Many buildings have at least one HVAC piping system that is used to provide comfort to occupants or handle a process. These systems typically include hot water, condenser water, chilled water and steam. The intent of this article is to discuss common issues faced with reusing existing piping infrastructure and recommended maintenance of piping to prolong life and increase reliability.
The most common materials used for piping in HVAC are steel and copper. Steel is generally reserved for piping larger than 2” but in many buildings older than 20 years it is common to see threaded steel piping smaller than 2”. Copper has now become the most popular material choice for smaller piping with the rise of press fittings, which is less labor intensive than threaded pipe and fittings. While steel generally has a thicker wall than copper pipe, it has a lower electrode potential and thus more readily corrodes in systems with both copper and steel pipe.
Why care about whether the piping in your building is steel or copper?
If your building is being renovated there is a good chance it was built more than 20 years ago and has a good amount of steel piping. More often than not the steel piping will be the first to fail. One of the most common causes of failure in piping is corrosion which is often caused by poor water quality. All piping systems require treatment of the fluid they convey whether they are open or closed to atmosphere, liquid or steam. Most piping systems are designed with a water treatment system which introduces chemicals and removes air to improve water quality and extend the life of the piping system. These systems typically work well when the system is first installed but are often neglected after the specified maintenance period has elapsed. The more the system is renovated, the more likely untreated city water is introduced which dilutes important stabilizing chemicals and introduces oxygen to the water. Each of these contributes to piping corroding away over time.
A second item that causes issues is sediment build up. Sediment in pipe in the form of dissolved piping from corrosion or dirt and grease introduced during installation of new systems will collect in points of the system. Common places are low points such as the base of risers, which is where drain valves are located (or should be). These can fill up and render them useless.
The third most common item that is often overlooked is the location and operability of isolation valves. Isolation valves are strategically placed in systems to allow areas of piping to be shut down without having to turn off the entire system. You wouldn’t want to turn off your entire building if you were renovating a small office suite on the fourth floor, would you? The problems with isolation valves is that they are rarely used or simply don’t exist. Without being exercised, when water quality is poor and sediment builds up valve seats will degrade, stems will leak and the valves will no longer provide positive shut off. When it comes time to renovate an area you may find you can’t isolate the area and must drain down large parts of the building at a cost of time and money.
In closing, the importance of maintaining piping systems to prevent costly change orders during renovation projects cannot be overstressed. Proper maintenance will lengthen the life of piping systems, reduce catastrophic pipe failures and reduce unforeseen conditions on projects which cause change orders and schedule delays. When developing a maintenance plan or considering a renovation project, consider the following:
When was the last time I flushed out my system to remove dirt and cleaned or blew down strainers, including those located at terminal equipment?
Does my pumping system have an air or combination air/dirt separator that is functional and properly located on the suction side of the pump?
When was the last time I had the water in my piping systems tested and do I have an annual preventative maintenance program?
Can I achieve positive shutoff with major isolation valves or are the seats and seals failing? If I don’t have isolation valves is there a project coming up where we can add some?
Do I have a way to drain down the system without causing major interruptions to other areas not being renovated? Do my drain valves flow water when opened or are they plugged?