Energy Efficient Climatization for Rooms with Cooling Demand: -based on a Concept with Displacement Ventilation and Low Supply Air Temperature
In relation to new building directives and regulations there is much focus on energy efficiency
and reducing the use of electricity. There is therefore a need for ventilation systems with low
Specific fan power (SFP) and to limit or avoid the need for mechanical cooling.
At the same time questions are raised concerning whether increasingly complicated
ventilation systems are the best way to achieve energy efficiency. They are more vulnerable
for poor design and maintenance which especially school buildings have suffered from.
This has led to the development of several natural and hybrid ventilation concepts. One of
these which has had success in school buildings the last 15 years in Sweden and Norway is
the so-called Swedish model. Characteristic of this solution is that sub terrain culverts are
used for passive cooling and heating of the ventilation air which passes through double inner
walls and is supplied to the room high on the inner wall. The supply air falls towards the floor
mixing in the surrounding air and spreads along the floor as displacement flow with an outlet
in the ceiling. This works particularly well in classrooms where the high occupation density
creates a cooling demand large parts of the year. These schools therefore have a very low SFP
factor and no mechanical cooling.
In the following report a classroom model with the Swedish ventilation concept is studied
with the aim of developing a method of dimensioning such air flow. CFD simulations are
used to confirm expected behaviour and the resulting thermal comfort and air quality at
typical winter, spring and summer scenarios. Finally a Guide for preliminary design and
sizing for climatization of rooms with cooling needs using the Swedish model is presented.
The most important results were that there was a good correspondence between the empirical
calculations and CFD simulations. Adequate carbon dioxide levels and temperature can be
achieved without use of primary energy for heating at for outdoor temperatures above 5 ºC.
There was a substantial risk of draft unless a near zone of 2-3 m is used. However the CFD
model was limited to a slice of the classroom and the accuracy of the results suffers somewhat
Guidelines are developed for preliminary design and sizing of supply air plumes based on
empirical expressions of air flow by Eimund Skåret(2000) and can be found in the appendix.
Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2008. , 125 p.
ntnudaim:4375, MTENERG energi og miljø, Energibruk og energiplanlegging
IdentifiersURN: urn:nbn:no:ntnu:diva-18329Local ID: ntnudaim:4375OAI: oai:DiVA.org:ntnu-18329DiVA: diva2:565824
Tjelflaat, Per Olaf, ProfessorVik, Tor Arvid