M. Krus, D. Rösler, A. Holm

Fraunhofer-Institut for Building Physics, 83626 Valley, Germany

As a countermeasure to global warming, the energy demand of buildings is to be reduced by specific measures, for example thermal insulation or intelligent ventilation systems. A demand-based (moisture-controlled) exhaust ventilation system is assessed in comparison to a supply and exhaust ventilation system with heat recovery by means of computational investigations. This assessment of different ventilation systems is performed by means of the newly developed hygrothermal indoor climate simulation model WUFI®-Plus. By implementing the individual ventilation systems the energy demand, especially the primary energy consumption on the basis of applying various fuels, as well as the effects on the indoor climate and the C02 content of the indoor air are calculated and compared. Moreover, air change rates are investigated resulting from the use of a demand-based exhaust ventilation system. The calculations are based on a model apartment with a ground floor of 75 m2 and an assumed 3-person household. These investigations comprise 3 different climates in Germany (cold, medium and hot climate).

Despite the high heat recovery coefficient of the supply and exhaust ventilation system an only slightly higher energy use occurred for the demand-based exhaust ventilation system. If regenerative energy sources such as wood are used, primary energy consumption of the demand-based exhaust ventilation system is even lower in comparison to the supply and exhaust ventilation system with heat recovery. With demand-based exhaust ventilation system, the C02 concentration of the indoor air remains permanently below 1200 ppm.


NANOSAFE1 – Final report

This is the final report published by the VDI Technologiezentrum GmbH inDusseldorf,Germany, which presents the results of the EU funded project NANOSAFE, the project which preceded NANOSAFE2.

CLICK HERE TO DOWNLOAD Nanosafe1_final_report

Health risk associated with passive houses: An exploration

Evert Hasselaar*
Delft University of Technology, The Netherlands
*Corresponding email:

The passive house standard of northern European countries functions as an inspiration for home owners and project developers for building or retrofitting with high energy ambitions.
Passive houses typically involve high insulation levels and heat recovery ventilation. Residual heating is based on heating of the inlet airflow, but other solutions (stove etc.) are applied as well. The development of energy-efficient building is technology driven. The feedback from the consumers is low and there have been complaints by occupants about perceived health effects of heat recovery ventilation. Examples of passive houses are analyzed to find
indicators of “emerging” health risks. Potential problems are overheating, noise from installations, legionella contamination of domestic water buffers, low ventilation volumes, complex control mechanisms and lack of flexibility of ventilation services.

are given for the improvement of the user friendliness of indoor climate systems for passive houses.

Energy performance, Passive house, Health, User influence

In the Netherlands the energy use of new buildings is subject to performance based legislation. The energy consumption is calculated on the basis of a physical model and results in a dimensionless Energy Performance Coefficient (EPC). Since its introduction in 1996 the EPC-value has become stricter and was reduced from 1.4 in 1996 to 0.8 in 2006, which is an improvement of 43%. Each step supported the market growth of certain products or systems.
Since 1998 the application of heat recovery balanced ventilation systems in newly constructed dwellings grew from 5% to about 40% (Hasselaar, 2006). Heat recovery ventilation represents a cost-effective way to reduce the EPC-value, because of the highly efficient heat exchanger (>80% thermal efficiency) and improved motorized fans that save approximately 50%
electrical energy compared to conventional fans.
The ambition to reach high energy performance has led to the development of the Passive house standard, where the strategy to reduce the energy demand is followed to such extremes, that a central heating system is not required. The energy demand for space heating and cooling of passive houses is limited to maximum 15 kWh/m2y of treated floor area (in Western European climate regions). The primary energy use of all appliances including domestic hot water, space heating and cooling, lighting and domestic appliances must not exceed 120 kWh/m2y. Many passive houses have been built in Austria and Germany and other countries follow: Sweden, Belgium, while the interest in passive houses and passive renovation is increasing in the Netherlands as well (Mlecnik, 2005). Because innovative concepts are often driven by top-down energy policy and the most economic way to meet regulations, the building sector tends to focus on the reduction of the Energy Performance Indoor Air 2008, 17-22 August 2008, Copenhagen, Denmark – Paper ID: 689 Coefficient rather than the actual energy performance. The technology driven approach creates the risk of poor user orientation or conflicts with indoor environmental quality.
In energy efficient designs, a three step strategy is followed: reduce the demand for energy, supply energy through sustainable sources and finally apply systems with high energy efficiency. The leading paradigm of achieving energy quality is to apply improved technology without change of behavior required, but occupants of collectively self-built projects have the opinion that behavior does matter in reaching the maximum energy effect (Ornetzeder, 2001).
User friendly technological solutions will provide control functions to make performance behavior dependent and with flexibility to allow individual adaptations. This requirement turns the “trias energetica” into a four step strategy, the fourth step being: provide control systems in support of energy conscious handling of processes by the users. Direct involvement of occupants in the design process of dwellings and climate systems is one way of promoting the user friendliness, allowing occupants to “learn” behavior that is more adapted to the needs of sustainable housing (Ornetzeder, 2001). The question is how to organize participation in the design of new buildings and of renovation projects.
Passive house designs typically involve very high insulation levels, triple glazed windows in frames with thermal barrier and perfect sealing. The envelope is without thermal bridges. Heat recovery ventilation is standard. Often, solar thermal and photovoltaic systems are applied.
Because of overheating risk in the summer, services for night time cooling (ventilation) are provided, in certain cases by applying ground-to-air heat exchangers. Residual heating can be a simple electrical heat resistance radiator or wood burning stove. Often, however, floor or wall heating are applied, which are systems based on low temperatures and large surfaces.
Low temperature systems increase the efficiency of solar systems and heat pumps. Passive houses require space for a thick layer of insulation materials in the envelope and space for equipment such as a buffer for the solar domestic system, ducts and unit for HRV or a heater/hot water back-up for the solar system. Sun shading is provided in most houses (Strom, 2005).

The relationship between occupant behaviour and technical services in dwellings represents an interdisciplinary research field that links the social en technical sciences. Work in this field started with involvement in problem analysis and technical trouble shooting and expanded towards studies of user complaints about environmental health. The home visits (500 dwellings) provide data on technical performance, perception and behaviour.
The paper presents an exploration into the indoor environment of passive houses, based on dscribed cases (Daniels, 2007; Greml, 2004; Mlecnik, 2005-2008; Castagna, 2008; Römer, 2005; Strom, 2005) and participating in international discussions on passive houses (Demohouse, Green Solar Cities, Passive House expert meetings). Field data are collected in two passive houses, in minimum energy houses and standard houses, that include installations or design features that are common in passive houses. Therefore the focus is on discussion rather than the presentation of results.