The amount of heat Q carried by a fluid depends on the available mass flow m, the specific heat capacity c, and the temperature spread ΔT.
Within the temperature range normally used in the HVAC field, the specific heat capacity c of water changes only slightly. Therefore, the approximate value used for the specific heat capacity c is 4.19 kJ/(kg·K). This makes it possible to apply a simplified formula with a constant of 1.163 kWh/(m3·K) for calculating the volumetric flow V in m3/h:
If watery solutions, such as mixtures of water and antifreeze, or other fluids like heat transfer oils are used for the transmission of heat, the required volumetric flow V is to be calculated with the density ρ and the specific heat capacity c at the operating temperature:
The specific heat capacity of fluids is specified in trade literature. For mixtures, the specific heat capacity c is calculated on the basis of the mixture’s mass proportions m1 and m2:
In the case of heating applications, the specific heat capacity c1 or c2 at the highest temperature must be used, and in the case of cooling applications that at the lowest temperature.