Displacement ventilation

Short description: Room air distribution strategy

Diagram of displacement ventilation

Displacement ventilation (DV) is a room air distribution strategy where conditioned outdoor air is supplied at a low velocity from air supply diffusers located near floor level and extracted above the occupied zone, usually at ceiling height.[1]

## Contents

* 1 System design
* 2 History
* 3 Applications
* 4 General characteristics
* 4.1 Airflow distribution
* 4.2 Conditioning type
* 4.3 Space requirement
* 5 Benefits and limitations
* 5.1 Local discomfort: vertical temperature difference and draft
* 5.2 Indoor air quality
* 5.3 Energy consumption
* 6 Design guidelines
* 7 List of buildings using displacement ventilation
* 8 See also
* 9 References

## System design

A typical displacement ventilation system, such as one in an office space, supplies conditioned cold air from an air handling unit (AHU) through a low induction air diffuser. Diffuser types vary by applications. Diffusers can be located against a wall ("wall-mounted"), at the corner of a room ("corner-mounted"), or above the floor but not against a wall ("free-standing").[2] The cool air accelerates because of the buoyancy force, spreads in a thin layer over the floor, reaching a relatively high velocity before rising due to heat exchange with heat sources (e.g., occupants, computers, lights).[3] Absorbing the heat from heat sources, the cold air becomes warmer and less dense. The density difference between cold air and warm air creates upward convective flows known as thermal plumes. Instead of working as a stand-alone system in interior space, displacement ventilation system can also be coupled with other cooling and heating sources, such as radiant chilled ceilings[4] or baseboard heating.[1]

## History

Displacement ventilation was first applied in an industrial building in Scandinavia in 1978, and has frequently been used in similar applications, as well as office spaces, throughout Scandinavia since that time.[1] By 1989, it was estimated that displacement ventilation comprised the 50% in industrial applications and 25% in offices within Nordic countries.[5] Applications in the United States have not been as widespread as in Scandinavia. Some research has been done to assess the practicality of this application in U.S. markets due to different typical space designs[1] and application in hot and humid climates, as well as research to assess the potential indoor environmental quality and energy-saving benefits of this strategy in the U.S. and elsewhere.

## Applications

Displacement ventilation has been applied in many famous building such as the Suvarnabhumi International Airport in Bangkok, Thailand, the NASA Jet Propulsion Laboratory Flight Projects Center building,[6][7] and the San Francisco International Airport[8][9] Terminal 2 among other applications.

## General characteristics

### Airflow distribution

The thermal plumes and supply air from diffusers, which determines the velocity of airflow at floor level, play an important role in DV systems. It is necessary to carefully set the airflow rate from the diffuser to avoid drafts.

### Conditioning type

Due to the unique properties of thermal stratification, displacement ventilation is typically used for cooling rather than for heating. In many cases, a separate heating source, such as a radiator or baseboard, is used during heating periods.[1]

### Space requirement

Displacement ventilation is best suited for taller spaces (higher than 3 meters [10 feet]).[2] Standard mixing ventilation may be better suited for smaller spaces where air quality is not as great a concern, such as single-occupant offices, and where the room height is not tall (e.g., lower than 2.3 meters [7.5 feet]).[2]

## Benefits and limitations

### Local discomfort: vertical temperature difference and draft

Displacement ventilation systems are quieter than conventional overhead systems with better ventilation efficiency. Hence, it could enhance indoor air quality and provide desirable acoustic environment. Displacement ventilation systems are appropriate in space where high ventilation is required, such as classrooms, conference rooms, and offices.

Displacement ventilation can be a cause of discomfort due to the large vertical temperature gradient and drafts.[10] According to Melikov and Pitchurov's research, sensations of cold caused by vertical temperature difference and draft are usually occurred at the lower leg/ ankle/ feet region, while warm sensations at the head are reported.[11] The research also indicates, that the draft rating model could predict the draft risk with good accuracy in rooms with displacement ventilation systems.

There is a tradeoff inherent in these two issues: by increasing the flow rate (and the ability to remove greater thermal loads), the vertical temperature gradient can be reduced, but this could increase the risk of drafts.[1] Pairing displacement ventilation with radiant chilled ceilings is an effort to mitigate this problem.[12] According to some studies, displacement ventilation systems can only provide acceptable comfort if the corresponding cooling load is less than about 13 Btu/h-sf or 40 W/m2.

### Indoor air quality

One benefit of displacement ventilation is possibly the superior indoor air quality achieved with exhausting contaminated air out of the room. Better air quality is achieved when the pollution source is also a heat source.[1][2]

The effectiveness of displacement ventilation at removing particulate contaminants has been investigated recently.[13][14] Small aqueous droplets containing infectious nuclei are frequently released in hospital rooms and other indoor spaces, and tend to settle through the ambient air at a speed of order 1–10 mm/s typically. In cold climates or seasons, sufficiently small droplets are extracted from the top of a displacement-ventilated space if the mean upward air speed exceeds the particle settling speed. However, laboratory experiments have shown that larger droplets may settle faster than the air moves. In this case, the large droplets are not extracted effectively from a space with upward displacement ventilation, and their concentration increases if the ventilation rate is increased.[13] In warmer climates or seasons, large-scale instabilities in the concentration of contaminants may occur within a space with downward displacement ventilation.[14]

### Energy consumption

Some studies have demonstrated that displacement ventilation may save energy as compared to standard mixing ventilation, depending on the use type of the building, design/massing/orientation, and other factors.[1] However, for the evaluation of energy consumption of displacement ventilation, the numerical simulation is the main method, since yearly measurements are too expensive and time consuming. Hence, whether displacement ventilation could help with saving energy is still debated. In general, displacement ventilation is attractive to the core region in a building since no heating is needed. However, the perimeter zones require high cooling energy.

## Design guidelines

Different guidelines have been published to provide guidance on designing displacement ventilation systems, including:

* Skistad H., Mundt E., Nielsen P.V., Hagstrom K., Railo J. (2002). Displacement ventilation in Non-Industrial Premises. Federation of European Heating and Air-conditioning Associations.[2]
* Skistad, H. (1994). Displacement ventilation. Research Studies Press, John Wiley & Sons, Ltd., west Sussex. UK.
* Chen, Q. and Glicksman, L. (2003). Performance Evaluation and Development of Design Guidelines for Displacement ventilation. Atlanta: ASHRAE.[1]

Among guidelines listed above, the one developed by Chen and Glicksman are aimed specifically at fulfilling U.S. Standard. Below is a brief description of each step of their guideline.[15]

Step 1) Judge the applicability of displacement ventilation

Step 2) Calculate summer design cooling load.

Step 3) Determine the required flow rate of the supply air for summer cooling.

Step 4) Find the required flow rate of fresh air for acceptable indoor air quality.

Step 5) Determine the supply air flow rate.

Step 6) Calculate the supply airflow rate.

Step 7) Determine the ratio of the fresh air to the supply air.

Step 8) Select supply air diffuser size and number.

Step 9) Check the winter heating situation.

Step 10) Estimate the first costs and annual energy consumption.

## List of buildings using displacement ventilation

Building  | Year  | Country  | City  | Architects  | Space Type

|
|
|
|
|

Jewish Museum Berlin  | 1999  | Germany  | Berlin | Daniel Libeskind  | Exhibit space
Bangkok International Airport  | 2006  | Thailand  | Bangkok | Helmut Jahn of Murphy / Jahn Architects  | Airport terminal
Hearst Tower  | 2006  | United States | New York City, NY  | Norman Foster of Foster + Partners  | Large public space
Newseum  | 2011  | United States  | Washington, D.C. | Polshek Partnership  | Large public space
Modesto Medical Center  | 2008  | United States  | Modesto, California  | KP Architects  | Health-care
St. John's University, St. John's Hall  | 1950s  | United States  | New York City, NY  | unknown  | Teaching environment
Carnegie Hall  | 1891  | United States  | New York City, NY  | William Burnet Tuthill  | Theater
Samuel J. Friedman Theater  | 1920s  | United States  | New York City, NY  | Herbert J. Krapp  | Theater
National Center for the Performing Arts  | 2007  | China  | Beijing | Paul Andreu  | Theater
The Copenhagen Opera  | 2004  | Denmark | Copenhagen | Henning Larsen  | Theater
Prince Mahidol Hall  | 2014  | Thailand  | Nakornpathom  | A49  | Theater
Sky Central  | 2014  | United Kingdom  | London | PLP & Arup  | Office

## See also

* Underfloor air distribution (UFAD)

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Chen, Q.; Glicksman, L. (1999). Performance Evaluation and Development of Design Guidelines for Displacement Ventilation. MA.: ASHRAE.
2. ↑ 2.0 2.1 2.2 2.3 2.4 REHVA. (2002). Displacement Ventilation in Non-Industrial Premises. Federation of European Heating and Air-conditioning Associations.
3. ↑ Novoselac, Atila; J., Srebric (June 2002). "A critical review on the performance and design of combined cooled ceiling and displacement ventilation systems". Energy and Buildings 34 (5): Energy and Buildings. doi:10.1016/S0378-7788(01)00134-7. Bibcode: 2002EneBu..34..497N.
4. ↑ Schiavon, Stefano; Bauman, F.; Tully, B.; Rimmer, J. (2012). "Room air stratification in combined chilled ceiling and displacement ventilation systems". HVAC&R Research 18 (1): 147–159. doi:10.1080/10789669.2011.592105. https://escholarship.org/uc/item/980931rf.
5. ↑ Svensson, A.G.L. (1989). "ordic Experiences of Displacement Ventilation Systems". ASHRAE Transactions 95 (2).
6. ↑ "NASA's Out of this World Green Building – Web Exclusives – EDC Magazine". edcmag.com. http://www.edcmag.com/Articles/Web_Exclusive/BNP_GUID_9-5-2006_A_10000000000000933412.
7. ↑ "Jet Propulsion Laboratory Flight Projects Center building". 2017-01-26. https://www.energystar.gov/sites/default/uploads/buildings/old/files/50_Flight_Project_508.pdf.
8. ↑ "San Francisco Airport aims to achieve zero net energy (USGBC Northern California) | U.S. Green Building Council". https://www.usgbc.org/articles/san-francisco-airport-aims-achieve-zero-net-energy-usgbc-northern-california.
9. ↑ "Zero-energy green building in a data-enlightened era". 12 September 2018. https://medium.com/the-fourth-wave/zero-energy-green-building-in-a-data-enlightened-era-70c84300df4c.
10. ↑ ANSI/ASHRAE Standard 55 (2002). Thermal Environmental Conditions for Human Occupancy
11. ↑ Melikov, Arsen; Pitchurov, G.; Naydenov, K.; Langkilde, G. (June 2005). "Field study of occupants'thermal comfort in rooms with displacement ventilation". Indoor Air 15 (3): 205–214. doi:10.1111/j.1600-0668.2005.00337.x. PMID 15865620.
12. ↑ Loveday, D.L.; Parsons, K.C.; Taki, A.H.; Hodder, S.G. (July 2002). "Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate". Energy and Buildings 34 (6): 573–579. doi:10.1016/S0378-7788(02)00007-5. Bibcode: 2002EneBu..34..573L.
13. ↑ 13.0 13.1 Woods, Andrew W.; Mingotti, Nicola (June 2015). "On the transport of heavy particles through an upward displacement-ventilated space". Journal of Fluid Mechanics 772: 478–507. doi:10.1017/jfm.2015.204. ISSN 0022-1120. Bibcode: 2015JFM...772..478M. https://www.repository.cam.ac.uk/handle/1810/247941.
14. ↑ 14.0 14.1 Woods, Andrew W.; Mingotti, Nicola (July 2015). "On the transport of heavy particles through a downward displacement-ventilated space". Journal of Fluid Mechanics 774: 192–223. doi:10.1017/jfm.2015.244. ISSN 0022-1120. Bibcode: 2015JFM...774..192M. https://www.repository.cam.ac.uk/handle/1810/248124.
15. ↑ Chen, Q; Glicksman, L.R (January 1, 2003). System performance evaluation and design guidelines for displacement ventilation. Atlanta: American Society of Heating, Refrigerating, and Air-conditioning Engineers, Inc. ISBN 978-1931862424. https://books.google.com/books?id=Q9EmAAAACAAJ.

* v
* t
* e

Heating, ventilation, and air conditioning

Fundamental concepts|

* Air changes per hour
* Bake-out
* Building envelope
* Convection
* Dilution
* Domestic energy consumption
* Enthalpy
* Fluid dynamics
* Gas compressor
* Heat pump and refrigeration cycle
* Heat transfer
* Humidity
* Infiltration
* Latent heat
* Noise control
* Outgassing
* Particulates
* Psychrometrics
* Sensible heat
* Stack effect
* Thermal comfort
* Thermal destratification
* Thermal mass
* Thermodynamics
* Vapour pressure of water

Technology|

* Absorption refrigerator
* Air barrier
* Air conditioning
* Antifreeze
* Automobile air conditioning
* Autonomous building
* Building insulation materials
* Central heating
* Central solar heating
* Chilled beam
* Chilled water
* Constant air volume (CAV)
* Coolant
* Dedicated outdoor air system (DOAS)
* Deep water source cooling
* Demand-controlled ventilation (DCV)
* Displacement ventilation
* District cooling
* District heating
* Electric heating
* Energy recovery ventilation (ERV)
* Firestop
* Forced-air
* Forced-air gas
* Free cooling
* Heat recovery ventilation (HRV)
* Hybrid heat
* Hydronics
* HVAC
* Ice storage air conditioning
* Kitchen ventilation
* Mixed-mode ventilation
* Microgeneration
* Natural ventilation
* Passive cooling
* Passive house
* Radiant heating and cooling system
* Radiant cooling
* Radiant heating
* Radon mitigation
* Refrigeration
* Renewable heat
* Room air distribution
* Solar air heat
* Solar combisystem
* Solar cooling
* Solar heating
* Thermal insulation
* Underfloor air distribution
* Underfloor heating
* Vapor barrier
* Vapor-compression refrigeration (VCRS)
* Variable air volume (VAV)
* Variable refrigerant flow (VRF)
* Ventilation

Components|

* Air conditioner inverter
* Air door
* Air filter
* Air handler
* Air ionizer
* Air-mixing plenum
* Air purifier
* Air source heat pumps
* Automatic balancing valve
* Back boiler
* Barrier pipe
* Blast damper
* Boiler
* Centrifugal fan
* Ceramic heater
* Chiller
* Condensate pump
* Condenser
* Condensing boiler
* Convection heater
* Compressor
* Cooling tower
* Damper
* Dehumidifier
* Duct
* Economizer
* Electrostatic precipitator
* Evaporative cooler
* Evaporator
* Exhaust hood
* Expansion tank
* Fan coil unit
* Fan filter unit
* Fan heater
* Fire damper
* Fireplace
* Fireplace insert
* Freeze stat
* Flue
* Freon
* Fume hood
* Furnace
* Furnace room
* Gas compressor
* Gas heater
* Gasoline heater
* Geothermal heat pump
* Grease duct
* Grille
* Ground-coupled heat exchanger
* Heat exchanger
* Heat pipe
* Heat pump
* Heating film
* Heating system
* High efficiency glandless circulating pump
* High-efficiency particulate air (HEPA)
* High pressure cut off switch
* Humidifier
* Infrared heater
* Inverter compressor
* Kerosene heater
* Louver
* Mechanical fan
* Mechanical room
* Oil heater
* Packaged terminal air conditioner
* Plenum space
* Pressurisation ductwork
* Process duct work
* Radiator
* Radiator reflector
* Recuperator
* Refrigerant
* Register
* Reversing valve
* Run-around coil
* Scroll compressor
* Solar chimney
* Solar-assisted heat pump
* Space heater
* Smoke exhaust ductwork
* Thermal expansion valve
* Thermal wheel
* Thermosiphon
* Thermostatic radiator valve
* Trickle vent
* Trombe wall
* Turning vanes
* Ultra-low particulate air (ULPA)
* Whole-house fan
* Windcatcher
* Wood-burning stove

Measurement
and control|

* Air flow meter
* Aquastat
* BACnet
* Blower door
* Building automation
* Carbon dioxide sensor
* Clean Air Delivery Rate (CADR)
* Gas sensor
* Home energy monitor
* Humidistat
* HVAC control system
* Intelligent buildings
* LonWorks
* Minimum efficiency reporting value (MERV)
* OpenTherm
* Programmable communicating thermostat
* Programmable thermostat
* Psychrometrics
* Room temperature
* Smart thermostat
* Thermostat
* Thermostatic radiator valve

Professions, trades,
and services|

* Architectural acoustics
* Architectural engineering
* Architectural technologist
* Building services engineering
* Building information modeling (BIM)
* Deep energy retrofit
* Duct leakage testing
* Environmental engineering
* Hydronic balancing
* Kitchen exhaust cleaning
* Mechanical engineering
* Mechanical, electrical, and plumbing
* Mold growth, assessment, and remediation
* Refrigerant reclamation
* Testing, adjusting, balancing

Industry organizations|

* ACCA
* AHRI
* AMCA
* ASHRAE
* ASTM International
* BRE
* BSRIA
* CIBSE
* Institute of Refrigeration
* IIR
* LEED
* SMACNA

Health and safety|

* Indoor air quality (IAQ)
* Passive smoking
* Sick building syndrome (SBS)
* Volatile organic compound (VOC)

See also|

* ASHRAE Handbook
* Building science
* Fireproofing
* Glossary of HVAC terms
* World Refrigeration Day

* Template:Home automation
* Template:Solar energy

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Displacement ventilation. Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Engineering:Displacement_ventilation&oldid=4207551"
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template