Calculate Radiator Output
Performance and Selection of Radiators, Calculating Radiators Correctly
How do I correctly calculate the necessary output of a radiator?
The performance of the radiators in this shop is specified for the parameters 75/65/20°C and 55/45/20°C (flow temperature / return temperature / room air temperature). To select a suitable heating system for the room to be equipped, a heat balance must be calculated according to the applicable standards.
To calculate the heat demand for the room, the following rules can be applied:
• For rooms and hallways in standard buildings with a ceiling height of 2.6 m and a room temperature of 20°C, we suggest 70-80 W/m². If the room has more than one window or more than one exterior wall, 80-100 W/m² should be assumed.
• For bathrooms in standard buildings with a ceiling height of 2.6 m and a room temperature of 24°C, we suggest 100-120 W/m². If the bathroom has a window or an exterior wall, 130-150 W/m² should be assumed.
The values provided are estimates. To determine the exact performance requirements for the room, you should obtain the relevant data from your building manager. These must be considered when planning the plumbing, or a project manager should be hired for the necessary measurements.
Example:
Room: Bathroom, area S = 5m², height 2.6m with one window. Assumed guideline value q = 140 W/m².
We calculate the required heat demand for the room Q as follows:
Q = S x q
Q = 5 x 140 W/m²
Q = 700 W
The estimated heat demand for the room mentioned above is approximately 700 W.
Correction Factor Table
The correction factor table is used to calculate heating output for other parameters than 75/65/20°C.
Example:
The calculated heat demand for a given room is 1120W.
The installation design includes the following parameters:
Flow temperature Tz = 70°C
Return temperature Tp = 55°C
Room temperature Ti = 24°C
Return temperature Tp = 55°C
Room temperature Ti = 24°C
For these parameters, we take the factor from the table below k = 1.42. By multiplying the required heat demand (1120W) with the observed factor k, we get the value of 1590W. With this value, we can select a radiator with the specifications 75/65/20°C from the catalog.
In summary: To achieve the heating output of 1120W at the "lower" network parameters (in the example: 70/55/24°C), a radiator must be selected that delivers 1590W at the "higher" parameters (75/65/20°C).
