additional liquid line cooling

[knighty]

I'm sure I asked this before but can't find the thread :-o

I've had a lot of different opinions from different engineers, some aay what I want to do will work, some say it won't work at all

I'm using truck body freezers as blast freezers (with my own equipment on them)

expanding and adding 7 more

I'm trying to get the best out of what I already have / what I buy

I'm thinking about adding heat exchanges to the liquid lines to chill them using a water chiller

water chiller seams the best option here, good second hand units are quite cheap, I appreciate direct cooling via refrigeration would be better but it would be murder to balance the system out if I have 20 separate systems all running at different loads and temperatures

I have an abundance of solar power, so power use / efficiency isn't as important as it normally is


I thought about this originally for summer time high temperatures, but now I'm wondering if it would be better to run year round

I guess my questions are...

is it worth it?
will it work?
how will it effect system capacity?
should I cool before or after the receiver? - liquid line to evaporator is much simpler, but would pre-receiver be better?

looking at the capacity chard of my condensing units, for example...
https://www.elektronika-sa.com.pl/tc...FD&RID=3&Tab=2
(404a)

will cooling just the liquid line to the evaporator shift me up the capacity chart?

e.g. -20 evap temp
27'C evap/ambient temp is 7.75kw cooling
43'C evap/ambient temp is 5.80kw cooling

almost 2kw difference... will chilling the liquid line increase system capacity like this?

[mbc]

HI

Min. temp for glycol is about -34 c

In indirect system you have less Efficiency than direct system

you can increase condenser capacity by bring condensing temp down ( using water condenser or vapor condenser or other system ) this for changing refrigerant phase from gas to liquid .
Also you should cool liquid line after receiver again ((we call it sub cooling liquid and it increase system efficiency)) this is just cooling liquid in certain pressure .

[knighty]

hi

sorry I don't think I explained well

I meant leavening standard system as it is

then add a heat exchanger to the liquid line and cool it via water chiller/glycol loop

[mbc]

Hi
It is external sub cooling system
It also increase our efficiency in system

[Rob White]

.

In principle you get more efficiency with good sub-cooling.

There are a few points to consider controlling the discharge pressure
to ensure correct pressure difference over the expansion valve is very important.

So if you add extra sub-cooling to your system make sure you control the discharge
pressure with a good controller for fan speed or pressure regulator on the condenser.

If you can control the condensing temperature and pressure and you add extra sub-cooling
it will make the system more efficient but also it will reduce the load onto the compressors
which will hopefully increase their life span.

If the chillers are running from solar power so relatively cheap to do so and if you have good
close control over the discharge pressures then adding extra sub-cooling will help but the
balance is critical. Don't drop the discharge pressure lower than about 10bar above the evaporating
temperature. You need the pressure difference over the valve (about 6 bar minimum) for them
to work correctly.

Rob

.

[Rob White]

.

Have you thought of using the old fashioned heat exchangers that are placed in the liquid and suction lines?

Rob

.

[knighty]

.Don't drop the discharge pressure lower than about 10bar above the evaporating
temperature. You need the pressure difference over the valve (about 6 bar minimum) for them
to work correctly.

Rob.

that's what I was worried about... condensing units don't have any fan control, I can add it, but I'm a bit fan of the keep it simple idea

.Have you thought of using the old fashioned heat exchangers that are placed in the liquid and suction lines?
Rob.

yes... and I'm really keen on that idea... a bit worried about any chance of the water side leaking into the refrigerant side... but as it'll be the liquid line before evap the refrigerant pressure should always be way higher than the water side



the other option is to skip the water idea and add a medium temp condensing unit to each container and have that cooling the liquid lines.... but I'm worried I'll struggle to match the load/capacity up :-o

[Rob White]

that's what I was worried about... condensing units don't have any fan control, I can add it, but I'm a bit fan of the keep it simple idea

It would be more cost efficient to control the discharge pressure / temp with a fan speed controller.
Or you could simply put 2 fans on and cycle one on a pressure switch.

yes... and I'm really keen on that idea... a bit worried about any chance of the water side leaking into the refrigerant side... but as it'll be the liquid line before evap the refrigerant pressure should always be way higher than the water side

The type I mean use the suction gas in the bigger pipe to cool the liquid in the smaller line. Very efficient :-)

the other option is to skip the water idea and add a medium temp condensing unit to each container and have that cooling the liquid lines.... but I'm worried I'll struggle to match the load/capacity up :-o

Back in the day when R22 was liquid subcooled to 2 DegsC we used to cool the liquid line with an expansion device fed from it's own system and the cool gasses used to return down the suction back to the compressor.
Be careful not to cool the liquid too far because if the system shuts down the liquid expands extremely high and causes valves, seals, joints or elbows to rupture with complete loss of gas as a result.
Running an extra unit is expensive a water chiller is proberly the cheapest option as an add on.

Regards
Rob

.

[skarrs71]

Suction/liquid heat exchangers sounds a much less complicated option to me

https://www.thermofrostcryo.co.uk/re...eat-exchangers

Use the suction vapour to add additional subcooling to the liquid line.

[knighty]

I have those on some other systems

I'm under the impression they don't add a lot of system capacity?


I've also been warned / worried about them increasing head pressure/temperature making the system struggle in high ambient tempritures?

[knighty]

thinking of scrapping my chiller water plan and add a medium temp condensing unit instead...

liquid/vapor heat exchangers from here...

https://www.thermofrostcryo.co.uk/re...eat-exchangers

5/8 liquid line (to match freezer systems), 1 3/8 suction line and 3.7kw capacity

mount the 3 heat exchangers vertically in parallel
liquid feeds split from MBP condensing unit into the bottom of each heat exchanger
txv for each one
T suction lines back together out of the top

any ideas/input before I order the parts?


for a moment there I was thinking I could add a liquid/suction heat exchangers to be used in the normal way for each system too, to help keep head pressure up.... but I think that would just over complicate things?

[RANGER1]

thinking of scrapping my chiller water plan and add a medium temp condensing unit instead...

liquid/vapor heat exchangers from here...

https://www.thermofrostcryo.co.uk/re...eat-exchangers

5/8 liquid line (to match freezer systems), 1 3/8 suction line and 3.7kw capacity

mount the 3 heat exchangers vertically in parallel
liquid feeds split from MBP condensing unit into the bottom of each heat exchanger
txv for each one
T suction lines back together out of the top

any ideas/input before I order the parts?


for a moment there I was thinking I could add a liquid/suction heat exchangers to be used in the normal way for each system too, to help keep head pressure up.... but I think that would just over complicate things?

Knighty,
If you install a suction/liquid heat exchanger it will do nothing to increase cooling capacity.
I think more advice needed before you purchase parts

[knighty]

a suction liquid heat exchanger... but cooling the suction side from a separate system?

[RANGER1]

a suction liquid heat exchanger... but cooling the suction side from a separate system?

Okay, sorry, missed that bit, but think you will not be able to control superheat because circuit to short.
Also not enough time to subcool much.
Normally use a PHE.
If you could say 1 deg C is 1% increase in efficiency, how many degrees of sub cooling would you need
10,20,30,40 deg C
On industrial plant 40 deg C not out of the question.
If to cold on a pull down & you had a lot of sub cooling, might flood back, or not control!

[knighty]

ah, that's a good point

if I swap to phe - is there any down side to oversizing them?

normally I wouldn't want to oversise an evaporator, but with a phe there's no worry about frosting etc. ?

there's no distributor on the txv etc. so it'll be a simple case of mount them vertically, liquid in at the bottom gas out at the top?

I guess I should add a evaporating pressure regulator(s) to prevent flooding the compressor - with 3 TXVs and 3 phe, will one valve for the system do or do I need 3, one for each phe?).... maybe a suction acumilator would be a better option?