ACTIVE HOUSES REALISE THE GREAT POTENTIAL TO USE ENERGY MORE EFFICIENTLY IN BUILDINGS
An Active House is energy efficient and supplied by renewable energy sources integrated in the building or from the nearby collective energy systems, including possible zonal or national electricity grids.
Globally, heat and electricity in buildings account for 40% of all energy consumption. Considering the total energy consumption throughout the whole life cycle of a building, the energy performance and energy supply are important issues in the concern about climate changes, reliability of supply and reduced global energy waste.
The design, orientation and products for an Active House are optimised to use as little energy as possible and to utilise renewable energy sources as much as possible.
The design of an Active House should be based on the Trias Energetica approach to sustainable design. The main focus of the concept is the fact that the most sustainable energy source is the energy being saved. From bottom to top of the Trias Energetica pyramid, the messages are as follows:
- Minimise the energy demand of the building. To do so, use energy-efficient solutions and architectural measures, such as orientation, awnings and shading, materialisation and shape of the building.
- Source the remaining energy requirement as much as possible from renewable and CO2-free energy sources, either on the building, the plot or from the nearby energy systems.
- Any remaining energy demand may be met by using fossil fuels through highly-efficient energy-conversion processes.
Energy plays a vital role in buildings. To the user, energy consumption during the use-stage is most visible, as it is directly linked to energy demand of the building, on-site renewable energy production and to energy bills. However, the materials used to build the house contain a large amount of embodied energy that should not be overlooked. To stimulate the conscious use of different energy sources, distinction is made between final energy (which is metered at the building) and primary energy.
EXTENDED ENERGY DEMAND, PRIMARY ENERGY PERFORMANCE AND ENERGY SUPPLY
The building energy demand, primary energy performance and energy supply are calculated according to the diverse national building energy assessment methods to enable comparison of projects in a country and to create a common energy evaluation platform based on the different national building energy requirements in the building permit process.
In case of interest in deeper insight in building energy performance, or need for comprehensive comparative analysis between design concepts under different climate conditions, dynamic energy performance calculations can be used. Dynamic energy simulations enable to consider time dependent design factors such as hourly resolution of yearly climate data (seasons, time of day), building types, space and façade (window) orientation, precise location (latitude), usage (light, equipment, occupants), losses and gains, shading and glare prevention, as well as operation. In addition to winter comfort and heating performance, the modelling can include detailed summer thermal comfort, cooling energy efficiency and high-resolution mechanical and natural ventilation assessments as well.
The distinguished handling of the diverse weather profiles helps to characterize and compare projects in the same or in different geographic site-locations in a sophisticated way.
Since the main purpose of the national building energy calculations is to secure the ‘worst case’ scenario, the oversizing of the HVAC systems is state-of-the-art in common design practice. As a result, investment, operation and LCA-LCCA costs increase. Application of dynamic energy simulations ensure lower system sizing with all of its benefits.
The workflow is mainly identical to the one of a thermal and air hygiene comfort simulation, by 3d-modelling of the spaces, modelling of the HVAC systems and the controlling. The definition of time basis occupancy, equipment and lighting schedule profiles are recommended to keep results as realistic as possible. ‘Mimicking’ the real usage and operation of the building, occupant and equipment user ‘behaviour’ are to be included in the simulations with detailed lighting operation. Comparison of in-situ, real building monitoring measurements and the simulation model, the operation management can be significantly improved and optimized. In the simulation framework three main calculation goals can be achieved:
- Building performance (effect of space organization, shape, wall-window-ratio, orientation, neighbourhood-landscape, structures and materials)
- Services systems (heating-cooling, AHU, lighting) and natural ventilation systems performance
- Building management system (BMS automation, monitoring-controlling) performance
Most dynamic thermal simulation programs possess a unified simulation environment of comfort and energy performance, ensuring a comprehensive evaluation platform between them. In this way more realistic energy demand and consumption results are gained.
Results are to be calculated using a dynamic simulation tool validated by the US BESTEST (ANSI/ASHRAE Standard 140). Examples of applicable daylight and thermal (comfort and energy) simulation programs can be found at:
It is recommended that energy simulations deliver high-resolution information about the buildings energy usages and – if in the simulation software included – about comfort performance, such as to enable higher level of design optimisation.
QUALITATIVE CRITERIA – ENERGY VALIDATION ON SITE
In addition to focus on energy performance in the design phase, proper execution of the design is crucial to achieve the desired energy performance. Consequently, it is deemed most appropriate to consider the following criteria: