Installation of a Fujitsu Aquila XLTH dual-zone heat pump in Ville-Marie, Montreal

A rooftop installation designed for the real constraints of an urban building

Installing a Fujitsu Aquila XLTH dual-zone heat pump in Ville-Marie requires different planning from a residential project carried out at ground level. In this dense area of Montreal, outdoor units often have to be positioned on a flat roof, surrounded by parapets, mechanical ducts, neighboring structures, and equipment already in place.

For this project, our AirGreen team installed a Fujitsu AIRSTAGE outdoor unit on an elevated metal base. The photograph shows a clean, unobstructed installation, with the unit securely fastened above the roof membrane. The R32 marking is visible on the front panel, as is the A2L safety classification associated with this new generation of refrigerant.

This outdoor unit supplies two separate indoor zones. The owner therefore benefits from a system capable of heating and cooling two areas of the building from a single outdoor unit, without multiplying the equipment on the roof.

The installation had to meet several objectives simultaneously:

• maintain sufficient airflow around the unit;
• keep the unit above snow and defrost water;
• properly distribute its weight across the roof;
• maintain access to the service panels;
• limit the transmission of vibrations to the building;
• properly organize the refrigerant lines and wiring;
• provide a solution suited to Montreal winters.

The result therefore depends not only on choosing a reputable heat pump. It depends above all on the quality of the support structure, clearances, sizing, and execution of each connection.

Why a dual-zone heat pump was suitable for this Ville-Marie project

A dual-zone heat pump consists of one outdoor unit connected to two indoor units. Each zone has its own control, allowing the temperature to be adjusted according to the use and needs of the area served.

In a Ville-Marie building, this configuration can be used for cooling and heating:

• two separate dwellings or spaces, depending on the system design;
• a main area and a bedroom;
• an office and a reception area;
• two floors;
• a front section and a rear section of the building;
• an extension that is difficult to serve with the existing system.

One of the main advantages is the reduction in the number of outdoor units. In an urban environment where roof space is limited, every square foot counts. Installing a single outdoor unit for two zones frees up space and simplifies the overall arrangement of the mechanical equipment.

Each indoor unit can be adjusted independently. Occupants can request different temperatures, select their fan speed, and adapt operation to the room’s use.

However, it is important to understand that the two zones share the same primary operating mode. They can heat or cool with separate settings, but one indoor unit cannot provide heating while the other simultaneously provides cooling.

This characteristic must be considered during the design, especially when the two zones have significantly different solar exposures.

A Fujitsu AIRSTAGE unit installed on an elevated base

The photograph clearly shows that the outdoor unit was not placed directly on the membrane. It rests on a metal structure installed above crossbeams that distribute the load.

This elevation serves several important purposes.

Protecting the unit from snow accumulation

Montreal’s flat roofs can accumulate a significant amount of snow, particularly near parapets and obstacles that alter wind movement.

A heat pump installed too low may have its coil or ventilation grille blocked by snow. An obstruction reduces airflow and can impair heating capacity.

Blown snow can also accumulate beneath the unit and then turn into ice when temperatures fluctuate. By installing the system on a sufficiently elevated base, we create clearance that helps the unit continue to breathe throughout the winter.

The required height always depends on the building. Consider:

• typical accumulations;
• the prevailing wind direction;
• the height of the parapets;
• the presence of nearby equipment;
• areas where snow is deposited during snow removal;
• the necessary space beneath the unit for drainage.

Facilitate the drainage of defrost water

When a heat pump operates in heating mode, ice can form on the outdoor coil. The system periodically initiates a defrost cycle to melt this accumulation.

The water produced must be able to drain freely. If the unit is too close to the roof, this water can freeze beneath the chassis and form a block of ice.

A significant accumulation can eventually reach the underside of the unit, block the drainage openings, or create a slippery surface around the installation.

The raised base visible in the photograph maintains a gap between the machine and the membrane. This arrangement facilitates drainage and provides more room to inspect the area beneath the unit.

Distributing the weight across the roof

The weight of an outdoor unit and its support must not be concentrated on a few small contact points. Poor weight distribution can damage the membrane or create unnecessary stress on the structure.

The long bases visible beneath the support help distribute the load over a larger surface. They also prevent the metal feet from resting directly on the roofing membrane.

In a rooftop HVAC project, we must consider not only the equipment’s static weight, but also vibrations, wind-induced movement, and future technician access.

Airflow around the large front-mounted fan

The Fujitsu heat pump shown has a large front-mounted fan. Its role is to move air through the outdoor coil to enable heat exchange.

In heating mode, the unit removes energy from the outdoor air. In cooling mode, it releases the heat extracted from the building outdoors. In both cases, unrestricted airflow is essential.

The unit’s front panel was therefore oriented toward a clear area. No adjacent wall directly obstructs the fan outlet.

Insufficient clearance can cause recirculation. The discharged air then returns toward the coil instead of dispersing. This situation can lead to:

• reduced capacity;
• higher electricity consumption;
• more frequent defrost cycles;
• an abnormal operating temperature;
• extended operation;
• accelerated wear of certain components.

On a Ville-Marie rooftop, this question is particularly important because parapets, neighboring buildings, and other equipment can significantly alter the natural airflow.

Maintaining access to the service compartment

The service panel is located on the right side of the unit. It provides access to the connections, electrical components, and points needed for diagnostics.

The unit must therefore be positioned so that a technician can work without moving the entire system.

Installing it too close to a parapet or mechanical duct makes the following more difficult:

• electrical checks;
• connection tightening;
• valve inspection;
• operational tests;
• error code diagnosis;
• the repair or replacement of certain parts.

Preserving this access from the time of installation reduces the time required for future service calls and helps keep the appliance in good condition throughout its service life.

R32 refrigerant and A2L classification

The photograph shows the marking R32 as well as the A2L safety pictogram. R32 is a refrigerant used in several new-generation appliances.

Its A2L classification indicates low flammability. This does not mean that an installation is dangerous when properly carried out, but this characteristic requires appropriate procedures.

The work must take into account, in particular:

• compatible tools;
• evacuation and vacuum procedures;
• leak tests;
• the amount of refrigerant;
• the type and diameter of the lines;
• the manufacturer’s requirements;
• the ventilation and volume of the spaces served;
• protecting the connections during the work.

An R32 heat pump should not be treated exactly like an older system using a different refrigerant. Technician expertise and adherence to proper work procedures are therefore essential.

Available capacities in the Fujitsu Aquila range

Fujitsu documentation presents 18,000, 24,000, 36,000 and 45,000 BTU/h multi-zone outdoor units. Depending on the model, they can power two to five indoor units.

For a dual-zone configuration, the 18,000 BTU/h model is shown with several permitted combinations, including:

• 7,000 + 7,000 BTU/h;
• 7,000 + 9,000 BTU/h;
• 7,000 + 12,000 BTU/h;
• 7,000 + 15,000 BTU/h;
• 9,000 + 9,000 BTU/h;
• 9,000 + 12,000 BTU/h;
• 9,000 + 15,000 BTU/h;
• 12,000 + 12,000 BTU/h.

The larger-capacity outdoor units also allow only two indoor units to be used in certain combinations, depending on the building’s needs.

Fujitsu’s document specifies that these tables are used to verify permitted combinations, but they do not replace capacity selection. The manufacturer recommends using its Design Simulator software to select H-series AIRSTAGE equipment.

The exact capacity of the installation shown in the photograph is not sufficiently legible on the nameplate to be stated with certainty. Sizing must therefore be matched to the actual model numbers, the load calculation, and the building’s conditions.

Why Adding Up BTUs Is Not Enough

In a multi-zone system, the rated capacities of the indoor units can sometimes exceed the outdoor unit’s rated capacity.

Fujitsu indicates that a multi-zone outdoor unit can accept a connected capacity of up to 130 %, depending on the permitted configurations. However, this does not mean that the compressor will simultaneously produce the full sum of the capacities listed for all indoor units.

When both zones require high output at the same time, the available capacity is distributed.

Sizing must therefore take into account:

• the heat load of each zone;
• the likelihood that both zones will operate at full demand simultaneously;
• solar exposure;
• the number and type of windows;
• insulation;
• ceiling height;
• air infiltration;
• how the spaces are used;
• the design outdoor temperatures;
• the system’s minimum and maximum modulation.

A homeowner should not simply choose the combination with the highest total BTU rating. An oversized selection can reduce summer comfort and lead to less favorable dehumidification cycles.

A dual-zone heat pump designed for Montreal’s climate

Cold-weather heating down to -26 °C

Fujitsu’s Aquila series documentation indicates that the CTEB cold-climate versions can provide heating down to -26 °C.

This value is particularly relevant for an installation in Ville-Marie. Even if the lowest temperatures do not persist throughout the season, the system must remain operational during cold snaps.

However, low-temperature operation does not mean that capacity remains identical to that measured under milder conditions. As with any heat pump, available capacity and efficiency vary according to the outdoor temperature.

A good design must therefore analyze:

• low-temperature heating capacity;
• the building’s heat losses;
• the presence of supplemental heating;
• the control strategy;
• the expected comfort level;
• anticipated energy consumption.

Depending on the building, the heat pump can serve as the primary source for much of the winter, with a supplementary system available when conditions require it.

The variable-speed compressor

The Fujitsu AIRSTAGE range uses an inverter-driven compressor. This technology allows the compressor speed to be adjusted according to demand.

Rather than operating only at full capacity and then shutting off, the unit can modulate its output. This modulation helps maintain a more stable temperature and reduce repeated starts.

In a dual-zone system, it also allows output to be adjusted when:

• only one zone is operating;
• both zones require little capacity;
• one zone is approaching its setpoint;
• both units are operating simultaneously;
• the outdoor temperature changes rapidly.

Modulation does not replace proper sizing, but it improves the system's ability to follow the building's varying needs.

Corrosion resistance on an urban rooftop

Fujitsu documentation mentions a heat exchanger equipped with blue cooling fins designed to improve corrosion resistance and coil longevity.

On a Ville-Marie roof, the unit may be exposed to:

• rain;
• snow;
• freeze-thaw cycles;
• urban dust;
• leaves;
• airborne pollutants;
• windblown debris.

This protection does not eliminate the need for maintenance. The coil must remain clean and unobstructed to maintain heat exchange.

Avoid using harsh products or excessive water pressure, which could bend the fins or damage the surface treatments.

Roof stability and vibrations

An outdoor unit contains a compressor and a fan, two components that may produce slight vibrations.

On a roof, these vibrations can be transmitted to the building if the support is insufficiently rigid or improperly positioned. In some cases, an unobtrusive piece of outdoor equipment can generate a perceptible humming in the rooms directly below.

The quality of the support depends on several factors:

• the rigidity of the metal structure;
• the alignment of the feet;
• the bearing surface;
• the materials used beneath the support;
• the tightness of the fasteners;
• the proximity of structural elements;
• the compressor's operating frequency.

The goal is not only to prevent the equipment from moving. It is also necessary to avoid amplifying vibrations through the roof structure.

The refrigerant line routing

A dual-zone heat pump requires two connection circuits to the indoor units, depending on the outdoor unit configuration.

Each branch generally includes:

• a liquid line;
• a gas line;
• insulation;
• a communication and power cable;
• a drain for the indoor unit.

On a roof, the lines must be protected against:

• ultraviolet rays;
• standing water;
• abrasive contact;
• frequent foot traffic;
• snow;
• mechanical damage;
• bends that are too tight.

The total line length, the length of each branch, and the elevation difference between the units must comply with the manufacturer’s limits.

When the piping exceeds the factory-specified refrigerant charge, a precise addition may be required according to the model’s technical instructions.

Evacuation and leak testing

The quality of the refrigerant connections plays a major role in system reliability.

Before commissioning, the circuit must be checked to confirm that it is leak-free. An adequate vacuum pull can then remove the air and moisture present in the lines.

Residual moisture can lead to:

• acid formation;
• oil contamination;
• restrictions;
• reduced performance;
• compressor damage;
• problems that are difficult to diagnose several months later.

This step is invisible in the final photograph, but it is one of the most important elements of a professional HVAC installation.

Mistakes to avoid during a similar installation

Installing the unit directly on the membrane

This practice restricts drainage, increases the risk of ice buildup, and can damage the roof.

Underestimating windblown snow

An area that appears clear in autumn can become an accumulation point during a storm.

Pointing the fan toward a parapet that is too close

Discharged air can recirculate toward the coil and reduce performance.

Blocking access to the service panel

A compact installation should not make future repairs nearly impossible.

Choosing BTUs based solely on floor area

Two buildings of the same size can have very different heat loads.

Adding up indoor capacities without considering the outdoor capacity

The connected capacity is not always equal to the power available simultaneously.

Neglecting to insulate the lines

Open or water-saturated insulation reduces efficiency and promotes condensation.

Failing to plan for defrost water

Drainage must be planned in advance to prevent an ice block from forming beneath the unit.

Recommended maintenance for this rooftop installation

A heat pump installed on a roof should be inspected periodically, even if it is operating normally.

Maintenance should include:

• checking the outdoor coil;
• removing leaves and debris;
• inspecting the support;
• checking the fasteners;
• checking the lines;
• examining the insulation;
• looking for traces of oil;
• checking the drainage;
• inspecting the electrical connections;
• cleaning the indoor unit filters.

During winter, snow accumulation around the unit must also be monitored. Snow removal must be carried out carefully to avoid bending the fins or damaging the lines.

Do not use an aggressive metal tool against the coil or chassis.

An AirGreen installation adapted to Ville-Marie

This Fujitsu Aquila XLTH dual-zone heat pump installation in Ville-Marie illustrates the importance of adapting each project to its environment.

The challenge was not simply to deliver a unit capable of heating and cooling two zones. It was also necessary to properly integrate the outdoor unit on a flat roof, preserve its airflow, manage defrost water, distribute its weight, and ensure convenient access for maintenance.

The elevated base visible in the photograph addresses the realities of Montreal’s climate. The unit remains raised above the membrane, its front-facing fan has ample clearance, and its panels remain accessible.

At AirGreen, we install dual-zone heat pumps, multi-zone systems, and HVAC solutions in Montréal, Laval, Longueuil, on the North Shore and the South Shore.

We analyze the needs of each zone, the building structure, electrical capacity, line-set routes, and outdoor location before recommending a configuration.

A quality heat pump can deliver the expected results only if every installation step is completed correctly. The support, clearances, sizing, vacuum evacuation, and commissioning are just as important as the brand shown on the casing.

It is this attention to detail that makes it possible to achieve a reliable, accessible dual-zone system truly suited to Ville-Marie’s conditions.