A Passion for High-Performance Plumbing Systems
Turn on the faucet, then wait, wait, wait for the water to get hot. Many owners of older homes are familiar with this scenario. Fortunately for buyers of new homes, home builders now have a bucketful of options that can cut the wait, helping homeowners save water, energy, time, and money. This article looks at ten new homes that employ high-performance plumbing solutions. It is based on data I collected directly from participating homeowners—all compiled with the idea of saving time and water while waiting for hot water.
Nearly all of these homes met the EPA WaterSense delivery standard for providing hot water—the water has to be hot before 0.6 gallons (9.6 cups) has gone down the drain.
With only one possible exception, all hot water deliveries in all ten homes met this standard. The average amount of water wasted was 2.8 cups, and the average amount of waiting time was 7.8 seconds. (See Figure 1.) These results show that municipalities and/or water agencies can set a higher standard than they are setting at present while letting home builders determine how they want to meet that standard. The EPA WaterSense hot water delivery standard is a good place to start, even though these ten homes produced results significantly better than the standard.
Table 1 describes the ten plumbing systems that I evaluated for this article. To protect the anonymity of the homeowners and builders, the ten homes are designated by the letters A through K (excluding the letter I).
These systems comprised three different pump technologies: timer, demand-controlled (DCP), and schedule adaptive (SA). These technologies include one, two, and three loops; a multiple point of use (POU); and whole-house manifolds (WHMs). (Note: I define manifold as spaghetti tubing that goes to all of the fixtures from the water heater within the homes.) Only two of the ten homes had a centrally located water heater (CWH).
Time and Water Wasted
Table 1. The Ten Plumbing Systems
Table 2. Cups of Water per Demand
Table 3. Normalized Annual Data per Home Based on 16 Total Daily Demands
Table 4. Annual Degree-Gallons and Energy Saved
Comparing Plumbing Solutions
People are different, lifestyles vary, homes are different, even homes of the same size built in a similar style in the same locale. Therefore, the amount of water wasted each year while waiting for hot water can vary widely from house to house. For example, in standard plumbed homes with no pump technologies or design strategies incorporated, annual water wasted ranges from 3,600 to 12,000 gallons. This range is based on several independent studies, as well as a 2006 EPA report that combined four studies on the energy savings potential of demand pumping systems. For comparative purposes, I assumed an average of 7,300 gallons of water wasted annually for existing homes with standard plumbing; this became the baseline for evaluating the ten homes in this article.
The total daily hot water demands in the average home vary widely, from 12 to more than 20 demands per day (EPA 2006). In this article, I have assumed 16 daily demands in the average home. That’s 5,840 demands for hot water annually per home.
Based on an average of 7,300 gallons of water wasted and 5,840 hot water demands per home per year, the average amount of water wasted while waiting for hot water works out to 21.6 cups per demand. In a study that I conducted of 70 homeowners in two Arizona cities and 106 homeowners nationwide, actual self-reported results for the number of cups of water wasted per demand varied from 12.9 to 31.5 for kitchen sinks and 14.7 to 30.2 for master bathroom sinks. (See Table 2.)
From previous collection efforts, I had sufficient data to establish average daily hot water demands per household of 6.2 at the kitchen sink and 3.9 in a master bathroom. Those demands were normalized to the baseline for comparative purposes. Therefore, 7,300 annual wasted gallons, 16 daily hot water demands, and 52 seconds waiting per demand represent the status quo for this article. They also represent the key baseline for evaluating the ten plumbing systems discussed above.
What Does Table 3 Reveal?
Table 3 presents data for each of the ten homes in the study, including the amount of time wasted each year and the amount of water wasted each year while waiting for hot water to reach the tap. Hours wasted and gallons wasted in the ten study homes with efficient plumbing are compared to the baseline values for homes with standard plumbing of approximately 84 hours of time and 7,300 gallons water wasted annually. The percent reduction, or amount of savings, in the ten study homes compared to the baseline amounts for homes with standard plumbing are shown in columns 4 and 6. Table 3 also introduces the term gallons circulated. This is the best estimate of the gallons of water moved through each plumbing system per year. The gallons circulated can be compared to the gallons wasted while waiting for hot water. This is a useful metric for any DCP, WHM, POU, or timer pump (TP) plumbing system.
As seen in Table 3, all ten homes show significant reductions in annual wasted hours while waiting for hot water, with percent reductions ranging from 67% to 96% compared to the baseline. These are significant time and water savings. This also means that the water saved did not have to flow to sewage treatment, where chemicals and power were consumed, and then be discharged back to a watershed, very likely less potable than it was before.
For homes A, B, C, and K (all with DCPs), wasted gallons (and gallons recirculated) vary noticeably. This is not unexpected. The length of the branch lines affects the number of wasted gallons; the longer the branch line, the more gallons are wasted waiting for hot water. The gallons recirculated are a function of the length of the trunk line(s) and number of plumbing loops.
Homes D, E, and F have the most wasted hours, yet they have the fewest gallons wasted and circulated. The wasted gallons and the gallons circulated are the same because no pump technologies are involved in these plumbing systems. This is trade-off number one in high-performance plumbing system designs.
When compared to the baseline, all ten homes show significant reductions in annual hours waiting for hot water. If there is one thing I have learned working with homeowners and their plumbing systems, it is that they all want to save water, time, energy, and money. Yet, when homeowners are surveyed, they always cite saving time (convenience) first; and the initial costs incurred to do so are soon forgotten.
Annual water use estimates in homes vary greatly. EPA estimates 210 gallons per day in the average American home; this comes to 76,650 gallons per year. New residential construction could avoid 4–7% of water waste with any of the plumbing systems described in this article. To put that in perspective, 1.06 million new single-family homes were started in 2014. Had those new homes incorporated any of the high-performance plumbing systems described above, 3–7 billion gallons of water waste per year could have been avoided. Saving that amount of water won’t save the planet, or even California for that matter, but these plumbing systems are more efficient, and they do save time, energy, and money.
Homes G and H show extremely high values for gallons circulated relative to the wasted gallons. This is because the TPs are operating and circulating hot water whether a hot water demand is being made or not. Home G’s low-flow TP operates 24/7 with an assumed 0.4 gpm flow rate. Home H’s TP is on continuously for 16.5 hours a day with an assumed 1.0 gpm flow rate. Trade-off number two: convenience can have a price.
Home J with its SA pump shows a dramatic reduction in gallons circulated when compared to homes G and H. This is because the SA is operating in its cycle mode: on for 5 minutes, then off for 40 minutes.
Homes C and K both have CWHs serving all the loops in each home. Previous research that I conducted (almost 100 data sets) showed that homes with water heaters in a garage wasted 420 more gallons annually than homes with water heaters located in the home. Those gallons, if normalized for this article, demonstrate that water heater location plays a material role when designing high-performance plumbing systems.
Homes G and K present an interesting contrast. Home G was designed to minimize the length of any branch lines between the main trunk line and the hot water fixtures themselves. That design concept required an exceptionally long trunk line to create the loop with a low-flow TP. Conversely, home K used two loops and two DCPs tied to a CWH. Two very different design and technology approaches—with very similar annual wasted hours and wasted gallons, but with dramatic differences in annual circulated gallons, and ultimately the associated energy costs.
Each home’s plumbing system met the EPA WaterSense hot water delivery standard of 0.6 gallons wasted while waiting for hot water. The EPA guidelines state that a 10°F temperature increase is required within 0.6 gallons (9.6 cups). For this study, hot water is defined as hot enough to shower. For all intents and purposes, this means a temperature increase of somewhere between 45°F and 70°F—far more than the 10°F required by the EPA standard.
The Water/Energy Nexus
No discussion of the water wasted annually while waiting for hot water would be complete without recognizing the water/energy nexus and its implications for the gallons circulated.
The concept of degree-gallons (D-G) is now introduced. This concept is not new. D-G examines the annual reheating (and initial heating) of water associated with the annual gallons-circulated due to the annual gallons of wasted water while waiting for hot water for each plumbing system. The gallons circulated are a function of the type of plumbing design, technologies incorporated, hot water heater location, number of plumbing loops, and size and style of a home. That is, the D-G values that follow are home specific and should be considered in the context of relative value.
D-G equals gallons circulated multiplied by the temperature loss for homes with pump technology. Circulation losses also include the ambient temperature of the water first entering the home, then heated, and eventually lost while waiting for hot water.
D-G is a number: gallons x temperature loss. One Btu is defined as the energy required to raise the temperature of 1 lb of water 1°F. There are 8.34 lb in a gallon. Hence, D-G x 8.34 = x-Btu. I leave it to you to translate into kWh or therms the energy costs for your area (1 kWh = 3,412 Btu; 1 therm of natural gas = 100,000 Btu). Table 4 ties together the following values:
- The annual energy (Btu) required to reheat the annual gallons circulated. (All water heater sources are assumed to be 100% efficient.)
- The assumed plumbing system temperature loss (Δ°F) for each home. In the case of the SA pump (home J), it is assumed that when the pump is running, the first two minutes of operation are spent clearing the plumbing system with usable hot water with a 25°F loss; and the remaining three minutes have a circulation loss of 3°F or 11.8°F weighted average. Note that there is no known official guidance from EPA’s Office of Water as to whether SA pumps may satisfy EPA’s hot water delivery standard cited earlier. In my recent communications with EPA contacts, they have indicated that “technical guidance on which pumps may satisfy EPA’s requirements is expected in 2016.”
- The annual energy percentage saved for each home versus the baseline status quo (4.14 MBtu) is then compared for each home: 7,300 gallons x 68 (Δ°F) x 8.34 lb/gallon = 4.14 MBtu.
What Does Table 4 Reveal?
Table 4 compares each of the ten homes against the baseline status quo for standard plumbed homes with traditional trunk, branch, and twig configurations.
Homes D, E, and F saved the greatest percentage of energy, because they circulated the fewest gallons of water. The gallons of water circulated also equaled annual gallons wasted because these homes had no pump technologies installed.
Homes A, B, C, and K, all of which had DCPs, showed 50–75% energy savings. Homes C and K saved the most energy; this was due in part to their CWHs.
Homes G, H, and J had higher energy requirements than the baseline status quo. This is because in all three houses hot water is circulating for periods of time when no hot water demands are being made. Again, convenience has a price.
The water/energy nexus is too important to ignore when designing high-performance plumbing systems. The fact that DCPs minimize the impact of the water/energy nexus, and that they are eligible for HERS-approved credits, makes DCPs an appealing choice.
Potential Best Management Practices Year 3 Report. Koeller & Company, January 2007. Chapter 7, “Residential Hot Water Distribution,” provides a basis for the on 5 minutes/off 40 minutes design incorporated in SA pumps, such as that in Home J.
Get more information on EPA guidelines for hot water.
It’s important to keep in mind that owners of existing homes who wish to save time, water, and energy on their hot-water usage will have to install a pump. (Note that I am not talking about replacing water heaters or using low-flow fixtures; this article is about plumbing solutions.) Pumps may incorporate different technological approaches, they may or may not be code compliant, and they may or may not meet independent certifications for plumbing use. However, for new-home construction, the choices are numerous—as I have explained above. These various choices have relative strengths and weaknesses in terms of system cost, hours waiting for hot water, and energy consumed while waiting for hot water. (See Figure 2.) This last fact should not be lost on municipalities and water agencies (or builders) who are examining hot water delivery standards, various design trade-offs, policy, and possible rebates associated with reducing wasted hot water.
We Can Do Better
There can be a better status quo for hot water delivery! In these times of drought (especially in the southwestern United States), we must save every gallon of hot water in new homes that we can. 2015 codes and compliances are in place for every state that is willing to adopt them, whether in specific sections or in their entirety.
Well-designed high-performance plumbing systems save in five ways:
- They reduce the amount of water wasted in the home while waiting for hot water.
- They reduce the energy used in the home to heat water.
- They reduce sewage treatment expenses and the gallons of sewage discharged.
- They reduce the monthly costs of home ownership.
- They reduce the amount of time that the occupants spend waiting for hot water.
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