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Blue RidgeParkway
Re: Weather Response Heating Control System

Ecker, Susan, "Scald prevention" Plumbing Engineer, a TMB Publication, August 2008,

Scald Prevention
By Susan Ecker

As plumbing engineers, we are constantly walking a tightrope when designing hot water systems. On one hand, the water needs to be heated so that it is hot enough to kill Legionella bacteria. On the other hand, it needs to be cool enough so that the user does not get scalded. Many experts suggest turning the hot water heater down to temperatures that prevent scalding (120 F or less); this, however, creates a perfect climate for the Legionella bacteria. Tempering the hot side of a valve in order to limit the maximum outlet temperature available to the user when mixed with cold water is a solution to this problem. Installing a device at the water heater, such as a thermostatic mixing valve, is a way to accomplish this.

Thermostatic mixing valves are designed to prevent scalding but to allow storage of hot water at a Legionella-safe temperature of 140 F. A device that restricts or limits the maximum temperature of the hot water supplying a fixture or fitting ensures that water to baths, showers and sinks is safe at the point of use. See Table 1. This article will examine the problems and review the ASSE standards that apply to temperature-limiting devices.

Legionnaires' disease
Legionnaires' disease is a severe respiratory infection that is caused by bacteria that grow in hot water heaters, cooling towers, etc; the disease can be contracted through inhalation. Some victims develop pneumonia, which can lead to death. These bacteria survive in water temperatures less than 140 F. According to the CDC, Legionella bacteria have a broad range of potential growth. "Legionella bacteria exist in the biofilm on the inside of pipes. Legionella grows rapidly between 77 F and 108 F. Although it may seem feasible to raise the water temperature to 140 F, this leaves the water in the scald temperature range." 1
Occurrences of Legionella have happened when people have been exposed to an infected water source and inhaled contaminated water from sources including cooling towers, whirlpools, bathtubs, showers or even a steamy faucet. Legionella has been shown to most greatly affect people with low immune systems. For example, in a hospital setting, patients that are most susceptible to Legionella infection include cancer patients who are in radiation or chemotherapy treatments, organ transplant recipients, HIV positive individuals, elderly and surgical patients. Severe Legionnaires' disease has an overall mortality rate of 10% to 30%, and 30% to 50% of patients require admission to an intensive care unit. 1

Scalding
Although water temperatures of 140 F and higher do not allow Legionella to survive, they may allow scalding to occur. Children and elderly people are especially likely to suffer scald burns at temperatures higher than 120 F. On many hot water heaters, the thermostat does not have a temperature dial, but rather cold and hot dials; therefore, specific temperatures cannot be set. The most effective solution for these heaters is to install a thermostatic mixing valve.

Here are some scalding statistics:
65 percent of hospitalized children are admitted for scald burn injuries.

27 percent of children under the age of 14 admitted to hospitals each year are treated for scald related injuries.

Each year, 30 percent of children five years of age and younger are involved in bathtub and shower-related accidents that result in scald burn injuries. 70 percent of these burn injuries result in death.

More deaths and hospitalizations result from hot tap water burns than from burns caused by other liquids.

The kitchen is the most common location where scald burns are inflicted upon children between the ages of six months and 2 years, due to hot foods or liquids being spilled.

According to the National Safe Kids Campaign, the average full-thickness, third-degree scald burn from bathtubs covers 12 percent of the body.1
Standards
The American Society of Safety Engineers (ASSE) has established performance requirements for temperature-limiting devices located at the hot water source and for those installed at the point of use. Following is a review of the ASSE standards.

(removed the review of ASSE standards portion due to post truncation will insert in subsequent post)

Conclusion
The information provided here may help the plumbing engineer better understand the types of temperature limiting devices that can be installed in a system. These devices prevent the forming of Legionella by keeping water at a high temperature in the storage tank, and they prevent scalding by limiting the temperature of the water at fixtures or fittings. Using temperature-limiting devices allows the plumbing engineer to address the health and safety issues that are associated with water storage and delivery.

Blue RidgeParkway
Re: Weather Response Heating Control System

Cont.

Standards
The American Society of Safety Engineers (ASSE) has established performance requirements for temperature-limiting devices located at the hot water source and for those installed at the point of use. Following is a review of the ASSE standards.
ASSE 1016 - Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub/ Shower Combinations: ASSE 1016 covers both wall-mounted shower valves and tub/shower combination valves that are supplied by both hot and cold water. They are designed to "reduce the risk of scalding and thermal shock by protecting the user from exposure to excessive changes in water temperature." The three valve types defined by this standard are:
Type P, pressure balancing valves. Type P valves must maintain temperature (3.6 F) when 50% pressure changes occur to the incoming hot and/or cold water supply to the valve. Type P valves cannot compensate for changes to incoming supply temperatures.
Type T, thermostatic valves. Type T valves must hold temperature, while accounting for 20% pressure changes to the hot and cold water supplies, as well as for a 25 F hot water temperature increase (5 F per minute).
Type T/P, combination thermostatic/pressure balancing valves. Type T/P valves must account for both 50% pressure changes and the 25 F (5 F per minute) hot water increases while maintaining 3.6 F.2
The minimum flow tested to maintain temperature control is 2.5 gallons per minute (gpm), the typical flow for most common showerheads. An ASSE 1016-listed device can flow no more than 0.5 gpm upon cold water failure within a plumbing system. An ASSE 1016 device is the final tempering device; no further mixing can occur downstream. An ASSE 1016 valve mixes hot and cold water to individual showers and can be adjusted by the bather or the bather's attendant.
ASSE 1017 - Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems: Temperature actuated mixing valves for hot water distribution systems are used for controlling in-line water temperatures in domestic potable hot water systems and shall be installed at the hot water source. They are not intended for end use application. Temperature actuated mixing valves for hot water distribution systems shall consist of a hot water inlet connection, a cold water inlet connection and a mixed water outlet connection, plus a temperature sensing and controlling element and a means for adjusting the outlet water temperature.
ASSE 1069 - Performance Requirements for Automatic Temperature Control Mixing Valves: ASSE 1069 defines these valves as, "devices that service end use fixture fittings, including but not limited to, gang showers and sitz baths, by supplying tempered water at a pre-set temperature through a single pipe supply." The most common product types would include pushbutton metering showers, on/off valves, infrared showers or other types of electronically actuated single temperature showers.
This valve can be used only if the shower valve is a single-pipe supply, i.e., pre-tempered water to a metering shower. It is not intended for individual showers or tub/shower combinations that are covered by ASSE 1016, where the bather controls final water temperature. Here is some additional information:
Further mixing downstream is not allowed from an ASSE 1069 device.
ASSE 1069 covers single and multiple fixtures for pre-tempered water.
ASSE 1069 does test for cross flow. Many valves now feature checks or check stops that are integral to the valve.
The minimum tested flow is the lesser of 2.5 gpm or the manufacturer's stated minimum.
The control of the final outlet temperature can only be set by the installer or the building owner. In most cases, the user will not have access to the valve.
The maximum allowable outlet temperature is 120 F, which is accomplished with an adjustable handle rotation or limit stop. The limit stop prevents the valve from over-rotation to the extreme hot position.2
ASSE 1070 - Performance Requirements for Water Temperature Limiting Devices: ASSE 1070 is for devices that limit water temperature to a fixture or fixtures, such as sinks, lavatories or bathtubs, to reduce the risk of scalding. They are not intended to provide protection from thermal shock.
Thermal shock is the result of sudden and drastic changes in water temperature that are the result of changing supply conditions (fluctuating pressures and temperatures) and are most dangerous in showering applications. Sudden movements by the fixture user to avoid dramatic temperature change can result in the user slipping and falling, which can cause serious injury. In strictly bathing and hand washing applications, this issue is eliminated.
The device can be the final tempering device, or it can have water further tempered downstream (with the addition of cold water). In this case, the valve supplies tempered water to the hot side of a two-supply fitting; further mixing with cold water at the point-of-use takes place. Here is some additional information:
ASSE 1070 covers devices that supply single or multiple point-of-use fixtures.
An ASSE 1070-approved device must have a means to prevent cross flow, i.e., checks or check stops.
It may be adjusted by the user, or it may be inaccessible to the user and set by the installer or building owner.
A valve will be rejected if, at any time during a Temperature Variation Test, the outlet temperature exceeds 120 F. Each valve must have an adjustable and lockable means to limit the setting of the device to the hot position.2

Conclusion
The information provided here may help the plumbing engineer better understand the types of temperature limiting devices that can be installed in a system. These devices prevent the forming of Legionella by keeping water at a high temperature in the storage tank, and they prevent scalding by limiting the temperature of the water at fixtures or fittings. Using temperature-limiting devices allows the plumbing engineer to address the health and safety issues that are associated with water storage and delivery.

havanagranite
Re: Weather Response Heating Control System

while Legionnaires' disease is a very real risk and not to minimize it at all. most people are not at risk from Legionnaires' and so for the majority of homes energy usage is going to be the more important especially with the economy in the state it is in right now. so for most people 120 is going to be much more cost effective then 140 with out posing any realistic health risk. and their water heater will last longer without having near as much sediment buildup.

sparky672
Re: Weather Response Heating Control System
havanagranite wrote:

while Legionnaires' disease is a very real risk and not to minimize it at all. most people are not at risk from Legionnaires' and so for the majority of homes energy usage is going to be the more important especially with the economy in the state it is in right now. so for most people 120 is going to be much more cost effective then 140 with out posing any realistic health risk. and their water heater will last longer without having near as much sediment buildup.

I totally agree... most people would never spend the extra cash hiring plumbers to install mixing valves let alone all the extra energy needed to keep the water at 140+. Plus the extra maintenance cost removing sediment.

You'd think that if this was something that critical...

1. water heaters would have a 140 min setting & include a mixing valve
2. it would be part of the national building code for all new homes
3. and that TOH would strongly be endorsing retrofits.

From what I've been reading, most of the risk of Legionnaires is not going to be in the average home but in institutional and commercial systems... hospitals, nursing homes, cruise ships, office buildings, factories, etc. Probably the reason (along with efficiency) that Rich Trethewey & TOH are saying to just set it at 120 or 125.

Something from OSHA with no big alarm bells for homeowners...

http://www.osha.gov/dts/osta/otm/legionnaires/faq.html

OSHA wrote:

Q. Can my home water heater also be a source of LDB contamination?

A. Yes, but evidence indicates that smaller water systems such as those used in homes are not as likely to be infected with LDB as larger systems in workplaces and public buildings.

Q. Do you recommend that I operate my home water heater at 60°C (140°F)?

A. Probably not if you have small children or infirm elderly persons who could be at serious risk of being scalded by the hot water. However, if you have people living with you who are at high risk of contracting the disease, then operating the water heater at a minimum temperature of 60°C (140°F) is probably a good idea. Consider installing a scald-prevention device.

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