Paper 5
Representing Top-hung Windows in
Thermal Models
David
A. Coley
Centre for
Energy and the Environment, Physics Building, Stocker Road, Exeter, EX4
4QL, UK
Abstract
The UK climate is
moderately mild and natural ventilation by window opening and passive
‘trickle’ vents is very common. In this paper the natural ventilation
rates provided by top-hung windows open to small angles in single-sided
designs have been studied using a common whole building simulation tool.
It was found that the amount of ventilation greatly depends on how the
windows are represented. Such software tools usually assume that the
opening area has the same vertical separation as the underlying window
(i.e. it is modelled as an arrow slit). This is a reasonable approximation
when windows are opened to a large angle, but not for small angles, when
most of the opening will be at the base of the window. This work has shown
that this can have substantial consequences for the simulated airflow into
and out of a room. By modelling such openings more accurately, it has been
found that the usual way of treating top-hung openings can give rise to an
over-estimation of the ventilation rate at low wind speeds by a factor of
five or more. The problem has been tracked to the over-estimation of the
effectiveness of temperature-induced air exchange. This could have
important consequences for meeting parts of the building regulations in
the UK, for example minimum ventilation rates in schools. It is
recommended that engineers use the representation developed here in future
modelling work.
Key words: natural
ventilation, windows, airflow calculation, calculation errors, window
opening.
References
Allocca C, Chen Q and Glicksman LR: (2003) “Design
analysis of single-sided natural ventilation”,
Energy and Buildings, 35, (8), pp785-795.
Beisteiner A and Coley DA:
(2003) “Carbon dioxide levels
and summertime ventilation rates in UK schools”, International
Journal of Ventilation, 1, (3), pp181-187.
CIBSE:
(1999) “CIBSE Guide A”, CIBSE London.
CIBSE:
(2005) “CIBSE Guide B”, CIBSE London.
CIBSE: (1997) “Applications
Manual AM10: Natural ventilation in non-domestic buildings”,
CIBSE London.
Coley D, Greeves R and Saxby B: (2007) “The effect of low
ventilation rates on the cognitive function of a primary school class”,
International Journal of Ventilation,
6, (2), pp107-112.
Coley DA and Beisteiner A:
(2002) “Carbon dioxide levels and ventilation rates in schools”, International
Journal of Ventilation, 1, (1), pp45-52.
Dascalaki E, Santamouris M, Argiriou A, Helmis C,
Asimakopoulos DN, Papadopoulos K and Soilemes A: (1995) “Predicting
single sided natural ventilation rates in buildings”, Solar
Energy, 55, (5), pp327-341.
Heiselberg
P: (2004) “Natural ventilation
design”, International
Journal of Ventilation, 2, (4), pp295-312.
IES:
(2007) “MacroFlo calculation
methods”. Reference manual for IES, IES Ltd.
Li
Y and Heiselberg P: (2003) “Analysis
methods for natural and hybrid ventilation - A critical literature review
and recent developments”,
The International Journal of
Ventilation, 1 Hybvent
Special Edition, February, pp3-20.
Murakami
S, Kato S, Akabayashi S and Mizutani, K: (1991) “Wind tunnel test on velocity-pressure field of cross-ventilation with
open windows”, ASHRAE
Transaction, Vol. 1,
Part 1.
Warren PR and Parkins LM:
(1984) “Window opening
behaviour in office buildings”,
Building Serv. Eng. Res. Technol. 5, (3), pp89-101.
|
Contents
Paper 1
The Influence of Evenly Distributed
Ceiling Mounted Personalized Ventilation Devices on the Indoor Environment
Paper 2
Ventilated Airflow Windows for Comfort in a Hot and Humid Climate
Paper
3
Effect of Free Cooling on the Operation of a Desiccant Evaporative Cooling
System
Paper 4
Analysis of the Ventilation System of an Isolation Room for a Hospital
Paper 5
Representing Top-hung Windows in Thermal Models
Paper 6
Multizone
Age-of-Air Analysis
Paper 7
Active Chilled Beam Wall Jet Prediction by the Free Convection Model
Paper 8
Estimation
of the Effectiveness of Cross Ventilation as a
Passive
Cooling Method for Houses
|
