Units

Every value in WS.PEMS has a unit of measurement. Units that measure the same quantity form a unit group, for example Pressure or Power. Each group has one base unit. This page lists the 35 unit groups and 112 units that every installation has.

How conversion works

Each unit has a factor and an offset relative to the base unit of its group:

value in unit = value in base unit × factor + offset

The base unit has factor 1 and offset 0. Most units have an offset of 0. Temperatures and gauge pressures (barG, psiG and the others) have an offset. To convert between two units of the same group, the system goes through the base unit. A standard tag stores its values in one unit. You can show a tag in any other unit of the same group.

Normal and standard conditions

The thermodynamic code uses a normal temperature of 273.15 K (0 °C) and a reference pressure of 101325 Pa (101.325 kPa). The values come from Constants.cs in the thermodynamics code. Units with "N", such as Nm³/s and mg/Nm³, refer to these normal conditions.

The seed converts 1 Nm³/s to 1.0549 Sm³/s. This factor is the ratio 288.15 K / 273.15 K. Units with "S", such as Sm³/h, thus refer to 15 °C at the same reference pressure. The scf-based units (SCFM, SCFH, MSCFD and the others) use the same 15 °C basis.

Unit groups

Group	Base unit	Units
Temperature	K	3
Pressure	bar	18
Mass flow	kg/s	8
Mass concentration	mg/Nm³	1
Mass fraction	kg/kg	2
Power	kW	9
Ratio	Decimal Fraction	2
Rotational speed	rpm	2
Length	m	4
Standard volume flow	Nm³/s	13
Volume flow	m³/s	6
Density	kg/m³	1
Volume concentration	ppm	3
Relative humidity	Fraction	2
Speed	m/s	1
Standard volume	Nm³	2
Energy	kJ	10
Mass	kg	3
Area	m²	1
Volume	m³	1
Emissivity	Emissivity	1
Specific energy	MJ/kg	1
Molar energy	MJ/kmole	1
Specific entropy	kJ/kg·K	1
Integer	Integer	1
Standard density	kg/Nm³	1
Molar flow	kmole/s	1
Emissions per fuel energy	mg/kJ	1
Boolean	Boolean	1
Efficiency	Fraction	2
Time	s	4
Number	Number	1
Location	°	1
Heat transfer coefficient	W/(m²·K)	1
Rotational speed pct	Fraction	2

Temperature

Group Temperature, id 1. Base unit: K.

Id	Unit	Symbol	Conversion from the base unit
1	Celsius	°C	°C = K − 273.15
2	Fahrenheit	°F	°F = K × 1.8 − 459.67
3	Kelvin	K	Base unit

Pressure

Group Pressure, id 2. Base unit: bar.

Id	Unit	Symbol	Conversion from the base unit
4	Bar	bar	Base unit
5	InHg	inHg	1 bar = 29.52998 inHg
6	InH₂O	inH₂O	1 bar = 401.865 inH₂O
7	Hectopascal	hPa	1 bar = 1000 hPa
8	kPaG	kPaG	kPaG = bar × 100 − 101.325
9	BarG	barG	barG = bar − 1.01325
10	Kilopascal	kPa	1 bar = 100 kPa
11	Psi	psi	1 bar = 14.50377 psi
12	PsiG	psiG	psiG = bar × 14.50377 − 14.6959
13	Millibar	mbar	1 bar = 1000 mbar
14	mmH₂O	mmH₂O	1 bar = 10197.2 mmH₂O
15	mmHg	mmHg	1 bar = 750.062 mmHg
16	Torr	torr	1 bar = 750.062 torr
17	kg/cm²	kg/cm²	1 bar = 1.01972 kg/cm²
18	Standard atmosphere	atm	1 bar = 0.986923 atm
19	Standard atmosphere G	atmG	atmG = bar × 0.986923 − 1
20	mbarG	mbarG	mbarG = bar × 1000 − 1013.25
102	Megapascal	MPa	1 bar = 0.1 MPa

Mass flow

Group MassFlow, id 3. Base unit: kg/s.

Id	Unit	Symbol	Conversion from the base unit
21	kg/h	kg/h	1 kg/s = 3600 kg/h
22	Ton/h	ton/h	1 kg/s = 3.6 ton/h
23	lb/s	lb/s	1 kg/s = 2.20462 lb/s
24	MPPH	MPPH	1 kg/s = 7.93664 MPPH
25	lb/h	lb/h	1 kg/s = 7936.64 lb/h
26	kg/s	kg/s	Base unit
27	mg/s	mg/s	1 kg/s = 1000000 mg/s
28	kg/day	kg/day	1 kg/s = 86400 kg/day

Mass concentration

Group MassConcentration, id 4. Base unit: mg/Nm³.

Id	Unit	Symbol	Conversion from the base unit
71	mg/Nm³	mg/Nm³	Base unit

Mass fraction

Group MassFraction, id 5. Base unit: kg/kg.

Id	Unit	Symbol	Conversion from the base unit
79	mg/kg	mg/kg	1 kg/kg = 1000000 mg/kg
83	kg/kg	kg/kg	Base unit

Power

Group Power, id 6. Base unit: kW.

Id	Unit	Symbol	Conversion from the base unit
29	kW	kW	Base unit
30	MW	MW	1 kW = 0.001 MW
31	Horsepower	hp	1 kW = 1.34102 hp
32	BTU/s	BTU/s	1 kW = 0.947817 BTU/s
33	BTU/h	BTU/h	1 kW = 3412.14 BTU/h
34	kJ/h	kJ/h	1 kW = 3600 kJ/h
35	MJ/h	MJ/h	1 kW = 3.6 MJ/h
36	GJ/h	GJ/h	1 kW = 0.0036 GJ/h
94	Watt	W	1 kW = 1000 W

Ratio

Group Ratio, id 8. Base unit: Decimal Fraction.

Id	Unit	Symbol	Conversion from the base unit
40	Decimal Fraction	(none)	Base unit
41	Percentage	%	1 Decimal Fraction = 100 %

Rotational speed

Group RotationalSpeed, id 9. Base unit: rpm.

Id	Unit	Symbol	Conversion from the base unit
43	Hertz	Hz	1 rpm = 1/60 Hz
44	RPM	rpm	Base unit

Length

Group Length, id 10. Base unit: m.

Id	Unit	Symbol	Conversion from the base unit
45	Meter	m	Base unit
46	Kilometer	km	1 m = 0.001 km
47	Inch	in	1 m = 39.3700787 in
48	Foot	ft	1 m = 3.2808399 ft

Standard volume flow

Group StandardVolumeFlow, id 11. Base unit: Nm³/s.

Id	Unit	Symbol	Conversion from the base unit
49	SCFM	SCFM	1 Nm³/s = 2235.24 SCFM
50	MMSCFD	MMSCFD	1 Nm³/s = 3.21874 MMSCFD
51	Nm³/s	Nm³/s	Base unit
52	SCFH	SCFH	1 Nm³/s = 134114 SCFH
53	MSCFD	MSCFD	1 Nm³/s = 3218.74 MSCFD
54	MMSCFH	MMSCFH	1 Nm³/s = 0.134114 MMSCFH
55	MSCFH	MSCFH	1 Nm³/s = 134.114 MSCFH
56	Nm³/h	Nm³/h	1 Nm³/s = 3600 Nm³/h
57	Sm³/s	Sm³/s	1 Nm³/s = 1.0549 Sm³/s
58	Sm³/h	Sm³/h	1 Nm³/s = 3797.64 Sm³/h
59	kNm³/h	kNm³/h	1 Nm³/s = 3.6 kNm³/h
96	Sm³/d	Sm³/d	1 Nm³/s = 91143.36 Sm³/d
106	kSm³/h	kSm³/h	1 Nm³/s = 3.79764 kSm³/h

Volume flow

Group VolumeFlow, id 12. Base unit: m³/s.

Id	Unit	Symbol	Conversion from the base unit
60	mbd	mbd	1 m³/s = 543.4397 mbd
61	MGPM	MGPM	1 m³/s = 15.85032 MGPM
62	GPM	GPM	1 m³/s = 15850.32 GPM
63	m³/s	m³/s	Base unit
104	m³/h	m³/h	1 m³/s = 3600 m³/h
105	l/min	l/min	1 m³/s = 60000 l/min

Density

Group Density, id 13. Base unit: kg/m³.

Id	Unit	Symbol	Conversion from the base unit
64	kg/m³	kg/m³	Base unit

Volume concentration

Group VolumeConcentration, id 14. Base unit: ppm.

Id	Unit	Symbol	Conversion from the base unit
84	Percentage	%	1 ppm = 0.0001 %
85	ppm	ppm	Base unit
86	ppb	ppb	1 ppm = 1000 ppb

Relative humidity

Group RelativeHumidity, id 15. Base unit: Fraction.

Id	Unit	Symbol	Conversion from the base unit
65	Percentage	%	1 Fraction = 100 %
95	Fraction	(none)	Base unit

Speed

Group Speed, id 16. Base unit: m/s.

Id	Unit	Symbol	Conversion from the base unit
69	m/s	m/s	Base unit

Standard volume

Group StandardVolume, id 17. Base unit: Nm³.

Id	Unit	Symbol	Conversion from the base unit
117	Normal cubic meter	Nm³	Base unit
118	Thousand normal cubic meters	kNm³	1 Nm³ = 0.001 kNm³

Energy

Group Energy, id 18. Base unit: kJ.

Id	Unit	Symbol	Conversion from the base unit
107	Joule	J	1 kJ = 1000 J
108	Kilojoule	kJ	Base unit
109	Megajoule	MJ	1 kJ = 0.001 MJ
110	Gigajoule	GJ	1 kJ = 0.000001 GJ
111	Calorie	cal	1 kJ = 239 cal
112	Kilocalorie	kcal	1 kJ = 0.239 kcal
113	British Thermal Unit	BTU	1 kJ = 0.948 BTU
114	Foot-pound	ft-lb	1 kJ = 737.463 ft-lb
115	Kilowatt-hour	kWh	1 kJ = 1/3600 kWh
116	Megawatt-hour	MWh	1 kJ = 1/3600000 MWh

Mass

Group Mass, id 19. Base unit: kg.

Id	Unit	Symbol	Conversion from the base unit
66	Kilogram	kg	Base unit
67	Gram	g	1 kg = 1000 g
103	Metric Tonne	t	1 kg = 0.001 t

Area

Group Area, id 21. Base unit: m².

Id	Unit	Symbol	Conversion from the base unit
72	Square Meter	m²	Base unit

Volume

Group Volume, id 22. Base unit: m³.

Id	Unit	Symbol	Conversion from the base unit
73	m³	m³	Base unit

Emissivity

Group Emissivity, id 23. Base unit: Emissivity.

Id	Unit	Symbol	Conversion from the base unit
74	Emissivity	(none)	Base unit

Specific energy

Group SpecificEnergy, id 24. Heating/energy per Mass. Base unit: MJ/kg.

Id	Unit	Symbol	Conversion from the base unit
75	MJ/kg	MJ/kg	Base unit

Molar energy

Group MolarEnergy, id 25. Base unit: MJ/kmole.

Id	Unit	Symbol	Conversion from the base unit
76	MJ/kmole	MJ/kmole	Base unit

Specific entropy

Group SpecificEntropy, id 26. Heat Capacity Mass. Base unit: kJ/kg·K.

Id	Unit	Symbol	Conversion from the base unit
77	kJ/kg·K	kJ/kg·K	Base unit

Integer

Group Integer, id 27. Integer number without unit. Base unit: Integer.

Id	Unit	Symbol	Conversion from the base unit
68	Integer	(none)	Base unit

Standard density

Group StandardDensity, id 28. Base unit: kg/Nm³.

Id	Unit	Symbol	Conversion from the base unit
70	kg/Nm³	kg/Nm³	Base unit

Molar flow

Group MolarFlow, id 29. Base unit: kmole/s.

Id	Unit	Symbol	Conversion from the base unit
78	kmole/s	kmole/s	Base unit

Emissions per fuel energy

Group EmissionsPerFuelEnergy, id 30. mass of emission per fuel heat/energy. Base unit: mg/kJ.

Id	Unit	Symbol	Conversion from the base unit
80	mg/kJ	mg/kJ	Base unit

Boolean

Group Boolean, id 31. A value which can either be true or false. Base unit: Boolean.

Id	Unit	Symbol	Conversion from the base unit
81	Boolean	(none)	Base unit

Efficiency

Group Efficiency, id 32. Base unit: Fraction.

Id	Unit	Symbol	Conversion from the base unit
82	Fraction	(none)	Base unit
93	Percentage	%	1 Fraction = 100 %

Time

Group Time, id 33. Base unit: s.

Id	Unit	Symbol	Conversion from the base unit
87	Seconds	s	Base unit
88	Minutes	min	1 s = 1/60 min
89	Hours	h	1 s = 1/3600 h
90	Days	day	1 s = 1/86400 day

Number

Group Number, id 34. Base unit: Number.

Id	Unit	Symbol	Conversion from the base unit
91	Number	(none)	Base unit

Location

Group Location, id 35. Base unit: °.

Id	Unit	Symbol	Conversion from the base unit
92	Degrees	°	Base unit

Heat transfer coefficient

Group HeatTransferCoefficient, id 36. Base unit: W/(m²·K).

Id	Unit	Symbol	Conversion from the base unit
97	WattPerM2K	W/(m²·K)	Base unit

Rotational speed pct

Group RotationalSpeedPct, id 37. Base unit: Fraction.

Id	Unit	Symbol	Conversion from the base unit
100	Fraction	(none)	Base unit
101	Percentage	%	1 Fraction = 100 %