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Lecture 12: Building Technology and Strategies for Sustainability

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1 Lecture 12: Building Technology and Strategies for Sustainability
Notes: __________________________________________________________________ ________________________________________________________________________ Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2 Importance of this Lecture to the Simulation of Buildings
Energy consumption of buildings (heating, cooling, and lights) is a significant fraction of energy consumption worldwide Many energy sources are finite so we must slow down energy consumption as much as possible Simulation can help reduce energy consumption by modeling various strategies before they are built thus minimizing energy costs Knowledge of various techniques for “sustainable design” and what can be simulated is crucial

3 Purpose of this Lecture
Gain an understanding of: Some basic strategies for reducing the energy cost of buildings Various technology solutions that are currently available A few “green” capabilities of EnergyPlus

4 General Strategies for Reducing Building Heating and Cooling
Non-mechanical system approach Should always try to minimize heating and cooling requirements first Mechanical system efficiency important also Building Envelope: Insulation and/or Isolation Solar Strategies (Passive Heating) Alternate Cooling Strategies

5 Building Envelope: Insulation and/or Isolation
Goal: Attempt to minimize the adverse effects of the environment on a building Note: effect of environment is always changing Note: in some cases (e.g., temperate/mild climates and high internally loaded buildings), we may want to maximize impact of environment because it is beneficial (Climate Specific Strategies) Adjust volume to exterior area ratio Volume/living space desirable (maximize volume) Minimizing exterior surface area (usually) since it affects conduction, convection, and radiation

6 Building Envelope: Change Wall Construction
Reduce conduction by adding insulation Conduction (q=ADT/R)increase in R decreases q Note differences in R-values of various exterior surfaces and their relative areas Windows vs. walls: windows generally have a lower R-value Walls vs. roofs: building shape determines where to focus attention Consider the possibility of movable insulation for various surfaces Potentially reduce conduction by adding thermal mass “Interior” internal mass damps various short term effects, reducing or shifting conditioning needs “Exterior thermal mass delays impact of exterior temperature swings, may send some/much of effect back to exterior side Thermal mass discussed in more detail later in this lecture

7 Building Envelope: Change Exterior Boundary Conditions
Create a local “micro-climate” Air vs. ground temperature Ground can be a thermal mass and insulator Air temperature changes more extreme (harm or help?) Modification of air temperature using site water resources (evaporative cooling to reduce local air temperature) Wind exposure Use of vegetation as wind breaks in winter (evergreens on north side—location specific) Allow air movement for cooling? Note surroundings and impact on air movement around building Surface properties

8 Solar Radiation: Light and Heat
General concepts Use solar energy when heating required, avoid it when cooling is required Sun angles (particularly altitude) can vary with time of yearthis can work to our advantage Solar adds heat and light, but only during the day Orientation of openings (windows) critical to the success of the design; in general: Maximize southern exposure Minimize east/west exposure

9 Solar Radiation: Light and Heat (cont’d)
“Passive solar” increasingly important in design A definition: “a system that collects, stores, and redistributes solar energy without the use of fans, pumps, or complex controllers” (Lechner) Lower first costs than active solar systems because they are part of the building rather than an additional syste

10 Solar Radiation: Light and Heat (cont’d)
Using Direct Solar Gain (Windows) Utilize the “greenhouse effect” of windows which allow solar radiation to be transmitted but block most thermal radiation Benefit is maximized with south facing windows Low winter sun more directly impacts this direction High summer sun has little effect on south windows, can be easily shaded Potential for overheating during the day and underheating at night Thermal mass (interior) helps reduce this effect Need to exercise caution about thermal mass color and location relative to insulators such as carpet, furniture, etc. Direct gain easy to provide but there are limitsincreasing windows to increase gain also increases heat loss through windows (at night) or heat gain when undesirable (in summer)

11 Solar Radiation: Systems
Trombe Wall Systems (more details later in this lecture) Sunspaces (more details later in this lecture) Transpired Solar Collector Perforated metal wall covering Solar energy heats up wall Fan assists in drawing air through panels Panels reject heat to air, heating the air before introduction into building

12 Solar Radiation: Shading
Attempt to block solar radiation from impacting the building during cooling season Devices can be: Natural or constructed Fixed or variable (trees of differing types, movable shades, etc.) Opaque or somewhat transparent Indoor or outdoor Categories/characteristics Overhang—panels or louvers, can be rotated Fins/wings—panel(s), slanted or rotating “Eggcrate”—reduced depth combined overhang/fin, slanted or rotating Roller shades/awnings Trees/vines—free standing, trellis, “attached”

13 Solar Radiation: General Shading Guidelines
Exterior shading more efficient, but weather can take its toll on mechanized variable systems that are outdoors South windows Easiest to shade, overhangs very effective Fins may be needed for early morning, late afternoon Trees typically not much help to the south East/west windows Difficult to shade due to low altitude angles Fins (slanted) more effective or eggcrates Trees best on the east, west, southeast, and southwest (northern hemisphere) North windows Little shading required Desirable and even diffuse daylight Fins typically enough, if needed at all Skylights can be problematic Potential for leaks is greater Solar/light gain maximized at wrong time of year (summer) Can be more difficult to shade Other orientations may require combination solutions

14 Alternate Cooling Techniques: Air Movement
Ventilation Comfort ventilation: increase comfort by increasing air flow rates with the building Night purge ventilation: ventilate (naturally or mechanically) at night when the outside air temperature is presumably cooler than inside Technology Windows (various types of openings) Cool Towers (Down Draft Coolers) Thermal Chimney

15 Alternate Cooling Techniques: Roof Cooling
Basic concept: block solar radiation during the day, then take advantage of radiation to cold sky during the night (clouds will significantly decrease nighttime performance) Roof Pond Simply a layer of water contained on a flat roof or containers of water Daytime operation Pond is covered with insulation to deflect solar heat and reduce connection to outside environment Thermal mass of water soaks up heat from the interior space Nighttime operation Pond is left uncovered to reject heat from water to outside environment Heat is rejected via convection to surrounding air and to sky via radiation Cycle can be reversed in winter to provide a Trombe Wall type roofing system

16 Roof Pond: Drawbacks Added cost of system and extra maintenance
Movable insulation systems are typically not very successful Concerns about leaks

17 Alternate Cooling Techniques: Roof Radiator
Similar in concept to roof pond, but replaces water and movable insulation with a metal deck that is elevated above the roof Can use interior movable insulation with a “closed” deck Can be fan assisted with an “open” deck Can be used as a heating system in winter if solar energy is trapped between metal deck and roof Hot air is then circulated to interior spaces Drawbacks Added costs of roof deck Reliability/longevity of movable insulation

18 Roof Radiator: Cooling Operation
Daytime operation Metal panel reflects a portion of the solar radiation Insulation blocks heat transfer to building interior Or ventilation air reduces heat transfer from roof deck to actual roof Nighttime operation Roof radiates heat to sky Roof temperature may be low enough to actually cool outside air even further

19 Earth Coupling: Direct Earth Coupling
Underground or berms Ground temperatures can be lower than outside air, making this a good heat sink Concerns about winter may require insulation of ground and/or building surfaces in contact with ground Potential moisture problems

20 Earth Coupling: Indirect Earth Coupling
Buried supply air tubes Inlet air diverted through pipes that are buried Air is cooled by the cooler ground, providing some free cooling Pipes must be buried significantly deep Maintenance and moisture issues Ground “micro-climate” change using evaporation Cool the ground surrounding a building using evaporation Ground connected buildings Elevated buildings

21 EnergyPlus Modeling Capabilities
Thermal Mass Trombe Wall Sunspaces Movable/transparent insulation

22 Thermal Mass/Energy Storage within Buildings: Theory
Storage energy (heat) within building elements (exterior or interior) for use or release at a later time/date (analogy of a sponge or a rechargeable battery) Building materials store heat as “internal energy” Thermal mass a function of material properties (specific heat and density) as well as volume of materialhow much thermal mass is “enough”? Energy stored in a building material will eventually be release—either to the interior or exterior depending on placement of mass, environmental conditions, etc.

23 Thermal Mass: Examples
Traditional Examples Dense building types with very thick walls Ice blocks from Lake Michigan More Modern Examples “Trombe Walls” Interior Water Walls or Containers Phase Change Materials

24 Thermal Mass: Seasonal Effects
Cooling Season Dampen the effect of outside temperature variations Shift time of highest cooling loads to the night hours (offices) Absorb excessive internal gains during daytime hours (usually combined with night ventilation strategies) Heating Season Store solar energy absorbed for use during the nighttime hours when temperatures are low and the sun is not visible Avoid potential overheating problems due to excessive direct solar gains Note: thermal mass effects will not show up in a winter design day run—must look at an annual simulation with actual weather data

25 Thermal Mass: Key Terms in EnergyPlus IDF
Material:Regular—specification of specific heat and density Construction—reference to a material layer definition Surface—reference to a construction definition

26 Trombe Walls: Theory Primarily a passive heating element used to delay the impact of solar radiation Intended to cooperate with direct gain through windows to provide heating via solar radiation during all parts of the day and night Most useful on south, southeast, and southwest facades

27 Trombe Walls: System components
Thermally massive wall (brick, concrete, stone, water) painted a dark color to absorb solar radiation Air gap Wall cover (transparent glass) to allow sun light to get through to the thermal mass and to block some of the heat loss to the outside environment

28 Open vs. Closed Trombe Walls
Open System Similar to a mini-sunspace where the air in the gap between the cover and the wall mass is allowed to circulate to an interior space More important if no visual link to the outside These have fallen out of favor (in US) due to difficulty in controlling the amount of exchange between the air gap and the attached space and due to the loss of delay factor (easier to combine wall with windows); also maintenance issues

29 Open vs. Closed Trombe Walls
Closed System Air gap between the wall mass and the cover is sealed Heat is trapped and absorbed better into the thermal mass

30 Trombe Walls: Performance
Best for heating when wall mass has both a high storage capacity and a high thermal conductivity High thermal conductivity increases heat gain/loss of overall wall assembly Wall cover should be as transparent as possible but also resistive Solar must be kept out of the Trombe wall in summer through use of: Shading devices Specialized transparent insulation materials Electrochromic or thermochromic glazing

31 Trombe Walls: Examples
Trombe walls are usually but not necessarily restricted to simple flat south-facing walls (compare Zion National Park Visitor’s Center to NREL Visitor’s Center) Photos courtesy of

32 Trombe Walls: Key Terms in EnergyPlus IDF
Material:WindowGlass—specification of window properties Construction—definition of wall and window constructions Surface—specification of wall and cover (separate) with wall defined as an “interzone partition Zone—definition of Trombe Wall air gap as a separate thermal zone Cover is specified as a window covering a fictitious exterior wall Trombe wall shows up in TWO zones (equal and opposite interzone partition) Zone definition must include syntax to use special Trombe wall coefficients

33 Trombe Walls: Example of Trombe wall syntax (Zone)
ZONE, Lounge, !- Zone Name 0.0, !- Zone North Axis (relative to Building) 10.0, !- Zone X Origin {m} 14.9, !- Zone Y Origin {m} 0.0, !- Zone Z Origin {m} 1, !- Zone Type 1, !- Zone Multiplier 4.0, !- Zone Ceiling Height {m} 0.0, !- Zone Volume {m**3} TrombeWall; !- Zone Inside Convection Algorithm

34 Sunspaces and Double Skinned Buildings
Sunspaces and double skinned buildings can also be modeled as separate zones Note that in EnergyPlus solar radiation will pass through one space and into another but that once it gets to the second zone it is assumed to be all “diffuse” Both sunspaces and double skinned buildings provide an extra buffer from the outside Sunspaces add potentially usable space For systems which exchange heat through air transport, definition of a MIXING or CROSS MIXING statement required (not very accurate)

35 Movable Insulation: Purpose
Apply insulating layer to exterior (or interior) of building that can be scheduled for various times of day or year Intended to trap heat inside a building or block heat from coming into a building during certain times Many applications, but in reality, most of these are not feasible due to complexity of the systems

36 Movable Insulation: Process
In EnergyPlus, movable insulation can be applied to the interior or exterior side of a surface (but not windows) Window insulation must be specified as window blinds Exterior insulation may be transparent

37 Movable Insulation: Syntax
Insulation type: must be keyword “Interior” or “Exterior” Surface name: surface that insulation will be applied to (link to a surface definition within the input file) Material name: composition/description of material layer that makes up the insulation (link to a material definition within the input file) Schedule: when the movable insulation is applied (link to a schedule definition within the input file)

38 Movable Insulation: Example
Example of IDD format and IDF: MovableInsulation, A1, \field Insulation Type ( Exterior or Interior ) A2, \field Surface Name (heat transfer surface to which insulation applied) A3, \field MaterialMovInsul- Name of the material used for movable insulation A4; \field SchedMovInsul-Schedule for movable insulation Schedule controls if insulation is present and acts as a multiplier on the R-value of the material Material layer can be transparent if exterior insulation MovableInsulation, Exterior, Zn001:Wall001, MovableInsulationMaterial, ON; MATERIAL:REGULAR-R,MovableInsulationMaterial,Rough,2.0,0.9,0.7,0.7;

39 Summary Careful attention to climate and building heating and cooling needs as well as knowledge of passive strategies can help significantly reduce the amount of energy consumed to condition a building EnergyPlus “green” building modeling capabilities: Thermal Mass Trombe Wall Sunspaces Movable/Transparent Insulation

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