designing high performance schools in new orleans
TRANSCRIPT
NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC
Gulf Coast Green
Ian Doebber
April 16, 2009
Designing High Performance Schools in New Orleans
NREL Building Technologies Program
NREL is a national lab for the US Department of Energy with a single mission to develop and promote renewable and energy efficiency technologies
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• Commercial & Residential Building Energy Efficiency
• Technical Assistance to DOE’s EnergySmart Schools Program
• Advanced Energy Design Guides
• Computer Simulation Tool Development
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Presentation Overview
• K-12 Advanced Energy Design Guide
• Rebuilding New Orleans Schools : Quick Start Schools
• High Performance Schools in Humid Climates
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K-12 Advanced Energy Design GuideGuidelines, based on climate zones, to help K-12 school owners and designers achieve 30%
energy savings over ASHRAE 90.1 – 1999
• Recommendations only, not a code
or standard
• Applies to new construction and
major renovation• Case studies showcase schools
nationwide that have achieved or
exceeded 30% energy savings
Focus of Recommendations
Building envelope– Fenestration– Wall/Roof Insulation
Lighting systems– Daylighting– Electrical lights
Heating, ventilation and air-conditioning (HVAC) systems– Building automation and controls– Outside air (OA) treatment
Service water heating (SWH)
Guide looks at integration of these systems – savings goal dependent on the interaction
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Where to get the K-12 AEDG?
www.ashrae.org/freeaedg
• 170,500 AEDGs
have been
downloaded or sold
• 13,000 AEDG-K-12
hard copies provided
to every school
district
Download a copy at no charge -or- Purchase a print copy
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Quick Start Schools
RFQsSchematic
DesignConstruction Documents
Construction 2009 Opening
Next 10 Years
~44 New Schools
>40 Major Renovations
LEED for Schools Silver : 30% Utility Savings over AHSRAE 90.1 - 2004
Kick Off Design Charrette – Guided based on the K-12 AEDG
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Quick Start Schools: Lighting Design
ZONE CATEGORYPROPOSED LPD
[W/ft2]
OFFICE 1.0
CONFERENCE ROOM 1.0
GENERAL CLASSROOM 1.2
COMPUTER CLASSROOM 1.2
ART CLASSROOM 1.3
SCIENCE LAB 1.4
MEDIA CENTER 1.1
LOBBY/PREFUNCTION 0.8
AUDITORIUM n/a
MUSIC/THEATER/DANCE 1.4
GYM (play area) 1.2
GYM (spectator area) 1.2
FITNESS CENTER 0.8
LOCKER ROOMS 0.6
KITCHEN 1.1
WALKIN FREEZER D 0.4
WALKIN COOLER D 0.4
SERVERY 1.2
DINING AREA 0.7
CORRIDOR 0.5
ASHRAE 90.1 – 2004
1.4 W/ft2
K-12 AEDG
1.1 W/ft2
Quick Start Schools
0.8 – 0.9 W/ft2
8% - 10% saving!!
Quick Start Schools: Daylighting Design
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From AEDG Classroom Daylighting Recommendations
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Quick Start Schools: Cooling Systems
OA Pre-Treatment Main System
Desiccant WheelWater Cooled
Magnetic BearingCentrifugal Chiller
Chilled Water
Enthalpy Wheels&
Packaged DX Units
Water CooledHigh EfficiencyScrew Chillers
Air CooledScrew Chillers
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Quick Start Schools: Savings
Percent Savings Annual Utility Savings*
30.5% $98,000 [$0.61/ft2]
35.1% $77,500 [$0.80/ft2]
26.2% $98,000 [$0.45/ft2]
*Based on Energy Model
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Quick Start Schools: Lesson Learned
Feedback to the next phase K-12 AEDG• More Aggressive Lighting Design• Classroom Daylighting (Solving Glare-More Flexibility)• Demand Controlled Ventilation (System or Zone)
• Insulation Levels (integrate with infiltration reduction)
Major Short Coming was FOCUSING how following the K-12 AEDG Recommendations REQUIRED a dedication to conquering Humidity otherwise forgo significant thermal comfort and energy performance
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High Performance in Humid Climates
Story of an Architect and Two Engineers…
Previous Success : LEED Platinum on a High Rise Office Building in Phoenix, AZ
Project Scope
100,000 ft2 K-5 Elementary School in New Orleans
Conceptual Design thru Construction Administration
LEED for Schools Silver
Minimum of 23% Utility Savings over ASHRAE 90.1-2004
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Designing within Silos
Architect Silo
Engineer 1 Silo
“Loads Based”
Engineer 2 Silo
“System Based”
Maximized Daylighting
0.8 W/ft2 LPDbuilding [1.1 W/ft2 LPDclassroom ]
High Performance Glazing
Zone by Zone Humidistats
Ventilation : ∑cfm/occ + ∑cfm/ft2
Loads as Usual : 1.4 W/ft2 LPDclassroom
0.3 ACH Infiltration…
High EER Roof Top Units
High COP/IPLV Centrifugal Chiller
Premium Motors
Efficient Centrifugal Airfoil Fans
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Resultant School’s Performance
After a year of operation…
Complaints of Cold, Damp Conditions
Extremely High Utility Bills
Each Silo’s Design Focus was Implemented EXACTLY
With 4 more schools under design, School District decided to form a Forensics Team
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Building Forensics : Infiltration
Problem : Increased Fenestration Details
0.3 ACH
1.0 to 1.5 ACH
Remedy : Sealed Construction Details but too expensive to fix vestibules
Can not rely on Building Pressurization!
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Building Forensics : Duct Leakage
Looking at Testing and Balancing Report yielded ~30% Leakage Rate
Remedy : Reduced to ~10% Leakage Rate by improving to seal class B based on ASHRAE 90.1 following SMANCA Guidelines
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Building Forensics : RTU Sizing/Control
Remedy : Replaced with smaller Roof Top Units?
Anyone else got any cheaper ideas?
Roof Top Units oversized and short cycling
Problem : Relying on Rules of Thumb and Lack of Communication
Direct Evaporative Cooling
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Building Forensics : Ventilation
Problem : Misinterpretation of ASHRAE 62.1 Ventilation Rate Procedure for Multi-Zone Systems
Ventilation =∑cfm/occ + ∑cfm/ft2 All Zones All Zones
No Diversity 50 ft2 / occ
4 – 6 times actual school population
Remedy : Calculated necessary Ventilation and reduced Outdoor Air Intake
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Building Forensics : Reheat Dilemma
Problem : Limitation of using only DX or Chilled Water Coils to provide both Cooling and Dehumidification
Result 1 : Cold, Damp Conditions
Remedy 1 : Eliminate Zone by Zone Humidistats
When the supply air flow required to dehumidify the space exceeded the supply air flow required to meet 75ºF.
Result 2 : Significant Reheat yielding High Utility Bills
Remedy 2 : Do Nothing
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Psychometric Review 1
Properties of Air
Temperature Moisture Content
Relative
Humidity
mass of water
mass of dry airMoisture Content =
grains of water
pound of dry air=
Imagine 100% Relative Humidity at these Temperatures
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Psychometric Review 2
40ºF
40 gr/lb
50ºF
55 gr/lb
80 gr/lb
60ºF
110 gr/lb
70ºF
100% Relative Humidity
50% Relative Humidity
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Conventional System
75ºF
FanDX-or-
Chilled Water
52ºF 55ºF
57 gr/lb
65 gr/lb
75ºF
Moisture Potential
Temperature Potential
Siamese Twins : Temperature & Moisture Content
North Facing Classroom
1,000 ft2 Classroom
31 occupants
1.4 W/ft2 Lighting
0.9 W/ft2 Plug Load
0.3 ACH Infiltration
Supply Air = 55ºF & 57 gr/lb
R-13 Walls / 0.5 SHGC
0.4% Design Day Conditions (Sunny)
Space Air = 75ºF & 65 gr/lb
Thermal Load Requires = 1,000 cfm
Moisture Load Requires = 850 cfm
Cloudy
Lights Off
No Plug Load
500 cfm
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Psychometric Chart
75ºF
65 gr/lb
Cold and Damp are the Worst Conditions in Regarding Reheat
Technologies to Battle Humidity
1. Hot Gas Reheat
2. Heat Pipe or Sensible Wheel
3. Desiccant Wheels
4. Enthalpy Wheels
5. Combination of all of the above
Following Systems provide Energy Efficient way to
Supply Air at HIGHER Temperature (55ºF to 65ºF) but
LOWER Moisture Content (57 gr/lb to 53 gr/lb)
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Hot Gas Reheat
65 gr/lb
75ºF
DX Hot Gas
53 gr/lb
65ºF50ºF
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Heat Pipe or Sensible Wheel
65 gr/lb
75ºF
DX
Heat Pipe or Sensible Wheel
53 gr/lb
65ºF50ºF
Exhaust Air
-or-Chilled Water
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Desiccant Wheels
65 gr/lb
75ºF
DX
53 gr/lb
65ºF57ºF
Hot Gas
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Enthalpy Wheels - Regenerative Braking
65 gr/lb
75ºF
DX
Exhaust Air
Hot Gas
53 gr/lb
65ºF50ºF
Most Cost Effective Means of Dehumidification
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Enthalpy Wheel & Heat Pipe
65 gr/lb
75ºF
Exhaust Air
53 gr/lb
65ºF50ºF
Heat Pipe or Sensible Wheel
DX-or-
Chilled Water
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Dedicated Outdoor Air System (DOAS)Trifecta Decouple
1. Moisture - Centralized System that provides “Dry” (~50 gr/lb) Outdoor Air between 55ºF-75ºF (~65ºF)
2. Temperature – Local Fan Coil Units or Water Source Heat Pumps to maintain 75ºF setpoint
K-12 AEDG
3. Ventilation – Dampers on 100% Outdoor Air Supply controlled by Zone CO2 sensor
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What Happened to our Design Team
1. Used the K-12 AEDG as a starting point :-Lighting Design-Daylighting Design-Envelope Design-Started the Discussion of Mechanical Systems EARLY in Conceptual Design
2. Focused on how to conquer humidity by balancingEnergy Efficient Dehumidification while minimizing Reheat
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Architects Review
Infiltration : Focus on Construction Details and Vestibule Design to minimize Infiltration
Access to Exhaust Air : Coordinate room layout to provide access to Exhaust Air
Coordinate Space Requirements : Equipment using Desiccantor Enthalpy Wheels often need double height space
Reference : “ASHRAE Humidity Control Design Guide”
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Engineer
Start the Mechanical Conversation EARLY : Work with the rest of the Design Team in Conceptual or Schematic Design to determine the Optimal System
Duct Leakage : at least leakage class B
READ “ASHRAE Humidity Control Design Guide”
Ventilation : Understand ASHRAE 62.1 Ventilation Requirements but do not need to Over Ventilate
Energy Efficiency Dehumidification without Comprimising Reheat