As I set down to work on this article, I have just returned from the “end of the world” and the “bottom of the world.” My wife and I visited South America and Antarctica. The southern tip of Argentina, at the terminus point of the Pan-American Highway, is in the Puerto Madryn National Park. And after visiting the “end of the world,” it only seemed logical that we continued on to the area of the South Pole, Antarctica, or the “bottom of the world.” It was a trip of a lifetime, allowing me to observe the differing styles of plumbing found in those parts of the world. I’ll save those observations for another time, while I get into my topic for this article, “Identifying back-feed potentials within domestic hot water risers.”

Much of this article is pulled from an article on “Commissioning” by Miles Ryan, PE, in which he discussed the typical issues found in high-rise residential buildings. While, in my view “residential” is a misnomer, since we are discussing a high-rise structure. Regardless of what is contained within the high-rise structure: offices, retail, hotel spaces or individual residential units, the mechanical systems that support their operations are basically the same. And for the purpose of this article, we shall restrict ourselves to the domestic hot water and associated return systems.

As Mr. Ryan points out in his article, his involvement has never been in new construction commissioning. In his area of expertise, commissioning is typically “value engineered” out of the project delivery process for these types of buildings. After all, in the developers’ view, it is better to put more effort and money into making these condominiums look pretty than to ensure the building systems operate properly. It will be several years after the completion of the project before operational issues are really noticed, and by that time, the developer is long gone and the new condo association will be the group that has to deal with any such issues.

As with many things in life, each of us has a different perspective on what a high-rise condominium means. Some would simply look at it as a collection of individual residential units stacked on top of each other. And, to some extent, that is true. However, I would look at it as a grouping of individual residential homes collected into a neighborhood (high-rise building) that is served by central services (water, drainage, gas, electric, etc.) that must be independent for each unit. Every unit must be able to be isolated from the central services, so as to avoid impacting other units within the area. Issues within a single unit should never interfere or become a concern of the neighboring units.

These types of issues were the basis of Mr. Ryan’s article. As he states, inevitably there will come a time when owners of individual units will need to repair or replace fixtures or associated piping. Unfortunately, fixtures and/or branch lines serving such fixtures were not provided with local isolation valves. These were either value-engineered out of the project or the design team lacked sufficient knowledge of the operation and service needs associated with such a facility. This becomes a failure to provide adequate and strategically placed service valves resulting in sections of risers or branch distribution lines being taken out of service and potentially drained as part of the service on a single unit or fixture.

When a system is properly designed, one should never need to isolate a riser or drain it down to service a single unit.

While this certainly will be an inconvenience to the surrounding units, it will also add time, costs and coordination hassles for what should be a simple repair or replacement within a localized unit.

When a system is properly designed, one should never need to isolate a riser or drain it down to service a single unit. However, there may be occasions when risers might need to be isolated; generally, this would be if a block of units were being renovated at the same time. And the number of risers will increase if the original design utilized poor piping layouts and allowed crossovers at fixtures. It all goes back to the fixture layout and how the engineer designed the systems.

Often, one will find that the floor plans are identical from floor to floor. This configuration is conducive to collecting various like fixtures on a common riser such as water closets, hand sinks, tub/shower units or kitchen sinks. This is when one needs to add a service/isolation valve at each branch from the riser. Without such an accessible valve, multiple units will be impacted because the fixture could not be isolated from the others on the riser. As an engineer who grew up in the skilled trades as a service plumber, I have always viewed my designs in such a manner as to allow for service with minimal impact on fixtures or piping around any specific point. While you can save costs by minimizing the number of valves in a system; someone will have to bear the added costs of service and maintenance at some point in time. This cost could be borne by the units’ occupants or possibly the condo association which passes those increased costs to everyone in the building.

Mr. Ryan uses riser diagrams to demonstrate his points. Domestic water being up-feed with domestic hot water return (individually balance controlled) taken from the top of the domestic hot water riser to return to the central plant or domestic water being up-feed with hot water risers inter-connected at the top (without directional control) and those collected risers being connected through a single balancing valve to be taken from the top and returned to the central plant or a similar arrangement that inter-mixes lavatory, tub/shower and kitchen sink risers, making it very difficult to isolate units. While such riser arrangements may be useful in some applications, a high-rise condominium is not one of those applications.

It was suggested that the following principles be applied to both new and existing buildings to provide value to the clients and unit owners:

  • Fight for isolation valves — being overly frugal in the installation of valves is often a false economy according to Dr. Alfred Steele;
  • Appropriately group risers — so that they serve as the main or express risers while serving the unit fixtures from dedicated branches that serve a single unit;
  • Develop a facility standard on mixing valves to minimize crossover — there are some makes/models of temperature/pressure mixing valves that are problematic for failures and allowing crossover between the hot and cold services.
  • Include vents and drains at the top of risers in common areas or make the piping arrangement such as to serve this purpose — this will prevent having to drain the riser at fixtures within the lowest level units and venting the riser at the highest level units. Appropriate piping arrangements can minimize these issues;
  • Do not allow isolation valves on the return hot water lines to be used as balance valves — this throttling if the isolation valve promotes scaling accumulation, which will eventually prevent the valve from full closure. Isolation valves and balance valves are constructed differently and designed to serve two different purposes; and
  • Exercise riser and isolation valves regularly to ensure they will work when needed. Yes, I know this is not a common practice and does have an associated cost. However, I would suggest that it is less costly in the long run as compared to having valves that cannot be closed or will not seal tight.

Mr. Ryan’s experiences are not unique and can represent a significant cost to the unit owner or the condominium association over time. The best approach, in my judgment, is to design the system to avoid these issues. In high-rise design, we use express risers and must also take into consideration “pressure zones.” So work your design to minimize risers, provide branches that can be isolated to serve each unit individually and possibly use individual domestic hot water heaters in the spaces versus a central hot water plant.

Yes, this may have some upfront costs, but in the long run, it will provide better value to the owners and condominium association, just some food for thought when beginning your design. Upfront costs are always a concern, but one must look at things over the long term and how such costs best serve the owners and occupants.