An HVAC rooftop installation designed for two independent comfort zones
In Saint-Bruno-de-Montarville, we installed a HITACHI airHome Multi dual-zone multi-zone heat pump in a building where the heating and cooling equipment is grouped on a flat roof. The project required much more than simply installing an outdoor unit: the new equipment had to be carefully integrated into an already occupied technical space, the refrigerant lines had to be protected, equipment accessibility had to be preserved, and a durable installation had to be ensured despite the conditions specific to Quebec rooftops.
The site photograph clearly shows the conditions encountered by our technicians: several outdoor units are located nearby, ventilation ducts cross the roof, and the connections must be routed to a central technical cabinet without hindering future maintenance. In this type of environment, every placement matters. A unit installed just a few inches too close to another piece of equipment can reduce airflow, complicate coil cleaning, or make a repair unnecessarily difficult.
We therefore planned this HVAC installation in Saint-Bruno while considering all of the following simultaneously:
- the necessary clearance around the outdoor unit;
- the direction of the air discharge;
- the routing of the two refrigerant circuits;
- access to the electrical disconnect switches;
- protection for the cables and pipes;
- the stability of the unit on the roof;
- maintenance and diagnostic options;
- the presence of the other heating and cooling systems.
The result is a compact, organized installation suited to year-round use.
Why a dual-zone heat pump was suitable for this building
A multi-zone heat pump can power multiple indoor units from a single outdoor unit. In this installation, the dual-zone configuration serves two separate spaces. Each room can therefore have its own temperature and ventilation settings.
This operation is particularly useful when a building includes, for example, a very busy main area and a secondary room used intermittently. Heating and cooling needs are not always identical. A sun-exposed zone may require more cooling, while a room located in the center of the building may retain its temperature longer.
With the HITACHI airHome Multi system, each indoor unit can be controlled individually. One zone can be turned off while the other continues to operate. Occupants can also select their setpoint and fan speed separately.
However, it is important to understand how a multi-zone system works: all indoor units connected to the same outdoor unit must operate in a compatible mode. In summer, they can operate in cooling, dehumidification, or fan mode. In winter, they can operate in heating or fan mode. One unit therefore cannot heat while the other cools at the same time.
This feature is explained in the manufacturer’s technical documentation, which also indicates that the airHome Multi range can power up to five indoor units, depending on the outdoor model selected.
An outdoor unit designed for two independent connections
In the HITACHI airHome Multi range, the outdoor unit designed for a configuration with up to two indoor units is model RAM-G18N2HAA, with a nominal cooling capacity of 18,000 BTU/h and a nominal heating capacity of 22,000 BTU/h.
However, the actual capacity distributed between the two zones depends on several factors:
- the capacity of each indoor unit;
- the length of the lines;
- the outdoor temperature;
- the simultaneous demand of both rooms;
- the building’s heating and cooling load;
- insulation, windows, and sun exposure.
A dual-zone installation therefore does not simply involve automatically dividing the BTUs into two equal parts. The indoor units must be selected based on the heating and cooling load of each room. A combination of two heads with the same capacity may be suitable for some properties, while an asymmetrical combination is preferable when the dimensions or uses differ.
For this reason, at AirGreen, we never determine capacity based solely on floor area. We also assess ceiling height, the number of windows, the building’s orientation, the level of insulation, and internal heat sources.
Performance suited to heating and cooling in Quebec
The HITACHI airHome Multi series uses Inverter technology. The compressor modulates its output rather than constantly operating at full capacity. This modulation generally helps maintain a more stable temperature and reduce start-and-stop cycles.
For the RAM-G18N2HAA dual-zone outdoor model, the manufacturer's documentation presents the following data, among others, for a ductless configuration:
- rated cooling capacity: 18,000 BTU/h;
- modulating cooling capacity: from 7,000 to 20,500 BTU/h;
- rated heating capacity: 22,000 BTU/h;
- modulating heating capacity: from 9,000 to 24,000 BTU/h;
- TRÉS2 reaching up to 23,0;
- Region 5 CPSC reaching up to 7,85;
- heating operation down to -20 °C;
- cooling operation from -10 °C to 46 °C;
- announced outdoor sound level of 52 dB(A);
- refrigerant R32.
These values must always be interpreted according to the exact combination of indoor units and the certification applicable to the installed system. Nevertheless, they demonstrate that airHome Multi is designed to provide a wide modulation range and attractive seasonal efficiency.
In Saint-Bruno, as elsewhere on the South Shore, a multi-zone heat pump must be selected with particular attention to its cold-weather performance. The rated capacity shown at moderate temperatures does not necessarily represent the capacity available during the coldest days of January or February.
According to the manufacturer's technical table, the dual-zone model can provide a maximum heating capacity of approximately 14,300 BTU/h at -15 °C and 9,700 BTU/h at -20 °C. This gradual decrease is normal for a heat pump. It must be considered when calculating heating requirements and planning supplemental heating when necessary.
What the photo reveals about the complexity of the project
The project photo shows several important details that homeowners do not always see once the work is complete.
A roof already occupied by several pieces of equipment
The HITACHI outdoor unit was installed near other air-conditioning units. Our team therefore had to prevent excessive recirculation of the air discharged by the different units. When one unit draws in the hot air discharged by another during air-conditioning operation, its operating pressure may increase and its efficiency may decrease.
We preserved a service clearance around the heat pump while making efficient use of the available space. The side with the fan remains unobstructed, and the service panel remains accessible.
An installation on wooden supports
The unit is placed on sturdy supports that separate it from the roof gravel. This elevation serves several purposes:
- stabilize the equipment;
- limit contact with standing water;
- facilitate drainage beneath the unit;
- reduce the direct transfer of vibrations to the membrane;
- maintain an accessible base for inspections.
On a flat roof, the unit must never be placed directly on the membrane or on an unstable surface. The weight must be properly distributed, and the supports must withstand moisture, freeze-thaw cycles, and movement caused by vibrations.
Two protected refrigerant circuits up to the technical cabinet
Two sets of insulated lines can be seen running from the outdoor unit toward the central cabinet. Each zone has its own refrigerant connection. In a HITACHI dual-zone configuration, the outdoor unit has two liquid connections and two gas connections. 1/4 po and two gas connections 3/8 po.
Insulation for the refrigerant lines is essential. It prevents condensation, reduces heat loss, and protects the pipes against the elements. In the photo, the line sets are grouped and wrapped before entering the technical structure.
This part of the work must be carried out precisely. Insulation that is open, crushed, or degraded by ultraviolet rays can lead to:
- condensation;
- water marks;
- a loss of efficiency;
- premature deterioration of the materials;
- water infiltration around the penetrations.
Accessible electrical connections
Two electrical boxes are visible on the technical cabinet. Their position allows technicians to quickly isolate the power supply during maintenance or repairs. The HITACHI dual-zone unit operates on a 208-230 V, single-phase, 60 Hz power supply.
For model RAM-G18N2HAA, the documentation specifies a minimum circuit ampacity of 16 A and maximum overcurrent protection of 25 A. The final selection of the wiring, circuit breaker, and disconnect must nevertheless comply with the nameplate of the installed unit and applicable electrical requirements.
Commissioning: a step that determines system reliability
A heat pump may appear to be properly installed while having an invisible problem: an imperfect flared connection, moisture in the lines, a slow leak, an incorrect charge, or reversed communication wiring. That is why commissioning must never be reduced to simply starting the unit.
As part of this HITACHI heat pump installation in Saint-Bruno, our procedure includes in particular:
- checking the supports mechanically;
- inspecting the refrigerant connections;
- a leak-tightness test;
- an adequate vacuum pull;
- checking the wiring for each zone;
- confirming the correspondence between the outdoor ports and indoor units;
- a cooling or heating test, depending on conditions;
- measuring supply and return air temperatures;
- listening for vibrations or unusual noises;
- explaining the controls to the occupants.
Circuit matching is particularly important in a dual-zone system. If the communication wiring for an indoor unit is connected to the wrong refrigerant circuit, the system may display an error or distribute refrigerant inconsistently. Clearly identifying the lines during installation prevents this error.
What to Keep in Mind Before Choosing a Multizone Heat Pump in Saint-Bruno
The Practical Benefits of the HITACHI airHome Multi System
The main advantage of this installation is the ability to control two spaces using a single outdoor unit. This approach reduces rooftop clutter while providing independent control of indoor temperatures.
The airHome Multi system also offers several types of compatible indoor units:
- airHome 400 wall-mounted units;
- airHome 650 wall-mounted units;
- floor consoles;
- mini-cassettes;
- ducted units.
This flexibility makes it possible to design a solution based on the building’s layout. A wall-mounted unit may be suitable for an open room, while a concealed ducted unit may be preferred when you want to hide the equipment. A floor console can also be useful when available wall space is limited.
The range also includes air quality and maintenance features, depending on the indoor unit selected. FrostWash technology uses a freeze-and-thaw cycle to clean the coil. The Mold Guard function helps dry the internal components after cooling or dehumidification. Some units also offer a PM2.5 activated carbon filter or a ViroSense S filter.
Mistakes to avoid in a multizone installation
Oversize the outdoor unit
A larger heat pump is not automatically more comfortable. An oversized system may run in cycles that are too short, dehumidify less effectively, and create temperature fluctuations.
Choose indoor units solely based on their appearance
The format and capacity must be suited to each zone. An oversized unit in a small bedroom can produce an uncomfortable airflow, while an undersized head in a space with many windows will operate constantly at high speed.
Neglecting minimum and maximum piping lengths
The manufacturer specifies precise limits. For the RAM-G18N2HAA dual-zone unit, the maximum total length indicated is 165 feet, the maximum length between an outdoor unit and an indoor unit is 82 feet, and the prescribed minimum total length is 16 feet.
These values affect the route selection, refrigerant charge, and project feasibility.
Installing the unit too close to an obstacle
On a rooftop like the one at the Saint-Bruno project, clearances are essential. A heat pump must not be wedged between two units, in front of a ventilation outlet, or against an enclosure that blocks its intake.
Forgetting about future maintenance
Service panels, valves, electrical connections, and the coil must remain accessible. A compact installation must never become an installation that cannot be serviced.
An installation suited to Saint-Bruno, the South Shore, and Greater Montreal
This project illustrates the approach we apply to every multi-zone heat pump installation: analyzing the building, selecting capacities based on actual needs, planning the pipe routing, and integrating the equipment neatly into its surroundings.
Whether the installation is carried out on a rooftop in Saint-Bruno, on a balcony in Montreal, on a slab in Laval, in a building in Longueuil, on the North Shore, or elsewhere on the South Shore, the same principles remain essential: airflow, drainage, insulation, electrical protection, watertightness, and accessibility.
In this project, the main challenge was fitting a new HITACHI airHome Multi dual-zone heat pump among several existing pieces of equipment without compromising its performance or serviceability. Positioning it on supports, grouping the refrigerant lines, and routing them in an organized manner into the technical enclosure resulted in a neat installation suited to long-term use.
For homeowners and property managers looking to heat and cool two zones with a limited number of outdoor units, this configuration is a particularly suitable solution. However, the quality of the result depends as much on equipment selection as on site preparation and execution.