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Little did the author of Catch-22 know, when the novel was published in 1961, that the title would live on as a motto to mutually conflicting conditions. Why, even in the world of plumbing and mechanical systems, there’s a “Catch-22” faced by facility managers worldwide. Still mired in our mid-COVID circumstances, one of the toughest dilemmas faced by building owners is commercial-scale “germ warfare.”
Applicable to large plumbing systems – especially those that serve hospitals and nursing facilities where people are most vulnerable – is the challenge of killing pathogens, including legionella, while also protecting users from the risks of scalding.
Tied to that is a facet of the challenge that complicates efforts to control temperatures within domestic water systems, known as “thermal creep” – which can lead to thermal shock. Thermal creep is an anomaly that can give users (bathers or washers) a rather unpleasant surprise when unexpectedly high temperatures are possible, especially in the morning after periods of low use.
So, there’s the Catch 22: How can we store and circulate domestic hot water within large facilities at temperatures meant to mitigate bacteria, while also preventing burns at points of use?
Unfortunately, hot water scalding is one of the leading causes of serious burns in the US. Studies show that scald injuries from tap water send more than 100,000 people to the emergency room each year, with approximately 7-10 percent of them requiring hospitalization.
Some of the leading scald burn studies show that it takes 7 to 8 minutes of exposure at about 120 degrees to develop a serious scald burn. Small children and people with disabilities and the elderly – those unable to move quickly to avoid burns – are the highest risk groups. Scald burns can be fatal if a large area of the body is burned, and this can happen, especially if a person would fall in a shower, exposed to high-temperature water for a length of time.
Fortunately, we’ve come a long way in protecting people from the risks of scalding, and also thermal shock, thanks to advances in technology.
Preventing burns from water are at highest risk within facilities where patients (babies, the infirm or elderly) may not have the quick reflexes or ability to move away from water at points of use – whether sink or shower head.
Thermal shock often refers to a rapid and uncomfortable change in water temperature. While standing at a sink, this problem doesn’t seem too threatening, but if it happens within a hospital or nursing facility shower, it’s not uncommon for a person to react suddenly, slip and fall.
If that’s not bad enough, as people fall they may grab for some way to stabilize themselves, inadvertently turning the temperature control all the way to its hottest setting. At this point, it doesn’t take much exposure to hot water to significantly increase the problem.
The figures are rather grim at this point: Scientists and mechanical experts have developed charts that accurately calculate the threat of first-, second- or third-degree burns based on varying degrees of water temperature, and length of exposure. (See Figure 1.)
A common cause of a sudden change in domestic water temperature often stems from a pressure increase in either side of the plumbing system. For example, a pressure imbalance creating higher pressure in the cold water line and lower pressure in the hot could lead the water temp to plummet quickly.
The opposite happens if there is a sudden increase in pressure within the hot water line, causing immediate risk of scalding. This emphasizes the need for constant control and stabilization of both water pressure and temperature.
It wasn’t long ago that two-handled bathtub and shower valves were common; in fact, there are still plenty of them in use today.
They do, however, contribute to thermal shock and scalding incidents. That’s why manufacturers developed single-handled shower valves – those with a mechanical valve that mixed water temperature.
When these valves first emerged, however, they didn’t offer a maximum temperature limit or pressure control. So, the risk of thermal shock or scalding remained.
Eventually, valves evolved to include mechanical means of maintaining the user’s desired temperature for water delivery.
To help develop products designed to control water temperature, the American Society of Sanitary Engineering issued standards to establish performance requirements to protection against thermal shock and scalding.
For showers, ASSE 1016 standard was developed. The standard applies to automatic compensating valve designs intended to be installed at the point of use and separated into three categories: Type P, Pressure Balancing; Type T, Thermostatic; and Type T/P, Temperature and Pressure.
• Type P devices include a pressure-balancing function to protect against pressure fluctuations up to 50 percent, but are limited in their ability to control temperature fluctuations.
• Type T devices have a temperature-sensing element that protects against temperature fluctuations up to 25 degrees, but are limited in their ability to control pressure fluctuations.
• Type T/P devices have pressure-sensing and temperature-sensing elements to protect against pressure fluctuations up to 50 percent and temperature fluctuations up to 25 degrees, assuring the very best guard against water temperature changes.
For sinks, bidets, lavatories and bathtubs, ASSE 1070 was developed. While these devices are designed to reduce the risk of scalding, they are not designed to address thermal shock.
Finally, for systems that use multiple showers and lavatories, ASSE 1069 was developed for valves designed to supply only tempered water to the end-user. Like ASSE 1016, valves covered by this standard compensate for pressure and/or temperature variations in water distribution systems.
Clearly, POE delivery temperatures above 120 degrees pose great risk, though at those temperatures and higher, legionella and other harmful bacteria are either unable to multiply or killed. (See Figure 2.)
While there are benefits at increased temperatures, with greater temperatures and “germ warfare” comes the higher risk for burns.
ASSE developed a standard for devices that regulate water temperatures generated by hot water devices, such as boilers and water heaters.
ASSE Standard 1017 for hot water distribution system temperature-actuated mixing valves sets performance criteria for mixing valves designed to control water temperature from ±5 degrees to ±7 degrees depending on the plumbing system’s required flow rate.
This standard provides added system temperature control since the hot water generating source cannot be considered a temperature-regulating device. Per the 2006 Universal Plumbing Code, section 413.1, “The water heater thermostat shall not be considered a control for meeting this provision [tempering public lavatories]”
Additionally, ASSE 1017 has no test for compensation during pressure fluctuation. As a result, in order to minimize pressure fluctuations between the hot and cold water lines, point-of-use mixing valves are best located near the end-use device.
The tandem use of ASSE 1017 valves along with ASSE 1016, 1069 and 1070 valves are meant to assure that water used by a bather is delivered at temperatures within a comfortable setpoint.
Digital mixing, like mechanical mixing, addresses the Catch 22 paradox by offering more precise temperature control while also providing overall energy savings.
The technology tops off the thermostatic peaks and valleys within a domestic water system – between the point of heat generation and points-of-use. For facility managers concerned about thermal shock or thermal creep issues, digital mixing is the great stabilizer.
If, through some miracle of modern technology, digital mixing had been around when facility managers first faced the challenge of water temperatures hot enough to kill or neutralize bacteria, while also mitigating scalding and temperature creep, there’d have been no Catch 22. Problem solved.
Todd McCurdy is the national sales manager for Watts.
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