Journal of Building Physics current issue

A Differential-difference Approach for the Modeling of Electrical Floor Heating Systems

Pakanen, J.E., Saastamoinen, J.J. — Mon, 05 Oct 2009 04:15:47 PDT

During recent years, many papers have been published concerning dimensioning, analysis, and control of floor heating. A central issue in all these activities is to create a suitable model, which explains the thermal behavior of the floor and its environment. The article introduces a differential-difference approach, which is believed to be new in floor heating modeling. The proposed method is applied in a slab, a semi-infinite and infinite solid, which are connected to electrical heating. The results are compared with the corresponding analytical solution. This also concerns the proportional heating control applied in the infinite solid. The comparison reveals the characteristic features of the differential-difference solution, which are briefly discussed. The first results are encouraging and show good model behavior.

Uncertainty and Sensitivity Analysis for Building Energy Rating

Corrado, V., Mechri, H. E. — Mon, 05 Oct 2009 04:15:47 PDT

One of the main tasks of the European Energy Performance of Buildings Directive 2002/91/EC (EPBD) pertains to energy building certification. For this purpose, recent European standards have defined a methodology for the assessment of the energy use of buildings through the calculation of energy ratings. The accuracy of the energy rating depends both on the detail level of the model and on the confidence of the input data. In this work, the quasi-steady simplified monthly method, presented in the ISO 13790: 2008 standard, has been applied to a dwelling in Turin, Italy, in order to calculate its energy rating. A widespread list of 129 input data was identified and grouped into three sets: climatic data, envelope data, and building use data. Probability density functions were assigned after a detailed bibliographic research. The Monte Carlo Latin hypercube sampling technique has been used to assess the building energy needs confidence interval and the energy performance class uncertainty. A sensitivity analysis based on the Morris method, has also been performed for the different building heat balance terms, in order to identify the most important parameter set that takes into account for the uncertainty in the model output. The main results demonstrate that the asset energy rating is only slightly affected by data uncertainties; moreover, the analysis highlights the importance of associating an operational energy rating to the asset rating in order to show the influence of user behavior on building energy performance. On the other hand, the results show that less than 10 input data, among the considered 129 ones, have a significant influence on the energy rating uncertainties.

An Experimental Device for the Measurement of Hygroscopic Inertia Influence on RH Variation

Ramos, N.M.M., De Freitas, V.P. — Mon, 05 Oct 2009 04:15:48 PDT

This article reports the development of an innovative flux chamber that is specifically developed for the support of experimental work that is aiming at a systematic measurement of the hygroscopic inertia influence on relative humidity (RH) variation inside rooms. This flux chamber is a flexible infrastructure where different test configurations can be run. The precise control of vapor production, inside air renovation, and system temperature allow for the reproduction, in a small-scale room, of hygrothermal scenarios that can be fully repeated in an unlimited number of cycles. Results obtained are presented in this article, relating especially to the testing and calibration procedures and highlighting the limitations and possibilities of the facility. The hygroscopic inertia effect on RH variation is demonstrated. A discussion on the perfect mixing of the air inside a room is also addressed, based on the obtained results.

Thermal Benefits of Tiled Roofs with Above-sheathing Ventilation

De With, G., Cherry, N., Haig, J. — Mon, 05 Oct 2009 04:15:48 PDT

Computer simulations are conducted to demonstrate the thermal benefits of good roofing design in hot climates. The work is aimed to quantify the thermal benefits from batten-space ventilation, commonly referred to as above sheathing ventilation (ASV), and thermal mass. Both roof features are effective in reducing the heat transmission into the habitable space. Nevertheless, the use of roof ventilation is often misunderstood and most procedures for energy assessment of building structures do not recognize the contribution from ASV and thermal mass.

As part of this work, a computer algorithm is developed to predict the heat, air and moisture (HAM) transport in the building envelope. The algorithm predicts the transient temperature and moisture behavior in the building envelope and takes account of the air movement from bouyancy and wind driven airflows.