Current Research

The aim of HVAC is to provide good air quality and a comfortable thermal environment that will ensure occupants' satisfaction, health and high productivity. The challenge for engineers is to achieve this aim while keeping energy costs at a low level.

Total-volume ventilation and air-conditioning of rooms is at present the method most used in practice. Mixing and displacement room air distribution are the main principles applied. Displacement ventilation has been shown to achieve better ventilation effectiveness than mixing ventilation, especially in rooms with non-passive, heated contaminant sources. However, unlike mixing ventilation, the air temperature gradients in rooms with displacement ventilation are greatest at low air temperatures near the floor. High air velocities often exist near the floor as well. Thus, if not well designed, the risk of local discomfort due to draught and vertical temperature difference in rooms with displacement ventilation is high.

This has been shown in a field survey of occupants' response to the thermal environment and indoor air quality in eight office buildings with displacement ventilation performed at the Centre (Melikov et al. 2002; Pitchurov et al. 2002; Naidenov et al. 2002). Analyses of the response of 227 occupants revealed that 24% of the occupants surveyed were daily bothered by draught and almost one half (49%) by uncomfortable room temperature. The displacement ventilation systems in the rooms surveyed failed to provide the occupants with satisfactory air quality, as half of them were not satisfied with the air quality.

In both rooms with mixing ventilation and those with displacement ventilation, the temperature of the air that will reach the breathing zone of occupants will be relatively high and will decrease the perceived air quality. The air quality perceived by the occupants will improve when more fresh air is supplied to the space. However, this will cause draught discomfort for some occupants. Furthermore in practice, rooms are used by occupants with different physiological and psychological response, clothing, activity, individual preferences to the air temperature and movement, time response of the body to changes of the room temperature, etc.

Thus, total-volume ventilation has limitations and is often unable to provide each occupant simultaneously with high thermal comfort and air quality. Often, occupants in rooms with mixing or displacement ventilation have to compromise between preferred thermal comfort and perceived air quality, because some people are very sensitive to air movement while others are sensitive to the air quality. The compromise is different for each occupant and also differs in time. The disadvantage of the total-volume ventilation principle is that often room air movement is changed due to furniture rearrangement and this may increase occupants' complaints of draught and/or poor air quality.

Environmental conditions acceptable for most occupants in a room may be achieved by providing each occupant with the possibility to generate and control his/her own preferred local environment. Personalized ventilation (PV) aims to provide each occupant with clean air direct to the breathing zone. Each occupant can control the environment at his/her workplace. Thus occupants' satisfaction and productivity can be increased as a result of improved air quality, thermal comfort and control over the environment. Energy use may be lowered, depending on system design and operation.

Different air supply terminals tested.

The supply air terminal device is an essential part of any personalized ventilation system. It plays a major role in the distribution of personalized air around the human body and thus determines occupants' thermal comfort and perceived air quality. Studies on performance of different supply air terminal devices (Melikov et al. 2002, Melikov et al. 2002, Melikov 1999, Melikov et al. 2001, Cermak et al. 2002) reveal that the interaction between the airflow from the personalized ventilation, the free convection flow around the human body and the airflow of exhalation has been studied and assessed in regard to both occupants' thermal comfort and perceived air quality.

A new index, personal exposure effectiveness, identifying the amount of clean personalized air inhaled by occupants, was introduced to assess the performance of the air terminal devices. A breathing thermal manikin has been used previously to study concentration of pollution in the inhaled air (Hyldgaard 1994, Brohus and Nielsen 1996). A unique "breathing" thermal manikin, equipped with an artificial lung that simulates and controls the breathing cycle and mode, the amount of respiration air as well as temperature, humidity and gas concentration of the exhaled air, was developed and has been used during the physical measurements (Melikov et al. 2000, Melikov et al. 2002a). The manikin allows for measurement of temperature and humidity of the inhaled air, in addition to measurement of inhaled concentration of gases. The physical measurements performed by the breathing manikin, by Particle Image Velocimetry, and by a Laser Doppler anemometer confirm the advantages of personalized ventilation in improving the quality of the inhaled air in comparison with total volume ventilation systems.

The design of personalized ventilation aiming to increase occupants' satisfaction and performance and decrease energy use requires a knowledge of temperature ranges and velocity, the direction of personalized air as preferred by occupants, the degree of individual control, strategies for coupling of the personalized ventilation system with total volume ventilation systems, etc. Several series of comprehensive human subject experiments have already been performed at the Centre. Improvement in perceived air quality and occupants' performance have been documented in the range of comfortable temperatures as recommended in the present standards (Kaczmarczyk et al. 2002a). Human response to personalized ventilation in warm environments has been investigated. Design recommendations in respect to maximum and minimum temperature of the supplied personalized air as well as maximum supply flow rate have been developed (Zeng et al. 2002, Kaczmarczyk et al. 2002a). Experiments are planned to study the importance of the degree of individual control, methods for enhancing the performance of personalized ventilation systems and their coupling with total volume ventilation systems, especially for minimising airborne transmission of infectious agents between occupants. Validation of the advantages of the system in practice is an important part of the Centre's research plan for the next five years.

References
Melikov, AK, Pitchurov, G., Naydenov K, Langkilde, G. (2002) Field study on occupant comfort and office thermal environment in rooms with displacement ventilation, in preparation for submission to HVAC&R Research Journal.

Naydenov K, Pitchurov G, Melikov A, Langkilde G. (2002). Performance of Displacement Ventilation in practice. In: Proceedings of ROOMVENT'2002, pp. 483-486.

Pitchurov G, Naidenov K, Melikov AK, Langkilde G. (2002). Field survey of Occupants Thermal Comfort in Rooms with Displacement Ventilation. In: Proceedings of ROOMVENT'2002, pp. 479-482.

Melikov A., (1999). Design of localised ventilation, Proceedings of the 20th International Congress of Refrigeration, IIR/IIF, Sydney, Paper 746.

Melikov A., Cermak R., Mayer M., (2001). Personalized ventilation: evaluation of different air terminal devices, Proceedings of CLMA 2000, Napoli, Paper 524.

Melikov A., Cermak R., Mayer M., (2002). Personalized Ventilation - Part 1: Criteria for Design and Performance Assessment, in preparation for submission to HVAC Research.

Melikov A., Cermak R., Mayer M., (2002). Personalized Ventilation - Part 2: Performance Evaluation and Comparison of Five Design Options, in preparation for submission to HVAC&R research journal.

Hyldgaard, C.E. (1994). Humans as a source of pollution. Proceedings of ROOMVENT'94, 4th International Conference on Air Distribution in Rooms, June 15-17, Cracow, Poland, pp. 413-433.

Brohus, H. and Nielsen, P. V. (1996). Personal exposure in displacement ventilated rooms. Indoor Air: 6, 157-167.

Melikov A, Kaczmarczyk J, Cygan L. (2000a) Indoor Air Quality Assessment by A "Breathing" Thermal Manikin, Proceedings of ROOMVENT'2000, vol(1), Reading, UK.

Melikov A, Kaczmarczyk J, Cygan L. (2000) A "Breathing" Thermal Manikin for indoor air quality assessment, in preparation for submission to Indoor Air Journal.

Kaczmarczyk J, Zeng Q., Melikov A., Fanger PO, (2002a). The effect of a personalized ventilation system on air quality prediction, SBS symptoms, and occupant's performance. In: Proceedings of Indoor Air 2002, Monterey, pp. 1042-1047.

Kaczmarczyk J, Zeng Q., Melikov A., Fanger PO, (2002). Individual control and people's preferences in experiments with Personalized Ventilation System. In: Proceedings of Roomvent 2002, pp. 57-60.

Cermak, R., Majer, M., Melikov, A.K. (2002), Improved quality of inhaled air with personalized ventilation. In: Proceedings of Indoor Air 2002, Monterey, pp. 1054-1059.

Zeng Q, Kaczmarczyk J, Melikov A, Fanger PO, (2002). Design ranges for acceptable air temperature and flow rate for Personalized Ventilation System, in preparation for submission to HVAC&R Research.