Page 28 - Oil & Energy - March 2013

28 • OIL&ENERGY
Hydronics
IN A RECENT ARTICLE I WROTE ABOUT TAKING
a holistic approach to looking at heating
systems. It’s important to look at the system
as a whole, rather than the sum of its parts.
When we design and install a heating
system, we are creating a group of ele-
ments that form a complex machine that is
designed to keep people comfortable while
minimizing energy usage. When it comes
to comfort, it’s all about the BTUs and sup-
plying the right amount of them to the right
places at the right time.
Variable speed pumps were introduced
in the US in 2004 by Taco. These types of
circulators have been in use in Europe for
years and the concept has been around for
quite a while. But exactly what is “variable
speed pumping?”
As the name suggests, a microprocess
attached to the pump changes the speed
based on some sort of feedback from the
system. Presently there are two types of
variable speed pumps on the market today;
Delta T & Delta P. The Delta T pump varie
its speed by comparing the temperature
of two points in the system to maintain
a fixed temperature differential across
the system. The Delta P pump varies
its speed based on system pressure
differential.
MATCH THE CONDITIONS
To fully understand what these
pumps do in a system, we have to go
back to the whole system approach and se
Variable Speed Pumping Delivers Heat Accurately
Delta T circulator maintains program temperature by adjusting speed as load changes
By Bruce Marshall, Emerson Swan
how they perform under certain conditions.
Delta P pumps are essentially a European
designed system component. Heating
systems in Europe are very different from
American systems. They use a lot of panel
radiators with TRVs (thermostatic radiator
valves). This type of system makes every
radiator an individual zone. When the area
around the panel radiator is up to tempera-
ture, the TRV closes and the water bypasses
back to the main.
The Delta P pump is programmed for the
pressure drop of the system and if all TRVs
are open, the pump will run at full speed.
As the TRVs close, the pump would see a
rise in pressure and slow down. Picture a
vertical pipe filled with water. Now punch
some holes at various places in the pipe.
If there is a pump at the bottom of the pipe
it would have to speed up to keep the holes
filled with water. But as the holes closed
down the pump would not have to supply
as much water and would slow down.
In a system, as the TRVs on the radiators
call for heat, the pump runs faster and slows
down as they are satisfied. This concept
works great in European-designed systems,
and those pumps are the right component.
This type of pump also works quite
well in a large commercial hydronic
system.
HE AMERICAN WAY
Now come back across the pond to the
good old USA. Our systems are typically
fin tube baseboard in different zones
of the house; typically first floor,
second floor, family room. When the
system was designed, the universal
hydronics formula was used.
GPM = BTUH ÷ ΔT x 500
GPM is the gallons per minute flow
e the system requires at any given
me; BTUH is the heating load at any
given point in time; Delta T (ΔT) is
the designed temperature drop of the
fluid; and 500 (8.33 x 60) is constant,
or
s
e
T
rat
ti
Taco’s Bumble Bee
high-efficiency
variable speed
circulator.