MODERN
HYDRONICS
20ii
CREATE
SYSTEM
STABILITY
CIRCULATOR
AND BOILER
TECHNOLOGIES
Balancing
Valves
LOW TEMPERATURE
HEATING SYSTEMS
PRODUCT
SHOWCASE
CONTROLS
TERMINOLOGY
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1 | APRIL 2011
MODERN HYDRONICS
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Contents
MODERN
HYDRONICS
is a supplement of Heating Plumbing Air Conditioning Magazine
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22 System Hydraulics
Chiropractic Solutions To Hydronic Problems
Robert Bean discusses what it takes to create
stability in a system.
42 Boilers
Realize The Benefits Of Retrofits
Rakesh Zala identifies several ways to
improve the efficiency of steam boilers.
26 Valves – Part I
Holding The Flow
John Siegenthaler provides an introduction to
Pressure Independent Balancing Valves (PIBVs).
44 Valves – Part II
Staying On The Line
PIBVs bring a
new era to
balancing
hydronic
systems,
according
to John
Siegenthaler.
30 Technology
A Steady Evolution
Revolutionary change will be determined by
today’s trends, says Steve Goldie.
32 Controls
The Terminology Behind The Technology
Mike Miller explains some of the lingo you will run
into with hydronic controls.
34 Product Showcase
38 Tubing
Select The Best Pattern For The Job
Michael Gordon discusses the tubing layout options.
40 Sustainability
Increased Comfort = Improved Performance
Low-temperature heating solutions
improve comfort and reduce costs
for schools, says Christopher Makarewicz.
Radiant Heating
and Potable
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HeatWeave® Electric Floor Warming
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Infrared image of a radiant heated home
Learn more at
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MODERN HYDRONICS
APRIL 2011
| 21
System Hydraulics
Chiropractic Solutions
To Hydronic Problems
➤ Remember these words of wisdom…“when you have control
over pressure you’ll have control over the flow, when you have
control over the flow you’ll have authority over the system.”
What does this mean? It means that fluid based heating
and cooling systems are based on system hydraulics. Lose
control over the hydraulics and you lose control over the sys‐
tem – lose control over the system and there is not a zippy
electronic device available that can completely solve the
thermal and pressure oscillations in a system that has lost its
rhythm and harmony.
So what does it take to create stability? It all starts with
your knowledge of control components, including the per‐
sonalities or characteristics defining the individual elements
in a control loop as shown in Figure 1, and then applying that
knowledge appropriately for each application.
Figure 1 Typical control loop showing input (settings) and feedback
(sensor) and chain of responses.
setting
comparison
controller
actuator
linkage
sensor
room
heat terminal
unit
valve
Once you get your head around the control loop, then you
need to understand that the most stable system is one under
full load and fully balanced, i.e. all valves open, circulator run‐
ning at its optimized operating point, temperature adjusted
to design conditions and circuits balanced for flow according
to required differential pressures. This is not trivial stuff, as it
is the closure of valves, which creates the disturbances in the
system hydraulics. This leads to over and underflows through‐
out the plant…thus pressure disturbances never occur under
full load…meaning (wait for it) valves do not open to provide
comfort – they close to prevent discomfort.
By default, when plants are not designed, assembled, bal‐
22 | APRIL 2011
anced and controlled properly; occupants or operators will
resort to what I call “chiropractics for hydronics” or the man‐
ual manipulation of the system in an often futile attempt to
provide comfort. In my books, balancing and commission‐
ing should be a requirement for every system otherwise why
even bother doing a heat loss to head loss calculation (a ther‐
mal to hydraulic process)?
Last but not least, stability during the swings between
minimum loads to maximum loads comes from using vari‐
able temperatures and if necessary variable flow to compen‐
sate for unsteady state (transient) conditions.
CONTROL VALVE DESCRIPTORS
Amongst a number of other control descriptors in the man‐
ufacturer’s data sheets you will find the terms Cv, flow char‐
acteristics, close‐off rating and rangeability. These terms are
critical in selecting the proper valve and actuator for the cir‐
cuit as each plays a significant role in the control loop.
The control loop in many ways is analogous to the strat‐
egies used in football, for example, where the quarterback
and coaches call out a play according to what they think
will achieve success. It is a graphical representation of the
responsibilities and relationships of the players, but not
shown is the personalities or characteristics of each ele‐
ment and how they can either help or destroy the ability to
achieve control.
First let’s define the difference between “control valves”
and “zone valves.” Zone valves typically are on/off devices
that open and close in under 45 seconds and whose flow is
prevented or permitted with the rotational closing of a ball
or gate against an orifice. They are defined appropriately as
“quick opening” valves.
In contrast, the control valve with a modulating actuator ‐
taking a multitude of signals (three point, 4‐20ma, 0‐10v) sees a vertical stem closing against a single or double seated
orifice and whose full stroke (typically three mm for a radia‐
tor style valve) can take from say 120 seconds to as much as
nine minutes.
Furthermore, the plug of a control valve is an engineered
shape that defines its flow characteristic (Figure 2) based
on its opening (h) and valve Cv. As shown in Figure 2, con‐
MODERN HYDRONICS
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trol valves are described by their linear or equal percentage
characteristics and various derivatives proprietary to each
manufacturer.
Figure 2 Valve characteristics based on % of Cv to % of lift (h).
Basic terms and definitions
1) Balancing: a measurement and control process to
obtain required flows in circuits (note the “measurement” requirement).
2) Differential pressure: the pressure difference measured between two points (there’s that word ‘measure’ again!).
3) Pressure drop: the loss of pressure determined by
friction in pipes, fittings, valves and heat exchangers calculated at full load.
The application for each type of valve is a function of the
characteristics of the heat terminal unit (Figure 3), which is
defined in part by the logarithmic mean temperature vari‐
ations, specific heat output coefficients and power factor
(n‐values).
Figure 3 Typical flow (q) output (P) characteristics for a heat
terminal unit using aggressive temperatures and narrow delta ts.
4) Pump head: differential pressure generated by the
circulator to overcome resistance defined by the
pressure drop.
5) Valve authority: the differential pressure across the
fully open control valve at design flow divided by
pressure applied to the valve when it is closed. This
ratio in part defines the characteristic distortion of
the control valve.
6) Valve Cv: is the valve flow coefficient. It defines the
differential pressure required across the valve at a
design flow rate.
7) Valve characteristic: is the relation created between
the fluid flow through the valve and the valve lift,
assuming the differential pressure across the
valve remains constant. The flow and the lift are
expressed as a percent of their maximum value.
The objective in control design is to achieve linear out‐
put (Figure 4) through the proper combination of heat
exchanger and valve so that 50 per cent flow delivers 50 per
cent output.
Due to the “postal” personalities of fan/coils, baseboard,
panel and free standing radiators, and based on the tradi‐
tional aggressive design (ts > 180F and < 20F delta ts), out‐
puts (P) of 65 per cent or more are achieved with as little as
25 per cent flow (q) (Figure 3). This is the number one rea‐
son why quick opening “zone valves” should never be used
with “postal” heat exchangers based on high fixed tempera‐
tures and narrow delta ts.
What is needed to balance the highly responsive heat
exchanger is a slow opening “laid back” device with an inverse
characteristic to the heat terminal unit so that the marriage
between crazy and calm is one where each personality balances
www.hpacmag.com
8) Valve rangeability: ratio between the maximum flow
obtained with the valve fully open and the minimum
controllable flow for the same differential pressure.
Rangeability depends on the valve characteristics
and the manufacturing tolerances.
out the other where valve lift (U) provides linear output (P). You
can appreciate the magnitude of this concept given that typi‐
cally, for 80 per cent of the season less than 20 per cent of the
flow is required. Twenty per cent flow is not possible with on/
off zone valves nor is it possible with oversized control valves in
an unbalanced system.
In order for the control valve to have control and provide the
above relationship, they must take at least 50 per cent of the
circuit differential pressure (Δpcv >= 50% of ΔpH), which they
are to control; this in part is the definition of valve authority.
MODERN HYDRONICS
Continued on page 24
APRIL 2011
| 23
System Hydraulics continued from page 23
Figure 4 Linear output from a heat exchanger is accomplished with
the correct selection of valve type, rangeability and Cv; linear output
comes from marrying the inverse characteristics of the components.
Figure 5 Valve authority principle
When valves have no resistance their personalities become
distorted ‐ they take on the characteristics of other valves.
For example an oversized equal percentage valve behaves
as a linear valve and an oversized linear valve behaves as a
quick opening valve. To help you understand this flow/pres‐
sure control concept, it would be like comparing flow con‐
trollability with your thumb over a garden hose or the end
of a fire hose. You see it’s the resistance that provides the
control.
This is also where rangeability comes into consideration.
For the audio buffs, rangeability is comparable to “sound
fidelity” or for the lighting crowd it would be like rangeabil‐
ity of a dimmer switch. Rangeability is based on the coars‐
est link in the valve/linkage/actuator and control chain with
coarse rangeability having less “fidelity” particularly at low
loads in comparison to high rangeability.
Rangeability of 25:1 to 50:1 are common in HVAC control
valves with lower rangeability acceptable for base load heat
exchangers where valves operate mid stroke for most of the
24 | APRIL 2011
time. However, for applications where the valve must fre‐
quently operate diversely between minimum and maximum
loads greater rangeability is required.
This is where the fun in control forensics begins. When you
have oversized valves in an unbalanced system with a mis‐
match between control valves to heat exchangers and where
the rangeability is coarse – you will undoubtedly have com‐
plaints over comfort and energy use due to distorted valves
now behaving as on/off devices contributing to overflows
and underflows.
Now all of the preceding was to introduce the principles of
balancing. When you as a designer convert zone by zone heat
losses into flow rates and then flow rates into pipe diameters
based on flow velocities leading to pressure drops, you do so
in part to assist in selecting a circulator but that in of itself is
a very limited “end game” since the real control problem is
not yet solved.
Under full or partial load how does the water know which
way to go and in what quantity? Water molecules do not come
with preprogrammed directions nor are they smart enough
to divide up into your calculated flow rates and travel in
appropriate groups as you would want. You need a director
and that director is pressure control. Without the prescribed
control over pressure you get overflows and underflows,
which distorts the valve and heat terminal characteristics
and thus destroys the circuit controllability.
Figure 6 Control valve selection with balancing ensures that only
the calculated pressure is applied across each circuit so that the control valve retains its authority over the circuit.
The world of balancing has made and continues to make
improvements in technology starting with (left to right) the
traditional manual balancing valve with calibrated flow/
pressure characteristics and measuring ports, valves with
integral Cv setters for adaptability, spring loaded pressure
bypass valve (middle picture) for maintaining constant
flow or preventing overflows, self acting pressure control
MODERN HYDRONICS
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Figure 7 Typical balancing devices for fluid based heating and
cooling systems.
valves for stabilizing pressure across risers, branches or
control valves and pressure independent control valves
which integrate several features into a single unit with or
without actuators.
Basic systems, at the very least, should incorporate
References:
ASHRAE Systems and Equipment Handbook, Chapter 12, Hydronic
Heating and Cooling System Design, 2000
Petitjean, R., Total Hydronic Balancing, Tour and Andersson, 1994
and 2004 Editions
Siegenthaler, J., Modern Hydronic Heating, 3rd Edition, 2011
NTI_Ad_HPAC_TrinityLx_HP_JBH_Feb0111.pdf
www.hpacmag.com
1
11-02-01
manual and spring-loaded bypass valves or valves in conjunction with variable speed pumps (proportional or constant depending on application). As the system becomes
more diverse and complex, designers should incorporate
integrated Cv selection with stabilized risers and branches and for optimum integrated control one should use
pressure independent control valves (see p. 26 for more
on this topic. – ROBERT BEAN
Robert Bean, R.E.T., P.L.(Eng.), is a registered
practitioner in building construction engineering technology (ASET) and a professional
licensee in mechanical engineering (APEGGA).
He has over 30 years experience in the construction industry specializing in energy and indoor environmental quality and is the author and lecturer for professional
development programs addressing building science, thermal
comfort quality, indoor air quality and radiant based HVAC
systems. www.healthyheating.com
2:22 PM
MODERN HYDRONICS
APRIL 2011
| 25
Valves
holding the flow – part i
An introduction to Pressure Independent Balancing Valves.
26 | APRIL 2011
PIBVs are available in different body designs. Some have a
simple cylindrical body, while others combine pressure testing
ports, and an isolating ball valve along with the internal compensating mechanism. That mechanism is known as the valve’s
“cartridge.” It consists of a cylinder, a spring-loaded piston,
and a combination of fixed and variable shape orifices through
which flow passes. This cartridge is what gives a PIBV the ability to maintain a relatively stable flow rate over a wide range of
differential pressure. A cut-away view (see Figure 2) of the valve
shown in Figure 1 shows the internal cartridge assembly.
FIGURE 1 Example of a small cylindrical PIBV
Figure 2 PIBV body contains a spring-loaded cartridge
assembly that is designed to maintain a specific fixed flow rate
over a wide range of differential pressure.
MODERN HYDRONICS
Graphics courtesy Caleffi North America
➤ As Robert Bean discussed on pages 22-25, attaining proper
flow rates through all parallel branches of a hydronic distribution system is a vital part of delivering the expected comfort.
The usual intent of balancing is for the installer, or perhaps a separate testing and balancing contractor, to adjust
the manually-set balancing valves so that the flow rates in
each branch of the system are at, or very close to, a listing of
flow rates prescribed by the design engineer. The implication is that achieving these listed flow rates, or values close
to them, constitutes successful balancing of the system.
There are no doubt hundreds of thousands of hydronic heating and cooling systems installed with manually set balancing
valves. In most cases these are globe type valves with precision shafts for precise movement of the plug relative to the
seat. The shape of the plug in these valves is likely to give them
an equal percentage characteristic. As explained previously,
this makes the relationship between the valve’s shaft movement and the heat output of the terminal unit through which it
regulates flow, approximately proportional. Thus, opening the
valve’s shaft 50 per cent of its total travel will yield approximately 50 per cent heat output from the terminal unit, relative
to its full heat output when the balancing valve is fully open.
One nuance of any hydronic system with manually set balancing valves, with equal percentage characteristics or otherwise, is that a change in the flow rate in any branch of a
multi-branch system causes the flow rates in other branches
to change. This happens because the differential pressure
changes across branches that remain open whenever another
branch opens or closes.
A relatively new type of hydronic balancing valve has been
developed to mitigate this undesirable effect. It is called a pressure independent balancing valve (PIBV). These valves are
configured to maintain a preset flow rate over a wide range of
differential pressure. They rely on an internal compensating
mechanism to adjust a specially tapered flow orifice within
the valve so that a calibrated flow rate is maintained, typically
within a tolerance of +/- 5 per cent of the flow rating.
www.hpacmag.com
“One nuance of any hydronic system with manually set balancing
valves, with equal percentage characteristics or otherwise, is that
a change in the flow rate in any branch of a multi-branch system
causes the flow rates in other branches to change.”
Each cartridge used in a PIBV is manufactured to maintain
a specific flow rate. Manufacturers can change the internal
cartridge within a given body to produce a range of various
(fixed) flow rates (e.g. 2.0 gpm, 3.0 gpm, etc).
At low differential pressures, (less than 2, 4, or 5 psi
depending on the specific valve make and model), the internal compensating mechanism of the cartridge does not
move. This allows the maximum free flow passage through
the valve. Flow passes through both the fixed- and variable
orifices. However, at such low differential pressures the
cartridge cannot adjust to maintain a fixed flow rate. Thus,
flow rate through the valve increases if differential pressure across the valve increases. The “inactive” position of the
internal cartridge is shown in Figure 3.
Figure 3 Under very low differential pressure the spring does not
compress, and the cartridge cannot maintain a fixed flow rate.
internal spring is partially compressed by this action. Under
this condition, the piston partially obstructs the tapered slot
through which flow must pass. However, the flow passage is
now automatically adjusted so that the valve can maintain its
calibrated flow rate at the higher differential pressure.
The cartridge’s ability to hold its calibrated flow rate remains
in effect until the differential pressure across the valve exceeds
an upper threshold limit of 14, 32, 34, or 35 psi (depending on
the valve make and model). Such high differential pressure is
relatively uncommon in most well-designed hydronic systems
that include some means of differential pressure control.
If the differential pressure across the valve does exceed the
upper pressure threshold, the piston and counterbalancing
spring can no longer maintain the calibrated flow rate. The
piston’s position completely blocks flow through the tapered
orifice. All flow must now pass through the fixed orifice. This
condition is shown in Figure 4. The result will be an increase
Continued on page 28
Figure 4 Cartridge is fully compressed when differential pressure across valve reaches its upper limit. At or above this differential
pressure the PIBV cannot maintain its calibrated flow rate.
If the differential pressure across the PIBV exceeds the
minimum threshold pressure of 2, 4, or 5 psi (depending on
valve make and model), the internal piston assembly begins
to move in the direction of flow due to thrust against it. An
www.hpacmag.com
MODERN HYDRONICS
APRIL 2011
| 27
Valves continued from page 27
FIGURE 5 Differential pressure versus flow rate curve for a PIBV.
FIGURE 6 With PIBVs installed, the flow rate in each branch
holds constant when other branches open or close.
in flow rate if differential pressure increases above the upper
pressure threshold.
The flow rate versus differential pressure characteristics of a given PIBV is shown in Figure 4. The desired condition is to maintain the differential pressure across the valve
between the lower and upper threshold values, (in this case
2 psi to 32 psi), so that the internal cartridge remains active,
and the valve maintains its calibrated flow rate. This desirable operating range is represented by the vertical green line
in Figure 5.
When a PIBV is installed in each parallel branch of a system, flow rates through each active branch will remain at
their design values, regardless of the flow status in other
crossovers. This is shown in Figure 6. However, this desirable
condition is contingent upon keeping the differential pressure across the PIBV between its lower and upper threshold
values. This condition is vitally important to proper application of such valves and will be discussed in Part II of this
article (see p. 44). – JOHN SIEGENTHALER
John Siegenthaler, P.E. is the author of Modern
Hydronic Heating. The third edition of this book
is now available. Visit his website hydronicpros.
com for reference information and software to
assist in hydronic system design. Siegenthaler
can be reached at siggy@dreamscape.com.
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28 | APRIL 2011
MODERN HYDRONICS
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Technology
A Steady Evolution
A look at trends that will lead to revolutionary change in the coming years.
➤ I recently had the opportunity to attend the International
Air Conditioning, Heating & Refrigeration Exposition (AHR
Expo), which is held annually in conjunction with the winter ASHRAE conference. The AHR Expo is probably the largest HVAC and Refrigeration trade show in North America and
therefore provides an excellent opportunity to see the latest
and greatest in tools, equipment, training, controls and more.
Considering it is my job to keep on top of everything new and
great in our industry I figured it was best that I attend, it honestly had nothing to do with getting away from our horribly
long winter for a few days in Las Vegas, the location of this
year’s Expo.
The last time I attended an AHR Expo was two years ago
when it was held in Chicago, so having missed last year’s
show I was hoping, but not expecting, that maybe I would
see something at this show that would be truly new and revolutionary. After spending two days walking the aisles and
checking out displays of the over 1,900 exhibitors, I knew
this hope was not to be realized. This is not to say the show
was disappointing, I did say I was not expecting revolutionary change. I have learned that I need to look for the emerging
trends that will point the way to the revolutionary changes
More than 54,000 registered HVAC/R professionals (over 34,000 attendees and
20,000 exhibitor personnel) filled the aisles of the 63rd AHR Expo at the Las Vegas Convention
Center, January 31-February 2, to see the latest products and innovations on display from
1,938 exhibiting companies. In addition to being the largest ever Western AHR Expo, this year’s
event was also the largest show ever held outside of Chicago or New York. The total attendance
surpassed the 2004 Anaheim Show by over 40 per cent while the 379,360 square feet of
exhibit space was 16 per cent bigger than the Anaheim Show. The 1,938 exhibiting companies
also rank as the second largest number for any show.
30 | APRIL 2011
that will evolve over the coming years.
The past few years in our industry the major trend has
been a move to better efficiencies. This may be a case of overstating the obvious and this is a trend that is not unique to
our industry. Everywhere people are more and more concerned about the impact our daily lives have on our environment. Energy costs are constantly rising, and where and how
that energy is produced is of growing concern. You do not
need to be a soothsayer or a marketing genius to recognize
that any business success in this industry will continue to be
closely tied to how successfully a company can address these
types of concerns.
What I saw at the Expo this year confirms that this trend
is continuing. Refrigeration manufacturers are pushing SEER
ratings higher; more and more solar and geo thermal options
seem to be emerging, and there are definitely a growing
number of manufacturers of heat pump water heaters. All
of these things represent the steady evolution in the direction of efficiency, but none are revolutionarily new. I did see
a couple of new condensing boiler designs, and this is welcome, but again this is more of a refining of what we already
have rather than a redefining. With respect to condensing
boiler technology the limits of combustion efficiency have
already been pushed as far as they can go, so further devel-
MODERN HYDRONICS
www.hpacmag.com
opments would be in the direction of improved reliability
and durability I would expect.
table 1
Speed
Flow
Head
BHP
100%
100%
100%
100%
75%
75%
56%
42%
50%
50%
25%
12.5%
25%
25%
6%
1.2%
ON THE CIRCULATOR SIDE
One segment where I do see some more significant changes
emerging on the not so distant horizon is the area of
pump design and control. Fellow HPAC contributor, John
Siegenthaler, wrote an excellent article in the March issue
(available at www.hpacmag.com) in which he highlights the
emergence of small wet rotor circulators with variable speed
“ECM” motors. John refers to this change in pump technology
as revolutionary rather than evolutionary and I agree completely. We already see on the market a growing number of
these small “smart” pumps which can automatically adjust
their speed to account for changes in pressure, or Delta P, as
well as others that can adjust their speed to maintain a correct change in temperature, or Delta T.
When we can reduce the speed of a pump, the electrical
savings can be dramatic. The Pump Affinity Laws are a series
of relationships relating, Flow (Q), Head (H), Horsepower
(BHP), and Speed (N in units of R.P.M.) The Affinity Laws
relating to speed change are as follows:
Flow: Q2 = Q1 X (N2/N1)
Head: H2 = H1 X (N2/N1)2
Horsepower: BHP2 = BHP1 X (N2/N1)3
Reducing the speed of a pump has a cubed effect on HP 1/2
Speed = 1/8 HP and therefore a cubed reduction in electrical
consumption. Table 1 shows how dramatic the savings can
be. A pump running at half speed for example would use 87.5
per cent less electricity.
REDUCED ELECTRICAL CONSUMPTION
I have been involved in many boiler room efficiency retrofits
over the years, and have seen properly sized and operated
www.hpacmag.com
condensing boilers reduce gas consumption in apartment
buildings by upwards of 40 per cent, but I think we can
expect to see even more dramatic reductions in electrical
consumption as we see these newer technologies developed
and properly applied. Granted the gas bill is proportionally
much higher than the electrical bill, but with electrical costs
going ever higher, this kind of development of technology is
inevitable. In addition to being more efficient, this type of
pump technology will help us to achieve better overall system efficiency as well.
No matter how much we move towards better efficiency, the
most common error I continue to see involves over-sized equipment, especially when it comes to pumps. Oversized equipment
is the enemy of efficiency. Modulating boiler technology helped
mitigate, but not eliminate over-sizing of boilers, I expect as we
see smart pump technology emerge this will help us to see far
better and more efficient pump application as well.
The 2012 AHR Expo is happening January 23-25 once
again in Chicago. It won’t allow us to escape winter this time,
but I hope to see some of you there, and who knows, maybe
we will get to see the next great thing. - STEVE GOLDIE
Steve Goldie worked as a plumbing and heating
contractor for almost 20 years before joining
Noble as manager of the heating department.
In his current position Goldie focuses on product specification and system design solutions.
He can be reached at sgoldie@noble.ca.
MODERN HYDRONICS
Photo Oscar Einzig
APRIL 2011
| 31
Controls
The Terminology Behind
The Technology
Actual Supply Return Average is the current real-time average of the supply and return temperature sensors for the
water channel. Average = Supply Temp. + Return Temp.
2
Design Day refers to the coldest day of the heating season.
Design Delta T is the expected Delta T (change in temperature) of the water being supplied to and returning from the
service area of a water channel on Design Day.
Design Indoor Temperature is the indoor target temperature to be met on Design Day.
Design Mix Supply Temperature is the required temperature
of the water supplied to the service area of a water channel on
Design Day needed to meet the heating load for that area.
Design Outdoor Temperature is the outdoor temperature
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Idle Enable enables the idle function of the system.
Idle Slab Target is the minimum temperature that the system
will maintain the snow melt slab if idle is enabled.
Max Delta T is the maximum change in temperature between
the supply and return water temperatures that the system
will allow.
Maximum Supply Fluid Temperature is the maximum supply fluid temperature that the system will allow to enter the
snow melt slab.
Maximum Supply Water Temperature is the high protection
limit for the fluid or water serving a system or subsystem.
Melting Slab Target is when the snow melt zone receives a
melting call, either automatic or semiautomatic, it will heat to
and stay at this temperature until the snow is melted (auto3:25
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32 | APRIL 2011
MODERN HYDRONICS
Untitled-2 1
www.hpacmag.com
3/17/11 2:58:09 PM
Mix Channel is a numeric reference for individual mixing devices.
Semi-automatic Runtime is the length of time the snow melt
system will run if a “semi-auto call” has been initiated.
Port is a term for the RJ45 or Cat5 connectors on the right
hand side of the control.
WWMT: Warm Weather Mix Temperature is the temperature
of the water channel required to meet the heat demand at the
Warm Weather Outdoor Temperature.
Minimum Supply Water Temperature is the minimum
water temperature that this channel will produce (other than
at cold start).
Primary Loop is a segment or portion of the mechanical piping in the mechanical system connected to the
boiler(s). This is often considered the “high temperature”
side of the system.
Secondary Loop is a segment or portion of the mechanical
piping of the mechanical system connected to the primary
loop. These loops have lower temperature requirements than
the primary loop. A mixing device (modulating valve or injection pump) is required.
Target Supply Return Average is the average of the supply
and return temperature sensors for a water channel at the targeted average temperature.
WWODT: Warm Weather Outdoor Temperature is the outdoor temperature at the Warm Weather point of the temperature graph of the water channel.
WWWT: Warm Weather Water Temperature is the water temperature needed at the WWODT. – Mike Miller
Secondary Pump refers to a single pump that is used after a mixing
device. It circulates water to RFH manifolds or snow melt.
25753_Combi2_HalfPage_CAN.qxd 3/16/11 10:15 AM Page 1
Mike Miller is a controls specialist with experience
in the manufacturing, distribution and contracting sectors of the industry. He can be reached at
mike.miller@uponor.com.
The Convenience of Combined
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The Combi2 ™ is the ultimate system for home
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COMBI2™ FEATURES
• Double wall 11∕2" O.D. glass
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• Up to 10 GPM flow, with less
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• Vitraglas lining provides a
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• Integrated Mixing Device
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Combi2 ™ models heat the potable water in the
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www.hpacmag.com
MODERN HYDRONICS
APRIL 2011
| 33
Products
HeatLink’s SOL080 integrates the control
components of a solar system into a compact appliance. Features include stainless
steel piping, a heat exchanger to isolate
the glycol in the solar collector circuit from
the domestic water, and separate pumps
for each circuit. The secondary pump is
activated once every 24 hours, for 15 minutes, to ensure that potable water in the
piping or heat exchanger is not stagnant.
www.heatlinkgroup.com
The Peerless Purefire Series
stainless steel condensing boilers are available
from 50 to 399mbh inputs
for natural and LP gas use.
Features include ASME stainless steel heat exchanger
and modulating burner; front
mounted LCD controls capable of cascading up to 16
boilers; DHW Priority; built
in condensate neutralizer;
wall mount kits and more.
www.hydronicpartsgroup.com
www.peerlessboilers.com
34 | APRIL 2011
Available in both standard and high velocity, with or without a removable cover, Taco’s
4900AD Series air and dirt separators have
a scrubber system with stainless steel PALL
rings and basket assembly. The PALL ring technology removes system water micro-bubbles
and separates out dirt particles. Dirt is then
removed through a factory provided blowdown
valve. Suited to pipe sizes ranging from two to
36 inches, the 4900 Series helps to reduce
system pressure drop so that smaller pumps
can be used. www.taco-hvac.com
Industrial Glycol Make-Up packages from HG Spec Inc.
monitor and maintain the set minimum pressure in the
system by automatically adding make-up glycol solution
as it is required. Design enhancements include: a plug;
simpler piping; and the low water cut off sensor is in the
tank to allow a visual check. Skirts are available as an
option. The Light Commercial GMP is now available in 37
and 85 gallon formats. www.hgenviro.com
Uponor has launched an online
engineering resource centre, which
provides a one-stop portal for engineers to access specifications, submittals, CAD details, Revit files,
design guidelines and other tools
for designing sustainable, costeffective structures.
www.uponorengineering.com
Bell & Gossett has introduced the
Optiflo Pressure Independent Control
Valve, which combines an externally
adjustable automatic balance valve
and a full modulating control valve
to provide full modulating control
with 100 per cent valve authority.
Providing a desired flow (+/- 5 per
cent of setting) regardless of fluctuations in system pressure, the valve
is available in sizes between 1/2" to
1 1/4". It also features flow rates
from .3 GPM through 13.2 GPM.
www.bellgossett.com
Offered for cascade or parallel applications Tamas VFD pump
stations feature Variable Frequency Drive, three contactor
bypass, manual and auto select switch, triple duty valves and
skid-mounted setup. The stations can run up to five pumps.
www.tamashydronic.com www.hbxcontrols.com
MODERN HYDRONICS
www.hpacmag.com
The Envision Water-to-Water Series from
WaterFurnace offers a range of operating
temperatures, compact size and reversible control box. The hydronic heat pump
can be used for heating only, cooling only
(field converted for chilled water applications), or heating/cooling. A microprocessor controls the pumps and compressor
by sampling the entering water temperature. The controller enables the user to
view all modes of operation and easily
adjust temperatures. The unit’s cabinet
is fabricated from heavy-gauge steel and
finished with a corrosion-resistant polyester coating. www.waterfurnace.com
The wall-mounted, condensing Mascot II boiler
by Laars is a low NOx, sealed-combustion, fullymodulating system. It is available as a 125
MBH input boiler or combination boiler and
water heater. The boiler has a built-in condensate trap and auto air-elimination vent. The gas
valve is accessible directly behind the front
lower panel that rotates down via a hinged
connection. While the lower panel is open, the
centre console that houses the control display
remains closed and fully visible. Also included
is a sealed condensate trap that does not need
to be primed at startup. www.laars.com
Rinnai Corporation has introduced four new
hydronic furnace models, which work in conjunction with its tankless water heating
system. The units feature electronically commutated motor (ECM) technology and accommodate standard cased evaporator coils. A
lower speed range supports continuous fan
operation, resulting in improved filtration and
reduced temperature swings throughout the
conditioned space. An intelligent microprocessor controller regulates the pump and fan
sequence according to available hot water flow
and stops operation to ensure that domestic
hot water needs are satisfied. www.rinnai.us
Hydronic radiant heating manifold stations from Hydronic Panel
Systems Inc. are customized, preassembled and tested units.
Options include, but are not limited to, a single zone manifold with
or without constant circulation, and multiple zones on one manifold.
A manifold station with a built in heat exchanger covers an array of
special applications when the supply fluid must be isolated from the
heating liquid. www.hydronicpanels.com
www.hpacmag.com
The Magna 32-100 variable-speed wet
rotor circulator from Grundfos has a permanent magnet motor design to reduce
power consumption. An Autoadapt feature controls pump performance automatically within a defined performance
range. To simplify installation, a 10' cord
connects the circulator to a wall outlet,
with no wiring required. The integrated
frequency converter allows built-in intelligence, analyzes current conditions and
adjusts performance accordingly. When
in operation the noise level of the MAGNA
is less then 35 db. www.grundfos.ca
The Most Experienced &
Respected Name in Geothermal
With over two centuries of combined
experience, GeoSmart has earned a
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and expertise in the geothermal
industry. We offer premium
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and cooling
solutions for your
home or business.
For more information or to become a Geothermal Specialist:
866.310.6690 GEOSMART ENERGY.COM
MODERN HYDRONICS
APRIL 2011
| 35
April 2011
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HPAC_WB10JACNX
The REHAU Smart Controls System allows
users to set distinct comfort settings for
each controlled zone. Service contractors can access the system and diagnose
potential issues before arriving at the site.
Settings are stored and maintained in a
database accessible worldwide via the web.
Specific on/off events may be defined in
the settings. The point-and-click interface is
accessed through a standard web browser.
www.na.rehau.com/controls
tekmarNet2 house controls and thermostats
utilize two-way communication to provide
benefits that surpass basic thermostats and
outdoor reset controls. Communication benefits include zoning with indoor feedback,
heating and cooling interlocking, shared
schedules and outdoor temperature display
on any thermostat. The thermostats only
require two wires for communication and
power. The product line also offers home
automation and/or web access capabilities.
www.tekmarcontrols.com
Slant/Fin offers the LYNX 150 modulating, condensing gas boiler. Three
models are available to suit most residential applications: 90/120/150
MBH max input. Features include long
life cast aluminum silicon alloy heat
exchanger, natural or L.P. gas, and
digital electronic control with outdoor
reset (sensor included). The boilers
are compact and lightweight for easier
handling. www.slantfin.ca
PSS-6R
(Primary/Secondary
Control
Station) from HPS Controls consists of a
pre-piped primary loop and one to six secondary zones. Stations have left or right
side supply and return to a condensing
boiler. All field settings can be adjusted
using jumpers. They can be upgraded to
UPS26-99FC/BFC, UPS15-55SFC or Alpha
15-55F/LC pumps. www.hpscontrols.com
The Challenger Combination boiler from
Triangle Tube combines a high efficiency modulating, condensing boiler with on-demand
domestic hot water production. The instant
hot water feature eliminates the need for a
separate hot water tank while still providing
up to 3 GPM of hot water. Offered in three
models from 84,000 to 124,000 Btuh, the
boiler will accept either natural gas or propane, and has a turndown ratio of nearly 4
to 1. The dual function heat exchanger features dual copper waterways that provide
both space heat and domestic hot water
directly in the primary heat exchanger. The
compact size and lightweight design make
the Challenger easy to handle. Concentric
venting is available to minimize wall penetrations. www.triangletube.com
www.hpacmag.com
State-of-the-Art Geothermal
Training & Testing Facility
We offer a wide range
of hands-on geothermal
courses designed for
homeowners, well drillers
and HVAC contractors.
For more information or to become a Geothermal Specialist:
866.310.6690 GEOSMART ENERGY.COM
MODERN HYDRONICS
APRIL 2011
| 37
Tubing
SELECT THE BEST
PATTERN FOR THE JOB
There are a number of possible patterns with which the tubing in a radiant system can be laid
out within a room or zone. Selecting a pattern that best suits the heat loss of the room will
greatly enhance the ef�iciency and performance of the system.
➤ We know that heat loss is not always
even within a room. Areas near windows or
outside walls will need more heat energy
than interior areas. Also, more energy is
available at the beginning of a loop than
towards the end. Therefore, it makes good
sense to route the beginning of a loop along
walls with high heat losses.
The single wall serpentine tubing layout
pattern is used when the major heat loss
factor of the room comes from a single outside wall. As shown in Figure 1, the beginning of the loop is routed against the wall
and then, in a serpentine pattern, is routed
inward to �inish off the room.
FIGURE 1 Single Wall Serpentine Pattern
TIME SAVER WHEN
INSTALLING TUBING
IN JOIST AREAS
A great deal of time and effort can be
saved when installing radiant tubing
within the joist or rafters if the following method is used. First, drill the holes
through the structure and feed the tubing out and back to the manifold. Then, beginning at the furthest joist cavity,
carefully pull the loop into position while feeding the tubing off the coil. Be
extremely careful not to kink the tubing. With a little practice this method can
save a lot of aggravation.
DOUBLE WALL SERPENTINE
FIGURE 2 Double Wall Serpentine
The tubing layout pattern shown in
Figure 2 is used when the major heat loss
factor of the room comes from two adjacent outside walls. The beginning of the
loop is routed against the walls and then,
in a double serpentine pattern, is routed
to �inish off the room.
COUNTER-FLOW SPIRAL
LAYOUT PATTERN
When heat loss is distributed evenly
throughout the room a counter�low
spiral layout pattern may be used. The
beginning of the loop is routed from
38 | APRIL 2011
MODERN HYDRONICS
WWW.HPACMAG.COM
FIGURE 3 Counterflow Spiral Layout Pattern
FIGURE 4 Single Wall Joist Pattern
the outside perimeter to the interior of the room at double
spacing and then returned alongside the supply.
FIGURE 5 Double Wall Joist Pattern
sive drilling. Instead the beginning of the loop is concentrated
along the high heat loss wall by the use of intermediate loops.
INSTALLING TUBING IN JOISTS AND RAFTERS
DOUBLE WALL JOIST PATTERN
When installing radiant tubing between joists or rafters, this
pattern becomes somewhat limited by the orientation of the
joists or rafters. Even so, it is possible to keep the beginning
of the runs near the walls with high heat losses by the creative use of looping.
In Figure 5 the intermediate loops have been shortened. This
method is appropriate when the orientation of the joists will
not permit a double wall serpentine pattern without excessive drilling. Shortening the loops allows installers to concentrate the beginning of the loop along each of the high heat
loss walls. – MICHAEL GORDON
SINGLE WALL JOIST PATTERN
In the pattern shown in Figure 4 the orientation of the joists
will not permit a single wall serpentine pattern without exces-
Michael Gordon is vice president of engineering with Bradford
White Corp.
AVAILABLE NOW
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MODERN HYDRONICS
most appropriate hydronic heating methods and hardware to create systems that
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APRIL 2011
| 39
Sustainability
Increased Comfort =
Improved Performance
Solution delivers "triple bottom line" of people, planet and profit.
➤ Many reading this article can likely remember days sitting in a classroom that never seemed to be the right temperature. As the clanking iron radiators heated up, the room
was cold for hours, later becoming too hot in the middle of
the day, forcing the teacher to open a window even if it was
snowing outside. Other times, the opposite held true and
students sat attentively listening to the teacher, teeth chattering from the chill.
With the developments in heating technology and the
prevalence of alternative energy sources and high-condensing boilers, more school administrators are looking at
maximum energy efficient solutions that not only heat the
building more effectively, but more economically as well. It
has been found that sustainable heating solutions such as
low-temperature heating reduces costs and can improve student and teacher comfort, also improving productivity and
student performance. Long gone are the days when energy
and heat literally go out the window.
WASTED HEAT - WASTED MONEY
One particular challenge of heating schools is hours of operation. Because schools are vacant for approximately the
FIGURE 1 Causes of Burns
Low temperature radiator
40 | APRIL 2011
same amount of time they are in operation, buildings do
not require ongoing heat during evening hours. This has
long been a challenge for school boards and administrators.
Due to the inherent inefficiencies of older boilers and castiron radiator systems, there was no way to avoid heating the
building during hours when it was not in operation.
Today, low-temperature heating (95F EWT) systems
incorporating low-temperature radiators, high-performing
condensing boilers, are able to react quickly and efficiently,
promoting energy efficiency. For example, rather than requiring start up several hours before teachers and students arrive
for the day, the system provides output within minutes, generating enough energy to heat the space.
On warmer days the school is able to take advantage of
the natural solar loads and internal loads (see figure 2). This
results in energy savings because the thermostat can be
set to cooler temperatures for the evening hours when the
school is unoccupied. Technology today can allow advanced
radiators to function down to 95F entering wet-bulb (EWT).
This is common in most European markets allowing maximum operational efficiencies with maximum outputs and
maintaining minimum product sizing too.
Realizing these benefits, more low-temperature heating
systems are typically being installed in both new build and
retrofit applications where coal and oil-fired boiler systems
have been providing heat. School boards are realizing energy
savings of up to 30 to 40 per cent above ASHRAE 90.1 and
ROI of less than five years with low temperature systems.
In addition to the financial and environmental benefits of
these new heating technologies, schools are also starting to
realize improvements in student and teacher comfort, and
enhanced safety (see Figure 1). Studies have shown that
improved comfort can also impact occupant productivity.
According to David Pogue, national director of sustainability
at CB Richard Ellis, worker performance increases with tem-
MODERN HYDRONICS
www.hpacmag.com
FIGURE 2 Free Heating Sources
peratures up to 72F, and decreases with
temperatures above 73 to75F.1
With the increasing focus on high-performing building envelopes and the prevalence of well-insulated buildings, installing
a heating system that reacts quickly helps
improve the overall performance of both
the building and students (see Figure 3).
Icons: Istockphoto.com
WILL IT WORK?
It has been said that low temperature
heating can work in a number of applications, including retro�its and new build
scenarios. For any heating system that
operates using a low-temperature heating
source, such as a condensing boiler, solar
or geothermal application, low-temperature radiators get the most energy ef�iciency from the system.
While proper use of the new technology requires some training, it is nominal.
Teachers and students tend to operate by
the traditional "hotter is better" mentality when setting the thermostat, meaning
that if they want to quickly increase the
temperature, they tend to set it to a temperature setting hotter than the desired
�inal output. As a result, the room quickly
overheats and occupants become uncomfortable. This issue is quickly resolved
WWW.HPACMAG.COM
CASE IN POINT
with basic education and training.
Due to its numerous bene�its and return
on investment, low-temperature heating
(95F EWT) is a system more schools are
starting to explore. For a solution that delivers the "triple bottom line" of people, planet
and pro�it, it is a sustainable solution that
makes sense for both today and tomorrow's
heating needs. – CHRISTOPHER MAKAREWICZ
Christopher Makarewicz, Dipl.T, B. Eng, is
an engineering advisor for Jaga Climate
Systems. www.jaga-canada.com
1 http://www.facilitiesnet.com/green/article/StudiesLink-Green-Design-Occupant-Productivty--11283
Structure: Single-storey school building
Locale: Kingston, ON
Age: Approximately 50 years
Occupants: 324 students plus staff
Engineer: David W. Downey
Engineering, Ltd
Original System: Condensing boiler
system; finned tube radiators located
throughout the school
Replacement System: Natural gasfired, wall mounted condensing boilers.
Each unit serves as a fully modulating condensing boiler. Solar panels mounted on the roof provide an
offloaded energy source from the new
boiler plant. 107 low-temperature radiators, installed in classrooms, corridors
and offices, operate at water temperatures of 130F and 20F dT. Individual
classroom thermostats. Radiators linked
to timed schedule.
Result: Boiler firing rate reduced by
30 per cent
Estimated cost savings: $15,000 to
$20,000 per year with $100,000
expected in the first five years.
Comments: "Since installing the new
system, we have substantially reduced
the firing rates for each of the boilers," said David Downey. "In fact, it
is not uncommon for all five boilers
to be operating in condensing mode
during peak times. During the spring
or fall, only one or two boilers may be
operating. This has resulted in substantially less natural gas consumption, as much as 25 to 30 per cent
over what was previously used."
FIGURE 3 Reaction Time - Comfort
MODERN HYDRONICS
APRIL 2011
| 41
Boilers
Realize The Benefits
Of Retrofits
➤ As a contractor, you know how critical steam can be to
a building’s power, process heat and indoor climate control
needs. Additionally, one-third of a facility’s energy bill stems
from the boiler room and system inefficiency leads to higher
energy costs. Replacing an older boiler is one way to achieve
significant energy savings, but it is not the only option. There
are other ways to improve efficiency. Retrofitting an old
boiler is one way to bring it nearly up to par with today’s
new systems.
The main cause of energy inefficiency is system heat loss.
The average level of efficiency for industrial boilers is only 75
to 77 per cent.
TAKE CONTROL OF YOUR SAVINGS
The first place to look for improvements is in the control system. The following new control developments produce measurable efficiency increases and fuel-cost reductions and
they can be retrofitted into an existing system.
1. Parallel Positioning -- Many boiler burners are controlled by a single modulating motor with jackshafts to
the fuel valve and air damper. This arrangement, set during startup, fixes the air-to-fuel ratio over the firing range.
Unfortunately, environmental changes such as temperature,
pressure and relative humidity alter the fixed air-to-fuel
ratio, making combustion inefficient. To account for these
conditions, boilers with jackshaft systems are typically set
up with a high amount of excess air. This higher excess air
level reduces boiler efficiency and, over time, linkages wear
-- making repeatability impossible.
To solve this problem, consider incorporating parallel positioning into the control system. It is a process using
dedicated actuators for the fuel and air valves. Burners that
incorporate parallel positioning can be set with lower excess
air levels. Energy savings of up to five per cent can be realized by introducing a parallel positioning system.
2. O2 trim - Another way to ensure peak efficiency is to
use an oxygen sensor/transmitter in the exhaust gas. The
sensor/transmitter continuously senses oxygen content
42 | APRIL 2011
and provides a signal to the controller that “trims” the air
damper and/or fuel valve, maintaining a consistent oxygen
concentration. This minimizes excess air while optimizing
the air-to-fuel ratio.
3. Variable speed drive - Variable speed drives enable a
motor to operate only at the speed needed at a given moment,
rather than a constant 3,600 RPM as a drive runs. This speed
variance results in the elimination of unnecessary electrical
energy consumption. A variable speed drive can be used on
any motor but is most common on pumps and combustion
air motors of greater than five HP. These drives also produce
quieter operation compared to a standard motor and they
reduce maintenance costs by decreasing the stress on the
impeller and bearings.
4. Lead lag – Lead lag sequences the operation of multiple
boilers, matching system load. Lead lag enables the boilers
to operate at peak efficiency, reduces cycling and decreases
maintenance and downtime.
TAKE BACK THE HEAT
Another way to please budget scrutinizers, while improving
energy efficiency, is to incorporate heat recovery retrofits
into the boiler system.
1. Economizers -- Economizers transfer energy from the
boiler exhaust gas to the boiler feed water in the form of
“sensible heat.” Sensible heat is created by the transfer of the
heat energy of one body, in this case exhaust gas, to another,
cooler body -- the boiler feed water. This reduces the boiler
exhaust temperature while preheating the boiler feed water,
increasing overall efficiency. Economizers typically increase
energy savings by 2.5 percent to 4 per cent.
2. Two-stage condensing economizers -- This type of
economizer combines the functions of both a standard noncondensing economizer and a condensing economizer. The
first section of the economizer recovers energy by preheating boiler feed water. The second section recovers energy
by preheating a cool liquid stream such as make-up water.
Sensible and latent energy is captured from the flue gases
MODERN HYDRONICS
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that leave the boiler. Condensing economizers can increase
energy savings by up to 10 per cent, depending on design
and operating conditions.
3. High turndown burner -- Increasing burner turndown
rate will increase energy savings and reduce maintenance.
Energy savings is realized due to a reduction in on-off cycles.
Each on-off cycle is followed by purge cycles. During a purge
cycle, large volumes of room air pass through the boiler,
resulting in heat being blown out the stack.
4. Blowdown heat recovery -- All boilers must remove
dissolved solids from the boiler to maintain water purity and
ensure a long boiler life. Many boiler rooms route blowdown
to a flash tank that allows safe discharge of the steam by
reducing (flashing) the steam pressure in an enclosed tank.
Low-pressure steam is vented from the tank and condensate
is discharged to the drain. In many cases, these tanks are not
insulated nor do they allow recovery of the lost heat. A blowdown heat recovery system transfers the blowdown steam
energy to the boiler feed water, recuperating about 90 per
cent of this energy. - RAKESH ZALA
Adding a standard
economizer to a
boiler can increase
energy savings by
2.5 to four per cent
on average.
Rakesh Zala is
director of product
engineering, with
Cleaver-Brooks.
www.cleaver
brooks.com
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Runtal North America Inc.
www.hpacmag.com
MODERN HYDRONICS
APRIL 2011
| 43
Valves
staying on the line – part ii
Applying Pressure Independent Balancing Valves
FIGURE 1 Differential pressure versus flow rate curve for a PIBV.
44 | APRIL 2011
Consider the situation shown in Figure 2. It consists of six
parallel branches, each with a terminal unit, zone valve, and
a PIBV. The latter have been selected for the different design
flow rates required for each crossover.
Figure 2 Each branch with a PIBV selected for a specific flow rate.
For proper operation, the PIBV in the flow path having the
highest hydraulic resistance must have a differential pressure across it that is at least as high as its minimum activation threshold of the PIBV, which we will assume is two psi
(based on the characteristic curve shown in Figure 1).
If the terminal units are similar or identical, and thus all
operate at approximately the same flow rate, it is likely that
the flow path through the crossover furthest from the circulator will have the highest hydraulic resistance.
If the terminal units are significantly different, and operate
at significantly different flow rates, the flow path of greatest
hydraulic resistance must be determined by calculating the
head loss along the flow path through each crossover at its
design flow rate, and comparing the results to find the path
with the highest total head loss.
The circulator should be sized to provide the design flow
rate when all zones are open, with a head equal to the head
loss of the most restrictive flow path. The latter must include
the head loss of the supply and return mains, the branch piping, terminal unit, and the minimum operating differential
pressure of the PIBV.
The calculation for head loss will typically require the
MODERN HYDRONICS
www.hpacmag.com
Figure 1 Courtesy Caleffi North America
➤ The pressure-independent balancing valves (PIBV) discussed in the earlier article (Holding the Flow, p.26) make
it easy to achieve and maintain fixed flow rates within each
crossover and branch of a system. When properly applied,
PIBV also minimize variations in flow rates as zone valves or
thermostatic radiator valves begin closing within the system.
Holding the Flow discussed how PIBVs use a specially
shaped, spring-loaded cartridge to maintain their factory
set flow rate over a wide range of differential pressure. Most
currently-available PIBVs can maintain their factory set flow
rate within a relatively narrow (+/- 5 per cent) tolerance
provided that the differential pressure across them remains
between a specific minimum and maximum value. This characteristic is depicted by the green line in Figure 1, where a
valve with a minimum differential pressure of two psi, and a
maximum differential pressure of 32 psi is assumed. These
minimum and maximum differential pressure thresholds
vary with the manufacturer, type and size of the PIBV.
head loss of each segment of the supply and return mains, out to and back
from the most restrictive crossover, to be individually calculated and then
added together.
This head loss could also be estimated by assuming a typical main’s piping sizing criteria of three to five feet of head loss per hundred feet of pipe.
For example: Assume the piping mains in the system shown in Figure 3 have
been sized for a head loss of five feet per 100 feet of pipe. Also assume that
all terminal units and associated branch piping are identical, and require
four gpm each while operating. The minimum operating pressure differential of the PIBV is two psi. The system operates with water at an average temperature of 140F. Based on this description, you then determine the
minimum circulator flow/head requirement for this system.
Figure 3 System assumed for the example calculations.
The total head loss through the most restrictive flow path can now be found by adding
these individual head losses together:
The minimum operating requirement for the
circulator is therefore the total flow rate of all
crossovers (e.g. 6 x 4 gpm = 24 gpm), at 23.7 feet
of head, as shown by the yellow dot in Figure 4.
The pump curve shown slightly exceeds the
minimum operating point, and thus would be
an acceptable choice.
Figure 4 The yellow dot is the calculated operating point of this system when all zone valves
are open.
Solution: The total head loss of the flow path through the most remote
heat emitter is the head loss of the mains, plus the head loss of the heat
emitter and branch piping, plus the minimum operating head loss of the
PBV. These can be determined separately and then added.
The graph on the right side of Figure 3 shows that each heat emitter creates six feet of head loss at the desired operating flow rate of four gpm.
The total estimated head loss of the supply and return piping mains, out
to and back from the farthest branch is:
The PIBV minimum required head loss needs to be calculated from its
minimum required pressure drop. This requires the density of water at an
average temperature of 140F, which is 61.3 lb/ft3. The head loss across the
PIBV is then calculated as follows:
When one or more of the zone valves in
the system close, the operating point shifts
left and upward along the pump curve. This
increases the head available across the supply and return mains. The PIBVs in the active
branches immediately react to absorb the
extra head, and therefore maintain the same
differential pressure across the active crossovers. This reaction, depicted in Figure 5,
allows the flow rates in the active crossovers
to remain unchanged.
Continued on page 46
www.hpacmag.com
MODERN HYDRONICS
APRIL 2011
| 45
Valves continued from page 45
FIGURE 5 When some zones close, the system head loss curve
steepens, and PIBVs in active branches adjust to absorb the
increased head. This preserves the same differential pressure
across these active branches, and thus preserves the flow rates
in these branches.
In most systems, there is no need to use a differential pressure bypass valve in a system equipped with PIBVs on each
crossover. The PIBVs directly absorb the excess circulator
head under partial load conditions.
In summary, PIBVs bring a new era to balancing hydronic
systems. Each PIBV is selected for a specific flow rate.
Provided the system maintains the differential pressure
across each PIBV within a fairly wide range, (as shown by
the green line in Figure 1), the cartridge inside each PIBV
will automatically adjust to hold the flow rate constant
within its branch. – JOHN SIEGENTHALER
John Siegenthaler, P.E. is the author of Modern
Hydronic Heating. The third edition of this book
is now available. Visit www.hydronicpros.com
for reference information and software to assist
in hydronic system design. Siegenthaler can be
reached at siggy@dreamscape.com.
HPGSales_HPAC
11/24/2010
1:56 PM
Page 1
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46 | APRIL 2011
MODERN HYDRONICS
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