Design of Active Chilled Beam systems: Detailed economic analyses for different design temperatures and airflows
Publicerad
Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The predominant space-cooling system prevailing in Swedish commercial buildings
today is the variable air volume (VAV) system. The system efficiently modulates
the supplied air volume to meet changing cooling demands. An alternative cooling
system is active chilled beams (ACB). ACB is a ceiling-mounted convection unit
that decouples ventilation from thermal conditioning facilitating a potential for energy
and cost savings.
This thesis aims to compare the energy and life-cycle costs (LCC) between the VAV
and ACB systems, highlighting the impact of the cooling system choice on building
energy demand and energy source design. The study grounds its investigations
on the energy simulations of a case building located in Gothenburg, Sweden. The
building is a six-story lightweight commercial building constituted primarily of open
office landscapes. The energy is sourced from a combination of district energy and
borehole heat-exchanger (BHE).
The study concludes that ACB systems can be designed at costs commensurate to
comparable conventional VAV systems due to the savings attained from a smaller
air-handling unit and ductwork, attributed to reduced airflows, exceeding the investment
cost of ACB units and accessory equipment. Although the study can confirm
energy savings achieved through reduced airflows, it could not validate other sources
of energy savings. It was observed that VAV consumes less total energy but requires
higher total power compared to ACB. Translated into annual costs, the higher power
consumption of the VAV pertains to larger power costs which, combined with larger
fan energy, results in higher operational expenses for the VAV system. Maintenance
costs cause a further divergence between the systems, in favor of the ACB.
Investigating the different design parameters found that increasing the airflow of
ACB systems generally leads to more balanced building loads. Contrarily, increasing
supply air temperature cause an opposite effect on the specific component energies
and the balance of building loads. Modulation of air temperature should conclusively
be accompanied by proportional alterations to airflow rate to reduce the impact
on investment costs; prioritizing a lower number of units over minimum airflow.
Beskrivning
Ämne/nyckelord
space-cooling, high-efficiency, free cooling, active chilled beam, variable air volume, borehole, energy, investment cost, life-cycle cost