PR1996

Electric utilities in the Pacific Northwest have spent over $100 million to support energy efficiency improvements in the HUD-code manufactured housing industry in the Pacific Northwest over the past several years. Over 65,000 manufactured housing units have been built since 1991 that exceed the new HUD standards for both thermal performance and mechanical ventilation that became effective in October, 1994. All of these units included mechanical ventilation systems that were designed to meet or exceed the requirements of ASHRAE Standard 62-1989.

This paper reports on work carried out at BRE to address the need for guidance on designing for natural ventilation via single-sided and cross-ventilation in office spaces and the limits of application in terms of plan depth. Present guidance suggests that natural ventilation will be adequate up to 6 m from the ventilating facade. This leads to the conventional design of offices up to 6 m deep on either side of a central corridor, giving as a rule of thumb a width of 15 m for a building with natural cross-ventilation.

Wind pressures can significantly affect ventilation performance. However often they are overlooked in the design of a naturally ventilated building, with buoyancy forces presumed to offer the worst case scenario for design. The result is that airflow patterns and the ventilation performance of the building is often different from the design intent. Successful natural ventilation design requires careful consideration of the building form, and so must involve the architect at the early stages of fabric development.

The work described in this paper is aimed at predicting the local values of the ventilation eflectiveness parameters of large industrial buildings by a technique which involves the use of computational fluid dynamics and multizonal modelling. A modelling technique is described and applied to a typical modern industrial building equipped with both, mixing and displacement ventilation systems. The results of modelling each of the above systems are presented and discussed.

Many dwellings with natural or gravity ventilation systems suffer from poor airchange rates. In Sweden, especially houses built in the 1960-ies and 1970-ies heated with electric resistance heating and thus without chimneys, are at risk. Improving the airchange rate in these houses is to some extent performed to decrease Radon gas concentrations where appropriate. For comfort, most homeowners learn to live with low airchange rates, accepting e.g. odours or window condensation and trying to compensate this with increased airing.

System safety of the performance of mechanical ventilation systems can of course be analysed by means of general methods for system safety analysis. Such methods are used a lot in industrial practice, especially in manufacturing industry. However applications on ventilation systems are more or less non-existing today. This paper summarises today's methods for system safety analysis and shows possible future ways of applying the methods on performance analyses of mechanical ventilation systems.

The suitability of night ventilation for cooling for the UK is first assessed by presenting plots of summer weather data on the bioclimatic chart for three locations within the country. These indicate that most of the external weather conditions lie within the thermal mass and ventilation effectiveness areas of the charts. To confirm this, thermal simulations of a typical office module under a variety of internal conditions and summer weather data were performed.

This paper reports on the use of BRE's domestic ventilation model, BREVENT, to predict subfloor and whole house ventilation rates in a BRE/DoE test house. Before the model could be used though some minor adjustments were necessary because one of its underlying assumptions was that the subfloor temperature was equal to the external temperature. Temperatures measurements over a number of months showed this assumption to be false and so an extra stack term was introduced into the model. However, the overall difference this makes is still quite small, only a few percent at most.

Natural ventilation is being applied to an increasing number of new buildings to minimise reliance on mechanical ventilation and so reduce emission of greenhouse gases. However, passive stack ventilation (PSV) systems are currently designed without incorporating heat recovery leading to significant wastage of energy. Heat recovery systems have not been used in naturally-ventilated buildings because the pressure loss caused by a conventional heat exchanger is large compared to the stack pressure and could cause the ventilation system to fail.

A Probabilistic model of air change rate in a single family house based on full-scale measurements has been developed. The probability of air change rate exceeding certain prescribed limits (risk of improper ventilation or excessive heat flow) is evaluated by utilising the distribution function based on calculated air flow rate. In this way the results are expressed in terms of the R-S model generally used in the safety analysis of structures.