mELEC-03
M	Total combined mass kgHVAC-18
ṁ	Air mass flow kg/sHVAC-08 Mass flow kg/sHVAC-17 Recirculation mass flow kg/sPHE-13 Water mass flow kg/sHVAC-09 PHE-11
m	Combined mass kg/mHVAC-18 Design margin (blank = 0) %ELEC-05 Storage margin (0.1 = 10 %)PHE-12
ṁ₁	Stream 1 dry-air mass flow kg/sHVAC-03
ṁ₂	Stream 2 dry-air mass flow kg/sHVAC-03
ṁ₃	Mixed dry-air mass flow kg/sHVAC-03
ṁ_da	Dry-air mass flow kg/sHVAC-05 HVAC-06
MF	Maintenance factor 0–1ELEC-12
M_f	Total fluid mass kgHVAC-18
m_f	Fluid mass kg/mHVAC-18
M_p	Total pipe mass kgHVAC-18
m_p	Pipe mass kg/mHVAC-18
ṁ_w	Moisture added kg/hHVAC-06 Moisture added kg/sHVAC-06 Water removed kg/hHVAC-05 Water removed kg/sHVAC-05
N	Air changes per hour 1/hHVAC-10 Recommended luminaires countELEC-12 Target air changes per hour 1/hCLEAN-03
n	Quantity no.ELEC-01 Quantity of units no.PHE-10 Recommended FFU quantity countCLEAN-03 Speed (optional) rpmELEC-08
N′	Raw luminaire quantity countELEC-12
n′	Raw FFU quantity countCLEAN-03
P	Active load (after diversity) kWELEC-05 Active power kWELEC-10 Electrical input kWHVAC-08 Heater input kWPHE-11
p	Atmospheric pressure kPaHVAC-01
P_a	Air power WHVAC-11
P_c	Total connected load kWELEC-01
P_d	Total demand load kWELEC-01
PF	Load power factor 0–1ELEC-03 Power factor 0–1ELEC-05 ELEC-08
PF₁	Existing power factor 0–1ELEC-10
PF₂	Target power factor 0–1ELEC-10
P_h	Hydraulic power kWPHE-07
P_in	Electrical input kWELEC-08 Motor input kWHVAC-11 Motor input power kWPHE-07
P_out	Rated output (shaft) power kWELEC-08
P_s	Pump shaft power kWPHE-07 Shaft power kWHVAC-11
P_u	Load per item kWELEC-01
P_v	Total diversified load kWELEC-01
p_w	Vapour pressure kPaHVAC-01
p_ws	Saturation vapour pressure kPaHVAC-01
Q	Air heat duty kWHVAC-08 Cooling load kWHVAC-17 Heat rejection kWHVAC-09 Heat transfer WHVAC-04 Heat transfer kWHVAC-04 Water heat duty kWPHE-11
Q₁	Existing reactive power kvarELEC-10
Q₂	Target reactive power kvarELEC-10
Q_c	Required capacitor kvarELEC-10
q_d	Daily hot water per unit L/unit/dayPHE-10
q_FFU	Airflow per FFU m³/hCLEAN-03
Q_l	Heat loss of the circulation loop kWPHE-13
Q_s	Room sensible load kWHVAC-10
R	Conductor resistance Ω/kmELEC-03 Range KHVAC-09
r	Length-to-width ratioPHE-03
R_n	Resistance of each layer m²K/WHVAC-04
R_si	Inside surface resistance m²K/WHVAC-04
R_so	Outside surface resistance m²K/WHVAC-04
R_T	Total resistance m²K/WHVAC-04
S	Apparent power kVAELEC-08
s	Wall thickness mmHVAC-18
S₁	Existing apparent power kVAELEC-10
S₂	Target apparent power kVAELEC-10
S_b	Base required kVA kVAELEC-05
S_d	Design required kVA kVAELEC-05
sin φ	Sine of the load phase angleELEC-03
T	Shaft torque N·mELEC-08
t	Dry-bulb temperature °CHVAC-01
t₁	Inlet temperature °CHVAC-08 PHE-11
t₂	Leaving dry bulb °CHVAC-07 Outlet temperature °CHVAC-08 PHE-11
t_cw	Cold-water temperature °CHVAC-09
t_db	Entering dry bulb °CHVAC-07
t_hw	Hot-water temperature °CHVAC-09
t_wb	Entering wet bulb °CHVAC-07
U	Supply voltage VELEC-08 U-value W/m²KHVAC-04
UF	Utilization factor 0–1ELEC-12
U_n	Nominal voltage VELEC-03
U_r	Receiving voltage VELEC-03
V̇	Airflow L/sHVAC-10 Airflow cfmHVAC-10 Airflow m³/hHVAC-10 Airflow m³/sHVAC-08 HVAC-10 HVAC-11 Flow m³/sHVAC-15 PHE-07 Recirculation flow L/sPHE-13 Recirculation flow m³/sPHE-13 Required airflow m³/hCLEAN-03 Volume flow L/sHVAC-17 Volume flow m³/sHVAC-17
V	Capacity LPHE-03 Capacity / required volume m³PHE-03 Room volume m³CLEAN-03 Water volume LHVAC-21 Water volume m³HVAC-21
v	Target velocity m/sHVAC-15
V_d	Required drawdown LPHE-09
V_day	Total daily hot water LPHE-10
V_n	Net storage required LPHE-12
V_p	Peak-period demand LPHE-12
V_ph	Total peak-hour hot water LPHE-10
V_r	Heater recovery during the peak LPHE-12 Room volume m³HVAC-10
V_req	Required volume m³PHE-03
V_s	Design storage LPHE-12
V_t	Required nominal tank volume LPHE-09
W	Humidity ratio g/kg dry airHVAC-01 Humidity ratio kg/kg dry airHVAC-01 Room width mELEC-12 CLEAN-03 Width mPHE-03
W₁	Entering humidity ratio kg/kg dry airHVAC-05 HVAC-06 Stream 1 humidity ratio kg/kg dry airHVAC-03
W₂	Leaving humidity ratio kg/kg dry airHVAC-05 Stream 2 humidity ratio kg/kg dry airHVAC-03 Target humidity ratio kg/kg dry airHVAC-06
W₃	Mixed humidity ratio kg/kg dry airHVAC-03
X	Conductor reactance Ω/kmELEC-03
Δp_t	Fan total pressure PaHVAC-11
ΔT	Allowable supply-return ΔT KPHE-13 Chilled-water supply-return difference KHVAC-17 Inside-outside temperature difference KHVAC-04 Supply-to-room temperature difference KHVAC-10 Temperature rise KHVAC-08 PHE-11
Δt_a	Approach to wet bulb KHVAC-07
ΔU	Voltage drop VELEC-03
ΔU_%	Voltage drop %ELEC-03
ε	Cooler effectiveness 0–1HVAC-07
η	Heater efficiency 0–1HVAC-08 PHE-11 Motor efficiency 0–1ELEC-08
η_d	Drive efficiency 0–1HVAC-11
η_f	Fan efficiency 0–1HVAC-11
η_m	Motor efficiency 0–1HVAC-11 PHE-07
η_p	Pump efficiency 0–1PHE-07
λ	Layer thermal conductivity W/m·KHVAC-04
ρ	Air density kg/m³HVAC-08 HVAC-10 Fluid density kg/m³PHE-07 PHE-13 Water density kg/m³HVAC-17
ρ_f	Fluid density kg/m³HVAC-18
ρ_p	Pipe material density kg/m³HVAC-18
Φ	Required lumens lmELEC-12
φ	Relative humidity 0–1HVAC-01
φ₁	Existing phase angleELEC-10
φ₂	Target phase angleELEC-10
Φ_L	Luminous flux per luminaire lmELEC-12

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