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Calculation of heat load is a crucial step in planning an efficient heating system. Errors in this calculation can result in oversized or undersized systems, which have a negative impact on both comfort and energy costs. In this article, you will learn how errors occur when calculating heating loads, what consequences they have and how they can be avoided or corrected.

An overview of the most important things

• The heat load calculation determines the required heating output for a building.
• Errors are often caused by inaccurate data bases, incorrect assumptions or outdated values.
• The consequences are inefficient heating systems, higher energy costs or loss of comfort.
• Errors can be corrected through precise recalculation and professional support.

How do errors occur when calculating the heat load?

Failure with Heat load calculation arise when important influencing factors are not fully or correctly recorded. The most common cause is a inadequate data basis. If precise information about insulation, window surfaces, air exchange rates or thermal bridges is missing, the calculation can only be carried out imprecisely.

Another cause is general assumptions, which are not tailored to the specific building. Standard values are often used without taking into account individual circumstances such as regional climate conditions or remediation measures. Outdated construction plans or inaccurate documentation from the construction period also contribute to errors.

In addition, errors occur due to lack of expertise or the Using outdated calculation methods, which no longer comply with current standards. Inaccurate climate data or the absence of more modern software solutions exacerbate the problem.

What mistakes are made when calculating the heat load?

Errors in heating load calculation often occur because decisive factors are overlooked or calculated incorrectly. The most common types of errors are described in detail below:

Inadequate data basis

The most common source of error is an incorrect or incomplete data basis. If basic building data such as insulation values, window areas, room sizes or construction methods are recorded inaccurately, this will necessarily lead to incorrect results.

examples:

• Wrong assumptions about the thickness or quality of insulation.
• Modernizations such as new windows or façade insulation have not been considered.
• Missing or outdated plans of the building.

Neglecting air exchange rates

A common mistake is insufficient consideration of the air exchange rate. Ventilation heat losses play a major role, particularly in buildings with controlled residential ventilation. If the actual ventilation losses are not included, the calculation is incorrect.

examples:

• Ignoring mechanical ventilation systems with heat recovery.
• Assumption of too low air exchange in old buildings without ventilation systems.

Flat assumptions instead of individual calculations

Flat-rate guidelines lead to significant deviations, as they are not tailored to the building. Instead of object-specific data, general values are used that do not reflect the actual properties of the building.

examples:

• Using standard insulation values for walls without checking the actual insulation quality.
• General assumption of heat losses for window surfaces without taking into account their specific U-value.

Wrong assumptions about outdoor temperatures and climate zones

Standard outdoor temperatures vary from region to region and play a decisive role in heating load calculation. If local climate conditions are ignored or misjudged, the result is inaccurate.

examples:

• Using the wrong standard outdoor temperature for a region.
• Failure to take into account altitudes that influence the climate.

Failure to take internal heat gains into account

Heat gains generated by residents, appliances, lighting or other sources are often not calculated correctly. These internal heat sources can balance a significant part of the heating load, particularly in well-insulated buildings.

examples:

• Neglecting waste heat from electrical devices.
• Does not take into account heat gains from solar radiation.

Neglecting thermal bridges

Thermal bridges are a critical factor that is often overlooked. They increase heat losses and must be taken into account in the heat load calculation. If thermal bridges are ignored or calculated incorrectly, the results are inaccurate.

examples:

• No separate consideration of window connections, corners or transitions.
• General assumptions that underestimate actual heat losses.

Incorrect consideration of building orientation

The orientation of the building and solar radiation play an important role in calculating the heating load. If these factors are ignored, the results are inaccurate.

examples:

• Neglecting solar radiation on window surfaces.
• No consideration is given to the building's location, e.g. whether it is sheltered from the wind or exposed.

Wrong assumptions about renovated buildings

After a renovation, the insulation values and therefore the heating load change significantly. If these changes are not included in the calculation or are included incorrectly, the heat load remains inaccurate.

examples:

• Use of original building plans without updating insulation values.
• Ignoring energy improvements such as new windows or an insulated roof.

What are the consequences of errors in heating load calculation?

Errors in calculating heating loads can have far-reaching consequences for the efficiency, operating costs and comfort of a heating system. The main consequences are clearly presented below:

• Oversized heating system: A heating system that is too large causes high purchase and installation costs, as larger heat sources and pipe networks are more expensive. It works inefficiently because it often runs at partial load, which increases energy consumption. Frequent cycling also leads to faster wear of components and increases maintenance costs. Overall, more energy is consumed than is actually necessary.
• Undersized heating system: A system that is too small cannot generate enough heat to completely compensate for the building's heat loss. On cold days, this results in an insufficiently heated living space and a noticeable loss of comfort. Additional electrical heating systems are often used, which cause high electricity costs. Continuous operation of the heater also increases wear and can significantly shorten its service life.
• Inefficient use of energy: Incorrect heating load calculations mean that heating systems do not make optimal use of energy. Oversized systems waste energy, while additional electrical heaters work inefficiently in undersized systems.
• Comfort issues: Errors in calculating the heat load result in an inadequate heating result. Undersized systems do not generate enough heat in some rooms, resulting in cold areas or temperature differences. Oversized systems can cause temperature fluctuations and uneven heating cycles, which also have a negative impact on comfort.
• Problems with funding: Heating subsidies such as KfW subsidy No. 458 for heating replacement require precise calculations of the heat load. Incorrect calculations can result in applications being rejected or funding being reclaimed. Without funding, the total heating costs rise, which affects the profitability of the entire project.
• Bad planning during renovations: An incorrect calculation can incorrectly evaluate energy-related renovations such as insulation or window replacement. Too high a heating load suggests that such measures are less effective, while too low a heating load underestimates necessary investments. In both cases, the building is not being optimally modernized, which causes higher costs and energy losses in the long term.

Can errors be corrected?

Errors in heating load calculation can be caused by a professional review and adjustment be corrected. An energy consultant or specialist planner can check and correct the calculation based on current building data. Accurate measurements and thermographic investigations are used to identify thermal bridges and other weak points.

In addition, oversized heating systems can be equipped with a hydraulic balancing And the Adjustment of heating control be operated more efficiently. For undersized systems, additional heating surfaces or supplementary heating systems be created. Software-based recalculation involving current standards is also useful.

How can mistakes be avoided?

Errors in calculating heating loads can be effectively avoided through careful planning and the use of modern technologies. Accurate data, professional expertise and suitable tools play a central role here. The following measures are decisive:

• Precise data collection: A correct heating load calculation starts with the precise recording of all relevant building data. This includes information on insulation, window surfaces, air exchange rates and possible thermal bridges. Up-to-date data should be used, particularly for renovated buildings, as outdated information can lead to incorrect results.
• Use of professional software solutions: Modern software tools such as ours Autarc heat load calculation help with precise Calculation in accordance with the current standard DIN EN 12831. They take into account regional climate data, the orientation of the building and individual factors such as internal heat gains. Such tools minimize human errors and ensure accurate calculation.
• Expert support: The involvement of a certified energy consultant or specialist planner ensures that all necessary parameters are professionally taken into account. These experts also know current funding conditions and help to prepare the calculation optimally for applications.
• Taking future requirements into account: When calculating the heating load, not only should current requirements be taken into account, but also possible future adjustments such as energy renovations or expansions. In this way, the plant remains efficient and flexible in the long term.

Plan efficiently with modern heat load calculation!

Optimize your heating planning with a precise heat load calculation! Take advantage of this opportunity and book a free demo. Convince yourself of the benefits without obligation and experience how easy and efficient our calculation tools make your work easier.

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Photo by Lisa Fotios