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New office building for the Aummüller Aumatic company: The photo shows the south-west elevation. The shading elements are largely closed. A narrow escape route is provided between the shading elements and the actual windows for the offices.
© Aumüller Aumatic GmbH
Ventilation of non-residential buildings
09.02.2017

The photo shows the front side of the new office building for the Aumüller Aumatic company with the main entrance.
© Aumüller Aumatic GmbH

Fresh air without mechanical ventilation

Ventilating non-residential buildings naturally but in a controlled manner saves primary energy and requires lower investment and operating costs than mechanical ventilation systems. Scientists from Stuttgart University have therefore developed a ventilation concept that ensures a good indoor environment and reduces the electricity consumption for operating the ventilation system.

Previous research focused on investigating the achievable air exchange rates and air quality when using manual natural ventilation. However, this type of ventilation is not suitable for enabling buildings to be cooled by night owing to the need to provide burglary and storm protection. This therefore provided the starting point for the work conducted by Stuttgart University. The research team began by systematically investigating the efficiency potential of motor-controlled, natural ventilation in non-residential buildings. Automatically opening windows in the facade and in the roof ensure a sufficient supply of fresh air. Suitable window systems are already available on the market. Simulations enabled precise conclusions to be drawn about the energy savings potential of identical reference buildings. The results show that, in the Central European climate, it is possible to save between 30 and 60 kilowatt-hours per square metre and year in regards to the electricity required for cooling and fans, especially in non-residential buildings with high internal loads and low heating energy requirements. This is provided that the building has sufficient and freely accessible thermal storage mass.

A good indoor air quality is possible with all controlled, natural ventilation concepts, whereby the thermal comfort depends on the dimensioning of the openings and the control strategy selected. Air flow rate measurements show that in the case of one-sided natural ventilation, side-hung floor-to-ceiling windows have a five-fold greater air flow rate than wide bottom-hung windows. Compared with mechanical ventilation systems with supply and exhaust air, installing controlled natural ventilation in most existing buildings is both easier and less work intensive.

Rooms with fluctuating and high occupancy

If rooms are not constantly used, it makes sense to provide a temperature- and CO2-dependent control system for the window openings. This is because there is otherwise a risk that the internal temperature will drop too much when there are cold outdoor temperatures. The results of the research team show that hybrid ventilation with heat recovery provides a particularly good alternative in training and meeting rooms as well as in comparable large-scale event rooms with many people.

Lifecycle analysis

The aim of the lifecycle analysis is to compare controlled natural ventilation with mechanical ventilation in economic and ecological terms. For this purpose, the scientists drew on the actual investment costs for the Aumüller company's new office building as well as the costs for a new energy-plus apartment building in Tübingen. The results show that the investment and lifecycle costs are about twelve per cent less than those for an exhaust air system. During a twenty-year review of the use, it was shown that the ventilation heat saved through using mechanical ventilation with heat recovery is not enough to compensate for the additional costs for production and recycling.

Case studies confirm the simulation results

The scientists measured the thermal comfort with controlled natural ventilation both in the new-build office scheme for Aumüller Aumatic in Thierhaupten and in an existing building belonging to the HFT University of Applied Sciences in Stuttgart. The measured indoor temperatures lay within the comfort range in both the new building and the existing city centre building. "The design of the office building for Aumüller demonstrates the performance capability of controlled natural ventilation if this is correspondingly taken into account when planning the building," explains Dr Tobias Erhart from HFT Stuttgart. Temperatures only increased by more than one Kelvin above the permissible value stipulated by the DIN standard for less than five per cent of the usage time. This presupposes that the building has sufficient and freely accessible thermal storage mass.

HFT Stuttgart's "Intelligent Motorised Window" successor project is concentrating on controlled, natural ventilation with windows that have integrated sensors. One focus is on the external noise damping of window systems. It is planned to use the window systems in both residential and non-residential buildings.

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HFT Stuttgart