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ASHRAE Journal Refrigeration

3 0 A S H R A E J o u r n a l w w w. a s h r a e j o u r n a l . o r g A u gu s t 2 0 0 1

Douglas T. Reindl, Ph.D., P.E., isassociate professor and director of theIndustrial Refrigeration Consortium atthe University of Wisconsin, Madison,Wis. James L. Denkmann is presi-

dent of DTS, Chicago.

A

Automatic Purgers inRefrigeration Systems

About the Authors

By Douglas T. Reindl, Ph.D., P.E., and James L. DenkmannMember ASHRAE Member ASHRAE

purger is an essential component for the proper and efficient opera-

tion of an industrial refrigeration system. A purger gathers, separates

and expels non-condensable gases from the system. Successfully

purging non-condensables from a refrigeration system leads to increased re-

frigeration capacity, improved system efficiency, and enhanced system safety.

In this article, we review the types of non-

condensable gases (NCG) that can accu-

mulate in systems, consequences of NCG,

purger operation, application consider-

ations and factors that influence purger per-

formance. Our emphasis is on vapor com-

pression-based industrial refrigeration sys-

tems that use anhydrous ammonia as the

refrigerant because this choice covers the

majority of industrial systems in use today.

BackgroundMost industrial refrigeration systems

currently in use are based on the vapor

compression cycle. Vapor compression re-frigeration systems function through a con-

tinuous closed cycle whereby a volatile

working fluid (refrigerant) undergoes a se-

ries of phase changes, which leads to the

ability for providing a useful refrigeration

effect. In the condenser, heat is rejected

from the system converting hot gaseousrefrigerant at high pressure to pure liquid-

phase refrigerant also at high pressure. The

high-pressure liquid is subsequently

throttled to lower pressures to be available

for absorbing heat into the system throughthe evaporator as part of a refrigeration pro-

cess. In the evaporator, low-pressure liq-

uid refrigerant boils as a result of heat

added from a space or a process load. The

low-pressure vapor refrigerant generated

is then raised in pressure by the compres-

sor and directed to the condenser to reject

heat from the system again. The effective-

ness of a refrigeration system is dependent

on the ability for the phase-change pro-

cesses to proceed unimpeded.

Non-Condensable GasesIn the context of vapor compression-

based ammonia refrigeration systems, we

want only pure refrigerant (anhydrous am-

monia) present in our systems. Unfortu-

nately, refrigeration systems can and will

accumulate “foul substances.” Apart

from water, the foul substances, gaseous

in nature, are commonly referred to as

non-condensable gases (NCG). Foul gas

is another term used to describe a gas-eous refrigerant stream that contains NCG.

Non-condensable gases eventually will

accumulate in all ammonia vapor-compres-

sion refrigeration systems if adequate

means are not provided for their removal.

In some cases (i.e., newly built high-suc-

tion temperature systems with screw compressors), it may be many years before

abnormal operation becomes evident.

Non-condensable gas constituents com-

monly include air, nitrogen, hydrogen, and

hydrocarbons. The nomenclature “non-condensable” means that these gases will

not liquefy at the temperatures and pres-

sures present in condensers consistent

with industrial refrigeration systems. For

example, anhydrous ammonia will change

phase from gas to liquid if heat is removed

while at a temperature of 95°F (35°C) and a

pressure of 196 psia (1349 kPa). At the same

pressure, any nitrogen present would have

to be cooled to –264°F (–164°C) in order

to liquefy. As a result, any nitrogen thatmay accumulate in a refrigeration system

always will remain in a gaseous state. Let’s

take a closer look to see how non-

condensables infiltrate into, or accumulate

within, ammonia refrigeration systems.Air is the most abundant non-condens-

able gas impacting industrial refrigeration

systems. Air can infiltrate into systems

during continuous operation and as a re-

sult of system servicing. Most low-tem-

perature refrigeration systems (i.e., work-

ing temperatures below –28°F [–33°C])

have a significant proportion of the sys-

tem piping, valves, and vessels operating

with working pressures below atmospheric

pressure. Any pathways for leaks will re-

sult in air infiltrating into the system rather

than the refrigerant leaking out. Pathways

for air leakage during operation include:

valve stem packings, bonnet gaskets,

compressor shaft seals, non-welded con-

nections, and control transducers.

Another pathway for air entry into sys-tems occurs as a result of inadequate

evacuation after system servicing. For ex-

ample, if a portion of the system is opened

to clean a strainer or replace a component,

air will occupy that part of the system im-

mediately after reassembly. Ideally, the ser-

vice technician will evacuate the air fromthat part of the system prior to bringing it

back into service. Unfortunately, this is sel-

dom done. The net result is that the refrig-

eration system ingests a large gulp of air

when brought back into service and the

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A u gu s t 2 0 0 1 A S HR A E J o u r n a l 3 1

Refrigeration

trapped air must be removed by purging.

Secondary types of NCG include hydrogen and nitrogen.Hydrogen and nitrogen gases accumulate as a result of the

refrigerant (NH3) dissociating (breaking-down) over time. The

two most important factors that influence the breakdown of

ammonia into its constituent parts are temperature and pres-sure. At higher temperatures, ammonia is more prone to irre-

versibly breaking down into nitrogen and hydrogen. Older sys-tems (>25 years) and those with reciprocating compressors

appear to experience an accelerated rate of breakdown. How-

ever, the gross quantity of NCG generated by this mechanism is

relatively small. Even small dissociation rates lead to the accu-

mulation of large quantities of hydrogen and nitrogen over time

if they are not removed from the system on a regular basis.Tertiary sources of NCG arise from the breakdown of lubri-

cating oils. Most industrial refrigeration systems use mineral-

based lubricating oils. As a result, the oil will breakdown and

liberate a complex series of hydrocarbon gases. Some of the

gases will have lower molecular weights when compared withammonia (e.g., CH

4) while others will be heavier (e.g., C

8H

18).

Table 1 lists each of the gases potentially present in a non-

condensable gas mixture, along with their molecular weights

and densities at a design condensing pressure for many ammo-

nia refrigeration systems (196 psia [1349 kPa]). Refrigerant R-22

is also shown for reference.

Consequences of Non-Condensable GasesThe total heat rejection requirement for a vapor compression

system is the sum of the gross refrigeration effect plus the

aggregate work input to the system by the compressors. Indus-

trial refrigeration systems commonly use evaporative condens-

ers as the means of rejecting heat from the system to the out-

side environment. The heat rejection capacity of any given

evaporative condenser is dependent upon:

• Outside air wet-bulb temperature (lower wet-bulb tempera-

tures translate into greater heat-rejection capacity);

• Refrigerant saturated condensing temperature (higher satu-ration temperatures translate into increased heat rejection ca-

pacity at the condenser);

• Wet operation (water flow over the outside surface of the

condenser tubes greatly enhances heat-rejection capacity); and

• Airflow rate (increased airflow rate will increase heat-rejec-tion rates).

One of the places where NCG accumulate is in the lower

portions of evaporative condenser heat exchange coils. This is

because the refrigerant has been liquefied at that point and the

NCG are prevented from flowing further downstream (due to P-

traps located at the drop leg for each condenser outlet) or up-

stream (due to convective forces as a result of the continual

flow of gas into the condenser).

Since the NCG remain in their gaseous state, they will occupy a

relatively large volume of the evaporative condenser’s heat ex-

changer. Their presence interferes with the condenser’s ability to

change the phase of the gaseous refrigerant to a liquid. With the

heat transfer capacity of the evaporative condenser diminished

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negordyH 2 )19.0(750.0

ainomm A 71 )3.8(25.0

negortiN 82 )7.21(97.0ri A 92 )1.31(28.0

noitisopmoceDliO 44–51 )6.23–1.7(30.2–54.0

22-R 68 )9.34(57.2Table 1: Gas properties including common NCG and indus-

trial refrigerants for reference.

The need for purging exists in all refrigeration systems. A

question often asked is: “Do I need an automatic purger?”

This question has to be answered on a case-by-case basis.

Generally speaking, systems with reciprocating compressorsor any systems operating under sub-atmospheric conditions

will directly benefit from an automatic purger.

Before the days of reliable automatic purgers, this process

was accomplished using manual purgers. Typically, individual

purge points were each provided with a manual globe valve.Separate purge piping was run from each valve into the engineroom, then this piping was combined into a single header that

connected to the purger. This consisted of a modified inverted

bucket steam trap with an internal heat exchanger. To purge an

individual condenser, the operator would open individual globe

valves from condensers suspected of having non-condens-

able gases. A bucket of water and a rubber hose served in lieu of

today’s water bubblers integrated with automatic purgers.

This manual method continues to be viable and cost-effective

today, especially on smaller systems. However, manual purgers

require direct operator interface during the purging process; typi-

cally, more ammonia vapor is expelled along with foul gas. Manual

purgers also cost more to operate (compressor energy) than

automatic purgers, because the only source of makeup liquid to

their flooded evaporators must come from a high-pressure source.

On the other hand, the chief advantages of a manual purger are

that they cost less to install, they can be arranged to quantify

foul gas entering the system and are normally less susceptible

to foreign substances in the piping system (dirt).The following are advantages and disadvantages in an au-

tomatic purger system:

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Automatic vs. Manual Purging?

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3 2 A S H R A E J o u r n a l w w w. a s h r a e j o u r n a l . o r g A u g u s t 2 0 0 1

ASHRAE Journal

due to the presence of NCG, the tempera-

ture of the condensing refrigerant (and its pressure) must increase to reject the nec-

essary heat from the system. The conse-

quences of increased condensing (or head)

pressure are undesirable and include:• Decreased system refrigeration ca-

pacity;• Increased system electrical demand

and energy consumption (attributed to

compressors and condenser fans);

• Decreased system efficiency;

• Increased compressor discharge su-

perheat (accelerating oil breakdown andrefrigerant dissociation);

• Increased head pressure leading to

increased compressor wear and tear and

greater likelihood of system shutdowns

due to high head pressure; and• Increased condenser scaling, which

leads to increased maintenance costs and

decreased condenser life.

How A Purger WorksFunctionally, there are two types of

purgers—automatic and manual. The au-

tomatic purger is a mechanical device in-

tegrated into a system that gathers, sepa-

rates, and removes NCG from multiple

points in the refrigeration system with-

out operator assistance. A manual purger

can be as simple as an angle valve that

requires a mechanic or technician to manu-

ally open the valve and dispel any vapor

(which will include mixture of ammonia

and NCG) into a water bucket.

A diagram of how most automatic purg-ers function is shown in Figure 1. A single

condenser purge solenoid valve has been

shown for simplicity although all systems

will have a multiplicity of purge points. A

mixture of NCG and ammonia vapor should

be drawn into a purge connection during

the time its respective solenoid valve isopen. This gas mixture flows down the foul

gas line to the purger unit piping connec-

tion. It is important that all gas purge lines

are free of any places where vapor can con-

dense and collect, blocking further NCGremoval. Liquid traps cannot be tolerated

in this piping, particularly as it pertains to

some purger models. All purge piping

should be pitched down to the purger as

recommended by purger manufacturers.

The foul gas line is connected to a drain

trap at the purger. The function of the drain

trap is to separate and expel any liquid

erant inside the air separation chamber is

returned back to the system.

The high-pressure ammonia liquid sup-

ply line is installed to make up any short-

fall of needed liquid inside the evapora-

tor. If little or no liquid enters a purge

point, more makeup liquid from the high-

pressure receiver will be required in order

to maintain an adequate liquid level in the

evaporator. However, if the reverse oc-

curs and excessive liquid is present in

the foul gas line, two events occur: head

pressures rise and the purger temporarily

stops condensing vapor until it is able to

push all the excess liquid out of the va-

por condenser. This takes time because

the orifices in purgers are very small.

Do I Need a Purger?The need for purging exists in all am-

monia refrigeration systems. However, the

need for automating this procedure is not

so clear. Generally speaking, systems with

reciprocating compressors or any sys-tems operating under sub-atmospheric

conditions will directly benefit from an

automatic purger. Before the days of reli-

able automatic purgers, this process had

to be done manually.One indicator suggesting the presence

of NCG is excessive operating compressor

head pressures. High head pressures are

most pronounced on hot, humid days

when most compressors are working at

their maximum capacity and compression

ratio. However, winter head pressures are

affected as well. During wintertime opera-

Figure 1: A simplified diagram of how an automatic purger functions.

ammonia entrained with the gases drawn

at the purge point. Separated high-pres-

sure liquid flows out of the bottom of the

drain trap through a throttling device (a

metering valve or an orifice), is flashed,

then passes into a flooded evaporator—

a vessel containing a vapor condenser and

an air-separation chamber. Cold boiling liq-

uid completely surrounds the vapor con-

denser and the air-separation chamber.

The temperature of the cold liquid ammo-

nia corresponds to the saturation pres-

sure at which it evaporates. This is equal

to the suction-side pressure connecting

the purger. The resulting vapor is returned

to the system via the suction connection.

Meanwhile, the gaseous mixture leavingthe drain trap is comprised of a condens-

able gas (ammonia), plus NCG (air, nitro-

gen, etc.). After this mixture leaves the

upper portion of the drain trap it enters

the vapor condenser.

Upon entering the vapor condenser, the

ammonia vapor is gradually liquefied outof the gaseous mixture by the surround-

ing cold-boiling ammonia. At the end of

the cool-down cycle, only NCG along

with some ammonia liquid will remain in

the vapor condenser. These proceed intoa separation chamber where the heavier

liquid falls by gravity to the bottom of

the chamber and the lighter air and other

NCG are discharged out to a water bub-

bler, where any residual ammonia vapor

is absorbed. The resulting weak aqua am-

monia mixture is then discharged down

the sewer drain. Remaining liquid refrig-

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tion, operators are doing their best to keep

head pressures up anyway, so few look for

NCG during cold weather. If a refrigeration

system has been designed for a maximum

head pressure of 196 psia (1349 kPa) (i.e.,95°F [35°C]) saturated condensing tempera-

ture) and the system operating head pres-

sure begins to exceed that maximum, you

should suspect accumulation of NCG. If

your system is controlled to some mini-

mum head pressure during winter months,

detection of NCG becomes problematic.

If any of the following apply to your

system, either invest in an automatic purger

or perform frequent manual purging as part

of normal preventive maintenance.

• System operating temperatures be-

low –28°F (–33°C);

• Presence and use of reciprocating

compressors; and

• Older refrigeration systems or sys-

tems requiring frequent servicing.

Application ConsiderationsTo maximize the benefit of a purger, it

is important to understand where NCG

tend to accumulate in systems and the

other factors that influence the perfor-

mance of a purger.

Where to Purge Non-CondensablesIt is commonly believed that any gas

lighter than ammonia will be preferentially

purged from a high point in the high-pres-

sure hot gas piping system. We were notable to find any published papers, research,

or experimental data that corroborated this

claim. In operating systems, it is unlikely

that non-condensable gas constituents

would accumulate at high points of the sys-

tem since the convective forces of ammo-

nia gas flow would quickly dominate the

buoyancy forces (driven by density differ-

ences) of the non-condensable gas in theammonia stream. In idle systems, NCG con-

stituents will stratify only when the buoy-

ancy forces exceed the diffusive forces.

Assuming evaporative condensers are

located at the highest physical elevation inyour refrigeration system, NCG will tend to

migrate down through the high-pressure

piping system driven by convective forces

until it is trapped from falling further.

One type of trap is formed by the pres-

ence of liquid ammonia in the piping

(highly undesirable in foul gas lines as

mentioned previously). If liquid completely

seals a section of pipe, then NCG are

blocked from passing any further, so long

as the seal remains under all pressure fluc-

tuations across it. The presence of a “liq-

uid trap” affords the most opportune place

for purging NCG in the vapor space above

the trap. Since all evaporative condenser

heat exchangers are provided with a liquid

trap at the base of each drain leg, placing a

purge connection at the uppermost por-tion of the drain leg affords the surest place

for gathering a NCG-rich gas mixture.

Figure 2 shows recommended purge

connections with their respective sole-

noid valves at the top of each condenser

drain leg. If condenser drain leg traps have

been constructed of sufficient depth suchthat they do not “blow through” due to

pressure imbalances (discussed later), the

need for purging piping and vessels

downstream of the trap(s) is eliminated.

NCG will also be found on the low-pres-sure side of systems operating below at-

mospheric pressure due to leaks as pre-

viously discussed. NCG will also be found

on the low-pressure side of systems us-

ing hot gas for defrosting evaporators.

In this situation, the source of NCG is

from foul gas that accompanies the hot

gas for defrosting the evaporators. A

Figure 3: Twelve-pass evaporative con-

denser heat exchanger.

Figure 2: Purge connection with their

respective solenoid valves atop con-

denser drain legs.

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small concentration of NCG on the low-pres-

sure side of a system will be relatively “be-nign” since it does not interfere with the phase

change process in the evaporators and has

no effect upon gas/liquid separation in accu-

mulators and knockout vessels. Compressorsquickly move any NCG from the low-pressure

side to the high-pressure side of the systemwhere it can be removed by the purger.

Purging From High-Pressure VesselsThermosiphon receivers are not customar-

ily provided with purge connections. One rea-

son is that any NCG that enters this vessel is pushed out the oil cooler gas return line and

back up to the condensers. Since this vessel

is not designed with heat transfer in mind, a

slight accumulation of NCG can be tolerated.

But this same rule could also apply to a high- pressure receiver (HPR) as well. If one cubic

foot (28 L) of liquid enters this vessel, it will

displace an equal volume of NCG. This will be pushed up the

gas return line (commonly referred to as an “equalizer line”) and

into the evaporative condenser gas inlets. If the gas return line

is too small (which the authors have found to be quite com-

mon), the pressure in the HPR increases. Even slight pressure

differences between the HPR and condenser drain outlets can

pose difficulties with proper condenser drainage.

Many HPRs are installed outdoors, and with few exceptions

are located on-grade. Most HPR foul gas line installations form

liquid traps whenever the outside air ambient dry-bulb tem-

perature is below the refrigerant saturation temperature. At-

tempting to remove NCG from an HPR can be problematic if this

situation is not recognized.

Factors Influencing Purger PerformanceSeveral factors influence the ability of a purger to collect

NCG from the system:

• More than one purge solenoid valve is open simultaneously.

This should never occur.

• Pressure imbalances exist between adjacent evaporative

condenser heat exchangers, creating opportunities for liquid

“hang-up.” In some cases,

the liquid hang-up in the

evaporative condenser is

so severe that the purge

solenoid opens only to

“see” liquid refrigerant.

• Foul gas piping that

creates liquid traps leads

to difficulty in establish-

ing an unimpeded flow of

foul gas to the purger.

• The purger is located

above one or more con-

denser purge points.

• The purger is mal-

functioning, usually due to dirt.While purgers normally are equipped with liquid drain traps,

the liquid-handling capacity of these traps is quite small. If a

purge point gathers liquid refrigerant instead of vapor, all of this

liquid cannot be completely passed by the liquid drainer; exces-

sive quantities then back up into the purger’s vapor condenser.

If the vapor condenser fills with liquid, it becomes subcooled as

it passes through to the air separation chamber. A control sensesthe higher liquid level in the air separation chamber and expels it

to the flooded evaporator. If the evaporator is already full of

liquid, then liquid will exit the purger via the suction line. This is

why purgers must be connected to a “protected” (wet) suction

line and not piped directly to the compressor suction.A fundamental requirement for purging NGC from a system is

to get NCG into the purger. Although this sounds trivial, com-

plexities in system operation often prevent the purger from pro-

cessing foul gas. One of the most overlooked conditions pre-

venting a purger from receiving foul gas is “liquid hang-up” in

evaporative condensers.

It is not uncommon for a large evaporative condenser in an

ammonia refrigeration system to hold up >700 lb (318 kg) of liquid

Figure 5: Evaporative condenser

with extra deep condenser drain

traps.

Figure 4: Diagram of multiple evaporative condensers showing the effect of unequal pressures between heat exchangers and pressure differences between

condensers and thermosiphon receiver.

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Refrigeration

with only a 0.25 psi (1.7 kPa) pressure difference between adjacent

circuits in the condensers. A pressure difference on the order of 0.25 psi (1.7 kPa) is normally sufficient to flood the liquid drain

header box and bottom two passes of most evaporative condenser

heat exchangers as shown in Figure 1. Under this situation, the

purge point becomes flooded with subcooled liquid. When the purge solenoid opens to draw foul gas—it draws in liquid refriger-

ant. If this continues over days or weeks, non-condensables willcontinue to accumulate in the system and the condenser will slowly

lose heat-transfer effectiveness. In some severe cases, entire

evaporative condensers have been rendered nearly useless by

the end of a season (usually during winter). It now appears that

this may be more commonplace than originally thought.

Figure 3 shows a 12-pass evaporative condenser heat ex-changer. The single condenser heat exchanger shown in this

figure is comprised of one inlet connection (the header at the

top of the tube bundle) and one outlet connection (the header

at the bottom of tube bundle) with many parallel tubes intercon-

necting the upper and lower header boxes. Individual tubelengths vary between condenser sizes, ranging from approxi-

mately 70 lineal feet (21 m) (six-pass models) up to >200 lineal

feet (61 m) (12 pass models). Evaporative condenser heat ex-

changers are typically fabricated from nominal 1 in. (25 mm) hot-

dipped galvanized steel tubing. Evaporative condensers hav-

ing dual inlet and outlet connections are equipped with two

heat exchangers. In this configuration, ammonia is prevented

from flowing from one heat exchanger directly into its neigh-

bor. However, any slight pressure difference between evapora-

tive condensers will force refrigerant liquid and/or vapor from

one condenser into another via the outlet drain piping when-

ever P-traps are shallow. This is mainly true of ammonia, and to

a lesser extent, the halocarbon refrigerants.

Condenser Drain Traps: How Deep Should They Be? Figure 4 presents a typically accepted arrangement for drain-

ing multiple evaporative condensers. This figure assumes that

all drain connections are on a common elevation, but the heatexchangers are of different sizes and the fans on condenser C-

3 have stopped. The condensers are shown draining to a com-

mon vessel. A thermosiphon receiver (TSR) is shown, although

an HPR also is common when thermosiphon oil coolers are not

used. In some cases, the HPR and TSR are combined into a

single vessel. The pressures at each node are numbered P1, P2,

etc. This figure also assumes that the oil cooler gas return lineimposes an excessive pressure drop.

From this figure it is evident that purging NCG has been

impaired in active condensers C-1 and C-2. Why does this oc-

cur? Three reasons explaining the phenomena are shown in

Figure 4:• The pressure within the thermosiphon receiver is greater

than the pressure at any of the condenser drain outlet connec-

tions, P1 > P5, P6, P7. This occurs as a result of an excessive!"

in the oil cooler gas return line.

• “Active” condensers C1 and C2 are built from different

tubing lengths, therefore each imposes a different pressure drop,

(P2–P5) – (P3–P6) $ 0.

• The pressure at the bottom of condenser C3 is nearly equal

to the pressure at its inlet, P4–P7 % 0, whenever the condenser

fans stop.The aforementioned scenario is encountered frequently, rep-

resenting roughly half of all industrial refrigeration systems

that the authors have seen. This phenomenon can be felt by

holding the evaporative condenser drain legs. Cool legs de-note the presence of sub-cooled liquid; hot legs denote the

presence of vapor. Another sign is a nearly continuous frostlayer on the 0.25 in. (6 mm) stainless steel line (inside the purger)

that runs between the bottom of the purger’s liquid drainer and

the flooded evaporator.

In view of the these findings, drain trap depths should be sized

to withstand the greater of these two pressure differences:

•!" between individual heat exchangers under all operatingconditions, or

• !" between each heat exchanger and the receptor vessel

under all variances in mass flow.

Nothing can be done about operating pressure differences be-

tween dissimilar sized evaporative condensers. However, increas-ing the condenser drain trap depths to overcome any operating

!" can easily mitigate this impact. Doing so increases the ability

of the purger to collect NCG instead of high-pressure liquid, which

it was not built to handle in any substantial quantities.

Figure 5 shows an ammonia evaporative condenser with

deeper drain traps than customarily installed. This particular

condenser does not experience any cool weather liquid hold-

back problems nor any difficulty in purging NCG. The traps

shown in this photo are each 15 in. (381 mm) deep, which was

sufficient for the operating conditions at this particular facility.

This condenser has a total of four heat exchangers and four

drain traps. Note that the condenser gas inlets have not been

yoked as normally recommended. However, if the drain traps

are deep enough (which they were here), this added cost is no

longer necessary. The only additional recommendation (not

shown) would be to move the drain leg pipe reducers down a

point to immediately above the condenser outlet stop valves.

Another possible (but less desirable) solution is to add astatement to the condenser purge solenoid valve control algo-

rithm that blocks gas purging from a particular point if the re-

spective fan is running and any other fans are stopped. This

solution is less desirable because liquid management difficul-

ties have not been addressed, nor are the condensers able to

operate under reduced compressor head pressures during win-

ter months. The inability of achieving “floating head pressures”will have significant annual energy implications.

ConclusionsHistorically, purging non-condensable gases from systems

was a manual operation. Today, reliable mechanical purgers can be installed and controlled to operate on a continuous basis.

However, the effectiveness of any purger to collect and remove

NCG is governed by the external influences discussed here.

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