1 Introduction - Basic principles.

Transcription

1 entilation 1 Introduction - Basic principles ladimír Zmrhal (room no. 814) Dpt. Of Environmental Engineering 1 Principle of ventilation entilation is intentional supply of outdoor air into the buildings (cars, trains ) to dilute and remove indoor air contaminants affect the indoor air quality healthy buildings Good indoor air quality (IAQ) is necessary for maintaining health and high productivity!!! 2 1

2 Principle of ventilation Natural ventilation is driven by pressure differences across the building envelope, caused by wind and air density differences because of temperature differences between indoor and outdoor air the flow of air through open windows, doors, grilles and other planned building envelope penetrations Mechanical (forced) ventilation intentional movement of air into and out of building using mechanical force is driven by fans 3 Terminology Nominal air exchange rate (ventilation rate). I = e r [1/h] Space air exchange rate I S = s = + r s e c [1/h] [m 3 /h] e outdoor air volume air flow rate [m 3 /h] c recirculation air flow rate [m 3 /h] r interior volume of space [m 3 ] 4 2

3 Terminology Outside air fraction X oa.. e e = = + s e c Percent outside air X oa. e = e c [-] [%] X oa = 100 % means no recirculation of return air 5 Terminology Airflows 1 Outside air 2 Supply air 3 Return air 4 Exhaustt air 5 Recirculated air 6 Indoor air 7 Transfer air 8 Mixed air 9 By-pass air 6 3

4 Terminology Air-Handling Unit 7 Heat and Pollutants Sources of heat and pollutants internal - persons - electronic appliances, lighting, technology, electric motors - animals, biological processes in agriculture, external - outdoor air - external climatic conditions 8 4

5 Indoor Contaminants CO 2 water vapour combustion products tobacco smoke OC aldehydes pesticides asbestos radon 9 entilation Requirements hygienic for the people technological for technology processes biological agricultural processes micro-biological safety fire 10 5

6 Parameters of the pollutants Concentration of pollutants mass [mg/m 3 ] volumetric [cm 3 /m 3 ] ppm (parts per million) 1 ppm = 10-4 % number of particles in m 3 clean rooms Dimension of the particles a = µm 11 Parameters of the pollutants 12 6

7 Parameters of the pollutants Conversion X [mg/m 3 ] Y [ppm] Y M 24,44 3 [ppm] = X [mg/m ] M molecular weight of the gass [g/mol] Note: 1000 ppm = 0,1 % vol. 13 Mass Balance of the entilated Room Gdτ + c τ = τ + sd c d r dc source supply exhaust storage 14 7

8 Mass Balance of the entilated Room τ ; steady state G dτ c d + s τ = c d τ + r dc solution G G = = c c PEL c G+ cs c dτ = r dc c c s τ dc = d G + c s c 0 r 0 s τ 15 Mass Balance of the entilated Room G G + cs c cs + c ln r = τ τ = ln G G + c r s c cs + c 0 0 τ τ G r r 0 s 1 c = c e + + c e G r G r G r = + + 2( c c ) τ ( ) 0 2 c c0 τ c c0 τ

9 Concentration of the pollutant 0 m 3 /h 1 Concentration c [g/m 3 ] 2 = 2 1 G = const. Time τ [h] 17 Thermal Balance of the entilated Room Q dτ + ρ c t dτ = ρ c t dτ + ρ c dt s i r source supply exhaust storage 18 9

10 Thermal Balance of the entilated Room t ; steady state Q dτ + ρcts dτ = ρcti dτ + r Q = ρc t t ( ) i s ρcdt c specific heat of the air = 1010 [kj/kgk] ρ density of the air = 1.2 [kg/m 3 ] 19 Limit Concentrations Maximum permission concentration (MPC) cmax MPC in any time!! for τ and steady state c max G = + c s 20 10

11 Návrh větrání Permission exposure limitpel for τ and steady state = G PEL c p?! WHY? c = PEL 21 Limit Concentrations Permission exposure limitpel cavg τ 1 = cτ dτ τ 0 1 G τ I = ( ) + G c + avg c0 cs 1 e c s τ I cavg,8 PEL where τ = 8 hours 22 11

12 Limit Concentrations Average concentration for periodical pollutant generation n 1 1 Gi τ ii = ( ) + G i i c + τ avg c τ 0, i cs 1 e cs i i= 1 tot Ii i i τ tot n = τ = 8 hours i= 1 i 23 Limit Concentrations c c max prům < MPC PEL! 24 12

13 Example 1 Permanent pollutant generation entilation strategy: 1) c max,1 > MPC c avg,1 > PEL!!! e 2) c max,2 < MPC c avg,2 < PEL OK 25 Example 2 ariable pollutant generation entilation strategy: 1) c max,1 < MPC c avg,1 > PEL!!! e, τ 2) c max,2 > MPC c avg,2 < PEL!!! e, τ 26 13

14 Example 3 Periodical pollutant generation entilation strategy: c max < MPC OK c avg > PEL!!!!!! e, τ 27 Hygienic aspects Adition of the pollutants for two and more chemical substance c1 c2 cn PEL PEL PEL 1 2 c1 c2 cn MPC MPC MPC 1 2 n n G1 G2 Gn = + ; PEL PEL PEL 1 2 n 28 14

15 Hygienic aspects The pollutants with independent effect G1 G2 Gn e,1 = ; e,2 = ;... e, n = PEL PEL PEL 1 2 (,1,2, ) = max ; ;... e e e e n n 29 Carbon dioxide CO 2 Mauna Loa (Havaj) > 380 ppm 30 15

16 Example1 Example 1: Pettenkoffer s criterion 1 people exhale 0.42 m 3 /h of air Concentration of CO 2 in exhaled air is 4 % vol. Concentration of CO 2 in outdoor air C CO2 = % vol. = 350 ppm Max. concentration of CO 2 in the room C max = 0.1 % vol. = 1000 ppm Calculate volume air flow rate of outdoor air e =? [m 3 /h] 31 Pettenkofer s criterion Max von Pettenkofer ( ) main metabolite: CO 2 a water vapour CO 2 production depends on activity level - 16 dm 3 /h CO 2 for unsleeping person (10 dm 3 /h when sleeping) CO 2 concentration in indoor environments informs about quality of ventilation CL = 0.1 vol. % = 1000 ppm Pettenkofer criterion 25 m 3 /h per person 32 16

17 Carbon dioxide CO ppm: concentration in outdoor air ppm: recomended indoor air concentration až ppm: maximum (real) indoor air concentration > ppm: tideness, sleepiness, lethargy, headache < ppm: maximum safety concentration without health risk > ppm: sickness, higher pulsation (sick building syndromme - SBS) > ppm: health hazards > ppm: dangerous to live ppm = 0,1 % obj. 33 entilation Requirements 34 17

18 entilation Requirements EN Indoor environmental input parameters for design and assessment of energy performance of buildings- addressing indoor air quality, thermal environment, lighting and acoustics Space Occupancy [m 2 /person] Required air flow rate [m 2 /h.person] Office spaces Land-scape office Classroom 2 29 Kidergarten 2 30 Conference room 2 36 Department store entilation Requirements ASHRAE 10 cfm = 17 m 3 /h 36 18

19 Health Risk Group 1 Group 2 Group 3 Risk of death or sickness Risk of respiratory sickness Risk of less important sickness or discomfort Radon Fungi Temperature Carcinogenic OC Allergens Noise Asbestos Dust particles Lighting Passive smoking (ETS) NO x Non-carcinogenic OC CO (high concentrations) Ozone CO (low concentrations) 37 Example 2 Example 2: Calculation of volume air flow rate Mass flow of pollutant G = 0.2 kg/h of Fe x O y Permission exposure limit PEL = 0,015 g/m 3 Concentration in outdor air c s = 0 Calculate volume air flow rate =? 38 19

20 Example 3 Example 3: Calculate time τ of ventilation after accident of NH 3 in machine room. olume of the machine room r = 500 m 3 Amount of escaped NH 3 m = 1.2 kg Max. permission concentration MPC = g/m 3 entilation rate I = 5 h -1 How long it takes achieving of MPC τ =? 39 Thank you for your attention 40 20