looking for help of low temperature chiller design

hi every one,i need some help about designing of a low temperature air water chiller (R134a,250kW cooling capacity @-15degree C leaving water temperature and 45degree C condensing temperature).the system use a screw compressor with the economizer.the compressor do 260kw cooling @-15 with the economizer.the compressor suction size is 5",and discharge size is 3" . the compressor selection told me i need a heat exchanger that can do 30kw cooling to use as the economizer.the problem is the heat exchanger's connection size is only 1",so i am worrry about 1" liquid line will be too small for the system.can anyone give me some advice about the pipe sizing? thanks

i am new ,i don't know much about chiller design, my chief engineer design the systems .can anyone one give me some advices?thanks for help

The problem is like this :
Who designed the heat exchanger ? u can have 30 Kw at many many many different temperatures and flows).

But the problem is like this, an economizer is not a typical HX, because on one side you have a large flow (because there is the entire flow from the COMP).
Wen you size the economizer you have to calculate the large flow, and then you will have a larger connexion (not necessary the suction 5"), and then make shore you order it with the 5" connexion , and have a small size side that goes to the the economizer port

Devil ,thank you for you help.the unit is design to run at -15degree supply and 45degree condensing.the system use refcomp screw compressor,from the compressor selection program it show the economizer capacity need to be around 30kw at the running condition.so you think selection the size of economizer should be able to do most mass flow of compressor ,not only the 30 kw capacity? can you provide me some hand books that i can read about how to select and the enconmizer.thank you

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Originally Posted by cool_hot_wind

Devil ,thank you for you help.the unit is design to run at -15degree supply and 45degree condensing.the system use refcomp screw compressor,from the compressor selection program it show the economizer capacity need to be around 30kw at the running condition.so you think selection the size of economizer should be able to do most mass flow of compressor ,not only the 30 kw capacity? can you provide me some hand books that i can read about how to select and the enconmizer.thank you

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You size your economizer heat exchanger to the economiser duty (respective mass flow), in this case 30Kw, your selection program should also give you the pressure at with this duty is occurring. You then have to decide how you are going to use this side load.
If you are not going open flash, but liquid subcooilng and reciever outlet pressure.
You size your heatexchanger one side for total compressor mass flow (liquid sub cooling) the second side is an evaporator and is sized to meet economiser duty.
I presume you are designing a glycol chiller, not a water chiller, I think you would "really" struggle to get -15C water!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I would start back from zero. First of all: why R134a @ -15°C?
Is there any good reason? Why don't you increase the low side pressure with some other refrigerant, like R507?
My rough calculation shows that the volume rate flow for uneconomized R134a operation is in the range of 850 m3/h, while is around 500m3/h with R507 (same conditions).
That reduces a lot the capital cost for the compressor and for the piping.

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Originally Posted by mad fridgie

You size your heatexchanger one side for total compressor mass flow (liquid sub cooling) the second side is an evaporator and is sized to meet economiser duty.

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I think you are confusing the ECO with the IHX. The Economiser is a Voorhees cycle heat exchanger, which is basicly a spill of few % of liquid flow to subcool the remaining liquid. The resulting vapor is inject through an intermediate port of the screw compressor. The flow rates across the HE are the liquid flow on the warm side and the spilled evaporated liquid on the cold side. The sum of the two mass flows equates the liquid mass flow leaving the condenser.
The economiser at all effects is a PHE to subcool the liquid before the EV, and to increase at the same time the density of the vapour in the compression chamber.
The pressure of the vapour leaving the economiser shall be greater than the intermediate injection pressure inside the screw compression chamber, to avoid counter flows.

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Originally Posted by mad fridgie

I presume you are designing a glycol chiller, not a water chiller, I think you would "really" struggle to get -15C water!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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It's nor a water chiller, neither a glycol chiller. It is a liquid chiller or brine chiller.

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Originally Posted by NoNickName

I think you are confusing the ECO with the IHX. The Economiser is a Voorhees cycle heat exchanger, which is basicly a spill of few % of liquid flow to subcool the remaining liquid. The resulting vapor is inject through an intermediate port of the screw compressor. The flow rates across the HE are the liquid flow on the warm side and the spilled evaporated liquid on the cold side. The sum of the two mass flows equates the liquid mass flow leaving the condenser.
The economiser at all effects is a PHE to subcool the liquid before the EV, and to increase at the same time the density of the vapour in the compression chamber.
The pressure of the vapour leaving the economiser shall be greater than the intermediate injection pressure inside the screw compression chamber, to avoid counter flows.
Well I am sure I said that. trying to keep simple!
Keeping it simple
One side of heat exchanger all the refrigerant that comes out of the compressor.
second side need an expansion valve which you feed with liquid (like a normal evap) the design evap pressure (econ pressure/intermidiate pressure) as per software program, duty as per software program


It's nor a water chiller, neither a glycol chiller. It is a liquid chiller or brine chiller.

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Correct should be called a liquid chiller.

First,thanks to every one.It's a glycol solution chiller.Second this is a 750kW cooling capacity @ -15 degree with total 3 screw compressor ,3 evaporator and 12 condenser (4 for each circuit),because of the transport and site area we can't use more condenser ,so it's R134a.Third,today i have another look of the selection program ,the evap mass flow rate(@ -15degerr )is around 6000kg/h, one side of economizer is also 6000kg/h ,the other side is 750kg/h .but the connection (6000kg/h)from the economizer is only 1" , the other side is 7/8 and 1 1/8 . the compressor economizer port is 1 5/8 , the manufacture's manual said should use the 1 5/8 pipe from the heatexchanger. the other thing i am not sure what size of liquid line should be used,the original design was two 1 1/8 (come out from 2 condenser join together ),then join the two 1 1/8 ,reduced to 1" for the economizer , from outlet expand to 1 5/8 (size of EEV). the pipe work of whole system is not long .

mmmhh... it's not going to work.

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Originally Posted by cool_hot_wind

because of the transport and site area we can't use more condenser ,so it's R134a.

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This is irrelevant. Size and footprint of condensers can be arranged.
Despite, I can't see any difference in performance on the condenser for the same dT across of it, disregarding what refrigerant is used. Beside, reducing the mass flow, reduces the capital costs and pipe size.

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Originally Posted by cool_hot_wind

.but the connection (6000kg/h)from the economizer is only 1"

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That mass flow is liquid refrigerant. For a liquid refrigerant speed of 0.6m/s typical, and a mass flow of 6000Kg/h, the diameter shall be 4". This means that you need one economiser PER compressor (3 economisers in total), and in that case the diameter of 1" is marginally suitable.


The other diameters I would suggest, considering the total refrigerant flow, 4"1/4 discharge header, and DN300 or 12" suction header. Good luck for the fabrication.

We all 3 say mainly the same thing as for his question, but it's easy if you see it in color :))

http://fidelitas.ro/refrigeration-en...20Packages.pdf

on page 6 u can see and understand it better.

And as i said on the right side of the HX you have the entire flow of the system , the hex has one one side a large connexion.

To simplify when you size the ECONOMIZER you introduce in the software the flow calculated by the power you have for the designed pressure and temperature (on the specific refrigerant ) , but you don't have the exact displacement of the compressor because the refrigerant is liquid and holds more energy.
And a expansion valve for the designed power (30 Kw), and then it will result the flow on the low side.

ok following it's the data from selection program

refrigerant R134a
evaporating temp -19degree
evaporating pressure 1.39bar abs
condensing temp 45degree
condensing pressure 11.6bar abs
suction gas superheat 10K
liquid subcooling 5K

cooling capacity 230.5Kw
cooling capacity with ECO 264.4Kw
input power 128.9Kw
input power with ECO 141.9Kw
COP 1.79
COP with ECO 1.87
condenser capacity 360Kw
condenser capacity with ECO 405Kw
evaporator mass flow rate 5970.6kg/h
ECO mass flow rate 760kg/h
discharge temperature 101.5degree
injection pressure 1.9 bar
ECO pressure 5.0 bar
ECO saturated temperature 15.9degree

discharge connection 4 1/8"
suction connection 5"

like NoNickName said ,now i am worry about the system with R134a whether will work at that low temperature or not

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Originally Posted by NoNickName

That mass flow is liquid refrigerant. For a liquid refrigerant speed of 0.6m/s typical, and a mass flow of 6000Kg/h, the diameter shall be 4". This means that you need one economiser PER compressor (3 economisers in total), and in that case the diameter of 1" is marginally suitable.

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You need 6000Kg/h for one compressor and 18000Kg/h for the entire system.

So the connexion for the ECO should be the same as for the discharge for the high side (for his COMP should be 4 1/8") , or a little bit smaller and for the low side should be something like 1 1/8" (the same as the ECO port on the COMP)directly to the ECO port on the compressor.

And for the refrigerant type, i should admit i would go for R404A or R507A, because R134a is close to it's limits , but if the compressor can handle it you might go for it, but it's never recommended to go close to the edge

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Originally Posted by DEVIL

You need 6000Kg/h for one compressor and 18000Kg/h for the entire system.

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You are perfectly right. My bad.

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Originally Posted by DEVIL

So the connexion for the ECO should be the same as for the discharge for the high side (for his COMP should be 4 1/8") ,

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The size of the liquid line, not the discharge. Economiser is crossed by liquid, not by superheated vapour.

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Originally Posted by NoNickName

The size of the liquid line, not the discharge. Economiser is crossed by liquid, not by superheated vapour.

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Yes i agree that's way i wrote "or a little bit smaller"
Depending on the design you might not have big differences

Hello everybody,

the economizer has always to be layouted for a capacity that is corresponding to the difference between the cooling capacity with and without it. In this selection the cooling capacity with ECO is 264 kW, without economizer 230.

So the capacity of the economizer is 34 kW. It never gets the whole of the flow, but only a percentage that should not exceed 15%. When you go back to the compressor you have to connect to an intermediate ECO-port, which has a diameter varying between 3/4" and 1 1/2", depending on tìcompressor size.

The system will perfectly run with R134a @ -15°C. It is true that the motore is bigger size, but the efficiency is higher, so that the "ownership cost" over the life cycle of the machine should be lower.

Economiser can be simply designed by multiplying the flow rates , given in compressor selection, into enthalpy difference across shell side. Enthalpy difference across shell side can be calcualted as follows

1)enthalpy of liquid at condesing temperature

2) enthalpy of liquid at saturation temperature corresponding to pressure

Above calculation will simply give the kW for which economiser can be designed.

line sizing for economiser can be done by simple calculation of flow rates and by the formula Q= AXV,

where Ais the area , Q - mass flow rate of chiller/ economiser and v is the velocity

for liquid line design we can simply assume velocity of 0.8 to 1 m/sec velcoity .

If the value of line size coming after calculations is close to given line size provided in economiser then it is ok .

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Originally Posted by RCassist

Hello everybody,

the economizer has always to be layouted for a capacity that is corresponding to the difference between the cooling capacity with and without it. In this selection the cooling capacity with ECO is 264 kW, without economizer 230.

So the capacity of the economizer is 34 kW. It never gets the whole of the flow, but only a percentage that should not exceed 15%. When you go back to the compressor you have to connect to an intermediate ECO-port, which has a diameter varying between 3/4" and 1 1/2", depending on tìcompressor size.

The system will perfectly run with R134a @ -15°C. It is true that the motore is bigger size, but the efficiency is higher, so that the "ownership cost" over the life cycle of the machine should be lower.

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You are wrong , but whats true in your story is that on one side of the economizer you have 34 Kw.
BUT

On the other side you have the whole quantity of the liquid passing it.

I posted the documentation that makes you understand it better, find it and see on page 6

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Originally Posted by DEVIL

You are wrong , but whats true in your story is that on one side of the economizer you have 34 Kw.
BUT

On the other side you have the whole quantity of the liquid passing it.

I posted the documentation that makes you understand it better, find it and see on page 6

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On one side you are spilling a part of the liquid to be expanded for cooling down the main mass flow rate, which corresponds to the total MINUS the part spilled for cooling, and that you are injectin' in the ECO port. So please tell me where I am wrong.

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Originally Posted by cool_hot_wind

like NoNickName said ,now i am worry about the system with R134a whether will work at that low temperature or not

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You are right to worry. R134 is a bad choice for this application.

Here's a bit of history and contacts if you need them.

RefComp and Thermokey form together the RTH group which is an independent group which has one owner who is the original founder Mr. Candio.
RefComp makes the very same screw and piston compressors at their factories both near Vicenza in Italy and in Shanghai in China while Thermokey makes many types of heat exchangers for Air Con, Refrigeration , Process Control, Close Control , Power and Energy and Solar Energy markets and manufactures in Italy , China and Brazil.

About 30 years ago Mr. Candio used to own Artec (heat exchangers) which he after sold to Alfa Laval. After RefComp was then founded and was a pioneering company with screw compressor technology specifically designed for HVAC and Refrigeration applications. During this past century Bitzer used to sell the large RefComp screw compressors through their sales network because back then they did not manufacture yet this kind of new screw compressor.
After Thermokey was then founded. Nowdays Thermokey is pioneering in large aluminium microhannel heat exchangers specifically designed for HVAC and Refrigeration applications

you can contact them at :

sales@refcomp.it
sales@thermokey.it