Roger W. Griffith, P.E.

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Designing Plumbing Systems To Minimize Legionella

August 28, 2015 by Roger Griffith 2 Comments

legionella

The recent outbreak of legionnaires’ disease in New York City has brought renewed attention to the inherent risks from legionella bacteria in HVAC and plumbing systems. There are several things that plumbing engineers and designers can do to minimize the risk of legionella colonizing and growing in plumbing systems.

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Filed Under: Hot Water Systems, Legionella, Plumbing, Recent Posts

Thermal Expansion Tanks: Part 3

August 24, 2015 by Roger Griffith Leave a Comment

Selection and Installation of Thermal Expansion Tanks

thermal expansion tank support

See Part 2 for calculating the expansion tank volumes. Now, using the calculated acceptance volume and total volume for the tank, select an expansion tank from the manufacturer’s data that meets these requirements.

Be aware that in most states, unfired pressure vessels larger than a certain volume must have an ASME stamp. Check your state’s requirement for this limit. If the expansion tank you need is larger than this limitation, it must be constructed in accordance with ASME Section VIII requirements. ASME rated vessels are much higher in cost than non-ASME vessels. Installing multiple smaller tanks, which are below the volume limitation for ASME tanks, is also an option. Most tank manufacturers offer both ASME and non-ASME thermal expansion tanks.

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Filed Under: Hot Water Systems, Plumbing, Recent Posts, Water Heaters Tagged With: thermal expansion tanks

Thermal Expansion Tanks: Part 2 – Sizing

July 31, 2015 by Roger Griffith 1 Comment

How To Size Thermal Expansion Tanks For Hot Water Systems

thermal expansion tank

In Part 1 of this series, we looked at where thermal expansion tanks are needed. When it is determined that a tank should be included in the plumbing system, the next task is to determine the correct size for the tank. Referring to sizing tables in an expansion tank manufacturer’s catalog is the easiest method, although not the best method, for sizing thermal expansion tanks. Sizing tables provided by the manufacturers, give the tank model number and size based on the water heater’s volume and the system supply pressure. These tables, however, are based on three important assumptions that designers need to be aware of.

First, for most manufacturers, the tables are based on a maximum allowable line pressure of 150 psi. This is the maximum allowable working pressure of most water heaters and thermal expansion tanks. It is also the setting of the water heater relief valve. In other words, the thermal expansion tank, if selected by the tables, could accommodate the thermal expansion up to a system pressure of 150 psi, which is the relieving point for the water heater relief valve. Remember that the purpose of the thermal expansion tank is to avoid the relief valve from relieving. Sizing the thermal expansion tank for a maximum allowable pressure of 135 psi, which is 10% below the relief valve set point, is a better alternative.

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Filed Under: Hot Water Systems, Plumbing, Recent Posts, Water Heaters Tagged With: thermal expansion tanks

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Roger W. Griffith, P.E.
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RGriffith@GriffithEngineering.net

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(865) 471-8142

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