Interzonal Heat Research Articles

Investigation of inter-zonal heat transfer in large space buildings based on similarity: Comparison of two stratified air-conditioning systems

Stratified air-conditioning (STRAC) has been deployed in large space buildings to achieve vertical thermal stratification with significant energy-saving potential. This research focuses on two typical STRAC systems: floor-level sidewall air-supply system (FSAS) and nozzle sidewall air-supply system (NSAS). By employing experiment and CFD methods, airflow pattern and heat transfer between the unoccupied and occupied zone under the two air supply systems are investigated in a reduced-scale laboratory. The geometric models of the prototype building, with a geometrical scaling factor of 4:1, are established according to similarity principles and studied by CFD simulation. The results demonstrate that the two scales have similar indoor thermal performances. The numerical simulation results of the prototype building provide and compare commonly used inter-zonal heat transfer coefficients of actual large space buildings with the two typical STRAC systems. For FSAS, heat conduction caused by temperature gradient dominates the inter-zonal heat transfer. In NSAS, both heat conduction due to temperature gradient and heat convection due to airflow contributes equally to this heat transfer. The inter-zonal heat transfer coefficient Cb is affected by the airflow pattern and zonal division, and closely associated with local turbulence intensity.

Heat transfer between occupied and unoccupied zone in large space building with floor-level side wall air-supply system

The air supply terminal located at the floor level attached to side-wall is widely used in large space buildings, leading to potential energy saving as well as significant vertical thermal stratification. The cooling load calculation of such system is challenging, especially the calculation of the load gained from unoccupied zone. This paper adopts experiment and computational fluid dynamics (CFD) methods to study the heat transfer upward and downward across the stratified surface in large space building with floor-level side wall air-supply system. Five experimental cases with different heat source power and exhaust airflow ratios are performed to study their effects on the indoor thermal environment. We investigate the same cases in CFD and verify the result of vertical temperature distribution and cooling load components. As a critical parameter in evaluating the thermal stratification environment of large space building, the inter-zonal heat transfer coefficient Cb is emphatically discussed. By comparing the Cb value obtained through the two methods, the accuracy of the microscopic method is verified by the heat balance method. The results show that the Cb value is mainly affected by the zonal division and air distribution, but less prominently by exhaust airflow ratio and heat source in the occupied zone.

User’s Lifestyle and the Thermal Performance of the Compound House: An Appraisal

This study examines the impact of thermal performance of Yoruba compound house on the user’s lifestyle to cope with discomfort hours. A compound house was simulated using Autodesk Ecotect software. The study found that the front and right sides of the building have the lowest temperatures due to the combined effects of indirect and interzonal heat transfers. The research highlighted that while the user’s lifestyle in the Yoruba compound house relies on the veranda to cope with discomfort hours, residents of multi-dwelling compound houses rely on a lifestyle of housing adjustments. The study concludes that the thermal properties of the Yoruba compound house are complemented by the user’s lifestyle to cope with the discomfort hours.

On the calculation of heat migration in thermally stratified environment of large space building with sidewall nozzle air-supply

Vertical thermal stratification is typical for partially conditioned large space building. Heat accumulation in the upper part of unoccupied zone will have significant effect on the cooling load of occupied zone. In order to accurately estimate this cooling load, calculation of the heat migration occurs in the thermally stratified environment is critical. Heat migration in this study refers to the amount of heat transferred from unoccupied zone to occupied zone (or between other adjacent zones). This paper discusses the method to calculate heat migration through convection and conduction in a large space building served by side wall nozzle air-supply system. In a scaled laboratory, three experiment cases with different exhaust air flow ratio are investigated. CFD simulations of the same cases are performed. Vertical temperature distribution and detailed cooling load results of the whole system as well as those of occupied zone are validated against experiment result. A detailed analysis on the total heat migration and its components between different zones is conducted. Inter-zonal heat transfer coefficient Cb used in a zonal BLOCK model and heat conductivity across the intersection of zones is obtained by dividing the whole space into two and four zones vertically. It is found that both Cb and thermal conductivity value across the intersection is greater than expected and affected by the local turbulent intensity.

A generalised mathematical modelling methodology for design of horticultural food packages exposed to refrigerated conditions: part 1, formulation

A generalised mathematical modelling methodology to predict rates of key heat and mass transfer processes within refrigerated horticultural packages is described. A novel zoned approach with flexible geometry descriptions and flexible unifying concepts are used to ensure wide-ranging model applicability. The model component hierarchy, which treats the in-pack fluid, packaging and product as equally important components, closely aligns the modelled system and the physical system. This, together with the flexible zone definition methodology and associated definitions of sub-models for intra- and inter-zonal heat and mass transfer pathways support the use of an object-oriented simulation computer programme design. In Part 2, the heat transfer sub-models are presented, and the total model system tested against experimental data for several package-product combinations. In Part 3, the mass transfer sub-models are presented and further test results reported.

Measurement of interzonal heat and mass transfer by natural convection

Experiments to measure the interzonal heat and mass transfer were carried out in two full size adjoining rooms under two different conditions. Before starting the tests, one of the rooms was heated to an average temperature of 32°C, while the other room was cooled to an average temperature of 19°C. To start the first type of tests, the auxiliary heating and cooling were turned off and the door blocking the opening opened. For the second test, auxiliary cooling was turned off, while the auxiliary heat was left on in the heated room. Visual observations of the flow phenomenon were made. Velocity and temperature profiles of the air-flow through the opening, and air temperatures in the test rooms were measured. The experimental mass and heat flow rates were computed from the velocity and temperature data and compared with the values predicted by the existing algorithms based on the application of the Bernoulli's equation. The agreement between the measured and predicted values is better for a value of discharge coefficient C = 0.45 than it is for C = 0.611 (the theoretical value of C for a sharp edged orifice quoted in the literature).

Analysis and Measurements of Interzonal Natural Convection Heat Transfer in Buildings

Natural convection heat transfer through doorways can be an important process by which thermal energy is transferred from one zone to another zone of a building. The topic of this paper is interzonal natural convection in a two zone and a three zone multilevel full scale building. Aperture velocity and temperature distributions are measured and the experimental interzonal mass flow rate and heat transfer are determined. A Bernoulli model is derived to predict the neutral heights, velocity profiles, and interzonal heat transfer. The measured and predicted interzonal flow rate and heat transfer are compared and found to be in good agreement.

Optimization and Design of Zone Heating Systems, Energy Conservation, and Passive Solar

This paper addresses the problem of determining the optimal mix of energy conservation, passive solar, and zone heating systems in residential buildings. Analytic solutions to constrained and global optimization problems are presented. This work draws upon the Lagrangian multiplier technique used in related studies of energy conservation and passive solar design. Graphs are presented showing the optimal cost fractions for energy conservation, passive solar, and a zone heater as a function of the initial cost constraint, for a reference building in Dodge City, Kansas. The use of a zone heater is shown to reduce the annual energy requirements for space heating, and increase the life cycle savings. Also presented are design curves for the required zone heater capacity as a function of the thermal time constant for a given zone, heater response time, and interzonal heat transfer. Finally, design curves for the zone mean radiant temperature as a function of zone size, zone heater temperature, zone heater area, and interzonal heat transfer are presented.

Performance of Storage Walls with Highly Conductive Covering Plates and Connecting Fins

The thermal behavior of a storage wall, constructed of concrete, with highly conductive covering plates and connecting vertical fins, is investigated. The results demonstrate that, during the charging mode, the amount of energy released from the front surface is significantly reduced. A portion of the saved energy is stored for future discharge, but a large portion is transferred to the back surface and released. A selective front surface further reduces the energy released from the front surface, and this energy is stored. By properly selecting the fin spacing, plate-fin thickness, and plate-fin thermal conductivity, the rate and direction of thermal discharge can be controlled. The improved heat transfer capability and added thermal control provide new alternatives for interzonal heat transfer and multizone passive building designs.