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

University essay from Högskolan i Gävle/Avdelningen för bygg- energi- och miljöteknik; Högskolan i Gävle/Avdelningen för bygg- energi- och miljöteknik

Abstract:

Scandinavian countries have always been the first in investigation and development of

new ventilation systems. In the last years, engineers from Finland and Sweden are

studying a new ventilation system known “Confluent jet ventilation system” which is

trying to improve displacement and mixing results.

The aim of this thesis master is to study the behaviour of three different ventilation

systems, mixing ventilation, displacement ventilation and confluent jet ventilation, in an

office room by mean of three analysis, temperature gradient analysis, tracer gas analysis

and thermal comfort analysis, and to compare them to know if the new one, confluent

jet, increases the performance of mixing or displacement ventilation system. In case of

confluent jet ventilation system, there were two different cases: one with the supply air

device at 2.2m high, and the other with it at 1.7m high to compare which one was the

correct position and gets the best results. For each studied system 3 different cases were

analyzed, having the same parameters each one of them for the three ventilation

systems.The measurements were taken in an office room located in the laboratory of the

University of Gävle, Högskolan I Gävle, in collaboration with the Finnish company

specialized 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 other

measurements were being taken. For tracer gas analysis, a data logger took

measurements of the contaminant concentration, N2O, from when the contaminant was

thrown into the room until it disappeared following a Decay curve. Lastly, in thermal

comfort analysis 4 transducers took measurements each 12 minutes of air temperature,

operative temperature, air velocity and air humidity are measured in 6 different points

inside 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 the

best results were obtained by confluent jet system with the supply air device at 2.2m in

case of temperature gradient, since the difference of temperatures between the low and

the top level were the minimum and contaminants and indoor air were not in a

homogeneous mixing. In case of tracer gas, the results about air change efficiency were

not the expected because they showed a well-mixed situation for every system and it

should not have been like that. It was caused for the influence of a cooling system

situated in the ceiling of the room and the temperature difference between inside and

outside 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 the

supply 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 best

results and showed that it is a new ventilation system that must be taken in

consideration in the following buildings. Between supply air device at 2.2m and 1.7m

the results were very similar, but a bit better in case of the highest height. 

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