C.-A. Roulet

Real heat recovery with air handling units

Abstract More and more air handling units are equipped with heat recovery systems, with the aim of decreasing the energy use in buildings for heating and cooling. The efficiency of the heat recovery system is often used to calculate the energy saving. However, air-handling units do not always function as planned. In particular, parasitic shortcuts and leakage may decrease dramatically the efficiency of ventilation and heat recovery. In addition, these units need electrical energy for fans, which may be more precious than saved heat. Measurements, using tracer gas dilution technique have detected various malfunctions in several units. This paper addresses real energy recovery with air handling units from a theoretical point of view and presents results of measurements on 13 units. In the best three cases, the real, global heat recovery efficiency was between 60 and 70% for units having a 80% nominal efficiency. In the three worst cases, the global efficiency was less than 10%. For these cases, the heat recovery system uses more energy than it saves.

ORME : A multicriteria rating methodology for buildings

Abstract To check the compliance of a building with regulations, evaluate the efficiency of retrofit, or even label a building one would in most cases perform a comparison of a number of building qualities. Within the framework of the European Joule–Thermie OFFICE project, a multicriteria rating methodology was developed for this purpose, based on a rating method that uses principal component analysis, and a ranking method that uses a partial aggregation technique. The aim of this methodology is to rate or to rank office buildings and retrofit scenarios of the same building according to an extended list of parameters, including: • energy use for heating, cooling and other appliances, • impact on external environment, • indoor environment quality, • cost. The paper presents the principles used in the methodology, and some examples of application to actual buildings. More information is given in a complete report (ORME—Office building rating methodology for Europe, Office Project Report, University of Athens, 1999).

Natural Ventilation for Passive Cooling : Measurement of Discharge Coefficients

Abstract For the design of natural ventilation systems for passive cooling in buildings, engineers and architects are interested in the prediction of ventilation rates as a function of position and size of the ventilation openings. In common use, there are both simple and detailed (i.e., multizone) ventilation models which rely basically on the same Bernoulli algorithm to describe airflow through large openings. An important source of uncertainty is related to the attribution of discharge coefficients. The present study was undertaken to improve our knowledge on velocity and discharge coefficients when measured in real buildings. The experiments were performed on a naturally ventilated three-level office building where the staircase acted as exhaust chimney. In order to keep the flow pattern stable, a condition for air flow measurements to be reproducible, the experiments were performed on windless nights where the flow was only driven by stack pressure. Air flow patterns were traced with smoke and tracer gas. In a first set of experiments, air velocities, contraction and velocity coefficients and the position of the neutral pressure level (NPL) have been measured, in a second set of experiments, the resulting effective area of a combination of two openings in series. Air flow rates derived from velocity measurements in the open doorways were found to be in agreement with the flow rates obtained with a constant injection tracer gas technique, with an uncertainty of ± 20%. The velocity coefficient φ = 0.7±0.1 and jet contraction coefficients ɛ = 0.85±0.1 found in the experiments are shown to be in agreement with the generally accepted value of the discharge coefficient Cd = φ ɛ = 0.6±0.1, giving new justification for its use in the models. Basic configurations for ventilative cooling are given to illustrate how qualitative modeling used in simple models can give valuable information to the designer.

Elaboration of retrofit scenarios

Coherent and efficient retrofit scenarios are commonly built on the basis of the knowledge of the degradation state of the building and its obsolescence. The architect or building engineer prepares a list of refurbishment works required on the basis of the building audit, his experience and the available budget. This paper describes a systematic method, based on multicriteria analysis and a constructivist approach, which helps an expert in designing retrofit scenarios. This approach includes several steps and follows an iterative process. The associated computer tool takes charge of tedious tasks such as calculating the associated costs, performing an energy balance, and checking for coherence between actions; and presents various viewpoints to the expert. It also helps the user in quickly creating various scenarios. The expert can then interact with this information and makes the decision for selecting the final scenario. This interactive approach brings together expert intuition and rational systematic verification.

Why, when and how do HVAC - systems pollute the indoor environment and what to do about it ? The European AIRLESS project

From 1998 to 2000, a European project named AIRLESS was conducted by 12 institutes, universities and companies from seven European countries. The objective was to develop strategies, principles and protocols to improve and control the performance of HVAC-systems and its components for incorporation in codes and guidelines. The first step was to define air pollution caused by and/or originating from HVAC-systems, to investigate ways to prevent this pollution and to define strategies to keep this pollution away. A summary of this first phase of the AIRLESS project is presented.

TOBUS software — an interactive decision aid tool for building retrofit studies

The TOBUS software has been developed to facilitate the implementation of the TOBUS building diagnosis and decision-making method for retrofit studies. This user-friendly software runs under the Windows® operating system and includes several modules, each of which addresses a particular aspect of the diagnosis including: building description, dimensions, cost coefficients, building diagnosis of current physical state and functional obsolescence, indoor environmental quality (IEQ), energy use, elaboration of retrofit scenarios, cost analysis, reporting results. The software also includes comprehensive databases on the physical state of degradation, including hundreds of illustrations, retrofit work details, cost, etc.

Diffusion en surface de l'argent sur les plans (001), (111), (110) et des surfaces vicinales du cuivre

Abstract The diffusion coefficients of silver on singular and vicinal surfaces of copper have been measured using an oxidation method to determine the concentration profiles. The diffusion was carried out under ultra high vacuum at low temperature (250 to 500 °C) with a low concentration of the diffusing species (less than 0.5 monolayers). Comparison of the results with the terrace-ledge-kink model shows that the diffusion occurs along the ledges and also explains the diffusion on the vicinal surfaces. The differences between this model and the diffusion observed on the singular surfaces are explained by the presence of separated ledge loops on these surfaces.

Comparison and combination of factorial and Monte-Carlo design in sensitivity analysis

Abstract The sensitivity of building physics simulation programs to the uncertainty of input parameters is analysed. A comparison is drawn between the classical Monte-Carlo method and a new method based on fractional factorial design. Their numerical behaviour is analysed and their respective advantages are discussed. The new method provides more information for an equivalent number of simulation runs. It allows a real feedback process since the relation between the uncertainty of the input and output data is fitted on a linear model. It also allows a better understanding of the behaviour of the studied building. Both methods are illustrated with a three-storey building, in which ventilation is analysed for different ratios between the wind and buoyancy forces. However, the two methods can also be combined and a map of the uncertainty of the output for the whole domain, determined by the variation of a few input parameters, can be drawn.

Indoor environment quality in buildings and its impact on outdoor environment

Abstract The main purpose of buildings is to provide a comfortable living environment for their occupants. This includes, among others, thermal, visual and acoustic comfort as well as indoor air quality. Except during the 1950’s and 1960’s, it has always been considered important that an excess use of energy should be avoided in the construction and the management of a building, sometimes even at the cost of user comfort. Energy saving is, however, not the main purpose of the building. Indeed, if it were really so, the largest energy savings would be obtained by not erecting the building in the first place. Since the Rio conference, there have been more and more incentives to save energy and lower the impact of buildings on the environment. Therefore, there is no excuse for the building sector not to adopt a sustainable development policy. Some energy is required to control the indoor climate and indoor air quality. Therefore, it is often suspected that energy savings result in poorer indoor environment quality, or, on the contrary, that a high comfort level is the result of high technology and high energy consumption. This is not true. It is now generally admitted among building scientists that high quality energy services do not necessarily incur a high energy use, and that good environment quality can be obtained with a reasonable amount of energy and power, and with a low environmental impact. The presentation brings some evidence from past and current research to support this assertion.

Using large radiant panels for indoor climate conditioning

Abstract Large panels are used to control the indoor temperature, by cooling as well as by heating, in several types of buildings. The panels are made out of two corrugated stainless steel foils, seam welded on the perimeter and spot welded at many places on the area. Water at controlled temperature circulates in this cushion. These panels are either installed as conditioning ceilings or on walls. In well-insulated buildings, the power required to control indoor temperature is rather low, and a small temperature difference between the panel and the indoor environment suffice to deliver or absorb the required heat. The paper presents the panel itself and its use in residential and non-residential buildings, as well as some industrial and research implementations.