Active Chilled Beams - Air Distribution and Efficiency

Kozlowski, Bartosz Michal ; Vasilevskis, Sandijs

4. term

Indoor Environmental and Energy Engineering, Master

2017

2017-06-01

107

Dette speciale undersøger luftfordeling og termisk komfort i et kontorrum med aktive kølebafler (ACB). Hovedformålet var at vurdere trækrisiko via lufthastigheder og udarbejde et designdiagram med en grænse på 0,15 m/s baseret på CFD-beregninger. For at understøtte og validere de numeriske forudsigelser blev der udført fuldskala målinger i testrummet "Cube" og målt hastighedsprofiler i baffleudløbet. Isotermiske målinger blev gennemført med varmekugle-anemometre og PIV (Particle Image Velocimetry), og ikke-isotermiske fuldskala forsøg blev udført med varmekugle-anemometre placeret i rummet i et setup med én person ved et skrivebord med computer, skærm og lampe. CFD-modellen blev kalibreret med hensyn til randbetingelser, og den bedst egnede turbulensmodel blev udvalgt. Der blev analyseret fire CFD-scenarier for Annex 20-rummet: symmetrisk og asymmetrisk varmebelastning, personlig ventilation med to ACB’er samt et rum med 4 m loftshøjde; i hvert scenarie var der to personer ved skriveborde. Undersøgelsen viser, at ACB’er på grund af induktionsfænomenet adskiller sig fra tidligere testede ventilationssystemer: den tilførte luft består af en primær (friskluft) og en sekundær (induceret rumluft) stråle, hvilket betyder, at for at levere 20 l/s friskluft skal den samlede diffunderede luftmængde overstige 74 l/s, mod 20 l/s for tidligere systemer. Resultaterne giver grundlag for udformning af et designdiagram rettet mod at begrænse trækrisiko i praksis.

This thesis examines air distribution and thermal comfort in an office room ventilated by active chilled beams (ACB). The primary objective was to evaluate draught risk using air velocity and to develop a Design Chart with a 0.15 m/s velocity limit based on CFD predictions. To support and validate the numerical results, full-scale measurements were carried out in the "Cube" test room and velocity profiles were measured in the beam exit region. Isothermal measurements used hot-sphere anemometers and PIV (Particle Image Velocimetry), while non-isothermal full-scale tests deployed hot-sphere anemometers across the room in a setup with one seated occupant, computer, monitor, and desk lamp. The CFD model’s boundary conditions were adjusted and the most suitable turbulence model was selected. Four CFD scenarios were studied for the Annex 20 room: symmetric and asymmetric heat loads, personalized ventilation with two ACBs, and a 4 m high room; each scenario included two occupants at desks. The study highlights that ACBs are distinct from previously tested ventilation systems due to the induction phenomenon: the supplied flow consists of a primary (fresh air) and a secondary (induced room air) jet. Consequently, to deliver 20 l/s of fresh air, the total diffused airflow must exceed 74 l/s, unlike the 20 l/s used for earlier systems. These results underpin a practical Design Chart aimed at managing draught risk.

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acb ; cfd ; piv ; active chilled beam ; induction rate ; induction ratio ; hot-sphere anemometers ; design chart ; hvac ; ventilation

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