Analysis of three ventilation systems in an office: Mixing, displacement and confluent jet ventilation system. : Analysis of temperature gradient, tracer gas and thermal comfort.

Scandinavian countries have always been the first in investigation and development ofnew ventilation systems. In the last years, engineers from Finland and Sweden arestudying a new ventilation system known “Confluent jet ventilation system” which istrying to improve displacement and mixing results.The aim of this thesis master is to study the behaviour of three different ventilationsystems, mixing ventilation, displacement ventilation and confluent jet ventilation, in anoffice room by mean of three analysis, temperature gradient analysis, tracer gas analysisand thermal comfort analysis, and to compare them to know if the new one, confluentjet, increases the performance of mixing or displacement ventilation system. In case ofconfluent jet ventilation system, there were two different cases: one with the supply airdevice at 2.2m high, and the other with it at 1.7m high to compare which one was thecorrect position and gets the best results. For each studied system 3 different cases wereanalyzed, having the same parameters each one of them for the three ventilationsystems.The measurements were taken in an office room located in the laboratory of theUniversity of Gavle, Hogskolan I Gavle, in collaboration with the Finnish companyspecialized in ventilation systems, Stravent.For temperature gradient analysis, ten sensors took temperatures from the low level,0.1m high, to the top level of the room, 2.4m, during all the time that the othermeasurements were being taken. For tracer gas analysis, a data logger tookmeasurements of the contaminant concentration, N2O, from when the contaminant wasthrown into the room until it disappeared following a Decay curve. Lastly, in thermalcomfort analysis 4 transducers took measurements each 12 minutes of air temperature,operative temperature, air velocity and air humidity are measured in 6 different pointsinside the office room and at 3 different heights, 0.1m, 1.1m and 1.7m.After analyzing the results of temperature gradient, tracer gas and thermal comfort thebest results were obtained by confluent jet system with the supply air device at 2.2m incase of temperature gradient, since the difference of temperatures between the low andthe top level were the minimum and contaminants and indoor air were not in ahomogeneous mixing. In case of tracer gas, the results about air change efficiency werenot the expected because they showed a well-mixed situation for every system and itshould not have been like that. It was caused for the influence of a cooling systemsituated in the ceiling of the room and the temperature difference between inside andoutside the room that affected more than expected. Finally, in thermal comfort analysis,the best results were obtained by confluent jet ventilation, therefore in case of thesupply air device at 2.2m and in case of it at 1.7m.To sum up, taking account the results achieved, the confluent jet ventilation got the bestresults and showed that it is a new ventilation system that must be taken inconsideration in the following buildings. Between supply air device at 2.2m and 1.7mthe results were very similar, but a bit better in case of the highest height.