modern hydronics

7/25/2019 Modern Hydronics

1/32WWW.HPACMAG.COM1| APRIL 2011 MODERN HYDRONICS

20II

A PUBL ICATION OF

CIRCULATOR

AND BOILER

TECHNOLOGIES

BALANCING

VALVES

LOW TEMPERATURE

HEATING SYSTEMS

PRODUCT

SHOWCASE

CONTROLS

TERMINOLOGY

CREATE

SYSTEMSTABILITY

MODERNHYDRONICS


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THE ANSWER

IS SIMPLE.

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commutated/permanent

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Maintenance-free operation.

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For more information, contact your Bell & Gossett Representative

or visit www.bellgossett.com

2011 ITT Corporation

ITT is the largest pump manufacturer in the world providing system solutions for commercial and residential HVAC, water supply and

wastewater applications. ITT maintains one of the industrys most extensive sales and service organizations to ensure you get the advice

and support you need to successfully install, operate and maintain your systems.

Bell & Gossett | Goulds Pumps | A-C Fire Pump


5/32



CHIROPRACTIC SOLUTIONS

TO HYDRONIC PROBLEMSRemember these words of wisdomwhen you have control

over pressure youll have control over the flow, when you have

control over the flow youll 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 1Typical control loop showing input (settings) and feedback

(sensor) and chain of responses.

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 plantthus pressure disturbances never occur under

full loadmeaning (wait for it) valves do not open to provide

comfort they close to prevent discomfort.By default, when plants are not designed, assembled, bal-

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-

ufacturers 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 lets 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) basedon its opening (h) and valve Cv. As shown in Figure 2, con-

System Hydraulics

setting

comparison controller actuator linkage

sensor room heat terminalunit

valve


7/32WWW.HPACMAG.COM APRIL 2011 |23MODERN HYDRONICS

trol valves are described by their linear or equal percentage

characteristics and various derivatives proprietary to each

manufacturer.

FIGURE 2Valve characteristics based on % of Cv to % of lift (h).

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 3Typical flow (q) output (P) characteristics for a heat

terminal unit using aggressive temperatures and nar row delta ts.

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 marriagebetween crazy and calm is one where each personality balances

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 (pcv>= 50% of pH), which they

are to control; this in part is the definition of valve authority.

BASIC TERMS AND DEFINITIONS

1) Balancing: a measurement and control process toobtain required flows in circuits (note the measure-

ment requirement).

2) Differential pressure: the pressure difference mea-

sured between two points (theres that word mea-

sure again!).

3) Pressure drop: the loss of pressure determined by

friction in pipes, fittings, valves and heat exchang-

ers calculated at full load.

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.

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.

Continued on page 24



FIGURE 4Linear 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 5Valve 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 its 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 heatexchangers where valves operate mid stroke for most of the

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 youhave 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 characteristicsand thus destroys the circuit controllability.

FIGURE 6Control valve selection with balancing ensures that only

the calculated pressure is applied across each circuit so that the con-

trol 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 constantflow or preventing overflows, self acting pressure control

System Hydraulics continued from page 23


9/32

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

manual and spring-loaded bypass valves or valves in con-

junction with variable speed pumps (proportional or con-

stant depending on application). As the system becomes

more diverse and complex, designers should incorporateintegrated Cv selection with stabilized risers and branch-

es 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 engi-

neering technology (ASET) and a professional

licensee in mechanical engineering (APEGGA).

He has over 30 years experience in the con-

struction industry specializing in energy and indoor environ-

mental 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

WWW.HPACMAG.COM APRIL 2011 |25MODERN HYDRONICS

FIGURE 7 Typical balancing devices for fluid based heating and

cooling systems.

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

_ _ _ _ _ _



HOLDING THE FLOW PART IAn introduction to Pressure Independent Balancing Valves.

As Robert Bean discussed on pages 22-25, attaining proper

flow rates through all parallel branches of a hydronic distribu-

tion system is a vital part of delivering the expected comfort.

The usual intent of balancing is for the installer, or per-

haps 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 implica-

tion 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 heat-

ing and cooling systems installed with manually set balancing

valves. In most cases these are globe type valves with preci-

sion shafts for precise movement of the plug relative to the

seat. The shape of the plug in these valves is likely to give theman equal percentage characteristic. As explained previously,

this makes the relationship between the valves shaft move-

ment and the heat output of the terminal unit through which it

regulates flow, approximately proportional. Thus, opening the

valves shaft 50 per cent of its total travel will yield approxi-

mately 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 bal-

ancing valves, with equal percentage characteristics or oth-

erwise, 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 pres-

sure 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, typicallywithin a tolerance of +/- 5 per cent of the flow rating.

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 com-

pensating mechanism. That mechanism is known as the valves

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 abil-

ity 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 1shows the internal cartridge assembly.

Valves

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.

FIGURE 1 Example of a small cylindrical PIBV

Graph

icscourtesyCaleffiNorthAmerica



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 cartridges 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 doesexceed the

upper pressure threshold, the piston and counterbalancing

spring can no longer maintain the calibrated flow rate. The

pistons position completely blocks flow through the taperedorifice. All flow must now pass through the fixed orifice. This

condition is shown in Figure 4. The result will be an increase

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 inter-

nal 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 pres-

sure across the valve increases. The inactive position of the

internal cartridge is shown in Figure 3.

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 beginsto move in the direction of flow due to thrust against it. An

FIGURE 4Cartridge is fully compressed when differential pres-

sure across valve reaches its upper limit. At or above this differential

pressure the PIBV cannot maintain its calibrated flow rate.

FIGURE 3Under very low differential pressure the spring does not

compress, and the cartridge cannot maintain a fixed flow rate.

One nuance of any hydronic system with manually set balancing

valves, with equal percentage characteristics or otherwise, is thata change in the flow rate in any branch of a multi-branch system

causes the flow rates in other branches to change.




in flow rate if differential pressure increases above the upper

pressure threshold.

The flow rate versus differential pressure characteris-

tics of a given PIBV is shown in Figure 4. The desired condi-

tion is to maintain the differential pressure across the valvebetween 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 desir-

able operating range is represented by the vertical green line

in Figure 5.

When a PIBV is installed in each parallel branch of a sys-

tem, 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 pres-

sure across the PIBV between its lower and upper threshold

values. This condition is vitally important to proper appli-

cation of such valves and will be discussed in Part II of thisarticle (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 [email protected].

Valves continued from page 27

FIGURE 6With PIBVs installed, the flow rate in each branch

holds constant when other branches open or close.

FIGURE 5Differential pressure versus flow rate curve for a PIBV.

THIS COULD BE YOUR LAST ISSUE OF

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:KR 6D\V



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 win-

ter ASHRAE conference. The AHR Expo is probably the larg-

est 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 igured it was best that I attend, it hon-

estly had nothing to do with getting away from our horribly

long winter for a few days in Las Vegas, the location of this

years Expo.

The last time I attended an AHR Expo was two years ago

when it was held in Chicago, so having missed last years

show I was hoping, but not expecting, that maybe I wouldsee something at this show that would be truly new and rev-

olutionary. 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 revolution-

ary change. I have learned that I need to look for the emerging

trends that will point the way to the revolutionary changes

that will evolve over the coming years.

The past few years in our industry the major trend has

been a move to better eficiencies. This may be a case of over-

stating the obvious and this is a trend that is not unique to

our industry. Everywhere people are more and more con-

cerned about the impact our daily lives have on our environ-

ment. 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 conirms that this trend

is continuing. Refrigeration manufacturers are pushing SEER

ratings higher; more and more solar and geo thermal optionsseem to be emerging, and there are deinitely a growing

number of manufacturers of heat pump water heaters. All

of these things represent the steady evolution in the direc-

tion of eficiency, but none are revolutionarily new. I did see

a couple of new condensing boiler designs, and this is wel-

come, but again this is more of a reining of what we already

have rather than a redeining. With respect to condensing

boiler technology the limits of combustion eficiency have

already been pushed as far as they can go, so further devel-

Technology

MORE THAN 54,000 REGISTERED HVAC/R PROFESSIONALS (over 34,000 attendees and

20,000 exhibitor personnel) filled the aisles of the 63rd AHR E xpo at the Las Vegas Convention

Center, January 31-February 2, to see the latest products and innovations on display from1,938 exhibiting companies. In addition to being the largest ever Western AHR E xpo, this years

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.



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 eficient, this type of

pump technology will help us to achieve better overall sys-

tem eficiency as well.

No matter how much we move towards better eficiency, the

most common error I continue to see involves over-sized equip-

ment, especially when it comes to pumps. Oversized equipment

is the enemy of eficiency. 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 eficient pump application as well.

The 2012 AHR Expo is happening January 23-25 once

again in Chicago. It wont 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 prod-

uct specification and system design solutions.

He can be reached at [email protected].

opments would be in the direction of improved reliability

and durability I would expect.

ON THE CIRCULATOR SIDE

One segment where I do see some more signiicant 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 com-

pletely. 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 cor -

rect change in temperature, or Delta T.

When we can reduce the speed of a pump, the electrical

savings can be dramatic. The Pump Afinity Laws are a series

of relationships relating, Flow (Q), Head (H), Horsepower

(BHP), and Speed (N in units of R.P.M.) The Afinity 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 1shows 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 eficiency retroits

over the years, and have seen properly sized and operated

SPEED FLOW HEAD BHP

100% 100% 100% 100%

75% 75% 56% 42%

50% 50% 25% 12.5%

25% 25% 6% 1.2%

PHOTO OSCAR EINZIG

TABLE 1



THE TERMINOLOGY BEHINDTHE TECHNOLOGY

Actual Supply Return Averageis the current real-time aver-

age of the supply and return temperature sensors for the

water channel. Average = Supply Temp. + Return Temp.2

Design Dayrefers to the coldest day of the heating season.

Design Delta Tis the expected Delta T (change in tempera-

ture) 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 tempera-

ture to be met on Design Day.

Design Mix Supply Temperatureis 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

on the Design Day (coldest daytime temperature).

Idle Enableenables the idle function of the system.

Idle Slab Targetis 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 Temperatureis the maximum sup-

ply fluid temperature that the system will allow to enter the

snow melt slab.

Maximum Supply Water Temperatureis the high protection

limit for the fluid or water serving a system or subsystem.

Melting Slab Targetis 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 (auto-

matic call) or until the semi-auto runtime expires.

Controls

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Mix Channel is a numeric reference for individual mix-

ing devices.

Minimum Supply Water Temperature is the minimumwater temperature that this channel will produce (other than

at cold start).

Port is a term for the RJ45 or Cat5 connectors on the right

hand side of the control.

Primary Loop is a segment or portion of the mechan-

ical 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 primaryloop. These loops have lower temperature requirements than

the primary loop. A mixing device (modulating valve or injec-

tion pump) is required.

Secondary Pumprefers to a single pump that is used after a mix-

ing device. It circulates water to RFH manifolds or snow melt.

Semi-automatic Runtimeis the length of time the snow melt

system will run if a semi-auto call has been initiated.

Target Supply Return Averageis the average of the supplyand return temperature sensors for a water channel at the tar-

geted average temperature.

WWMT: Warm Weather Mix Temperature is the temperature

of the water channel required to meet the heat demand at the

Warm Weather Outdoor Temperature.

WWODT: Warm Weather Outdoor Temperature is the out-

door temperature at the Warm Weather point of the tempera-

ture graph of the water channel.

WWWT: Warm Weather Water Temperature is the water tem-

perature needed at the WWODT. Mike Miller

Mike Miller is a controls specialist with experience

in the manufacturing, distribution and contract-

ing sectors of the industry. He can be reached at

[email protected].

The Combi2 is the ultimate system for homespace heating and potable hot water from asingle energy-saving source. The secret lies inthe double-walled, heat exchanger coil. EachCombi2 model features a double-wall, carbonsteel heat exchanger coil that is Vitraglas-linedfor corrosion resistance and long life.

Combi2 models heat the potable water in thetank. Heat from the hot water is then efficiently

transferred through the heat exchanger to the fluidwi thin the coi l for use in radiant heatingapplications. The result is a highly effectivecombination systemand another great ideafrom Bradford White.

The Convenience of Combined

Space and Water Heating

Atmospheric VentingPower Venting

2011, Bradford White Corporation. All Rights Reserved.

Double wall 112" O.D. glasscoated (Vitraglas ) steel coilheat exchanger

Up to 10 GPM flow, with lessthan 5 ft. of head loss

Vitraglas lining provides atough, corrosion resistant

interior surface

Heavy gauge steel tankautomatically formed, rolled andwelded to assure a continuousseam for glass lining.

Integrated Mixing Devicesupplied with unit

Defender Safety System

on 50-gallon models

COMBI2 FEATURES

Built to be the Best

www.bradfordwhite.com

866.690.0961



Products

HeatLinks SOL080 integrates the control

components of a solar system into a com-

pact appliance. Features include stainless

steel piping, a heat exchanger to isolatethe 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 min-

utes, to ensure that potable water in the

piping or heat exchanger is not stagnant.

www.heatlinkgroup.com

The Peerless Purefire Seriesstainless steel condens-

ing boilers are available

from 50 to 399mbh inputs

for natural and LP gas use.

Features include ASME stain-

less steel heat exchanger

and modulating burner; front

mounted LCD controls capa-

ble of cascading up to 16

boilers; DHW Priority; built

in condensate neutralizer;

wall mount kits and more.

www.hydronicpartsgroup.com

www.peerlessboilers.com

Available in both standard and high veloc-

ity, with or without a removable cover, Tacos

4900AD Series air and dirt separators have

a scrubber system with stainless steel PALL

rings and basket assembly. The PALL ring tech-nology 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

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 fluctua-

tions 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

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 engi-

neers to access specifications, sub-

mittals, CAD details, Revit files,

design guidelines and other tools

for designing sustainable, cost-

effective structures.

www.uponorengineering.com

Offered for cascade or parallel applications TamasVFD 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



The Envision Water-to-Water Series from

WaterFurnaceoffers a range of operating

temperatures, compact size and revers-

ible control box. The hydronic heat pump

can be used for heating only, cooling only

(field converted for chilled water applica-

tions), or heating/cooling. A microproces-

sor controls the pumps and compressor

by sampling the entering water tempera-

ture. The controller enables the user to

view all modes of operation and easily

adjust temperatures. The units cabinet

is fabricated from heavy-gauge steel and

finished with a corrosion-resistant poly-

ester coating. www.waterfurnace.com

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

The wall-mounted, condensing Mascot II boiler

by Laarsis a low NOx, sealed-combustion, fully-

modulating system. It is available as a 125

MBH input boiler or combination boiler and

water heater. The boiler has a built-in conden-

sate 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

The Magna 32-100 variable-speed wet

rotor circulator from Grundfoshas a per-

manent magnet motor design to reduce

power consumption. An Autoadapt fea-

ture controls pump performance auto-

matically 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 intel-

ligence, 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 combinedexperience, GeoSmart has earned a

solid reputation for our knowledgeand expertise in the geothermalindustry. We offer premiumquality, cost-effective,energy efficient andrenewable heatingand coolingsolutions for yourhome or business.

For more information or to become a Geothermal Specialist:

866.310.6690 GEOSMARTENERGY.COM

Rinnai Corporation has introduced four new

hydronic furnace models, which work in con-

junction with its tankless water heating

system. The units feature electronically com-

mutated motor (ECM) technology and accom-

modate 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 micropro-

cessor 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


20/32

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Slant/Finoffers the LYNX 150 modu-

lating, condensing gas boiler. Three

models are available to suit most res-

idential applications: 90/120/150

MBH max input. Features include longlife 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

The REHAUSmart Controls System allows

users to set distinct comfort settings for

each controlled zone. Service contrac-

tors 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

tekmarNet2house controls and thermostats

utilize two-way communication to provide

benefits that surpass basic thermostats and

outdoor reset controls. Communication ben-

efits 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

PSS-6R (Primary/Secondary Control

Station) from HPS Controls consists of a

pre-piped primary loop and one to six sec-

ondary 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 Tubecombines a high efficiency mod-

ulating, condensing boiler with on-demand

domestic hot water production. The instanthot 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 pro-

pane, and has a turndown ratio of nearly 4

to 1. The dual function heat exchanger fea-

tures 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 penetra-

tions. www.triangletube.com

For more information or to become a Geothermal Specialist:

866.310.6690 GEOSMARTENERGY.COM

State-of-the-Art Geothermal

Training & Testing Facility

We offer a wide rangeof hands-on geothermalcourses designed for

homeowners, well drillersand HVAC contractors.



SELECT THE BEST

PATTERN FOR THE JOBThere 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 eficiency 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 out-

side wall. As shown in Figure 1, the begin-

ning of the loop is routed against the wall

and then, in a serpentine pattern, is routed

inward to inish off the room.

DOUBLE WALL SERPENTINE

The tubing layout pattern shown in

Figure 2is used when the major heat loss

factor of the room comes from two adja-

cent 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 counterlow

spiral layout pattern may be used. Thebeginning of the loop is routed from

FIGURE 2Double Wall SerpentineFIGURE 1Single 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 follow-

ing method is used. First, drill the holesthrough the structure and feed the tub-

ing 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.

Tubing



the outside perimeter to the interior of the room at double

spacing and then returned alongside the supply.

INSTALLING TUBING IN JOISTS AND RAFTERS

When installing radiant tubing between joists or rafters, this

pattern becomes somewhat limited by the orientation of thejoists or rafters. Even so, it is possible to keep the beginning

of the runs near the walls with high heat losses by the cre-

ative use of looping.

SINGLE WALL JOIST PATTERN

In the pattern shown in Figure 4the orientation of the joists

will not permit a single wall serpentine pattern without exces-

sive drilling. Instead the beginning of the loop is concentrated

along the high heat loss wall by the use of intermediate loops.

DOUBLE WALL JOIST PATTERN

In Figure 5the intermediate loops have been shortened. This

method is appropriate when the orientation of the joists willnot permit a double wall serpentine pattern without exces-

sive drilling. Shortening the loops allows installers to con-

centrate the beginning of the loop along each of the high heat

loss walls. MICHAEL GORDON

Michael Gordon is vice president of engineering with Bradford

White Corp.

FIGURE 4Single Wall Joist Pattern FIGURE 5Double Wall Joist Pattern

The full colour, 744-page edition by JohnSiegenthaler includes the latest infor-mation on solar thermal systems, geother-

mal heat pumps, variable speed pumping,

hydraulic separation, thermal accumula-

tors, web-enabled controls, Btu metering

and system balancing. From simple appli-

cations to multi-load/multi-temperature

systems, learn how to use the newest and

most appropriate hydronic heating meth-

ods and hardware to create systems that

deliver the ultimate in heating comfort, reli-

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level design information is transformed into

practical tools that can be used by technical

students and heating professional alike.

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Modern Hydronic Heating 3rdedition

FIGURE 3 Counterflow Spiral Layout Pattern



INCREASED COMFORT =

IMPROVED PERFORMANCE

Solution delivers "triple bottom line" of people, planet and proit.

Many reading this article can likely remember days sit-

ting in a classroom that never seemed to be the right tem-

perature. 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 chat-

tering from the chill.

With the developments in heating technology and the

prevalence of alternative energy sources and high-con-

densing boilers, more school administrators are looking at

maximum energy eficient solutions that not only heat the

building more effectively, but more economically as well. Ithas been found that sustainable heating solutions such as

low-temperature heating reduces costs and can improve stu-

dent 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 oper-

ation. Because schools are vacant for approximately the

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 ineficiencies of older boilers and cast-

iron 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 eficiently,

promoting energy eficiency. For example, rather than requir-

ing start up several hours before teachers and students arrive

for the day, the system provides output within minutes, gen-

erating 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 maxi-

mum operational eficiencies with maximum outputs and

maintaining minimum product sizing too.

Realizing these beneits, more low-temperature heating

systems are typically being installed in both new build and

retroit applications where coal and oil-ired 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 ive years with low temperature systems.

In addition to the inancial and environmental beneits 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 sustainabilityat CB Richard Ellis, worker performance increases with tem-

Sustainability

FIGURE 1 Causes of Burns

Low temperature radiator



peratures up to 72F, and decreases with

temperatures above 73 to75F.1

With the increasing focus on high-per-

forming building envelopes and the preva-

lence 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).

WILL IT WORK?

It has been said that low temperature

heating can work in a number of appli-

cations, including retroits 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-temper-

ature radiators get the most energy efi-

ciency from the system.

While proper use of the new technol-

ogy requires some training, it is nominal.

Teachers and students tend to operate by

the traditional "hotter is better" mental-

ity when setting the thermostat, meaning

that if they want to quickly increase the

temperature, they tend to set it to a tem-

perature setting hotter than the desired

inal output. As a result, the room quickly

overheats and occupants become uncom-fortable. This issue is quickly resolved

with basic education and training.

Due to its numerous beneits and return

on investment, low-temperature heating

(95F EWT) is a system more schools are

starting to explore. For a solution that deliv-

ers the "triple bottom line" of people, planet

and proit, it is a sustainable solution that

makes sense for both today and tomorrow'sheating needs. CHRISTOPHER MAKAREWICZ

Christopher Makarewicz, Dipl.T, B. Eng, is

an engineering advisor for Jaga Climate

Systems. www.jaga-canada.com

1http://www.facilitiesnet.com/green/article/Studies-

Link-Green-Design-Occupant-Productivty--11283

CASE IN POINT

Structure:Single-storey school building

Locale:Kingston, ON

Age:Approximately 50 yearsOccupants: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 gas-

fired, wall mounted condensing boilers.

Each unit serves as a fully modulat-

ing condensing boiler. Solar pan-

els mounted on the roof provide an

offloaded energy source from the new

boiler plant. 107 low-temperature radia-tors, installed in classrooms, corridors

and offices, operate at water tempera-

tures 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 boil-

ers," said David Downey. "In fact, itis 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 sub-

stantially less natural gas consump-

tion, as much as 25 to 30 per cent

over what was previously used."

FIGURE 3 Reaction Time - Comfort

FIGURE 2 Free Heating Sources

p



REALIZE THE BENEFITSOF RETROFITS

As a contractor, you know how critical steam can be to

a buildings power, process heat and indoor climate control

needs. Additionally, one-third of a facilitys energy bill stems

from the boiler room and system ineficiency leads to higher

energy costs. Replacing an older boiler is one way to achieve

signiicant energy savings, but it is not the only option. There

are other ways to improve eficiency. Retroitting an old

boiler is one way to bring it nearly up to par with todays

new systems.

The main cause of energy ineficiency is system heat loss.

The average level of eficiency for industrial boilers is only 75

to 77 per cent.

TAKE CONTROL OF YOUR SAVINGS

The irst place to look for improvements is in the control sys-

tem. The following new control developments produce mea-surable eficiency increases and fuel-cost reductions and

they can be retroitted into an existing system.

1. Parallel Positioning -- Many boiler burners are con-

trolled by a single modulating motor with jackshafts to

the fuel valve and air damper. This arrangement, set dur -

ing startup, ixes the air-to-fuel ratio over the iring range.

Unfortunately, environmental changes such as temperature,

pressure and relative humidity alter the ixed air-to-fuel

ratio, making combustion ineficient. 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 eficiency and, over time, linkages wear

-- making repeatability impossible.

To solve this problem, consider incorporating paral-

lel 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 ive per cent can be real-

ized by introducing a parallel positioning system.

2. O2 trim- Another way to ensure peak eficiency is to

use an oxygen sensor/transmitter in the exhaust gas. Thesensor/transmitter continuously senses oxygen content

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 ive 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 boilersto operate at peak eficiency, reduces cycling and decreases

maintenance and downtime.

TAKE BACK THE HEAT

Another way to please budget scrutinizers, while improving

energy eficiency, is to incorporate heat recovery retroits

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 eficiency. 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 non-

condensing economizer and a condensing economizer. The

irst section of the economizer recovers energy by preheat-

ing 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 lue gases

Boilers



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 turndownrate 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 lash tank that allows safe discharge of the steam by

reducing (lashing) 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 blow-

down 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 productengineering, with

Cleaver-Brooks.www.cleaver

brooks.com

Comfort without Compromise

RESIDENTIAL

Runtal Radiators

COMMERCIAL

TOWEL

RADIATORS

Comfort, style, versatility, durability and energy efficien-

cy are engineered into every radiator that Runtal builds.

Its exactly what youd expect from the world leader and

exactly what weve been delivering since we invented

panel radiators some fifty years ago. One look at our

craftsmans meticulous welds, precision bends and flaw-

less colours and youll know why hundreds-of-thousands

of installs worldwide bear the Runtal name.

Give your customers the quality they desire, and your

business the reputation it deserves. Specify and install

Runtal radiators today.

Visit us at www.runtalnorthamerica.com

SHOWROOM LOCATION:21 - 2861 Sherwood Heights Drive, Oakville, ON L6J 7K1

Tel:905-829-4943 or 888-829-4901

Runtal North America Inc.



STAYING ON THE LINE PART II

Applying Pressure Independent Balancing Valves

The pressure-independent balancing valves (PIBV) dis-

cussed 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 char-

acteristic is depicted by the green line in Figure 1, where avalve 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.

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.

For proper operation, the PIBV in the flow path having the

highest hydraulic resistance must have a differential pres-

sure across it that is at least as high as its minimum activa-

tion 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 circu-

lator 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 pip-

ing, terminal unit, and the minimum operating differential

pressure of the PIBV.The calculation for head loss will typically require the

Valves

FIGURE 2Each branch with a PIBV selected for a specific flow rate.

FIGURE 1Differential pressure versus flow rate curve for a PIBV.

Figure

1CourtesyCaleffiNorthAmerica



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 mains pip-

ing 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 3have

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 differ-

ential of the PIBV is two psi. The system operates with water at an aver-

age temperature of 140F. Based on this description, you then determine the

minimum circulator flow/head requirement for this system.

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 3shows that each heat emitter cre-

ates 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:

The total head loss through the most restric-

tive 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.

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 sup-

ply 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 cross-

overs. This reaction, depicted in Figure 5,

allows the flow rates in the active crossovers

to remain unchanged.

FIGURE 4The yellow dot is the calculated oper-

ating point of this system when all zone valves

are open.

FIGURE 3 System assumed for the example calculations.




In most systems, there is no need to use a differential pres-

sure 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 [email protected].

Valves continued from page 45

FIGURE 5When 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 ratesin these branches.

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_


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eLearning

TACO CANADA LTD.

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Tel. 905-564-9422 Fax. 905-564-9436

www.taco-hvac.com

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