Annex C — Unit code vocabulary — Building Understanding Standard

C Unit codes§

Normative. C.3 is informative.

C.1 Why this vocabulary exists§

A dimensional value needs a canonical unit representation or values cannot be compared, converted, or checked. This document defines one rather than adopting an external registry, for two reasons.

The first is legibility. A package is read by the engineers who operate the building, and the codes they meet should be the codes they write. The second is coverage: at least one unit in daily use across the industry — the ton of refrigeration — has no code at all in the registry this draft previously cited, which is a coverage failure rather than a matter of taste.

NOTE This is the same pattern used for classifications (7.7). Define the small thing that is needed, name the external vocabulary where one is used, and do not force everything through a foreign one.

C.2 The vocabulary§

Codes are case-sensitive and follow SI capitalization: kW, not KW. Compound codes that appear here are atomic tokens, not a grammar; m3/s is one code, not a construction. A unit not in this table is expressed by setting unitSystem and carrying that system's code (7.4), and is NOT invented as a new bus code.

Temperature§

Code	Unit	Quantity
`degF`	degrees Fahrenheit	temperature
`degC`	degrees Celsius	temperature
`K`	kelvin	temperature
`deltaDegF`	delta degrees Fahrenheit	temperature difference
`deltaDegC`	delta degrees Celsius	temperature difference

Pressure§

Code	Unit	Quantity
`Pa`	pascal	pressure
`kPa`	kilopascal	pressure
`inH2O`	inches of water column	pressure
`inHg`	inches of mercury	pressure
`psi`	pounds per square inch	pressure
`bar`	bar	pressure

Flow and velocity§

Code	Unit	Quantity
`cfm`	cubic feet per minute	volumetric flow
`m3/s`	cubic meters per second	volumetric flow
`m3/h`	cubic meters per hour	volumetric flow
`L/s`	liters per second	volumetric flow
`gpm`	US gallons per minute	volumetric flow
`kg/s`	kilograms per second	mass flow
`lb/h`	pounds per hour	mass flow
`fpm`	feet per minute	velocity
`m/s`	meters per second	velocity

Power and energy§

Code	Unit	Quantity
`W`	watt	power
`kW`	kilowatt	power
`MW`	megawatt	power
`Btu/h`	BTU per hour	power
`MBtu/h`	thousand BTU per hour	power
`tonRef`	tons of refrigeration. No equivalent exists in any external registry surveyed. One ton of refrigeration is 12000 Btu/h exactly.	power
`hp`	horsepower	power
`Wh`	watt hour	energy
`kWh`	kilowatt hour	energy
`MWh`	megawatt hour	energy
`J`	joule	energy
`MJ`	megajoule	energy
`Btu`	British thermal unit	energy
`therm`	therm	energy
`tonHours`	ton hours of refrigeration	energy

Electrical§

Code	Unit	Quantity
`V`	volt	electric potential
`A`	ampere	electric current
`kVA`	kilovolt-ampere	apparent power
`kVAR`	kilovolt-ampere reactive	reactive power
`Hz`	hertz	frequency
`ohm`	ohm	resistance

Length, area, volume, and mass§

Code	Unit	Quantity
`m`	meter	length
`mm`	millimeter	length
`ft`	foot	length
`in`	inch	length
`m2`	square meters	area
`ft2`	square feet	area
`m3`	cubic meters	volume
`ft3`	cubic feet	volume
`L`	liter	volume
`gal`	US gallon	volume
`kg`	kilogram	mass
`lb`	pound	mass

Time§

Code	Unit	Quantity
`ms`	millisecond	time
`s`	second	time
`min`	minute	time
`h`	hour	time
`day`	day	time
`yr`	year	time

Ratio, humidity, and concentration§

Code	Unit	Quantity
`pf`	power factor	ratio
`pct`	percent	ratio
`ratio`	dimensionless ratio	ratio
`pctRH`	percent relative humidity	relative humidity
`gPerKg`	grams of water per kilogram of dry air	humidity ratio
`grPerLb`	grains of water per pound of dry air	humidity ratio
`ppm`	parts per million	concentration
`ppb`	parts per billion	concentration
`mg/m3`	milligrams per cubic meter	concentration
`ug/m3`	micrograms per cubic meter	concentration
`count`	count	count

Rotation, light, sound, and angle§

Code	Unit	Quantity
`rpm`	revolutions per minute	rotational speed
`lux`	lux	illuminance
`fc`	foot-candle	illuminance
`dB`	decibel	sound level
`dBA`	A-weighted decibel	sound level
`deg`	degree of arc	angle
`rad`	radian	angle

C.3 Mapping to the Unified Code for Units of Measure§

Informative. Provided for implementations that exchange with systems using that registry. No conformance requirement depends on this table.

BUS code	Equivalent	BUS code	Equivalent
`degF`	`[degF]`	`degC`	`Cel`
`K`	`K`	`deltaDegF`	`[degF]`
`deltaDegC`	`Cel`	`Pa`	`Pa`
`kPa`	`kPa`	`inH2O`	`[in_i'H2O]`
`inHg`	`[in_i'Hg]`	`psi`	`[psi]`
`bar`	`bar`	`cfm`	`[cft_i]/min`
`m3/s`	`m3/s`	`m3/h`	`m3/h`
`L/s`	`L/s`	`gpm`	`[gal_us]/min`
`kg/s`	`kg/s`	`lb/h`	`[lb_av]/h`
`fpm`	`[ft_i]/min`	`m/s`	`m/s`
`W`	`W`	`kW`	`kW`
`MW`	`MW`	`Btu/h`	`[Btu_IT]/h`
`MBtu/h`	`k[Btu_IT]/h`	`tonRef`	(none defined)
`hp`	`[HP]`	`Wh`	`W.h`
`kWh`	`kW.h`	`MWh`	`MW.h`
`J`	`J`	`MJ`	`MJ`
`Btu`	`[Btu_IT]`	`therm`	`[Btu_IT]`
`tonHours`	(none defined)	`V`	`V`
`A`	`A`	`kVA`	`kV.A`
`kVAR`	(none defined)	`Hz`	`Hz`
`pf`	`1`	`ohm`	`Ohm`
`m`	`m`	`mm`	`mm`
`ft`	`[ft_i]`	`in`	`[in_i]`
`m2`	`m2`	`ft2`	`[sft_i]`
`m3`	`m3`	`ft3`	`[cft_i]`
`L`	`L`	`gal`	`[gal_us]`
`kg`	`kg`	`lb`	`[lb_av]`
`ms`	`ms`	`s`	`s`
`min`	`min`	`h`	`h`
`day`	`d`	`yr`	`a`
`pct`	`%`	`pctRH`	`%`
`ppm`	`[ppm]`	`ppb`	`[ppb]`
`ratio`	`1`	`count`	`1`
`mg/m3`	`mg/m3`	`ug/m3`	`ug/m3`
`gPerKg`	`g/kg`	`grPerLb`	`[gr]/[lb_av]`
`rpm`	`{rpm}`	`lux`	`lx`
`fc`	`[ftc]`	`dB`	`dB`
`dBA`	(none defined)	`deg`	`deg`
`rad`	`rad`

NOTE Three codes have no equivalent in that registry: tonRef, tonHours, and kVAR. All three are in daily use in building operations, which is part of why this document defines its own vocabulary.