ti = water temperature inlet (oC)
tr = water temperature outlet (oC)
ta = surrounding air temperature (oC)
n = constant describing the type of radiator (1.33 for standard panel radiators, 1.3 - 1.6 for convectors)
Note that radiators are in general designed for middle panel temperature 70oC - and surrounding air temperature 20oC (difference 50oC)
The heat emission from a radiator with nominal*) heat emission 1000 W with water inlet temperature ti = 70oC and outlet temperature tr = 50oC can be calculated
P = (1000 W) [(((70 oC) - (50 oC)) / ln(((70 oC) - (20 oC)) / ((50 oC) - (20 oC)))) (1 / 49.32)]1.33
= 736 W
*) nominal when inlet water temperature ti = 80oC, outlet water temperature out tr = 60oC and surrounding air temperature ta = 20oC
The calculator below can be used to calculate heat emission and water flow from a radiator operating outside the standard conditions - like increasing or decreasing the water inlet or outlet temperature or increasing or decreasing the surrounding room air temperature.
The calculator below can be used to calculate the water return temperature and the water volume flow through radiators based on actual heat emission and inlet water temperatures.
Oversized radiators are quite common since it is almost never possible to adapt a standard radiator exactly to the required heat loss from a room. With the calculator below it is possible to study the consequence of out of standard heat emission when a radiator is oversized.
- heat loss from the room covered by the radiator (W)
When checking heat emission capacities of radiators - be aware that testing standards differs. Examples of standards:
Testing the same radiator with BS EN442 compared to BS 3528 reduces the heat output with approximately 11%.
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