Clean water is essential for modern buildings and hospitals are no exception. Toronto and many cities usually supplies tap water at around 50 psig, which is only good for low rise buildings. At PMH the building on 610 University Ave. side is 20 story high (we got 2 levels on 19th floor and there is 13th floor which is not accessible by elevators) so there is no way city water can go that high. Thanks to some genius plumbing engineers many years ago, people developed several different systems to give water a boost so that people in modern skyscrapers don’t have to go downstairs to get water for everything. The domestic cold water (DCW) booster system installed at PMH is triplex single stage constant speed centrifugal booster pumps. Regardless of actual demand, the pumps will run at full speed all the time. To maintain stable water pressure to the building at around 200 psig, a pressure reducing valve (PRV) was installed on each pump discharge to consume excessive pressure head. Whenever you see those PRVs, you know there is an energy hog in your building. Most of the time, those PRVs were choking the pumps.
Figure 1: PRV on existing booster pumps.
Because there is not enough capacity of emergency power supply, only the lead pump is on emergency power circuit and the other 2 lag pumps are on normal power supply. The control panel cannot rotate the pumps automatically and the building operators are reluctant to run lag pumps manually since nobody knows when there will be a power outage. In the past 20 years we always run this single pump for DCW supply and it started to show signs of wear and tear while the other 2 booster pumps in like new conditions are sitting there doing nothing at all. This is not reasonable way to use our expensive equipment.
Replacing the booster pump package may be easy for commercial or residential buildings since you can shut down the DCW system but for hospitals it’s quite different. At PMH, 14th to 18th floor are patient rooms and many patients are immunocompromised individuals to the highest degree who are vulnerable to hospital acquired infections. Eric Devine, UHN’s Infection Control Practitioner – Construction Lead started to work with the project team at early stage. He pointed out that the predominant pathogens of concern in biofilms that form on plumbing surfaces are Pseudomonas, non-tuberculosis Mycobacterium and Legionella. To protect the patients, he requires no sudden flow or pressure fluctuation during the whole process of the pump package replacement to avoid disturbance on the biofilm.
Figure 2: Galvanized steel and cast iron on existing system may not be ideal for DCW supply.
Energy & Environment Dept. worked with PMH Facilities Management team to design a temporary DCW water supply from 2 new tie-ins on existing supply lines. From pre-project audit we know the demand is relatively stable during night time so it’s possible to use one of the new pumps to maintain water supply even without a controller or pressure sensor. However the new booster pump system must be installed and commissioned overnight since during day time there is quite some fluctuation of demand and we must rely on the factory supplied control panel to maintain the pressure.
Figure 3: Tie-in with isolation valve for temporary water supply. Note to protect the patients, new stainless steel pipes were installed by the contractor.
The other challenge the project team was facing is there was no shutoff valve in the pump room. PMH FM team identified 2 shutoff valves on ground floor but they are hidden in areas that are very difficult to reach. Energy & Environment team decided to freeze the pipe using liquid nitrogen and install 2 new shutoff valves in the pump room after the temporary pump is online. Once the new shutoff valves were installed, pipe freeze could be removed and new booster pump package installation could start. This saved a lot of time for the installation.
After careful planning and a lot of preparation work, eventually Canadian Tech Air Systems (CTAS), the contractor came in for new pump installation in August, 2017. First they connected one of the new pumps to previously installed tie-ins and run its VFD in manual mode for temporary water supply. Test run of the pump lasted one hour as directed by Leonard Fearon, manager of FM team, which is to make sure it was stable. Once this was verified, they shut down existing pump package and monitored pump discharge pressure. Just as we expected, without VFD speed control or PRV, the pump discharge pressure was very stable which means patients inside the building were protected. Following that pipe freezing for new isolation valves and pumps started. Since the water flow had stopped in that section of pipe, it only took about 30 minutes to freeze the pipe but remember there is 200 psi pressure on the building side of the ice plug and it was holding really well.
Figure 4: Pipe freezing in process with 200 psi pressure on building side. That’s 13.6 atmospheric pressure.
The next step is to install 2 isolation gate valves on the main headers and then the new DCW booster pump package. The mechanical room also has some other equipment and it’s quite some challenge for CTAS crew members to get rid of the old package and move the new package to the right location around the same time. The new booster pump package is lighter than old one but still weighs almost 4,000 lbs. At one moment we have over 10 people working diligently in this small mechanical room.
Figure 5: People working diligently in the mechanical room.
Eventually the new booster pump package was online and pump manufacturer representative came in to do pump startup and commissioning. Once everything was tested and verified, the temporary pump was put back to the package and another commissioning was done. When those were complete, it was almost 5 AM, well before the DCW demand started to go up. During the whole process there was no noticeable pressure fluctuation. As precaution, Leonard and Eric directed FM team to flush plumbing fixtures from top floor to ground floor for 10 minutes.
The new DCW booster pump package is sized properly to match the demand. To reduce friction loss we specified full port ball valves on each branch and increased branch pipe size. The new control panel monitors the discharge pressure continuously and modulates operating pump speed to just maintain the right pressure. This replaces the old PRV and there is no excessive pressure wasted.
Figure 6: New stainless steel DCW booster pump package before insulation was installed.
Due to limited capacity of existing emergency power supply, only one of the new pumps and the control panel are on emergency power. In case of power failure, the control panel will automatically switch on that pump regardless whether it’s lead pump or not. This gives us the peace of mind to rotate the pumps every 2 weeks to get equal running time on each pump although 2 out of 3 pumps are on normal power supply.
In addition to other benefits, the last thing we care about is energy (just for this project). Post-project monitoring proved the saving is about 189,500 kWh per year. That’s about 30 cars removed from the street. This is all because of seamless cooperation and team work between Facilities Management, IPAC, CTAS and many other people who got involved in the project.