SI guide.pdf

IRU

+9$&5

0D\

$PHULFDQ6RFLHW\RI+HDWLQJ5HIULJHUDWLQJDQG$LU&RQGLWLRQLQJ(QJLQHHUV,QF

7XOOLH&LUFOH$WODQWD*HRUJLD)D[

KWWSZZZDVKUDHRUJ

SI for HVAC& R

Revised June 1997

This guide conforms to ANSI SI 10-1997, Standard for Use

of the International System of Units (SI): The Modern Metric

System . See ANSI SI 10 for more information and a complete

list of conversion factors with more significant digits.

SI PRACTICE

1 General

1.1 The International System of Units (SI) consists of seven

base units listed in Table 1 and numerous derived units, which

are combinations of base units (Table 2).

ASHRAE METRIC POLICY

The metric unit use or application policy shall include, as a

minimum, time-dated directions on the use of SI and I-P

units in all ASHRAE publications.

Ta b l e 1 S I B a s e U n i ts

Quantity

Name

Symbol

length

metre

1. The Technical Committee on terminology, TC 1.6, shall

serve as the authority on SI and I-P usage and application.

2. Research projects, Standards and Guidelines, Special

Publications, Insights articles, Journal articles, and Hand-

books shall be prepared using inch-pound (I-P) units and/

or the International System of Units (SI) in formats

approved by the Publishing Council.

3. The Publishing Council shall review annually the

approved formats to be used in ASHRAE publications—

considering suggestions from members, Technical Com-

mittees/Task Groups/Technical Resource Groups, Stan-

dards Project Committees, Research and Technical

Committee, Journal, Handbook, and other General Com-

mittees, and shall establish any changes in the approved

formats.

4. The Publishing Council shall consider this policy annually

and shall recommend to the Board of Directors the formats

to be used in ASHRAE publications.

a. The format for ASHRAE publications shall be dual

units, except in cases determined by the Publishing

Council, where two separate versions are to be pub-

lished, one rational I-P and the other rational SI. For

selected ASHRAE Standards and Guidelines, the Stan-

dards Committee may approve use of SI units only.

b. In dual unit publications, the units used in calculating

the work being reported shall be listed first. The alter-

nate system of units should follow in parenthesis.

Authors shall round off equivalents in the alternate sys-

tem of units so that they imply the same accuracy as is

implied with primary units.

c. Exceptions require the approval of the Director of

Communications and Publications.

d. All Handbook volumes are published in separate I-P

and SI editions.

mass

kilogram

time

second

electric current

ampere

thermodynamic temperature

kelvin

amount of substance

mole

mol

luminous intensity

candela

2Uns

2.1 In SI each physical quantity has only one unit. The base

and derived units may be modified by prefixes as indicated in

Section 4. All derived units are defined by simple formulas

using the base units. The basic simplicity of the system can

only be kept by adhering to the approved units.

2.2 Angle. The unit of plane angle is the radian. The degree

and its decimal fractions may be used, but the minute and sec-

ond should not be used.

2.3 Area. The unit of area is the square metre. Large areas

are expressed in hectares (ha) or square kilometres (km 2 ). The

hectare is restricted to land or sea areas and equals 10 000 m 2 .

2.4 Energy. The unit of energy, work, and quantity of heat is

the joule (J). The kilowatthour (kWh) is presently permitted as

an alternative in electrical applications, but should not be intro-

duced in new applications.

1 kilowatthour (kWh) = 3.6 megajoules (MJ)

The unit of power and heat flow rate is the watt (W).

1 watt (W) = 1 joule per second (J/s)

2.5 Force. The unit of force is the newton (N). The newton is

also used in derived units which include force.

Examples :

pressure or stress = N/m 2 = Pa (pascal)

work = N· m = J (joule)

power = N· m/s = W (watt)

ASHRAE® has compiled this publication with care, but ASHRAE has not investigated, and ASHRAE expressly disclaims any duty to investigate, any product, service, process,

procedure, design, or the like that may be described herein. The appearance of any technical data or editorial material in this publication does not constitute endorsement, warranty,

or guaranty by ASHRAE of any product, service, process, procedure, design, or the like. ASHRAE does not warrant that the information in this publication is free of errors. The

entire risk of the use of any information in this publication is assumed by the user.

SI for HVAC&R

Table 2 Some SI Derived Units

2.8 Pressure. The unit of stress or pressure, force per unit

area, is the newton per square metre. This unit is called the

pascal (Pa). SI has no equivalent symbol for psig or psia. If a

misinterpretation is likely, spell out Pa (absolute) or Pa

(gage).

2.9 Vo lu me . The unit of volume is the cubic metre. Smaller

units are the litre, L (m 3 /1000); millilitre, mL; and microlitre,

Quantity

Expression in

Other SI Units Name

Symbol

acceleration

angular

rad/s 2

linear

m/s 2

angle

plane

dimensionless

radian

rad

solid

dimensionless

steradian

is used with litre.

2.10 Temperature. The unit of thermodynamic (absolute)

temperature is the Kelvin. Celsius temperature is measured in

degrees Celsius. Temperature intervals may be measured in

kelvins or degrees Celsius and are the same in either scale.

Thermodynamic temperature is related to Celsius temperature

as follows:

area

m 2

Celsius temperature

degree Celsius

°C

conductivity, thermal

W/(m · K)

density

heat flux

W/m 2

mass

kg/m 3

energy, enthalpy

work, heat

N· m

joule

specific

J/kg

t c = T

T 0

entropy

heat capacity

J/K

where

specific

J/(kg · K)

t c = Celsius temperature, °C

T = thermodynamic temperature, kelvins (K)

T 0 = 273.15 K by definition

2.11 Time. The unit of time is the second, which should be

used in technical calculations. However, where time relates to

life customs or calendar cycles, the minute, hour, day, and

other calendar units may be necessary.

flow, mass

kg/s

flow, volume

m 3 /s

force

kg ·m/s 2

newton

frequency

periodic

1/s

hertz

rotating

rev/s

inductance

Wb/A

henry

magnetic flux

V · s

weber

moment of a force

N·m

potential, electric

W/A

volt

Exception :

Revolutions per minute may be used, but

revolutions per second is preferred.

power, radiant flux

J/s

watt

pressure, stress

N/m 2

pascal

resistance, electric

V/a

ohm

3Symbo s

velocity

angular

rad/s

3.1 The correct use of symbols is important because an incor-

rect symbol may change the meaning of a quantity. Some SI

symbols are listed in Table 3.

3.2 SI has no abbreviations—only symbols. Therefore, no

periods follow a symbol except at the end of a sentence.

linear

m/s

viscosity

dynamic (absolute)(m) Pa ·s

kinematic (n)

m 2 /s

volume

m 3

volume, specific

m 3 /kg

2.6 Length. The unit of length is the metre. The millimetre

is used on architectural or construction drawings and

mechanical or shop drawings. The symbol mm does not need

to be placed after each dimension; a note, “All dimensions in

mm” is sufficient.

The centimetre is used only for cloth, clothing sizes, and

anatomical measurements.

The metre is used for topographical and plot plans. It is

always written with a decimal and three figures following the

decimal, i.e., 38.560.

2.7 Mass. The unit of mass is the kilogram (kg). The unit of

mass is the only unit whose name, for historical reasons, con-

tains a prefix. Names of multiples of the unit mass are formed

by attaching prefixes to the word gram. The megagram, Mg,

(1000 kg, metric ton or tonne, t) is the appropriate unit for

describing large masses. Do not use the term weight when mass

is intended.

Examples : I, not S.I.; s, not sec; A, not amp

3.3 Symbols appear in lower case unless the unit name has

been taken from a proper name. In this case the first letter of the

symbol is capitalized.

Examples : m, metre; W, watt; Pa, pascal

Exception : L, litre

3.4 Symbols and prefixes are printed in upright (roman) type

regardless of the type style in surrounding text.

Example : . . . a distance of 56 km between . . .

3.5 Unit symbols are the same whether singular or plural.

Examples : 1 kg, 14 kg; 1 mm, 25 mm

3.6 Leave a space between the value and the symbol.

Examples :

55 mm, not 55mm; 100 W, not 100W

L. No prefix other than m or

Revised June 1997

Table 3 SI Symbols

Symbol Name

3.8 Symbol for product—use the raised dot (·)

Quantity

Formula

Examples : · ; a · s; W/( 2 ·K)

3.9 Symbol for quotient—use one of the following forms:

ampere

electric current

base unit

atto

prefix

10 - 18

becquerel

activity (of a radio nuclide) 1/s

Examples :

m/s or or use negative exponent

----

coulomb

quantity of electricity

A·s

°C

degree Celsius

temperature

°C = K

Note: Use only one solidus ( / ) per expression.

3.10 Place modifying terms such as electrical, alternating

current, etc. parenthetically after the symbol with a space in

between.

centi

prefix

10 - 2

candela

luminous intensity

base unit

deci

prefix

10 - 1

deka

prefix

10 1

exa

prefix

10 18

farad

electric capacitance

C/V

Examples :

MW (e); not MWe; not MW(e)

V (ac); not Vac; not V(ac)

kPa (gage); not kPa(gage); not KPa gage

femto

prefix

10 - 15

giga

prefix

10 9

gray

absorbed dose

J/kg

gram

mass

kg/1000

henry

inductance

Wb/A

4 Prefixes

4.1 Most prefixes indicate orders of magnitude in steps of

1000. Prefixes provide a convenient way to express large and

small numbers and to eliminate nonsignificant digits and

leading zeros in decimal fractions. Some prefixes are listed in

Table 4.

hertz

frequency

1/s

hecto

prefix

10 2

hectare

area

10 000 m 2

joule

energy, work, heat

N· m

kelvin

temperature

base unit

kilo

prefix

10 3

kilogram

mass

base unit

litre

volume

m 3 /1000

lumen

luminous flux

cd · sr

Examples : 126 000 watts is the same as 126 kilowatts

0.045 metre is the same as 45 millimetres

65 000 metres is the same as 65 kilometres

4.2 To realize the full benefit of the prefixes when expressing

a quantity by numerical value, choose a prefix so that the num-

ber lies between 0.1 and 1000. For simplicity, give preference

to prefixes representing 1000 raised to an integral power (i.e.,

lux

illuminance

lm/m 2

mega

prefix

10 6

metre

length

base unit

milli

prefix

10 - 3

mol

mole

amount of substance

base unit

micro

prefix

10 - 6

newton

force

kg·m/s 2

nano

prefix

10 - 9

ohm

electric resistance

V/A

m, mm, km).

peta

prefix

10 15

pascal

pressure, stress

N/m 2

Exceptions :

1. In expressing area and volume, the prefixes hecto, deka,

deci, and centi are sometimes used; for example, cubic

decimetre (L), square hectometre (hectare), cubic centi-

metre.

2. Tables of values of the same quantity.

3. Comparison of values.

pico

prefix

10 - 12

rad

radian

plane angle

dimensionless

siemens

electric conductance

A/V

sievert

dose equivalent

J/kg

second

time

base unit

steradian

solid angle

dimensionless

tera

prefix

10 12

tesla

magnetic flux density

Wb/m 2

tonne, metric ton

mass

1000 kg; Mg

volt

electric potential

W/A

Table 4 SI Prefixes

Prefix Pronunciation

watt

power, radiant flux

J/s

weber

magnetic flux

V· s

Symbol Represents

Exception :

No space is left between the numerical value

and symbol for degree Celsius and degree of

plane angle.

exa

ex‡a (a as in about)

10 18

peta

pet‡a (e as in pet, a as in about)

10 15

tera

as in terra firma

10 12

giga

jig‡ (i as in jig, a as in about)

10 9

Note: Symbol for degree Celsius is °C; for coulomb, C.

mega

as in mega phone

10 6

kilo

kill‡oh

10 3

= 1000

Examples : 20°C, not 20 °C or 20° C; 45°, not 45 °

3.7 Do not mix symbols and names in the same expression.

hecto

heck‡ toe

10 2

= 100

deka

deck‡a (a as in about)

da*

10 1

= 10

deci

as in deci mal

10 - 1

= 0.1

Examples :

m/s or metres per second,

not metres/second; not metres/s

centi

as in centi pede

10 - 2

= 0.01

milli

as in mili tary

10 - 3

= 0.001

micro

as in micro phone

10 - 6

J/kg or joules per kilogram,

not joules/kilogram; not joules/kg

nano

nan‡oh (an as in ant)

10 - 9

pico

peek‡oh

10 - 12

*See paragraph 4.2 regarding use of this prefix.

SI for HVAC&R

4. For certain quantities in particular applications. For exam-

ple, the millimetre is used for linear dimensions in engi-

neering drawings even when the values lie far outside the

range of 0.1 mm to 1000 mm; the centimetre is usually

used for body measurements and clothing sizes.

4.3 Compound units. A compound unit is a derived unit

expressed with two or more units. The prefix is attached to a

unit in the numerator.

Examples : /m not mV/mm

mN·m not N·mm (torque)

MJ/kg not kJ/g

4.4 Compound prefixes formed by a combination of two or

more prefixes are not used. Use only one prefix.

Examples :

2 m not 2 m

6.2 Treat all spelled out names as nouns. Therefore, do not

capitalize the first letter of a unit except at the beginning of a

sentence or in capitalized material such as a title.

Examples : watt; pascal; ampere; volt; newton; kelvin

Exception : Always capitalize the first letter of Celsius.

6.3 Do not begin a sentence with a unit symbol—either rear-

range the words or write the unit name in full.

6.4 Use plurals for spelled out words when required by the

rules of grammar.

Examples : metre — metres; henry — henries;

kilogram — kilograms; kelvin — kelvins

Irregular : hertz — hertz; lux — lux;

siemens — siemens

6.5 Do not put a space or hyphen between the prefix and unit

name.

Examples : kilometre not kilo metre or kilo-metre;

milliwatt not milli watt or milli-watt

6.6 When a prefix ends with a vowel and the unit name

begins with a vowel, retain and pronounce both vowels.

Example : kiloampere

Exceptions : hectare; kilohm; megohm

6.7 When compound units are formed by multiplication,

leave a space between units that are multiplied.

Examples : newton metre, not newton-metre;

volt ampere, not volt-ampere

6.8 Use the modifier squared or cubed after the unit name.

6 m 3 not 6 kL

6 MPa not 6 kkPa

4.5 Exponential Powers. An exponent attached to a symbol

containing a prefix indicates that the multiple (of the unit with its

prefix) is raised to the power of 10 expressed by the exponent.

Examples :

1 3 = (10 - 3 m) 3 = 10 - 9 m 3

1 ns - 1 = (10 - 9 s) - 1 = 10 9 s - 1

1 mm 2 /s = (10 - 3 m) 2 /s = 10 - 6 m 2 /s

5 Numbers

5.1 Large Numbers. International practice separates the

digits of large numbers into groups of three, counting from the

decimal to the left and to the right, and inserts a space to sepa-

rate the groups. In numbers of four digits, the space is not nec-

essary except for uniformity in tables.

Examples : 2.345 678; 73 846; 635 041; 600.000;

0.113 501; 7 258

5.2 Small Numbers. When writing numbers less than one,

always put a zero before the decimal marker.

Example : 0.046

5.3 Decimal Marker. The recommended decimal marker is

a dot on the line (period). (In some countries, a comma is used

as the decimal marker.)

5.4 Billion. Because billion means a thousand million in the

United States and a million million in most other countries,

avoid using the term in technical writing.

5.5 Roman Numerals. Do not use M to indicate thousands

(MBtu for a thousand Btu), nor MM to indicate millions, nor C

to indicate hundreds because they conflict with SI prefixes.

Example : metre per second squared

Exception : For area or volume place the modifier before

the units. Example : square millimetre; cubic

metre

6.9 When compound units are formed by division, use the

word per , not a solidus ( / ).

Examples :

metre per second, not metre/second;

watt per square metre, not watt/square metre

TEMPERATURE CONVERSION

(exact)

t C = ( t F -

32)/1.8

t F = 1.8 t C + 32

t C = T

273.15

t F = T R

459.67

T = T R /1.8

T R = 1.8 T

T = t C + 273.15

T R = t F + 459.67

6Words

6.1 The units in the international system of units are called SI

units—not Metric Units and not SI Metric Units.

(Inch-Pound units are called I-P units—not conventional

units, not U.S. customary units, not English units, and not

Imperial units.)

where

t C = Celsius temperature, °C

T = thermodynamic (absolute) temperature, kelvins (K)

t F = Fahrenheit temperature, °F

T R = thermodynamic (absolute) temperature, degrees

Rankine (°R)

and °C = K = 1.8°F °F = °R = °C/1.8

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: