1. UNIQUE REQUIREMENTS FOR HOSPITAL HVAC
HVAC – Unique Requirements
Implement appropriate HVAC specifications for clinical environments
Tobias van Reenen

2. Context

3. 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

4. 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.

5. 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

6. 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)

7. 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

8. 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

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

10. 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)

11. 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

12. 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

13. STANDARDS AND REGULATIONS
Source: Riley et al., 1978

14. STANDARDS AND REGULATIONS
Source: Riley et al., 1978

15. 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

16. 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 = AC/h OA
Wards = 2 AC/h OA
APR = AC/h OA

17. Ducting

18. 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

19. 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

20. 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

21. Ducting
Ducting to be specified according to SANS 1238:2005
Pressure testing according to:
SANS 10173:2003
ANSI/SMACNA 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)

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

23. FANS
Fan discharge configuration

24. FANS
Fan discharge configuration

25. FANS
Fan discharge configuration

26. Exhaust Stack

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

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

29. 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

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

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

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

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

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

35. AIRHANDLING UNITS

36. ENERGY RECOVERY SYSTEMS
Energy recovery arrangement for operating theatres

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

38. THEATRE ZONES
General Theatres

39. THEATRE ZONES
UDAF Theatres

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

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