Design is the process of taking an action to meet specific requirements in our effort to provide a complete system. Regardless of the size of any given project, it consists of a series of select design packages. As we accomplish each of the smaller packages, we develop the overall project.
As design professionals, engineers and designers are all part of the design team. Each team member contributes within their discipline to the overall development of the project. As part of any team, engineers must coordinate with many others who make up the total team. These team members may be within the same office or may be part of another firm’s team, but all team members must keep each other informed to ensure that everything will work together and remain within budget.
Through this coordination effort, various design concepts can be discussed that will assist in the development of specific systems. It also allows for the shifting of design elements between various teams or team members. Remember that one’s actions and design approach may enhance our discipline, but at the same time it may have a negative or unintended impact on other disciplines’ designs. With that in mind, I am going to discuss recent exchanges related to domestic hot water systems.
Case in Point: POU Water Heaters vs. Centralized Systems
Point-of-use (POU) water heaters were prominently featured in recent discussions on the ASPE Connect Open Forum (and if you are not yet part of the ASPE Connect community, please consider joining in), as well as in some industry publications. The discussions related to the idea that it was better to generate hot water for the user at the point of use versus having a centralized system with distribution and return piping. While this might conserve piping, piping insulation, hangers, labeling, etc., the question becomes at what cost.
Yes, for the plumbing discipline, dollars could be returned to the project’s budget. However, most POU units are electric, so these costs would be moved to the electrical discipline. Thus, changing to POU units would save dollars on the plumbing side but add dollars on the electrical side.
Generally, POU units do not have an integral electrical disconnect. Therefore, the electrical team will need to provide a means of disconnecting the POU unit from its power source. The disconnect generally needs to be within the line of sight of the POU unit. It is also generally larger than the POU unit and requires physical space that may not be appealing to the architect or interior designer. The small POU units that can fit under the fixture and in many cases be hidden by a lav shield or sink shield are not generally a concern to the architect or interior designer from an aesthetic standpoint. However, trying to fit an electrical disconnect under a fixture is generally difficult, if not impossible. Also, is it wise to place an electrical disconnect or device under a fixture that could drip water onto those electrical components? You can see that the problem is finding space for the electrical disconnects that is out of sight from an architectural/interior design standpoint yet in line of sight to conform to the electrical code requirements.
Also, what impact will the utilization of POU units have on the electrical consultant’s design? Load is load regardless of it being BTUs (British thermal units) on the plumbing side or kWs (kilowatts) on the electrical side. Both have an impact on the budget—it’s just a question of where those line item costs are placed. Transferring the load over to the electrical design will require additional circuits, conduits, wiring, breakers, etc. It may also require larger breaker panels, switchgear, and potentially a larger electrical service to accommodate the increased electrical load.
While these issues may only have a minimal impact on the project’s budget, if any, they will impact both the plumbing and electrical budgets. They also will alter the amount of design work associated with both the plumbing and electrical consultants.
As with any design, it’s a matter of choice in coordination with the owner and design team. These choices need to consider the pros and cons of each possible option and how those choices will best serve the intended use. There is no right or wrong selection, just options that may better serve the design than others. As design professionals, we are charged with finding balance between the various options and ensuring that the client understands the pluses and minuses of the agreed-upon design path. It should not just be about first cost; the choice needs to consider the associated service and maintenance costs over the life of the project. For the engineer, the potential impact on the public’s health, safety, and welfare must also be considered. While this last point is not always appreciated or understood by contractors and sometimes the owner, it is nonetheless an obligation to the public good that the engineer is duty-bound to incorporate into the design.
How to Make the Right Choice
So let’s consider the implications of providing POU hot water versus conventional hot water distribution and return. Keep in mind that it may not necessarily be an either/or situation—the design may need to incorporate both types of systems to best serve the owner’s needs.
The POU system will reduce the amount of water piping, provided that other fixtures do not need a circulated system. The volume of water within the piping network and the age of the stored water will decrease as well, which in this case is positive in relation to waterborne contaminants in potable water systems, but remember that the hot water system is not the only concern related to the potential for pathogenic growth. Legionella and other pathogens enter the building water system though the cold water system. While the cold water system may not be as much of an incubator as the hot water system, both need to be monitored and maintained as part of any water management plan.
Electrical systems, when considered in their entirety, are not truly efficient, so increasing the electrical load may not be in the best interest of the public. While electrical systems within the building may be efficient, the losses between the generation point and delivery to the building are not, but that is not, generally, a consideration of the owner or construction team.
As you can see, nothing is simple and straightforward. Either approach will provide the user with hot water, but which approach best serves the owner and fits within the budget? Should we increase the electrical costs and energy consumption by going to POU devices? Or should the conventional plumbing system be used with the increased risk of pathogenic contamination? These are valid considerations that the design team must consider.
As you can see, design involves much consideration and must be done in a cooperative manner. What one member of the design team considers being the best approach may have a very different impact on other members of the design team and the owner’s budget. No one on the team can work in a vacuum; we must communicate and coordinate our efforts.
As for the selection of a conventional hot water system design versus the use of POU units, this is a design decision that needs careful consideration and coordination. One choice is not necessarily right or wrong; everyone just needs to understand the reasoning behind the different design approaches and select the most appropriate choice for the project.
About the Author
David D. Dexter, FNSPE, FASPE, CPD, CPI, LEED BD+C, PE, is a Registered Professional Engineer, Certified Plumbing Inspector, and Certified Plans Examiner with more than 40 years of experience in the installation and design of plumbing systems. He specializes in plumbing, fire protection, and HVAC design as well as forensics related to mechanical system failures. Dave serves as Chair of ASPE’s Main Design Standards Committee, Chair of the Bylaws Committee, Co-Chair of the College of Fellows Selection Committee, and Co-Chair of the Professional Engineer Working Group. He also was the 2008–2009 President of the Engineering Foundation of Ohio, 2010–2011 President of the Ohio Society of Professional Engineers, and 2012–2014 Central Region Director for the National Society of Professional Engineers.
The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.