What's in a Passive House Feasibility Study?

Intention and Goals:

• Design Upgrades: Identify minimal set of design changes and upgrades required to meet Passive House (PH) standards.
• Cost Estimation: Collaborate with FM and suppliers to estimate the cost of design changes and upgrades.
• Capital Cost Optimization: Determine the optimal combination of measures to minimize capital expenditure while achieving PH standards.

Scope of the Study:

• Insulation levels
• Window & Curtain Wall (CW) format
• Window, CW, and glazing performance
• Thermal bridging
• Ventilation supply, exhaust and control strategies
• Zone and whole building heating and cooling loads
• Mechanical equipment sizing and selections
• Lighting efficiency and controls

Where is the energy used?

Where's the Heat Loss?

Tower A heating energy balance

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In-depth Findings:

Opaque Assemblies:

• Current State: Fairly well insulated due to TGSv3 T2 targets. However, some assemblies are minimally or not insulated and can be improved.
• Challenges and Opportunities:
  • Insulating walls adjacent to parking areas may pose challenges.
  • Potential Improvement: Space Heating Demand can be reduced by 4.5 kWh/m²/year.

Recommendations:

• Increase insulation levels per above Table

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Transparent Components:

• Window and CW Systems:
  • Currently, no PH certified window wall is available, but a suitable product has been identified.
  • High Basecase Window Wall Ratio (WWR) at ~45%. Reducing WWR to ~30% by switching to punched windows can optimize performance.
  • Evaluation included 3 window suppliers and 2 CW suppliers. Performance and longevity were similar, so cost is the primary deciding factor.
  • Canadian PVC windows emerged as the most cost-effective option.
• Primary Strategies:
  • PH CW is the largest upgrade expense.
• Opportunities include:
  • Deleting opaque elements like spandrels and louvres.
  • Increasing curb height to 0.8m.
  • Simplifying layouts by combining individual lites.
  • Replacing sections with PH certified storefront windows.
• Recommendations:
  • Reduce tower WWR to approximately 30%.
  • Switch to PH certified punched windows and CW systems.
  • Modify CW format to reduce capital costs.
  • Explore additional summer shading options.

Shading:

• Difficult to balance space heating and cooling demands without external shading

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Thermal Bridging:

• Key Areas Identified:
  • Window and CW installations, along with balconies, intermediate floors, parapets, planter boxes, and suite demising walls, are major contributors.
  • Addressing storm and sanitary pipe stack losses can provide easy wins.
• Recommendations:
  • Implement thermal bridge mitigation measures as proposed in the report.
  • Eliminate redundant thermal bridge mitigation measures.
  • Potential Improvement: Space Heating Demand can be reduced by 9.8 kWh/m²/year.

Airtightness:

• PH Requirement: 0.6 ACH@50Pa, with large buildings able to achieve better results.
• Current Assumption: 0.3 ACH@50Pa for analysis, facilitated by using precast concrete panels.
• Recommendations:
  • Appoint an Air Boss to ensure consistent implementation of a continuous air barrier.

Ventilation:

• PH Requirement: Some form of heat recovery on all airstreams is essential.
• Challenges:
  • Make-up air (MUA) and garage exhaust without heat recovery are significant issues.
  • Single rooftop ERV serving ground floors needs return air ducting.
• Recommendations:
  • Switch MUA/exhaust fans to PH certified ERVs.
  • Use elevator shafts and garbage chutes as return plenums for rooftop ERVs.
  • Add fire/smoke dampers to garbage chutes.
  • Install ground-level ERVs for each tower to serve specific areas.

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Suite HVAC Layout:

• Opportunities:
  • Significant reduction in insuite ducting and bulkhead area.
  • Example: Typical 1-bedroom suite can achieve 82% less ducting and 48% less bulkheads.
• Recommendations:
  • Upgrade to PH certified ERVs and relocate to living room exterior wall.
  • Ensure acoustic isolation of ERVs and ducts.
  • Add preheaters for continuous operation during frosting periods.
  • Switch to recirculating range hoods and condensing dryers.
  • Separate ventilation and heating ducting in 1-bedroom suites.

ERV Operation:

• Findings:
  • Operational ventilation rates significantly impact space heating demand.
  • Excessive rates prescribed by standard building codes.
• Recommendations:
  • Size ERVs per code but operate suite ERVs at PH recommended rates.
  • Reduce corridor ventilation rates.
  • Tie garage ventilation rate to pollutant sensors.

Glycol DHRC:

• Potential Downsizing:
  • PH envelope upgrades reduce or eliminate the need for unit heaters within the thermal envelope.
  • All duct heaters can be eliminated due to new ERVs.
  • Capacity of Glycol DHRC can be reduced by 56%.
  • Unit heaters serving spaces outside the thermal envelope can also be downsized.
• Recommendations:
  • Eliminate or downsize unit and duct heaters.
  • Downsize Glycol DHRC.
  • Investigate further downsizing potential.

DHW Peak Loads:

• Insights from Monitoring:
  • Peak GPM is much lower than conventional design estimates.
  • Tools like Ecosizer and WDC can be used for more accurate sizing.
  • Result: Potential reduction in total DHRC capacity by 75%.‍
• Recommendations:
  • Use available tools to right size DHRC and piping
  • Specify pressure compensating fixtures to mitigate absolute peak peaks

Heating & Cooling Loads:

• Detailed Analysis:
  • More accurate heating and cooling loads due to improved building performance and reduced WWR.
  • Load diversity and shading considerations integrated.

• Suite Peak Loads:
  • Secondary WSHP in suites can be eliminated.
  • Remaining WSHPs and those serving amenity spaces and ERVs can be downsized.
  • Eliminate corridor WSHPs.

• Peak Building Loads:
  • PH calculations show much lower peak loads compared to basecase.
  • Geothermal Field Balancing:
  • Requires auxiliary system for annual balance.
  • Small ASHP can rebalance system during non-peak times.

Geothermal Field Balancing:

• Geothermal system requires auxiliary system to ensure geofield remains balanced over the course of a year
• In PH case, imbalance shifts from heating to cooling.  
• If additional summer shading is provided, imbalance can reduced to minimal amount
• In either case, a small ASHP running during non-peak periods during the summer and shoulder seasons can rebalance the system.

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Central Plant Sizing:

• Optimizations:
  • 100% coverage of heating, cooling, and DHW with a smaller geothermal system.
  • Consider reducing geothermal and ASHP systems based on PH calculations.
  • Potential downsizing: System to 730 kW (26 W/m² TFA), 58 borehole geothermal field, and 17 ton ASHP (2 W/m² TFA).
  • Eliminate gas boilers.

Heating, Cooling, DHW Generation Equipment

• Recommendations: ‍
  • Eliminate second WSHP in each suite and all corridors
  • Downsize suite, amenity, and ERV WSHPs
  • Downsize geothermal system to meet 100% heating and cooling peak loads and portion of DHW load
  • Downsize ASHP to meet residual DHW load
  • Delete gas boiler
  • Work with mechanical engineer to gain confidence in PH calculations to further downsize geothermal and ASHP systems

‍Other Energy Uses:

• Efficiency:
  • Interior lighting already efficient and well-controlled.
  • Additional opportunities: Occupant sensors in stairwells.
  • Potential savings in exterior lighting, suite appliances, and elevators (pending further data).

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Heating Energy Balance: Basecase vs PH Case

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‍Energy and GHG Savings:

• Significant Reductions:
  • 40% reduction in energy use and GHG emissions over TGSv3 T2.
  • Reduced pump energy requirements.
  • Effective System Coefficient of Performance (SCOP): 1.4-2.4 for heating & cooling.

Cost Analysis

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• Capital Costs

• Includes substantial allowance for additional design fees and Air Boss
• Does not account for reduction in heating circulation piping (14” is largest pipe)
• Modified CW = swap some areas for PH storefront and delete louvres
• Opportunity to optimize opaque assembly insulation levels

Monthly Cost of Ownership (Scenario 1)

• Additional loan @5%: $159,378
• Electricity Cost Savings @0.10 $/kWh: $163,430
• Does not capture reduced maintenance costs or replacement costs

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‍The Passive House Benefits:

• Comprehensive Financial and Environmental Advantages:
  • High-quality indoor environment: Thermal comfort, good air quality, low dust, no noise.
  • Futureproof: Reduced maintenance costs, protection against rising energy prices.
  • Resiliency during power outages.
  • ESG benefits and marketing advantage.

Conclusion: The feasibility study demonstrates a clear path to enhancing the TGSv3 T2 basecase building to meet Passive House standards. With targeted design changes, optimized performance, and strategic upgrades, significant energy savings and cost reductions are achievable. This not only aligns with sustainability goals but also brings broad financial and environmental benefits to future projects.

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