Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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7 points every architect, engineer, contractor and their clients should know about pressure in systems. For additional support visit our visitor services page.

Our integrated design program has over 2100 slides illustrating architectural, interior design and HVAC engineering principles which contribute to indoor environmental quality and energy allocation for conditioning the occupants and building.

The following course materials on pressure are samples from the lecture and based on a Steven Covey principle of "Begin with the End in Mind". They are a very small but important sample of the Covey principle and are provided here to give you an idea of what kind of materials we'll be discussing during the program.

The course is also registered with AIA and participants can earn up to 21 Learning Units.

For more sample slides visit our list of training modules.

Figure 1: In a closed loop hydronic cooling and heating system the designer is concerned about static pressure, dynamic pressure (aka differential pressure or head pressure) and pressure changes created as a result of fluid expanding and contracting. All three of these pressure are connected and if improperly handled can cause damage to equipment and systems and elevate risks related to health and safety.

Figure 2: In our program we'll discuss the relationship between pressure and boiling points (above). Though the boiling point is controlled by the relationships between fill and relief pressure and fill and operating temperatures;  pressures drops due to fluid in motion can drop below the vapour pressure of the fluid causing cavitation.

Figure 3: It matters not if it is a 20 story or 2 story building the static pressure must be sufficient enough to displace the air in the uppermost pipes with water plus additional pressure to prevent cavitation in fluids in motion through pipe, valves and fittings. We will explain this is much greater detail during the lecture.

Figure 4: The slide is self explanatory but the topic is usually of great discussion in class as we explain why in a closed loop system molecules of water are circulated and not pumped; and why you still have to account for the friction loss in vertical pipes even in the presence of gravity.

Figure 5: One of our favourite topics which is tied into the history behind the Carlson-Holohan Industry Award of Excellence. The effects of "pumping away" or "pumping towards" an expansion tank is not trivial as shown above. This was explained by engineer Gil Carlson and his colleagues decades ago but remains an elusive topic even amongst seasoned designers.

Figure 6: The location of the expansion tank is important and so is its air charge. The expanded volume of the system will park itself wherever the tank is located. For this reason the tank pressure needs to be adjusted for the static pressure at connection location.

Figure 7: As per ASHRAE definition, cavitation is the formation by mechanical forces of vapour in liquids; specifically, the formation of vapour cavities in the interior or on the solid boundaries of liquids in motion, where the pressure is reduced to a critical value without a change in ambient temperature. This can occur in circulators and valves when the pressure of the fluid is below the vapour pressure of the fluid at that temperature. Cavitation is very destructive causing mechanical failure on surfaces and its energy will also show up in part as noise (above graph)

So there you have it, a few sample slides from our pressure lecturer...just a hors d'oeu·vre from our library of over 2100 slides addressing a small but important element of integrated design and radiant based HVAC systems. In the program we will get into this and a whole lot more? How much more? Well just follow the links to the other parts of our website and you’ll get a feel for the scope of materials that we’ll be covering.

See you soon.

Robert Bean, R.E.T., P.L.(Eng.)
Registered Engineering Technologist - Building construction (ASET #8167)
Professional Licensee (Engineering) - HVAC (APEGA #105894)
Building Sciences / Industry Development
ASHRAE Committees: T.C.61. (CM), T.C.6.5 (VM), T.C. 7.04 (VM), SSPC 55 (VM)
ASHRAE SSPC 55 - User Manual Task Leader

Note: The author participates on several ASHRAE and other industry related committees but be advised the materials and comments presented do not necessarily represent the views of these societies, only the president of the society or nominated representative may speak on behalf of the organization.

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