Since air con­di­tion­ing sys­tems affect the air, it is very impor­tant to know its com­po­si­tion and oth­er para­me­ters. Air con­sists of water vapor and dry parts (oxy­gen, nitro­gen and oth­er gas­es). But for heat­ing and air con­di­tion­ing sys­tems, air para­me­ters such as tem­per­a­ture (T), atmos­pher­ic pres­sure (B) and mois­ture con­tent (D) are also impor­tant, as well as dry air pres­sure (Pg), rel­a­tive humid­i­ty (F), air den­si­ty ℗, enthalpy (H), impu­ri­ty con­tent.

Basic con­cepts and def­i­n­i­tions


This is a term that reflects how much a sub­stance or body is heat­ed or cooled. Most often, tem­per­a­ture is mea­sured in degrees Kelvin (ther­mo­dy­nam­ic or absolute tem­per­a­ture), as well as in degrees Cel­sius.
1. Cel­sius scale (°C): the boil­ing point of water is 100 degrees, and the freez­ing point is 0 degrees.
2. The Kelvin scale (K): the absolute zero of this scale is the tem­per­a­ture when the ther­mal move­ment of par­ti­cles stops. On the Kelvin scale, the boil­ing point is 373.15 K and the freez­ing point is 273.15 K.
To con­vert the tem­per­a­ture to the Kelvin scale from the Cel­sius scale, you need to use the fol­low­ing for­mu­la: T (tem­per­a­ture on the Kelvin scale) u003d t + 273.15.
In prac­tice, tem­per­a­ture is mea­sured by two types of ther­mome­ters: a wet bulb ther­mome­ter and a dry bulb ther­mome­ter.

If the rel­a­tive humid­i­ty of the air is less than 100% (that is, the air does not appear to be water vapor), then the wet and dry bulbs will show com­plete­ly dif­fer­ent tem­per­a­tures. The dry bulb tem­per­a­ture will be high­er than the wet bulb tem­per­a­ture. And the tem­per­a­ture dif­fer­ence will be greater at low­er rel­a­tive humid­i­ty.


1. Mois­ture con­tent (d), which is expressed in g/kg and is the amount of vapor per kilo­gram of dry air.
2.Absolute humid­i­ty is mea­sured in kg/cu. m and dis­plays how much steam is in a cubic meter of air.
3. Rel­a­tive humid­i­ty (F) is the ratio of the max­i­mum pos­si­ble mois­ture con­tent at a giv­en tem­per­a­ture and pres­sure to its actu­al con­tent. If Ф=0, then there is no water vapor in the air and it is absolute­ly dry. Ф=100% cor­re­sponds to wet steam. For humans, com­fort­able humid­i­ty is approx­i­mate­ly 50–70%.

Quan­ti­ty of heat

This is the ener­gy that is trans­ferred to a sub­stance or body as a result of its heat exchange with the exter­nal envi­ron­ment. The unit of mea­sure is the joule (J).
Heat­ing or cool­ing pow­er is a quan­ti­ta­tive char­ac­ter­is­tic of the abil­i­ty to cool or heat bod­ies. It is denot­ed in watts (W), and 1000 watts is equal to a kilo­watt (kW). Pow­er also depends on the time dur­ing which heat is trans­ferred. For exam­ple, if the pow­er of your heater is 3000 W, then this means that it gives off 3000 J of heat in one sec­ond.

Units of mea­sure­ment of phys­i­cal quan­ti­ties

SI — the inter­na­tion­al sys­tem of units of mea­sure­ment is cur­rent­ly rec­og­nized as the main sys­tem of units in physics (includ­ing refrig­er­a­tion and air con­di­tion­ing). Its basic units are meter (length), sec­ond (time), kilo­gram (mass), kelvin (tem­per­a­ture), ampere (cur­rent), can­dela (light inten­si­ty) and mole (amount of sub­stance).

Air con­di­tion­ing also uses many derived quan­ti­ties, such as spe­cif­ic heat capac­i­ty. It is equal to the amount of heat that, in order to increase the tem­per­a­ture of a body by 1 K, must be brought to a unit of its mass. Spe­cif­ic heat capac­i­ty is mea­sured in J / (kg * K).

In for­eign tech­ni­cal lit­er­a­ture, off-sys­tem units of mea­sure­ment are also often used.

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