Correction factors for the selection of Purmo heaters with other than nominal operating parameters of the central heating system.

An example is the data from the table for Purmo radiators. It follows from them, that the radiator used in a room with an installation with parameters e.g.. 75/55° C should have an area of ​​over 50% greater than the nominal parameters, Ie. 90/70°C. The selection of a radiator is a complex issue, so it should be thought out and based on the analysis of a number of criteria, among which are the most important:

– thermal performance under comparable design conditions (Ie. for t1 = +90°C, t2 = +70°C, ie = +20°C => ΔIgo = 60K),

– technical and occupational safety assessment (for example. checking the allowable pressure),

– assessment of obtaining the desired thermal comfort in rooms,

– assessment of aesthetics with regard to shape, forms of housing and execution.
Of fundamental importance for the selection of the radiator is its thermal efficiency and heat transfer coefficient. This coefficient is determined from the formula:where a is the coefficient, and b – exponent, they are determined on the basis of experiments in experimental chambers (is accepted, e b ng – 1).

Ultimately, the selection of a radiator is made on the basis of dependencies:

or when there are no heat gains from heating pipes (Qz = o)are coefficients depending on whether the radiator is equipped with a valve with a thermostatic head (T), the location in the room (U), shields (O) and the method of connection to the installation (P – when a solution other than the method was used, for which thermal characteristics were developed). These coefficients are presented in the table,

Most often, the selection of the thermal power of radiators is made using tables developed by manufacturers. For Purmo radiators, this characteristic is the relationship in the form:where H and L are the height and length of the radiator (m), ΔT = Δℑg is the difference between the average water temperature in the radiator and the air temperature in the room (K), C, Z and n are experimentally determined quantities, and ε is a correction factor equal to:where α is the ratio of temperature differences, with a = (t2 – you)/(t1 – you), t1 and t2 are the heating water supply and return temperatures, respectively, and ti is the air temperature in the room.