Chilled Ceilings / Beams Working Principles & Applications

Transcription

1 5 th International Conference on Energy Sustainable Energy Polices and Technologies October 2014 Chilled Ceilings / Beams Working Principles & Applications Francis W H Yik ATAL Building Services Engineering Ltd. 16 October

2 Contents Chilled Ceilings / Beams Working Principles & Application Introduction Operating principles Key advantages and concerns Application to buildings in Hong Kong Trial calculations Experience with pilot installations 2

3 Introduction 58% Overall Reduction in Energy Consumption Chilled ceilings or chilled beams are widely used in buildings designed for an energy use level below those of conventional buildings by 50% or more 3

4 Introduction Chilled ceiling / beam originated and are widely used in Europe 4

5 Introduction Chilled ceiling / beam are penetrating the US market 5

6 Introduction Chilled ceiling / beam projects in Beijing 6

7 Introduction Chilled ceiling / beam projects in Guangzhou PEARL RIVER TOWER 2.3 million sq ft 71 storeys, 310m 7

8 Introduction Chilled ceiling / beam projects in Hong Kong # Project Project Nature System installed Area (m 2 ) Year of Completion Owner/ User 1 HAECO CLK Building - Office Renovation Chilled Ceiling HAECO 2 Chinese University, meeting room Renovation Chilled Beam Chinese University 3 Wong & Ouyang BS Ltd. Office, Renovation Chilled Beam W&O BS Ltd. 4 Hang Seng Tower, 10 Floors Renovation Chilled Beam 10, Hang Seng Bank 5 Hang Seng Management College, Block D, 3/F 8/F (6 Floors) New Construction Chilled Ceiling 5, Hang Seng Management College 6 HSBC Data Centre at STTL 433, Shek Mun, Shatin, 7/F 10/F office New Construction Chilled Ceiling + Chilled Beam 9, HSBC 7 Hong Kong Science Park Phase 3, Conference Room New Construction Chilled Beam 80 in progress HK Science Park 8

9 Introduction What are the key concerns that hinder wider adoption of chilled ceilings / beams in buildings in Hong Kong? How can the perceived problems be resolved? 9

10 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Heat transfer by radiation, R Heat transfer by convection, C 10

11 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Conventional AC system Heat transfer by radiation, R SA Heat transfer by convection, C RA EA FA AHU Ch. W S&R 11

12 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Conventional AC system Heat transfer by radiation, R SA Actively controlling the indoor air temperature, t a Heat transfer by convection, C No active control over the temperatures of surfaces enclosing the space RA EA FA AHU Ch. W S&R 12

13 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Conventional AC system Heat transfer by radiation, R SA Actively controlling the indoor air temperature, t a Heat transfer by convection, C No active control over the temperatures of surfaces enclosing the space RA EA FA AHU t r = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed) Ch. W S&R 13

14 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Conventional AC system Heat transfer by radiation, R SA Actively controlling the indoor air temperature, t a Heat transfer by convection, C No active control over the temperatures of surfaces enclosing the space Operative temperature, t o, represents the combined RA EA effect of t a and t r AHU t r = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed) FA t o hrtr = h r + + hct h c a Ch. W S&R 14

15 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Conventional AC system Heat transfer by radiation, R SA Actively controlling the indoor air temperature, t a Heat transfer by convection, C No active control over the temperatures of surfaces enclosing the space Operative temperature, t o, represents the combined RA EA effect of t a and t r AHU t r = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed) FA t o hrtr = h r + + hct h c a Ch. W S&R 15

16 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Heat transfer by convection, C Heat transfer by radiation, R Lowering mean radiant temperature (t r ) allows indoor air temperature (t a ) to be raised without affecting operative temperature (t o ) and thus thermal comfort sensation of occupants SA RA Conventional AC system Actively controlling the indoor air temperature, t a No active control over the temperatures of surfaces enclosing the space Operative temperature, t o, represents the combined EA effect of t a and t r AHU t r = mean radiant temperature (a weighted mean value of temperatures of all surfaces to which the occupant is exposed) FA t o = hrt h r r + + hct h c a Ch. W S&R 16

17 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Chilled ceiling panels Heat transfer by radiation, R PA Ch. W S&R Heat transfer by convection, C DOAS or PA system RA EA OA PAU Ch. W S&R DOAS = Dedicated Outdoor Air System PA = Primary Air 17 17

18 Operating principles Comfort air-conditioning Heat exchange of human body with the environment Chilled ceiling panels Heat transfer by radiation, R PA Ch. W S&R Sensible heat only Sensible heat only Heat transfer by convection, C DOAS or PA system Sensible and latent heat RA EA OA PAU Ch. W S&R DOAS = Dedicated Outdoor Air System PA = Primary Air 18 18

19 Operating principles Chilled ceiling 19

20 Operating principles Chilled ceiling Where the cooling requirement exceeds the capacity limit of chilled ceiling panels (~80W/m 2 ), chilled beams may be used instead 20

21 Operating principles Chilled beam 21

22 Operating principles Chilled beam The cooling capacity of passive chilled beams can be up to W/m 2 (Based on their exposed face area clearance spaces needed between chilled beams) 22

23 Operating principles Chilled beam Active chilled beam 23

24 Operating principles Chilled beam Active chilled beam The cooling capacity of active chilled beams can be up to W/m 2 (Based on their exposed face area even greater clearance spaces needed between chilled beams) 24

25 Operating principles Key characteristics of a chilled ceiling or chilled beam system: There must be two systems operating in parallel: Chilled ceiling panels or chilled beams Which extract (only) sensible heat from the spaces A primary air (PA) system or dedicated outdoor air system (DOAS) Which supply ventilation air as well as remove ALL moisture gains (latent cooling loads) and a fraction of the sensible heat gains of the spaces 25

26 Key advantages and concerns Key advantages Radiant cooling by using chilled ceiling Enhances thermal comfort and Allows use of slightly higher indoor dry-bulb temperature set point ASHRAE Handbook, HVAC Systems and Equipment, 2008, Chapter 6 Panel Heating and Cooling Principal advantages of panel systems are the following: Because not only indoor air temperature but also mean radiant temperature can be controlled, total human thermal comfort may be better satisfied. Comfort levels can be better than those of other space-conditioning systems because thermal loads are satisfied directly and air motion in the space corresponds to required ventilation only. 26

27 Key advantages and concerns Key advantages Separation of dehumidification (solely by PA system) from sensible cooling (by both PA system and chilled ceiling / beams) allows: Air flow rate (V PA < V SA ), and thus fan power and noise, to be reduced (although fan power saving also achievable in VAV systems) Use of higher temperature chilled water for the chilled ceilings / beams, which helps save chiller energy use (low temp. Ch.W. still needed for PA system unless desiccant dehumidification is used) 27

28 Key advantages and concerns Key advantages Reduced ceiling space required for installation Reduced maintenance cost When controlled properly, will not promote the formation of condensate which can lead to bacterial and mould growth Do not require drain pans which require cleaning Do not contain fans or filters to maintain and require only simple periodic service including vacuuming of the dry coil 28

29 Key advantages and concerns Must ensure: The PA supply flow rate (V PA ) is sufficient, and the difference in moisture content between the indoor air and the PA supply (w r w s ) is large enough for the PA to offset the total moisture gain (M r ) of the room s r M = ρ V r a PA( wr ws ) w r w s t s t r 29

30 Key advantages and concerns Must ensure: The surface temperatures of the chilled ceilings / beams must be above the dew point temperature of the indoor air (t dpr ) M = ρ V r a PA( wr ws ) t dpr s r w r w s t s t r 30

31 Key advantages and concerns Must ensure: The total sensible cooling capacity of the chilled ceilings / beams (Q SCC/B ) is sufficient to offset the remainder of the room sensible load (with the sensible cooling effect of the PA discounted) Q SR = Design room sensible cooling load Q SPA = Sensible cooling capacity of PA Where Q SPA = ρ V a PA Cp a ( tr ts ) Required sensible cooling capacity of chilled ceilings / beams Q SCC/B >= Q SR Q SPA 31

32 Key advantages and concerns Key concerns Stagnant air flow and cold air dumping onto occupants Condensation risk Limited cooling capacity of chilled ceiling / beam modules Impact on whether CC/B can be used 32

33 Key advantages and concerns Key concerns Stagnant air flow and cold air dumping onto occupants Condensation risk Can be overcome by careful building and system design and operation Maintain at least 1m clear headroom between passive chilled beam and occupied zone (1.7m from finished floor level) Limited cooling capacity of chilled ceiling / beam modules Use active chilled beam Adequate selection and layout of chilled beams and/or diffusers for PA Raise PA supply flow rate if absolutely needed 33

34 Key advantages and concerns Key concerns Stagnant air flow and cold air dumping onto occupants Can be overcome by careful building and system design and operation Minimize moisture gains of spaces Condensation risk Limited cooling capacity of chilled ceiling / beam modules Ensure PA system has sufficient dehumidification capacity; if needed, use heat pipes or desiccant dehumidification Use an appropriate Ch.W supply temperature setting Monitor and control ceiling / beam surface temperature 34

35 Key advantages and concerns Key concerns Stagnant air flow and cold air dumping onto occupants Can be overcome by careful building and system design and operation Minimize envelope heat gains Condensation risk Limited cooling capacity of chilled ceiling / beam modules Use energy efficient lighting Use energy efficient appliances Use active chilled beams 35

36 Application to buildings in Hong Kong Trial calculations reference conditions (office building in HK) Design conditions Unit Value Design conditions Unit Value Design OA temperature, To oc 33.3 Design OA RH, RHo % 66 Design OA moisture content, wo kg/kg Design OA enthalpy, ho kj/kg Design RA temperature, Tr oc 25 Design RA RH, RHr % 55 Design RA dew point, Tdpr oc 15.4 Design RA moisture content, wr kg/kg Design RA enthalpy, hr kj/kg Room floor area (Interior Zone) m Room height m 3.2 Room volume m Lighting and app. power density W/m2 35 Lighting and appliances heat gain, Qsi kw Occupancy rate m2/p 9 No. of Occupants No Sensible heat gain per person W/p 75 Rad. Sen. heat gain from occupant % 60 Latent heat gain per person W/p 55 Moisture gain per person g/s-p Sensible load from occupants, Qsp kw Latent heat gain from occupants, Qlp kw Moisture gain from occupants, Mp kg/s FA requirement l/s-p 10 FA flow rate, Vfa m3/s Infiltration ACH ACH 0.1 Infiltration flow rate, Vinf m3/s Sensible load from infiltration, Qsinf kw Latent load from infiltration, Qlinf kw Moisture gain from infiltration, Minf kg/s

37 Application to buildings in Hong Kong Trial calculations cooling load intensity Design cooling load predictions for Model Office Building by BEEP Floor Space DSL DLL DTL Area DSL DLL DTL kw kw kw m2 W/m2 W/m2 W/m2 Typical North Typical West Typical East Typical South Typical Interior Typical SimTot

38 Application to buildings in Hong Kong Trial calculations cooling load intensity Design cooling load predictions for Model Office Building by BEEP Floor Space DSL DLL DTL Area DSL DLL DTL kw kw kw m2 W/m2 W/m2 W/m2 Typical North Typical West Typical East Typical South Typical Interior Typical SimTot Shared between chilled ceilings / beams and PA system By PA system 38

39 Application to buildings in Hong Kong Trial calculations PA flow rate PA Supply Flow Rate m3/s FA Flow Rate 25oC / 55% RH (tdpr 15.40oC) 24oC / 55% RH (tdpr 14.41oC) 25oC / 50% RH (tdpr 13.87oC) 24oC / 50% RH (tdpr 12.95oC) PA Supply Dew Point Temperature oc Indoor design temperature, relative humidity and dew point temperature 39

40 Application to buildings in Hong Kong Trial calculations PA flow rate PA Supply Flow Rate m3/s The higher the t dpr, the smaller the V pa The required PA supply flow rate (V pa ) is highly sensitive to the choices of the indoor air state (t dpr ) and the PA supply air state (t dps ) FA Flow Rate 25oC / 55% RH (tdpr 15.40oC) 24oC / 55% RH (tdpr 14.41oC) 25oC / 50% RH (tdpr 13.87oC) 24oC / 50% RH (tdpr 12.95oC) The lower the t dps, the smaller the V pa PA Supply Dew Point Temperature oc Indoor design temperature, relative humidity and dew point temperature 40

41 Application to buildings in Hong Kong Trial calculations PA flow rate 3 PA Supply Flow Rate m3/s Selected condition: Sensible cooling provided by PA = 18.13W/m 2 FA Flow Rate 25oC / 55% RH (tdpr 15.40oC) 24oC / 55% RH (tdpr 14.41oC) 25oC / 50% RH (tdpr 13.87oC) 24oC / 50% RH (tdpr 12.95oC) PA Supply Dew Point Temperature oc Indoor design temperature, relative humidity and dew point temperature 41

42 Application to buildings in Hong Kong Trial calculations Required chilled ceiling / beam cap. Floor Space DSL PA S Cap CC/B Cap W/m2 W/m2 W/m2 Typical North Typical West Typical East Typical South Typical Interior Chilled beams need to be used for the perimeter zones but chilled ceilings may be used for the interior zone 42

43 Application to buildings in Hong Kong Key design considerations Minimize sensible cooling load through Reducing external heat gains by improving thermal performance of building envelope Reducing internal heat gains by using energy efficient lighting and appliances Minimize latent cooling load through reducing ingress of humid air into airconditioned space by Improving air-tightness of building envelope Positive pressurization of air-conditioned space Use of anteroom (lobby with double-door) if needed 43

44 Application to buildings in Hong Kong Key design considerations Adequate selection of design indoor air state (an increase in RH by 5% can make a big difference) Adequate selection of design PA supply air state (the lower the moisture content in it the smaller the required PA supply flow rate), subject to the constraints of Temperature of chilled water supply to PAU (may use desiccant dehumidification) Minimum FA supply flow rate for air-conditioned spaces Adequate selection of temperature of chilled water supply to chilled ceilings / beams (at or slightly above dew point temperature of indoor air) 44

45 Experience with pilot installations Hui & Leung (2012) Study on chilled ceiling application in Hong Kong Simulation results: ~20% energy saving achievable Field study offices of an aircraft engineering company: Chilled ceiling in use since mid % of the occupants satisfied with thermal sensation, though 40% felt temperature sometimes too hot 51% felt air movement too low Findings similar for another field study (construction site office) 45

46 Experience with pilot installations 46

47 Experience with pilot installations 47

48 Experience with pilot installations 48

49 Experience with pilot installations 49

50 End of Presentation Thank you 50