Buildings are aired to evacuate indoor pollutants, in particular those produced by the occupants. CO2 is a good indicator of occupancy, as long as there is no other significant source. This is the case in most buildings. Cheap, portable analysers and loggers that allow easy recording of the CO2 concentration in a room or in the exhaust duct of a ventilation system are available on the market. The peak value of CO2 concentration during occupancy is an indicator of the minimum air flow rate per person.
It is well known that iterative solution processes can lead to divergence when dealing with coupled airflow and thermal analyses for buildings ventilated either naturally or by a mixed-mode system. The Newton-Raphson method or its variants are used in almost all existing multi-zone airflow models. This paper discusses the qualitative features of the iterative solution processes of the Newton-Raphson method when used for coupled thermal and ventilation analyses of a simple one-zone building with two openings.
A Moisture Admittance Model, which takes into account absorption and desorption, has been developed to simulate moisture behaviour in dwellings. The model has been integrated with the BREEZE computer model used to simulate air and contaminant flow. Simulations from the combined model have been compared with predictions using the Louden model and with measurements of vapour pressure taken in a test house. The Louden model tended to over-predict experimental values but there was reasonable agreement between the MAM-BREEZE model results and measured values.
This paper examines the impact on domestic background air infiltration of replacing ‘old windows’ with modern double-glazed and draught sealed windows, both with and without controllable ventilation (e.g. trickle ventilators). Methods of estimating the change in infiltration rate produced by such a window replacement are reviewed. A simple model has been developed which, using laboratory measurements of window air permeability, predicts the reduction in infiltration that can be expected when a given number of windows are replaced in a dwelling.
The ventilated ceiling is a flexible solution for kitchen ventilation where heat loads are relatively low and aesthetics is a concern. By using a capture jet in the ventilated ceiling, it is possible to improve the total effectiveness of the ventilation system. This means better indoor air quality and thermal comfort. In addition, the energy consumption of a capture jet ceiling is lower than that of a traditional ceiling concept.
Passive stack ventilation systems have been used for a number of years throughout the world. They were specifically mentioned within the 1995 revision of the Building Regulations for England and Wales as a means of compliance. BRE Information Paper 13/94 gives recommendations for the design of duct systems within dwellings that place restrictions upon the number and severity of bends that may be used. These restrictions limit the scope for the use of passive stack ventilation within dwellings.
This paper presents an overview of systems that utilise thermal mass in conjunction with night ventilation. It discusses the concepts behind and development of a system (CoolDeck) to improve the performance of systems where air is ventilated through false ceiling and floor voids to access hidden mass. The system improves thermal interaction between the circulating air and the thermal mass of the slab. A case study is presented demonstrating the effectiveness of the system in a refurbishment application (Stevenage Borough Council (UK) offices).
The research described in this paper is part of a project aimed at improving energy costs and the indoor environment of atrium buildings. Tracer gas techniques were used to assess the ventilation performance in terms of air distribution and contaminant migration patterns and to measure the air infiltration rate of a three-storey atrium. This atrium serves as an entrance to a large office-laboratory complex.
This paper reports the results of a study to test two novel procedures to model dynamic thermal conditions of an enclosure within Computational Fluid Dynamics (CFD). The main area of investigation is the performance of the procedures in simulating the varying thermal response of the building fabric, the effects of external thermal load changes and the consequential effect on the air inside the enclosure. The dynamic thermal modelling procedures proposed utilise a transient time-varying grid schedule and Freeze-Flow techniques.
The effectiveness of a ventilation system in terms of the age of air and its ability to remove contaminants will be significantly affected if part of the exhaust air is recirculated. In this paper the consequences of recirculation of air in mechanical ventilation systems on ventilation effectiveness parameters is examined. Two alternative methods of establishing ventilation effectiveness parameters relating to air change efficiency and contaminant removal effectiveness when recirculation of air is present are presented.
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