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Large Buildings

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IntroductionWe’ll look at common features of commercial, industrial, and institutional buildings.We’ve already covered lighting, and we’ll spend next several weeks focusing on other energy-related aspects of large buildings: HVAC equipment, power and motors, boilers, steam...We’ll examine simplified ways to compute building energy usage and energy bills.We will focus on general energy aspects of large buildings plus HVAC systems.

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ASHRAE 90.1 and EPACTASHRAE Standard 90.1, "Energy Efficient Design of New Buildings Except Low- Rise Residential Buildings,” is a model energy code.Much of this standard is now incorporated into U.S. law governing minimum energy efficiency for new federal construction through the Energy Policy Act (EPACT) signed by President Bush in 1992, and is incorporated into the three building codes used in the U.S.EPACT is a huge, omnibus bill that covers many aspects of energy usage, e.g., buildings and alternative fueled vehicles.

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Principal Coverage of ASHRAE Standard 90.1

Electric powerLightingAuxiliary systems and equipmentBuilding envelopeHVAC systemsHVAC equipmentService water heating systems and equipmentEnergy management

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Electrical OverviewThe distribution, metering, transformation and direct conversion of electricity to mechanical power (motors) is covered.Power shall be distributed so that individual customers are independently metered and so that the main categories of power use for individual customers are capable of being independently metered.Transformer selection optimized with respect to energy and economics (if customer owned).

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Commercial Power Meter

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Electrical Systems (Cont’d)Electric motors must meet specific efficiency standards depending on their rated power.Motors shall not be excessively oversized (efficiency drops off significantly at part loads).Variable speed motors will be used where practical (better part-load efficiency).Although power factor is not specifically addressed Standard 90.1, achieving high PF makes good economic sense (and saves energy for the nation and utility, if not the customer).

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LightingLighting of interior and exterior spaces covered.90.1 prescribes lighting in W/ft2 (electric power for lighting per ft2 of space) for various activities, which encourages high efficacy.Methods of lighting control are specified to turn off unused lighting.

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Auxiliary Systems and Equipment

Sets standards for:Elevators and escalatorsFreeze protection systemsRetail food and restaurant refrigeration

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HVAC Systems OverviewSpecifies load calculations; allowable indoor design conditions, outdoor conditions, calcu-lation procedures, and sizing proceduresEncourages zone control (different zones main-tained at different conditions). "Why heat whole building when only one area is occupied?"Sets ventilation air distribution requirements.Temperature controls: zone controls are to be used, range at least from 55 to 85ºF, automatic set-back is to be used.

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HVAC Cont’dHumidity control requirements are established.Ventilation: specifies minimum ventilation rates for various activities- e.g., bars with smoking (60 cfm) vs. offices (20 cfm); economizing.Materials and construction: pipe and duct insulation, requirements and specifications for duct leakage tests, etc.Energy recovery: e.g., recover heat during ventilation with air-to-air heat exchanger.Completion requirements: testing and balancing.

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HVAC Equipment

ASHRAE 90.1 sets more stringent requirements for energy efficiency for a broad range of equipment.

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Service Water HeatingRequirements, e.g., stand-by losses and minimum efficiencies, for water heating and hot water storage equipment are specified.Piping and tank insulation standards are provided.Maximum hot water flow rates in public restrooms are specified. Flows can be higher if self-closing valves are used.Use of waste heat, solar energy and thermal energy storage are encouraged.

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Two Methods of ComplianceSystem component method: simply use equipment efficiencies and systems design techniques that meet 90.1 standards.Building energy cost budget method: prove that the system design and proposed equipment result in a building energy operating cost that is less than the maximum set by Standard 90.1 (for the buildings specified size, activities, etc.).The system component method is simpler and requires less engineering brainpower and creativity...

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Building Envelope Issues

In many respects similar to residential building envelope issues. Focus is on:• Floors• Roofs• Opaque walls• Windows

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Differences between Large Buildings and Residences

Compared to homes, the primary difference with larger buildings is additional complexities:• Multiple stories• Varied roof designs• Many more wall construction materials• Varied window types• Variety of possible building occupation

patterns: 8 hours/day, 6 hours/week, 24 hours/day, etc.

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Skin-Load-Dominated Buildings

Tall, ThinBuildings

Climate and wall sunshadingdetermine relative importance of heating and cooling.Internal heat generation is minimal.Natural ventilation is easily accomplished.Plentiful window daylighting for most spaces.

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Skin-Load-Dominated Buildings

Short, ThinBuildings

Climate, roof exposure and wall sunshading determine relative importance of heating and cooling.Internal heat generation is minimal.Natural ventilation is easily accomplished.Plentiful window daylighting for lower floor(s) and skylightingfor upper floor.

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Internal-Load-Dominated Buildings

Roof, wall important…, but:Lights, equipment, people in central core generate heat: A/C is needed year-round.Window side lighting is limited to perimeter.Opportunities in winter to heat perimeter with waste core heat, cool core with cold outside air.

Tall, Thick Buildings

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Internal-Load-Dominated Buildings

Uncovered atrium aids venti-lation but admits more sun load to top floors.For very tall buildings, window lighting reduced for lower floors.Translucent atrium cover reduces overall lighting diffuses more to lower floors.Covered atrium conserves heat (Yankeeland); creates surplus internal heat gain over skin heat loss (Dixieland, Sunbelt)

Tall, Thick Atrium Buildings

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Internal-Load-Dominated Buildings

Envelope dominated by roof, floor.Internal loads of core require cooling all the time.Skylighting and rooftop ventilation available for upper floor, but increase roof HVAC load.

Short, Thick Buildings

Can use surplus core heat for perimeter in winter, and cool core with outside cold air.

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Using the Envelope for HVAC

Use of roof for heating:

Water absorbs heat to store until cold night

Sunlight heats interior through roof windows

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Using the Envelope for HVAC

Use of walls for heating

Trombe walls: glass with heavy wall

behind. Stores heat in day. Air circulates

over it at night to heat house.

South windows for heating with covers to shade

summer sun

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Using the Envelope for HVAC

Use of roof for ventilation

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Using the Envelope for HVAC

Use of walls for ventilationDon’t forget plain old windows!

Trombe wall as summer exhaust

Winter fresh air preheating through mini-solar collector

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Using the Envelope for HVAC

Ventilation of hot air

Roof “pond” (summer cooling)

using the roof for cooling

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Using the Envelope for HVAC

Inexpensive, fixed shading

of glazing

Use of walls to reduce cooling load

Awning

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Using the Envelope for HVAC

Use of roof for day-lighting

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Using the Envelope for HVAC

Use of walls for daylighting

Light shelf