Air Temperature Stratification Research Articles

Air Flow Modelling of a Multi-Storey Office Building

Indoor fresh air distribution, temperature stratification and temperature distribution are consider to be the essential indicators when comes to evaluation of the comfort level for internal ventilation environment, particularly for natural ventilated space as target office building. It can be identified that the targeting building has been well designed in the respect of natural ventilation strategies where both cross and stack strategies have been adopted, but it is also obvious that under combined buoyancy and wind driven mode alternative problems appears.

Thermal and ventilation performance of a naturally ventilated sports hall within an aquatic centre

There has been an increasing demand for sports facilities in urban areas recently. As a result of this, more attention is drawn towards not only the energy performance of these building typologies, but also creating a healthy indoor environment for its users. This study investigates the thermal and ventilation performance of a naturally and hybrid (assisted by exhaust fans) ventilated sports hall within an aquatic centre situated in the temperate climate of Victoria, Australia. Its evaluation predominantly considers continuous on-site measurements of air temperature stratification, thermal comfort, CO2 levels, thermal images and tracer gas ventilation studies. Further ventilation analysis is accompanied by CFD simulations towards the development of optimised conditioning strategies. A high level of thermal discomfort was observed for this space during a late summer period when over-heating is a concern. A number of energy efficient strategies are considered to improve the thermal comfort condition without adopting refrigerant conditioning and not sacrificing indoor air quality. A better understanding of how to improve and control such spaces primarily under a naturally ventilated condition is the outcome of this study.

Heat balance for two commercial broiler barns with solar preheated ventilation air

In temperate climatic zones, solar air heaters can reduce heating loads, and increase winter ventilation rates thereby improving inside air quality and livestock performance without additional fuel input. A heat balance was carried out to measure bird heat production under field conditions on two commercial broiler barns to evaluate the impact of solar heated ventilation air on bird performance, and identify strategies to reduce winter heating load. Located 40 km east of Montreal, Canada, the experimental broiler barns were identically built with three floors housing 6500 birds per floor in an all-in all-out fashion. Equipped with solar air pre-heaters over their fresh air inlets, the barns were instrumented to monitor inlet, inside and outside air conditions, ventilation rate and heating system operating time. The effects on bird performance were observed from November 2007 to March 2009 by alternating their operation between the barns. The measured sensible and total heat productions of 4.5 W and 8.4 W, respectively, for 1 kg birds corresponded to laboratory measured values. Bird performance was not affected by the solar air pre-heaters which increased the ventilation rate above normal during only 20% of the daytime period. Room air temperature stratification resulted in 20–40 kW of heat losses during the winter, representing 25% of the total natural gas heat load. Because inside air moved directly to the fans, large and rapid increases in ventilation inlet air temperature, produced by the solar air pre-heaters, resulted in further heat losses equivalent to 15% of the solar energy recovered. Sustainable energy management in livestock barns requiring heating should incorporate an air mixing system to eliminate air temperature stratification and improve fan flows.

Instrumentation strategies for energy conservation in broiler barns with ventilation air solar pre-heaters

Abstract At the present consumption rate, world fossil-fuel reserves are expected to be depleted by 2050 unless their consumption is optimized and supplemented with renewable energy sources. The objective of this project was to evaluate the performance of a simple data acquisition system installed to conduct an energy balance and identify energy saving strategies in two commercial broilers barns with ventilation air solar pre-heaters. Located near Montreal, Canada, the two identical barns were instrumented for inside and outside air conditions, ventilation rate and energy recovery by the solar air pre-heaters. Whereas the temperature, relative humidity and radiation sensors were reliable, inside air temperature stratification complicated energy balance analyses and broiler heat production rate calculations. Lack of room air mixing resulted in the loss of 25 and 15% of the generated heater load and recovered solar energy. The proper monitoring of all environmental conditions required their measurement every 5 rather than 20 min. Instead of using a data transmission service found to be unreliable in rural areas, all data loggers were downloaded onto a portable computer every 45 days during regular instrument maintenance. Accordingly, room air mixing is recommended to facilitate energy balance studies and improve the efficient use of heating energies.

Investigation on the impacts of different genders and ages on satisfaction with thermal environments in office buildings

This paper investigates the effects of occupant gender and age on thermal satisfaction in office environments. The data used for the analyses was collected from 40-sampled occupants and their workstations on 38 floors in 20 office buildings in the U.S. with support from the U.S. General Services Administration. The field measurements include data collection for air temperature, radiant temperature, temperature stratification, relative humidity and air velocity of the sampled workstations. Occupant satisfaction surveys were distributed to each occupant in the workstations measured, and the thermal attributes of building systems were recorded. The objective and subjective data sets support statistical correlation analysis between environmental qualities and user satisfactions. The statistical analysis of air temperatures, occupant thermal satisfaction, age and gender revealed that females are more dissatisfied with their thermal environments than males especially in the summer season with high significance, and occupants over 40 years old are more satisfied than under 40 in the cooling season with marginal significance.

MODEL EXPERIMENT ON NATURAL VENTILATION ASSISTED BY A ROOF SYSTEM INTEGRATED WITH SOLAR PHOTOVOLTAIC CELL PANELS

Most solar photovoltaic (PV) cells are incorporated in building only for electricity supply. As the temperature of interior surface of the photovoltaic cells is increased to about 60°C, the air nearby is heated. If the PV cells are used as roof materials in the atrium space, the stack effect can also be expected, which will assisted the natural ventilation in the building. Here a roof system integrated with amorphous silicon PV cells is proposed in a model house. The air temperature stratification is measured by model experiment, as well as the air change rate by stack effect. Results show that the proposed roof system can turn 5% of solar radiation into electricity, and the other 5%-7% of the solar radiation can be discharged by natural ventilation. When the solar transmission of the solar roof is too strong, a curtain can prevent the room being overheated. In total, the proposed roof with an interior curtain can use about 10% of the solar irradiation by natural ventilation and electricity generation, while the room temperature is similar to that in the conventional room with insulated roof system.

Numerical study on temperature stratification in a room with underfloor air distribution system

In this study, numerical prediction using computational fluid dynamics (CFD) was utilized to investigate air temperature stratification in a room with an underfloor air distribution (UFAD) system. The numerical modeling using CFD computation was validated with physical test in a full size experimental room with an UFAD system. The different supply air conditions and heat loads were discussed. The results show that the effect of three parameters, heat load, supply volume flux and supply air velocity, on room air temperature would be expressed by the length scale of the floor supply jet. When the length scale increased from 0.8 to 1.56 m, the ratio of vertical temperature difference between 2.5 and 0.1 m at the occupied zone to the difference between return and supply air temperature decreased from 0.62 to 0.25. When there was only one local heat source in the room, there was a thermal stratified interface at the occupied zone. The interface height was about 1.42 times the length scale. The results may suggest ways to optimize UFAD design and operation.

Numerical procedure for predicting annual energy consumption of the under-floor air distribution system

As compared with the mixing system, indoor air temperature stratification in the under-floor air distribution (UFAD) system offers an opportunity for cooling load reduction in the occupied zone. This stratification is a major feature that offers the energy saving potential, but it has not been thoroughly taken into account in most energy simulation programs. In this article, a numerical procedure, based on coupling two types of modeling, i.e., CFD (computational fluid dynamic) simulation and dynamic cooling load simulation, is proposed to predict annual energy consumption. The dimensionless temperature coefficient is first defined in the UFAD system and obtained from CFD simulation, based on the boundary conditions from a cooling load program ACCURACY. According to this coefficient, temperature stratification input to ACCURACY is then revised to calculate the updated supply and exhaust air temperatures for final annual energy prediction. To demonstrate the method, a small office room is investigated using Hong Kong weather data. With the constant air volume (CAV) supply in the UFAD system, it is found that the dimensionless temperature coefficient is almost a constant, when the locations of heat sources are fixed. As compared with the mixing system, the UFAD system derives its energy saving potential from the following three factors: an extended free cooling time, a reduced ventilation load, and increased coefficients of performance (COP) for chillers.

Stratification of welding fumes and grinding particles in a large factory hall equipped with displacement ventilation

The purpose of the study was to investigate the performance of displacement ventilation in a large factory hall where large components of stainless steel for paper, pulp and chemical industries were manufactured. The performance of displacement ventilation was evaluated in terms of concentration distributions of welding fumes and grinding particles, flow field of the supply air and temperature distributions. Large differences in vertical stratification patterns between hexavalent chromium (Cr(VI)) and other particulate contaminants were observed. The concentration of Cr(VI) was notably lower in the zone of occupancy than in the upper part of the factory hall, whereas the concentrations of total airborne particles and trivalent chromium (Cr(III)) were higher in the occupied zone than in the upper zone. The stratification of Cr(VI) had the same tendency as the air temperature stratification caused by the displacement flow field.

Stratification of welding fumes and grinding particles in a large factory hall equipped with displacement ventilation

The purpose of the study was to investigate the performance of displacement ventilation in a large factory hall where large components of stainless steel for paper, pulp and chemical industries were manufactured. The performance of displacement ventilation was evaluated in terms of concentration distributions of welding fumes and grinding particles, flow field of the supply air and temperature distributions. Large differences in vertical stratification patterns between hexavalent chromium (Cr(VI)) and other particulate contaminants were observed. The concentration of Cr(VI) was notably lower in the zone of occupancy than in the upper part of the factory hall, whereas the concentrations of total airborne particles and trivalent chromium (Cr(III)) were higher in the occupied zone than in the upper zone. The stratification of Cr(VI) had the same tendency as the air temperature stratification caused by the displacement flow field.

ENERGY SAVINGS WITH CEILING FANS IN BROILER HOUSES

Electrical, gas, and total energy requirements during cool weather were compared for broiler housesequipped with ceiling fans and houses without fans. Fans were operated at speeds which were effective in disruptingvertical air temperature stratification but slow enough that air velocity at bird level was not measurable. Electricalenergy requirements were 5.5% higher, while gas requirements were 11% lower and overall energy requirements were 8%lower for houses equipped with ceiling fans than for houses without fans. Vertical temperature gradients were eliminated.There were no differences in bird performance as measured by market weight.