Diagnostics of natural ventilation in buildings is problematic, as the airflow rate changes considerably over time. One constant average airflow is usually assumed when calculating energy demand for a building, however, such a simplification could be fraught with considerable error. The paper describes a comprehensive methodology for the diagnostics of a natural ventilation system in a building and its practical application. Based on in situ measurements and simulations in two existing buildings (dwelling house and school) in Poland, the real values of the ventilating airflows were analyzed and resulting heat demand was compared with the design values. The pros and cons of various methods for evaluation of natural ventilation are discussed. The real airflow was determined by measurements in a ventilation grille or by a tracer gas concentration decay method. The airtightness of the buildings’ envelope was evaluated based on the fan pressurization test. The last stage entailed computer simulations of air exchange in buildings using CONTAM software. The multizone models of the buildings were calibrated and verified with existing measured data. Measured airflow in a multifamily house was small and substantially deviated from the Polish standard. In case of a school, the air flow rate amounted to an average of 10% of the required value. Calculation of the heat demand for ventilation based on the standard value of the airflow led to a considerable overestimation of this value in relation to the real consumption. In the analyzed cases, the difference was 40% for the school and 30% for the residential building.
In mixing ventilation systems, diffusers are often located on side walls and supply quasi-free air jets above the occupied zone. The data presented in this paper shows a new CFD 3D benchmark with two well-defined characteristic zones in the room, i.e., the quasi-free jet zone and the occupied zone. Measurement methods adequate for air velocity and speed measurement were applied: laser Doppler anemometry for the axial velocity component in the jet and low velocity thermal anemometry for the air speed in the occupied zone. Measurements were performed in a physical scale model (1:5) of the room. The kinematic similarity criterion was fulfilled by the equality of the Reynolds numbers in the model and in the prototype. To identify boundary conditions, additional measurements were carried out in the inlet region (as close as possible to the supply opening). The CFD results validation and reporting methods applicable for the benchmark data are proposed in Hurnik et al. (2015) [1].
The widespread thermal improvement in residential buildings involves not only the insulation of outdoor walls but also window replacement. In Poland it is the residents of individual premises who manage the replacement and in order to keep their heating bills low, they seek airtight solutions to minimize the cooling of premises due to air infiltration. In this situation the indoor air quality is not considered at all and no exchange of used air and fresh air occurs. Unawareness on the part of residents and the increased costs of replacing the windows which need additional devices to ensure the inflow of air are the main reason for the deteriorating microclimate conditions in residential dwellings. The present paper demonstrates the measurement of indoor air quality, the building leakage test and the measurement of air flow in exhaust opening a four-bedroom dwelling located in Gliwice, Poland. In order to evaluate the air exchange within a longer period and in different outdoor climate conditions, the measurements were supplemented with numerical simulation of ventilating airflows. Modifications to improve the indoor air quality in the examined flat were also suggested.
The paper presents a part of project entitled "Development of thermal diagnostics of buildings", which related to reduced of energy consumption in the buildings. The detailed scope of the project is described in [1]. As part of the research task, a method of a rapid diagnosis of heating system [2], cooling sources [3] and airconditioning systems was developed as well as a method of calculate building energy performance certificates based on measurements [4]. This paper presents the research done in two office buildings. The obtained results were referenced to the design documentation. The results of the inspections and measurements on the mechanical ventilation system were discussed. Attention was paid to the divergence between the documentation and the installation status of both buildings. The problems encountered during the measurements were discussed. 2. THERMAL DIAGNOSIS AND MEASUREMENT METHODS FOR THE INSTALLATION OF MECHANICAL VENTILATION In developed countries, almost 40% of the consumed energy is used in the buildings. There have been repeated attempts to reduce this energy consumption
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