hybrid ventilation_mazo_2014.pdf

Principles of hybrid ventilation

Department of Building Energetics and Building Service Engineering

Zoltán MAGYAR, PhD

Reasons for ventilation Need for ventilation Consequences of poor air quality IAQ Strategy Ventilation volume Natural ventilation Mechanical ventilation Typical energy consumption for different types of office buildings Hybrid ventilation Mechanical and natural ventilation Ventilation strategy Demand Controlled Hybrid Ventilation

Flow versus time over the year

Flow stability

Ventilation for IAQ

Classification

Hybrid ventilation strategies

Components for hybrid ventilation concepts

Natural ventilation concept based on wind effect

Development stages for hybrid systems

Detailed classes of hybrid ventilation systems

Variability of Flow Pattern, optimisation, control, BBBRI example

Summary

Reasons for ventilation

3

source

load

exposure

concentrations

dose

health effects

persons

Building

Emissions from:

materials

furniture

installations

crawlspace

Source: Technical Note AIVC 59, Air Infiltration and Ventilation Centre Operating Agent and Management, INIVE EEIG, Brussels, Belgium

4 4

AIR QUALITY COMFORT HEALTH

Required:

STUFFY

ODOUR

HOT

TOXIC

SICK BUILDING

COLD

DRAUGHTY

VENTILATION

A Solution:

CAN REMOVE POLLUTANTS

CAN REMOVE HEAT

ENERGY

A Problem:

LOSS OF CONDITIONED AIR

FAN ENERGY

Ventilation and Air Quality

5

Ventilation background

5

Before 1973

1973 Petroleum crisis

1985

Thermal Regulations

1996

Reinforced thermal regulations

Tomorrow

NOT insulated NEITHER airtight

JUST insulated roof Double glazing

Insulated Airtight housing

Insulated Airtight housing

Ventilation system

“Man is a funny creature When it’s hot he wants it cold When it’s cold he wants it hot Always wanting what is not Man is a funny creature” ASHRAE Journal, unknown author

Need for ventilation

Windows cannot be a replacement for a proper ventilation system!

• supply oxygen we need • eliminate odors,

pollutants and allergens • eliminate the excess of

humidity in the air • provide a sense of well-

being.

Source: Natural Ventilation in the Urban Environment, Assessment and Design, Edited by Cristian Ghiaus and Francis Allard, ISBN: 1-84407-129-4 hardback, 2005

Fig.1

Consequences of poor air quality

7

• increase in airborne contamination • health hazards such as allergies, headaches,

rhinitis and asthma • reduction in air circulation • condensation and could growth • accumulation of radon • accumulation of carbon monoxide.

Source: Ventilation for acceptable indoor air quality, ASHRAE 62-1989

Fig. 2 a,b,c

IAQ Strategy

8 .

Source control Elimination Replacement

Insulation

Local exhaust

Only for unavoidable

sources

Mixing ventilation

For unavoidable emissions of the

unavoidable sources Displacement

ventilation

Source: Ventilation for acceptable indoor air quality, ASHRAE 62-1989

Ventilation volume

9

Ventilation purpose

IAQ Control Temperature Control

Passive Cooling

Flow rates

5 – 10 l/s per person Air Change Rate

5 – 10 h-1

4 – 8 l/s per m2 floorarea

Source: Technical Note AIVC 59 , Air Infiltration and Ventilation Centre Operating Agent and Management, INIVE EEIG, Brussels, Belgium

10

TWO ways of building ventilation

10

Mechanical ventilation Natural ventilation

Single sided ventilation

•supply and extraction through the same openings

•openings ~4% of floor area

•less efficient

•internal door remain closed

Cross ventilation

•supply and extraction at the same level in the building

•good result when wind exists

•internal doors opened or equipped with ventilation grilles

Stack ventilation

•air supply through louvers and extracted through chimneys

•wind not needed

Mechanical supply ventilation

•a fan supplies air to spaces

•ventilation openings in building’s envelope are used for extraction

•usually used where high ventilation rates are needed and air has to be heated before entering the room

Mechanical extract ventilation

•a fan draws air from spaces

•fresh outdoor air enters into rooms either through the leakage routes of building envelope or through ventilation openings in the building envelope

Mechanical extract & supply ventilation

•a balanced ventilation system

•it must always include a supply and a return air fan

•an air heater is almost always installed in the supply air side

Suitable for many types of buildings located in mild or moderate climates;

The 'open window' environment associated with natural ventilation is often popular, especially in pleasant locations and mild climates;

Natural ventilation is usually inexpensive when compared to the capital, operational and maintenance costs of mechanical systems;

High air flow rates for cooling and purging are possible if there are plenty of openings;

Short periods of discomfort during periods of warm weather can usually be tolerated;

No plant room space is needed;

Minimum maintenance;

Can be less expensive to install and operate than HVAC but this need not always be true;

No fan or system noise.

11 Source: F. ALLARD, Natural ventilation in buildings, James & James, London, 1998

Natural ventilation Review of its advantages:

The two natural mechanisms of ventilation

Wind

Negative pressure region

Wind driven flow

1. Wind Driven Ventilation

Cross Flow Wind

Wind Tower

Badgir (WindCatcher)

Wind tower

2/2vCp pw

F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011 Natural ventilation system

single sided type tropical climate

Yazd, Iran

Natural ventilation cross tropical climate

IUT building La Réunion Island

Fig.1 (a,b,c) Fig.2

Fig.3

Fig.4

Fig.5

Neutral pressure plane

Temperature driven flow

Stack (Flue)

Stack (Atrium)

(Courtesy M. Liddament)

Air Pressure

Pressure of air increases closer to the ground due to the extra amount of air above.

The pressure gradient of air increases indoors because warmer air is less dense.

A

'Stack' pressure between openings is given by A + B

'Neutral' Pressure Plane

B

2. Stack Driven Ventilation

The two natural mechanisms of ventilation

13 F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011

Stack height

Fig.6

14

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10

6pm 6am 6am midnight 12noon

day night

Outside temperature

Source: Natural Ventilation – capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch

presentation, April 2008, Jim Lambert

Natu

ral ve

ntilation

princ

iples

15

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature

16

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature

Normal comfort range

Comfort range with moving air

17

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature


Comfort range with moving air Open all

windows

18

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature



windows

Close all windows

19

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature



windows

Close all windows

Start internal

fan

20

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature



windows

Close all windows

Start internal

fan

Open all windows

21

Summer Example

time

Tempe

ratu

re (deg

C)

30

20

10


day night

Outside temperature



Natu

ral ve

ntilation

princ

iples

Inside temperature



windows

Close all windows

Start internal

fan

Open all windows

Gentle forced ventilation overnight

22

Mechanical ventilation


Review of its advantages: •Quantity of ventilation can be controlled; •Exhaust moisture/odors out of sanitary rooms; •Less ducts compared to balanced ventilation; •Simple system and widely known; •Possibility of individual control per room.

23

Typical energy consumption for different types of office buildings


Fig. 3

24

Hybrid ventilation ??? GENERAL DESCRIPTION

A hybrid ventilation system allows the controlled introduction of outdoor air ventilation into a building by both mechanical and passive means;

it is sometimes called mixed-mode ventilation; it has built-in strategies to allow the mechanical and passive portions to work in

conjunction with one another so as to not cause additional ventilation loads compared to what would occur using mechanical ventilation alone;

it thus differs from a passive ventilation system, consisting of operable windows alone, which has no automatic way of controlling the amount of outdoor air load; two variants of hybrid ventilation are:

the changeover (or complementary) type: spaces are ventilated either mechanically or passively, but not both simultaneously;

the concurrent (or zoned) type: both methods provide ventilation simultaneously, though usually to zones discrete from one another.

control of hybrid ventilation is obviously an important feature; with the changeover variant, controls could switch between mechanical and

passive ventilation seasonally, diurnally, or based on a measured parameter; in the case of the concurrent variant, appropriate controls are needed to

prevent “fighting” between the two ventilation methods.

Source: ASHRAE Green Guide, The Design, Construction, and Operation of Sustainable Buildings, 2006

25

Hybrid ventilation ??? WHEN/WHERE IT’S APPLICABLE

when the owner and design team are willing to explore employing a nonconventional building ventilation technique that has the promise of reducing ongoing operating costs as well as providing a healthier, stimulating environment;

when it is determined that the building occupants would accept the concept of

using the outdoor environment to determine (at least, in part) the indoor environment, which may mean greater variation in conditions than with a strictly controlled environment;

when the design team has the expertise and willingness—and has the charge from

the owner—to spend the extra effort to create the integrated design needed to make such a technique work successfully;

where extreme outside conditions—or a specialized type of building use—do not

preclude the likelihood of the successful application of such a technique; buildings with atriums are particularly good candidates.


26

Hybrid ventilation ??? PROS AND CONS PRO

HV is an innovative and potentially energy-efficient way to provide outdoor air ventilation to buildings and, in some conditions, to cool them, thus reducing energy otherwise required from conventional sources (power plant);

could lead to a lower building life-cycle cost; could create a healthier environment for building occupants; offers a greater sense of occupant satisfaction due to the increased ability to

exercise some control over the ventilation provided; there is more flexibility in the means of providing ventilation; the passive variant

can act as backup to the mechanical system and vice versa; could extend the life of the equipment involved in providing mechanical ventilation

since it would be expected to run less.


27

Hybrid ventilation ??? CONS

failure to integrate the mechanical aspects of a HV system with the architectural design could result in a poorly functioning system;

additional first costs could be incurred since two systems are being provided

where only a single one would be provided otherwise, and controls for the passive system could be a major portion of the added cost;

if automatic operable window openers are utilized, these could result in security

breaches if appropriate safeguards and overrides are not provided; building operators may have to have special training to understand and learn how

best to operate the system; occupants would probably need at least some orientation so that they would

understand and be tolerant of the differences in conditions that may prevail with such a system;

special attention would need to be given to certain safety issues, such as fire and

smoke propagation in case of a fire; difficult to predict conditions under all possible circumstances;


28

natural mechanical

use as much as possible natural forces:

• wind • temperature difference

2 mode system

apply fans in case natural forces can not fulfil the required ventilation level

Hybrid ventilation


29

Mechanical and Natural Ventilation

windspeed

ventilation

mechanical ventilation

natural ventilation

Req. level


. 30

Ventilation Strategy

natural mechanical alternate mode

mixed mode

IAQ thermal comfort


31

fan energy or transport energy

energy for heating ventilation air

demand hybrid

Demand Controlled Hybrid Ventilation


Fig. 4 a,b

32

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 20 40 60 80

volume flow rate l/s

tim

e f

racti

on

natural

mechanical

hybrid

Flow versus time over the year

Classification

Alternate use of natural and mechanical

Fan assisted natural

Stack and wind supported mechanical

Non of them are optimal hybrid

34 .

Hybrid ventilation strategies for IAQ control

Approaches: • Mechanical air extraction with natural supply inlets • Mechanical air supply with natural extraction • Mechanical cooling or heating combined with natural ventilation. HYBRID VENTILATION system should be designed with three factors being considered: 1 Provision of sufficient air leakage rate at different environmental conditions. 2 Ability to control or throttle back the leakage rate under severe weather conditions, e.g. during high winds. 3 Prevention of back-draught or over-extraction through the extract openings, such as stacks, during high winds.

35 .


Alternate use of natural

and mechanical ventilation

Commerzbank

Frankfurt

Norman Foster


Fig. 5 a,b

36

Typical 2 mode system

Natural In case weather conditions allow

Mechanical In case weather conditions require


Fig. 6 a,b

37


Fan assisted natural ventilation

Media school Grong Norway Source: Technical Note AIVC 59 , Air Infiltration and Ventilation Centre Operating Agent and Management, INIVE EEIG, Brussels, Belgium

Fig. 7 a,b

38



Fig. 8

39

COMPONENTS FOR HYBRID VENTILATION CONCEPTS

• Low pressure fans with advanced control mechanism • Low pressure static heat exchanger • Low pressure ductwork • Wind towers, solar chimneys or atria for exhaust. Underground

ducts, culverts or plenums to pre-condition supply air


Fig. 10

40

Solar assisted ventilation

40 Tech

nica

l so

lution

s fo

r Natu

ral Vent

ilation

Source: C. Ghiaus, F. Allard, J. Axley, C-A. Roulet, Natural ventilation: principles, solutions and tools

Tw1

h1

Tw2

h2

Ti

Te

Ti

Glass

Wall

Outdoor

air

To<Ti

Te

Ti

(a) (b)ip

dp

epSolar collector (Trombe wall) (Awbi,1998)

Source: Awbi, H. (1998). Ventilation. Renewable and Sustainable Energy Reviews 2: 157-188.

ventilator heater

Source: Rakesh Khanal, Chengwang Lei, Solar chimney—A passive strategy for natural ventilation, Volume 43, Issue 8, 2011, Pg 1811–1819

Cross section of Victoria Barracks, Sydney, showing air

flow path of cross flow natural ventilation incorporating a solar chimney

41 41

Single sided, cross flow and stack ventilation for air quality and cooling;

Key Features:

Case

stu

dies

BRE Office Building, Watford, UK Year of completion:1996 Type of building: Office Site: Urban Project Manager: Bernard Williams and Associates Architect : Feilden Clegg Bradley Architects Services Engineers: Max Fordham and Partners

Optional occupant controlled openable windows; Solar heated fan assisted stack and wind driven design for first two floors; Good internal air contact with thermal mass through hollow sinusoidal

concrete ceiling elements; BEMs controlled openings of stack vents to control cooling and air quality; Cellular and open plan offices; Daylighting and low energy lighting; Active external solar shading; Some groundwater cooling; BEMS system controls air quality and night cooling ventilation; Air change rates as high as 30 h-1 could be achieved to meet cooling needs; The top floor of the building was separately ventilated by cross flow.

Source: http://www.feildenclegg.com Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

Fig.18

http://www.feildenclegg.com/

42 42

Case

stu

dies

BRE Office Building, Watford, UK Ventilation & Cooling

five cooling stacks towering over the south side of the building which hint at the building's complex ventilation system that takes advantage of the building’s narrow layout for cross-ventilation purposes; the curved, hollow, concrete floor slabs also aid in the building‘s ventilation by

drawing air in through the passages in the floor/ceiling on hot, windy days; cooling can be managed also by circulating water through the passages in the

curving slab; this cold water is supplied by a 70-meter-deep bore hole where the

temperature is a constant 10° Celsius. this cold water is used in heat exchangers to chill circulatory water;

the floor can also then use the water to store “coolness” from the night for the next day. In the winter time, the water is heated by condensing gas boilers that are 30% more efficient than traditional boilers by recovering heat lost in flue gases. All heating and cooling systems are managed by the Trend building management system (BMS).

Source: http://www.feildenclegg.com Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

http://www.feildenclegg.com/

43 43

Case

stu

dies

BRE Office Building, Watford, UK Solar Control and Daylighting

the building’s glazing is optimized by a louvered exterior shading system that is designed to allow maximum daylighting while minimizing glare; the louvers in the shading system have a translucent ceramic

coating on their underside to filter direct sunlight as it reflects off it; the louvers change position corresponding to the time of day and

season; they are controlled by the automated functions of the BMS, but can be overridden by occupants via a remote control; the louvers are oriented so the views of the occupants are not

obstructed while either seated at desks or standing in circulation spaces.

Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

Fig. 19 a,b

44

Monitoring in winter and summer showed that design conditions were fully satisfied; During hot weather the

inside air temperature remained at between approximately 3-5 K below the outdoor peak temperature; The inside peak design

temperature of 28°C was not exceeded. 44

Case

stu

dies

BRE Office Building, Watford, UK

Statistics and Studies

Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

Building Area: 2,200 m2

Site Area: 6,400 m2 Density: 100 people @ 12 m2 /person Energy Use Predicted Total:

83 KWhr/ m2 /annum (0.3GJ/m2/annum) Heating: 47 kW/h/ m2 /annum Artificial lighting: 9 kW/h/ m2 /annum Cooling: 2-3.5 kW/h/ m2 /annum Mech Vent: 0.5 kW/h/ m2 /annum General elec: 23 kW/h/ m2 /annum

45

Development stages for hybrid systems

local exhaust versus central exhaust balancing supply and exhaust controlled supply low pressure systems supported by wind and

buoyancy demand control optimisation

sizing demand control

logi

cal

com

bin

atio

ns

46


Overview of different types

Hybrid ventilation based on mechanical

exhaust (Heinonen and Kosonen, 2000)

Concept 1

Source: Hybrid ventilation, Guidelines 2007

Fig. 13

47



Hybrid ventilation with supply air duct

(Heinonen and Kosonen, 2000).

Concept 2


Fig. 14

48



Hybrid ventilation based on balanced

ventilation (Heinonen and

Kosonen, 2000).

Concept 3


Fig. 15

49 .

Optimisation

energy

IAQ thermal comfort

life cycle analysis

hybrid

ventilation system

50

IAQ demand control

time

occupancy

sensor

what indicator CO2

mixed gas

Thermal comfort Temperature

Air temperature

Operative temperature

Air velocity

RH

Control algorithm's

Control Strategy

ASHRAE

Summer Winter


Fig. 16

51 .

Final Remark

Many ventilation systems may called hybrid

Many ventilation systems may called demand controlled

Hybrid ventilation systems are available in several stages of technical development

Comparisons in terms of objective performances is the only correct one!!

Optimization of hybrid ventilation systems is still a difficult task

52

References Technical Note AIVC 59 , Air Infiltration and Ventilation Centre Operating Agent

and Management, INIVE EEIG, Brussels, Belgium

Chapter 8 : Thermal Comfort. In: ASHRAE handbook of fundementals. SI

Edition. Atlanta: ASHRAE, 1997, p. 8.1-8.28.

Ventilation for acceptable indoor air quality, American Society of Heating,

Refrigerating and Air Conditioning Engineers, Inc., 1989 ASHRAE 62-1989

ASHRAE Green Guide, The Design, Construction, and Operation of Sustainable

Buildings, 2006

International energy agency energy conservation in buildings and community

systems, Pilot study report: PROBE Limelette, Belgium

Hybrid ventilation, Guidelines 2007

F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011

F. ALLARD, Natural ventilation in buildings, James & James, London, 1998

Natural Ventilation in the Urban Environment, Assessment and Design, Edited by

Cristian Ghiaus and Francis Allard, ISBN: 1-84407-129-4 hardback, 2005

hybrid ventilation_mazo_2014.pdf

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