R404a water cooled condensing unit with 8oC cooling water

[wta12]

Hello. i got selection for water cooled condensing unit with R404A for cold/vegetable storage application (-20 and 5 oC). The problem come when we have only cooling source stable 8oC chilled water. The application limit for system is temp. condensing (TC) of R404A system (bitzer as reference) is only 20oC. The selection software for condenser can choose with Tc =24oC with condenser sub-cooling 1 oK as default of selection software. Anyone have this kind of condenser
i worry about the stable of system especially when the system start-up or back to work after long time - condensing maybe hardly or non stable working cause too much cold water .

If anyone had experience with similar situation (equip selection, commissioning, operation), please give me some advices and recommendation.

[nike123]

If you use water flow regulating valve for condensation temperature control, you can adjust it for normal 40-50°C range!

[Brian_UK]

As Nike states use a control valve....

http://www.danfoss.com/Products/Categories/Group/RA/Water-Valves/568ab45f-94f0-4aa9-9955-c67369fb9f20.html

[wta12]

If you use water flow regulating valve for condensation temperature control, you can adjust it for normal 40-50°C range!
We cant not have leaving cooling water more than 15oC that why Tc is low. We just use water flow for leaving cooling water temp <15oC. I have checked again with selection software. The result attached. Please help me to check this selection, i have no ideal about operation conditions of low temperature application. Regards
11061

[AlexG]

Use air cooled condenser.

[wta12]

Use air cooled condenser.
IF i could do like this, the machines room is basement without outdoor asset.
Anyone know about this please help me
Regards

[AlexG]

Use water condenser with small (3...4 times smaller) surface. Or remote air condenser.

[nike123]

We cant not have leaving cooling water more than 15oC that why Tc is low. We just use water flow for leaving cooling water temp <15oC.
I dont see why you cannot have condenser leaving water temp higher than 15°C. Explain why!

In the meantime, think about mixing condenser leaving water of 40° with 8°C entering water at some ratio with 3Way mixing water valve
https://www.google.hr/search?q=esbe+3way&client=opera&hs=POW&channel=suggest&source=lnms&tbm=isch&sa=X&ei=eVDOUrWoOIGwyAPlw4C4Dg&ved=0CAkQ_AUoAQ&biw=1280&bih=668
after condenser which will produce at its exit water temperature of your liking between 8°C and 40°C if there is no other option with that water coming from condenser.

[Magoo]

computer driven selection programs, rubbish in equals rubbish out.
SDT at 21' C is blatantly wrong, more like an intermediate booster stage.
Sorry for being so blunt.
magoo

[Peter_1]

Use this http://titaniccontrols.com/wp-content/uploads/2012/06/Johnson-Controls-V46-Pressure-Actuated-Water-Regulating-Valve--298x300.png and all your problems are gone.
Ever thought how they do iit on a ship with sewater at 8°C? I first read 80°C.

[wta12]

I dont see why you cannot have condenser leaving water temp higher than 15°C. Explain why!

In the meantime, think about mixing condenser leaving water of 40° with 8°C entering water at some ratio with 3Way mixing water valve
https://www.google.hr/search?q=esbe+3way&client=opera&hs=POW&channel=suggest&source=lnms&tbm=isch&sa=X&ei=eVDOUrWoOIGwyAPlw4C4Dg&ved=0CAkQ_AUoAQ&biw=1280&bih=668
after condenser which will produce at its exit water temperature of your liking between 8°C and 40°C if there is no other option with that water coming from condenser.
Cause they use water from an big exiting chilled water in basement. this once could be use plate-heat exchanger instead of chilled water for different water cooling ?
@ Alex-G : condenser selection is ok with 8/14oC but i want to check for control and automatic control part (safety). Could you give me some source of technical guideline for my case.
@Magoo: I'm pretty newbie on this detail. I have no ideal why we can use 21oC SDT with suction gas temp like -20oC like this selection. Could you point me some technical problem with this selection ? Like oil lubrication,low limit ....
@all : what they do with seawater-cooled condensing unit ? the cooling water is similar to my case
Regards

[nike123]

Cause they use water from an big exiting chilled water in basement. this once could be use plate-heat exchanger instead of chilled water for different water cooling ?
I knew some part of English language, but this 2 sentences does not make sense to me! Sorry!

[AlexG]

wta12, to calculate your condenser you need just basic knowledge.
Q=k x F x dT
Q is capacity, F is surface of your condenser, dT is temperature difference between refrigerant and cooling water. Usually in water cooled condenser dT is 5 K. In your case dT should be 15...20 K. So your surface should be 3...4 times smaller. But pay attention to pressure drop if you apply small condenser.
good luck

[wta12]

wta12, to calculate your condenser you need just basic knowledge.
Q=k x F x dT
Q is capacity, F is surface of your condenser, dT is temperature difference between refrigerant and cooling water. Usually in water cooled condenser dT is 5 K. In your case dT should be 15...20 K. So your surface should be 3...4 times smaller. But pay attention to pressure drop if you apply small condenser.
good luck
Thank AlexG _ selection for condenser is no problem with me but the part for reliable operation is hardly preparing because rarely use 8oC water for condensing unit and i still not sure what problem should care with low suction temp. (0 oC) like my selection.
11085

[Gary]

wta12, to calculate your condenser you need just basic knowledge.
Q=k x F x dT
Q is capacity, F is surface of your condenser, dT is temperature difference between refrigerant and cooling water. Usually in water cooled condenser dT is 5 K. In your case dT should be 15...20 K. So your surface should be 3...4 times smaller. But pay attention to pressure drop if you apply small condenser.
good luck

The difference between refrigerant and water temps is TD, not dT.

dT is the difference between entering and leaving water.

[AlexG]

Gary, sorry for my poor English. Probably you are right! I have been educated by Russian books... Cyrillic...

[Gary]

In thermodynamics, a delta-T (dT) is a change in the temperature of a single substance or flow stream.

A temperature difference (TD) is a temperature comparison of two different substances or flow streams.

Hope that helps. :)

[nike123]

Your condenser water leaving temperature must be above 30°C, or you will not have enough pressure diferential required for proper function of TXV. Therefore, you will need to mix condenser leaving water with some portion of water coming in bypass with condenser in order to get water leaving temperature of less than 15 or whatever you prefer.

[Peter_1]

You only need to control the waterflow with a water regulating valve (PENN, Danfoss, Sporlan...) PENN in return water and connect the control capillary to the HP. That's all. You then can regulate to the desired HP within seconds. Don't make it more difficult than this, simply, no bypass, no mixing, no 3-way, no electronics,...just an ordinary valve.

[nike123]

We cant not have leaving cooling water more than 15oC that why Tc is low.

I taught that this is requirement and not inability.

[wta12]

You only need to control the waterflow with a water regulating valve (PENN, Danfoss, Sporlan...) PENN in supply water and connect the control capillary to the HP. That's all. You then can regulate to the desired HP within seconds. Don't make it more difficult than this, simply, no bypass, no mixing, no 3-way, no electronics,...just an ordinary valve.
Thank for your advice. i will check the data for this part. But the water valve regulator should be codenser pressure regulator type (with pressure sensor) or we can use water cooled valve (HVAC water valve) with normal thermos sensor, which trap-in the refrigerant pipe?
@nike 123: Could you point out some inabilities and their fault in data selection - i really appreciated them . For data sheet of compressor, the Tc less than 20 oC still in limit range with To= -20 oC or less. The only different is Toh (suction gas temp.) is not 20 oC like standard. My reference come from Bitzer Ecoline semi hermectic compressor
Regards

[nike123]

Thank for your advice. i will check the data for this part. But the water valve regulator should be codenser pressure regulator type (with pressure sensor) or we can use water cooled valve (HVAC water valve) with normal thermos sensor, which trap-in the refrigerant pipe?

Condenser pressure regulator type.


@nike 123: Could you point out some inabilities and their fault in data selection - i really appreciated them . For data sheet of compressor, the Tc less than 20 oC still in limit range with To= -20 oC or less. The only different is Toh (suction gas temp.) is not 20 oC like standard. My reference come from Bitzer Ecoline semi hermectic compressor
Regards


http://www.refrigeration-engineer.com/forums/showthread.php?13857-What-is-overcondensing

http://www.refrigeration-engineer.com/forums/showthread.php?27543-Over-Condensing

[Peter_1]

Pressure actuated, HP connected to any HP point, valve is mounted in the outlet, not the inlet so that you have a condensor full of water.

[wta12]

Pressure actuated, HP connected to any HP point, valve is mounted in the outlet, not the inlet so that you have a condensor full of water.
Thank for your answer. I found these valves type but still have confused for selection - too much model. I will ask Supplier
http://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/Products/Group/RA/Water-Valves/568ab45f-94f0-4aa9-9955-c67369fb9f20.html

Condenser pressure regulator type.

http://www.refrigeration-engineer.com/forums/showthread.php?13857-What-is-overcondensing

http://www.refrigeration-engineer.com/forums/showthread.php?27543-Over-Condensing

Thank for your links. From these discussion, i'm understanding my situation like an air cooled condensing unit along with low ambient temp. For this situation they often said about condensing pressure regulator on refrigerant link (danfoss KVR as reference). Should i apply both of water and refrigerant type condenser pressure regulator or only one of them ?

[Peter_1]

What capacity do you need? Pure water? What are your water connections? Seems you're confusded, only a water regulating valve like WVFX. See it as a proportional control of speed on condensor fans.

[wta12]

What capacity do you need? Pure water? What are your water connections? Seems you're confusded, only a water regulating valve like WVFX. See it as a proportional control of speed on condensor fans.
11092
As shown, i need est 6 kw come along with pure water (softened chilled water). Will this valve be help at the start-up stage, when we can help low condensing pressure condition ?
@all : i still have question about 0 oC or less suction gas temperature with r404a and piston compressor. Normally suction gas temp at 20 oC as standard. What problem will come when we have lower than standard suction gas temp ?

[nike123]

Superheat is required to make sure that liquid refrigerant cannot get in to the compressor.

If you have correct superheat, than suction gas temperature could be as low as evaporation temperature + evaporator (useful) superheat value. In air-conditioning, with TXV as expansion device, suction superheat can be as low as 5K (R404a) without any problem. In freezers superheat can be as low as 2K

In closely coupled devices as Air-to water heat pump or similar, there is not much un-useful superheat between evaporator and condenser, and having there total superheat as big as 15K will make it impossible, if suction line heat exchanger is not used.

Anyhow, device designer responsibility is to make check to be sure that suction accumulator or suction line HE is not required for that low superheat.


http://www.refrigeration-engineer.com/forums/archive/index.php/t-18295.html

In your case, you probably have suction line HE and that can rise your suction line temperature enough that there is no need for suction accumulator.
If your discharge temperature is to low, than high side of suction line HE is not heating enough suction line gases, and your suction temperature and suction superheat is to low. Therefore you must maintain condensation temperature at design level (which is usualy around 40°C) to ensure designed cca 10K superheat at suction line HE. With 10K superheat at any time there is no danger to liquid in compressor and therefore no requirement of 20°C liquid line temperature.

If you follow that rule blindly, at -25°C evaporation, you will be having 45K suction superheat, which will make discharge gases hot as hell.

[Peter_1]

Fit a WVFX10 in the water return and that's it. Nothing more. The valve will try to maintain a stable HP, so also at startup. At startup, valve will close because water will be colder after the last shutdown, and as soon the set HP is reached, valve will slowly open allowing cold water entering at the inlet.

[Peter_1]

... Therefore you must maintain condensation temperature at design level (which is usualy around 40°C) to ensure designed cca 10K superheat at suction line HE. ....

Nike, I disagree with this phrase - perhaps I misunderstood - but what about floating HP? SH is maintained even with floating HP.
I think WTA12 will become even more confused now, so don't listen to me now WTA12.

[nike123]

My reasoning is as folows, but maybe, I am wrong. I am not that god in theory.

Capacity of suction line HE depend on TD of that heat exchanger. If we have low discharge temperature, than TD of suction line HE is lowered, and therefore achieved superheat/subcooling is also lowered.


Nominal SLHE selections should be based on system horsepower, which will provide a nominal 10ºF subcooling and a nominal 20ºF suction superheat for R-22, R-502, R-404A, R-507, R-407A, R-504, R-134A, R-407C and R-410A at 110ºF condensing and 25ºF suction. For example, for a 1-1/2 HP system, select an SLHE 1-1/2. Do not select undersized models to avoid high suction pressure drops and gas whistling.

Selections based on suction and liquid line sizes are appropriate for standard low, medium and high temperature refrigeration systems provided the system HP rating closely matches the SLHE selection.

Selection of oversized models will provide additional liquid subcooling and suction superheat. Oversized models are acceptable only if the suction gas temperature to the compressor is not raised above 65ºF for proper compressor performance.

http://heatexchangers.doucetteindustries.com/viewitems/all-categories/suction-line-heat-exchangers?

[Peter_1]

Your expansion device - except capilary device - will maintain a stable SH, whatever HP may be.

[nike123]

Evaporator SH, yes!

[wta12]

Superheat is required to make sure that liquid refrigerant cannot get in to the compressor.

If you have correct superheat, than suction gas temperature could be as low as evaporation temperature + evaporator (useful) superheat value. In air-conditioning, with TXV as expansion device, suction superheat can be as low as 5K (R404a) without any problem. In freezers superheat can be as low as 2K


Anyhow, device designer responsibility is to make check to be sure that suction accumulator or suction line HE is not required for that low superheat.


http://www.refrigeration-engineer.com/forums/archive/index.php/t-18295.html

In your case, you probably have suction line HE and that can rise your suction line temperature enough that there is no need for suction accumulator.
If your discharge temperature is to low, than high side of suction line HE is not heating enough suction line gases, and your suction temperature and suction superheat is to low. Therefore you must maintain condensation temperature at design level (which is usualy around 40°C) to ensure designed cca 10K superheat at suction line HE. With 10K superheat at any time there is no danger to liquid in compressor and therefore no requirement of 20°C liquid line temperature.

If you follow that rule blindly, at -25°C evaporation, you will be having 45K suction superheat, which will make discharge gases hot as hell.

I checked selection condition. We always have 10oK superheat (will be set by TXV) : -30oC To(evaporation) + 10 oK superheat = - 20 oC suction gas temp. and -10oC To(evaporation) + 10 oK superheat = 0 oC suction gas temp..
Evaporator also chosen according -10oK superheat

Other Question:
1.In case we have shell and tube condenser, which may act as receiver also. should we have dedicated receiver for my case (r404a with low condensation temp) ?
2. Crankcase heater should be installed with low suction gas like this or not ? Normally we need not have this one in our country ever after long time turn back cause high ambient condition (lowest 8oC- normally 20-25oC) but i'm not sure if compressor and condenser inside room (20-28 oC).

Regards

[Peter_1]

I checked selection condition. We always have 10oK superheat (will be set by TXV) : -30oC To(evaporation) + 10 oK superheat = - 20 oC suction gas temp. and -10oC To(evaporation) + 10 oK superheat = 0 oC suction gas temp..
Evaporator also chosen according -10oK superheat

Other Question:
1.In case we have shell and tube condenser, which may act as receiver also. should we have dedicated receiver for my case (r404a with low condensation temp) ?
2. Crankcase heater should be installed with low suction gas like this or not ? Normally we need not have this one in our country ever after long time turn back cause high ambient condition (lowest 8oC- normally 20-25oC) but i'm not sure if compressor and condenser inside room (20-28 oC).

Regards

Don't understand why you subtract twice 10K and uses twice evaporation. When refrigerant is leaving your evaporator, it's all evaporated as a superheated gas.

You evaporate at -30°C, 10 K superheat is too much, 7K, so -23°C leaving evaporator and +/- 10K along suction line = -13°C inlet compressor

Select compressor for -30°C and 20K total SH and your evaporator at -30°C and 7K SH.

1. You don't need a receiver but charge is then somehow critical. You can install one but it isn't necessary.
And you will not see low condensing pressures, the WVFX will maintain a stable HP.
I feel you still doesn't get the whole picture.
Perhaps this will help http://www.danfoss.com/NR/rdonlyres/9CB06EF4-CABF-4A30-A1AF-4F012F81EBA0/0/PFD00A102.pdf


2. If you have pump down, no CCH needed. As you said, it's hot enough in your country to omit a CCH. The temperature of the returning gas has nothing to do with the need for a CCH.

[Peter_1]

Take the hottest temperature you will ever see for the water supply, add 5 to 7 K and use this to calculate your compressor and your expansion valve.
Regulate your valve in winter for the hotter conditions you will see in summer and it will save you a lot of energy.
And, your HP will be stable the whole year long.

[wta12]

Don't understand why you subtract twice 10K and uses twice evaporation. When refrigerant is leaving your evaporator, it's all evaporated as a superheated gas.

You evaporate at -30°C, 10 K superheat is too much, 7K, so -23°C leaving evaporator and +/- 10K along suction line = -13°C inlet compressor

Select compressor for -30°C and 20K total SH and your evaporator at -30°C and 7K SH.

1. You don't need a receiver but charge is then somehow critical. You can install one but it isn't necessary.
And you will not see low condensing pressures, the WVFX will maintain a stable HP.
I feel you still doesn't get the whole picture.
Perhaps this will help http://www.danfoss.com/NR/rdonlyres/9CB06EF4-CABF-4A30-A1AF-4F012F81EBA0/0/PFD00A102.pdf


2. If you have pump down, no CCH needed. As you said, it's hot enough in your country to omit a CCH. The temperature of the returning gas has nothing to do with the need for a CCH.

Sorry for my unclear statement. It's water cooled condensing unit for cold and chiller room.
First is for meat and sea food so they have -30 oC evaporation and -23 oC cold room temperature with suction gas temp -20oC for 10oK super heat

Second is a for higher condition (vegetable, beverage,....) so they have -10 oC evaporation and 0oC suction gas temp. (10o SH also) like compressor selection data This for worst case Maybe it's T evaporation will be raised up if have other requirement.

For SH calulation : for +10 oK along suction line as you said, could i avoid it because if suction line exposed to air room, we will have frost. i want to insulated it.

I have no experience with refrigerant line cause nearly all of my work before come with HVAC system so most of refrigeration work come from chiller's manufacture guys. and it's completely different condition with HVAC chiller. May be it's not all but i'm very appreciated your supports.
Thank alot

[wta12]

Take the hottest temperature you will ever see for the water supply, add 5 to 7 K and use this to calculate your compressor and your expansion valve.
Regulate your valve in winter for the hotter conditions you will see in summer and it will save you a lot of energy.
And, your HP will be stable the whole year long.
Please clarify for me the Hotter condition is the HP - discharge gas condensing temperature, Isn't it ? and why we need higher in winter cause i use chilled water with extremely stable 8oC (12 oC max but seem to never happen) ? All of my unit with cold room inside building so weather have very tiny affect.
Regards

[nike123]

Why are you wasting energy? You take electrical energy to cool cooldrom and then you spend more energy in chiller to transfer that heat out. Why you don't simply use water from fresh water supply (or some other, maybe free source of water) and dich it in sewage after heat is transfered from condenser to that water. Is it cheaper to use electricity twice than use (potable or brown) water for transferring heat, or you absolutely must use that chiller as source of cooling water.

[Peter_1]

OK then, you have in winter and summer water of 12°C,..if you use a Bitzer like your condensor, set watervalve fix to a condensation temperature of 20°C (even 15°C is possible) and select your expansion valve for a condensation temperature of 20°C as well. In that way, you will use less electrical power (like NIKE explained )

[wta12]

Why are you wasting energy? You take electrical energy to cool cooldrom and then you spend more energy in chiller to transfer that heat out. Why you don't simply use water from fresh water supply (or some other, maybe free source of water) and dich it in sewage after heat is transfered from condenser to that water. Is it cheaper to use electricity twice than use (potable or brown) water for transferring heat, or you absolutely must use that chiller as source of cooling water.
I also want to do like this but unfortunately we have no free source water. Fresh supply water, omg we will got a a lot complaint for fresh water waste. Otherwise, we have 8000 kw chiller plant, a half of them can run 24/24 so the cold room (total 60 kw cooling) is minor thing. We waste more with chilled water bypass than cold room :D.

[Gary]

Where there is refrigerant in both liquid and vapor form (condenser, evaporator), the temperature and pressure coincide.

If the condensing temperature is low, then the condensing pressure is also low. If the condensing pressure is too low then there isn't enough pressure in the condenser to push the liquid refrigerant through the TXV and into the evaporator.

The choices are to raise the temperature of the water or to reduce the flow of water through the condenser. Either of these strategies will raise the condensing temperature/pressure.

The purpose of the water regulating valve is to control the water flow in order to regulate the condensing temperature/pressure.

[wta12]

Where there is refrigerant in both liquid and vapor form (condenser, evaporator), the temperature and pressure coincide.

If the condensing temperature is low, then the condensing pressure is also low. If the condensing pressure is too low then there isn't enough pressure in the condenser to push the liquid refrigerant through the TXV and into the evaporator.

The choices are to raise the temperature of the water or to reduce the flow of water through the condenser. Either of these strategies will raise the condensing temperature/pressure.

The purpose of the water regulating valve is to control the water flow in order to regulate the condensing temperature/pressure.
Thank a lot for a comprehensive conclusion with my situation. How could i check the condensing pressure is enough to push liquid through TXV to select the design condition ?
Regard

[Gary]

The TXV manufacturer can tell you the minimum pressure drop (difference between high and low side pressures) needed for the TXV to operate properly. It varies with the model/type of TXV.

[Gary]

As a general rule of thumb, I like to keep a minimum of 30C condensing temperature. This should be enough for all types of TXV's.

[wta12]

The TXV manufacturer can tell you the minimum pressure drop (difference between high and low side pressures) needed for the TXV to operate properly. It varies with the model/type of TXV.

It's seem like i need contact Danfoss (the most popular brand in our country for TEV). I can not find this value in TEV calalogue

[Peter_1]

Danfoss TEV's = 2 bar minimum pressure drop but take perhaps 4 bar to have some safety margin. You will have anyhow 9 bar HP with R404a at 15°C condensing and a LP of +/- 3 bar which gives you 6 bar differential

[wta12]

Danfoss TEV's = 2 bar minimum pressure drop but take perhaps 4 bar to have some safety margin. You will have anyhow 9 bar HP with R404a at 15°C condensing and a LP of +/- 3 bar which gives you 6 bar differential
Thanks a lot. It's come from your experiences or any source ? i want to verify for model. Ever Danfoss tech. support have not answer for me.

[Peter_1]

Both, I have the books here form Danfoss as well. YOu then have bad Danfoss support in your country.

[wta12]

Could you spend me the soft-copy (pdf) file of this document ?
In case not available, Please let me the name or P/N of document/books, which say about this value.
Thank for your support

[Gary]

The selection software for condenser can choose with Tc =24oC with condenser sub-cooling 1 oK as default of selection software.


This seems a little low to me. Condensers should be sized for worst case scenario. In this case that would be a malfunction of the chiller system and switch to fresh water input. It would seem prudent to oversize the condenser a little (for worst case scenario) and then control the water flow volume (for best case scenario). The overriding question would be, what temperature is the fresh water input?