Information taken from Gary Chang’s, lead engineer of the HVAC Division at Mitsubishi Electric, Refrigeration Technical Training presentation titled “Case Study of Mitsubishi Electric’s Head Office Retrofit” on June 26.
Canada has cemented its position on electrification following its initial signing of the Montreal Protocol and then agreeing with the Kigali Amendment. Consequently, Canada has set targets to reach net zero by 2050.
This means that the residential, commercial, industrial, and institutional sectors will need to transition to energy-efficient technologies and solutions. This transition has started with the implementation of technologies, such as heat pumps. The next step for Canada is the transition to lower GWP refrigerants for certain types of air conditioning and refrigeration systems in Canada. For more information on the transition towards A2L refrigerants, visit Tim McRae’s article on page 26.
Since then, companies have accepted the challenge of adopting new refrigerants, embarking on new product lines and embracing them in their facilities. One such example is the retrofit of Mitsubishi Electric’s head office, which saw a variable refrigerant flow (VRF) heat recovery system replace its rooftop unit.
Net zero sustainable vision
Mitsubishi Electric has committed to following its company-wide net zero transition. The manufacturer has a sustainability vision for 2050, which consists of its subsidiaries being net zero by 2031. To achieve this goal, the company followed the greenhouse gas protocol, which provides organizations with a full picture of its environmental impact.
Scope one focuses on emissions created directly by a company. Scope two focuses on emissions indirectly created through purchased energy. Scope three focuses on the entire value chain.
Currently, Mitsubishi Electric is on scopes one and two. This was a driving force behind retrofitting its head office, which was constructed in 1991 in Markham, Ont, and consists of two floors and occupies 20,000 sq. ft.
The equipment for the building has been the same since the building’s construction. The equipment includes a 90-ton R-22 rooftop air handling unit with a VAV box for cooling, and baseboard and duct heaters for heating the first floor.
As stated in the testing and balancing report conducted in September 2019, the outside air damper is fixed at 10 per cent open and is mixed with return air, conditioned, and ducted to fan-powered boxes throughout the main floor. The central rooftop unit serves the whole first floor of the office, resulting in the fan-powered boxes having electric reheat coils to serve the perimeter spaces with heat while cooling the interior spaces.
The system had a partial retrofit done in the past, which saw the addition of a geo-exchange water source VRF system that was paired with a small ERV and ducted to the cassette fan coils in each of the spaces for conditioning and distribution.
There are also three dedicated cooling-only split systems to serve the computer server room in the central-western part of the office.
The rooftop unit was a Trane unit with two compressors, each with two stages. However, the heating coil inside the unit was never used, so the system relied on an electric duct heater and baseboard heater. Over the years, the rooftop unit had various issues, including compressor replacements and leaks.
Challenges
No retrofit project is ever straightforward. There were some challenges that needed to be solved. The first was that the existing VAV, ductwork, and baseboard heaters had to stay. The second was ensuring there was comfort throughout the entire first floor with various needs for large offices, meeting rooms, small offices, open spaces, and common areas. Lastly, the office’s innovation center would utilize the existing geothermal loop.
With this in mind, there were three potential solutions: replace both the cooling coil and R-22 compressors inside the existing RTU with a condenser and LEV kit, replace the entire RTU with a new packaged system with ERV and heat pump, or install a VRF system. The option that was chosen was installing a VRF with an ERV, with he VRF utilizing R-410A.
Compared to the previous system with electric heaters, the COP of the system was one, while the new VRF system has a COP of up to four.
Getting the job done
This retrofit project started in July 2022 and finished later that year. The full equipment list for this project included nine outdoor units, nine branch controller boxes, 44 indoor units (ducted and cassette), eight lossnay ERVs, two cooling-only P series, eight humidifiers, and a web-based central control system.
The benefits of choosing a VRF with an ERV system included reducing the cooling capacity from 90-tons to 60-tons, the ERV was now providing zone-to-zone ventilation while the VRF was providing zone-to-zone temperature control. With the office setup, the VRF system would be placed closer to the zone it serves. This decision reduced the amount of refrigerant, piping, and ductwork needed.
This setup also helped change the configuration of the data center. Before, the office’s entire server was dedicated to the 90-ton unit. Now, the 60-ton unit requires just two racks. Additionally, with the new setup, the office can do precision cooling for just the racks inside the room, reducing heat loss.
Energy analyses were conducted to determine which equipment would be used, alongside heat loss and gain calculations. Since the project required new condensers on the roof, a structural analysis was required to ensure all components of the system could safely be installed.
In 2023, the building was saving close to 50 per cent of electricity by switching to the VRF system. Additionally, the office saw its electricity usage reduced to 543,298 kWh, compared to 1,141,902 kWh in 2021, which resulted in savings of $53,000 in electricity usage.