wind effects

Analytical solutions are derived for calculating natural ventilation flow rates and air temperatures in a single-zone building with two openings when no thermal mass is present. In these solutions, the independent variables are the heat source strength and wind speed, rather than given indoor air temperatures. Three air change rate parameters α,β and γ are introduced to characterise, respectively, the effects of the thermal buoyancy force, the envelope heat loss and the wind force.

Passive cooling techniques driven purely by natural wind forces present a highly attractive environmental solution in the perspective of low energy architecture. The physics governing passive cooling are well understood and have been extensively discussed in the literature. Indeed the necessary design details that must be incorporated to achieve the full potential of the technique, such as exposed thermal massive and good internal and solar gain control, are also well understood.

A building's envelope is the product of the choice of framing materials and quality of craftsmanship. Exposed to weather, it may 1101 provide the same airtight conditions in which its insulation material had been tested. Air permeable insulation offers little resistance to pressure driven, or convective, heat loss. Air impermeable insulators can additionally reduce convective, as well as conductive, heat loss by being sprayed into and sealing up sources of infiltration normally addressed by caulks and sealants.

This paper presents an experimental study of natural ventilation induced by combined forces of thermal buoyancy and opposing wind in a single-zone building. Experiments demonstrated that for a certain range of buoyancy strength and wind speed, two different stable ventilation modes and thus flow rates exist for a fixed building geometry at given buoyancy and wind strength. In these situations, the final ventilation mode and the ventilation flow rate are dependent on the ventilation history of the building.

A programme of work involving the measurement of ventilation rates, air velocities and temperatures has been completed within a naturally ventilated auditorium in the Queens Building, De Montfort University. Measurements have been recorded for 'winter', 'mid-season' and 'summer' conditions, and average occupancy levels.

Fuel-burning appliances require air for combustion. When the appliances are located in enclosed spaces, provision must be made for supplying the required amounts of air. Depending on the specifics of the appliances and the enclosure, additional air may be required for draft hood dilution and space conditioning. An enclosed space can be a mechanical room in a building, a furnace room in a residence or the entire floor of a building if a separate enclosure is not used to isolate the combustion appliance(s).

Split-duct roof ventilators or windcatchers are used to provide both supply and extract ventilation to the spaces which they serve. However, buildings are often erected in conditions where there is no prevailing wind direction. An investigation into four and six segment windcatchers to determine their relative performances under different wind conditions was undertaken using scale models in a wind tunnel. Conclusions indjciate that six segment windcatchers have a more predictable, reliable performance in uncertain or variablewind conditions.

This paper examines theoretically the effects of wind on buoyancy-driven ventilation via some new analytical solutions recently developed by the authors. Three air change rate parameters are introduced to characterise respectively the effects of thermal buoyancy, the envelope heat loss and the wind force. The wind can either assist or oppose the airflow. For the first time, it has been found that for opposing winds, there are two stable ventilation flow rates for a given set of wind and thermal parameter, i.e. the natural ventilation flow exhibits hysteresis.

Breathing walls were installed on opposite sides of a scale mock-up model of a housing structure that was situated in an artificial climate test room. We analyzed the thermal insulation capability. heat recovery effect and indoor climate for the inflow of outdoor air across the breathing wall. The rate of heat recovery reached 30% under strong winds of up to 8 mis. Even when the ventilation rate tripled due to the strong wind, the temperature difference in the vertical direction was less than 2 K.