Auxilary receiver to increase subcooling?

[liptow]

Hello refrigeration fans,
Most of my work is cold storage boxes with a 1 to 5 HP air or water cooled condensing units on top of the box. I usually just use R-134A with box temps 0-10C.

Now I have a -20C R-404a walk-in cooler with the remote ACCU down stairs 3 stories (~40 feet verticle lift and 40 feet horizontal 2-pipe system with electric defrost).

I'm under the impression I need some sub-cooling due to the lift and was wondering if adding an auxillary receiver and sizing the liquid line up from 3/8" to 1/2" would accomplish this without adding a heat exchanger apparatus. I've heard pro & con on heat exchangers whether they be placed at the evaporator or within suction accumulator. The condensor size is fixed by Copeland/Emerson and I'm planning on CJAL-01500 CU(1.5 hp) to meet the load in the 6'X8' box. Hot gas bypass with liquid injection is also planned for off loading in low demand periods.
Finally, I truly believe mechanical refrigeration is one of the greatest inventions of the modern era and a great thank you goes out to REFRIGERATION ENGINEER. Regards, Joe J. Liptow

[mad fridgie]

Hi Liptow, firstly I would not install the hot gas injection (you really do not have low load in this type of application) Room Cntrol by thermostat.
I dedicated liquid sub-cooler (not reciever) is always a good idea. This should be done after the outlet of the present reciever. All you need to do is install a small addional (coil and fan) . You will need to check the design pressure drop, being a liquid it should be quite small.
Do not know your paticular model number, but ensure the compressor has liquid injection (your actual suction superheat may be high)

[liptow]

Hello mad fridgie,
I thought I would get low load when there is no product to pull down, light and elec. devices being off. TXV would choke flow down, no? We do hot gas bypass and liquid injection at compressor to keep it running (sorry, not very green). I will check out finned liquid subcoolers, thanks.
I just thought maybe adding an aux. receiver would allow some sub-cooling because headmaster would only be bypassing hot gas into the first receiver. Also I'd get extra refrigerant for inventory for the 100 foot remote run.

I'm just not use to lifting refrigerant 50 feet or so and want to find simplest solution that taxes system the least.
Thanks again, anyone else?

[Peter_1]

Installing a liquid flooded coil with a fan will only work if the ambient is colder then your liquid.
Which is almost impossible because you condense with the ambient I suppose.

If you do it to be sure you have pure liquid at the inlet of your TEV, then let run the liquid line first some feet in the freezer (or bend some copper of he liquid line in front of the fan) and go then to your TEV.

Otherwise an in line HE but this will be possible not enough.

An additional receiver will not do anything to add subcooling. It's just the opposite which will happen, you're adding additional resistance into the liquid line and you will decrease subcooling.

Is it anyhow necessary? If you start with enough SC, then you don't need any additional SC.

As Madfridgie said, the hotgas bypass is something you have to avoid. When will you have low demand periods? The air blowing over the coil will always be something within some °F of your setpoint. The cooling will start when you go warmer than +/- 3°F of you setpoint and stops on the setpoint. The only thing which will happen is that the unit will run longer. That's all.

Just a general remark: you want to increase somehow the performance of your system - which is positive - with increasing SC and on the other hand, you loose it all again and even more with your HG bypass.

[Magoo]

The problem with long pipe runs and elbows etc., add vertical height separation is the combined pressure drop between the condensing unit and the TX vav, double check losses and find loss figure, with 404a I have found that I need to keep condensing temp at +40 'C .
A quick check is to install a sight glass before TX vav, any more than +5 'C pressure drop loss will create flash gas in liquid line reducing evap performance and create TX vav hunting.

[mad fridgie]

You have to be careful that the liquid is actually sub-cooled (I offer a different opion to most on this, but thats another subject) Without knowing your plant, I will take some guesses, I presume that your condensor is sized for about 15C (24F) TD, then if you get 5C sub-cooling or presure drop equivilent, then with a flooded coil and fan you have got the potential of 10C further sub-cooling (practically impossible) but you should with out any problem get 6C.
I would not use a straight for liquid line heat exchanger as this will increase your suction superheat, how ever if you install one directly after the evap outlet and have TEV bulb after the heat exchanger, then you will condense any flash gas in the liquid line whilst increasing the performance of the evap.
Remember the load is in the air (as far as the evap) no the product.
As far as reciever capacity, are you controlling as a pump down, if so you need to calculate the system charge, can you existing reciever hold this charge?

[desA]

You have to be careful that the liquid is actually sub-cooled (I offer a different opion to most on this, but thats another subject) Without knowing your plant, I will take some guesses, I presume that your condensor is sized for about 15C (24F) TD, then if you get 5C sub-cooling or presure drop equivilent, then with a flooded coil and fan you have got the potential of 10C further sub-cooling (practically impossible) but you should with out any problem get 6C.

MF, I know you raised this sub-cooling issue on another thread, but I'd like to ask you to explain your logic regarding achievable sub-cooling - in line with the current OP's question.

Why is 10'C further sub-cooling 'practically impossible'?

[mad fridgie]

MF, I know you raised this sub-cooling issue on another thread, but I'd like to ask you to explain your logic regarding achievable sub-cooling - in line with the current OP's question.

Mad Fridgie Response!!!!!!!!!!!!!!!!!!!!!!!
Ok (air cooled condensing units) we take the compressor outlet pressure (SCT or Ct) we measure the liquid temperature, so for example SCT is 45C liquid out of the reciever is 40C, so industry says we have 5C sub-cooling, but I have undertaken many experiments, we have 40C liquid temp, but the actual pressure is not the original 45C but somewhat lower, closer to the 40C. So in this paticular application, were liquid line pressure drop is likely to be excessive, genuine sub-cooling is needed, plus correct correct pressure is need for sizing of the TXV


Why is 10'C further sub-cooling 'practically impossible'?

MF!!!!!!!!!!!!!!!!!!!!!!!!!!
If the refrigerant is 10C warmer than the ambient, then cooling the refrigerant by 10C with the ambient, becomes nearly impossible (needs to be counter flow and have infinate thermal length)

[desA]

Thank 'mad fridgie'. Understood on both counts.

Why does the line pressure drop towards the 40'C, instead of the 45'C - in your estimation? Something to do with vapour-liquid equilibrium?

[mad fridgie]

I supose in simple terms, air cooled condensing circuits can be quite long, so pressure drop must occur. I have never really looked into the specifics of the condensor design (I just purchase of the shelf and apply using manufactures data) I have only given my opion based upon observation.

[lowcool]

proper pipe sizing and liquid temp control should do the trick

[Peter_1]

What do you mean with liquid temperature control?

[lowcool]

sorry peter.maintaining head pressures within spec

[liptow]

All,
The remote ACCU is down in 3rd basement level and evap is in 1st basement level. The air down there will be cool like 60-70F all the time. Condensor will have a Sporlan head master rated for 210psi/1450kPa on the r404 system. My thinking, by adding an auxilary receiver just down from the main receiver, is that the liquid would further cool being away from the introduction of bypassed hot gas. The Emerson 1 1/2 HP unit rating at 90F/32C ambient air is:

evap temp cap cond temp psi temp dif
-15f 7.5kbtuh 110f 271psi 20f

Thanks for sticking with me fellas.
ps- I believe Emerson has higher psi headmasters

[liptow]

1.5 hp copeland r404 accu in 90 ambient air

evap temp -15f /-26c
cap 7.5kbtuh / 2200w
cond temp 110f /43c
psi 271psi/ 1870kPa
temp dif 20f / 7c

[Magoo]

Did you install a sight glass before the TX valve. It will tell all and everything.

[lowcool]

you would have to have more temp loss over that distance than an extra bizzo.insulate the liquid line to keep refrig in spec especially if its a cooler area,fit a suction/liquid line heat exchanger at the coil if your concerned about losses at the valve,this way can also lessen liquid droplets in the suction line when working with narrow superheats.
correct system design out weighs all the bullpooh
ahh sorry mf i just had a look at other responses

size the bloody pipe right!1/2" all the way sounds dodgy to me

[mad fridgie]

you would have to have more temp loss over that distance than an extra bizzo.insulate the liquid line to keep refrig in spec especially if its a cooler area,fit a suction/liquid line heat exchanger at the coil if your concerned about losses at the valve,this way can also lessen liquid droplets in the suction line when working with narrow superheats.
correct system design out weighs all the bullpooh
ahh sorry mf i just had a look at other responses

size the bloody pipe right!1/2" all the way sounds dodgy to me

Why would you insulate the liquid line if a cooler area. If it is colder you get increased sub-cooling which is GOOD, and less chance of flash gas occurring. Perhaps all you have ever worked on is AC where the Expansion device is in the outdoor unit, in this case you insulate the liquid line (as is a low pressure and temp) or you insulate the liquid line if the area is warmer than the liquid exiting the reciever.
I think you need to go back to school and learn the basics.
I can agree good design sorts out all problems, "What is good design" especially when you are purchasing an off the shelf unit which is not specific to any application.
But I could be wrong!!!, "sub-cooling is bad, liquid flash gas is good, you believe this to be the case" Then prove to use all, I will soon change my mind if you can. look forward to you theory lowcool?

[liptow]

Hey guys,
Don't want to cause a virtual fight.....Oh what the hey, let 'em have it!

Here is my thinking to get some sub-cooling (so as not to flash) when pumping r-404 up 40 feet and over 40 feet.

Even though 1 HP would work I'm going to 1.5 HP with a little bigger condenser....I'm going to use a HeadMaster to keep condensing pressure at 210psi by bypassing hotgas into the first receiver.....a second receiver also placed in the incoming air stream would help deal with liquid inventory in the system and allow the liquid to maybe almost cool to the ambient which would be around 75F......finally, I might run the last leg of the liquid line in back of the evaporator and expose about 5' of 3/8" line to the box temp of -20C.
40' of rise is about 17 psi and misc pressure drops could put the total at around 20-22psi......also, Emerson doesn't publish this fact but they do make a r-404 headmaster with a 225 psi control point.......If I can afford the loss in NRE, wouldn't the higher pressure headmaster insure greater subcooling???????????? Any others want to weigh in or fight it out? Thanks, Joe.

[lowcool]

whatever you reckon mf lol lol

you idiot

[mad fridgie]

whatever you reckon mf lol lol

you idiot

Come on lowcool, I would expect a better insult from across the ditch than this!!!!!!! LOL

[lowcool]

cheers buddy
was gonna say something about lanolin poisoning but got over it pretty quick.have a good weekend mf and everyone else for that matter
cheers