The thermal dissipation of an electrical enclosures is one of the most important elements to consider before installing the cabinet itself. For this reason, it’s necessary to calculate the thermal balance of the electrical cabinet in order to preserve the devices correct functioning and to make any necessary adjustments to ensure an optimal temperature inside.
Why do calculate the thermal balance of an electrical enclosure?
The thermal balance for an electrical cabinet is the optimal condition to preserve the life of the installed components, but requires a careful evaluation of all the thermal powers acting on it: it’s valid if all the thermal powers sum gives a zero resultant. The goal of the engineer is therefore to obtain the desired conditions within the electrical panel, also called “design conditions”, especially in terms of temperature.
Evaluation of the environmental conditions of an electrical enclosure to calculate the thermal dissipation
In order to obtain the thermal balance of an electrical cabinet, the “design conditions” must be defined, i.e. the desired temperature inside the cabinet and the most critical one in the installation environment. In this regard, during the design of heating systems, the lowest verifiable temperature in the installation environment must be considered; on the contrary, for cooling system, one must consider the highest possible. A good rule is to impose 35°C for the internal temperature set point: 35°C inside the cabinet are in fact adequate to avoid overheating, dangerous for the electrical components and make very unlikely the risk of condensation, which could cause short circuit.
Thermal powers through the walls of the electrical enclosure
The thermal power, i.e. the amount of thermal energy exchanged in the unit of time, transmitted through the walls of the electrical cabinet is just one of the factors that guarantee the thermal balance and depends on:
- Environmental conditions in terms of temperature;
- Material of the electrical cabinet;
- Location of the electrical cabinet in space.
The knowledge of these three information allows the designer to calculate the thermal dissipations of an electrical cabinet.
Which factor influences the formation of condensation in an electrical panel?
The term “humid air” refers to the mixture of dry air, consisting of gas and water in the vapor state. This term is used, because water is the only component subject to phase transitions at the typical temperatures present on the Earth and by condensing it physically separates from the air. Psychrometry is the study of mixtures consisting of air and water and the related transformations and can be evaluated through a psychrometric diagram. Condensation may occur in an environment with high relative humidity, which could cause a short circuit on the electrical panel.
Which factor affects the calculation of thermal dissipation?
Thermal energy, also called heat, is a form of energy whose exchange between two physical systems is closely connected to a temperature difference. In other words, the electrical cabinet and the environment exchange thermal power only if they have different temperatures.
Do you want to know more? Read our #whitepaper about designing electrical panel thermal management
In on-board machine applications the electrical panel is one of the elements designers focus on and has now reached qualified standards, especially with reference to safety
One of the new topics designers now face is that of panel climate control The more demanding needs in terms of machine flexibility and connectivity, the adoption of increasingly small electronic devices, fully unexpected concurrent factors and the climate conditions of highly variable installations due to production delocalisation trigger a scenario where electrical cabinet climate design becomes a fundamental elements for system sturdiness, guaranteeing its durability and elimination of machine downtime.
We would like to offer you a series of technical booklets to assist the design of all the elements that contribute to the correct dimensioning of the electrical panel thermal balance.
To download all the PDFs below, click here: Critical elements fot correct climate control design for electrical panels
The following White Paper provides basic notions to understand the concept of moist air and psychrometry. The most common physical properties referred to the topic are then defined to study humid air transformations:
- dry bulb temperature
- wet bulb temperature
- dew point
- relative humidity
- specific humidity
- specific enthalpy
- mentions of psychrometric diagram and its use
The environmental conditions suited to the electrical cabinet interior and installation environment are defined in this White Paper:
- temperature (dry bulb temperature)
- relative humidity
- specific enthalpy
- specific humidity
- Mention of the CEI EN 61439 standard referred to low voltage electrical panels and the indications it provides for design temperatures (35°C electrical cabinet interior)
- CEI EN 61439 standard reference table
- ΔTrisc (temperature delta to design the electrical cabinet heating system)
- ΔTraff (temperature delta to design the electrical cabinet cooling system)
This publication defines the thermal balance equations of the electrical cabinet, both in the case of heating and cooling. The largest number of possible components is considered in the calculation formulas:
- power through the cabinet walls
- power dissipated by electrical components by JOULE effect
- power due to solar irradiation
- electrical cabinet heating power
- electrical cabinet cooling power
- a focus on thermal power through the walls of the electrical cabinet, where the general formula to calculate its thermal transmittance is defined.
The following White Paper includes an in-depth analysis on adduction coefficient calculation formulas according to the UNI EN ISO 6946 standard.
First of all, the formula for calculating the global adduction coefficient as the sum of the radiative and convective coefficients. The specifics are explained next:
- real radiative coefficient
- radiative coefficient of the black body
- superficial emissivity
- Stefan-Boltzmann constant
- thermodynamic temperature
Finally, the numerical values of the adduction coefficients for different design cases are reported.
This White Paper describes the formulas for calculating the thermal exchange surfaces for the 12 possible electrical cabinet layouts in the installation environment.
Following an initial introduction on the dimensions inherent to the cabinet surfaces, the area calculation formulas are explained, integrated with the name and drawing for each individual layout.
The objective of this White Paper is to summarise the factors required to calculate the electrical cabinet thermal dissipations. How to define the ΔT valid for determining the thermal dissipation in the cabinet heating condition and the one used to calculate the same in the case of cooling is explained.
To download all the PDFs above, click here: Critical elements fot correct climate control design for electrical panels
Sensis by Fandis
With Sensis by Fandis, the new intelligent device, it’s possible to measure the temperature from one to three different points in the panel, and combine the values with the measured relative humidity. Furthermore, Sensis constantly monitors the efficiency of the ventilation systems, thanks to an anemometric sensor that can be applied to any type of installation.
Visit our website fandis.it and discover our products for electrical enclosures, or leave a comment to this article. One of our technicians will answer you as soon as possible.