environmentally sound solutions for ventilation

SINTEF Energy Research

NATO/CCMS Sustainable Building for Military Infrastructure

Environmentally Sound Solutions for Ventilation

Hans Martin MathisenSINTEF Energy Research

Energy Processes2005-09-21

Outline of presentation


Ventilation principles:NaturalMechanicalHybrid

Heat recoveryCase study of hybrid ventilation

A sustainable solution requires source elimination:


Pollutions:Emissions from building materials => use low emitting materialsPolluting processes => remove them or encapsulate themEtc.

Heat:Solar irradiation => reduce glazed areas and use solar shadingHeat generating equipment => find another solution or encapsulate

Natural Ventilation


ghghppp i ρρρ ∆=−=∆+∆=∆ )( 021 where: ∆p1 =∆p2 – pressure difference over opening,h – height difference between openings, m ρ-density, kg/m³ g – gravity, m/s2

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

Natural ventilation


The Buoyancy Increases With Increased Height Difference


Availability of Buoyancy , Oslo

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2000 4000 6000 8000

timer

qopp

drift

ID TTghACq /∆=10 meter height difference between inlet and outlet openings. A=1m2

CD=0.6

q buo

yanc

y, m

3 /S

Hours (one year)


Natural Ventilation, Wind As Driving Force


Maximum availability of wind, Oslo

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2000 4000 6000 8000

timer

qvin

d

2/pRD CAUCq ∆=

CD – Coefficient for flow resistance through openings.A – Opening’s section, m2

UR – Wind velocity, m/s∆Cp – Wind pressure coefficient for the building

Hours (one year)

q win

d, m

3 /S

∆Cp=0.4, Cd=0.6, A=1m2


Availability of Buoyancy and Wind

00.5

11.5

2

2.53

3.54

0 % 20 % 40 % 60 % 80 % 100 %

Timer, % av undervisningstid

q=(q

vind

2 +q o

ppdr

2 )0.

5 ,m

3 /s

q is the sum of the air flow rate from buoyancy and wind. 10 meter height difference for buoyancy. Cp=0.4, Cd=0.6, A=1 m2.

Hours, % of one year working hours

q=(q

win

d2 +q b

uoya

ncy2 )

0,5 ,

m3 /s


Conclusion natural ventilation


No possibility for efficient heat recovery due to low driving forces ⇒ Higher energy consumptionDifficult to satisfy requirements for airflow rates all the time ⇒From time to time unacceptable air qualityNo 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 noiseThe conclusion is that natural ventilation can not be recommended for non-residential buildings for northern climates

Mechanical Exhaust Ventilation

Fan


Mechanical Balanced VentilationHeat recovery

unit

Fans


Mechanical ventilation, components

Constant air volume - CAV

Variable air volume - VAV

Constant air volume - CAVWater based cooling - Fancoil

Constant air volume - CAVWater based cooling – Chilled suspended ceiling

Hydronic heating


Energy Use for Fans in Mechanical Ventilation

SFP is defined as:

where V is air volume flow rate in m3/s and P is the sum of all fan power

SFP can simplified be written as:

VP

SFP&

∑=

where is total pressure loss and is the total efficiency

tot

tot

VpVSFPη&&∆

≈

totp∆ totη

Annu

al e

nerg

y us

e (k

Wh/

m2 /y

ear

Energy consumption for fans, operation time 8760 hours/year

Airflow rate[l/s/m2][m3/h/m2]


Heat Recovery


Heat

+Hea

t rec

over

y un

itOutdoor air Indoor

Exhaust airOut

Heat coil

16-20 °C

20-24 °C

t t

Liquid Based Heat Exchanger (Run around)

Avtrekkskanal

Tilluftskanal

Varmeveksler luft til glycol

Varmeveksler glycol til luft

Efficiency typically equals 50%Heat exchanger glycol to air

Heat exchanger air to glycol

Exhaust duct

Supply duct


Liquid Based Heat Exchanger


Plate Heat Exchanger

AvtrekkskanalTilluftskanal

Varmeveksler

Efficiency typically = 60%

Exhaust ductSupply duct

Heat exchanger


Plate Heat Exchanger


Rotary Heat Exchanger

Exhaust duct

Supply duct

Rotary wheel

Efficiency in the range 80 to 90%


Rotary Heat Exchanger


Close up of Wheel, Rotary Heat Exchanger


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


Displacement Ventilation


.

.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .............................................

.... .........

......

...........

......

.. . . . . . . . ..........

.. . . . . . . . .

Entrained air volume up to this height = V

Heatsource

Supplied air volume = V

.

.

•Displacement is used both for hybrid and mechanical ventilation•Pollutions are effectively transported away from the occupied zone

Advantages and Disadvantages of Mechanical Balanced VentilationAdvantages:

Relatively low investment costsGood possibilities for heat recovery from exhaust air with high efficiencyGood possibilities for central coolingGood 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


Hybrid Ventilation, Utilizes Both Mechanical and Natural Driving Forces


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).


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


Ventilation, PrincipleExhaust fan

Supply air fanFilter, heat recovery and heat coil


Ventilation, Principle

InntakstårnTilluftskasse med perforert front.Reguleringsspjeld innebygd i kassen.Det er en enhet for hvert kontor/modul.

Kulvert

Filter, vifte, varmegjenvinnerbatteriettervarmebatteri og spjeld kjøring av luftutenom varemebatterier

Supply air terminal device with perforated front. Air volume damper

in the device. One unit per office.Culvert

Air intake tower

Filter, fan, heat recovery exchanger,heating coil. A damper that makes it

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


Culvert


Full Scale Measurements of Office Rooms in “Nordlåna”

Full scale measurements were used to test the chosen ventilation solution:

Air velocitiesTemperature distribution in the room


The Solution in Practice


Full Scale Model, Cell office


Full Scale MeasurementsResults, Temperature Profile

0.00

0.50

1.00

1.50

2.00

2.50

3.00

15.0 17.0 19.0 21.0 23.0 25.0 27.0

Temperatur, °C

Høy

de o

ver g

ulv,

m

Med bokhylleUten bokhylle

More than 3 °C temperature difference between neck and ankles is uncomfortable

Hei

ght a

bove

the

floor

, m With bookshelfWithout bookshelf

Temperature, degrees Celsius


How they do it!


Measurements in “Nordlåna”

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


Nordlåna’s Façade Towards East

HiNT office wing


Energy Consumption per Month

-

5 000

10 000

15 000

20 000

25 000

30 000

6 7 8 9 10 11 12 1 2 3 4 5

Ener

gi, k

Wh Varmegjenvinner

Varmebatteri

Radiatorer

Elektrisitet

Heat exchangerHeat coilRadiatorsElectricity

Ene

rgy,

kW

h

Month


Energy Use for the HiNT-wing of “Nordlåna”


Electricity Hydronic Total

Energy consumption, kWh 39 673 88 192 127 865

Heated area, m² 792

Specific energy use, kWh/m² 50 111 161

Comparison With Energy Consumption in Norwegian Office Buildings

Fra: Bygningsnettverkets energistatistikk Årsrapport 2001

HiNT-fløyenHiNT-wing

kWh/

m2

heat

edar

ea

Source:

The average age of these office buildings are 40 years


LCC for hybrid and mechanical, HiNT-wing, annual costs


Hybrid MechanicalBuilding work (fan room, exhaust tower etc) 14 289 15 964Culvert 31 489Other ducts (from culvert to rooms) 25 610 19 800Mechanical equipment, fans and VAV-dampers

31 963 32 352

Control equipment/room sensors 5 660 5 685Total, exclusive energy 109 011 73 800

Hydronic energy 29 913 12 000

Electric energy 1000 5200

Total, inclusive energy 139 924 91 968

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.

The Impact of Increasing the Control Range for the Room Air Temperature

0

100

200

300

400

500

600

700

800

900

1000

22.3 23.0 24.0 25.0

Settpunkt

kWh Ventilasjon

Romoppvarming

Set point

VentilationSpace heating


The Impact of Improving the Efficiency of the Heat Recovery Unit

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

1000.00

45 % 55 % 80 %

Virkningsgrad

kWh Ventilasjon

RomoppvarmingVentilationSpace heating

Efficiency


Room Temperature and Damper Opening

10

15

20

25

30

03.6.30 0:00 03.7.1 0:00 03.7.2 0:00 03.7.3 0:00 03.7.4 0:00 03.7.5 0:00 03.7.6 0:00 03.7.7 0:00

Dag og klokkeslett

Tem

pera

tur,

°C

0

20

40

60

80

100

120

Påd

rag

Spj

eld,

%

RomtemperaturPådrag spjeld

Date and time

Damper openingRoom temperature


Outdoor Temperature, Temperature in Culvert Before Heat Coil (after fan and filter) and Temperature in Culvert after Heat Coil

10.0

15.0

20.0

25.0

30.0

03.6.30 0:00 03.7.1 0:00 03.7.2 0:00 03.7.3 0:00 03.7.4 0:00 03.7.5 0:00 03.7.6 0:00 03.7.7 0:00

Dag og klokkeslett

Tem

pera

tur,

°C

UtetemperaturTemperatur inntak kulvert før varmegjenvinnerTemperatur kulvert etter varmebatteri

Date and time

Outdoor temperature

Temperature air intake in culvert in front of heat recovery unintTemperature in culvert after heat coil


Airflow Due to Fan and Buoyancy (working hours, average per month)

0

1000

2000

3000

4000

5000

6000

5 6 7 8 9 10 11 12 1 2 3 4

Måned

Luftm

engd

e, m

³/h

Luftmengde oppdriftLuftmengde vifteAirflow rate buoyancyAirflow rate fan

Month

Airf

low

rate

, m3 /h


environmentally sound solutions for ventilation

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