Lecture Objectives Answer your questions related to CFD software Ventilation Effectiveness Thermal Comfort

IAQ parameters Number of ACH quantitative indicator ACH - for total air - for fresh air Ventilation effectiveness qualitative indicator takes into account air distribution in the space Exposure qualitative indicator takes into account air distribution and source position and intensity

IAQ parameters -Age-of-air air-change effectiveness (E V ) -Specific Contaminant Concentration contaminant removal effectiveness 

Single value IAQ indicators E v and ε 1.Contaminant removal effectiveness (  ) concentration at exhaust average contaminant concentration Contamination level 2. Air-change efficiency (  v ) shortest time for replacing the air average of local values of age of air Air freshness

Air-change efficiency (  v ) Depends only on airflow pattern in a room We need to calculate age of air (  ) Average time of exchange What is the age of air at the exhaust? Type of flow –Perfect mixing –Piston (unidirectional) flow –Flow with stagnation and short-circuiting flow

Air exchange efficiency for characteristic room ventilation flow types Flow pattern Air-change efficiency Comparison with average time of exchange Unidirectional flow1 - 2  n <  exc < 2  n Perfect mixing1  exc =  n Short Circuiting0 - 1  exc >  n

Contaminant removal effectiveness (  ) Depends on: -position of a contaminant source -Airflow in the room Questions 1) Is the concentration of pollutant in the room with stratified flow larger or smaller that the concentration with perfect mixing? 2) How to find the concentration at exhaust of the room?

Differences and similarities of E v and  Depending on the source position: - similar or - completely different air quality  v = 0.41  = 0.19  = 2.20

Thermal comfort Temperature and relative humidity

Thermal comfort Velocity Can create draft Draft is related to air temperature, air velocity, and turbulence intensity.

Thermal comfort Mean radiant temperature potential problems Asymmetry Warm ceiling (----) Cool wall (---) Cool ceiling (--) Warm wall (-)

Prediction of thermal comfort Predicted Mean Vote (PMV) + 3hot + 2warm + 1slightly warm PMV =0neutral -1 slightly cool -2cool -3cold PMV = [0.303 exp ( M ) ] L L - Thermal load on the body L = Internal heat production – heat loss to the actual environment L = M - W - [( C sk + R sk + E sk ) + ( C res + E res )] Predicted Percentage Dissatisfied (PPD) PPD = exp [ - ( PMV PMV 2 )] Empirical correlations Ole Fanger Further Details: ANSI/ASHRAE standard 55, ISO standard 7730