Abstract
In buildings, the HVAC systems are responsible for a major part of the energy consumption. Incorrect design or selection of the system and improper installation, operation, and maintenance of the systems’ elements may result in increased energy consumption. It is worth remembering that the main aim of the appropriate system is to maintain the high quality of the indoor environment. Appropriate selection of the HVAC solution ensures both thermal and quality parameters of the air, independently of the internal and external heat loads. The microclimate of a room is affected not only by air temperature, humidity, and purity, but also by air velocity in the occupied zone. The proper air velocity distribution prevents discomfort, particularly at workstations. Based on the measurements in the office building, an analysis of velocity profiles of air supplying two different types of linear diffusers was carried out. The analysis was made based on the results of measurements performed with thermoanemometers in the actual facility. During the study, temperature of the supply air was lower that the air in the room. Analysis was focused on the airflow fluctuation and its impact on the users’ comfort.
Introduction and Literature Review
Nowadays, we spend most of our time indoors, including homes, apartments, offices, and shopping centers. In conjunction with the increasing living standards, more and more attention is focused on indoor conditions and air quality. The environmental conditions directly affect our satisfaction and, consequently, the quality of our work or the possibility of focus and rest. Therefore, the comfort of users of buildings must be at the highest level, regardless of the purpose of a given facility [1,2]. Many factors directly affect the comfort of users. Besides the individual parameters related to users’ activities, metabolism, and the work performed, the parameters of the air surrounding the user, including temperature, humidity, and air velocity, are crucial. At the same time, it is important to remember that buildings account for a substantial proportion of global energy consumption and significantly contribute to CO2 emissions. The operation of the HVAC systems consumes a large amount of energy. It often accounts for the majority of the building’s energy use. High energy demand may be associated with inappropriate system design and incorrect installation or maintenance. Therefore, highly efficient innovative HVAC systems are increasingly often applied. These solutions, at the same time, should ensure appropriate indoor conditions and reduce maintenance costs. The combination of those two aspects, both economic and quality factors, is a great challenge for the designers. At the design stage, the facility’s functions, workplace locations, and general characteristics of the building should be considered.
In ventilating and air-conditioning systems, the most popular group of supply air diffusers used are ceiling diffusers. The advantage of this type of supply components arises from the popularity of overhead mixing ventilation. Easy access to the ceiling space as well as available space and easy installation of ventilation increase the popularity of this type of solutions. Ceiling diffusers can generate a limited or semilimited, attached to the ceiling, airflow. Depending on the type and structure of the supply air diffuser, the airflow can be swirling (with adjustable or nonadjustable blades), formed in a given direction (one-way, two-way, three-way, or four-way air discharge) [3]. Slot diffusers, perforated ceilings or, in tall structures, long-range nozzles are often used in addition to typical supply air diffusers. The stability of the supply airflow moving in the room depends on the supply air diffuser’s structure. From the point of view of proper air distribution in the room, the range of influence of the supply airflow and its parameters (temperature differential, velocity) at the input into the occupied zone are of great importance.
In recent years, a great interest in air-conditioned office rooms of a higher standard has been observed. Unfortunately, their users often express their dissatisfaction with the quality of internal environment. Among the facilities assessed negatively, there are also those in which investors, designers, and contractors tried to comply with all the recommendations and standards. Designing the air-conditioning installation for facilities intended for public use is particularly difficult due to the presence of many users with different requirements. Thermal requirements are the basic criterion for proper microclimate of a given room. However, the air-flow velocity in the occupied zone also affects thermal sensation. The air supplied to the rooms is very often cooler than the air in the room, which causes local discomfort due to the increase in the cooling capacity of air, as its flow velocity increases. When organizing an air exchange in the office premises, the airflow from the supply ventilation should not be directed toward the workstation in a direct way and should not cause draughts, chills, and overheating/overcooling of the workstation.