The Feasibility Of Natural Ventilation

Transcription

The Feasibility ofNatural VentilationErin McConahey, PE, FASHRAEArupNovember 7, 2019erin.mcconahey@arup.com

Learning Objectives Apply the appropriate codes and standardswhen considering natural ventilation Identify key steps in evaluating outdoorconditions for supporting natural ventilation Evaluate internal and external heat gains todetermine whether natural ventilation canprovide sufficient cooling

Session Summary This session will describe process of earlyphase analysis that a design team can to testwhether natural ventilation is a feasiblecomfort-conditioning system for a givenclimate and building configuration. Thespeaker will build on her “Natural VentilationTop 10 Feasibility Questions” from an ASHRAEJournal article to cover compliance withASHRAE Standards 55 and 62.1 and adiscussion of the impact of climate change.

ASHRAE JournalSeptember 2008 Table 4 NaturalVentilation Top 10FeasibilityQuestions These were rules ofthumb

Mechanisms of Natural VentilationThough obvious, the following basic natural ventilation principles bearrepeating:1. Natural ventilation only works if there are at least two openings (or avery tall opening that acts as a two-way opening).2. The amount of airflow is controlled by the size of the smallest opening.3. Air will always follow the path of least resistance.Images courtesy of CIBSE

Natural Ventilation vs Natural ConditioningNatural VentilationNatural ConditioningPer ASHRAE 62.1-2016 (ASHRAE2016b) the definition of NaturalVentilation is “ventilation providedby thermal, wind, or diffusioneffects through doors, windows, orother intentional openings in thebuilding.”Per ASHRAE 55-2017 (ASHRAE 2017a) page3, the definition of Occupant-controlledNaturally Conditioned spaces is “thosespaces where the thermal conditions ofthe space are regulated primarily byoccupant-controlled openings in theenvelope.”Essentially, direct air intake fromOutdoors into the occupied spaceto support only the Indoor AirQuality requirements.Essentially, direct air intake from Outdoorsinto the occupied space supportsabsorption of heat gains. This can occur via-direct cooling of occupants-removal of air heated from computers orlights-cooling of surfaces that then causesindirect cooling of occupants throughradiative heat exchange.

Natural Ventilation Codes & StandardsStandard/ Manual NameKey chapters/clauses pertaining tonatural ventilation and naturalconditioningANSI/ASHRAE Standard 62.1-2016.Section 6.4 with backup mechanicalVentilation for Acceptable Indoor Air Quality ventilation systems design perSection 6.2 and/or 6.3.ANSI/ASHRAE Standard 55-2017. ThermalSection 5.4Environmental Conditions for HumanOccupancy2016 Building Energy Efficiency StandardsSection 120.1.(b).1for Residential and Nonresidential Buildingsfor the 2016 Building Energy EfficiencyStandards: Title 24, Part 62015 IMC International Mechanical CodeSection 4022016 California Mechanical Code, California Section 402.2, essentially replicatesCode of Regulations Title 24, Part 4 based on ASHRAE Standard 62.12015 Uniform Mechanical Code

Other Applicable GuidanceStandard/ Manual NameKey chapters/clauses pertaining to naturalventilation and natural conditioningLeadership in Energy andMinimum Energy Performance Prerequisite p. 357,Environmental DesignOptimize Energy Credit (relies on calculation in(LEED ) Reference Guide for previously named Prerequisite), Minimum Indoor AirBuilding Design andQuality Performance Prerequisite pp.605-622,Construction v4.Enhanced Indoor Air Quality Strategies Credit pp.645656, and Thermal Comfort Credit p 695-710. (notethat this standard references ASHRAE Standard 62.12010 and ASHRAE Standard 90.1-2010.)Natural ventilation in non- Entire documentdomestic buildings, CIBSEApplications Manual AM10Mixed mode ventilation,Document addresses mixed mode or hybridCIBSE Applications Manual ventilation, within which natural ventilation isAM13:2000.discussed as one of the modes available

Natural Ventilation vs Mixed ModeASHRAE 55Adaptive Comfortstandard notapplicableASHRAE 55Adaptive Comfortstandard notapplicableImages courtesy of Dr. Gail Brager of UC BerkeleyASHRAE 55Adaptive Comfortstandard applicableto permanent NVspace

ASHRAE JournalSeptember 2008 Table 4 NaturalVentilation Top 10FeasibilityQuestions These were rules ofthumb

NV Top 10 Feasibility QuestionsData to ReviewQuestion to be Asked(If Answer is Yes, Move to Next Question)1. BuildingIs the building envelope performance optimized to minimizeEnvelopesolar gain into the building? Target a maximum total solar loadof 4 W/ft2 of sun patch floor area in a cooling condition.2. Internal HeatIs the total internal heat load minimized to less than 2 W/ft2Loadsfor naturally conditioned space or, within the cooling capacityof auxiliary systems?3. WeatherIn looking at the climate data’s monthly mean minimum andNormals:mean maximum, are there at least six months where theMean Maximum/ monthly maximum is less than 80 F but mean minimum isMean Minimum higher than 32 F?4. Frequency ofIn further looking at climate data, does the frequency ofOccurrenceoccurrence psychrometric chart for occupied hours have morePsychrometricthan 30% of the time between 60 F to 80 F and less than 70%Chartrelative humidity?5. AmbientIs the surrounding environment suitable for direct intake of airEnvironment,from outside? (i.e., there are no security concerns, the ambientPossible Locations environment is sufficiently quiet, air quality meets Standardof Openings62.1 standards, openings are not near street level, nearhighways or industrial plants, or at elevation of a neighbor’sdischarge).

NV Top 10 Feasibility QuestionsData to Review6. WindowLocationsand Sizes,Accessibility7. Wind Rose,Feasible FlowPaths: Inlet toOutlet Under AllWind Conditions8. High AfternoonTemperatures9. Diurnal Rangeon Hot Days10. Dew-PointTemperaturesThroughout YearQuestion to be Asked(If Answer is Yes, Move to Next Question)Can the equivalent of 4% to 5% of the floor area as windowopening area be found with direct access to the window byeveryone within 20 ft?Can one rely on wind-driven effects for cooling?Is there a direct low-pressure airflow path from a low-levelopening to a high-level opening within the space, and will it bepreserved once furniture/TI work is complete?Does the climate have regular outside air temperatures over80 F? If yes, review whether exposed thermal mass is possible.Does the climate have a diurnal range that has nighttimetemperatures below 65 F for at least 8 hours a night on theworst-case days?If yes, move to multizone modeling of thermal mass andconsider night purge.Throughout the year, do you have consistent outside air dewpoints throughout the year of less than 64 F? If yes, move tomultizone modeling and consider a radiant cooling system.

Some contentshared is from anupcoming DesignGuide for NaturalVentilation(coauthored withPeter Simmonds,FASHRAE)

Upcoming Design Guide Steps When Not to Pursue Natural VentilationOutside Air AssessmentFaçade and Building ConfigurationNavigating Natural Ventilation ComplianceDemonstrating Comfort Standard ComplianceControl of Natural Ventilation and NaturalConditioning

When Not to Pursue NaturalVentilation Strict Filtration RequirementsContaminant Dilution ConcernsSpecial Pressurization RelationshipsSpeech Privacy ConcernsInternal Heat Load Demands

Internal (and Solar) LoadsData to Review1. BuildingEnvelope2. Internal HeatLoadsQuestion to be Asked(If Answer is Yes, Move to Next Question)Is the building envelope performance optimized to minimizesolar gain into the building? Target a maximum total solar loadof 4 W/ft2 of sun patch floor area in a cooling condition.Is the total internal heat load minimized to less than 2 W/ft2for naturally conditioned space or, within the cooling capacityof auxiliary systems? Take a 100 sf office 1 person, one PC Targeting 5 ac/hr with a 4.5 F (2.5 C)differential to outdoors

CIBSE NV capacity chart Size no higher than 3K difference5.4R28 W/m2 9Btuh/sf10 W/m2 3.2 Btuh/sfImages courtesy of CIBSE

(1W/sf) According to CIBSE, you have a maximumof 28W/m2 (2.8W/sf) available at 3Kdifferential (indoor-outdoor Temp)

Will natural ventilation work?

Outdoor Air AssessmentData to ReviewQuestion to be Asked(If Answer is Yes, Move to Next Question)3. WeatherIn looking at the climate data’s monthly mean minimum andNormals:mean maximum, are there at least six months where theMean Maximum/ monthly maximum is less than 80 F but mean minimum isMean Minimum higher than 32 F?4. Frequency ofIn further looking at climate data, does the frequency ofOccurrenceoccurrence psychrometric chart for occupied hours have morePsychrometricthan 30% of the time between 60 F to 80 F and less than 70%Chartrelative humidity?5. AmbientIs the surrounding environment suitable for direct intake of airEnvironment,from outside? (i.e., there are no security concerns, the ambientPossible Locations environment is sufficiently quiet, air quality meets Standardof Openings62.1 standards, openings are not near street level, nearhighways or industrial plants, or at elevation of a neighbor’sdischarge).7. Wind Rose,Can one rely on wind-driven effects for cooling?Feasible FlowIs there a direct low-pressure airflow path from a low-levelPaths: Inlet toopening to a high-level opening within the space, and will it beOutlet Under All preserved once furniture/TI work is complete?Wind Conditions

EnergyPlus Weather Data https://energyplus.net/weather

Do Postprocessing yourself: Fresno passes Question 1

Can also drop the *.epw file into Climate Consultant (free software fromUCLA) and visually observe Average High and Average Low per ge courtesy of UCLA by virtue of software usage

Outdoor Air AssessmentData to ReviewQuestion to be Asked(If Answer is Yes, Move to Next Question)3. WeatherIn looking at the climate data’s monthly mean minimum andNormals:mean maximum, are there at least six months where theMean Maximum/ monthly maximum is less than 80 F but mean minimum isMean Minimum higher than 32 F?4. Frequency ofIn further looking at climate data, does the frequency ofOccurrenceoccurrence psychrometric chart for occupied hours have morePsychrometricthan 30% of the time between 60 F to 80 F and less than 70%Chartrelative humidity?

Do Postprocessing yourself on a spreadsheet with the *.epw 8760 hour fileFresno passes Question 2

Can also shortcut with the Climate Consultant (free software from UCLA)Psychrometric chart, pick the design strategies that apply only to thenatural ventilation state and check for comfortable hours instead of thefixed 60-80 F temperature rangeImage courtesy of UCLA by virtue of software usage

A note on rising OSA temperatures Professional integrity would require us toreview what the likely 20-50 year potentialincreases in local air temperature might be ifan engineered natural conditioning system isbeing proposed. Can purchase climate-shifted *.epw files forpurchase from one of the predominant energyanalysis software vendors

Sample from Los AngelesAnticipates a mean monthly temperature rise of 3 C (5.4F) by 2050 usingthe RCP 8.5 emission scenarios and 50% warming percentile

Check Air Quality and AccessData to ReviewQuestion to be Asked(If Answer is Yes, Move to Next Question)5. AmbientIs the surrounding environment suitable for direct intake of airEnvironment,from outside? (i.e., there are no security concerns, the ambientPossible Locations environment is sufficiently quiet, air quality meets Standardof Openings62.1 standards, openings are not near street level, nearhighways or industrial plants, or at elevation of a neighbor’sdischarge).7. Wind Rose,Can one rely on wind-driven effects for cooling?Feasible FlowIs there a direct low-pressure airflow path from a low-levelPaths: Inlet toopening to a high-level opening within the space, and will it beOutlet Under All preserved once furniture/TI work is complete?Wind ConditionsBased on general air quality data analysis, must get Client permission toproceed given non-attainment status of Fresno County/ San Joaquin Valleyto proceed past Question 5 generically (see below).Then do a Local site check: Check for effluents and emissions from roofsnearby, typically check the outside air quality results

Check whether the county isin a Nonattainment status forthe NAAQS standardsFresno is non-compliant for 5pollutants per EPA enbook/mapnpoll.html

Drilling into a deeper level for thenonattainment details, it appearsthat it is PM-2.5 and 8 hour Ozonethat are actually in non-complianceas part of the San Joaquin ok/ancl2.htmlPer ASHRAE 62.1, mustinform client with localair quality results

WindRose:prevailingwinds?Local wind regime check: are there any prevailing winds to accommodate?Can again use Climate Consultant (free software from UCLA) to generatewind rose or use other toolsImage courtesy of UCLA by virtue of software usage

Façade and Building ConfigurationData to Review6. WindowLocationsand Sizes,Accessibility7. Wind Rose,Feasible FlowPaths: Inlet toOutlet Under AllWind ConditionsQuestion to be Asked(If Answer is Yes, Move to Next Question)Can the equivalent of 4% to 5% of the floor area as windowopening area be found with direct access to the window byeveryone within 20 ft?Can one rely on wind-driven effects for cooling?Is there a direct low-pressure airflow path from a low-levelopening to a high-level opening within the space, and will it bepreserved once furniture/TI work is complete?Question 6 is related to the code/standard that is being appliedFor prescriptive compliance:StandardASHRAE Standard 62.1-2016California Title 24-2016 CaliforniaEnergy CommissionMaximum distanceto operableeleme

ASHRAE Standards 55 and 62.1 and a discussion of the impact of climate change. ASHRAE Journal September 2008 Table 4 Natural Ventilation Top 10 Feasibility Questions These were rules of thumb. Mechanisms of Natural Ventilation Images courtesy of CIBSE Though obvious, the following basic natural ventilation principles bear repeating: 1. Natural ventilation only works if there are at .