Amount Of Thermal Mass Research Articles

A porous building approach for modelling flow and heat transfer around and inside an isolated building on night ventilation and thermal mass

Abstract Recently, more and more attention is paid on passive energy saving technologies in buildings, including night ventilation and thermal mass. In the paper, a porous building model is proposed to investigate wind and thermal environment around and inside an isolated building on different amounts of night ventilation and amounts of thermal mass. Inside the building, the Brinkman-Forchheimer extended Darcy model (BFED model) and the local thermal non-equilibrium model (LTNE model) are first adopted, to represent flow and heat transfer between airflow and thermal mass. The reliability of the model is validated with published wind tunnel experimental data. After that, local wind and thermal characteristics, cooling effects of night ventilation are obtained. The effects of three key parameters: airflow velocity, airflow temperature and equivalent porosity of the building are investigated in detail. The results indicate that, the outdoor air temperature has a larger influence on the effects of night ventilation than airflow velocity. And the proposed porous building model shows great advantages in modelling heat transfer between airflow and thermal mass. The investigation provides thoughts for dealing with urban wind environment, outdoor thermal environment and wind environment of building arrays.

Annexing Green Building Rating Points through Multipurpose Vertical Light Pipes

Objective: To determine how many points can be annexed in a green building by a combination of the two processes and test the viability of combining daylight and rainwater harvesting in a pipe. Method/Analysis: An experiment was carried out using a 4m (width) x 6m(height) x 12m(depth) model at a scale of 1:25. Three light pipes of different transparency were used. The first pipe has a fully transparent surface, allowing most of the light to penetrate. The second pipe has a translucent surface. Light that penetrate through it would be partial, with the translucent surface acting like a layer of diffuser to diffuse the light. The third pipe is a combination of transparent and translucent surface. Water will act as the transporting medium for light and at the same time as a barrier for heat to enter. Although water does have certain amount of thermal mass, the heat stored in water can be minimized by circulating the water throughout the system. Findings: Up to 13 points could be earned in non-residential new construction (NRNC), while up to 15 points in Residential New Construction (RNC). Application/Improvement: The novelty of this study proposes the use of a tube for daylighting and rainwater harvesting simultaneously in a space through an experimental process at a small scale. This result could be further developed to an industrial scale for commercial purposes.

Design optimization of insulated cavity rammed earth walls for houses in Australia

This paper presents an optimization study of the design parameters for houses using rammed earth walls, including window sizes, window shading, the amount of thermal mass and the amount of insulation in the external walls. The optimization is based on two objectives: (1) energy use reduction and (2) life-cycle cost minimization.It was found that, in general, the thicker the walls/insulation was applied, the less the energy load, but the higher the life-cycle cost. In hot arid climates, small windows and large window shadings lead to a lower energy load while the minimum life-cycle cost was achieved with the smallest window and window shading. In warm temperate climates, the optimum size of north facing window was 30% and 40% of the wall area to achieve the minimum energy load and life-cycle cost while the sizes of the windows on the other walls as well as the window shading needed to be as small as possible. In cool temperate climates, small south facing windows and large windows in the other walls would result in the lowest energy load; however, to achieve the minimum life-cycle cost, all the windows and window shadings should be as small as possible.

Modelling of Thermal Characteristics of Insulated Mass in Zero-heating Passive Solar Houses: Part 2—Simulation Results

Results of indoor air temperature swings in zero-heating, passive solar houses with thermally massive walls using frequency domain techniques are presented in this paper. Theoretical analyses pertinent to the study were presented in Part 1 of the paper. The diurnal and annual indoor temperature swings predicted by the other computational methods (finite difference in SUNREL and time series in EnergyPlus) for a simple test house compare reasonably well with the results obtained by frequency domain techniques. Although there is an optimum mass (corresponding to minimum air temperature swing) for a given material for diurnal cycles, the annual swing is inversely proportional to the amount of thermal mass. The results further suggest that the degree of annual swing is also dependent on the level of insulation associated with the mass. The effect of the insulation on daily fluctuations is however insignificant.

Thermal Mass Design in Buildings – Heavy or Light?

Thermal mass, including the building envelope, the interior partition, the furnishing, or even the air inside a building, is defined as the mass that can store thermal energy (heat or cooling energy). For storing heat in buildings, there are two important thermal properties of the materials that need to be considered, i.e. the heat capacity by volume and the heat-absorption rate. The first property determines the ability of the element to store thermal energy, and the second property determines the ability of the element to conduct the thermal energy. The combined convective and radiative heat transfer coefficient and the surface area of the thermal mass determine the rate of heat transfer between the thermal mass element and the air. One of the good examples in using thermal mass is night cooling, which can avoid or minimize the need for mechanical cooling in buildings. We present a simple design formula for use by architects and engineers which involves only three design related parameters, i.e. the time constant of the system, the dimensionless convective heat transfer number and the Fourier time constant. The present method allows the fast determination of the amount of thermal mass as well as key design parameters when the phase shift of indoor air temperature and the attenuation of the indoor air temperature fluctuation are specified.

Designing Thermal Mass in Naturally Ventilated Buildings

According to its location, thermal mass can be approximately classified into two types: external and internal. Internal thermal mass, such as furniture and purpose-built internal concrete partitions, does not expose to ambient temperature directly, while external thermal mass, such as walls and roofs, expose directly to ambient temperature variation. A virtual sphere method for modelling thermal mass is introduced and its application in building thermal mass design is discussed. When the ventilation rate is constant, three key design related parameters are identified, and both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system, the dimensionless convective heat transfer number and the Fourier time constant. A simple design method for architects and engineers is described. The present method allows the rapid determination of the amount of thermal mass, as well key design parameters when the phase shift of indoor air temperature and the attenuation of the indoor air temperature fluctuation are specified. This paper also presents an explicit formula for predicting phase shift when the air flow is driven by buoyancy force alone.

Nonlinear coupling between thermal mass and natural ventilation in buildings

An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.

Investigation of thermal performance of a passive solar building with floor radiant heating

This paper presents a theoretical study of an integrated radiant floor heating–direct gain passive solar system. Thermal mass is utilized both for storage of auxiliary heating energy and direct solar gains incident on the floor. An explicit finite difference model is developed to accurately model nonlinear effects and auxiliary heating control. The numerical simulation model is employed to study the performance of a passive solar outdoor test-room with different amounts of thermal mass under various control strategies with constant and sinusoidal room thermostat setpoints. A satisfactory thermal mass is determined based on energy savings, reduction of room temperature swings, and prevention of floor surface overheating. Control of auxiliary heating based on a room effective (operative) temperature is shown to result in improved thermal comfort and higher utilization of passive solar gains as compared to room air temperature control.