Two condensers on a flat roof for balanced comfort in a typical urban building
At AirGreen , we installed two Gree FreeMatch R32 condensers on a flat roof of a residential building in the southwest of Montreal . The client's objective: to stabilize the comfort of two dwellings while limiting the floor space and nuisances at the facade level. The architecture of the building, the clearances available on the white roof and the accessibility via the interior staircase guided our strategy towards a MultiZone installation raised on supports, with routing of the refrigeration lines to the interior wall heads.
Context and reasons for the technical choice
The building, a renovated plex with a roof covered with a white elastomeric membrane , benefits from large open areas and favorable natural ventilation. We favored the FreeMatch R32 range , compatible with 2 to 3 zones per condenser , to efficiently serve the main living areas of each dwelling (living room and bedrooms). The determining points:
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R-32 refrigerant with lower GWP than R-410A and better heat exchange.
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Extreme cold operation down to −25°C , suitable for Greater Montreal winters.
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High efficiency and inverter modulation, guaranteeing savings in heating and air conditioning.
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Configuration flexibility (generous line lengths and multiple indoor unit formats).
Roof installation: structure, load and vibrations
To respect the membrane and ensure wind stability, we installed each condenser on an aluminum base placed on a treated wooden frame (4×4 soles) itself resting on distribution pads . This approach:
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Distributes the load without puncturing the membrane.
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Facilitates maintenance (360° clearance around the units).
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Reduces vibrations thanks to silent blocks inserted between the base and the chassis.
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Preserves the flow of rainwater , essential on flat roofs.
The two condensers are aligned in the direction of the prevailing winds , with optimized spacing to avoid recirculation of hot air in heating mode. The suction and discharge heights comply with the manufacturer's recommendations in order to maintain the efficiency of the exchangers.
Refrigeration and electrical path: cleanliness and durability
From each condenser, the insulated copper tubing and the communication/power cable are sheathed in a black UV sheath and secured at regular intervals. The route follows a common central path to the point of penetration, then splits to serve the dwellings.
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Waterproof roof penetration via a metal penetration cap and membrane-compatible flashings .
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Vapor barrier foam and reconstituted air barrier to prevent condensation in the thickness of the roof.
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Expansion loops near units to absorb thermal movements.
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Condensate management by gravity flow inside, with controlled slopes towards the wall outlets.
The dedicated electrical circuit for each condenser is connected to waterproof circuit breakers installed nearby, with UV-resistant conduits . The ratings and protections correspond to the nominal currents of the machines and the line lengths.
Interior integration: multi-room comfort without ducts
On the interior side, the MultiZone configuration allows two wall-mounted heads to be supplied per dwelling (living room + master bedroom). The wall penetrations have been drilled at a slope for condensate management, and the interior covers matching the decor ensure a discreet finish. The total lengths per zone remain within the recommended envelope to preserve overheating/subcooling and guarantee performance in accordance with the technical data sheets.
Air quality and seasonal performance
The selected FreeMatch R32 units combine:
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Multi-layer filtration (washable pre-filter and high surface area media) to limit dust and allergens.
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Intelligent defrosting in heating mode, limiting cycles and maximizing heat output.
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Automatic restart after power failure, a plus for urban buildings.
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Sound levels are kept low thanks to inverter compressors and optimized pitch fans.
Result: appreciable temperature stability during cool spring nights and heat waves, with a high COP in mid-season which significantly reduces operating costs.
Construction site challenges… and AirGreen solutions
Access and schedule. To minimize the impact on occupants, the lifting of equipment and the fixing of the legs were planned for the end of the day , when the roof is clear and surface temperatures drop, limiting the risks to the membrane.
Lighting and safety. The partial nighttime installation required directional work lighting , lifelines , and signage for traffic areas. Each frame anchor was checked to avoid any point stress on the membrane.
Air recirculation. The distance between the two condensers and the orientation of the discharges were calculated to avoid thermodynamic short-circuiting , while maintaining sufficient distances from the roof edges.
Route management. Grouping lines into a central shared sheath reduces wind resistance and simplifies future maintenance . Stainless steel clamps and abrasion-resistant pads prevent insulation wear.
HVAC Maintenance: What We Recommend to Homeowners
To maintain performance throughout the seasons, we offer an HVAC maintenance program :
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Spring : gentle cleaning of the condenser fins , checking of the silent blocks and the chassis seat, visual inspection of the flashings and the penetration cap.
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Summer : dusting of interior filters , checking of rare defrosting in air conditioning (signs of clogging).
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Autumn : inspection of electrical connections , terminal torque, overload and sensor testing.
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Winter : watch for snow accumulations ; even if the units are raised, periodic clearing improves air intake during very cold weather.
Annual maintenance by our technicians ensures the longevity of equipment, limits efficiency losses and extends the life of compressors and fans.
Grants and Compliance
High-efficiency MultiZone wall-mounted heat pumps using R-32 and offering sustained performance in cold weather are generally eligible for grant programs available in Quebec, subject to official criteria (minimum efficiencies, installation documentation, certification by a licensed contractor). We assist our clients in preparing files : serial numbers, detailed invoices, proof of testing and commissioning.
Results observed after commissioning
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Quick rise in comfort in the main rooms of both dwellings.
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Low exterior noise level , imperceptible from the street.
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Controlled consumption thanks to modulation and balancing room by room.
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Preserved aesthetics : no units on the ground or on the front facades, all connections being grouped on the roof and in a discreet duct.
Best practices to remember for installation on a flat roof
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Always distribute loads with chassis/soles adapted to the membrane.
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Ensure suction/discharge clearances and non-recirculated airflow .
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Protect lines from UV and abrasion; avoid tight beams.
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Ensure the sealing of the crossings (air barrier, vapor barrier, flashings).
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Plan for maintenance : safe access, circuit breakers within reach, removable covers.
AirGreen in Greater Montreal
Whether on a flat roof in the Southwest , in a house in LaSalle , a bungalow in Laval or a plex in Longueuil , we adapt the HVAC installation to the building, the local climate and the occupancy habits. Our strength: controlled execution details , which make the difference in the middle of winter as well as in heat waves.
Conclusion
This installation of MultiZone Gree FreeMatch R32 heat pumps on a flat roof in the Southwest combines efficiency, sobriety and urban integration . The choice of R-32, the installation on raised bases and the centralized routing of the connections guarantee a reliable, durable and easy-to-maintain system. It is the very illustration of the AirGreen approach: precise comfort, careful aesthetics and real efficiency for the residences of Greater Montreal .