temperature gradient

An accurate temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of supply air flow rate. Several simplified nodal models were developed and implemented in the various building simulation programmes in order to estimate the temperature stratification in rooms with displacement ventilation. However, the most commonly used models do not count the types and locations of the typical heat loads in rooms with displacement ventilation.

19 university students were asked about their thermal comfort while attending ordinary lessons in a displacement ventilated test room of typical classroom size. Two different ceiling heights were tested. Both the general temperature level and the strength of the vertical temperature stratification in the room increased continuously during the lessons due to the presence of the students, however slower with the higher ceiling.

Temperature efficiency is an important index to estimate the ventilation effectiveness. Usually ,the temperature efficiency is determined through field or model tests such as gas-tracing technology. The heat source structure(location, size, heat emission, etc) has a strong effect on the temperature efficiency. The heat sources present themselves or may be arranged in three basic models:(A)heat sources uniformly distributed in the space; (B) heat sources uniformly distributed on the floor; (C)concentrated heat sources at the bottom of a room.

This paper compares two well-known modelling approaches for natural ventilation in a multi-zone building with thermal stratification and large openings. The zonal approach in this paper assumes a fully mixed condition in each zone, and considers the bi-directional flows through all large openings. The zonal model is integrated into a thermal analysis code to provide simultaneous prediction of both ventilation flow rates and air temperatures in each zone. The CFD approach uses a finite-volume method for turbulent flows.

The aim of the research was to find out the indoor climate conditions in Finnish commercial kitchens by measurements and inquiries. Twelve kitchens were selected from the Helsinki metropolitan area. The measurements concentrated on thermal conditions. On the average thermal conditions in measured kitchens are not fully satisfactory and they varied considerably between the kitchens. Thermal conditions within kitchens varied also depending on the workplace. Heat stress harmful to health was only found in two kitchens.

The study reported in this paper is concentrated on the estimation of the heat transfer from air to ice due to convection. Together with measurements of temperature and moisture profiles, air movements have been visualised in a small-scale model of a planned indoor ice rink. Some field tests concerning moisture content and temperature also have been realized in two different ice rinks. The study indicates that a low emissivity layer in the ceiling decreases the risk for ceiling condensation, decreases the heat radiation on the ice and decreases the driving force for air mixing.

Displacement ventilation is acknowledged to be an efficient system for the removal of contaminants and excess heat from occupied zones of rooms, this system is aiming at supplying clean undiluted supply-air directly to the zone of occupation. Air flow rate, temperature and the design of the supply device strongly influence the parameters that determine thermal comfort. In the paper, one kind of displacement ventilation systems - ohair air supplying system is investigated.