The results of CFD numerical simulations show that the stairwell can have a fundamental role in the natural ventilation of low-rise multifamily buildings (three to five levels) in winter. The natural ventilation system here presented is characterized by low installation costs, quite easy operation and inexpensive management.

In this case-study, the main design rules to obtain an effective natural ventilation system are: location and size of inlet and outlet (to move upward the neutral pressure level above the upper extraction grille device) and the aerodynamic characteristics of the openings (to equalize the flow rates). CFD simulations showed effective behaviour of the above mentioned ventilation system.

The well known stack effect simplified model [2] cannot be used in the case studied because the stairwell was characterized by complex geometry and boundary conditions. So, CFD codes are an invaluable tool in the design and verification of the behaviour of the stairwell performing as a chimney.

The behaviour of the system studied is influenced by a great number of parameters depending on the external micro-climate (such as air temperature and solar radiation), the stairwell (such as the morphology and the geometry of the stairwell, the location and the aerodynamic characteristics of the openings, the thermal properties of the envelope), the dwellings (heating temperature, pressure losses along the internal flow path), the users (the control of the natural ventilation system and the heating scheduling/operation).

The results shown only concern a certain number of the typical boundary conditions. However, these results can be useful for the design of other similar natural ventilation systems.

Future research projects will concern the evaluation of different boundary conditions. The further aim is the definition of the most relevant parameters for the designing of similar systems.

Further CFD simulations will be run to test different boundary conditions and different scenarios (such as higher external air temperatures, one or more flats unheated, no ventilation in one or more units).

Different technical solutions of the stairwell envelope (such as a photovoltaic facade or solar wall) will be tested in order to enhance diurnal ventilation in winter and/or nocturnal ventilation in summer, especially in new buildings. In energy retrofitting, generally speaking, the design opportunities are reduced by inadequate building orientation, solar shadowing of neighbouring buildings and payback of intervention costs.

Ventilation rate varies depending on adjustment of air-inlets, windows and doors as perceived necessary by occupants. So, further models with different resistance and with partial use of the single-unit ventilation system will be run. The control system design

needs further study, especially into the automatic adaptation to external micro-climatic conditions (master) and to the partial extraction rate of one or more units.

REFERENCES

1. ASHRAE Standard 62: "Ventilation for acceptable indoor air quality”, American Society of Heating Refrigerating and Air-conditioning Engineers, Atlanta, GA, 1999.

2. Awbi H. B. "Ventilation of Buildings”, E. & F. N. Spon, London, UK, 1991.

3. Flomerics Ltd. "Flovent version 4.2 User Guide”. Flomerics Limited, UK, 2003.

4. lannone F. "Natural ventilation and sustainability: designing with Computational Fluid Dynamics”. Sharing Knowledge on Sustainable Buildings, Bari, Italy, 16-17/12/1999.

CONTRIBUTORS

M. Catalano planned and supervised the study, G. R. Dell’Osso codesigned the study and wrote the background (par.1), F. lannone codesigned the study, executed the CFD simulations, analysed the data (paragraphes 2.1 and 2.2) and wrote the conclusions.