A new office building is being planned for construction in Causeway Bay. The design team has the stated aim of providing

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A new office building is being planned for construction in
Causeway Bay. The design team has the stated aim of providing an
indoor air quality (IAQ) that conforms to Excellent Class of the
HKEPD IAQ certification scheme with the extra condition that there
should only be 10% dissatisfaction with the IAQ. The team has
proposed to use the olfactory method to determine the amount of
outdoor air required for ventilation.
To reduce the electrical energy consumption of the building, the
design team wishes to reduce the outdoor air requirement while
still maintaining an excellent level of IAQ environment. Reduction
of the amount of outdoor air is also desirable considering the poor
outdoor air quality (0.5 decipol) at Causeway Bay. The building has
therefore been designed to use a displacement ventilation system
(ventilation efficiency 1.5) and low sensory pollutant load
materials (equivalent to 0.1 olf/m2 of floor area).
Smoking will not be permitted. The design occupancy level is 0.08
occupants per m2 of floor area.
(a) It is intended that the outdoor
air ventilation rate should be low due to the use of low olf
materials. However, there is concern that that the emission of
VOCs, especially toluene, from surface finishes during the first
few weeks of operation, may exceed the Excellent Class of IAQ
certification scheme.
The
Excellent Class objective for toluene is 0.29 ppm (1092
mg/m3), about 10% of the odour threshold for toluene.
The wall to floor ratio is 40% and the following initial emission
data (i.e. valid for the first few weeks of operation) for toluene
is given.
Floor emission
1.3
mg/h/m2
Wall emission
0.3
mg/h/m2
Ceiling Emission
0.4
mg/h/m2
Determine, using the olfactory method, whether a higher
ventilation rate than that normally required for normal operation
will be needed during the first few weeks of occupancy.
(b) As an operational
control, it is proposed to monitor the carbon dioxide concentration
in the office. Determine, using calculations, whether this is a
sufficient measure to ensure good air quality.
The two equations for question b are
Qc = 10 x (G/Ci-Co)x1/Ev
and
Qh = (G/Ci-Co)x1/Ev
Useful Formulae and Information for Question 2:
Qc = ventilation rate for health (l/s)
G = sensory pollutant load (olf)
Ci = perceived (or desired) air quality indoors
(decipol)
Co = perceived outdoor air quality at air intake
(decipol)
ev = ventilation efficiency
Qh = ventilation rate for health (l/s)
G = pollutant load of chemical (mg/s)
Ci = allowable indoor concentration of chemical
(mg/l)
Co = outdoor concentration of chemical at air
intake (mg/l)
ev = ventilation efficiency
Three levels of perceived indoor air quality.
(from Report No 11. Guidelines for Ventilation Requirements in
Buildings, European Collaborative Action)
Quality Level
Perceived Air Quality
(category)
% dissatisfied
Decipol
A
10
0.6
B
20
1.4
C
30
2.5
Recommended Indoor Air Quality Objectives for Office Buildings
in Hong Kong.
(from Guidance Notes for Management of Indoor Air Quality in
Offices and Public Places).
Parameter or Compound
Excellent Class
Carbon Dioxide
< 800 ppm
Toluene
0.29 ppm (1092 mg/m3)
Outdoor Air Parameters
Excellent outdoor air quality
0.0 decipol
Good outdoor air quality
< 0.1decipol
Poor outdoor air quality
> 0.4 decipol
Outdoor CO2 Concentration
450 ppm
You can assume that occupants produce 19 l/h of
CO2 for sedentary activities and emit a sensory
pollutant load of 1 olf.