7 points every architect, engineer,
contractor and their clients should know about pressure in systems.
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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
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
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
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
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.
Registered Engineering Technologist - Building
construction (ASET #8167)
Professional Licensee (Engineering) - HVAC (APEGA
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.