As promised, in this post I’ll share the Toronto Western Hospital Existing Building Commissioning (EBCx) case study as follows:
Location: Toronto, Ontario
Project: Retro-commissioning of Toronto Western Hospital
HVAC Retro-Commissioning including AHUs and chiller operation performance study at Toronto Western started in late 2019. The investigation phase done in March 2021 and the implementation phase completed in Jan 2022. Smith and Anderson was retained by UHN as the consultant and collaborated with in-house staff for performing the study.
Size of Commissioned Area: Toronto Western Hospital is a major research and teaching hospital. TWH has 5 buildings with a total area of 1.2 million square feet.
Total Commissioning Investment: Plus$179,000
Energy Cost Savings: $102,000 (and 2.3%) per year
Simple Payback: 1.75 years
Energy Savings: 10,210 GJ (and 4.5%) per year
GHG Emission Reductions: 492 tonnes (6.47%) per year
Quantified annual non-energy benefits: Improving health, safety and comfort of the hospital patients and staff by complying with design and codes requirements. Enhancing the controllability of the HAVC system components such as fan speed, the status of the VAV box, damper positions etc. result in operational cost savings, more accurate fault detection and faster troubleshooting.
PROJECT OVERVIEW AND BACKGROUND
Toronto Western Hospital is a major research and teaching hospital with 275 beds and more than 66,000 visits to the emergency department annually. Toronto Western Hospital was originally built in 1905 and has undergone several renovations ever since, with 5 wings constructed in different years. Today, the size of the building is more than 1.2M ft2 and there are approximately 4,000 tenants/occupants in the building. The hospital used more than 24.3 GWh of electricity and 4M m3 of natural gas in 2020 amounting to an annual energy cost of $4.5M.
On the mechanical side, TWH has 50 AHUs, 3 Trane chillers with 4800-ton cooling capacity and 5 steam boilers which provide all indoor heating and process heating load. Though TWH has ongoing retrofit and renovation projects, most equipment is 20+ years old. Most of the major systems such as AHUs, boilers and chillers are controlled by the BAS. However, about 40% of the valve and damper actuators are pneumatic, as are nearly half of the terminal unit controllers. The interface between pneumatic and DDC systems can pose a challenge for retro-commissioning because pneumatic actuators tend to drift over time and their actual position may not be reflected at the BAS.
In order to improve the BAS and enhance the performance of the mechanical system, UHN hired an external consultant to perform retro-commissioning of the selected AHUs and the chiller plant. The work included site visits and review of the mechanical drawings and floor plans to identify the zones and field equipment served by respective AHUs, performance analysis of selected AHUs, investigation and control issues of chiller plant operation and terminal unit control issues. Our overall goal was to achieve a more efficient system with minimum investment.
The primary objective of this existing building commissioning (EBCx) project was to reduce the energy usage and carbon footprint of the hospitals by optimizing the energy use of the HVAC and mechanical systems. The secondary objective was to demonstrate the value of EBCx in healthcare facilities to the University Health Network’s senior management and encourage them to consider EBCx projects for other UHN facilities. We have used the term “retro-commissioning” rather than “recommissioning” throughout the document to reflect the significant changes and upgrades to the system relative to the original operation, as opposed to the reinstatement of the original design implied by recommissioning. The other objectives and benefits of the project included:
- Increase comfort level for building occupants and tenants.
- Reduction in utility costs, allowing for funds to be spent toward other initiatives in the building portfolio/healthcare.
- Improve day-to-day operations; retro-commissioning results in a reduction in the number of service calls and requests brought about by underperforming and inefficient systems that require high levels of reactive maintenance.
Environmental Stewardship, including the efficient use of energy, water and other resources, has been a central part of UHN operations for over 20 years. The Energy and Environment (E&E) department of UHN has taken a lead in the continuous improvement of mechanical systems from an energy efficiency standpoint. E&E manages: energy conservation projects, ongoing commissioning, BAS controls upgrades and scheduling, and Greenhouse Gas (GHG) emissions reductions. Performing retro-commissioning and BAS upgrade services are an ongoing mission of the E&E team which is done by the experienced internal BAS experts; however, for large-scale, comprehensive EBCx projects typically the E&E hires a third-party consultant to work with the in-house team. On this project, our E&E team led the work of the consultant and in-house BAS experts and ensured the operation team collaborated closely with the consultant during the project’s investigation phase.
The initial scope of the EBCx project was very broad. However, once we received a few quotes, we realized the original scope had to be limited to meet the allocated budget. Even after revising the scope, still the project cost became higher than the expected price due to the challenges we encountered, the major one being the COVID-19 pandemic.
As mentioned earlier, retro-commissioning at UHN has been recognized as an ongoing task and inherent duty of the Energy and Environment department and operation team. Hence the outcome of the project will result in adjustments in the associated building operation processes and improve the energy performance of the hospital.
INVESTIGATION AND ISSUES IDENTIFIED
Steam Trap Audit
- Several out of service or malfunctioned steam traps were identified
Chilled water system
- Automate chiller staging
- Expand free cooling capacity
- Replace leaky isolation valve and automate free cooling
- Replace supply air temperature sensor
- Operate free cooling during winter months
Air Handling Unit system
- Replace defective temperature sensors
- Replace pneumatic actuators with electrical actuators
- Optimize the control sequence
Although it was not possible to implement all of the recommended measures due to the COVID-19 situation in the hospital, we were able to retro-commission some AHUs, replace some steam valves and optimized the control sequence. The control sequence optimization included modification of PID loops and the addition of seasonal functionality. Instead of having one PID loop controlling heating and cooling valves for all the seasons, three different PID loops are now defined for each season (winter, summer and shoulder season), resulting in more stable heating and cooling valve operation. Sequence optimization has also enabled BAS operators to control the preheat valve and heating valve separately. The original sequence used one PID for both preheat valve and heating valve causing the valve hunting and thus supply air temperature setpoint could not be maintained properly.
The investigation revealed that, the heating valve was unable to close fully in almost 30% of the AHUs which resulted in overheated plenums. The replacement of the valve would result in fan energy and hot water savings. Based on the comparison of available trends for two similar AHUs that the valve was replaced on one of them, fan energy was saved by 56% and hot water usage decreased by 77%. Below is the energy-saving calculation for heating valve replacement of air handling unit MC-AH03.
UHN internal resources will keep working on the reprogramming and retro-commissioning of the remaining system.
IMPLEMENTATION AND RESULTS
The steam trap audit was completed in early 2020. According to the report, out of 626 steam traps, the contractor found 190 traps were out of service and the other 61 traps were defective. UHN Facilities operation team spent more than $25,000 and replaced almost all defective traps. Based on the audit results this would save around 200,000 m3 of natural gas annually.
The obsolete controllers were replaced with new Honeywell controllers and sensors. The new controllers came with a built-in optimization control in the terminal units which already has a positive result on the comfort level of the end-users and improved the energy efficiency of the HVAC system. The new controllers enabled the BAS to apply scheduling strategy during the unoccupied periods, which has led to additional energy savings.
Since the retro-commissioning study of the selected AHUs has identified several EBCx measures, the UHN BAS specialist has upgraded the controllers and re-commissioned 9 AHUs control systems. As a result, the zone temperature are more stable and the heating and cooling valves are less oscillating than before.
The recommendation to perform demand control ventilation may not be good practice at this time due to COVID-19 conditions in the hospital. Most of the units in the hospital are operating in 100% fresh air mode to avoid cross-contamination. This recommendation will be taken into consideration once the pandemic situation terminates.
Although the retro-commissioning study recommended several measures for the chilled water plant, there are various reasons why certain measures were not implemented. One such measure was full automation of the staging of the chillers at the site. The report viewed this as a low-cost controls upgrade, however upon further investigation, it was determined that the control valves on the chillers are leaking. Operators need to manually isolate the chillers in order to stage them. In order to complete this measure, 6-8 large valves would need replacement at an estimated cost of $200,000. This project will be added to our longer term goals and most likely rolled into a larger plant refurbishment. Similarly, the full automation of our free cooling loop would require the replacement of 4-6 large valves at an estimated cost of $100,000. It is useful to have these projects highlighted as future opportunities even though budgets haven’t allowed for implementation on the timeline of this retro-commissioning study.
World Health Organization (WHO) has recognized climate change as one of the most urgent threats to human health in the 21st century. Energy management plays a key role in mitigating the causes and impacts of climate change. A majority of the identified measures in the EBCx study improve the performance of energy use within the hospital so will have a positive impact on global warming and the health of all Canadians.
Below are the other benefits of this project:
- Reduction in utility costs, allowing funds to be spent toward other initiatives in the building portfolio/healthcare.
- Increased comfort level for building occupants and tenants.
- Improved day-to-day operations; retro-commissioning will result in a reduction in the number of service calls and requests brought about by underperforming and inefficient systems that require high levels of reactive maintenance.
The key takeaway from the project is that success is achieved by combining the fresh set of eyes of a third-party commissioning professional with the detailed historical and operational knowledge of HVAC systems held by the building owner/operators. On one hand, the building owner may have long-standing biases and tunnel-vision that can be a barrier to solving systemic issues. On the other hand, the commissioning professional might not understand some of the idiosyncrasies of the site and the history that led to the current state. There is some magic in bringing these two parties together to gain new insights and develop strategies to improve performance.
In order to facilitate this dynamic, scope of work and obligations of each party need to be very clear, while also somewhat flexible. When it comes to existing building commissioning, there are huge numbers of variables and potential paths to explore. This ambiguity and open-endedness can lead to confusion related to scope creep, level of detail of the investigation, calculation methods, monitoring and verification, etc. It is crucial to have a clear strategy, metrics, and goals in mind when undertaking existing building retro-commissioning.
When the experiences of the building owner/operators and the commissioning professional are properly balanced, many useful projects such as those described in this case study can result.
This EBCx is made possible by a financial contribution from Natural Resources Canada.