Passive cooling concepts for office and administrative buildings using earth-to-air and earth-to-fluid heat exchangers

Status

finished

Summary

The operation of ten thousand Austrian office and administrative buildings translates into an enormous annual consumption of energy. The supply of energy is not the only thing to play a central role in these buildings. To an increasing extent air conditioning already makes up for a considerable share of the energy consumed. Normally the cooling loads are compensated with conventional compression cooling plants (centrally respectively decentrally). This results in high energy requirements for electricity which leads to high operational costs.

Passive cooling concepts represent alternative cooling possibilities which require much less primary energy. It is possible to use natural heat sinks with these systems by employing some very simple measures (cool earth area, cold night air) by deliberately leading off heat or energy and making use of storage effects. Due to the limited temperature level of heat sinks which can be put to use in passive cooling systems it is imperative not to exceed a specific cooling load of a maximum of 45 W/m² by means of building optimisation (external loads) and equipment optimisation measures (internal loads). A sensitivity analysis was conducted on the basis of a representative reference office building for the passive cooling systems "night aeration", "earth-to-air heat exchangers (EAHE)" and " earth-to-water heat exchangers (EWHE) in combination with concrete slap cooling (CSC)". The models for this were worked out in the dynamic simulation environment TRNSYS.

The use of night air which is relatively cool in summer for space cooling produced good results with natural aeration from a window and also, however, led to a 50% reduction in the cooling energy requirements. The performance of natural window aeration can be given as a standard value of around 150 Wh/m²d. Night-time cooling via the mechanical aeration unit turned out to be inadvisable due to the high amount of energy required to operate the ventilating fan.

It is inadvisable to use EAHEs when the stream of air required is in the range for a change of air necessary in terms of hygiene. Otherwise both the driving energy requirements and the costs for pipelines and canal networks increase - in a similar fashion to the mechanical night aeration. The standard value for the performance of a EAHE equals around 300 Wh/m²d.

Compared to the systems named before EWHEs in combination with concrete slap cooling reveal advantages particularly with monovalent cooling systems of a higher performance since the performance of the heat sink can be considerably reduced as a result of activating the building mass. The standard value for the performance of EWHEs and CSCs equals around 480 Wh/m²d.

A comprehensive look at eight different cooling systems for the reference office building revealed that intelligently planned and operated cooling systems can also have economic advantages in addition to energetic advantages. The best result in the economic efficiency considerations was achieved by the "Variant EWHE and CSC" (surface ratio 3:1) with each displays more favourable annual costs than conventionally operated cooling plants.

The 64 participants who took part in the project-related planner workshop clearly demonstrate the interest in the technology and project work.

Project manager

Ing. Christian Fink, DI Ernst Blümel
AEE INTEC, Arbeitsgemeinschaft ERNEUERBARE ENERGIE
Institut für Nachhaltige Technologien

Sub contractor

Prof. Wolfgang Streicher, Dr. Robert Kouba, DI Richard Heimrath
Technische Universität Graz
Institut für Wärmetechnik

Partners

• Architekturbüro Andexer Moosbrugger
• Technisches Büro Ing. Walter Bierbauer
• Technisches Büro Ing. Alfred Herbst
• Strobl Bau GmbH

Contact

AEE INTEC
Arbeitsgemeinschaft ERNEUERBARE ENERGIE
Institut für Nachhaltige Technologien
Ing. Christian Fink, DI Ernst Blümel
Feldgasse 19
8200 Gleisdorf,
Tel.: +43 (3112) 5886 - 14
Fax: +43 (3112) 5886 - 18
E-Mail: c.fink@aee.at