Leveraging energy efficiency to finance HVAC system retrofits

Solar wall at CHUL allowing fresh air preheating.
Solar wall at CHUL allowing fresh air preheating.

Solar power for fresh air preheating

For CHUL, a 230-m2 (2475-sf) solar wall was installed to preheat the fresh air used in some ventilation systems. In optimal winter conditions, the heat gain can reach 12 C (22 F). During summer, dampers allow the fresh air intake to bypass the solar wall and enter the ventilation system without being preheated.

Dynamic ventilation in lab space

At the CHUL hospital,  there is an important laboratory/research department with 43 chemical hoods to ensure proper air quality. The air change per hour (ach) rate was maintained at 12 prior to the project. With 100 per cent fresh air systems, operating costs were high. Motion sensors were installed at each hood, allowing dampers to reduce the exhaust air speed. Additionally, a new air sampling system channelling samples from various areas to a central probe station was installed. This dynamic ventilation system enables efficient monitoring of contaminants and conditions in large areas. The limited number of probes/sensors reduces maintenance costs and the required recalibration for such components. Sensors in the centralized probe station can be changed periodically, ensuring they are always well calibrated. With this new system, as well as motion sensors on each hood and variable-speed drives on the ventilation fans, evacuation rates under normal operation can be reduced. However, if air contaminants are detected, fresh air and evacuation rates can increase rapidly. This translates to significant energy savings on air-conditioning, heating, cooling, and humidification.

Optimization of the various networks

Most of the water networks (chilled and hot water) were optimized to modulate according to the building’s cooling and heating loads. They primarily use two-way valves, making them variable flow networks where the main pumps are controlled by variable-frequency drives (VFDs).

For the chilled water networks, this system prevents excessive heat from the pumps dissipating in the water, an additional cooling load for the chillers. Thus, these optimizations generate savings from both the pumps and chillers. As for the steam networks, all the unused lines following the conversion were removed or capped to minimize heat losses. The supplied steam pressure was also optimized based on the needs of equipment requiring steam.

At HSFA, a stock room was converted into a mechanical space housing a 600-tonne (590-ton) chiller and a 235-tonne (231-ton) heat pump. This chiller rejects outside heat through two new adiabatic cooling towers installed on the roof above, while the new heat pump recovers internal cooling loads to provide hot water for the heating network. This also allowed for an increase in the cooling capacity of that part of the hospital and improved redundancy.

At Hôpital de l’Enfant-Jésus (HEJ), an old internal cooling tower was replaced by a new one located outside, while the room was repurposed to support the electrical load of some of the new equipment and other needs of the hospital.

Controls and buildings optimization

New controls and graphic displays were implemented where needed, along with probes and sensors required to optimize and manage the new systems.

A complete optimization of the systems was conducted at all four sites, including a review of the operating schedules. Simultaneous heating and cooling, occurring on some sites, was also reduced. With guaranteed savings on the line, the design-build firm remained fully involved after the completion of the implementation. Alongside CHU’s building operators, they were making sure the performance indicators were met without compromising comfort.

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