The heat demand is the amount of heat energy a building needs to maintain a desired internal temperature, depending on the external temperature conditions. This is especially important during cold periods when the building's energy consumption increases significantly.
Factors influencing heat demand
Building features:
- Thermal insulation: The thermal insulation capacity of a building's walls, roof and floor significantly affects heat loss.
- Windows and doors: The thermal insulation capacity (U-value) of windows and doors is key in minimizing heat loss.
Building size and shape: Larger buildings generally have higher heat losses, especially if their external surface area is large compared to their internal volume.
Outside temperature: The lower the outside temperature, the greater the heat loss .
Desired indoor temperature: Different rooms may require different temperatures due to their different functions (e.g. living room: 21-22 °C, bedroom: 18-20 °C).
Ventilation and air exchange: The airtightness of the building and the degree of ventilation required also increase the heat demand.
Heat sources and internal heat generation: Heat generated by people, electrical equipment and lighting can reduce the need for heating.
Calculating the heat requirement
There are both simplified and more detailed methods for determining heat demand:
Simplified calculation
The following formula can be used to approximate the heat requirement:
Q = U × A × ΔT
Q: Heat requirement (W)
U: Thermal transmittance (W/m²·K)
A: Surface area (m²)
ΔT: Temperature difference between the interior and exterior (K)
Detailed calculation
In a more detailed calculation, we take into account all elements of the building, such as:
- Heat transfer of walls, roof, floor.
- Heat loss from windows and doors.
- Heat loss due to air exchange.
By adding these together, we get the total heat loss of the building.
Peak heat demand
The maximum heat demand is usually determined based on the coldest outdoor temperature, taking into account the climatic conditions of the given region. Example: In Hungary, a design outdoor temperature between -12 °C and -15 °C is used.
Example of heat demand calculation
Determining the heat requirement of a 50 m² room:
Wall U-value: 0.3 W/m²·K
External wall area: 40 m²
ΔT (inside 21 °C, outside -12 °C): 33 K
Q = U × A × ΔT
Q = 0.3 × 40 × 33 = 396 W
This is just the heat loss from the walls, we can perform similar calculations for the roof, floor, windows and doors, and then sum up the total heat requirement.
Heat demand and energy efficiency
Insulation: Proper insulation of the building reduces heat loss and thus the heating energy requirement.
Modern windows and doors: Windows and doors with a low U-value contribute significantly to energy efficiency.
Energy-efficient heat sources: Heat pumps , condensing boilers or heating systems combined with solar panels can reduce the costs of heat production.
Adjustable heating system: Programmable thermostats and zoned heating systems optimize energy use.
The importance of determining heat demand
System sizing: Based on an accurate heat demand calculation, the appropriate size boiler, heat pump or other heat generating equipment can be selected.
Cost optimization: An oversized system generates unnecessary costs, while an undersized system does not provide the desired comfort.
Sustainability: Optimal heat demand calculation reduces energy consumption, thus contributing to environmental protection.
Summary
Determining the heat demand is a fundamental step in the heating and energy efficiency design of buildings. Its accurate calculation ensures the correct sizing, minimizes costs, and maximizes the efficiency of the system. The integration of modern insulation technologies, windows and doors, and energy-efficient systems further improves the performance of the building, contributing to the creation of sustainable and comfortable living conditions.