5508BESG Services and Utilities Lecture 5

1. 5508BESGServices and Utilities Lecture 5 Ventilation and Air Conditioning

2. Ventilation & Indoor Air Quality Good Indoor Air Quality: air with no known contaminants at harmful concentrations. Ventilation: ‘the deliberate introduction of sufficient quantities of outside air into the room or building to dilute the concentration of pollution to one which is both acceptable and safe’.

3. Ventilation is required to: • Provide sufficient air to enable the occupants to be comfortable by diluting and removing contaminating pollutants generated by people, equipment, materials and processes. • Removing contaminants at source. • Providing air for combustion processes • Provide some cooling of spaces and building fabric. • Pressurising spaces to prevent flow of pollutants from one area to another

4. Legislation and standards • Building Regulations Part F provision of fresh air by ventilation. • Building Regulations Part J air for combustion appliances. • British Standards (e.g. B.S. 5720 & 5925 CR 1752 and others) give guidance • CIBSE Guide A and Applications Manual 10 (AM10) gives guidance • Health & Safety at Work Act

5. Common Pollutants • Pollution from human occupancy • Carbon Dioxide • Moisture Vapour • Odours • Bacteria • Tobacco smoke • Particulates (dusts, aerosols, carpets and furnishings). • Pollution from processes • Cooking, chemical processes, combustion processes, manufacturing processes.

6. Ventilation rates • Two main methods of determination • Air Change rate – for a particular type of room a rate at which the air in the room is changed per hour may be specified • Air supply rate – is a specified rate of fresh air needed to be supplied per occupant (or sometimes for a particular process) in litres per second • 10 litres per second per person is the usual rate for non smoking rooms

7. Some typical ventilation rates Note: All ventilation rates given here assume no smoking allowed. Some text books still give figures for rooms where smoking is permitted

8. Air change rates - example • An office 3m x 4m x 3m high requires 2 air changes/hour, what air flow rate is required? Flow rate = 3 x 4 x 3 x 2 = 72m3/hour = 72000 litres/hour = 72000/3600 = 20 litres/sec

9. Air change rates - example • A gym 30m x 20m x 6m high requires 12 air changes/hour, what air flow rate is required in litres/sec?

10. Air supply rates – example • An auditorium has a capacity of 200 persons, if the fresh air supply rate is 10 litres/second/person what is the required air supply rate? Flow rate = 10 x 200 = 2000 litres/second

11. Methods of ventilation Natural • Wind effect • Windows • Trickle ventilation • Stack effect Mechanical • Mechanical supply, natural extract • Mechanical extract, natural supply • Mixed mode

12. Natural ventilation – wind effect • Air enters through openings in the windward walls, and leaves through openings in the leeward walls. • Pressures are positive on windward side and negative on the leeward side. • The occurrence and change of wind pressures on building surfaces depend on: • wind speed and wind direction • location and surrounding environment • shape of the building

13. Representation of wind effect

14. Natural ventilation – stack effect • Air movement is due to temperature difference between indoors and out and flow of air is in the vertical direction • Temperature difference causes density differentials, and therefore pressure differences, that drive the air to move • Winter operation is: • indoor temperature higher than outdoor • the warmer air in building rises • the upward air movement produces negative indoor pressure at the bottom • positive indoor pressure created at the top • warmer air flows out of the building near the top • colder outside air replaces lost air entering the building near its base.

15. Representation of stack effect Winter Summer

16. Low level inlet vents Roof exhaust terminal

17. Flow rates via Natural Ventilation Affected by: • Difference between inside and outside (air) temperature. • local wind speeds and pressure differences • location, size and nature of openings (infiltration and purpose provided openings) • nature of flow paths within a space

18. Design to maximise the potential use of natural ventilation.

19. Natural ventilation example

20. Limitations for natural ventilation • Weather dependent and therefore unreliable – there is no way of specifying what the ventilation rate is going to be on any particular day • Difficult to control and regulate • Generally only suited to rooms with an external wall or roof • Difficult to create high ventilation rates without causing draughts • Difficult to heat or to filter outside air. • Heat is not easily recovered from air leaving the building and therefore constitutes a heat loss in winter

21. Mechanical ventilation • Natural ventilation cannot be relied upon to always provide enough fresh air to meet requirements. • Also more control can be obtained by using fans to supply air to a space or to remove contaminated air from a space. • Some mechanical ventilation systems use fans for both supplying and extracting air, thus mechanical ventilation systems may be classified as follows: • 1. Supply system • 2. Extract system • 3. Balanced system

22. Mechanical supply, natural extract Fresh air supplied to space from outside, air is exhausted naturally through doors, windows etc. It is often advantageous to temper (heat) the incoming air to avoid cold draughts in winter. (Cooling is also possible but condensation can be a problem)

23. Mechanical supply, natural extract • Air can be heated to any required temperature prior to entering the room Air can be filtered before entering the building • Good control of temperature and volume • Good control of air distribution throughout the room • The air leaving the room naturally carries away heat energy which cannot easily be recovered • Air cannot normally be cooled due to likelihood of condensation

24. Natural supply, mechanical extract The principal function of an extract ventilation system is the removal of an unwanted contaminant, whether it is solid, gaseous or thermal. In this system air is extracted from the space and replaced by fresh air, which can come from outside or from a neighbouring space.

25. Natural supply, mechanical extract • Localised contamination can be removed at source. • Steam, smells, heat etc. can be removed • Heat energy can be recovered using suitable devices or re-circulating a proportion of the air • Waste materials can be recovered or removed from the exhaust air • Creates a negative pressure, air leakage is inwards. • Ideal for dirty industrial processes, kitchens and toilets (note that toilet systems must be separate and cannot be combined with other vent systems in a building).

26. Toilet ventilation Male WC Female WC Service duct Fresh air enters via transfer grilles from neighbouring area. Extract ductwork at high level Extract grille Extract grille Ventilation riser

27. Toilet ventilation – with crosstalk attenuation Male WC Female WC Service duct Fresh air enters via transfer grilles from neighbouring area. Extract ductwork at high level Offset connections helps to attenuate crosstalk. Extract grille Extract grille Ventilation riser

28. Natural supply, mechanical extract • Kitchens, both domestic and commercial are often ventilated in this way

29. Specialist Applications • Laboratory Fume Cupboards and biological safety cabinets. • Welding fumes. • Dust extraction. These usually require a supply of “make-up” air when in operation.

30. Balanced system - Mechanical supply & extract • System is a combination of the previous two and has the advantages of both systems without the disadvantages of either • System provides the most effective and controllable ventilation system but is the most expensive to install and requires the most space • Combined system can provide neutral pressurisation • Alternatively it can provide negative pressurisation by having the extract rate exceed the supply by 20% and vice-versa to obtain positive pressurisation.

31. Balanced system The amounts of fresh air in each section of ductwork are controlled by dampers, which can be set during commissioning so that the design quantity of air with the correct proportion of fresh air is supplied to the space. Recirculation is only allowed if the air has not been badly contaminated. In kitchens, toilets, smoke filled spaces, etc., where the air contains odours or contaminants all the extract air must be removed and no recirculationmay take place.

32. Balanced system – typical layout

33. Balanced system – typical detail

34. Balanced system • Filters are usually fitted in supply and balanced ventilation systems to remove any airborne particles in the fresh air intake duct. • A finer filter may be installed in a balanced ventilation system after the mix point to remove dust generated within the space. • The bag filters are for collecting fine particles of dust and are sometimes referred to as fine filters.

35. Displacement ventilation An air distribution system in which incoming air originates at floor level and rises to exhaust outlets at the ceiling. Incoming air is delivered to interior rooms by way of floor-level diffusers. This displaces upper air, which is exhausted through ceiling-level grilles.

36. Whole House Ventilation • Balanced systems are used in sustainable housing to recover the heat that would be lost by natural and local extract ventilation. Several manufacturers produce such systems.

37. Ventilation - summary • Ventilation needed to sustain human life and some processes • Minimum vent rates laid down in regulations and codes of practice • Vent systems can be natural or mechanical • Natural vent preferable as it uses little energy, but it is difficult to control • Mechanical vent can be effected by • Mechanical supply only, • Mechanical extract only • Balanced mechanical supply & extract • Displacement systems

38. Air Conditioning Air conditioning systems do essentially the same job as mechanical ventilation systems, but in addition air conditioning can cool a space and control its humidity.

39. What causes buildings to overheat? Internal heat gains • People • Lighting • Equipment

40. What causes buildings to overheat? External heat gains • Solar radiation on windows. • Solar radiation on opaque surfaces. • External air temperatures.

41. Determining cooling loads • Manual calculations and spreadsheets – eurgh!! • Rules of thumb: approximations based on case studies (e.g. BSRIA Rules of Thumb 2011) • Computer modelling: accurate, reliable, used for designing installations, predicting temperatures, annual energy requirements and carbon emissions.

42. Avoiding Air Conditioning • Can external heat gains be reduced? • Can internal heat gains be reduced? • Can natural ventilation & air movement be improved? • Will ‘passive’ cooling methods be sufficient?

43. Tell-tales when Air Conditioning is most likely to be unavoidable • High occupancy levels • High artificial lighting intensities e.g. display lighting • High equipment levels (e.g. IT suites and call centres) • South facing large un-shaded glazed areas. • Steam and water processes present (e.g. restaurants, kitchens) • Controlled conditions for specialist applications (e.g. museums)

44. To provide full air conditioning you need: • Source of heat – a boiler • Source of cooling - refrigeration plant. • Source of steam/water vapour to provide humidification • A medium to carry heat energy to or from the room- air, water or refrigerant. • A mechanism to remove moisture (dehumidification). • A supply of fresh air to provide ventilation All of which need space and use energy

45. Types of Air Conditioning – categorised by the medium used to transport energy • Centralised All Air. • Partially Centralised Air/Water • Partially Centralised Air/Refrigerant • Packaged Refrigeration systems

46. Centralised All Air

47. Centralised All Air Conditioning.

48. Centralised Air Conditioning. Features: • The air is heated or cooled in the central air handling unit. • Moisture is added or removed in the centralised all air unit. • The air is used to convey energy and provide ventilation (fresh air). • Air is supplied to the room via ductwork • A separate system is usually needed to extract the air.

49. Centralised All Air Conditioning • Provides good quality environmental control - air quality, cleanliness, temperature & humidity can all be controlled to high standard • Simple control strategies can achieve close control of controlled conditions • Can move from heating mode to cooling mode easily • Most plant is outside of the conditioned space, therefore ease of maintenance, less room noise, room pollution etc • Can provide free cooling relatively easily • Negative or positive pressurisation is easily achieved • Dedicated central plant space required for central plant (chiller, boiler, AHU, extract fans • Large space required for ductwork accommodation • Air flow rates and duct sizes tend to be large and can be difficult to accommodate if long runs are required or duct space is restricted

50. Partially Centralised Air/Water Systems