Stepwise Tower Retrofit

(NOTE: The November 4 Global Passive House Happy Hour will feature Stepwise Tower Retrofit in a presentation by Jennifer Hogan. Join us!)

The Raymond Desmarais Manor tower (the Manor) at 255 Riverside Drive East in Windsor, Ontario, is undergoing a rare transformation in North America: a stepwise retrofit of a tall multifamily building to the EnerPHit standard.

The owner, Windsor Essex Community Housing Corporation (CHC), spends an incredible half of its operating budget on energy, much of which is consumed by electrically provided space heating. Being a social housing organization, CHC sees providing affordability and occupant comfort as key factors in its decision-making process, so it looks for ways to reduce the occupants’ energy costs. While winter weather creates comfort issues, so do summer conditions. The hot and humid weather experienced in Windsor during peak summer poses challenges to passive cooling strategies. Many existing towers in the region do not include active cooling. The consequences are either the installation of low-efficiency window or through-wall air-conditioning units, or residents must endure uncomfortable—and potentially unhealthy—conditions.

The Manor is not the only tower attempting to achieve the EnerPHit standard. Another project, the Ken Soble Tower retrofit down the long road in Hamilton, Ontario, is also pursuing EnerPHit. However, there are three characteristics that make the Manor unique:

• The first is tenancy during construction. Whereas the Ken Soble Tower has been vacant for some time, the Manor is occupied and remains so during construction work. This is problematic for a variety of reasons, including that the HVAC installation in corridors and suites will disrupt tenants and testing the airtightness of the whole building becomes much more complicated.

• The second is the existing balconies. The Ken Soble Tower renovation includes removing the balconies. At the Manor, they are being kept per client request, as the tenants use them regularly.

• The third is the stepwise approach. Funding constraints made it impossible for CHC to implement all the required works in a single phase.

Standing 20 stories high, the 300-unit tower was built in 1974 as part of the government’s massive build-out of affordable apartment buildings. The existing building has a concrete structure and an exterior wall construction consisting of through-the-wall brick masonry, 1.5‑inch interior EPS insulation, and parging. The parged brick wall acts as the air-and-vapor control layer. Three inches of roof insulation was added as part of a roof upgrade over a decade ago. Windows are original aluminum frame with single-pane glazing. The HVAC system comprises a gas-fired makeup air unit pressurizing the corridors, local exhaust fans in the kitchen and bathroom, and electric baseboard heaters below the patio doors and living room windows. New gas boilers for domestic hot water (DHW) were installed about ten years ago, although the circulation piping is original and due for replacement. The elevators are also due for upgrades.

During the retrofit process, the building will be upgraded in four phases. The first phase, which is now complete, involved the replacement of all balcony doors and ground floor windows (see Figures 1 and 2). This phase was implemented without planning the subsequent measures, due to the funding timelines. The second phase involves HVAC upgrades, followed by envelope upgrades, and finally DHW piping and elevator upgrades. The team working on this project includes Pretium Engineering, Peel Passive House Consulting, CK Engineers, Zephir, and the Titan Group.

Envelope

The building will be clad in a mixture of mineral wool and an EPS exterior insulation and finish system (EIFS). For cost reasons, CHC would have preferred to use EPS for the whole building, but the choice of PVC windows (also due to cost) forced the use of mineral wool on the suite façades, due to fire code requirements. As mineral wool EIFS are currently only fully tested to 4 inches, this choice limited the thickness of the mineral wool to 4 inches. EPS was permitted on the windowless sidewalls, so the insulation on those walls was increased to 6 inches.

The insulation continues below grade along the basement wall to reduce thermal bridging and mitigate condensation and mold risk. Basement ceiling insulation was also required to meet the space heating demand target. The roof was upgraded recently and is covered by telecommunications equipment, so will remain as is. A continuous air barrier membrane will be installed against the existing brick wall and tied into the roof membrane. Verifying airtightness is a challenge with live-in tenants, as they enter and exit the building frequently. As of this writing, it had not been established how the whole building’s airtightness will be verified.

For the balconies, finding the right balance between cost, technical feasibility, impact on tenant space, thermal performance, and moisture risk was a challenge. After numerous iterations, the chosen solution was to insulate the entire soffit and create an insulated step on the top side. This approach mitigates current and future moisture risk.

HVAC

Numerous physical constraints severely limited viable options for providing dedicated supply and extract ventilation into each suite. There was insufficient space within the building to accommodate the dimensions of the vertical shaft ducts required for roof-mounted ERVs, and the roof space is limited, due to the various third-party communications equipment, which will remain in place as it provides a source of rental revenue for CHC. Running the supply and extract ducts along the suite-facing façades (north and south) was considered and rejected, due to the required length of ducting and number of penetrations. It was determined that ducts could feasibly be run down the side façades (east and west). However, the drop in ceiling height required to accommodate horizontal ducting would conflict with the building code mandated minimum of 7 feet. A fully decentralized system was not acceptable to the client on account of the required maintenance.

After further exploration, a viable solution was found: Install semicentral ERVs in a handful of existing suites on floors 6 and 17. Each ERV would serve one side of the building and five floors, either up or down (see Figure 3). CHC was initially hesitant to sacrifice the rental income from the four suites that would be converted to mechanical rooms, but the alternative of a fully decentralized system was less attractive, and so the strategy was approved. The entire building except for two floors is incorporated into this strategy, due to the DHW circulation return piping concealed in the suspended ceiling. For the corresponding suites that are not incorporated, decentralized ERVs were installed. Common areas are similarly ventilated to keep them separate from the suites.

The semicentralized ventilation presented the opportunity to supply all the heating and cooling needs of the suites via the ventilation air. Analysis revealed, however, that this air would not meet the peak loads of the building. A variable refrigerant flow (VRF) system was then proposed as an alternative. Initial estimates established that this system was going to increase the total construction costs by about 30%, which CHC’s budget could not accommodate. A novel third option was then proposed: installing a Passive House window in front of the existing air conditioner hole and replacing the air-conditioning unit with a high-efficiency model (see Figure 4). The design enables the tenant to use the air-conditioning unit during the summer by opening the window and plugging in the unit, while enabling CHC to lock the window in the winter to minimize heat loss. The cost savings of 80% over the VRF system were sufficiently compelling to convince the client to move forward with this first of its kind, higher-risk solution.

The building also contains a climate control system connected to the heating and cooling systems. This enables CHC to manage the heating and cooling to ensure that conditioned air will not be lost to the outside environment on a continual basis. For example, the system normally supplies sufficient energy to adequately heat or cool each unit independently. If, however, the windows are continually left open, the temperature in the unit will be either hotter or cooler than the setpoint (depending on the season), encouraging the tenants to close the windows or balcony doors.

The remaining mechanical and electrical upgrades include corridor lighting, replacement and insulation of the DHW recirculation pipes, and elevator equipment. Funding is not yet in place for these upgrades, so a time line has not been established.

An interesting discovery is the large discrepancy between the PHPP calculated occupancy (420 occupants) and the actual occupancy (320 occupants). This difference, combined with large corridor lighting and elevator loads, leads to a total primary-energy demand that exceeds the target. A project-specific primary-energy relaxation is being discussed with the Passive House Institute.

Andrew Peel is founder and principal of Peel Passive House Consulting.

PHPP Results:

Space Heating Demand: 25 kWh/m2/yr

Airtightness: 1.0 ACH50 (design)

Primary Energy: 178 kWh/m2/yr (target: 132)

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