An equation is developed for predicting the combined effect of naturally and mechanically induced air flows in buildings and solved by a combination of analytical and iterative methods. The resulting two-dimensional formulation, implemented as a simple computer program, allows rapid, hourly simulation of infiltration in domestic-scale buildings with a range of ventilation strategies. This implementation is used to compare energy use and carbon dioxide emissions for three ventilation strategies—natural ventilation, mechanical extract and balanced, whole-house mechanical ventilation— as a function of dwelling airtightness. This exercise confirms the need for airtightness if the benefits from balanced mechanical ventilation with heat recovery are to be maximised.List of symbols g Acceleration due to gravity (m s-1) F Flow function (kg M-2 S-1) H Height of building (ground floor to rooo (m) L Length on plan of building (m) cp Pressure coefficient (dimensionless) c Specific heat capacity of air at constant pressure C1 kg-I K-1) Ev Ventilation heat demand of the dwelling over a heating season (J) v Wind speed (m s-1) A Relative leakage area (dimensionless) 12 Ventilation rate (ac h-1) p Pressure (Pa) Q Mass flow (kg s-1) z Height (m) zo Mean height of neutral plane in building (m) 4z~ Tilt in neutral plane resulting from wind pressure (m)
It is important to limit dwelling infiltration to reduce energy demand and help meet national climate change commitments while concurrently providing sufficient ventilation to deliver adequate indoor air quality. DOMVENT3D is a model of infiltration and exfiltration that assumes a linear pressure distribution over any number of uniformly porous facades and integrates the airflow rate in the vertical plane to predict the theoretically correct airflow rate through them. DOMVENT3D is a new development of an existing two-dimensional model of infiltration that provides more opportunities for investigating a greater number of dwellings than was previously possible. Initial testing suggests that DOMVENT3D is mathematically robust and is suitable for modelling a wide variety of dwelling types and geometries to assist engineers and policy makers. Practical application: The modern building services engineer may be required to model airflow networks in a building to balance the conflicting needs of energy consumption reduction and occupant health. Limiting exfiltration is one method of reducing heat losses from a building and so there is a need to model it accurately. This article presents a new model of infiltration and exfiltration through a uniformly porous facade that can be incorporated within advanced complex airflow network tools or applied using a simple spreadsheet.
The central purpose of this paper is to develop and test a case for compulsory pressurisation testing for new dwellings. The authors have argued elsewhere in favour of such a policy. The paper reviews the available information on airtightness in the UK housing stock, the impact of airtightness on ventilation and fabric heat losses, the information that is available on the costs of making houses airtight and the logistics of pressurisation testing. The authors use this information to explore the costs and
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