A rooftop installation designed to cool and heat two zones with a single outdoor system
In this building in Brossard, the objective was clear: to provide independent comfort control in two interior spaces without adding multiple outdoor units to the property. We therefore completed the installation of a dual-zone HITACHI airHome Multi multi-zone heat pump, a solution that connects two indoor units to a single outdoor unit equipped with Inverter technology.
The most visible feature of this project is the location of the outdoor unit. Rather than installing it on the ground, against a façade, or on a balcony, we positioned it on a flat roof above the building. This configuration frees up space around the building and keeps the equipment away from traffic areas. However, it requires much more thorough preparation than a conventional wall-mounted installation.
The worksite photo notably shows:
- the HITACHI outdoor unit installed on an elevated support;
- a structure resting on protective crossbars adapted to the roof;
- the refrigerant lines grouped inside an insulated sleeve;
- an organized mechanical route along the roof;
- an electrical disconnect installed near the unit;
- sufficient clearance in front of the outdoor coil to promote airflow.
Every detail plays a role in the reliability of this HVAC installation in Brossard. On a roof, it is not enough to simply place the equipment on a platform. We must consider stability, drainage, wind exposure, vibrations, access for maintenance, and membrane protection.
Why was a dual-zone heat pump suitable for this building?
A single-zone wall-mounted heat pump generally serves one main area. In a building with two spaces having different needs, this solution can become restrictive. A very sunny room may require more cooling, while another, shadier zone quickly reaches its set temperature.
The HITACHI airHome Multi system allows each indoor unit to have:
- its own setpoint;
- its own fan speed;
- its individual settings;
- its operating schedule;
- independent start or stop.
One indoor unit can therefore operate while the other remains off. However, it is important to understand an essential characteristic of most multi-zone systems: units connected to the same outdoor unit must operate in a compatible mode. In summer, they can be used for cooling, dehumidification, or ventilation. In winter, they operate in heating or ventilation mode. One zone normally cannot request heating while another requests cooling.
This explanation is part of our approach at AirGreen. Before recommending a multi-zone heat pump, we assess not only the size of the rooms but also how the occupants intend to use each space.
A raised platform to protect the appliance and the roof
The outdoor unit was installed on a metal platform supported by crossbeams laid on the roof. This setup distributes the load and prevents direct contact between the equipment and the white membrane.
The elevation provides several benefits:
- Water can flow beneath the structure without becoming trapped around the appliance.
- The unit remains more accessible for inspections and future service work.
- Vibrations are better controlled thanks to a stable mounting.
- The heat pump base is elevated above the roof surface, which facilitates drainage produced during defrost cycles.
- The lines can be routed neatly to the appliance without placing excessive strain on the connections.
When a heat pump operates in heating mode, the outdoor unit may produce water during defrosting. On a flat roof, this water must be able to drain away without damaging the membrane or creating a problematic buildup around the base. That is why the support height, the roof’s natural slope, and the location of the drains must be assessed before the work begins.
Essential front clearance for performance
The large coil visible on the front of the outdoor unit must remain unobstructed. Ambient air passes through this coil so the system can absorb or release heat depending on the season.
A poor practice is to place the unit too close to a parapet, wall, other equipment, or architectural obstruction. This can cause recirculation of the discharged air, reduce efficiency, increase noise, and force the compressor to work harder.
In this installation in Brossard, the unit was positioned toward an open area of the roof. The clearance in front of the coil helps maintain efficient heat exchange, particularly on hot days when the roof temperature can be significantly higher than the ambient air temperature.
Refrigerant lines protected along their entire route
The lines connecting the outdoor unit to the two indoor units are visible at the base of the installation. They are grouped together and wrapped in protective insulation suited to the outdoor route.
In a dual-zone system, each indoor unit generally has its own piping circuit leading to the outdoor unit. Depending on the model and the capacity of the indoor units, the connection sizes may vary. The airHome Multi range notably uses liquid connections of 1/4 po, accompanied by gas lines whose diameter depends on the capacity of the connected unit.
HITACHI documentation indicates that the two-connection outdoor model can accommodate up to 165 feet of total piping, with a maximum of 82 feet between the outdoor unit and an indoor unit, provided that all of the manufacturer’s installation limits are respected.
These values do not mean that the lines must be this long. In practice, we seek a logical and efficient route in order to:
- limit performance losses;
- reduce the number of bends;
- protect the insulation from UV rays and the elements;
- avoid areas where water could accumulate;
- allow reasonable access for maintenance;
- preserve the building’s appearance.
An accessible disconnect switch for safe servicing
On the side of the support, we can see the electrical box serving as a disconnect point near the outdoor unit. This component makes it possible to isolate the equipment during maintenance, troubleshooting, or repairs.
For a rooftop heat pump, the location of the disconnect switch deserves particular attention. It must be accessible without requiring the technician to stand in an unstable position or pass in front of the unit’s fan. The wiring must also be protected against movement, moisture, and mechanical damage.
The HITACHI airHome Multi system operates on a nominal supply of 208 to 230 volts, single-phase, 60 Hz. The circuit capacity then depends on the selected outdoor model. For the two-connection version, the brochure specifies a minimum circuit ampacity of 16 A and maximum overcurrent protection of 25 A. Final sizing must always be based on the nameplate of the equipment actually installed.
What HITACHI airHome Multi technology brings to everyday use
The HITACHI airHome Multi range includes outdoor units from 18,000 to 42,000 BTU/h that can serve two to five zones. In a dual-zone configuration, a single outdoor unit serves two indoor units, reducing rooftop clutter and simplifying the overall installation layout.
Inverter modulation rather than on/off operation
Inverter technology adjusts the compressor speed according to actual demand. As the rooms approach their target temperature, the system can reduce its output rather than shutting down completely and restarting a few minutes later.
This modulation provides several practical benefits:
- more stable indoor temperature;
- fewer abrupt fluctuations;
- generally quieter operation;
- energy consumption better suited to actual needs;
- better management of partial-load demand when only one zone is operating.
In a two-zone building, this modulation capacity is particularly useful. The heating demand is not always the same in both spaces. The system therefore adjusts its operation based on the active indoor units and their respective loads.
Seasonal performance suited to year-round use
Depending on the combination of indoor units, the range can achieve a SEER2 of up to 23.0 and a HSPF2 Region 5 of up to 7.85. For the outdoor system with two connections, the stated rated capacity is 18,000 BTU/h in cooling and 22,000 BTU/h in heating.
The manufacturer also specifies heating operation down to -20 °C. At this temperature, the available capacity decreases compared with the rated capacity, which is normal for an air-source heat pump. The dual-zone version has a published maximum capacity of 9,700 BTU/h at -20 °C.
This information must be properly understood. An air-source heat pump is not selected solely based on the number of BTUs stated in its commercial name. We must also examine:
- the building’s heat loss;
- actual low-temperature capacity;
- insulation;
- the floor area and ceiling height of the rooms;
- the number of windows;
- solar orientation;
- the presence of auxiliary heating;
- the occupants’ usage habits.
An oversized unit is not automatically more comfortable. In a multi-zone system, the permitted capacity combinations between the different indoor units must also be respected.
Several indoor unit styles can be combined
One of the advantages of the airHome Multi range is the ability to connect different types of indoor units to the same outdoor unit. The brochure specifically presents:
- the airHome 400 wall-mounted units;
- the airHome 650 wall-mounted units;
- the airHome Floor floor consoles;
- the ducted units;
- the four-way mini-cassettes.
This flexibility makes it possible to adapt each zone to the building’s architecture. A wall-mounted unit may be suitable for an open area, while a ducted unit may be preferable when the equipment needs to be concealed. A floor console can be an interesting solution when overhead space is limited.
For this installation, the dual-zone configuration makes it possible to create two distinct comfort zones while retaining a single outdoor unit on the roof.
FrostWash, filtration, and internal humidity management
Some compatible indoor units incorporate FrostWash technology. It uses a freezing and thawing cycle to help clean the heat exchanger coil and remove accumulated contaminants.
The Mold Guard function helps dry the internal components after an air-conditioning or dehumidification operation. The fan may continue circulating air for approximately 60 minutes to reduce conditions that promote mold formation and odors.
Depending on the selected indoor unit, different filtration solutions are also available, including:
- a PM2.5 activated carbon filter;
- a ViroSense S filter;
- a washable pre-filter;
- features designed to reduce particles, odors, and certain contaminants.
These devices do not replace maintenance. Filters must be cleaned periodically, and the condition of the coils must be checked. A well-maintained heat pump maintains better airflow and operates under less strain.
Mistakes to avoid when installing a multi-zone system on a roof
This project highlights several important points for building owners and managers in Brossard, Montreal, Laval, Longueuil, the North Shore, and the South Shore.
Installing the unit directly on the membrane
Weight, vibrations, and movement caused by operating cycles can damage the roof surface. A suitable base and proper load distribution are essential.
Neglecting defrost water drainage
Water must not remain beneath the unit or form an ice zone near the service access. The mounting location must account for the slope and drains.
Leaving the lines unprotected
Degraded insulation reduces performance and can lead to condensation. Exposed lines must be supported, insulated, and protected along their entire length.
Choosing indoor capacities without validating the combination
In a multi-zone system, the total capacity of the indoor units cannot be chosen arbitrarily. Combinations must comply with the manufacturer's tables.
Overlooking future access
An installation may appear functional on the day it is commissioned while becoming difficult to maintain over time. We plan the space required to inspect the coil, connections, fan, and electrical components.
A clean installation today, but above all, one that can be serviced tomorrow
At AirGreen, we believe that a good heat pump installation in Brossard should remain logical for years after the work is completed. The mounting, lines, wiring, and clearances must allow a technician to service the system without unnecessarily dismantling the installation.
This rooftop project demonstrates that a HITACHI airHome Multi dual-zone multi-zone heat pump can be cleanly integrated into a building when mechanical planning is carried out precisely. A single outdoor unit serves both zones, the coil has unobstructed space, the lines are protected, and the entire assembly is raised above the membrane.
For homeowners who want to cool and heat two spaces independently, a multi-zone solution can reduce outdoor clutter while providing more precise comfort control. However, the outcome depends as much on capacity selection as on installation quality.