PR1982

Distinguishes the problems of designing natural ventilation systems for summer and winter conditions and discusses in detail the objectives, methods and some field studies directed towards the solution of winter ventilation problems.< Describes experimental work conducted in a low-energy house equipped with adjustable slot ventilators in the window frames. Both tracer gas decay methods and pressurization tests indicate similar increases of air flow when the ventilators are opened.

Describes a window opening survey concerned with identifying the objective correlates of window opening. Finds that the variation between households in terms of their total daily window opening is greater than that within households. Householders may adopt consistent window opening patterns. Hypothesises that although window opening is primarily a function of external air temperature, relative humidity and windspeed are influential at high values.

Outlines ventilation needs to show that odour dilution and moisture control are the major winter factors. Detailed studies on 24 well insulated houses show that window opening habits are clearly linked to outdoor temperature, more windows being opened in milder weather.< Shows from energy input analysis that space heating only provides a quarter of the total heat, the remainder coming from casual sources. Analysis of energy loss suggests that a third of the losses are attributable to ventilation, the remainder through the building fabric.

Describes a programme of ventilation measurements performed on a group of energy efficient houses built in the mid-1970's and situated in Abertridwr, S.Wales. Pressurization, tracer decay and British Gas autovent techniques were employed. Results show satisfactory whole-house ventilation rates (0.5 ac/h), but the living room and bedrooms had very low ventilation rates. Some cases showed serious condensation. "Trickle" ventilation installed in 18 of the houses improved internal ventilation patterns and condensation levels were substantially reduced.

Traces the relationship between ventilation needs and methods and the growth of civilization. Describes the development of ventilation methods and assessment of air quality, especially since the Industrial Revolution. Questions whether currently accepted ventilation criteria are still valid, andsuggests that ventilation is only one of several means of ameliorating the internal environment.

Describes a simple method of controlled ventilation comprising an extract system and air inlets. The extract system is effectively a flue connecting to vents in the kitchen and bathroom and relying on thermal differences and the wind to create air flow, air enters the house via slot vents over windows. Theproposed system has been installed in a timber framed house.

Outlines project where 25 representative dwellings from Birmingham Local Authority Housing stocks were monitored before and after energy retrofitting. Findings are presented as a set of case studies encompassing both fabric and infiltration measures. Suggests that simple energy conservation measures are successful but that more sophisticated combinations tend to under-achieve. Ventilation changes in several cases are impaired by increased use of windows and/or permanent ventilation. Where these effects are'nt operating, reductions of between 0.3 - 0.6 ac/hr appear typical.

Discusses air quality and the related definitions of ventilation efficiency. Suggests a definition of efficiency for ventilation systems in residential buildings that takes into consideration how ventilation air spreads within a dwelling. Measurements of the efficiency for exhaust, supply and combined systems show that for combined and supply systems the highest efficiency occurs in those parts where the air is supplied.

Detailed studies of public sector modernisation programmes show that the principal problem resulting from lack of thermal insulation and inappropriate methods of heating and ventilation is condensation and mould growth. Gives the optimum air change rate (for dwellings with particular heat loss characteristics) at which the heat input necessary to prevent the RH rising is at a minimum. The resulting temperatures are too low to be considered comfortable, so air change rates need to be less than the optimum.

Examines several ventilation strategies in tight houses for both impact on the total ventilation and effect on the energy balance of the system. Uses the single-zone infiltration model developed at LBL as part of the calculation of total ventilation load. Strategies covered include natural systems such as ventilation stacks as well as mechanical systems such such as air-to-air heat exchangers and exhaust fans with and without heat pumps.