Passive House
Photo: JB Clancy
Marc Rosenbaum, P.E., CPHC South Mountain Company West Tisbury, MA © copyright 2010 Introduction to Passive House • Passivhaus is a rigorous German building standard that combines very high levels of superinsulation with passive solar gain and fresh air distribution to achieve extremely low energy loads as well as a healthy, comfortable, and durable building • Approach focuses on minimizing losses and maximizing usable gains, for an optimal energy balance
Four criteria: - Annual heating load <15 kWh/m2/yr (4.75 kBTU/ft2/yr) - Annual cooling load <15 kWh/m2/yr (4.75 kBTU/ft2/yr) - Annual primary energy load <120 kWh/m2/yr (38 kBTU/ft2/yr) - Blower door tested to <0.6 ACH50
This is a small fraction of the heating load of a typical house (no more than 20%) and under half of the primary energy consumption (lots of “it depends on…” here).
• Begun in the early 1990s in Germany, PH is based on thinking and experience that originated in North America, such as the Lo-Cal House at University of IL and the Saskatchewan House • PH adopted the expression coined by Amory Lovins: “tunneling through the cost barrier” and traded off investments in conservation with minimized HVAC cost
• There are now >25,000 Passive House buildings world- wide • Not just houses, but most types of buildings – schools, offices, senior housing, etc. • PH housing in Europe is mostly multi-family • 25% of all new housing in Upper Austria are PH • Original German concept is that all heating energy is delivered in the ventilation air • PH has stimulated the market for higher performing windows and doors, heat and energy recovery ventilators, integrated mechanical appliances, and other components Basic Features of PHs • Compact form and superinsulation; thermal bridges accounted for • Solar and internal gains are significant offsets to load • Fresh air ventilation via heat recovery • Efficient DHW use plus SDHW or HPWH • Efficient Appliances
Differences from NA SI/ZNE Practice • Floor area and interior volume accounted for according to a strict standard • Very airtight and tested • Thermal bridging rigorously accounted for • Focus on primary energy • On-site renewable electricity is not counted • Still not based on verified post-occupancy performance
Certification of PHs is a rigorous process with a significant set of document submissions Challenges in the US • One size fits all criteria regardless of climate • Availability of windows, glazing, HRVs comparable to German products • Cooling is much more prevalent here • Based on floor area so favors larger buildings • Difficult in New England climate to deliver heating in ventilation air • Higher solar availability in the US shifts the optimum balance between investment in load reduction and renewable generation Primary Energy
• Site energy is the energy used at the building site. • Primary (or source) energy includes the energy used to extract, process, and distribute the energy used on site • Primary energy factor is highest for electricity – typically about 3 in the US (PHPP German default is 2.7)
Fuel Primary Energy Factor Electricity 2.7 Oil/gas/coal/propane 1.1 Wood 0.2 Solar electricity 0.7 • Houses designed to be PHs are analyzed in PHPP, a spreadsheet with over 30 tabs that describes the house in excruciating detail. • There is a maximum allowable thermal bridge value before the condition must be included as a separate heat loss entry.
Thermal bridges
• A thermal bridge is wherever the structure of the building (or other material) penetrates through the insulation layer. It compromises insulating value. • The effect is larger as the difference between the insulating value of the two materials increases. • Steel, aluminum, and masonry need to be completely inside or outside the thermal envelope. • The Passive House Planning Package accounts for TBs separately if they are above 0.006 BTU/hr-ft-˚F
PH thermal bridge slide courtesy David White, Right Environments Note that a thermal bridge can be positive or negative Air Tightness
• 0.6 air changes per hour at 50 Pascals is tight • The volume used for calculation is the actual volume enclosed by the thermal boundary minus the volume in the floors and walls • For a 2,000 gsf house, this will typically be well under 200 CFM50 • Mechanical penetrations are covered for the test Blower door installed – a C ring will be needed (works down to 85 CFM50 - maybe even a D ring, which works down to 30 CFM50!) Leaks can be located with a fog machine with the house under pressure The Passivhaus progress in Germany (>10,000 built) has led to tremendous product innovation in windows, doors, heat recovery ventilation, integrated mechanical systems, and construction materials for thermal bridge-free construction. In milder climates like Germany, the heat is delivered with the ventilation air. Introduction to PHPP • The original version of the Excel-based analysis tool is in SI units – PHIUS has converted it to IP units and added convenient features for US users • The cells with calculated values refer to the hidden underlying SI spreadsheet • The workbook is protected but not password-protected • To view any SI sheet, or hidden portions of any sheet: - Tools – Unprotect – Workbook - Format – Sheet – Unhide • Re-protect the workbook and don’t unprotect your original! • The software comes with an English language manual
Passive House Planning Package Areas U values Ground Windows Shading Ventilation Annual Heat Demand Monthly Heat Demand PE Case Studies
Photo: JB Clancy
Marc Rosenbaum, P.E., CPHC South Mountain Company West Tisbury, MA © copyright 2010 Passivhaus Development in Ulm, Germany Kat Klingenberg’s House, Urbana, IL Fairview II, an early US PH A project by the founders of PHIUS, this house is built as affordable housing in Urbana, IL • About 1,650 gsf, 4 BR, 2 baths • Pre-fab I joist walls, with second floor supported on additional interior 2x4 walls (~14 inch thick walls) • Truss roof with raised heels • Blown-in fiberglass insulation • Interior OSB air barrier • Triple glazed fiberglass windows • 16 inches of foam sub-slab • UltimateAir ERV • Samsung minisplit heat pump • Instantaneous electric DHW Andre House, West Tisbury, MA Biohaus, Bemidji, MN Green Mountain Habitat for Humanity All material courtesy of Peter Schneider of VEIC and JB Clancy of Albert Righter and Tittman Architects This home is a modular home with the components supplied by Preferred Building Systems of Claremont, NH.
Taggart Construction Terrapin House All material courtesy of Taggart Construction, Freeport, ME
Large south windows – recessed or not?
Innies Outies
4.46 kBTU/ft2/yr 3.88 kBTU/ft2/yr Tad Everhart’s PH Retrofit All material courtesy of Tad Everhart, Portland, OR
The GO Home All material courtesy of GO Logic, Belfast, ME
Southworth House Lancaster, NH Courtesy of Garland Mill Timber Frames
HVAC Systems for Passive Houses
Marc Rosenbaum, P.E., CPHC South Mountain Company West Tisbury, MA © copyright 2010 Balanced Ventilation: Heat and Energy Recovery Heat and energy ventilators Exhaust areas of pollutant generation; supply areas where people are; transfer air between the two. Kitchen exhaust is not over the range. Pressure differences not exceeding 1 Pa facilitate transfer air. In the PHPP, the Ventilation Sheet calculates vent rates. In this 2 BR, 1-1/2 bath house, exhaust air is the larger quantity and thus determines the system size (35+24+12=71 CFM, vs. 3.3x17.66=58 CFM) • Note that the PHPP multiplies the peak system size by a factor (0.77 is the default) for calculating heating and cooling energy use. • 0.3 ACH is a reasonable target for average ventilation rate; it will sometimes be higher in small homes and lower in large homes. • The baseline assumptions are: - exhaust flows are nearly continuous - kitchen hood is a recirculating hood • Note that the amounts are slightly different than what it is in ASHRAE 62.2, the residential ventilation standard. Heating and Cooling Systems
Design Heat Loss by Component
3500
3000
2500
2000
BTU/hr 1500
1000
500
0 Wall Roof Window Basement Infiltration Ventilation Cooling Loads • Cooling loads are more dynamic because the building peak load is lower than the sum of the room peak loads • Peak cooling loads are driven by solar gains and internal gains, not by envelope conduction, and by the choice of interior and exterior conditions (temperature and RH) • Cooling is split between latent load and sensible load Cooling Load by Component
Latent load • As buildings get more efficient, the cooling load shifts from being mostly sensible cooling to mostly latent (moisture removal). • This is a challenge for conventional cooling equipment, especially high SEER single speed central air conditioners. • Mini-split cooling systems help, because they run lower CFM/ton, and they are highly variable. • In some cases, additional dehumidification may be necessary. Small Efficient Equipment: Limited Choices
• Depending on building size and peak loads it can be hard to find equipment small enough. • Modulating equipment can meet low loads and maintain efficiency at low outputs. Passive House Heating • The original PH concept is based on the elegant idea that all heat can be delivered by the ventilation air. • To do this the peak heating load is held to 10W/ m2 or less (3.2 BTU/hr/ft2) - this is challenging in northern climates, yet possible in DC • For heating, assuming a maximum ∆T of 60°F, this is 65 BTU/hr/CFM - a house with 83 CFM ventilation requirement has 5,400 BTU/hr capacity • It's harder with cooling, because ∆T is lower - 20 - 25°F - so the same 83 CFM can deliver about 2,000 BTU/hr, or 1/6 ton System approaches
HRV/ERV with electric duct heater - heating only System approaches
HRV/ERV with hydronic coil - heating and cooling possible (with source of chilled water) System approaches
HRV/ERV supplies fresh air to ducted minisplit heat pump - recirculation air loop - heating and cooling System approaches
HRV/ERV supplies fresh air to fan coil - recirculation air loop - heating and cooling possible (with source of chilled water) System approaches
HRV/ERV is separate system - point source wall mounted minisplit heat pump(s) - heating and cooling Minisplit Heat Pumps - These are Japanese air-to-air heat pumps - Inverter-driven models now imported to North America - Rated outdoor air temperatures as low as -13F - Potential choice for non-fossil fuel energy source for low load building – simpler and cheaper than GSHPs - Heat output is rated at 47F – most units drop to 50 -60% of rated output at 0F - Terminal (indoor) units include wall mounted, ceiling recessed, floor console, or ducted - Rated outputs available as low as 9,000 BTU/hr - Multiple terminal units on a single outdoor unit - Multi-port and variable refrigerant systems – VRS start at systems rated at 36,000 BTU/hr - Systems that transfer heat from cooling zones to heating zones start at 72,000 BTU/hr - Zoned billing is possible - COP range from over 2 to over 3, depending on climate, model, fan power, etc. - As fossil fuel prices have increased, heat pumps have become lowest cost option for heating Single indoor unit on a single condenser Multiple indoor units - 2 wall mount, 1 ducted - on one condenser 11,000 sf dormitory with 11 zones - 9 ducted units, 1 wall mount, and 1 floor mount on 4 VRF condensers - design heat loss ~75,000 BTU/hour Thank You
Marc Rosenbaum, P.E. South Mountain Company West Tisbury, MA