BALANCING ENERGY EFFICIENCY & INDOOR THERMAL COMFORT

Transcription

1 BALANCING ENERGY EFFICIENCY & INDOOR THERMAL COMFORT Ashak Nathwani AM Adjunct Senior Lecturer

2 PRESENTATION THREE SESSIONS This presentation will be in three parts addressing how to achieve a balance between adoption of energy efficiency measures and maintenance of required Indoor Environmental Quality (IEQ) Part 1:- Outlining of the various HVAC systems and associated energy efficiencies - Q & A Part 2: secondly thermal comfort and what part clothing plays - Q & A Part 3: Balancing thermal comfort versus energy efficiency - Q & A

3 KEY OPERATIONAL DRIVER TYPICAL ENERGY PROFILE - WHOLE BUILDING Hea ng Ven la on & Air Condi oning Ligh ng Li s Misc 10% 5% 20% 65%

4 HVAC FUNDAMENTALS What are the key factors that contribute to determination of heat load to ascertain the capacity of AHU and Cooling / Heating capacities? Outdoor Conditions Temperature and Humidity Indoor Required Conditions Heat transmission through structure walls, roof, ground Heat transmission through glass radiant and conduction Heat Gain from People sensible and latent Heat Gain from Equipment & Lights Equipment heat gains Outside air heat gains sensible and latent Whilst all of the factors, especially orientation, structure, selection of glass, lights, etc help optimise design, there are items that have an impact on ongoing energy management such as variation in people loading and associated outside air requirements (as per code). 2

5 ZONING. INTERIOR & PERIMETER 100 M PERIMETER 4 M DEEP 50 M CORE 10 M 20 M N 5

6 HEAT GAIN BUILDING FABRIC FABRIC WALLS, ROOF & GROUND Roof, Walls, Ground Heat Gain - Conduction & Radiation Outdoor Indoor Area X Equivalent Temp difference* X U value** Dependant on mass and building orientation ** Depends on structural elements and finishes Note: Insulation has a major impact 3

7 HEAT GAIN - GLASS The total solar transmitted radiation through a glazed surface; Q (watts) = (transmitted direct radiation x sunlit area of glass) + (transmitted sky radiation x total area of glass) x glass factors x shading factors x window factors. The type of glazing, fixing, framing, shading and incidence angle all affect boundary layer. Plus conduction similar to wall but with instantaneous temperature difference 17

8 HEAT GAIN Calculations. Lights, Generally Watts per Unit Area with LED it is around 5-8 watts per sq M Equipment Generally for office say 15 watts per sq M Lecture rooms say 3-5 watts per sq M Computer based Lecture Rooms say watts per sq M People Generally 10 sq M per person office Allow 2 sq M per person lecture theatre Sensible & Latent dependent on activity. Office 70 watts sensible and 60 watts latent Lecture theatre 60 watts sensible and 40 watts (reduced metabolism) Outside air 7.5 l/s per person Sensible & Latent 7.5 l/s X no. of people X X (O/A temp indoor temp) Sensible 7.5 l/s X no. of people X 3 X (abs humidity difference) - Latent 4

9 OUTSIDE AIR IMPACT Sensible heat (temperature change) Watts= x air volume (l/s) x temperature difference Latent heat (moisture change) Watts = 3 x air volume (l/s) x absolute humidity difference (gms moisture/kg dry air) Total heat (enthalpy change, temperature & moisture) Watts= 1.2 x air volume (l/s) x enthalpy difference (kj/kg of dry air) 27

10 DESIGN PROCESS PACKAGED UNITS VS CENTRAL PLANT CENTRAL PLANT AIR COOLED VERSUS WATER COOLED TYPE OF AIR HANDLING SYSTEMS: CONSTANT VOLUME VARIABLE AIR VOLUME DISPLACEMENT / UNDER FLOOR AIR DISTRIBUTION CHILLED BEAMS COMBINATION OF ABOVE ASSOCIATED ELECTRICAL & CONTROLS (BMS)

11 COMMON AC SYSTEMS Constant Volume NORTH Variable Air Volume (VAV) Chilled Beams W E S T E A S T Under Floor Air Distribution (UFAD) INTERIOR SOUTH

12 COMMON AIR CONDITIONG SYSTEMS VARIABLE AIR VOLUME (VAV). Conditioned air, supplied through ceiling diffusers, varies to meet zone load. CHILLED BEAMS (CB) Cold surface provides, at ceiling level, convective and radiant cooling. UNDER FLOOR AIR DISTRIBUTION (UFAD) Conditioned air is supplied through an under floor plenum Active Passive

13 temperature of a space without changing the temperature of the supply air. There are several variations on the traditional VAV system, including VAV boxes with fan heating coils. These VARIABLE variations were created to counteract AIR some VOLUME of the negative effect traditional VAV system, which will be discussed below. Variable air volume (VAV) is a type of heating, ventilating, and/ or air-conditioning (HVAC) system. The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 13 to 15 C supply air. Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. There are two primary advantages to VAV systems. The fan capacity control, especially with modern electronic variable speed drives, reduces the energy consumed by fans which can be substantial. Dehumidification is greater with VAV systems than it is with constant volume system which modulate the discharge air temperature to attain part load cooling capacity. VAV System Schematic VARABLE AIR VOLU The graphic above outlines the major components included in a variable air volume sys

14 16 VARABLE AIR VOLUME VARIABLE AIR VOLUME Variable Air Volume Cost $ / sq M Energy 4 to 5 stars NORTH VAV Unit - terminal With Reheat W E S T E A S T INTERIOR SOUTH

15 WHAT IS A CHILLED BEAM? A chilled beam is a type of convection (& radiant) HVAC system designed to heat or cool large buildings. Pipes of water are passed through a "beam" (a heat exchanger) either integrated into standard suspended ceiling systems or suspended a short distance from the ceiling of a room. 4

16 WHAT IS A PASSIVE BEAM? Approx 40% Radiant Approx 60% Convective 3

17 WHAT IS AN ACTIVE BEAM? 5

18 lected services to the beams within the factory and delivery of elements that house all of these services to the job site in a just-in-time fashion. Upon arrival, these devices are hung, attached in a linear fashion and modular connections facilitate the installation of the various service systems. Figure 12 below illustrates an active multi-service beam and the services that can be easily integrated with it. The core of this device is a DID302 active chilled beam which incorporates a primary air duct (and plenum) a chilled water coil as well as inlet (perforated face) and discharge (linear slot) air passages. The outer frame of the device is designed to provide mounting surfaces and provisions for other services which are installed at the factory prior to shipment to the job site. Some of the services that can be integrated include: 1. Lighting fixtures and controls 2. Speakers 3. Occupancy sensors 4. Smoke detectors Multi-service chilled beams can be provided as either active or passive versions. In cases where passive beams are used, a separate air distribution system must be provided. Oftentimes this air supply utilizes the cavity beneath a raised access flooring system as a supply plenum and is referred to as Underfloor Air Distribution. The ACTIVE service fixtures provided with BEAM multi-service beams are usually provided by others and issued tom the factory for mounting and connection where possible. Upon completion, the beams are shipped to the job site for mounting and final connection. Lighting provided with these beams may be direct, indirect or both. In all cases, the lighting system designer should be consulted to assure that the beam design and placement also provides sufficient space lighting. Fire protection designers should also be consulted in order to assure that the placement of the beams does not conflict with that of the fire sprinklers. Figure 12: Multi-service Chilled Beams 11 7

19 KEY DESIGN ISSUES: 1. Heat removal Temperature Control (Sensible Cooling) 2. Moisture Removal Humidity Control (Latent Cooling) 3. Ventilation Fresh Air (Control of Odours and Contaminants) Chilled beams only provide Sensible cooling, therefore a separate supply air system is required to address items 2 and 3 above. This can either be via a totally independent system or via the air supply to an Active beam. 18

20 MULTI-SERVICE ACTIVE BEAM 7

21 ACTIVE & PASSIVE BEAMS NORTH Passive Active W E S T E A S T INTERIOR SOUTH

22 ACTIVE & PASSIVE BEAMS Potential Benefits: Savings in riser space piping vs ducting Reductions in slab to slab heights Good Image + Lower operating energy costs Points to consider High capital cost and tenancy modification costs Water in ceiling space & need to ensure good humidity control Time lag to achieve zone conditions 23

23 To avoid condensation the supply temperature of the water must be higher than the dewpoint of the air. Chilled beam systems usually operate with chilled water flow and return temperatures of 15 to 18 Deg C Active control of Humidity within the space is required Uncontrolled outside air needs to be minimised (Infiltration) KEY DESIGN ISSUES 17

24 UNDER FLOOR AIR DISTRIBUTION

25 UNDER FLOOR AIR DISTRIBUTION Displacement System Micro-Climate

26 UNDER FLOOR AIR DISTRIBUTION Displacement System - RSH < 30W/m 2 - Supply air > 20 C - S/R Air < 7 C - Displacement diffusers - <14 L/s per diffuser Micro-Climate - RSH < 80W/m 2 - Supply air > 17 C - S/R Air < 10 C - Induction diffusers - <50 L/s per diffuser

27 UNDER FLOOR AIR DISTRIBUTION NORTH UFAD outlet Approx 50 l/s W E S T E A S T INTERIOR SOUTH

28 UNDER FLOOR AIR DISTRIBUTION

29 DISPLACEMENT VENTILATION

30 DISPLACEMENT VENTILATION Displacement Ventilation Concept Typical Airflow Patterns

31 TEMPERATURE GRADIENT Typical Temperature Gradient

32 OVERHEAD AIR DISTRIBUTION

33 UNDER FLOOR AIR DISTRIBUTION

34 UNDER FLOOR AIR DISTRIBUTION

35 UNDER FLOOR AIR DISTRIBUTION

36 COMPARATIVE ANALYSIS BUILDING MODEL DESCRIPTION A hypothetical building model (similar to the reference building type A used for the National Construction Code, Section-J. The general arrangement of the building model is described below: square floor plate, 30m on all sides gfa / floor = 900 sq m oriented to cardinal directions greenfield site (no shading from adjacent buildings) 10 levels (ground plus 9 levels), plus an unconditioned basement floor a floor-to-floor height of 4.0 m, ceiling at 2.7m 2m high vision glazing at 700mm sill height (fac ade WWR = 50%) high performance glazing systems, SHGC=0.3 and U=3.4 W/m2-K external walls modelled to be R mm concrete roof construction insulated to R mm thick concrete floors 36

37 ceiling below non-conditioned space insulated to R1.35 exposed floors modelled as uninsulated slab 200mm thick concrete floors TEST CASE Figure 1: 3D visulation of the building with superimposition of annual sunpath for Sydney

38 Figure 2: Zoning for typical floors; the zones are separated by virtual walls, ie., heat transfer boundaries, typically used in HVAC design for open plan offices PARAMETERS Table 2: Internal loads Internal Load Occupancy density 1 per 10 m 2 as per PCA Guide (2012) Standard office occupancy Occupant load of 130 watts per person (55W latent/ 75W sensible) Lighting load: 8 watts per m 2 (this is 1 W/m2 less than current NCC Section-J, but about 2 W/m2 higher than most current designs) Equipment load: 15 watts per m 2 (as per current NCC Section-J allowance for modelling) Schedules Occupancy schedules: NABERS occupancy schedule, starting at 8am (at 15% occupancy) to 6pm HVAC schedule: 7am to 6pm (1 hour prior to occupancy) Lighting and equipment schedules in accordance with NABERS schedules for lighting and equipment Outside Air Rate Indoor Temperature 10 L/s per person as per AS without filtration for offices 22.5C +/- 1.5 (generally 21C for heating and 24C for cooling)

39 HYPOTHETICAL Figure 2: Zoning for typical floors; the zones are separated by virtual walls, ie., heat transfer boundaries, typically used in HVAC design for open plan offices Table 2: Internal loads

40 chiller efficiency (COP) at each time step. Each chiller has been modelled design coefficient of performance (COP) of 5.09 and with minimum part load ratio of 30%. Each chiller has been modelled with a dedicated chilled water pump. The pumping arrangement is set as constant volume primary flow with a 250 kpa head. CENTRAL PLANT - CHILLERS Figure 3: HVAC plant chilled water (CHW) loop

41 The chilled water plant for the UFAD configuration runs at an 8/14C split, since the AHU maintain a supply of 19C from the underfloor plenum. Realistic plenum constructions h modelled, and the AHU supply is required to be set to be 2C lower (about 17C) to comp the heat gain from underfloor plenums. COOLING TOWERS HEAT REJECTION PLANT Figure 4: HVAC plant heat rejection or condenser water (CW) loop

42 Cooling tower sizing is based on a 29.5C/35C loop split HEATING HOT WATER PLANT BOILER Figure 5: HVAC plant heating hot water (HHW) loop The heating hot water loop has been modelled to be a single natural gas fired non-condensin

43 RESULTS NOTES: ALL STANDARD VERSIONS OF HVAC SYSTEMS WEATHER DATA SYSDNEY BASED ON GOOD COMFORT CONDITIONS

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45 INDOOR THERMAL COMFORT Ashak Nathwani AM Adjunct Senior Lecturer

46 Indoor Thermal Environment - Temperature Air - Temperature Radiant - Air Velocity - Humidity Air Quality - Particulates, -(Filtration) - O2, CO2, VOC, etc Lighting - Day (glare) - Ceiling - Task Noise Audio & Acoustics KEY COMFORT VECTORS 46

47 THERMAL BALANCE FOR HUMAN BODY 47

48 WHAT IS THERMAL COMFORT? Thermal Comfort attained when total heat produced by metabolism equals the heat lost from the body, for a given level of clothing. The Comfort Balance Heat In Heat Out 48

49 PREDICTED MEAN VOTE (PMV) PMV-index (Predicted Mean Vote) is the subjective of the environment in a group of people, based on: - Temperature (Air and Mean Radiant). Humidity, Air Flow, Clothing ( Clo value) and Activity ( Met Value) 49

50 Predicted Mean Vote Scale 6

51 METABOLIC RATE 0.8 Met Energy released by metabolism depends on muscular activity. 8 Met Metabolism is measured in Met (1 Met=58.15 W/m 2 body surface). Body surface for normal adult is 1.7 m 2. 1 Met A sitting person in thermal comfort will have a heat loss of 100 W. Average activity level for the last hour should be used when evaluating metabolic rate, due to body s heat capacity. 4 Met

52 As per ISO 7730 & ASHRAE Standard 55 CALCULATION OF CLO VALUE (CLO)

53 WHO IS LAURA? Body Segment Text Area (m2) 1 L. foot R. foot L. foreleg R. foreleg L. front thigh R. front thigh L. back thigh R. back thigh Pelvis Backside Head Crown L. hand R. hand L. forearm R. forearm L. upperarm R. upperarm Chest left Chest right Back left Back right 0.07 Total 1.57

54 THERMAL MANIKIN LAURA - SKIRT & SHIRT File: Manikin skirt and short sleeve shirt standing.csv Manikin # Interval (sec) 60 Time Date time Temp Power Clo 21/09/ :

55 Predicted Mean Vote Scale - +3 Hot - +2 Warm - +1 Slightly warm - +0 Neutral Slightly cool - -2 Cool - -3 Cold 55

56 PRACTICAL RELATIONSHIPS AS PER ISO 7730 PPD (Predicted Percentage of Dissatisfied) quantifies the expected percentage of dissatisfied people in a given thermal environment. Fanger concluded in his studies that the variation of PMV index can be approximated by an analytic expression that corresponds to a curve, thus: 56

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58 BALANCING ENERGY EFFICIENCY & INDOOR THERMAL COMFORT Ashak Nathwani AM Adjunct Senior Lecturer

59 History Indoor Environment Quality (IEQ) LAB Next Generation with Ultimate Flexibility

60 UNIQUE EXPERIMENT C1 = C2 = 25 sq m - Both set up as Interior Zones of a typical commercial office Indoor Lighting = 340 lux and Temp = 22.5 deg C

61 between chambers whilst still energised with the stability criteria remaining within a preset value of 0.1. EXPERIMENT METHODOLOGY This procedure and sequence of movements between the chambers is schematically represented in figure 12 below: Figure 10. Chambers 1 & 2 Experiment Procedure 4.5 Measurements

62 LAURA as a subject

63 FEEDBACK & DATA GATHERING

64 PHYSICAL MEASUREMENTS WALL SENSORS Temp & 1.7 M 1.1 M 0.6 M 0.1 M ZONE SENSORS Air Velocity 1.1 M Air Velocity 0.1 M ZONE SENSORS Temp 1.1 M Temp 0.1 M Globe 0.6 M Fig.. Physical Measurements Examples Skin Temperature Measurement

65 PCB UFAD VAV RESULTS Head Crown Chest Le: Chest Right Backside L Upperarm R Upperarm L Forearm R Forearm L Hand R Hand Teq Deg C Back Le: Back Right Pelvis L. front thigh R. front thigh L.back thigh R. back thigh L Foreleg R. foreleg L Foot R Foot Teq Profil Clo value = 0.36 uncovered legs

66 Fig 11. T 0 eq C Profile With Respect To Body Segments For the three HVAC systems Clo= 0.36 The mean t eq for the Crown and L Foreleg for the three air RESULTS conditioning systems: Analysis of the equivalent temperature differences for Crown minus the L Leg for the three AC systems: Table 3. AC System Analysis Laura Clothing Value= 0.36 Uncovered legs Fig 12 Teq Deg C Crown & L Foreleg Thermal Manikin - Clothing value = 0.36 Uncovered legs AC System N Mean Std Deviation Minimum Maximum PCB UFAD VAV Test Statistics a UFAD - PCB VAV PCB Z b b a. Asymp. Sig. (2-tailed) b. Wilcoxon Signed Ranks Test c. Based on negative ranks

67 OUTCOMES Energy intensities obtained using thermal modeling, show VAV and UFAD. achieving an efficiency advantage over Chilled Beams UFAD and VAV displayed similar vertical profiles (for a clo value of 0.36) with cooler feet (t eq = C & C, respectively) and warmer head (t eq = C & C, respectively).

68 OUTCOMES PCB demonstrated relatively warmer feet (t eq = C) and cooler head (t eq = C). Compared to UFAD and VAV the differences were significant. Outcomes from similar experiments with human subjects indicated thermal preferences for PCB was significant when compared to VAV and UFAD. Hence the adage cooler head and warmer feet offers better comfort.

69 TAKE HOME MESSAGES FOLLOW HVAC FUNDAMENTALS SENSIBLE & LATENT HEAT UNDERSTAND EQUIPMENT SELECTION UNDERSTAND DIFFERENT TYPES OF HVAC SYSTEMS HEAT TRANSFER UNDERSTAND COMFORT VECTORS RELATE COMFORT TO HVAC SYSTEMS RELATE EFFICIENCY TO HVAC SYSTEMS 69

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