Proposed Fan System Measures for NCC Section J, 2019

Transcription

1 Proposed Fan System Measures for NCC Section J, 2019 Existing NCC 2016 DTS fan measures why change? Proposed NCC 2019 fan measures component based approach 2019 compliance methodology Comparison between 2016 v 2019

2 Fans only, sorry pumps

3 Existing NCC 2016 fan measures AHU supply and return air fans W/m 2, indexed by heat load General mechanical fans >1000 l/s W/(l/s) Car park ventilation fans > 1000 l/s W/(l/s)

4 NCC 2016 fan measures - issues Not very stringent Tedious and cumbersome to calculate Unjustified separation at 500m2

5 NCC 2016 fan measures - limitations Limitations of W/m2 and target W/(l/s) approach System scale issues How do you apply a blanket stringency across so many different fan system configurations, lengths, and with varying degrees of components? Requires concessions and adjustments - Requires fan motor power adjustments and concessions for different system configurations and components undermines simplicity of the approach Stringency level issues How many different fan systems do you have to analyse to determine appropriate stringency levels? Difficult to perform cost-benefit analysis on

6 Review of overseas codes Overseas codes typically use a W/(l/s) approach with fan power concessions UK Part L fan motor power provisions

7 Back to First Principles The basic equation for determining fan energy is Power = flow rate x pressure drop fan efficiency Power Flow rate W L/s = pressure drop fan efficiency = pressure drop fan efficiency

8 System pressure drop Total pressure drop for a fan system is a combination of factors including; System physical size and duct lengths. These are largely predetermined by external factors such as building height and configuration, but also partially controllable by the designer. Duct velocities. These are fully controllable by the designer. Bends, fittings and other details of the duct layout. These are generally a compromise between good practice and space limitations. These are somewhat controllable by the design team as a whole, but not completely controllable by the mechanical designer. Components & equipment. Components within the flow path will be to a large extent a function of the system service requirements and are as a result essentially fixed for a given system functionality. Component and equipment pressure drops. For components within the flow path, the designer will have some discretion over the pressure drops though some items while having less control over others.

9 Component based approach Possible to undertake benefit cost analyses for individual components For example Choice of duct size is a function of fan energy cost vs cost of the duct Advantage of being cost optimised at a component level Universal across all fan systems Component selection typically occurs prior to consideration of total fan energy

10 Components Straight Ducts limiting pressure drop per metre length (Pa/m) Bends compulsory use of turning vanes Filters maximum face velocity (m/s) Coils maximum face velocity (m/s) Attenuators - maximum passage velocity (m/s) Determine the associated DTS pressure drop through each component

11 Benefit cost analysis General Methodology Determine appropriate base cases for each component Run a series of test cases which alter the component pressure drop, resultant fan energy, and cost Use benefit-cost analysis to determine point where benefit-cost ratio = 1.0 Apply to real world duct systems to validate stringency levels

12 Straight Ducts Maximum straight duct pressure drop per metre length (Pa/m) Nine base case duct sizes/areas - 150x150, 200x300, 400x300, 550x300, 650x300, 700x350, 925x475, 850x700, 850x900 Three annual usage levels hours/year, 2500 hours/year and 8,760 hours per year Ten base case pressure drops - 10 Pa/m, 7 Pa/m, 5 Pa/m, 4 Pa/m, 3 Pa/m, 2.5 Pa/m, 2.0 Pa/m, 1.5 Pa/m, 1.0 Pa/m, 0.5 Pa/m Two system speeds - constant speed and variable speed From a base case duct size increase duct size by 10% keeping volumetric flowrate and fan efficiency constant

13 Straight Ducts Recommended maximum pressure drops for straight duct (Pa/m) Maximum Pressure Drop (Pa/m) Constant Speed System Maximum Pressure Drop (Pa/m) Variable Speed System <2000 hours hours >5000 hours <2000 hours hours >5000 hours Benefit-cost analysis result Proposed Stringency values Underlined figures reflect good practice limits (AIRAH, CIBSE) rather than the benefit-cost ratio analysis result.

14 90⁰ elbows (rectangular) Compulsory use of turning vanes 90⁰ rectangular elbows have a pressure loss coefficient up to 20 times greater than those with turning vanes System Single Floor Multi-floor Façade Single Zone Turning vanes Pressure Drop (Pa) Annual energy Use (kwh) Construction Cost ($) No ,567 35,376 Yes ,798 35,569 No ,998 39,440 Yes ,961 39,832 No 547 2,475 6,014 Yes 469 2,122 6,076 Benefit/Cost Ratio Requirement for turning vanes in all 90⁰ rectangular elbows (single skin or better)

15 Filters & Coils Maximum allowable face velocity (m/s) Filters and coils typically account for 40-70% of the total system pressure drop in a fan system Five (5) cooling/heating coil configurations - 2 row, 4 row, 6 row, 8 row, 10 row Eight (8) filter classes (EN779) G4, M5, M6, F7, F8, F9, H13, H14 Four (4) face velocities 2.5m/s, 2.0m/s, 1.50m/s, 1.0m/s Two (2) system speeds constant speed and variable speed From a base case face velocity of 2.5m/s decrease by 0.5m/s increments down to minimum of 1.0m/s keeping volumetric flowrate and fan efficiency constant A bespoke construction cost was applied to each test case to determine a benefit/cost ratio

16 Filters & Coils Maximum allowable face velocity (m/s) Recommended max average face velocity through various coil and filter arrangements in a fan system Filter/coil arrangement in a fan system Coil only Filter only Coil(s) + 1 filter Coil(s) + 2 filters HEPA filter Max average face velocity (m/s) 2.50m/s 2.50m/s 2.50m/s 2.00m/s 1.50m/s No differentiation between fixed and constant speed systems as it is assumed all systems will have a degree of variable control by 2019 Provisions to not apply to proprietary equipment such as off the shelf FCU s, PAC units etc

17 Attenuators Maximum allowable passage velocity (m/s) Passage velocity is determined by dividing the average face velocity by the free area of the attenuator. Benefit of passage velocity is it allows a single velocity number to be used for multiple percentage open area attenuators Rectangular Type Three (3) lengths 600mm, 1500mm, 2400mm length Two (2) base case passage velocities = 26m/s and 20.8m/s (10.0m/s and 8.0m/s face velocity at 38.5% free area) Circular Type Circular type, 6 lengths 600mm, 900mm, 1150mm, 1500mm, 1800mm, 2400mm length Two (2) base case passage velocities = 15m/s and 11.8m/s (10.0m/s and 8.0m/s face velocity at 64.0% free area) From base case, the face velocity was decreased in 2.0m/s increments down to minimum of 2.0m/s keeping volumetric flowrate and fan efficiency constant.

18 Attenuators Maximum allowable passage velocity (m/s) Rectangular attenuator Maximum allowable passage velocity (m/s) 13.0m/s (Equates to 5m/s face 38% free area) Maximum passage velocity does not apply to circular type attenuators as a benefit cost ratio greater than 1.0 was not achieved. Primary reason is circular attenuators have a smaller pressure drop

19 Minimum fan efficiency Determine appropriate minimum fan efficiency targets Numerous sources of fan efficiency data E3 Equipment Energy Efficiency Consultation RIS (MEPS) Carbon Credits Methodology Determination 2015 (ERF) ASHRAE 90.1 Consultation with fan industry determined that the Carbon Credits Methodology provided the most suitable performance

20 Carbon Credits vs MEPS

21 Minimum fan efficiency Carbon Credits methodology identifies the following equation to determine minimum peak fan efficiency Ƞmin = (a x ln(p) b + N) / 100 Ƞmin is the minimum peak fan efficiency (%) P is the motor input power of the fan (kw) N is the minimum performance grade based on fan type a & b are regression coefficients

22 Minimum fan efficiency Carbon Credits Methodology minimum fan performance grade based on fan type Fan type High efficiency grade (N) Installation category A or C Installation category B or D Axial fan* Centrifugal forward-curved fan Centrifugal radial bladed fan Centrifugal backward-curved fan Mixed-flow fan * Axial fans used in AHUs or FCUs must comply with the minimum fan efficiency for a centrifugal forward-curved fan. Installation category A,B,C,D relates to fan inlet/outlet conditions

23 Minimum fan efficiency Peak efficiency vs design duty Fans to be selected at design duty within 85% of the minimum peak fan efficiency Ƞdes = 0.85 x (a x ln(p) b + N) / 100 Ƞdes is the minimum fan efficiency at design duty (%) P is the motor input power of the fan (kw) N is the minimum performance grade based on fan type a & b are regression coefficients

24 Compliance methods 1. W/(l/s) calc Designer selects all fan system components to achieve their minimum DTS requirement Designer calculates total system W/(l/s) based on stringency-based pressure drop and minimum fan efficiency. Compliance is demonstrated by showing that the designed system achieves at least as low a W/(l/s) figure as the stringency based figure. Determine W l/s = Pa eff Calculate Apply Each fan system will have its own specific W/(l/s) target as opposed to a one size fits all W/(l/s) target as used in other codes This method allows for a degree of flexibility for the designer whereby the DTS fan power W/(l/s) target is achieved even though some of the individual components may not achieve their specific DTS requirement.

25 Compliance methods 2. Component by component Designer selects all fan system components to achieve their minimum DTS requirement. Ducts Filters Coils Fan Efficiency etc.

26 2016 v 2019 Example. Apply borderline compliance under NCC 2016 and NCC 2019 for a typical fan system Scenario Fan Power (kw) Fan Power W/(l/s) Fan Power (W/m 2 ) Difference 2016 (base case) low hours % reduc 2019 medium hours % reduc 2019 high hours % reduc

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