Subscribe to our newsletters & stay updated
ASHRAE recently held their meetings in St. Louis, Missouri, and there were numerous technical committee meetings. The following is a report on a few meetings related to plumbing.
The ASHRAE Technical Committee 6.6 that covers service water heating systems is concerned with two general areas:
The first area is identification of service hot water requirements at various fixtures and applications. The second area covers hot water system components including the heating equipment and distribution piping and components for the service hot water system piping and components. This coverage of the service hot water system components includes the heating equipment (water heater) and distribution piping and components.
Familiarization with water heating equipment includes knowledge of the water heater types and limitations of the different types of water heaters. It requires knowledge of the minimum amount of hot water to be stored to satisfy peak calculated hot water usage demand periods vs. the required continuous flows in gallons per minute and the energy input or BTUs/hr or KWs/hr required for instantaneous water heating. It also requires knowledge of appropriate temperature controls and flow balancing equipment in the distribution piping. It requires knowledge of the sizing methods, including velocity limitations at various temperatures and sizing methods for circulating pumps and how to calculate flow rates for each main and branch based on heat loss in order to maintain minimum circulation to maintain a minimum temperature in the hot water system. The designer should have knowledge of other hot water temperature maintenance systems (heat tracing) if a circulation system is not used. These temperature maintenance systems help maintain hot water temperatures to minimize wasted hot water and waiting times for hot water to arrive at fixtures and maintaining hot water above the Legionella growth temperature. It also requires familiarization with heat recovery systems.
ASHRAE research topic request
There was a recent request for the ASHRAE 6.6 Technical Committee to have research done to consider hot water storage temperatures between the 120 F limit for scalding and the 140 F recommended limit for storing water to control Legionella bacteria growth. A request for research is called a “research topic acceptance aequest” (RTAR), which is the process of requesting funding for research on a given subject. It looks like the research will now be moving forward.
There were people who want to study the existing and available data, reports and studies on scald incidents in the U.S. for the purpose of determining if storing hot water at 130 F would be better than storing at 120 F while also allowing 130 F hot water at showers.
A few people oppose using temperature controls in the hot water system distribution piping or at the point-of-use, citing controls fail. Currently, the plumbing codes do not allow the thermostat on the water heater to be the final temperature control for scald prevention because the thermostat on most water heaters does not accurately control the
The intent of the research project seems to be use the data to recommend a system thermostat set-point temperature in between 120 F (maximum temperature a showers) and 140 F (the minimum recommended storage temperature to control Legionella growth), so that in-line or point-of-use temperature controls are not needed.
Maintenance is essential in all mechanical systems. Systems that do not get regular preventative maintenance will eventually fail based on the service conditions and the water quality at a given location. The research is intended to justify proposing new temperature settings for water heaters. Plumbing design professionals should be able to assist with looking for temperature settings or system designs that would address both Legionella and scalding.
Recently, code change proposals proposing a 130 F maximum temperature for showers were unsuccessful, and demonstrated a lack of understanding of how to design hot water systems to control both Legionella and scalding concerns. There have been many design professionals and plumbing organizations that favor storing hot water at 140 F (which will kill Legionella bacteria in about 32 minutes) or some people even store hot water at even higher temperatures and reduce the hot water temperature down at the shower valve using the limit stop feature on all code compliant shower valves to provide a safe temperature at or below 120 F that will not present a significant scald hazard. Thermostatic valves can be used for point-of-use scald prevention.
There is not much accurate data that has been collected for scald burns across the country. However, there are extensive studies and research on the time vs. temperature exposure to the skin of adult males that was performed by Dr. Moritz and Dr. Henriques at Harvard University Medical School in the 1930s and 1940s. For Legionnaire’s disease, there are also inconsistencies in the data collection from one incident to another. There are various groups that collect data on scald burns, but reporting is sporadic at best and generally scald injuries are not reported fully because of lack of data collection or inconsistencies in data collection. The CDC collects data on larger Legionnaire’s disease outbreaks, but does not always collect data on occurrences on smaller or individual Legionnaire’s disease cases.
The Health Insurance Portability and Accountability Act of 1996 (HIPAA), Public Law 104-191, was enacted on August 21, 1996. HIPPA laws prohibited doctors, hospitals and fire or emergency medical services responders from releasing medical information on patients unless patients give written permission to release the medical information.
There needs to be better education of how domestic hot water systems are to be designed and controlled, because it is possible to control both hazards with one design. Water should be stored at or above 140 F, and a master thermostatic mixing valve should be installed on the outlet of a water heater to stabilize the hot water distribution temperatures where the entire circulated system should be kept above the upper limit of the Legionella growth temperature range of 122 F.
Domestic or service hot water circulation should be as close to the fixture supply valve connection as possible and the circulated system should be kept above 124 F at all places throughout the system using a master thermostatic mixing valve and proper balancing adjustments. Then all (code compliant) shower valves will have a maximum temperature limit stop that should be adjusted as part of a commissioning process for a building to be adjusted to limit the hot water flowing from the fixture to 110 F to 115 F. Normal showering temperature is 105 F to 109 F; code maximum is 120 F.
It would be nice to have a research task group develop a questionnaire for all hospitals and emergency responders to collect data on burn injury statistics and Legionella outbreak statistics. I would be able to supply lots of survey questions. Even if the emergency response agencies and hospitals collected generic burn information or Legionella information, they would still need to gather other significant data because what they gather on burn types does not always have accurate information on the type of scald burn (child in a sink, immersion in a tub, shower scald), what type of fixture controls, what temperature of hot water caused the burns, the length of time of exposure to the hot water and the conditions of the plumbing system that led to the scald incident or Legionella growth and transmission to a person.
It would be difficult to answer these questions without someone with an understanding of all of these concepts going to the site to do a site visit immediately after a scald incident or Legionella outbreak to collect relevant information before the system is changed, adjusted or cleaned. For Legionella outbreaks, it is important to get an accurate snapshot of the building water systems and possible sources, as well as the sub-type of the Legionella species from the building water system and from the patient in order to more accurately confirm the source.
ASHRAE Guideline 12
ASHRAE Guideline 12 Committee has recently been working on an update of the Guideline 12 document titled: “ASHRAE Guideline 12-2000, Minimizing the Risk of Legionellosis Associated With Building Water Systems.” ASHRAE Guideline 12 was last updated in 2000 and published as a guideline. The guideline has been undergoing the final stages of updating and will soon be published and may have a slightly different title, although, at the time of this writing, the title and the final text has not been finalized.
The purpose of ASHRAE Guideline 12 is to provide information and guidance to supplement the information in the ASHRAE 188 Standard. It provides specific environmental and operational guidelines that will contribute to the safe operation of building water systems to minimize the risk of Legionella bacteria growth and the occurrence of Legionellosis or Legionnaires disease.
The guideline states it is intended for use with non-residential building systems (including but not limited to hotels, office buildings, hospitals and other health care facilities, assisted living facilities, schools and universities, commercial buildings, industrial buildings, etc.) and centralized systems in multi-family residential buildings (including but not limited to central heating/cooling systems, central domestic water systems, common area fountains, etc.)
I have always said, “The Legionella bacteria does not care what type of building it is in, if the conditions are right, it will grow.” While the guideline is not specifically intended for non-centralized or single-family residential building systems, Legionella bacteria can grow anywhere the conditions are right for growth and the information in the guideline may be useful for prevention of Legionellosis in residential or non-centralized water distribution systems too.
The guideline is intended for the use of designers, installers, owners, operators, users, maintenance personnel and equipment manufacturers.
I like to use a minimum temperature of 124 F at the point of the hot water return connection at the water heater to assure the hot water temperature stays a couple of degrees above the Legionella growth temperature of 122 F at all points in the domestic hot water system. For this reason, balancing the hot water return system is very important in order to assure that each branch flow with a balancing valve is not reduced so much that the temperatures cannot be maintained at a temperature high enough to control Legionella bacteria growth. Pipe size, flow velocity vs. temperature, flow rate and insulation thickness will be important issues to consider for plumbing design.
The ANSI/ASHRAE Standard 188-2015 Legionellosis: “Risk Management for Building Water Systems” was published in June of 2015, and its purpose is to establish minimum Legionellosis risk management requirements for building water systems. The standard provides minimum Legionellosis risk management requirements for the design, construction, commissioning, operation, maintenance, repair, replacement and expansion of new and existing buildings and their associated water systems and components. The standard outlines when a building is required to have a water management program to assess the potential hazards in a building water system, then it addresses how to verify and validate that the water management plan is working.
The ASHRAE 188 standard applies to human-occupied commercial, institutional, multi-unitresidential and industrial buildings, excluding single-family residential buildings. There are some cases where the standard allows buildings or parts of a building water system to be exempt.
It was recently announced that the ASHRAE 188 Standard was one of the top-selling standards at ASHRAE. It is available in hard copies and in PDF format for online downloads.