Ventilation Strategies for Healthy IEQ and Energy Efficiency

Transcription

1 Ventilation Strategies for Healthy IEQ and Energy Efficiency Lars Ekberg Energy Management AB A Chalmers Industriteknik Company

2 The purpose of ventilation + - Pollution Climate Heat Pollution 2

3 Examples of IEQ factors Thermal climate Air Quality -operative temp. -surface temp. -air movements - -formaldehyde -nitrogen dioxide -particles Illustration: SP The Swedish Technical Research Institute - 3

4 HVAC systems should provide Good indoor air quality no health risk perceived as fresh and pleasant Good thermal comfort no draught risk temperature and humidity in the comfort range Good acoustical environment quiet supply and removal of air

5 What type of system is the best? Displacement ventilation Mechanical ventilation Natural ventilation Mixing ventilation Hybrid ventilation Air conditioning 5

6 What type of system is the best? A system suited for its purpose Designed with respect to the building, the activities and the requirements Correctly dimensioned and designed with respect to service and maintenance Designed not to cause disturbance (draught and noise) 6

7 The sub systems The Central Air Handling Unit The Ductwork The Air Distribution in the Room

8 Two important aspects Airflow rate control (CAV vs. DCV) Air distribution in the room (mixing vs. displacement)

9 What do we gain from DCV? Demand Controlled Ventilation Improved indoor environment airflow rate according to the actual demand based on thermal comfort and/or indoor air quality minimizing noise levels from ventilation system Energy savings of the system air flow rate according to the demand saves - energy for fans -Heating - cooling

10 The function of a traditional CAV System Exit air Outdoor air Duct system Fixed damper Air-handling unit CAV constant airflow rate Office room Illustration: Mari-Liis Maripuu (2009)

11 The function of a DCV System Fan speed control VAV box VAV diffuser IAQ Temp DCV demand controlled flow rate Office room Illustration: Mari-Liis Maripuu (2009)

12 Examples from case study buildings Electric Airflow Power [kw] rate [m³/s] Design value CFM Average CFM Time, [h/year] Airflow Supply rate airflow m3/s Electricity Power kw Electric Airflow Power [kw] rate [m³/s] Design value CFM Time, [h/year] Supply airflow, rate m 3 /s m3/s Electricity Power, kw kw Average CFM Case study 1 Case study 2A Fan electricity: from 1.5 kwh/ft 2 per year to 0.7 kwh/ft 2 per year Additional cooling: 2000 BTU/ft 2 per year (electricity equiv. about 0.2 kwh/ft 2 ) Heating of ventilation air: from BTU/ft 2 per year to 0 BTU/ft 2 per year Reference: Mari-Liis Maripuu (2009)

13 DCV is suitable for spaces with varying loads Conference rooms/auditoria Computer rooms Schools Restaurants Cinemas Office buildings The more the loads are varying in time, the more energy savings can be expected

14 DCV Control Main Challenges IAQ Relationships unclear: perceived air quality concentration levels comfort and health Available IAQ sensing technologies set the limits: humidity sensors occupancy sensors gas sensors combined sensors Sensing technologies must comply with certain requirements for ventilation control Reference: Mari-Liis Maripuu (2009)

15 The DCV air distribution components Airflow control in a wide flow range (5-100 %) Stable supply air pattern in a wide flow range Quiet diffuser operation in wide flow and operational pressure ranges Low supply air temperature (approx. 59 F = 15 C) without risk of draught Illustration: Swegon

16 Air Distribution in the Room Correct placement of air terminal units Appropriate supply air temperature Correct adjustment of the throw length Sufficient airflow rates

17 Three Principles Uni directional Displacement Mixing Laboratories Operating theatres Industries Auditoria Offices Classrooms 17

18 Displacement ventilation Right! Heat sources in the room Relatively cooler supply air Wrong! The supply airflow rate may also be too low! Too high supply air temperature! Illustration: SP 18

19 Risk of annoyance! Displacement ventilation Illustration: SP Cold air and air movements close to the air terminal unit Always high risk of draught within about 3 6 ft 19

20 Mixing ventilation Right! Relatively cooler supply air Sufficient throw-lenght Too high supply air temperature! Wrong! Too low supply air velocity! 20

21 Risk of annoyance! Mixing ventilation Downdraught if supply air velocity is too low Risk of draught if incorrect design or operation 21

22 The room air distribution can be checked by tracer gas measurements Air change efficiency Ventilation efficiency Local air change index Local air quality index.. Caution! This may be time consuming and expensive! 22

23 The air change efficiency, a Mixing ventilation = 0.45 Displacement ventilation = 0.65 Piston flow = % higher efficiency with displacement ventilation 23

24 Ventilation effectiveness Local ventilation index Contaminant removal effectiveness C exhaust C breath Illustration: Skistad (2003) 24

25 Ventilation effectiveness Local ventilation index Contaminant removal effectiveness When cooling Mixing ventilation Displacement ventilation Reference: CEN CR % higher effectiveness with displacement ventilation 25

26 40 % higher efficiency with displacement ventilation? Let s take a look at the basic principles 26

27 The plume is influenced by the ventilation system Very high ventilation rate Way too low ventilation rate Intermediate ventilation rate Stratification 27

28 The ventilation rate required to maintain the stratification at a certain height h The ventilation rate must match the airflow in the plume 28

29 The Stratification Supply airflow rate 17 CFM per person Walking speed 2.3 FPS (138 FPM) Reference: Mattsson, M. (1999) 29

30 People moving Supply airflow rate 17 CFM per person Walking speed 4.3 FPS (255 FPM) Reference: Mattsson, M. (1999) 30

31 Displacement vent. in a simulated office Tracer gas measurements Tracer gas generation Reference: Mattsson, M. (1999) 31

32 Displacement vent. in a simulated office 8.2 ft 6.6 ft 4.9 ft 3.3 ft 1.6 ft 0 ft 44 CFM and heat gen BTU/h (295 W) 44 CFM and heat gen BTU/h (395 W) 78 CFM and heat gen BTU/h (395 W) No disturbance by movements Reference: Mattsson, M. (1999) 32

33 Person moving in the office 0 FPS 1.0 FPS 2.0 FPS 3.0 FPS Breathing zone concentration relative to extract [ ] Pollution spread to the breathing zone The computer was the only source of contamination 33 Reference: Mattsson, M. (1999)

34 The examples indicate that displacement ventilation works: without disturbance from movements if the supply airflow rate is high enough Typical applications Industry Theatres, opera houses. When large airflows are required for removal of heat 34

35 Why not displacement in offices? Major risk of discomfort due to draught Reduced useable floor area Because it may need 3 4 times higher airflow rate than required for air hygiene Displacement ventilation may require CFM per person Air hygiene requirement is about 20 CFM per person 35

36 Literature Mari Liis Maripuu (2009) Demand Controlled Ventilation (DCV) Systems in Commercial Buildings Functional Requirements on Systems and Components, Ph.D. Dissertation, Building Services Engineering, Chalmers University of Technology, Gothenburg, Sweden Im, P. (2005) Literature review on underfloor air distribution (UFAD) system, Energy Systems Laboratory, Texas A&M University System Mattsson, M. (1999) On the efficiency of displacement ventilation with particular reference to the influence of human activity, Royal Institute of Technology, Stockholm Novoselac and Srebric (2001) A critical review on the performance and design of combined cooled ceiling and displacement ventilation systems, Energy and Buildings, 34, Matsumoto,H. and Ohba, Y. (2004)The influence of a moving object on air distribution in displacement ventilated rooms, Jour. Asian Arcitecture and Bldg Eng. Fitzner,K. (1996) Displacement ventilation and cooled ceilings, Results of laboratory tests and practical installations, Proceedings of the Conference Indoor Air 96, Nagoya Lau, J. And Chen, Q. (2006) Energy analysis for workshops with floor supply displacement ventilation under the U.S. climates, Energy and Buildings, 38, Kim, I.G., Homma, H. (1992) Distribution and ventilation efficiency of CO2 produced by occupants in upward and downward ventilated rooms. ASHRAE Technical Data Bulletin, Vol. 8, No. 2. Mattsson, M. (2002) Vertical distribution of occupant generated particles in a room with displacement ventilation, Proceedings of the Indoor Air 2002 Conference, Vol. 1, pp , Monterey, California Nielsen, P.V. (1993) Displacement Ventilation Theory and design, Dept. Of Building Technology and Structural Engineering, Aalborg University, Denmark REHVA Design Guidebook No. 1, Displacement Ventilation in non industrial Premises, 2 endition, 2002, Federation of European HVAC Assoc 36

37 Healthy IEQ and energy efficiency Deviation from desired climate Loads Sun irradiation, people, equipment, lighting, pollution generation, building products, furniture Desired climate Minimize the energy use and the complexity: -Minimize the loads -Motivate the requirements Compensation by installations 37

38 Energy Management AB A Chalmers Industriteknik Company Thank you! lars.ekberg@cit.chalmers.se management.se 38

39 Extra material 39

40 The supply airflow rate will match the thermal plume 36 m 3 /h = 10 l/s 200 m 3 /h = 55 l/s 36 m 3 /h = 10 l/s 200 m 3 /h = 55 l/s 40

41 A sportshall Height = 4.2 m CO 2 measurement Reference: Matson, M. (1999) 41

42 The sportshall IAQ CO l/s 3 l/s per m 2 floor Six people W lighting Reference: Matson, M. (1999) 42

43 Experiments by Kim & Homma ,4 1,2 Ventilation efficiency 1 0,8 0,6 0,4 Kim & Homma (1992) Three out of 15 "Upward" experiments beytter than mixing ventilation Upward Downward 0,2 The "Downward" experiments indicate poor function at low ventilation rates Ventilation rate (l/s per person) 43

44 Further examples Source: Novoselac and Srebric (2001) 44

45 No draught The right temperature Clean air No noise Possibility to control the climate No unpleasant smells 45

46 Air change rates (ACH = air changes per hour) Control of air quality by removal of air pollutants Residential buildings ACH Office rooms with hydronic cooling ACH Operating theatres in hospitals ACH Clean rooms >200 ACH Control of temperature by removal of heat surplus Office rooms with an all air system 3 6 ACH Supermarkets, department stores 6 10 ACH Auditoriums, lecture rooms, theatres 5 12 ACH Compensation of air exhaust required for safety ventilation, process air flows Laboratory rooms with fume hoods Restaurant kitchens ACH ACH 46

47 How the indoor climate occurs Deviation from desired climate Desired climate 47

48 How the indoor climate occurs Deviation from desired climate Desired climate Loads Sun irradiation, people, equipment, lighting, pollution generation, building products, furniture 48

49 How the indoor climate occurs Deviation from desired climate Desired climate Loads Sun irradiation, people, equipment, lighting, pollution generation, building products, furniture Compensation by Compensation by installations Heating or cooling Removal of pollutants 49

50 How the indoor climate occurs Deviation from desired climate Desired climate Loads Sun irradiation, people, equipment, lighting, pollution generation, building products, furniture The complexity and size of the installations depend on The strength of the loads The indoor climate requirement Compensation by installations 50

51 Air Quality CO 2 Portugese offices Swedish offices Your experiences? Reference: Stoops, J. (2001) 51

52 The CO 2 requirement CO 2 - indicator for the perception of pollutants from people Percentage dissatisfied (%) Note, Valid for visitors! (Fanger, 1988) CO 2 concentration (ppm) 52

53 The CO 2 requirement 60 Percentage Dissatisfied, dissatisfied % (%) North Americans Common air hygiene criterion of today Europeans Japanese Ventilation rate, l/s per standard person Outdoor air supplied (CFM) and the technical solution 53

54 The Central Air Handling Unit t r Exit air Return air Outdoor Supply air t o t m t s

55 The Air Distribution system

56 Air Distribution in the Room

57 Person moving in the office 0 FPS 1.0 FPS 2.0 FPS 3.0 FPS 0 FPS 1.0 FPS 2.0 FPS 3.0 FPS Breathing zone concentration relative to extract [ ] Breathing zone conc. Rel. ambient [ ] Pollution spread to the breathing zone The computer was the only source of contamination 57 Reference: Mattsson, M. (1999)