ASHRAE 188P and the effects on steam process

With a new standard under review, the HVAC industry prepares to adjust the new processes of preventing Legionellosis within building water systems.


With the outbreak in the past few years of Legionella, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has reviewed the previous guidelines developed and collaborated with industry scientific and medical communities to develop a more comprehensive focused approach to help businesses mitigate the risks of infection.

The new standard, ASHRAE Standard 188P: Prevention of Legionellosis Associated with Building Water Systems, is still in “preliminary” format (thus the “P” notation) and is under public review for a possible release by the middle of 2013.

With the medical and scientific communities involved, details of the growth, methods of infection, and parameters to remediate the disease have provided a better insight to how the HVAC industry can adjust the processes with end users and test it to better remediate any findings at their facility.

While ASHRAE 188P does not define specific HVAC processes to change, they do list typical areas of possible contamination and remediation methods. Those areas of possible contamination can include:

  • Cooling towers
  • Evaporative condensers
  • Domestic hot water systems operating below 104 F supplied with water taps temperature of less than 122 F
  • Humidifier systems
  • Decorative fountains
  • Spas and whirlpools
  • Dental water lines
  • Any stagnant water systems

As you will note, both hot water systems and cold water systems are affected (80% and 20%, respectively). The standard focuses on the domestic hot water manufacturing and distribution systems so it will allow remediation and control of the disease.

The standard recommends storage and distribution of domestic hot water of 140 F and not less than 122 F at the point of use. Eliminate dead lead when possible, allow recirculation pumps to run continuously, and key to the remediation by providing a “Super Heat and Flush” of the distribution legs.

The “Super Heat and Flush” is of major discussion since it will require a supply temperature of 160 to 170 F for a minimum of 30 minutes as to effectively “kill” the disease in the system. These temperatures may cause damage to gaskets, water lines, valves or worse, scalding of individuals if not managed by the facility. Design and implementation of this flush is still being considered and may change as needed by standard or local codes.

ASHRAE 188P does provide the implementer methods and parameters to help remediate the disease as well as develop a plan to provide continuous remediation of the disease. The outlined plans include a water system treatment management plan (WSTMP) and a hazard analysis and critical control points plan (HACCPP). With these plans in place and working in conjunction with HVAC operational parameters, it is the opinion of the ASHRAE committee that the disease will be remediated and eliminated from active growth.

The ASHRAE standard also mentioned other processes that can be used and implemented to help control the spread or eliminate the growth of the disease. Each has recognized pros and cons and should be viewed and implemented how the local jurisdiction and client will find acceptable to their customers. The processes include hyper-halogenation, silver-copper ionization, and ultraviolet light.

While the implementation of any of these guidelines working together can control and mitigate the spread of the disease, it is still a strong requirement that the local facility personnel actively involved in the periodical testing of the water systems and ensure the implemented control processes and functioning as designed, at required set points and maintained.

Ray Prosise is the government business development manager at Spirax Sarco. Content provided by Spirax Sarco, originally published in Steam News Magazine.

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