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Energy management of low opaque buildings
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Building simulation

What is an energetically dynamic building simulation?

The energetically dynamic building simulation is the balancing of all relevant energy flows of a building at selected times. Especially the transmission heat flows, the enthalpy flows, the change of the internal energy by storage processes and also electrical performances are balanced. The balancing is usually carried out over fixed time steps, often at intervals of 1 hour over a certain period, usually a whole year or even only over the period of the heating or cooling period.
For this purpose, the object to be calculated, such as a building, is divided into zones. For these zones, e.g. individual rooms, an energy balance, or mass balance, can then be drawn up. If zones, rooms or the building services are in interaction, an equation system is created in this way, which the simulation has to solve numerically. In contrast to the flow simulation, which uses spatial discretization, the energetic building simulation only requires precisely defined zones. For this reason, one likes to speak of the method of zone balancing.

Subdivision of a task into individual zones with interaction to each other

The temporal resolution through defined time steps must be sufficient for the physical process. In building services engineering, the main influencing factor is the weather. In order to be able to take the weather into account as accurately as possible in a simulation, so-called annual test reference data (TRY - Test Reference Year) is usually used, which contain the most important averaged weather data, such as air temperature, wind, humidity and solar radiation from previous recordings of past years, and provide them in a temporal resolution of 1 h for different regions.

While the use of averaged weather data enables the most exact possible result with regard to expected energy flows and thus energy efficiency, extreme climatic years are often used to design the building services. In this way, the dimensioning of the building services can be carried out without the usual safety surcharges and thus without significant overdimensioning.

The accuracy of standard demand forecasts, energy certificates based on simplified regulations, is limited. This becomes particularly clear in the following example, which shows the heat transfer coefficient for a selected double glazing insulation window and thus the transmission losses as a function of wind conditions. It becomes clear that, depending on the wind speed, very different heat flows pass through the window and thus contribute to significantly different heat and cold loads. This is particularly important for low opaque buildings.

Example of the dynamic influence of the weather

When does the building simulation make sense?

In contrast to the classical analytical heating and cooling load calculation, the building simulation is usually much more complex due to the depth of detail to be taken into account. Its use is therefore particularly profitable for larger buildings or for buildings in series production. A significant benefit is the reduction of the planning risk, especially with new or innovative building concepts.

o Reduction of the planning risk

A relatively frequent misplanning of modern low opaque buildings is the underestimation of the cooling load in warm, sunny summer months. The high-quality simulation provides a multitude of physical results per time step, such as the room air and felt temperature. The calculation of the room temperature shows at an early stage to what extent heating and cooling load peaks can be expected.

By analysing the frequency of the cooling and heating loads that occur, it is not only possible to coordinate the sizes of the heat and cooling generators, but also to dimension their size in relation to each other as a function of the highest possible base load coverage and the lowest possible peak load coverage.
This procedure allows the investments in the producer park and/or the efficiency of the producers to be designed depending on their expected capacity utilisation.

o Economic and ecological optimisation of the refrigeration and heat generation park

Insulating is now standard in new construction. In this context, it should be noted that the increasing insulation thickness does not result in an equal proportional increase in energy savings. The following figure shows an example of the degressive course of transmission savings over the increase in insulation thickness.

Example of the influence of insulation thickness

The strength of the insulation and its influence on the energy costs can be varied and optimised within the framework of regulatory requirements with the share of renewable energy supply.

o Economic and ecological optimisation of thermal insulation

A frequent weak point of modern buildings is inadequate ventilation with regard to the air tightness achieved in new buildings. In many cases, the air tightness required by law is exceeded. The result is reduced air quality in the residential unit.

The building simulation allows the variation and optimisation of the free and fan-supported air exchange and the necessary measures to compensate for air exchange enthalpy losses. Air quality can be quantified and evaluated taking into account the occupancy function, demand-driven ventilation strategies and the influence of heat recovery efficiencies.

o Evaluation of expected room air qualities from an economic point of view

The efficiency of individual heat and cooling generators varies considerably depending on their type and use. Their evaluation in terms of climate law via the level of the associated primary energy factors makes this even more complicated. Compared to a water/water heat pump, the air/water heat pump is significantly less expensive in terms of total investment costs up to commissioning, and is significantly less efficient for heat input, depending on the outside temperatures and type of heating system. The building simulation can compare such correlations as the demand, the operation-dependent efficiency and thus the operating costs to the investment costs and thus helps to make a decision in the planning process.

What are the benefits of building simulation?

The greatest benefit of building simulation is certainly the reduction of planning risks in new building concepts for which there is insufficient operating experience. Subsequent corrections, such as additional cooling generators and their necessary heat exchangers to prevent the buildings from overheating in summer, are often associated with considerable costs.

An optimisation of building physics, especially in transient processes such as energy storage via component activation or adapted storage systems, can hardly be achieved without the use of building simulation.

The relationship between building standards, such as energy efficiency, comfort and indoor air quality, and the expenditure to be made for them, such as investments and operating costs, can be reliably and accurately assessed with the use of building simulation.

Selection, dimensioning and prioritisation of individual producers in the operation of the producer park for the provision of cooling and heat can be carried out precisely by using the building simulation under consideration of base load and peak load depending on specified planning directives, such as investment or efficiency optimisation.

Innovative building concepts, increasing concepts of networking building services or the choice of location can be quantitatively analysed with the aid of building simulation and are therefore easy to evaluate.

The building simulation is always worthwhile to reduce the risk, especially in the case of larger buildings and when breaking new innovative ground. For large buildings, the building simulation already pays for itself through the more exact selection of the building services and the associated reduced investment costs.

Energy certificates make it easy to evaluate building standards today. High building standards reduce the energy costs and the attractiveness for the use by increased quality of life of the inhabitants. This also increases the attractiveness and thus the long-term value of the property.