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Net-Zero Energy Homes: The Basics of What You Need to Know Building Science Corporation Kohta Ueno, Senior Associate The 2010 HVACR & Plumbing Instructor Workshop: Advancing Green Mechanical Concepts March 24-26, 2010. 1. Background. Definitions. - PowerPoint PPT Presentation
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© 2009Building Science
Corporation
1
Net-Zero Energy Homes:The Basics of
What You Need to Know
Building Science Corporation Kohta Ueno, Senior Associate
The 2010 HVACR & Plumbing Instructor Workshop:Advancing Green Mechanical Concepts
March 24-26, 2010
© 2009Building Science
Corporation
Background
© 2009Building Science
Corporation
Definitions
• NZE: A building that produces as much energy in a typical year as it consumes.– Consumes grid power when it needs it– Feed power to grid when it has extra
• ALL energy considered– Electric is not special.
• NOT Zero Carbon, or Zero GHG• NOT off-grid
– Much more difficult
© 2009Building Science
Corporation
Why Buildings?
• Building Sector is largest energy consumer and GHG emitter
© 2009Building Science
Corporation
NZE Design Targets
• Produce as much as we consume• Production is usually MUCH more
expensive than reducing waste (efficiency/conservation)– Hence the energy demanded by
building should always be reduced, reduced, reduced before adding production
– Check cost of reducing demand vs cost if supplying energy
© 2009Building Science
Corporation
Capital Investment vs. Operating Cost
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Fig. 1: Conceptual plot of the path to ZNE.
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Fig. 1: Conceptual plot of the path to ZNE.
Incremental, Energy Related MortgageCosts
Minimum Cost Point
“Least Cost”Curve
Neutral Cost Point
Source Energy Reduction
All E
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d Co
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$
Underlying Source: Dr Ren Anderson, NREL
Lower cost conservation
Higher Energy costs
© 2009Building Science
Corporation
Takeaway Lessons• Conservation measures first! Good
design/orientation, good enclosure (shell), good mechanicals
• Then start adding renewable energy• Insulation has diminishing returns• Renewables can be more cost-
effective than insulation after a point! • Net zero energy: good & noble target,
but out beyond “neutral cost”
© 2009Building Science
Corporation
Renewables
© 2009Building Science
Corporation
Energy Supply• Renewable energy (RE) or cleaner energy
(CE)• Net Zero currently demands site
production– This eliminates some good economical RE
• Common choices– Photovoltaic: Electricity– Solar thermal Warm / Hotwater– Combined heat and power– Wind electricity
© 2009Building Science
Corporation
• PVphotovoltaic
© 2009Building Science
Corporation
Energy Supply (RE)
• PV– Straightforward installation, easy to
predict output– Expensive but electricity is very useful and
excess can easily be sent to the grid (grid=battery)
– Rated by peak output under standard solar conditions (“peak Watt” or Wp)
– Costs now $8/Wp (before subsidy) installed
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• Solar Thermal“hot water”
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BuildingScience.com
Solar thermal• Intermittent source of hot water• Well developed• Requires big storage tanks in
most application• Freezing, over heating, glycol
thickening failures, and low temperature efficiency are issues
• Not the most economically-viable choice ($6-10 K): but if going to net zero…
© 2009Building Science
Corporation
BuildingScience.com
© 2009Building Science
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Combined heat and power•Aka “CHP”
•Efficient use of fuel to produce heat & electricity within the building complex (e.g. hospital) or home
•Remember: grid ~30% efficient; waste heat = cooling towers, river water
•Much lower GHG emissions
•Supplies on demand
•Ratio of electricity to heat is fixed
•Effectiveness varies on case-by-case basis
© 2009Building Science
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Mechanical Systems
© 2009Building Science
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Mechanical Systems
Energy consuming functions• Heating• Cooling• Domestic Hot Water• Ventilation & Filtration
Fundamental problem: small loads!
© 2009Building Science
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18
Furnaces• Condensing gas
furnaces: 90%+ AFUE—mature technology
• Sealed combustion
• ECM motors (“variable speed”) reduces fan electrical energy
© 2009Building Science
Corporation
19
Ground-source heat pumps• Uses constant ground
temperature to provide heating & cooling
• Fluid pumped through underground tubes; heat extracted or rejected
• One of the highest efficiency space conditioning systems (measured ~3.5 COP)
• But….
© 2009Building Science
Corporation
20
Ground-source heat pumps• Installed cost of system very high
(drilling ground loops)• Nameplate efficiency < actual efficiency
(previous example: 5 COP rated number)• Pumping energy• Systems with problems—difficult to
diagnose, expensive to fix• Can still suffer from normal ductwork-
based system problems• For small loads, is it worthwhile?
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• 80% & 90%+ options
• Condensing boilers (90%+)—needs some thinking/design
• Outdoor reset controls for 90%+
• Can’t add cooling
Heating: Hydronic Systems
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22
Radiators/Radiant Floors
Baseboard radiators
Radiant floor heat
© 2009Building Science
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23
Mini Splits
Mini-split non-ducted head
Mini-split short ducted system
Mini-split outdoor unit
•Both heating & cooling
•Multi-splits (single outdoor unit)
•Systems with SEER26 and HSPF=11 available
© 2009Building Science
Corporation
Mini-Splits Heating/Cooling in Cold Mini-Splits Heating/Cooling in Cold ClimateClimate
•1818 sf house, solar-oriented, superinsulated (12“ spray 1818 sf house, solar-oriented, superinsulated (12“ spray foam walls, R-80 roof), triple glazed windows, very airtightfoam walls, R-80 roof), triple glazed windows, very airtight•Central Massachusetts locationCentral Massachusetts location•Net zero performanceNet zero performance
© 2009Building Science
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•Provides for both heating & cooling; 11,000 BTU heating loadProvides for both heating & cooling; 11,000 BTU heating load•Installed costs in the 1,818 square foot “Farmhouse” was $6,850Installed costs in the 1,818 square foot “Farmhouse” was $6,850•Two 9,000 BTU heads upstairs, One 12,000 BTU head downstairsTwo 9,000 BTU heads upstairs, One 12,000 BTU head downstairs•Electric heater back up, no heat production below zero degrees outsideElectric heater back up, no heat production below zero degrees outside
© 2009Building Science
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Ventilation
© 2009Building Science
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Need for Ventilation
• Greater airtightness for energy reasons, in net zero houses
• Also improves sound, odor, pest control
• But people still stink! (+ activities)• Controlled mechanical ventilation
– Point source control (exhaust fans)– General dilution ventilation
© 2009Building Science
Corporation
Air Change Driving Forces
Wind Effect Stack Effect Combustion and Ventilation
© 2009Building Science
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Indoor Air Quality
• Pollutant production• Pollutant removal• Dynamic Balance= pollutant level
– Not a IAQ problem if it is not in the air
• Solutions– Reduce pollutant production– Increase pollutant removal
© 2009Building Science
Corporation
Ventilation• Given sensible source control, constant
ventilation can dilute pollutants to a low level– Ventilation rates are mostly about odor
and humidity, not oxygen– 7.5 cfm/person + 0.01 cfm / sq ft– Commercial and highrise 15 cfm/person (!)
• Mixing is necessary or separate supply to each room to achieve best IAQ
© 2009Building Science
Corporation
Types of Controlled Ventilation Systems
• Exhaust Ventilation
• Supply Ventilation
• Balanced Ventilation
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Exhaust Only: Depressurize
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• Lowest cost installed system (typical), but problems associated:
• Carbon monoxide alarms• Lack of filtration
• Dust marking on light carpets• Dirt/grit particles settling on horizontal surfaces
• Lack of distribution• Moisture accumulation and odor buildup in rooms
remote from exhaust fan
• Objections to fan noise
Exhaust pros and cons
© 2009Building Science
Corporation
Supply Only: Pressurized
Not common, although most commercial buildings have more supply than exhaust
© 2009Building Science
Corporation
35
Plus “fan cycling” controller (runs air handler periodically + motorized damper to prevent overventilation)
© 2009Building Science
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Central fan-integrated ventilation
• “Smart” controller (accounts for previous runtime)
• Set minimum runtime (e.g., 20 min/hour)
• Provides distribution of ventilation air throughout house
© 2009Building Science
Corporation
Balanced Supply and Exhaust
Common for commercial solutionsResidential often combine with HRV/ERV
© 2009Building Science
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Balanced Ventilation (with Heat Recovery)
• HRV/ERV• Point exhaust• Fully ducted
(need not be)
© 2009Building Science
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3911/19/2008
Heat Recovery Ventilation
© 2009Building Science
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Efficient Equipment
• HRV/ERV always– choose better than 1 CFM/Watt
(current high end ~2 CFM/Watt)– Choose > 60% efficient– Right size ventilation!—
overventilation can defeat the benefits of adding heat recovery!
© 2009Building Science
Corporation
Humidity
© 2009Building Science
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4211/19/2008
Recommended Range of Relative Humidity• 25 percent during winter• 60 percent during summer
© 2009Building Science
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Supplemental Humidity Control• Good energy efficient design reduces
sensible cooling loads—insulation, good windows, airtightness
• Latent load remains the same!• Thermostat (temperature control) →
humidity is not controlled• Need supplemental dehumidification
in hot-humid and mixed-humid climates (high performance houses)
• Demonstrated in 20 research housesInformation Sheet 620: Supplemental Humidity ControlRR-0505: Residential Dehumidification Systems Research for Hot-Humid Climates
© 2009Building Science
Corporation
44
Dehumidification High efficiency
supplemental dehumidification options (standalone ducted boxes)
E.g., draw from main space, dehumidified air to supply duct
Humidistat control in main space (near thermostat)
© 2009Building Science
Corporation
© 2009Building Science
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© 2009Building Science
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Combustion Safety
© 2009Building Science
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4811/19/2008
Combustion Safety• Backdrafting risk in tighter houses• Combustion air should be drawn
from outside (“sealed combustion”)
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Case Study:Westford
© 2009Building Science
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Case Study House (Westford Habitat for
Humanity)• Based on recently-built house• Super-insulated enclosure• Very airtight (1.5 ACH 50)• Best-in-class mechanical systems• Energy Star appliances• Compact fluorescent lighting• No renewable energy added: not NZE
(PVs or solar DHW)
© 2009Building Science
Corporation
51
Westford House Under Construction
Westford House: 1.5 Story Single Family Home with Conditioned Basement (2200 ft2 total)
© 2009Building Science
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527 October 2008
Enclosure Details
• R-66 roof insulation
• R-45 walls• R-26
basement walls
• R-10 basement slab
• Low e double glazed windows
• 1.5 air changes per hour at 50 Pascals (“ACH50”)
© 2009Building Science
Corporation
© 2009Building Science
Corporation
Mechanical Details 96% AFUE Gas
Furnace, ECM motor 0.82 EF
Instantaneous Water Heater
Fantech Energy Recovery Ventilator (ERV)
MEL reduction 10% 19.3 MBH Heating 13.5 MBH Cooling
54
Instantaneous Water Heater
Fantech ERV
© 2009Building Science
Corporation
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53%
Enclosure improvements
Mechanical improvements
Appliance, lights
Parametric Analysis
© 2009Building Science
Corporation
Final Points
© 2009Building Science
Corporation
What about LEED?• A green points-based rating
system: energy is only one component
• Some serious disappointments in actual energy performance
• USGBC nowrequires usage data
• How is the house/building operated?
• ASHRAE 90.1 problems?Source: BSI-007: Prioritizing Green—It's the Energy Stupid*
© 2009Building Science
Corporation
Questions/Comments
© 2009Building Science
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To Take it Further…
© 2009Building Science
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Mitsubishi SEZ Ducted Indoor unitsMitsubishi SEZ Ducted Indoor units•Provides for both heating and cooling, 17,000 BTU peak heating loadProvides for both heating and cooling, 17,000 BTU peak heating load•Installed costs in the 4 BR 2,612 square foot “Carlisle” model was $7,600Installed costs in the 4 BR 2,612 square foot “Carlisle” model was $7,600•One 15,000 BTU heads upstairs, One 18,000 BTU head downstairsOne 15,000 BTU heads upstairs, One 18,000 BTU head downstairs•20,000 BTU gas fireplace as back up heating system20,000 BTU gas fireplace as back up heating system
© 2009Building Science
Corporation
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