Environmentally Sound Solutions for Ventilation

Transcription

1 NATO/CCMS Sustainable Building for Military Infrastructure Environmentally Sound Solutions for Ventilation Hans Martin Mathisen Energy Processes

2 Outline of presentation Ventilation principles: Natural Mechanical Hybrid Heat recovery Case study of hybrid ventilation

3 A sustainable solution requires source elimination: Pollutions: Emissions from building materials => use low emitting materials Polluting processes => remove them or encapsulate them Etc Heat: Solar irradiation => reduce glazed areas and use solar shading Heat generating equipment => find another solution or encapsulate

4 Natural Ventilation Warm air is lighter than cold air: In the lower part of the building cold outdoor air presses inwards In the upper part warm indoor air tries to flow out p = p 1 + p 2 = ( ρ 0 ρ i ) gh = ρ gh where: p 1 = p 2 pressure difference over opening, h height difference between openings, m ρ-density, kg/m³ g gravity, m/s 2

5 Natural ventilation

6 The Buoyancy Increases With Increased Height Difference

7 Availability of Buoyancy, Oslo q = C A Tgh / D T I 10 meter height difference between inlet and outlet openings A=1m 2 C D =06 q 3 buoyancy, qoppdrift m /S Hours timer (one year)

8 Natural Ventilation, Wind As Driving Force

9 q = Maximum availability of wind, Oslo C D AU R C p / 2 qvind q 3 wind, m /S C D Coefficient for flow resistance through openings timer Hours (one year) A Opening s section, m 2 U R Wind velocity, m/s C p Wind pressure coefficient for the building C p =04, C d =06, A=1m 2

10 Availability of Buoyancy and Wind q=(q vind +qoppdr ) 05 q=(q 2,m 3 wind +qbuoyancy 2 ) 0,5, m /s 3 /s % 20 % 40 % 60 % 80 % 100 % Hours, Timer, % av of one undervisningstid year working hours q is the sum of the air flow rate from buoyancy and wind 10 meter height difference for buoyancy C p =04, C d =06, A=1 m 2

11 Conclusion natural ventilation No possibility for efficient heat recovery due to low driving forces Higher energy consumption Difficult to satisfy requirements for airflow rates all the time From time to time unacceptable air quality No possibility for efficient cleaning of outdoor air Can only be used in areas with clean outdoor air Natural ventilation generates no noise by itself, but admits noise from outdoor and between rooms Wind can generate noise The conclusion is that natural ventilation can not be recommended for non-residential buildings for northern climates

12 Mechanical Exhaust Ventilation Fan

13 Mechanical Balanced Ventilation Heat recovery unit Fans

14 Mechanical ventilation, components Constant air volume - CAV Water based cooling Chilled suspended ceiling Constant air volume - CAV Water based cooling - Fancoil Hydronic heating Variable air volume - VAV Constant air volume - CAV

15 Energy Use for Fans in Mechanical Ventilation Energy consumption for fans, operation time 8760 hours/year Annual energy use (kwh/m 2 /year Airflow rate [l/s/m 2 ] [m 3 /h/m 2 ] SFP is defined as: P SFP = V& where V is air volume flow rate in m 3 /s and P is the sum of all fan power SFP can simplified be written as: V& ptot SFP V & ηtot where p tot is total pressure loss and ηtot is the total efficiency

16 Heat Recovery Out Exhaust air Outdoor air Heat recovery unit Heat t t C Indoor C Heat coil

17 Liquid Based Heat Exchanger (Run around) Heat exchanger air to glycol Varmeveksler luft til glycol Avtrekkskanal Exhaust duct Tilluftskanal Supply duct Efficiency typically equals 50% Heat exchanger glycol to air Varmeveksler glycol til luft

18 Liquid Based Heat Exchanger

19 Plate Heat Exchanger Supply Tilluftskanal duct Avtrekkskanal Exhaust duct Efficiency typically = 60% Varmeveksler Heat exchanger

20 Plate Heat Exchanger

21 Rotary Heat Exchanger Exhaust duct Supply duct Rotary wheel Efficiency in the range 80 to 90%

22 Rotary Heat Exchanger

23 Close up of Wheel, Rotary Heat Exchanger

24 Complete Mixing Ventilation Complete mixing is only used together with mechanical ventilation Requires relatively high pressure to work Chilled air can be supplied without draft in the occupied zone Pollutions is mixed with the room air and diluted

25 Displacement Ventilation Entrained air volume up to this height = V Heat source Supplied air volume = V Displacement is used both for hybrid and mechanical ventilation Pollutions are effectively transported away from the occupied zone

26 Advantages and Disadvantages of Mechanical Balanced Ventilation Advantages: Relatively low investment costs Good possibilities for heat recovery from exhaust air with high efficiency Good possibilities for central cooling Good possibilities for demand controlled ventilation (variable air volume=vav) Disadvantages: Uses electrical energy for running fans (Can be reduced by proper design) Fans generates noise (Can be reduced by proper design) Requires operators with technical skills Includes many mechanical and electrical components

27 Hybrid Ventilation, Utilizes Both Mechanical and Natural Driving Forces

28 Comparison of Natural, Hybrid and Mechanical Ventilation Principal connection between driving pressure and flow section for a given duct layout, airflow rate, outdoor temperature and height Pressure loss coefficient varies from 33 to 5 (shown at the bars)

29 Case study: Office Building With Hybrid Ventilation ( Nordlåna at HiNT) The building is called Nordlåna and is a part of the Nord-Trøndelag University College The case study concentrated on one part of the building This wing is called the HiNT-wing The SINTEF research project was financed by Statsbygg - The Directorate of Public Construction and Property

30 Ventilation, Principle Exhaust fan Filter, heat recovery and heat coil Supply air fan

31 Ventilation, Principle Supply air terminal device with perforated front Air volume damper in the device One unit per office Tilluftskasse med perforert front Reguleringsspjeld innebygd i kassen Det er en enhet for hvert kontor/modul Kulvert Culvert Air Inntakstårn intake tower Filter, Filter, fan, vifte, heat varmegjenvinnerbatteri recovery exchanger, heating ettervarmebatteri coil A damper og spjeld that makes kjøring it av luft utenom varemebatterier possible to bypass heat exchanger at summer time Demand controlled ventilation: The damper in the air terminal is controlled from a presence detector and the room temperature

32 Culvert

33 Full Scale Measurements of Office Rooms in Nordlåna Full scale measurements were used to test the chosen ventilation solution: Air velocities Temperature distribution in the room

34 The Solution in Practice

35 Full Scale Model, Cell office

36 Full Scale Measurements Results, Temperature Profile Height Høyde above over the gulv, floor, m m Med With bokhylle bookshelf Uten Without bokhylle bookshelf Temperature, Temperatur, degrees C Celsius More than 3 C temperature difference between neck and ankles is uncomfortable

37 How they do it!

38 Measurements in Nordlåna When the building was finished and occupied the autumn 2002, measurements were started to study the energy use

39 Nordlåna s Façade Towards East HiNT office wing

40 Energy Consumption per Month Energy, Energi, kwh Varmegjenvinner Heat exchanger Heat coil Radiators Varmebatteri Radiatorer Elektrisitet Electricity Month

41 Energy Use for the HiNT-wing of Nordlåna Electricity Hydronic Total Energy consumption, kwh Heated area, m² 792 Specific energy use, kwh/m²

42 Comparison With Energy Consumption in Norwegian Office Buildings kwh/m 2 heated area HiNT-fløyen HiNT-wing Source: Fra: Bygningsnett verkets energistatistikk Årsrapport 2001 The average age of these office buildings are 40 years

43 LCC for hybrid and mechanical, HiNTwing, annual costs Hybrid Mechanical Building work (fan room, exhaust tower etc) Culvert Other ducts (from culvert to rooms) Mechanical equipment, fans and VAVdampers Control equipment/room sensors Total, exclusive energy Hydronic energy Electric energy Total, inclusive energy

44 Weaknesses of the Chosen Solution There is a heat loss from the ducts between culvert and the office rooms Temperature sensors for supply air is placed above the air intakes in the culvert Temperature stratification makes it difficult to control the supply air temperature

45 The Impact of Increasing the Control Range for the Room Air Temperature kwh Ventilation Space heating Ventilasjon Romoppvarming Settpunkt Set point

46 The Impact of Improving the Efficiency of the Heat Recovery Unit kwh Ventilation Space heating Ventilasjon Romoppvarming % 55 % 80 % Efficiency Virkningsgrad

47 Room Temperature and Damper Opening Temperatur, C Pådrag Spjeld, % Romtemperatur Room temperature Pådrag Damper spjeld opening : : : : : : : :00 Dag og klokkeslett Date and time

48 Outdoor Temperature, Temperature in Culvert Before Heat Coil (after fan and filter) and Temperature in Culvert after Heat Coil 300 Outdoor Utetemperatur temperature Temperature air inntak intake kulvert in culvert før varmegjenvinner front of heat recovery unint Temperature in kulvert culvert etter after varmebatteri heat coil 250 Temperatur, C : : : : : : : :00 Dag og klokkeslett Date and time

49 Airflow Due to Fan and Buoyancy (working hours, average per month) Airflow Luftmengde, rate, m 3 /h m³/h Luftmengde Airflow rate buoyancy oppdrift Luftmengde Airflow rate fan vifte Month Måned