pressure drop between expansion valve and distributor

Hello,
In a heat pump system termostatic expansion valf and distributor with capilary tube have totally 13 unit PD. I want to ask, in this kind of system , If the pressure drop of distributor with capilary tubes is higher than expansion valve (5unit from expansion valve, 8unit from distributor) , what kind of problem can be occurred ?, how can I solve this problem? For example, do I have to change distributor or capilary tube design ? And what is the reason of these problem?
I hope I explain my questions enough...
I am looking forward to hearing your opinions…

Regards

The Prof will assume an R-22 heat pump, in which your units of pressure drop would be in either bar or kg/cm2. If the Prof is allowed to use I-P units, we would have about 70 psi across the TEV and 115 psi across the distributor and tubes.

It is possible to size the TEV for this situation and obtain correct system operation. But there are good reasons not to take a pressure drop this high across the distributor and tubes.

Changes in evaporator load affect distributor pressure drop. With a 115 psi pressure drop at design conditions, variations in load will have a substantial effect on the remaining pressure drop across the TEV. The TEV will invariably starve at startup conditions. With refrigeration systems, changes in evaporator loading are more significant when you consider the load following a defrost, hot gas, electric, or off-time. On a refrigeration system having this type of distributor and tube pressure drop, you would have no pulldown capacity.

With a heat pump system, you must also consider the liquid flow across the distributor and tubes in the reverse cycle. With a 115 psi pressure drop in the normal distributor flow direction, you could have perhaps 20 psi pressure drop in the reverse direction which could cause flash gas problems.

The Prof would recommend no more than a 50 psi pressure drop across the distributor and tubes, and only if there is sufficient pressure drop for the entire TEV, distributor, and tubes. Normally, a 35 psi pressure drop is adequate for proper refrigerant distributor for most applications.

Hello everybody, Hello Prof Sporlan,

In your answer you wrote "The Prof would recommend no more than a 50 psi pressure drop across the distributor and tubes,"

Could you please tell me "50 psi is total pressure drop (distributor+capillary tubes), what is allowable pressure drop for capillary tubes?"

According to the sporlan distributor selection document, (in table C-page 13) for R407C
%50 capacity ratio:
min nozzle dp: 7 psi
min capilary tube dp: 3 psi
min total distributor dp: 10psi

%200 capacity ration:
max nozzle dp: 80psi
max capilary tube dp: 34psi
max distributor dp: 114 psi

1- Does the system work correctly in these min and max pressure drops conditions?...

2- If tubes dp are equal 3 psi , does any problem occur in the system?

3- In sporlan distributor selection document , page 10, table A , there is a correction factor for distributer tube lengths. According to this table, when the tube length is increased, correction factor is decreased. Could you please tell me what is the reason?...
If I use longer tube length i will obtain lower capacity...

4- what is the recommended capacity ratio (actual / teoric)?
%50-%100 or %50-%200

5- Could you please tell me which points are important for selecting distributor ?

Thanks for your helps
Best regards

Again, so many points to address while the Prof is enjoying his fine Belgian style Trippel ale… :)

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1- Does the system work correctly in these min and max pressure drops conditions?...

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The simple answer here is that it should. But one should not size the distributor nozzle and tubes at either of these endpoints at design conditions. The 100 percent loading values are meant for this purpose.

The endpoint conditions are really meant for analysis at high and low load conditions. For example, one may be interested in the pressure drop across the distributor and tubes at the pulldown load for a freezer following a defrost, or at a low load condition for commercial a/c system where the compressor is operating unloaded.

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2- If tubes dp are equal 3 psi , does any problem occur in the system?

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Generally, no. But as with many other things, exceptions exist.

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3- In sporlan distributor selection document , page 10, table A , there is a correction factor for distributer tube lengths. According to this table, when the tube length is increased, correction factor is decreased. Could you please tell me what is the reason?...
If I use longer tube length i will obtain lower capacity...

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That is correct… same with a suction, liquid, or discharge line.

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4- what is the recommended capacity ratio (actual / teoric)?
%50-%100 or %50-%200

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At your “design” condition, you normally want to be around 100 percent loading. If your system can unload substantially, i.e., 1/3 or less, you probably want to opt for pushing the loading up to 130 percent or so if possible.

Thanks Prof Sporlan,

We did a distributor selection with sporlan selection program. Our unit is heatpump, so we have an indoor and outdoor side.

For indoor side we obtain following:

REFRIGERANT DISTRIBUTOR SELECTION DATA

Refrigerant R- 407C Number of Circuits: 30

Evaporator Temperature (°F): 43
Dist Tube Length (in): 28

Liquid Temperature (°F): 93
Evaporator Capacity (tons): 16.0


Tube OD Tube DP Percent Nozzle Orifice Nozzle DP Percent Total DP

(in) (psi) Loading Number (psi) Loading (psi)

1/4 3.1 49 20 22 91 25


For outdoor unit we obtain following:
REFRIGERANT DISTRIBUTOR SELECTION DATA


Refrigerant R- 407C
Number of Circuits: 28

Evaporator Temperature (°F): 43
Dist Tube Length (in): 43

Liquid Temperature (°F): 93
Evaporator Capacity (tons): 19.5


Tube OD Tube DP Percent Nozzle Orifice Nozzle DP Percent Total DP

(in) (psi) Loading Number (psi) Loading (psi)

1/4 6.3 74 25 20 85 26


What do you think for this system?

Do we have to increase tube length?
If we obtain 10psi dp for tube length , tube length will be increased 80 inc...

As you see our pressure drops are very low... Only i can change tube length...

I am looking forward to waiting your answer...

Thanks & Regards

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Originally posted by Prof Sporlan
Again, so many points to address while the Prof is enjoying his fine Belgian style Trippel ale… :)

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From what brand Prof? We have many Tripples here. (Chimay, Westmalle, Hoegaarden, Tongerlo, ...)
We have in Belgiumm more then 400 different sorts of beer (and only 10 million people)
Even my wife sells them in here tearoom.
You're in Belgium for the moment?

I can imagine that these beers are rather expensive over there.

Even after one, you feel a little bit heaven in your body.

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What do you think for this system?

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The Prof will assume this system has two TEVs with check valve bypasses and side connection type distributors. If we are reverse flowing thru the distributor nozzle which would be the case with a non-side connection distributor, we would want to consider upsizing the nozzle to keep pressure drop to a minimum.

For the indoor coil, and entering a "?" for distributor tube OD and nozzle size, the program selects 3/16" OD tubing and a #20 nozzle. You're actually between the 3/16" and 1/4" OD distributor tube sizes here, and using 1/4" OD here is no problem. Specifying a 1/4" OD tube size, the program selects a #15 nozzle. The Prof would suggest the latter for a heat pump application

For the outdoor coil, the program selects 1/4" OD tubing and a #20 nozzle. Pressure drops are fine here.

The Prof can see you are using a reasonably current version of the program as he can duplicate your output. But it is easier if you first enter "?" for distributor tube OD and nozzle size and let the program make the selection. You can enter other values if you want to see pressure drops from alternate tube and nozzle combinations. In fact, you can enter ranges for both tube OD and nozzle sizes, e.g., "3/16,1/4" for tubes, and "12,25" for nozzles. The program will dutifully calculte pressure drops for all combinations.

The current Sporlan product selection program (version 3.51.5) can be downoaded from here: http://www.sporlan.com/pgm/svc.html

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From what brand Prof? We have many Tripples here. (Chimay, Westmalle, Hoegaarden, Tongerlo, ...)

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The Prof has had the occasion to partake of the Chimay and Westmalle. Both excellent! Was it Westmalle the brewery that recently changed ownership? The beer the Prof was enjoying yesterday was brewed from the New Belgium Brewery in Ft. Collins, Colorado. http://www.newbelgium.com/ The U.S. microbrewery industry is alive and well, and learning from the masters... :)

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Even after one, you feel a little bit heaven in your body.

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Until the following morning, unfortunately... :)

Thanks Prof Sporlan,

"The Prof will assume this system has two TEVs with check valve bypasses and side connection type distributors. "

The system has a biflow exp. valf and heat pump so there is no any check valve bypasses...

Could you please examine the above datas according to the last situation?

Best regards

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Originally posted by Prof Sporlan
The Prof has had the occasion to partake of the Chimay and Westmalle. Both excellent! Was it Westmalle the brewery that recently changed ownership? The beer the Prof was enjoying yesterday was brewed from the New Belgium Brewery in Ft. Collins, Colorado. http://www.newbelgium.com/ The U.S. microbrewery industry is alive and well, and learning from the masters... :)


Until the following morning, unfortunately... :)

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One the leading world companies of these micro breweries is located in my street

http://www.packo.com/en/products_cat...tml?group_id=2

Indeed, they're all excellent but geez, after 3 or 4, you can walk and leave your car where it stands.

I don't know if ownership is changed.

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Originally posted by Prof Sporlan
The Prof has had the occasion to partake of the Chimay and Westmalle. Both excellent! Was it Westmalle the brewery that recently changed ownership? The beer the Prof was enjoying yesterday was brewed from the New Belgium Brewery in Ft. Collins, Colorado. http://www.newbelgium.com/ The U.S. microbrewery industry is alive and well, and learning from the masters... :)


Until the following morning, unfortunately... :)

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One the leading world companies of these micro breweries is located in my street

http://www.packo.com/en/products_cat...tml?group_id=2

Indeed, they're all excellent but geez, after 3 or 4, you can walk and leave your car where it stands.

I don't know if ownership is changed.