Energy use, modern heat generation and the optimization of existing heating systems are key issues of our time - which makes precise heating load calculation all the more important. This can be simplified by heat load calculation software, as a room-by-room heat load calculation makes calculating the heat load child's play. In addition, software can make heat requirement calculations easier and a heat load calculation with Excel in accordance with DIN 12831 is a thing of the past.
The heating load is the decisive indicator for an indoor climate that is perceived as comfortable. A heating system works best when it is correctly designed and dimensioned. This ensures that a pleasant level of warmth is generated during the heating season and that the system operates as energy-efficiently as possible.
A heating load calculation is used by an expert to determine the optimum size of a heating system, which is crucial for optimized energy efficiency, especially with heat pumps and modern condensing hybrid appliances. In this article, you will learn how to carry out a precise heating load calculation, which factors need to be taken into account and which pitfalls can lead to incorrect calculations.
The most important facts in brief
A correct heating load calculation is the basis for an adequately designed heating system
The respective values are determined in a standardized manner in accordance with DIN EN 12831
Appropriate heating load calculation software facilitates the integration of the heating load calculation into the TGA planning
Why is it important to calculate the heat output?
Turn up the thermostat and enjoy the comforting warmth - what works so wonderfully simply in practice is ideally based on complex calculations in advance in order to avoid energy losses and insufficient heat supply as far as possible.
In a building, it is essential to calculate the required heat output in order to select the right heating system for the room and determine the heat requirement per m². A heat load calculation is an essential part of energy efficiency planning and can help to reduce energy consumption and increase comfort. This can save costs and conserve resources.
This is because if the output of a system is not sufficiently designed for the building and the respective conditions, the rooms may be undersupplied at peak times. At certain room and wall surface temperatures, this can lead to moisture damage or mold growth.
On the other hand, a heating system that is too large can cause the burner to switch on and off frequently because the heat extraction is insufficient - and the burner components wear out much more quickly as a result.
What does the heating load calculation measure?
A heating load calculation measures the heat output in relation to the temperature of the building. The power requirement for each room in the building is determined and the heat sources and type of insulation in the building are taken into account.
The results of the calculation can then be used to find out which type of heating system is best suited to the building in question.
What is the difference to the heating requirement?
Heating load and heating demand are both important components of an energy assessment. Both terms are used to determine the thermal energy requirements of the building.
The room-by-room heat load calculation is of decisive importance for the optimum performance of the heating system or boiler. The output of the boiler is measured in kilowatts (kW). In contrast, the heat load is a consumption value and refers to the energy required for heating and hot water in a year. It is stated in kilowatt hours (kWh).
Ultimately, both values are very similar to those of a car: the heat load indicates the performance of the vehicle in horsepower, while the heating requirement shows the fuel consumption.
How does a standardized heating load calculation work?
Standards are the basis for precision and transparency. Accordingly, the heating load calculation is also carried out according to clearly defined parameters, in this case according to the DIN EN 12831 standard (Energy performance of buildings - Method for calculating the standard heating load)
A standardized heating load calculation in accordance with DIN EN 12831 supports planners in determining the required heating output. The calculation is based on the data of the building, the climatic conditions, the technical requirements and the individual conditions of use
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The general formula for calculating the heating load transmission heat losses in watts + ventilation heat losses in watts = heating output in kilowatts takes three different factors into account.
Transmission heat loss
The loss of thermal energy through the components of the building envelope is referred to as transmission heat loss. This is determined on a room-by-room basis and takes into account all surfaces that border either on the outside, on less heated rooms or on unheated rooms.
If the transmission heat loss is low, the heating load of the building is also reduced. As a result, the energy requirement is comparatively low. Overall, good insulation of the building envelope contributes to an efficient energy balance.
Air heat loss
The loss of heat through ventilation refers to the heat loss caused by ventilation behavior. In the context of calculating the heating load, this loss is determined for each room and depends on the volume flow of ventilation through leaks, chimneys or the minimum air exchange required for hygienic reasons.
Additional heating capacity
The additional heating capacity of the heating load calculation describes the short-term capacity that a heating system requires to heat up again after a heating break. This is determined room by room and then added to the required heating load in the design case.
The individual values are finally added together to give the total heat loss. Excel or corresponding software is recommended for the correct representation of the individual areas when calculating the heating load.
What influencing factors need to be taken into account?
Overall, although the main aim of calculating the heating load is to summarize the heat losses of a building as a whole, the calculation is much more complex and multi-layered than a simple addition. The following factors are decisive for a correct result.
U-values of the building envelope
The heat transfer coefficient shows how much heat energy escapes through a building element. This value is calculated for all building surfaces, from the façade to the windows and roof areas. The lower the calculated U-value (formula: [W/(m²K)]), the less heat escapes through a building component.
Storage mass
A simple factor, but one with an enormous influence. The larger and more massive the building, the longer it takes to heat up.
Air exchange
Continuous ventilation or leaky windows can lead to an exchange of air, causing heat to be lost - whether intentionally or accidentally.
Heating temperature
The heating load calculation depends on the selected temperatures and influences the result. The DIN specifies standard values for outdoor and indoor temperatures to ensure a reliable heat supply. Incidentally, the outdoor temperature standard depends on the location and can vary within Germany. For example, the standard outdoor temperature for Frankfurt a. M. is -9 degrees Celsius, while for Leipzig it is -11 degrees Celsius.
What are the consequences of an inaccurate calculation?
Imprecise or incorrect calculations are always problematic, but have a particularly negative impact on the heating load calculation in the long term - because the entire heating system is often designed incorrectly in advance.
If the heating load is not calculated correctly or is only roughly estimated, this can have unfavorable effects on the building and its owner. For example, this can lead to the entire heating system being either oversized or undersized.
An under-designed heating system can both affect comfort and cause moisture problems, while an oversized heating system may lead to increased heating costs.
This is because condensing boilers may not be operated in the ideal output range, circulation pumps may consume excessive amounts of electricity or hydraulic balancing may be difficult to implement.
How digitized TGA planning and heating load calculation software can efficiently simplify calculations
A correct heat load calculation is essential for the sustainable design and operation of a building - and is becoming increasingly important as awareness of energy efficiency and resource-conserving management grows.
This requires a system that makes it easier to use. Modern building technology planning is a complex task, but it lays the foundations for efficient building heating right from the start.
A room-by-room heating load in accordance with the double standard DIN TS 12831-1 and DIN EN 12831-1 is easier to calculate with the right software than was previously possible. A software solution is also more accurate than various online calculators and offers more options with regard to types of radiators, such as underfloor heating, making it easier to calculate an optimally dimensioned heating system.
A system for sustainable heating operation
Trimble Nova offers an effective solution here - a high-performance CAD and calculation software that enables the comprehensive realization of building services projects.
The complete solution for building services engineering ensures a seamless BIM workflow and the precise implementation and integration of the heating load calculation thanks to its special CAD core, the option of 3D modeling, collision detection and precise manufacturer information.
With its shared data environment, Trimble Connect also ensures that the corresponding calculations are available to all relevant trades and project participants - promptly and without any loss of efficiency.
Both programs thus lay the foundations at an early planning stage to bring the concepts of sustainability and efficient heating control to life.
