This paper is a keynote address presented at Ventilation, Humidity Control and Energy 24th AIVC Conference.It is a warning for HVAC professionals that are however walking a tightrope. How provide sufficient ventilation for IAQ that yet maintain an appropriate moisture balance without using excessive energy ?Mold is having a severe impact upon us; excessive ventilation and reducing the energy to control the humidity are oftentimes being blamed. Claims have skyrocketed for mold , mildew and humidity-related problems cases.

In the frame of the IEA Future Buildings Forum, a workshop was held January 15 -17 2003 in St. Moritz, Switzerland. The goal of the proposed workshop was to discuss and to decide upon an international collaboration to promote a program for advanced retrofit of existing buildings and community systems.
The proposed topics dealing with energy conservation and renewable energy use in retrofit buildings were:

In recent years, poor indoor climate has caused health problems for building occupants. Sometimes these problems have been so serious that these buildings have, quite rightly, been labelled sick buildings.Today, there is good evidence in some areas as to why such problems arise. Unhealthy substances given off by various building materials, the existence of mould and general air pollution are the main causes. Another important factor is the high level of humidity in buildings and indoor air.In general, the most important way to remedy the problem is to improve ventilation.

In January 2002 the EU RESHYVENT project started, a three-year project within the EU Fifth Framework Programme on the investigation and development of demand controlled hybrid ventilation systems in residential buildings. The project is a clustering of four industrial consortia with a multi-disciplinary scientific consortium. Each of these industrial consortia will develop a working prototype of a hybrid ventilation system for a specific climate.

The goal of this study was the determination of the existing situation in houses with regard to air quality and energy used for ventilation in relation to the health of inhabitants. For the energy policy the Government is considering increased energy requirements for dwellings. They are permanently opposed in doing so by people who are concerned about negative health effect due to increased requirements on for instance air tightness of buildings. To have at least a reference point, they are interested in the existing situation.

In order to facilitate nationwide analysis of ventilation and indoor air quality issues in residential buildings, a set of homes has been defined to represent the housing stock of the United States. This so-called 'suite of homes' is based on two residential housing surveys, the U.S. Department of Energy Residential Energy Consumptions Survey (RECS) and the U.S. Census Bureau American Housing Survey (AHS). The RECS dataset includes about 6000 U.S. residences and the AHS covers about 60000, and are both intended to periodically characterize the U.S. housing stock.

Twenty homes were tested and monitored in Houston, Texas, U.S.A. to evaluate humidity controlperformance and operating cost of six different integrated dehumidification and ventilation systems that could be applied by production homebuilders. Fourteen houses had one of the six integrated dehumidification and ventilation systems and also met a high standard of energy efficiency criteria.

Passive cooling strategies require strict adherence to the physical world. Ones imagination creates the flow of ideas that can blossom into a comfortable setting, but the reality of design, construction and cooperation has to be observed and accepted. Physical laws govern as natural processes follow the path of least resistance. In order for us to overcome these laws extra energy is required. That is why passive cooling designers must investigate how to create a comfortable setting by understanding how natural procedures work.

The thermal performance of a monozone building located in Lisbon is studied when night ventilation combined with radiative cooling is used in order to remove the heat from indoors. For simulating the thermal behaviour of the building, a commercial energy building software is used. The potential for radiative cooling in Lisbon, as well as the efficiency of the radiative cooling system were investigated previously. A validated numerical model is used in order to predict the temperature of the air at the outlet of the radiative system.

Cavity wall is often proposed in the building envelope design as a solution for improving the thermal comfort of the inhabitants and reducing the adverse condensation effects on the building fabric. In order to evaluate the thermal effect of ventilated air gaps on building energy demand and comfort, an experimental ventilated cavity wall has been built and tested. The cavity wall separates two ambients at different temperatures that are assumed to be constant over the time required to perform the experimental analysis.