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San Francisco Bay Area Net Zero Urban Infill2011 ASHRAE Annual Conference, June 25-29, 2011, Montreal, QC
Kohta UenoASHRAE is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to ASHRAE Records for AIA members. Certificates of Completion for non‐AIA members are available on request.
This program is registered with the AIA/ASHRAE for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Learning Objectives for this Session
• Compare the present and predicted future affordability of net‐zero energy homes. • Provide an estimate of required PV price for NZEH to be an optimal solution in 2030. • Describe measures leading to market‐rate net‐zero houses. • Describe the temperature distribution due to minimally distributed heating.• Explain that whether or not an overall net‐zero balance is achieved is highly dependent on the user.• Describe that in very efficient homes, standby loads become more and more important and unnecessary standby losses (for example a crankcase heater for a heat pump) can sum up to a significant part of the overall energy consumption
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Live/Work Urban Infill Townhome
1540 sf, 2 bedroom, 2 storyOakland, CA; ½ mile from train station (BART)USGBC LEED Platinum Rating2009 Green Builder Home of the Year
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Modular Construction
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Modular Construction
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Enclosure Design
6Wall Section (c/o DSA Architecture)
R-32 Roof (nominal)Low density urethane foam under roof deck)R-23 Walls (nominal)2x6 framing at 24” o.c. w. low density urethane foam or denim batt + 1” R-5 XPSFoundationR-7.5 XPS on crawl space walls; R-5 under crawl space slabWindowsLow-E double pane + film / krypton filled, U=0.23 SHGC=0.42Airtightness 964 CFM 50 (3.1 ACH 50) measured
2011 ASHRAE Annual Conference San Francisco Bay Are Net Zero Urban Infill June 28, 2011
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Exterior Enclosure Features
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Mechanical Design, Lights, Appliances16 SEER/9.5 HSPF air source heat pumpHeat pump water heater in mechanical room/garage (2.11 EF rating) w. electric backupHRV (“minimally” ducted) ventilationCentral fan integrated supply-only ventilationResidential-scale economizer (off the shelf components, custom controller)CFL/LED lighting, Energy Star appliancesDrainwater heat recoverysystem
CENSORED
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Renewable Energy5.4 kWp photovoltaic systemInverter in garageSystem covers ~½ of roofCovered 90%+ predicted energy use (simulation)California net metering laws
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Parametric Energy Simulations
0
20
40
60
80
100
120
140
160
180
200
US Ave
rage
Benchm
ark
As-buil
t base
Skylig
ht
Air seal
Duct le
ak
Wall R
-19 O
VE
Wall R
-5 XPS
Roof R-38
Crawl wall
R-7.
5
Crawl fl
oor R-5
Gar ce
il R-3
8
Serious
725s
9.5 H
SPF
16 S
EER
HP DHW
GFX drain
water
CFLs
ES App
lianc
es
5.4 k
W P
V
mill
ion
Btu
/yea
r (so
urce
ene
rgy)
Heating Cooling Hot Water Lighting Other 40% Reduction
44.7%
94.8%
Enclosure ImprovementsΔ≈19%
Mechanical Improvements
Δ≈19% Appliances, LightingΔ≈10%
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Valuing energy upgrades relative to PVs
Savings [106 Btu / yr]
$ per 10^6 Btu Saved
(1 year)Estimated
Lifetime [yr]$ per 10^6 Btu
Saved (Lifetime)
Extended Cost Effectiveness Analysis
Source Energy Savings (from typical analysis)
“Cost per unit of energy saved”
Component lifetime
Energy saved over lifetime of
measure
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Results of Economic Comparison
Shows value of long-lived measures (e.g., enclosure upgrades)PVs $9 per 106 Btu Saved (Lifetime)Assumed 30 year lifespan, $4/installed Wp (peak watt) (actual cost with rebates)Losing items in energy simulation analysis:
Heat recovery ventilator ($64 per 106 Btu Saved)16 SEER air conditioner ($44)Triple glazed (double + film) fiberglass windows ($19)Drainwater heat recovery ($11)
2011 ASHRAE Annual Conference San Francisco Bay Are Net Zero Urban Infill June 28, 2011
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Water Heating: Conventional Options
Conventional gas tank (~0.59 EF) site
Conventional electric tank (~0.92 EF) site
“Source Efficiency” ≈ 54% “Source Efficiency” ≈ 27%
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Water Heating: Best Options?
Condensing instantaneous tankless (~0.9 EF) site
ASHP (electric) water heater (2.11 EF) site
“Source Efficiency” ≈ 82% “Source Efficiency” ≈ 63%California Title 24 Requirements: Time Dependent Valuation (TDV) Energy Calculations
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Residential Economizer
Motorized skylight provides pressure relief
CENSORED
CENSORED
CENSORED
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Residential Economizer Results
Air handler efficiency 6.2 CFM/W total flow(vs. 2.5 CFM/W typical for ECM)170 CFM outside air drawn, 120 W →1.4 CFM/W outside airCooling efficiency calculated at various ΔT; compared to DX coolingDX cooling more efficient than economizer when indoor-outdoor ΔT < 13°FDamper design vs. commercial economizersRisk of duct system leakage to outside in future
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Heat Pump Water Heater Performance
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Heat Pump Water Heater Performance
2011 ASHRAE Annual Conference San Francisco Bay Are Net Zero Urban Infill June 28, 2011
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Heat Pump Water Heater Performance
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Heat Pump Water Heater Performance
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Heat Pump Water Heater Performance
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Drainwater Heat Recovery System
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40
45
50
0 50 100 150 200
Time (Minutes)
Tempe
rature (C
)
50
60
70
80
90
100
110
120
Tempe
rature (F)
Drainwater T In
Drainwater T Out
Tempered Out
Cold Mains Supply
Kitchen Sink @133 F/56 C(129 F/54 C @ drain)
Shower @130 F/ 53 C(109 F/43 C @ drain)
Shower @111 F/ 44 C(100 F/38 C @ drain)
Cold water run to chill drain line
Hot water bucket poured out to
Hot water bucket poured out to drain
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Drainwater Heat Recovery Results
% recovery 19% at multiple temperaturesLong term testing—0%-22% daily averages (13%±5%)Cast iron drain pipe thermal mass small effect (steady state ~5-6 minutes)Heat loss through pipe walls (3-5°F)Shower water temperature loss (130°F at the shower head to 109°F at the drain)
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Submetered Net Energy Use
Unoccupied Data
2011 ASHRAE Annual Conference San Francisco Bay Are Net Zero Urban Infill June 28, 2011
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Submetered Net Energy Use
Unoccupied Data
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Submetered Net Energy Use
Unoccupied Data
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Overall Performance (Summary)
17 months’ data (13 months occupied data)7560 kWh generated/7100 kWh consumed (past 12 months): 15% excess10,556 kWh generated/9165 kWh consumed (all data): 7% excessData collection continuing
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Questions?Kohta [email protected]
This presentation is based on a peer-reviewed paper (Paper 6733), which is available for sale in the onsite ASHRAE bookstore and the online ASHRAE bookstore following the conference.
A complete list of references can be found in this paper.
2011 ASHRAE Annual Conference San Francisco Bay Are Net Zero Urban Infill June 28, 2011
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