Load and Energy Calculations

Transcription

1 BBSE2008 Air Conditioning and Refrigeration Engineering Load and Energy Calculations Dr. Sam C. M. Hui Department of Mechanical Engineering The University of Hong Kong Jan 2012

2 Contents Basic Concepts Outdoor and Indoor Design Conditions Cooling Load Components Cooling Load Principles Heating Load Load & Energy Calculations Transfer Function Method Energy Estimation

3 Basic Concepts Heat transfer mechanism Conduction Convection Radiation Thermal properties of building materials Overall thermal transmittance (U-value) Thermal conductivity Thermal capacity (specific heat) Q = UA(Δt)

4 Four forms of heat transfer CONVECTION (Source: Food and Agriculture Organization of the United Nations,

5 Basic Concepts Heat transfer basic relationships (for air at sea level) (SI units) Sensible heat transfer rate: q sensible = 1.23 (Flow rate, L/s) (Δt) Latent heat transfer rate: q latent = 3010 (Flow rate, L/s) (Δw) Total heat transfer rate: q total = 1.2 (Flow rate, L/s) (Δh) q total = q sensible + q latent

6 Basic Concepts Thermal load The amount of heat that must be added or removed from the space to maintain the proper temperature in the space When thermal loads push conditions outside of the comfort range, HVAC systems are used to bring the thermal conditions back to comfort conditions

7 Basic Concepts Purpose of HVAC load estimation Calculate peak design loads (cooling/heating) Estimate likely plant/equipment capacity or size Specify the required airflow to individual spaces Provide info for HVAC design e.g. load profiles Form the basis for building energy analysis Cooling load is our main target Important for warm climates & summer design Affect building performance & its first cost

8 Basic Concepts General procedure for cooling load calculations 1. Obtain the characteristics of the building, building materials, components, etc. from building plans and specifications 2. Determine the building location, orientation, external shading (like adjacent buildings) 3. Obtain appropriate weather data and select outdoor design conditions 4. Select indoor design conditions (include permissible variations and control limits)

9 Basic Concepts General procedure for cooling load calculations (cont d) 5. Obtain a proposed schedule of lighting, occupants, internal equipment appliances and processes that would contribute to internal thermal load 6. Select the time of day and month for the cooling load calculation 7. Calculate the space cooling load at design conditions 8. Assess the cooling loads at several different time or a design day to find out the peak design load

10 Cooling load profiles

11 Basic Concepts A building survey will help us achieve a realistic estimate of thermal loads Orientation of the building Use of spaces Physical dimensions of spaces Ceiling height Columns and beams Construction materials Surrounding conditions Windows, doors, stairways

12 (Source: ASHRAE Handbook Fundamentals 2005)

13 Basic Concepts Key info for load estimation People (number or density, duration of occupancy, nature of activity) Lighting (W/m 2, type) Appliances (wattage, location, usage) Ventilation (criteria, requirements) Thermal storage (if any) Continuous or intermittent operation

14 Basic Concepts Typical HVAC load design process 1. Rough estimates of design loads & energy use Such as by rules of thumb & floor areas See Cooling Load Check Figures See references for some examples of databooks 2. Develop & assess more info (design criteria, building info, system info) Building layouts & plans are developed 3. Perform detailed load & energy calculations

15 Outdoor Design Conditions They are used to calculate design space loads Climatic design information General info: e.g. latitude, longitude, altitude, atmospheric pressure Outdoor design conditions include Derived from statistical analysis of weather data Typical data can be found in handbooks/databooks, such as ASHRAE Fundamentals Handbook

16 Outdoor Design Conditions Climatic design info from ASHRAE Previous data & method (before 1997) For Summer (Jun to Sep) & Winter (Dec, Jan, Feb) Based on 1%, 2.5% & 5% nos. hours of occurrence New method (ASHRAE Fundamentals 2001+): Based on annual percentiles and cumulative frequency of occurrence, e.g. 0.4%, 1%, 2% (of whole year) More info on coincident conditions Findings obtained from ASHRAE research projects Data can be found on a relevant CD-ROM

17 Outdoor Design Conditions Climatic design conditions (ASHRAE, 2009): Annual heating & humidif. design conditions Coldest month Heating dry-bulb (DB) temp. Humidification dew point (DP)/ mean coincident drybulb temp. (MCDB) and humidity ratio (HR) Coldest month wind speed (WS)/mean coincident drybulb temp. (MCDB) Mean coincident wind speed (MCWS) & prevailing coincident wind direction (PCWD) to 99.6% DB (Latest information from ASHRAE Handbook Fundamentals 2009)

18 Outdoor Design Conditions Climatic design conditions (ASHRAE, 2009): Cooling and dehumidification design conditions Hottest month and DB range Cooling DB/MCWB: Dry-bulb temp. (DB) + Mean coincident wet-bulb temp. (MCWB) Evaporation WB/MCDB: Web-bulb temp. (WB) + Mean coincident dry-bulb temp. (MCDB) MCWS/PCWD to 0.4% DB Dehumidification DP/MCDB and HR: Dew-point temp. (DP) + MDB + Humidity ratio (HR) Enthalpy/MCDB

19 Outdoor Design Conditions Climatic design conditions (ASHRAE, 2009): Extreme annual design conditions Monthly climatic design conditions Temperature, degree-days and degree-hours Monthly design DB and mean coincident WB Monthly design WB and mean coincident DB Mean daily temperature range Clear sky solar irradiance

20 Outdoor Design Conditions Other sources of climatic info: Joint frequency tables of psychrometric conditions Annual, monthly and hourly data Degree-days (cooling/heating) & climatic normals To classify climate characteristics Typical year data sets (1 year: 8,760 hours) For energy calculations & analysis

21 Recommended Outdoor Design Conditions for Hong Kong Location Hong Kong (latitude N, longitude E, elevation 33 m) Weather station Royal Observatory Hong Kong Summer months Winter months June to September (four hottest months), total 2928 hours December, January & February (three coldest months), total 2160 hours Design temperatures: For comfort HVAC (based on summer 2.5% or annualised 1% and winter 97.5% or annualised 99.3%) For critical processes (based on summer 1% or annualised 0.4% and winter 99% or annualised 99.6%) Summer Winter Summer Winter DDB / CWB 32.0 o C / 26.9 o C 9.5 o C / 6.7 o C 32.6 o C / 27.0 o C 8.2 o C / 6.0 o C CDB / DWB 31.0 o C / 27.5 o C 10.4 o C / 6.2 o C 31.3 o C / 27.8 o C 9.1 o C / 5.0 o C Note: 1. DDB is the design dry-bulb and CWB is the coincident wet-bulb temperature with it; DWB is the design wet-bulb and CDB is the coincident dry-bulb with it. 2. The design temperatures and daily ranges were determined based on hourly data for the 35-year period from 1960 to 1994; extreme temperatures were determined based on extreme values between and (Source: Research findings from Dr. Sam C M Hui)

22 Recommended Outdoor Design Conditions for Hong Kong (cont d) Extreme temperatures: Hottest month: July mean DBT = 28.6 o C absolute max. DBT = 36.1 o C Coldest month: January mean DBT = 15.7 o C absolute min. DBT = 0.0 o C mean daily max. DBT = 25.7 o C Diurnal range: Summer Winter Whole year - Mean DBT Daily range Wind data: Summer Winter Whole year - Wind direction 090 (East) 070 (N 70 E) 080 (N 80 E) - Wind speed 5.7 m/s 6.8 m/s 6.3 m/s mean daily min. DBT = 20.9 o C Note: 3. Wind data are the prevailing wind data based on the weather summary for the 30- year period Wind direction is the prevailing wind direction in degrees clockwise from north and the wind speed is the mean prevailing wind speed. (Source: Research findings from Dr. Sam C M Hui)

23 Indoor Design Conditions Basic design parameters: (for thermal comfort) Air temp. & air movement Typical: summer o C; winter o C Air velocity: summer < 0.25 m/s; winter < 0.15 m/s Relative humidity Summer: 40-50% (preferred), (tolerable) Winter: 25-30% (with humidifier); not specified (w/o humidifier) See also ASHRAE Standard 55 ASHRAE comfort zone

24 ASHRAE Comfort Zones (based on 2004 version of ASHRAE Standard 55)

25 Indoor Design Conditions Indoor air quality: (for health & well-being) Air contaminants e.g. particulates, VOC, radon, bioeffluents Outdoor ventilation rate provided ASHRAE Standard 62.1 Air cleanliness (e.g. for processing), air movement Other design parameters: Sound level (noise criteria) Pressure differential between the space & surroundings (e.g. +ve to prevent infiltration)

26 (Source: ASHRAE Handbook Fundamentals 2005) (NC = noise critera; RC = room criteria) * Remark: buildings in HK often have higher NC, say add 5-10 db (more noisy).

27 Cooling Load Components External 1. Heat gain through exterior walls and roofs 2. Solar heat gain through fenestrations (windows) 3. Conductive heat gain through fenestrations 4. Heat gain through partitions & interior doors Internal 1. People 2. Electric lights 3. Equipment and appliances

28 Cooling Load Components Infiltration Air leakage and moisture migration, e.g. flow of outdoor air into a building through cracks, unintentional openings, normal use of exterior doors for entrance System (HVAC) Outdoor ventilation air System heat gain: duct leakage & heat gain, reheat, fan & pump energy, energy recovery

29 Components of building cooling load External loads Internal loads + Ventilation load & system heat gains

30 Cooling Load Components Total cooling load Sensible cooling load + Latent cooling load = Σ(sensible items) + Σ(latent items) Which components have latent loads? Which only have sensible load? Why? Three major parts for load calculation External cooling load Internal cooling load Ventilation and infiltration air

31 Cooling Load Components Cooling load calculation method Example: CLTD/SCL/CLF method It is a one-step, simple calculation procedure developed by ASHRAE CLTD = cooling load temperature difference SCL = solar cooling load CLF = cooling load factor See ASHRAE Handbook Fundamentals for details Tables for CLTD, SCL and CLF

32 Cooling Load Components External Roofs, walls, and glass conduction q = U A(CLTD) U = U-value; A = area Solar load through glass q = A (SC) (SCL) SC = shading coefficient For unshaded area and shaded area Partitions, ceilings, floors q = U A(t adjacent - t inside )

33 Cooling Load Components Internal People q sensible = N (Sensible heat gain) (CLF) q latent = N (Latent heat gain) Lights q = Watt x F ul x F sa (CLF) F ul = lighting use factor; F sa = special allowance factor Appliances q sensible = q input x usage factors (CLF) q latent = q input x load factor (CLF)

34 Cooling Load Components Ventilation and infiltration air q sensible = 1.23 Q (t outside - t inside ) q latent = 3010 Q (w outside - w inside ) q total = 1.2 Q (h outside - h inside ) System heat gain Fan heat gain Duct heat gain and leakage Ceiling return air plenum

35 Schematic diagram of typical return air plenum (Source: ASHRAE Handbook Fundamentals 2005)

36 Cooling Load Principles Terminology: Space a volume w/o a partition, or a partitioned room, or group of rooms Room an enclosed space (a single load) Zone a space, or several rooms, or units of space having some sort of coincident loads or similar operating characteristics Thermal zoning

37 Cooling Load Principles Definitions Space heat gain: instantaneous rate of heat gain that enters into or is generated within a space Space cooling load: the rate at which heat must be removed from the space to maintain a constant space air temperature Space heat extraction rate: the actual rate of heat removal when the space air temp. may swing Cooling coil load: the rate at which energy is removed at a cooling coil serving the space

38 (Source: ASHRAE Handbook Fundamentals 2005) Conversion of heat gain into cooling load

39 Cooling Load Principles Instantaneous heat gain vs space cooling loads They are NOT the same Effect of heat storage Night shutdown period HVAC is switched off. What happens to the space? Cool-down or warm-up period When HVAC system begins to operate Need to cool or warm the building fabric Conditioning period Space air temperature within the limits

40 Thermal Storage Effect in Cooling Load from Lights (Source: ASHRAE Handbook Fundamentals 2005)

41 Cooling Load Principles Space load and equipment load Space heat gain (sensible, latent, total) Space cooling / heating load [at building] Space heat extraction rate Cooling / heating coil load [at air-side system] Refrigeration load [at the chiller plant] Instantaneous heat gain Convective heat Radiative heat (heat absorption)

42 Convective and radiative heat in a conditioned space (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

43 (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

44 (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

45 (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

46 (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

47 Cooling Load Principles Cooling load profiles Shows the variation of space cooling load Such as 24-hr cycle Useful for building operation & energy analysis What factors will affect load profiles? Peak load and block load Peak load = max. cooling load Block load = sum of zone loads at a specific time

48 Cooling load profiles Total cooling load (Source: D.G. Stephenson, 1968)

49 North West East South Block load and thermal zoning

50 Cooling loads due to windows at different orientations (Source: D.G. Stephenson, 1968)

51 Cooling Load Principles Cooling coil load consists of: Space cooling load (sensible & latent) Supply system heat gain (fan + air duct) Return system heat gain (plenum + fan + air duct) Load due to outdoor ventilation rates (or ventilation load) Do you know how to construct a summer air conditioning cycle on a psychrometric chart? See also notes in Psychrometrics

52 Typical summer air conditioning cycle Cooling coil load Ventilation load Return system heat gain Space cooling load Supply system heat gain (Source: Wang, S. K., Handbook of Air Conditioning and Refrigeration, 2nd ed.)

53 Cooling Load Principles Space cooling load Supply airflow (L/s) Sensible load (kw) 1.2 t To determine supply air flow rate & size of air system, ducts, terminals, diffusers It is a component of cooling coil load Infiltration heat gain is an instant. cooling load Cooling coil load To determine the size of cooling coil & refrigeration system Remember, ventilation load is a coil load

54 Heating Load Design heating load Max. heat energy required to maintain winter indoor design temp. Usually occurs before sunrise on the coldest days Include transmission losses & infiltration/ventilation Assumptions: All heating losses are instantaneous heating loads Credit for solar & internal heat gains is not included Latent heat often not considered (unless w/ humidifier) Thermal storage effect of building structure is ignored

55 Heating Load A simplified approach to evaluate worst-case conditions based on Design interior and exterior conditions Including infiltration and/or ventilation No solar effect (at night or on cloudy winter days) Before the presence of people, light, and appliances has an offsetting effect Also, a warm-up/safety allowance of 20-25% is fairly common

56 (Source: ASHRAE Handbook Fundamentals 2005)

57 Load & Energy Calculations From load estimation to energy calculations Only determine peak design loads is not enough Need to evaluate HVAC and building energy consumption To support design decisions (e.g. evaluate design options) To enhance system design and operation To compile with building energy code Energy calculations More complicated than design load estimation Form the basis of building energy and economic analysis

58 Load & Energy Calculations Load estimation and energy calculations Based on the same principles But, with different purposes & approaches Design (peak) load estimation Focus on maximum load or worst conditions For a particular hour or period (e.g. peak summer day) Energy calculations Focus on average or typical conditions On whole year (annual) performance or multiple years consumption May involve analysis of energy costs & life cycle costs

59 Load & Energy Calculations Tasks at different building design stages Conceptual design stage: Rules of thumb + check figures (rough estimation) Outline/Scheme design: Load estimation (approximation) Design evaluations (e.g. using simplified tools/models) Detailed design: Load calculations (complete) Energy calculations + building energy simulation

60 Load & Energy Calculations Basic considerations 1. Peak load calculations Evaluate max. load to size/select equipment 2. Energy analysis Calculate energy use and compare design options 3. Space cooling load Q = V ρ c p (t r t s ) To calculate supply air volume flow rate (V) and size the air system, ducts, terminals 4. Cooling coil s load To size cooling coil and refrigeration system

61 Load & Energy Calculations Basic considerations (cont d) Assumptions: Heat transfer equations are linear within a time interval (superposition principle holds) Total load = sum of individual ones Convective heat, latent heat & sensible heat gains from infiltration are all equal to cooling load instantaneously Main difference in various methods How to convert space radiative heat gains into space cooling loads

62 Different methods have different ways to convert space radiative heat gains into space cooling loads Conversion of heat gain into cooling load (Source: ASHRAE Handbook Fundamentals 2005)

63 Thermal Load Heat Gains/Losses Heat storage (Source: ASHRAE Handbook Fundamentals 2005)

64 q ko = convective flux into the wall, W/m 2 q ki = convective flux through the wall, W/m 2 T so = wall surface temperature outside, ºC T si = wall surface temperature outside, ºC Possible ways to model this process: 1. Numerical finite difference 2. Numerical finite element 3. Transform methods 4. Time series methods (Source: ASHRAE Handbook Fundamentals 2005) Wall conduction process

65 Load & Energy Calculations Common methods: Transfer function method (TFM) Cooling load temperature difference/cooling load factor (CLTD/CLF) method Total equivalent temp. differential/time averaging (TETD/TA) method Other existing methods: Finite difference method (FDM) CIBSE method (based on admittance)

66 Load & Energy Calculations Transfer Function Method (TFM) Laplace transform and z-transform of time series CLTD/CLF method A one-step simplification of TFM TETD/TA method Heat gains calculated from Fourier series solution of 1-dimensional transient heat conduction Average heat gains to current and successive hours according to thermal mass & experience

67 Basic concepts of TFM, CLTD/CLF and TETD/TA methods (Source: ASHRAE Handbook Fundamentals 2005)

68 (Source: ASHRAE Handbook Fundamentals 2005)

69 Load & Energy Calculations Other methods: Heat balance (HB) method The rigorous approach (mainly for research use) Requires solving of partial differential equations and often involves iteration Radiant time series (RTS) method A simplified method derived from HB procedure Finite difference/element method (FDM or FEM) Solve transient simultaneous heat & moisture transfer

70 Load & Energy Calculations Heat Balance (HB) Method Use heat balance equations to calculate: Surface-by-surface conductive, convective & radiative heat balance for each room surface Convective heat balance for the room air Calculation process Find the inside surface temperatures of building structures due to heat balance Calculate the sum of heat transfer from these surfaces and from internal loads

71 (Source: ASHRAE Handbook Fundamentals 2005)

72 Transfer Function Method Transfer Function Method (TFM) Most commonly adopted for energy calculations Three components: Conduction transfer function (CTF) Room transfer function (RTF) Space air transfer function (SATF) Implemented numerically using weighting factors Transfer function coefficients, to weight the importance of current & historical values of heat gain & cooling load on currently calculated loads

73 Input Transfer Function Output Transfer function (K) Polynominals of z-transform Y = Laplace transform of the output G = Laplace transform of the input or driving force When a continuous function f(t) is represented at regular intervals Δt and its magnitude are f(0), f(δ), f(2δ),, f(nδ), the Laplace transform is given by a polynominal called z-transform : φ(z) = f(0) + f(δ) z -1 + f(2δ) z f(nδ) z -n where Δ = time interval, hour z = e tδ v 0, v 1, v 2, & w 1, w 2, are weighting factors for the calculations

74 Three components of transfer function method (TFM) (Source: ASHRAE Handbook Fundamentals 2005)

75 Transfer Function Method Sol-air temperature (t e ) A fictitious outdoor air temperature that gives the rate of heat entering the outer surface of walls and roofs due to the combined effect of incident solar radiation, radiative heat exchange with the sky vault and surroundings, and convective heat exchange with the outdoor air Outdoor air temp Surface absorptance Surface emittance

76 Heat balance at a sunlit surface, heat flux is equal to: R t t h E A q s o o t ) ( Assume the heat flux can be expressed in terms of sol-air temp. (t e ) Thus, sol-air temperature is given by:

77 Transfer Function Method External walls and roofs: Sol-air temperature Ceiling, floors & partition wall: aj = adjacent r = room

78 Transfer Function Method Window glass Solar heat gain: Shading coefficient (SC) Solar heat gain factor (SHGF) Sunlit Conduction heat gain: U-value Shaded Sunlit Shaded

79 Transfer Function Method Internal heat gains People (sensible + latent) Lights Machine & appliances Infiltration (uncontrolled, via cracks/opening) If positive pressure is maintained in conditioned space, infiltration is normally assumed zero

80 Transfer Function Method Convert heat gain into cooling load Space sensible cooling load (from radiative): v 0, v 1, v 2, & w 1, w 2, are weighting factors Space sensible cooling load (from convective): Space latent cooling load:

81 Transfer Function Method Convert heat gain into cooling load (cont d) Heat extraction rate & space air temperature Cooling coil load (sensible & latent) Air mixture & air leaving the cooling coil Ventilation load

82 Energy Estimation Two categories Steady-state methods Degree-day method Variable base degree-day method Bin and modified bin methods Dynamic methods Using computer-based building energy simulation Try to capture dynamic response of the building Can be developed based on transfer function, heat balance or other methods

83 Energy Estimation Degree-day method A degree-day is the sum of the number of degrees that the average daily temperature (technically the average of the daily maximum and minimum) is above (for cooling) or below (for heating) a base temperature times the duration in days Heating degree-days (HDD) Cooling degree-days (CDD) Summed over a period or a year for indicating climate severity (effect of outdoor air on a building)

84 Heating degree-day: Cooling degree-day: + Only take the positive values t bal = base temperature (or balance point temperature) (e.g o C or 65 o F); Q load = Q gain + Q loss = 0 t o = outdoor temperature (e.g. average daily max./min.) * Degree-hours if summing over 24-hourly intervals Degree-day = Σ(degree-hours) + / 24

85 To determine the heating degree-day:

86 To determine the heating degree-day (cont d):

87 Correlation between energy consumption and degree days

88 Energy Estimation Variable base degree-day (VBDD) method Degree-day with variable reference temperatures To account for different building conditions and variation between daytime and nighttime First calculate the balance point temperature of a building and then the heating and cooling degree hours at that base temperature Require tedious calculations and detailed processing of hourly weather data at a complexity similar to hourly simulations. Therefore, does not seem warranted nowadays (why not just go for hourly simulation)

89 Energy Estimation Bin and modified bin methods Evolve from VBDD method Derive building annual heating/cooling loads by calculating its loads for a set of temperature bins Multiplying the calculated loads by nos. of hours represented by each bin (e.g , 20-22, o C) Totaling the sums to obtain the loads (cooling/heating energy) Original bin method: not account of solar/wind effects Modified bin method: account for solar/wind effects

90 Energy Estimation Dynamic simulation methods Usually hour-by-hour, for 8,760 hours (24 x 365) Energy calculation sequence: Space or building load [LOAD] Secondary equipment load (airside system) [SYSTEMS] Primary equipment energy requirement (e.g. chiller) [PLANT] Computer software Building energy simulation programs, e.g. Energy-10, DOE-2, TRACE 700, Carrier HAP

91 Weather data Building description Simulation tool (computer program) Simulation outputs - physical data - design parameters - energy consumption (MWh) - energy demands (kw) - environmental conditions

92 Energy Estimation Building energy simulation Analysis of energy performance of building using computer modelling and simulation techniques Many issues can be studied, such as: Thermal performance (e.g. bldg. fabric, glazing) Comfort and indoor environment Ventilation and infiltration Daylighting and overshadowing Energy consumption of building systems

93 Major elements of building energy simulation

94 Seven steps of simulation output (Source: equest Tutorial Manual) 6 7

95 Building energy simulation process Energy storage HVAC air systems HVAC water systems Thermal Zone Systems (air-side) Plant (waterside & refrig.) Energy input by appliance Energy input by HVAC air/water systems Energy input by HVAC plant

96 Software Applications Examples of load calculation software: Carmel Loadsoft 6.0 [AV L79] Commercial and industrial HVAC load calculation software based on ASHRAE 2001 Fundamentals radiant time series (RTS) method Carmel Residential 5.0 [AV R43] Residential and light commercial HVAC load calculation software based on ASHRAE 2001 Fundamentals residential algorithms

97 Software Applications Examples of load/energy calculation software: TRACE 700 TRACE = Trane Air Conditioning Economics Commercial programs from Trane Most widely used by engineers in USA Building load and energy analysis software Carrier E20-II HAP (hourly analysis program) LI1_DIV12_ETI495,00.html

98 Software Applications Examples of energy simulation software: Energy-10 A software tool that helps architects and engineers quickly identify the most cost-effective, energy-saving measures to take in designing a low-energy building Suitable for small commercial and residential buildings that are characterized by one, or two thermal zones (less than 10,000 ft 2 or 1,000 m 2 ) MIT Design Advisor (online tool)

99 ENERGY-10 Design Tool Example: Energy-10 ENERGY-10 ENERGY-10 focuses on the first phases (conceptual design) Phase Develop Brief Activity Develop reference case Develop low-energy case Rank order strategies Initial strategy selection Set performance goals Tool ENERGY-10 Pre-design Schematic Design Design Development Construction Documents Review goals Review strategies Set criteria, priorities Develop schemes Evaluate schemes Select scheme Confirm that component performances are as assumed Preliminary team meetings ENERGY-10 EnergyPlus or other HVAC simulation and tools

100 ENERGY-10 Design Tool Example: Energy-10 ENERGY-10 Creates two building descriptions based on five inputs and user-defined defaults. Location Building Use Floor area Number of stories HVAC system Gets you started quickly. For example: apply Reference Case Low Energy Case R-8.9 walls (4" steel stud) R-19.6 Walls (6" steel stud with 2" foam) R-19 roof R-38 roof No perimeter insulation R-10 perimeter insulation Conventional double windows Best low-e double windows Conventional lighting Efficient lights with daylight dimming Conventional HVAC High efficiency HVAC Conventional air-tightness Leakage reduced 75% Uniform window orientation Passive solar orientation Conventional HVAC controls Improved HVAC controls Conventional duct placement Ducts located inside, tightened

101 ENERGY-10 Design Tool Example: Energy-10 ENERGY ,000 m 2 office building ANNUAL ENERGY USE Reference Case Low-Energy Case 96.5 kwh / m² Heating Cooling Lights Other Total

102 ENERGY-10 Design Tool Example: Energy-10 ENERGY-10 RANKING OF ENERGY-EFFICIENT STRATEGIES Duct Leakage Glazing Insulation Ene rgy Efficie nt Lights HVAC Controls Air Leakage Control Shading Daylighting High Efficiency HVAC Economizer Cycle Thermal Mass Passive Solar Heating Net Present Value, 1000 $

103 ENERGY-10 Design Tool Example: Energy-10 ENERGY-10 Sample - Lower-Energy Case Energy, kwh Temperature,? -50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Hourly HVAC Energy Use by Month -20 Heating Cooling Inside T Outside T

104 References Air Conditioning and Refrigeration Engineering (Wang and Norton, 2000) Chapter 6 Load Calculations ASHRAE Handbook Fundamentals (2009 edition) Chapter 14 Climatic Design Information Chapter 15 Fenestration Chapter 17 Residential Cooling and Heating Load Calculations Chapter 18 Nonresidential Cooling and Heating Load Calculations

105 References Remarks: Load & Energy Calculations in ASHRAE Handbook Fundamentals The following previous cooling load calculations are described in earlier editions of the ASHRAE Handbook (1997 and 2001 versions) CLTD/SCL/CLF method TETD/TA method TFM method