hfc 410a and water cooled application.pdf

8/9/2019 HFC 410A and Water Cooled Application.pdf

http://slidepdf.com/reader/full/hfc-410a-and-water-cooled-applicationpdf 1/14

1

McQuay International

Water cooledapplications with

Single ScrewTechnology andHFC 410A

-

PROXIMUS



2

Contents

What is a refrigerant ................................................................... 3

What makes a good refrigerant .................................................. 5

Peculiarity for HFC 410A ............................................................ 8

Water cooled application with HFC 410A – Proximus ............... 12



3

What is a refrigerant ?

Refrigerants are the working fluids in refrigeration, air-conditioning, and heat pumpingsystems. They absorb low-temperature heat energy from one source, for example an air-

conditioned space, and reject it into another, for example outdoor ambient, usually throughevaporation and condensation respectively.There are many substances classified as refrigerants by ASHRAE Standard 34, but only

few are used for commercial air conditioning.The most common refrigerants are the fluorinated hydrocarbons, but numerous othersubstances also function well as refrigerant, including many inorganic compound and

hydrocarbons.Following is quick a rundown of the common refrigerant groups that are either in use or

have been used in the past.

Water, R-718Most refrigeration processes use either an absorptioncycle or a vapor compression cycle. Commercialabsorption cycles typically use water as the refrigerant

with a salt solution such as Lithium Bromide as theabsorbent. Water is non toxic, non-flammable, abundantand of course it is a natural refrigerant.

Ammonia, R-717

Ammonia (NH3) is a natural refrigerant and considered to

be one of the most efficient. It is one of the only “original”refrigerants still in use today. It is used in vapor

compression processes, typically with positivedisplacement compressors. Ammonia is mostly used in industrial applications,although there are many large commercial air

conditioning installations that utilize it as well.

Hydrocarbons

Propane (R-290) and isobutane (R-600a), among other

hydrocarbons, can be used as refrigerants in the vaporcompression process. In Northern Europe, about 35% of

refrigerators are based on hydrocarbons. They can havelow toxicity and good efficiency but they are highlyflammable.



4

Hydrochlorofluorocarbons (HCFCs)

Hydrochlorofluorocarbons (HCFCs) have been aroundalmost as long as CFCs. HCFC-22 is the most widely

used refrigerant in the world.They are used in vapor compression processes will alltypes of compressors.

These refrigerants are phased out, as required by theMontreal Protocol, in many countries. Others countries(extra EU) also have a phase-out schedule but on an

extended timeline.

Hydrofluorocarbons (HFCs)

Hydrofluorocarbons (HFCs) are relatively newrefrigerants whose prominence arose with the phase out

of CFCs. HFCs have no ozone depletion potential(ODP=0).They are used in vapour compression processes with all

types of compressors. The common HFCs are efficientand classified as A1 (lower toxicity – no flame

propagation) in the ASHRAE Standard 34.

Following is a table with some general information about these refrigerants.

RefrigerantNumber

Chemical NameChemicalFormula

SafetyGroup

ODP GWP

718 Water H2O A1 0 <1

717 Ammonia NH3 B2 0 0

290 Propane CH3CH2CH3 A3 0 0

600 Butane CH3CH2CH2CH322 Chlorodifluoromethane CHClF2 A1 0.055 1500

134a 1,1,1,2-tetrafluoromethane CF3CH2F A1 0 1300

407C 32/125/134a (23%/25%/52) A1 0 1530

410A 32/125 (50%/50%) A1 0 1730



5

What makes a good refrigerant ?

At first glance properties such as lower toxicity, no flame propagation, efficiency, and costeffectiveness come to mind. Certainly these are important characteristics and ones that

are well advertised. But selecting a refrigerant for use in a refrigeration or air conditioningprocess goes far beyond just these properties. For example, “efficiency” can mean manydifferent things and can therefore cause misunderstanding and confusion.

Of all the properties of refrigerants, eff iciency is the most misunderstood and mostabused. To most people efficiency means “how much energy do I have to provide to get afixed amount of cooling”?

COP =

The more efficient the system, the less energy required to do the same amount of cooling.The issue is that eff ic iency is a sys tem pro perty not a refr igerant property .

Many parameters control how efficient a refrigeration system is, many of which have littleto do with refrigerants. The list includes motor efficiency, compressor efficiency (both at fulland part load), heat exchanger design and materials, operating conditions etc.

The refrigerant can affect the system efficiency in many ways including transfer properties(how easy is it to pump), heat transfer properties and so on.

Efficiency, however is a difficultparameter to comprehend. Carnotefficiency is the ultimate, but

doesn’t even take into account therefrigerant.Ideal cycles allow comparisons butagain, these cycles cannot beobtained in the real world.

Model l ing real world eff ic iencies

means taking into accou nt heat

transfer propert ies, transport

propert ies and refr igerat ion

sys tem des ign .

The main purpose of refrigerationis to move heat from where it is notwanted to where it is wanted (or atleast not a problem). Heat transfer

properties are key to this process.It is possible for a refrigerant to

have run of the mill theoreticalefficiency yet be an excellent performer because of its strong heat transfer performance.Good heat transfer allows close approaches in the heat exchangers. This in turn means

smaller lifts for the compressor and improved efficiency.Many factors affect heat transfer. Several have to do with the refrigeration system itself

such as piping design and material and flow rates (Reynolds numbers).

Useful refrigerating effectNet energy supplied from external

COMP

WORK

COOLINGEFFECT

O

T R

T O

3

1

ENTROPY, S

A B S O L U T E

T E M P E R A T U R E , T

Carnot Ideal Cicle on T,s diagram



6

Three key properties of the refrigerant also affect the overall heat transfer capability of the

system. These are viscosity (µ), specific heat (Cp) and thermal conductivity (k).The factors are used to calculate Prandtl numbers (Pr= µ·cp/k) which are used in the

design of the heat exchangers. The goal is to work with substances that can carry a lot ofenergy (high specific heats) and can transfer the energy easily (high thermal conductivity).

It is also desirable to have low viscosity to enhance turbulence and reduce the workrequired to move the fluid .

With these important considerationtaken in consideration, let’s see aquick comparison between HFC

134a, that is, from athermodynamic point of view, one

of the most efficient refrigerantavailable on the market, and another refrigerant, HFC 410A that at

this time is known only in efficientsplit system application.

Fig 2 shows an ideal refrigerantcycle reported on ( T,s ) diagram fora water cooled application with

R410A. The cycle parameters areshowed in the following table:

Evaporating Condition 3 °C

Condensing Condition 40 °CSuperheat 5 °C

Subcooling 5 °C

DP evaporator 0,0 bar

DP condenser 0,0 bar

Suction piping lenght 0 m

Discharge piping lenght 0 m

η compressor 1

As you can appreciate by the values reported in table, the cycle shown is an idealrefrigerant cycle (no Entropy increase).Comparing the same cycles, with the same parameters, for HFC 134a, HFC 407C andHFC 410A we can found:

COPwith HFC 134a = 6,40

COPwith HFC 407C = 6,24

COPwith HFC 410A = 6,02

R - 410A

Fig. 2



7

and looking at the “volumetric cooling capacity” parameter we found:

Volumetric Cooling Capacity with HFC 134a = 2429 kJ/m3

Volumetric Cooling Capacity with HFC 407C = 3629 kJ/m3

Volumetric Cooling Capacity with HFC 410A = 5599 kJ/m3

From the figures above we cam assert :

• HFC 401A, in an ideal refrigerant cycle for a water cooled application, has a COP

almost same of HFC 134a that is the best on the market from a thermodynamic

efficiency point of view ;

• Utilizing the same compressor size, with the same swept volume capacity, we can

improve the chiller cooling capacity by more than 200 percent.

This is one of the great advantage of R410A: the extremely high refrigerant effect perswept volume which can be up to 150% compared to R407C or up to 200% compared to

R134a.In this way smaller plant and components may be used, allowing more compact units withsmaller footprint be developed in comparison to HFC 134a.



8

Peculiarity of HFC 410A

This hydro fluorocarbon refrigerant is a blend of HFC 32 and HFC 125, both theserefrigerants are at concentration of 50%.

Even if it is a blend, its temperature glide is negligible: only 0,2 K .For this reason the general behaviour of this refrigerant is almost identical to a pure one,as HFC134a for example.

No glide means much easier refrigerant re-charging in case of refrigerant loss, and noneed to take any particular attention during refrigerant charge.

As very well know, on a chiller working with a refrigerant blend presenting a “strong”temperature glide a leakage results in a change of components proportions in the mixture,because the relative losses of its most volatile components will be disproportionately high.

If a simple standard refilling is adopted, there is no guarantee that the new refrigerantmixture has the same proportions as it had before the leakage. For this reason to guarantee the unit performance, it is preferable to remove the remaining

charge, to make the vacuum in the circuit and re-charge it with new refrigerant (necessarilyin liquid state).

Of course only skilled personnel can perform this service activity.R-407C and R-410A are both zeotrope, however the glide for R-407C is 5 K while the glidefor R-410A is only 0,2 K.

Also the high glide for HFC 407C means that it can be practically used only in DX systemwhile HFC 410A can be also used in flooded system, without problems.

50% 50%

Glide temperature

0,2 KNO

GLIDE



9

Another strength point of HFC 410A is that heat transfer propert ies [thermal

conductivity (k)] and transport propert ies [viscosity (µ)] are very goo d for th isrefrigerant.

These properties aren’t the refrigerant’sthermodynamic characteristics but are

very important to realize an efficientsystem, an efficient chiller from a “real”point of view.

All refrigerants, whether in vapor or liquidform, suffer pressure drop as they flow

through the refrigeration circuit: both in thepiping and in the components themselves(i.e. a compressor passageway). As thepressure changes, the temperature of therefrigerant changes as well, with aproportion which depends on the

refrigerant; there temperature variationsadversely affect system performance.

Consider the pressure drops in the suctionand discharge lines: starting from the actual pressure (and temperature) in the evaporator

and in the condenser, the pressure drops (and hence temperature changes) will have tobe added to the total lift that the compressor provides. The type of refrigerant used impactson the temperature change relative to the pressure change.

A quickly comparison between HFC134a liquid viscosity and HFC410A liquid viscosity canshow that the visc os ity fo r HFC410A is abou t 40% less than HFC134a visco sity ,consequently the pressure drops described above and their effect on chiller efficiency is

reduced.This advantage is especially very important for Dry-eXpansion evaporators, where therefrigerant flows as a mixture liquid-vapour (saturated) and the refrigerant pressure dropscan reach considerable values.

Another important physical parameter to consider for an efficient system is the heattransfer coefficient in both the evaporator and condenser. Higher is this parameter, higheris the potential for increased efficiency.

As sh own in the above f igures thermal con duct iv i ty for HFC410A, both for saturated

l iquid and saturated vapour, is much high er than HFC134a thermal con duc t iv i ty: for

satu rated v apo ur is 17,9% hig her , fo r sat ur ated l iq ui d i s 3,6% hi gh er (at 25 °C).

0,08

0,081

0,082

0,083

0,084

0,085

0,086

0,087

0,088

0,089

0,09

[ W / ( m K ) ]

R-410AR-134a

Thermal conductivity of saturated liquid (25°C)

+ 3,6%

0,0125

0,013

0,0135

0,014

0,0145

0,015

0,0155

0,016

0,0165

0,017

[ W / ( m K ) ]

R-410AR-134a

Thermal conductivity of saturated vapor (25°C)

+ 17,9%



10

Good refrigerant thermal conductivity helps achieve good heat transfer and this allows

close approaches in the heat exchangers. This in turn means smaller lifts for thecompressor and improved efficiency.

Thanks to these good refrigerant characteristics McQuay is able to offer two efficiency line

for PROXIMUS, its water cooled unit equipped with single screw compressor:

• SE with a COP up to 4,3

• XE with a COP up to 5

COP of 5 means fast pay back time for the investment and big savings in the future chiller

operating costs.

The HFC410A advantages described and

the exceptional volumetric cooling capacityallows us to obtain very high performance

from each single screw compressor. As shown on Fig. 3, the R410A specificvolumetric cooling capacity is more than

200% greater then HFC134a. This meansthat with the same compressor swept

volume the unit can give a availablecooling capacity more then twice greaterthan that with a HFC134a.The main advantage of that is the

extremely compact dimensions of unitsand a highly competitive cost perrefrigeration ton.

Small footprints and reduced weight obviously facilitate installation and leave more space

for other equipment. A compact design also helps installation through most standard industrial doorwayswithout modification, saving introduction time and costs

.

0

1000

2000

3000

4000

5000

6000

k J / m 3

R134a R410A

Volumetric Cooling Capacity [kJ/m3] Fig. 3



11

Higher working pressure.

We have seen that HFC410A have some advantages like good heat transfer properties,low viscosity, very high specific volumetric cooling capacity; the only disadvantage is that

operating pressures are higher.The internal mechanical loads in the compressors are obviously proportional to the

pressure, and therefore compressors presenting relevant axial and radial thrusts arepenalized in the use of this kind of refrigerant, and require redesign of some components(such as bearings).

McQuay Single Screw technology presents perfectly balanced internal loads, so to workwith higher pressures does not pose any problems.

Whilst it should be noted that the maximum pressure inside the refrigerant circuits is higher

compared to R134a and R407C, it is also important to understand that this could be a limitonly in air-cooled units. On water cooled units this problem basically don’t exist, becausewater cooled condensers can keep the condensing temperature considerably lower

compared to air cooled condenser working, for example, with R407C.Let’s have a look to the following table:

As you can appreciate the highest pressure levels (condensing section) are almost thesame. This means that work with HFC 410A in water cooled applications, from amechanical point of view, is equivalent to work with HFC 407C in air cooled applications.

Is important take in consideration that also ∆P between suction and discharge compressor

side is almost the same for two refrigerants and it allows the compressor to work with a

volumetric efficiency that is the same, both in the case of R407C and of R410A. This isbecause the internal leakage of the compressor, between discharge and suction side, areequal for both refrigerants.

McQuay has also obtained the full PED (Pressure Equipment Directive) certification for

R410A heat exchangers (both evaporator and condenser); PED certification, establishedby the European Community in May 2002, is one of the most restrictive standards onpressure equipment and requires high safety margins on pressure calculations and tests.

All McQuay heat exchangers are PED approved, another warranty for safety, reliability andefficient chiller operation.

with HFC 410A LCWT [°C] Tcond [°C] Pcond [bar]

Proximus SE 35 40 24,4

Proximus XE 35 38 23,2

with HFC 407C OAT [°C] Tcond [°C] Pcond [bar]

McPower SE ST 35 55 24,7

McPower SE XXN 35 65 28,3

LCWT = Leaving Condenser Water Temperature

OAT = Outside Ambient Temperature



12

Water cooled application with HFC 410A - Proximus

Proximus is the new water cooled chiller equipped

with McQuay Single Screw compressor andworking with HFC 410A.

The evaporator is a Dry-eXpansion type with adiffuser at inlet to allow a perfect refrigerant fluiddistribution to all tubes inside the evaporator schell.With Proximus McQuay continues using a DX,single pass, counter flow evaporator that

guarantees an excellent heat transfer propertiesand a perfect oil circulation.

We have do not forget that in a single pass evaporator there are any vertical tube part that

can cause, during partial cooling loads and so with small refrigerant velocity inside tubes,an little oil stagnation inside the evaporator.

In other words with a DX-double-passevaporator the oil circulations can be not sogood during partial loads and so is not

guarantees a perfect oil return to thecompressor.

Proximus is equipped with an electronic expansion device, the

only device that can match the infinitely variable cooling load

compressor system and the PID controller to achieve a perfectleaving evaporator water temperature control.

The set-point for the chilled water that the user sets on the controlpanel will be always respected, in all operating conditions within +

0,1°C.Electronic EXpansion Valve (EEXV) is a device that gives thepossibility to reach, if the chiller is “well managed”, a bigeconomical saving in the operating unit cost. As you know, in these years the energy saving problems are evenmore actual, important for all the communities both in theEuropean area and outside it.

All the system that allow a energy saving are promoted and often there are publiceconomical helps to push the adoptionof these efficient plant solution.In a water cooled chiller is possible toreach very high EER values when agood condensation’s control is

adopted, in other words, when theminimum Entering Condenser Water

Temperature (ECWT) allowed by unitsis reached.

Double-pass evaporator

3

4

5

6

7

8

25 30 35 40 45 50

Condensation Temperature [°C]

E E R

Evaporator conditions: IN 12°C – OUT 7°C

Fig. 4



13

This is possible of course when spring, river, lake water is available to cool the condenser

or when the cooling tower fan control is implemented to supplies the chiller’s condenserwith the coolest water.

Take in consideration that during all the year the Outside Ambient Temperature (OAT) iswell below 20°C for the 65% of the time (this is true in the South-Europe, in the North the

percentage can increases). With this temperature is possible supply to unit an ECWTbelow 30 °C with a relevant EER increases. (see Fig. 4)In a chiller supplied with Thermostatic Expansion Valve (TEXV) is not possible to reach

these energetic benefits because the system is obligated to operate with highercondensation pressure to ensure correct working condition to the lamination device.

Proximus, for sizes with acooling capacity more than1000 kW, is equipped with two

Single Screw McQuay Frame 4compressor that working in two

“real” independent circuits: twocompressors, two refrigerantspiping lines, two electronic

expansion valves (EEXV), twoexternal oil separator.

This means a more reliableunit because in case oftechnical problems for a

components, you can supply HVAC plant with more then 50% of cooling capacity (morethan 500kW) and so can satisfy the major necessities.In a chiller equipped with only one compressor and with a very big cooling capacity (morethan 1000 kW) the part load efficiency is made bad by the strongly unloaded condition forthe electric motor that works with low cosϕ values.

If this chiller is equipped with a thermostatic expansion device, or with a fixed orifice, alsothe refrigerant flow control became no so good because of the unstable behaviour of this

lamination device at strongly unloaded conditions. That can give problems in EvaporatorLeaving Water Temperature (ELWT) control.

In a chiller equipped with two “real” independent compressors, at part load conditions, youcan have:

• a compressor at nominal working condition, with the nominal cosϕ value ;

• more than 50% of the total unit cooling capacity ;

• always an optimum EWLT control thanks the electronic expansion valve that worksat nominal condition too.

McQuay International is the first manufacturer in “European HVAC Market” to offer a water

cooled chiller working with HFC 410A: an ecological, efficient, safe, easy to managerefrigerant.Thanks this HFC is possible to make, and so to offer, a unit with the best compromise

among: efficiency, compactness, reliability and price.

Proximus is the best choice both to make a new HVAC system and to replace an oldexisting refrigerator.



14

We reserve the right to make changes in design and construction at any time without notice, thus the cover picture is not binding.

McQuay Italia S.P.A.S.S. Nettunense, km 12+300 – 00040 Cecchina (Roma) Italia – Tel. (06) 937311 – Fax (06) 9374014 – E-mail: [email protected]

hfc 410a and water cooled application.pdf

Documents