keoto | 1st. Prize: Competition Greencity Zürich, Sustainability Strategie

1st. Prize: Competition Greencity Zürich, Sustainability Strategie

Competition: 1st. Prize ,
Building owner: Losinger Marazzi AG, Zürich
Project: Greencity Zürich, Sustainabiltiy Strategie
Architect: Märkli Architekten, Zürich

Zero Emissions through efficiency and sufficiency

In the past, the conception of sustainable buildings focused on reducing energy consumption. This is, however, a short-sighted strategy to avoiding CO2 emissions. The buildings of the future need to amount to less than 1 kg CO2 emissions/m2 per year of occupation, yet the occupants and their needs should be the center of attention, since their living conditions are significantly influenced by their residential environment. Therefore, construction materials and their haptics play a large role in the planning of a building project. For example, massive walls create a greater sense of security than well-insulated lightweight walls. Furthermore, occupants find themselves in a more comfortable spatial situation when they can influence their environment. That is: are occupants able to open the windows without remorse, or will this cause greater CO2 emissions, especially in winter? The energy concept arose from these considerations.

The buildings’ energy concept is efficiently integrated into the planned district structure. The planned anergy ring makes use of both groundwater and geothermal energy and, by hydraulically connecting the individual buildings to the distribution ring, it forms an efficient anergy source for the operation of heat pumps throughout the year. With this in mind, it is important to determine the economic and ecological optimum for the creation and operation of the buildings. In doing so, the building must be considered as a system, since both the building services to be installed as well as the performance of the architecture must be considered.

In order to achieve this, the architecture is also developed based on energetic considerations. From the point of view of building service efficiency, an optimum design should include a large, south-facing window front that can be shaded by balconies in summer, as well as a window to wall ratio of 70% on the west-facing wall, 35% to the east, and 18% to the north.

The building service system itself benefits from its own simplicity. The goal is to provide the users with the highest level of comfort while allowing them to influence the individual room conditions in response to the outdoor climate. Implementing radiant floor heating with low operating temperatures ensures an efficient heat pump operation. Controlled ventilation was not included, since the architecture itself takes care of the occupants’ environmental needs; that is, the external wall temperature never drops below 19°C and the operating temperature of the radiant floor heating cannot exceed 29°C. Thus, temperature symmetry in the rooms is ensured. Furthermore, the apartments are allowed to cross-ventilate as usual, while mechanical ventilation in the bathrooms is of course included.

The increased energy requirements caused by relinquishing controlled ventilation can be compensated in various ways. On the one hand, the installation costs during building construction are reduced. Since ventilation ducts in the roofs are not required, the amount of concrete required is reduced, which also translates to lower gray CO2. Additionally, the economic savings from the reduced installation costs can be utilized to compensate for the costs of CO2-free electricity generation. Approximately 12,000 CHF per apartment can be saved by this strategy, which is equal to the cost of a PV panel area of 20m2. This area can supply each apartment with 30 kWh/m2 of electrical energy. This electricity can not only compensate for the increased energy losses by ventilation, but is also enough to supply the heat pumps’ electricity demand on a yearly balance.

In order to ensure this goal is met, the façade must possess certain insulating properties. Therefore, in this project, the costs of insulation were counted against the costs of the PV system. The economic optimum obtained through this calculation is shown in the accompanying graphic. In calculating this optimum, the effect of the insulation thickness on the energy demand of the building was also computed and included in the graphic. The resulting system therefore represents the best case in terms of both economics and CO2-free operation. The project is therefore not only extremely ecological, as it entails both less gray CO2 and no CO2 emissions during building operation, but also cost-effective through the balancing of structure and system.