UNIQUE REQUIREMENTS FOR HOSPITAL HVAC HVAC – Unique Requirements Implement appropriate HVAC specifications for clinical environments Tobias van Reenen tvreenen@csir.co.za

Context

Metrics and Definitions SI Units:- is the metric system; a coherent system of units of measurement built on seven base units. Appropriate derived units for South Africa: K S m kg cd mol A Unit Correct, (acceptable) Incorrect Flow rate (ventilation) m³/s, (l/s, ACH) m³/h, l/h, cfm Temperature Kelvin °K, (°C) °F Power Watt W, (kW) BTU, tonne, hp Mass Kilogram kg Stone, Pound Lbs Length Metre m Foot, “meter” Pressure Pascal Pa, (kPa) psi

Metrics and Definitions HVAC:- Heating Ventilation and Air Conditioning Ventilation:- The process of supplying air to or removing air from a space for the purpose of selectively controlling: -air contaminant levels (purity), -humidity - & sometimes temperature Air-Conditioning:- A process for controlling the: -Temperature, -Humidity and -Sometimes the Purity of the air.

Metrics and Definitions Ventilation rate:- Air Change Rate (Air changes per hour, ACH, AC/h, n) Supply Air:- Air forced into the space (m³/s, l/s) In/Exfiltration:- Air leaking into or out of a space (m³/s) Extract Air:- Air drawn from a space Exhaust Air:- Air exhausted to outside the HVAC system

Metrics and Definitions How to calculate “Air Changes per Hour”: Air Change Rate:- AC/h = (Q/V) Room Volume:- Vroom = L x B x H(mean) Where: Q = volumetric flow rate (m³/s *3600 = m³/h) V = room volume (m³)

Ventilation design philosophy Hierarchy of Design Solutions Fully mechanical ventilation Hybrid systems with climatic adaptability Fully passive ventilation Occupants/equipment NOT ADAPTABLE or tolerant of indoor conditions Occupants/equipment ADAPTABLE or tolerant of indoor conditions % Occupied areas

Ventilation design philosophy Planning for passive ventilation, heating and cooling: Layout and zoning for passive design responses Specialist areas (ICU, Surgery, CSSD) = Fully Mechanical Intermediate areas (Trauma, food services) = Hybrid General areas (Wards, waiting and public areas) = Mostly Passive

Ventilation System Types (Spot Test) Air Conditioning Ventilation Poor AIC Good AIC

STANDARDS AND REGULATIONS WHO RECOMMENDS: 60 litres per second per patient in medium risk settings (congregate areas) or 80 litres per second per patient for high risk areas ACH=12 𝑽 𝒓𝒐𝒐𝒎 =3×3×2.7𝑚 =24.3𝑚³ ∴𝑄=12×24.3 =81 𝑙/𝑠← Source: WHO policy on TB Infection Control; Reducing transmission of TB in health-care facilities (WHO)

STANDARDS AND REGULATIONS WHY NOT JUST USE 12 AIR CHANGES PER HOUR? Equation for probability of airborne infection: Where: Pinfection = the probability of infection Cases = the number of infection cases Susceptibles = number of susceptible individuals I = number of infector individuals p = pulmonary ventilation rate of a person (m³/hour) q = quanta generation rate (1/hr) t = exposure time (hr) Qoa = room ventilation rate with clean air (m³/hour) =1− 𝑒 −𝐼𝑞𝑝𝑡 𝑄 𝑜𝑎 𝑃 𝑖𝑛𝑓 = 𝑛𝑒𝑤 𝑐𝑎𝑠𝑒𝑠 𝑠𝑢𝑠𝑐𝑒𝑝𝑡𝑖𝑏𝑙𝑒𝑠 Source: Riley et al., 1978

STANDARDS AND REGULATIONS Probability of infection : P = D/S Where: D = number of infections arising from exposure S = number of susceptible exposure cases From: 𝑃= 1−𝑒 −µ ∴𝐷=𝑆∙(1− 𝑒 −𝐼𝑞𝑝𝑡 𝑄 𝑜𝑎 ) Source: Riley et al., 1978

STANDARDS AND REGULATIONS Source: Riley et al., 1978

STANDARDS AND REGULATIONS Source: Riley et al., 1978

STANDARDS AND REGULATIONS  Ventilation for IPC Patient/Staff Susceptibility to Infection** Low Moderate High Potential for cross infection* Fresh air (FA) supply >80L/s per person FA supply >80L/s per person Clean air supply >20AC/h and 80L/s per person Fresh air supply >60L/s per person FA supply >60L/s per person Clean air supply >60L/s per person and 20 AC/h No additional requirem ents Clean air supply >20 AC/h Source: Riley et al., 1978

Standards & Legislation ACH and litres/sec per person Outdoor Air - Demanded by National Building Regulations General Treatment = 12AC/h OA Waiting/ Assembly Areas = 10 AC/h OA Consulting = 12 AC/h OA Wards = 2 AC/h OA APR = 12 AC/h OA

Ducting

Ducting Causes constriction of duct cross-sectional area Avoid angled offsets Causes constriction of duct cross-sectional area Increases noise and energy usage Use two radiuses bends instead

Ducting Use medium radius soft or long radius hard bends Critical Areas (Fine filtered) Use medium radius soft or long radius hard bends Short radius bends can cause contaminant ingress into duct on inside of bend. Minimum throat radius = 100 mm SANS 1238:2005

Ducting Only final 1.5m Straight sections only No bends Minimise FLEXIBLE DUCTING as much as possible Only final 1.5m Straight sections only No bends Strap to rigid ducting Fire rating SANS 10177-3

Ducting Ducting to be specified according to SANS 1238:2005 Pressure testing according to: SANS 10173:2003 ANSI/SMACNA 016-2012 HVAC Air Duct Leakage Test Manual DW/144: Specification for Sheet Metal Ductwork (BESA, 2013a) (SANS 10173:2003 uses duct volume flow rate for % pressure leak tests while SNACNA and DW/144 use sheet metal area)

Ducting Internal Insulation SANS 1238 5.7.1 All ductwork, unless otherwise specified by the purchaser (see annex A), shall be acceptably internally insulated. PLEASE SPECIFY OTHERWISE!

FANS Fan discharge configuration

FANS Fan discharge configuration

FANS Fan discharge configuration

Exhaust Stack

Exhaust Stack Stack velocity > 13.5 m/s ACGIH®, Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition

Exhaust Stack: Location, location… ACGIH®, Industrial Ventilation: A Manual of Recommended Practice for Design, 28th Edition

Exhaust Stack Consider air bleed-in devices to increase velocity Stack velocity > 13.5 m/s prevents downwash Consider air bleed-in devices to increase velocity Stack discharge above roof and building recirculation wake boundaries Don’t use rain caps (Chinese hats) Causes blow-down

EXTRACTION FANS Passage / Waiting Area Passage / Waiting Area vs Outdoors Outdoors (View from top)

EXTRACTION FANS Empty Passage Internal Waiting Area vs Outdoors (View from top) (View from top) Outdoors

EXTRACTION FANS Recommended: 160-240 l/s (3ppl) Non-reversible Plug-in or hard wired Speed Controller Local Isolator

ROOM PRESSURE CASCADE Pressure cascades use excess fresh air Don’t assume ballpark oversupply rates Calculate infiltration/ exfiltration rates using orifice leakage rates

AIRHANDLING UNITS IUSS has a comprehensive AHU general specification for adoption Take note of correct arrangement of AHU and filtration components.

AIRHANDLING UNITS

ENERGY RECOVERY SYSTEMS Energy recovery arrangement for operating theatres

ENERGY RECOVERY SYSTEMS Energy recovery in airborne precaution areas is risky but not impossible

THEATRE ZONES General Theatres

THEATRE ZONES UDAF Theatres

IUSS www.iussonline.co.za Chartered Institute for Building Services Engineers (www.CIBSE.org) American Society for Heating Refrigeration and Air-conditioning Engineers (no ventilation?) (www.ASHRAE.org) South African Bureau of Standards (www.SABS.co.za) Filters and Filtration Handbook, Ken Sutherland 2008 (www.elsevier.com)

Tobias van Reenen (tvreenen@csir.co.za)