Building Automation System (BAS)
A BAS is a centralized network of hardware and software, which monitors and controls the environment in the building. At 720 King, the BAS controls the central mechanical system which includes the heat pumps, variable air volume terminals, thermostats, heating system main building pumps, boilers, fresh air fans and cooling towers. The automation system is a tool to assist building management in managing the operational performance of the facility as well as the comfort of building occupants. The system automatically notifies building staff of any performance issues outside of normal operating parameters.
While all tenant electrical and mechanical electrical consumption has been metered since the building was redeveloped over 20 years ago, the building is working on has expanded expanding the metering system to provide system-level metering of building equipment in order to better target and understand energy use on a building and tenant level.
The building replaced all of the incandescent and compact fluorescent lamps (lightbulbs) in common areas with more energy-efficient and environmentally-friendly LED lamps. This includes all public corridors, lobbies, washrooms and service rooms. In addition, the aging high-pressure sodium lighting in the parking garage was replaced with LED fixtures complete with occupancy sensors.
Cooling Tower Replacement
Cooling towers help cool the water used in the building’s air conditioning system using evaporation. As the water in the tower comes into contact with the air a small amount evaporates causing the remaining water to cool. This cooler water is then passed through a heat exchanger to cool the water that is being pumped through the building’s heat pumps which heat and cool tenant spaces. When the building was redeveloped a new cooling tower was added and the original cooling tower was refurbished. As this original tower reached the end of its service life the building replaced this with a new more efficient tower. The primary improvement of this new tower is the addition of a variable speed drive which automatically adjusts the speed of the fans in the tower to suit the demand so that additional energy is not consumed unnecessarily. This new tower operates so efficiently that for over 300 days each year the building only requires one cooling tower to meet the cooling needs of the building.
The only other major component of the central mechanical system that was refurbished rather than replaced during the redevelopment of the building were the boilers. As with the original cooling tower, these were refurbished but eventually also reached the end of the service life so required replacement. After much research of all possible options, the building elected to replace the three boilers with new high-efficiency boilers. At the same time, new balancing valves were added to the piping system and the heating water circulation pumps were replaced with new variable speed pumps. The combination of the new boilers with advanced automated controls and the variable speed pumps which adjust the water flow to the building based on heating demand have reduced both natural gas and electrical consumption at the building.
Heat Pump Replacement
The building uses individual heat pumps located in central mechanical rooms on each floor (10 units per floor for office floors) for the purpose of providing air conditioning. There are two main advantages to this approach: the multiple units on each floor reduce the amount of shared mechanical systems between tenants allowing for greater design flexibility and temperature control in each tenant suite, and this equipment has the ability to provide heating or cooling as required by the demands of the space. In 2020 the building completed a 5 year phased replacement of this equipment for all 101 heat pumps that are owned and maintained by the landlord. This new equipment is quieter and more energy-efficient than the original units.
Heat Pump Loop Circulating Pump Replacement
The building uses water source heat pumps (WSHP) which means that the heat pump uses water as a medium to exchange heat to allow for them to heat or cool air. When in cooling mode the units reject heat into the water and when they are heating they draw heat from the water. This water is pumped through the building using 3 large pumps. As these pumps were reaching the end of their service life a study was conducted to determine if there was a more efficient way of operating this system. Heat pumps require a constant volume of water to operate so variable speed pumps which are the simplest, most effective way to reduce energy were never an option. As part of our strategy of reviewing the building as a system, the project team integrated control valves for each heat pump into the heat pump replacement project. These valves close when the heat pump turns off which effectively shortens the length of pipe that the pumps need to keep filled with moving water which allows the pumps to slow down and consume less energy.
Heat Exchanger/Water Filtration
The last major part of the central mechanical system is the heat exchanger. This is basically a series of steel plates that allow water to pass through. The water from the cooling towers passes through one side and the water from the heat pump loop passes through the other. This allows the heat pump loop water to collect or reject heat as necessary to help maintain proper operating temperatures in the water. The building originally had a single heat exchanger with no water filtration which meant that sediment could build up in the plates reducing the efficiency of the exchange of heat requiring the heat exchanger and thus the entire mechanical system to be turned off for an extended period of time for cleaning. As part of the overall system improvements, the building reconfigured the existing heat exchanger and added two smaller units to share the load for the building. This also allows individual exchangers to be by-passed for maintenance while allowing the overall system to remain operational. A water filtration system was also added to each cooling tower loop entering the heat exchanger to reduce sediment and help maintain the optimal efficiency of the exchangers.