Natural and Hybrid Ventilation

8/13/2019 Natural and Hybrid Ventilation

1/4

tures relate to the health-care environment is included inthe appendix.

This chapter also addresses the therapeutic environment.Con cerns for water features that may soothe patients also maypose health risks. The appendix suggests because items suchas fountains and other open decorative w ater features may rep-resent a reservoir for opportunistic human pathogens they arenot recommended for installation within any enclosed spacesof health care environments. If provided, the space enclosingthe water feature should be exhausted. However, enclosedaquariums are not subject to exhaust recommendations.

Outstanding Issues for th e Nex t EditionSeveral issues are not resolved in the 2006 edition for various

reasons. Some of these items relate to boiler plant redundancyand emergency operation, refrigeration plant redundancy andemergency operation, surge capacity for airborne infectionisolation rooms in an emergency, coordination with proposedASHRAE Standard 170P, Ventilation of Healthcare Facili-ties ventilation of construction sites of renovation projects,and humidity conditions in operating rooms. To allow moreinformation to he provided for current issues, an approachis planned to disseminate formal interpretations and updatedinformation on a shorter cycle than the update of the maindocument is planned.

SummaryThe changes in the ventilation recommendations of the

Guidelines reflect:l he application of new research, e.g., operating rooms;^

and2. Consistency with the medical program requirements, e.g.,

Endoscopy, Procedure Room use, etc., established on evidence-based clinical research and sound principles of asepsis.^'^

These chang es are the result of a multidisciplinary review ofthe ventilation requiremen ts, and the ventilation recommenda-tions are based on deflnitive scientific basis.

References1. Guidelines for Design and Construction of Hospital and Health

Care Facilities. 2006. Washington, D.C.: The American Institute ofArchitects Press.

2. APIC. APIC Text of Infection Control and Epidemiology. Asso-ciation for Professionals in Infection Control and Epidemiology 2nded . 2005. Washington, D.C.: Association for Professionals in InfectionControl and Epidemiology. Aseptic Technique 20 .1 -3 .

3. CDC. 2003. Guideiine for Environmental Infection Controi inHealth-Care Facilities. 2003 Recommendations of CDC and theHealthcare Infection Control Practices Advisory Committee (HICPAC)www.cdc.gov/ncidod/dhqp/gl_environinfection.html.

4. M emarzadeh, F. and Z. Jiang. 2004 . Effects of operating roomgeometry and ventilation system parameter variations on the protec-tion oft he surgical site. IAQ 2004 : Critical Operation s: Supporting

m e r g in g Te c h n o l

Natural andHybrid

VentilationBy Kurt Roth Ph.D. Associate Member ASHRAE;

John Dieckmann RE. Member ASHRAE; andJames Br od rick Ph.D . Member ASHRAE

is the thirty-third column inspired by a DOE reportcovering energy-saving HVAC R technologies.

M ost commercial buildings use mechanical systems toventilate and cool commercial buildings. In contrasta building with natural ventilation (N V ) relies onatural forces, primarily wind and thermal buoyancy, to movair to ventilate and cool bu ildings. The two basic approaches to

N V are cross and stack ventilation.'-^ In both cases, the building designs allow for sufficient volume of outdoor air (OAto flow through building spaces. NV buildings typically havmore complex facade and window systems, such as operable(including automated) window s, dedicated air intakes, and roovents to effectively control building airflows.

Cross-ventilated buildings rely upon outdoor wind forceto generate a pressure gradient from one side of the buildingto another that drives OA through open windows (or other aiintake devices) on the high-pressure side ofthe building and ouof openings on the low-pressure side. In contrast, N V buildingbased on the stack effect often feature mu ltistory ch imney -lik

spaces such as atria, specially designed heat stacks, and doubleskin fagades.^ ^ Heat generated inside the building (e.g., bylights, people, and office equipment) and from the sun warma column of air, causing it to rise and exit near or at the top ofthe huild ings. As the warm air rises, it draws additional air intthe lower part oft he building to replace the rising air.

Hybrid ventilation (HV ) systems, also known as mixed-modsystems, have the infrastructure for both N V and conventionaair-conditioning systems. When po ssible, they use NV to provide space cooling and OA ventilation, and only operate aiconditioners when the N V system cannot meet space coolinrequirements.

Although all buildings before the 2 0* century were naturallyventilated and cooled, very few conditioned huildings in the US


2/4

E m e ii in g Technologies

Key barriers to greater use of hybrid ventilation in the U.S

inc lude un fam iliarity wit these appro ach e s c lim atic l im itation s

de s ign c ha lle n ge s fire c o de c o nc e rns and im ple m e n tati

cha l l enges .

more common outside of the U . S . , notably in the cooler climatesof no rthern Europe and the U.K. *' - Driving this renaissanceare two advantages of NV systems, reductions in ventilation andcooling energy consumption and potential for improved indoorair quality. Relative to conventional systems, NV can reduceventilation energy consumption because it uses natural forcesto move air instead of lowers and fans. Large volumes of O Aflowing through NV buildings also can reduce cooling energyconsumption by supplanting the need for cooling during periodswhen the OA temperature is below the indoor air temperatureand humidity levels are acceptable. In some cases, NV buildingsintroduce significantly higher levels of O A than economizers.'-'*

As such, they can achieve greater cooling energy savings thaneconomizers and, when used in conjunction with sufficientbuilding mass, can also enable more extensive use of nightpre-cooling of buildings. Furthermore, research suggests thatoccupants of N V buildings adapt to and can tolerate a greaterrange of indoor temperatures, well beyond ASHRA E-definedcomfort zones.^ This enables higher indoor air temperaturesetpoints and, thus, additional cooling energy savings.

Because OA quality usually exceeds that of indoor air, NVpotentially improves lAQ. Some studies suggest that this,in turn, can also reduce the incidence of sick building syn-drome,^ increase occupant satisfaction and, possibly, worker

productivity.' ' ^'

Energy Saving PotentialStudies suggest that NV-only systems can provide acceptable

comfort throughout the year in very limited portions of the U .S.,primarily in areas near the Pacific coast that have moderatetemperatures and low humidity.'*''^ O utside of these regions, N Vcannot, by itself, maintain acceptable indoor environmental con-ditions for significant periods due to temperature and humiditylevels.'* Consequently, the energy-saving potential assessmentand market factors discussions focus on HV systems.

Few studies have evaluated energy-saving potential of HV inthe U . S . To date, all of these studies have limitations. Emmerich,et al.,'* carried out simulations com paring HV performance and

f (

m^) office building in five different U.S. climates durinruary, April, and July. They found that HV could dramareduce (>50% ) fan energy consumption in all cities, excing colder months in the colder climates. The study alsmajor reductions (~50 +) in cooling loads in all but tand humid climates. On the other hand, HV moderately (~ increased h eating loads in the colder climates.

Another simulation-based study compared the annualperformance of H V to a conven tional system in 40 U.SThey found that HVAC energy consum ption decreased inthe hottest and most hum id climates, with an average of approximately 10%.'^

The U.S. energy-saving potential for HV is diffiquantify from available data. A preliminary estimateHV could reduce U.S. commercial building HVAC consumption by an average of approximately 10%number masks large geographical variations in total componen t (cooling, heating, and ventilation) savings,ing potential increases in some regions and componenlike many energy-efficiency meas ures, NV and HV arebuilding approaches that cannot be readily retrofittedlarger portion of buildings. This limits their applicabthe existing building stock.

iVIarket FactorsAlthough HV has become accepted in some regions

world, it has negligible market share for U.S. commbuildings.'* Key barriers to greater use of HV in the Uclude unfamiliarity with this approach, climatic limidesign challenges, fire code concerns, and implemechallenges.

If a team does know about HV and wants to build building, they face several additional challenges. Becaucessful HV buildings require strong integration of the building design with climate control systems, the systmore challenging to design and effectively implemeconventional systems. Designs must consider many fincluding prevailing local winds, temperature, and hu


3/4

Emerging T e ch n o l^te

building, and the building's thermal mass.^'^ Unfortunately,few solid design and analysis data are available, and there isa general lack of adequate design tools and methodologies.In particular, designers need to understand airflows inside the

building to ensure proper airflow distribution and enable effec-tive airflow control. Althou gh coup led building airflow-thermalsimulations can provide this information, they typically arecostly and complex to perform.^

Furthermore, the U.S. building ventilation code, ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable IndoorAir Quality, compromises the energy-saving potential of HVSpecifically, it requires a building to meet ventilation require-ments as either an NV or mechanically ventilated building,but does not allow the building to satisfy the standard for itsoperational mode at a given point of time.

or example, if the designers select the N V design method for anHV building, the building must always have the OA intakes openduring occupancy, even if the mechanical system operates andprovides sufficient airflow. During hot and hum id or cold periodswhere the HV building would logically use mechanical ventilation,this increases space conditioning loads. Conversely, an HV systemdesigned to m eet the mechanical ventilation design criteria must:

Provide the minimum OA ventilation levels during oc-cupancy via mechanical ventilation; or

Use natural ventilation but verify, per the IAQ Procedureof Standard 62, that the concentrations of all relevantcontaminants of concern lie within acceptable levels.^

Given the general confusion and legal concerns about prop-erly implementing the IAQ Procedure, most designers likelywould have the mechanical system p rovide the prescribed QAlevels during occupancy. This reduces or eliminates the ven tila-tion energy savings.

NV and HV buildings also encounter challenges related tofire codes because they are designed to enable large airflowvolumes between spaces. Although desirable from a ventilationperspective, this raises smoke and fire propagation concerns,which complicate design and implementation of the HV o rN Vsystem.^'^'' The associated project risk likely would deter manyteams from pursuing HV and NV Finally, an effective natural

or hybrid ventilation system requires integration of the buildingand HVAC system designs. In turn, this depends upon effectivecollaboration between architects, building d esigners, and HVACdesigners and installers. Such a collaborative design approachis uncommon for U.S. commercial buildings.2'3.i3

Assuming a good design, effective implementation of NVand HV is another challenge due to the uniquen ess and greatercomplexity of these systems. NV and HV systems actuallycan increase energy consumption if poorly designed or imple-mented.' To provide the intended OA to all spaees, NV andHV build ings need to have low infiltration levels. -'* They alsorequire well-implemented control systems to dynam ically co-ordinate OA intakes (automated windows, dam pers, etc.) withthe mechanical systems as outdoor and building conditions

^^ B ildi d l h

about the feasibility of maintaining the more sophisticatecontrols, as well as the general maintenance required for thairflow dampers and pow ered windows. *' Other poten tial issuerequiring attention include ou tdoor noise propagation througair intakes,'''^ insufficient treatment of low-quality OA, anoccupant discomfort caused by indoor airflows.''

eferen es

1. Brown, G.Z. and L. Huang. 2006 . Natural ventilation inorthwest buildings. ASHRAE Journal 48( l ) :47-52 .

2. Jones, J. and A.W. West. 200 1. Natural ventilation andcollaborative design. ASHRAE Journal (11):46-50.

3. Kosik W.J. 2001. Design strategies for hybrid ventilation.

4.E mm erich , S.J. and J. Crum . 20 05 . Sim ulated Performance of Natural and Hybrid Ventilation Systems in anOffice Bu ilding. Final Report Prepared by the NationaInstitute of Standard Technology for the Air-Conditioningand Refrigeration Technology Institute, AR TI-21 CR /61140076-01. www.arti-research.org/research/completed/fin-alreports/40076-final.pdf.

5. Brager, G.S., E. Ring, and K. Powell. 2000. Mixed-mo dventilation: HVAC meets Mother Ha.iwQr Engineered Systems(5):60-70.

6. Lawrence Berkeley National Laboratory. 2006. http://gaiaIbl.gov/hpbf/techno_c3.htm.

7. Emmerich, S.J., A.K. Persily, W.S. Dols, and J.W. Axley

2003. Impact of Natural Ventilation Strategies and Design Is-sues for C alifornia A pplications, Including Input to ASHRA EStandard 62 and California Title 24. Final Report Prepared forArchitectural Energy Corporation NISTIR 7062.

8. Brager, G.S. and R. deDear. 2000. A standard for naturaventilation. ASHRAE Journal (10):21-28.

9. Seppanen, O. and W.J. Fisk. 2002. Relationship of SBSSymptoms and Ventilation System Type in Office Buildings.Lawrence Berkeley National Laboratory Report LBNL-50046

10. Seppanen, O. and W.J. Fisk. 2005 . A procedure to esti-mate the cost effectiveness of indoor environmental improvements in office work. Proceedings ofClima2005.

11. Olesen, B. W. 2005. Indoor environment-health-comfortand productivity. Proceedings Clima2005.

12. Spindler, H., L. Glicksman and L. Norford. 2002 . Thepotential for natural and hybrid cooling strategies to reducecooling energy consumption in the United States.ProceedingsofRoomVent2002.

13. Delsante,A. and TA . Vik. 2000. HybridVentilation: State-of-the-Art Review. International Fnerg y Agency Annex 35Hybrid Ventilation in New and Retrofitted Office Buildings.

Kurt W Roth, Ph.D., is associate principal, and John Di-eckmann, P .E., is principal in the HVAC and R efrigerationTechnology sector of TIAX Cambridge, Mass. James BrodrickPh.D., is a project manager. Building Technologies Program,


4/4

Documents

Natural and Hybrid Ventilation