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dormy
31-12-2004, 01:18 AM
With regards to a flooded coil system. Now, I know that this way is more efficient than dx systems, and that it reletivly more expensive to install. But, thats about as much as I know on this subject...ok- here comes the question... would any of you guy`s be so kind as to explain to me (in plain english!!), exactly how a flooded coil system actually works???

Superheatman
31-12-2004, 05:52 PM
Hi..by flooded coil do you mean flooded evaporator ...are you talking about a chiller??

shogun7
31-12-2004, 10:37 PM
With regards to a flooded coil system. Now, I know that this way is more efficient than dx systems, and that it reletivly more expensive to install. But, thats about as much as I know on this subject...ok- here comes the question... would any of you guy`s be so kind as to explain to me (in plain english!!), exactly how a flooded coil system actually works???

Many large tonnage centrifugal chillers use a flooded type evaporator, which is very energy efficient and
these flooded evaporators have the chilled water in the tubes and the refrigerant in the shell. Some large chillers can have over five miles of tubing in their heat exchangers. For a full explanition go here:http://www.mcquay.com/mcquaybiz/literature/lit_corporate/AppGuide/AG_31_002.pdf

Abe
31-12-2004, 10:51 PM
Thanks Shogun, thats a very useful article / link you posted.

RogGoetsch
01-01-2005, 12:30 AM
With regards to a flooded coil system. Now, I know that this way is more efficient than dx systems, and that it reletivly more expensive to install. But, thats about as much as I know on this subject...ok- here comes the question... would any of you guy`s be so kind as to explain to me (in plain english!!), exactly how a flooded coil system actually works???
I'll give it a shot, with the disclaimer that other than school, my only experience with flooded evaps is as a sales engineer with 3-1 liquid overfeed ammonia systems. Mark C. may be a better source since he has designed those babies from his first day out of school.

In the evaporator, the difference between flooded and DX (direct expansion) is that the evaporator interior surface is completely in contact with liquid refrigerant, if flooded, but only partially with DX. This means the evaporator is more efficient, not the system.

Liquid overfeed means a liquid refrigerant pump deliver 3x as much liquid refrigerant as the load requires. This improves heat transfer in the evaporator by dislodging vapor bubbles from the evaporator surface as they form, allowing more liquid contact. This also assures oil return to the separator vessel and extra refrigerant for load extremes.

With ammonia, oil collects on the bottom of the separator vessel and can be removed with a float device. DX became necessary with the invention of CFC's (and perhaps earlier refrigerants?) because the oil floats above the liquid, hence is more difficult to get back to the compressor in flooded systems.

The main reason for flooded systems to be more efficient is that they can use a simple float to return liquid to the low side of the system, where DX systems require a significant pressure drop across the metering valve (TEV). So on cold days, the flooded system can allow condensing pressures to drop, but DX systems usually require low-ambient controls to artificially maintain high-side pressures.

In the systems I sold, the compressor(s) pumped out of the top of the separator vessel which used a high-side float to return condensed liquid to the vessel as it formed. Liquid refrigerant was pumped out of the bottom of the vessel and fed out to the system. Gas and liquid returned to the vessel.

Another efficiency improvement occurs because with lower average condensing pressures, there is less flash gas for the compressor to pump, and what there is returns to the compressor without being pumped out through the evaporator(s). There is a trade-off here with the liquid pump horsepower for 3-1 overfeed, but I don't recall what it is.

Rog

wesmax
01-01-2005, 05:57 AM
It realy was a good description of how it works but it has its uses so unless you are chilling in a beef killing operation or some place you need to remove a lot of heat very quickly. these coils have a short work time before defrost again it depends on the applaction. what do you want to cool.
wesmax

dormy
02-01-2005, 06:37 PM
thanks everyone.....a particular system at work that i managed to take a quick look at contained a surge tank. Im asumming then, that this is basicly a low pressure receiver????A couple more questions spring to mind
1. Is the liquid subcooled before entering the evap?
2. Is the evaporator pressure regulated by means of an m.e.v or something similar.

dormy
02-01-2005, 07:10 PM
by-the-way - superheat man, i was talking about flooded evaporator coils, but notfluid chillers. (would have replied sooner but my wife insisted we go out and get drunk for the newyear celibrations)!!!!

RogGoetsch
02-01-2005, 08:47 PM
a particular system at work that i managed to take a quick look at contained a surge tank. Im asumming then, that this is basicly a low pressure receiver????
It's probably serving the same purpose as an accumulator in a DX system. If there is no receiver, it is probably fed from a high-side float and serves as a low-pressure receiver as well.



A couple more questions spring to mind
1. Is the liquid subcooled before entering the evap?
2. Is the evaporator pressure regulated by means of an m.e.v or something similar.
1. Depends on the design. If no refrigerant pump is used, high-pressure liquid is probably fed into the evaporator directly, so the amount of subcooling would depend on design and conditions.

If the evap is fed from a low-pressure reservoir, by gravity or pump, the liquid should be near saturation. Since subcooling refers to liquid temp below saturation, then the answer is actually no. But if you are thinking of liquid temperature below condensing temperature, then the answer would be yes.

2. Just as in a DX system, many types of controls can be used, depending on the application. The main difference is in the oil return.

Rog

dormy
02-01-2005, 09:10 PM
another question Rog,.... Are flooded coils exclusive to mediam temp applications or does this type also work well as a freezer too??I have some many questions because the only time ive ever really touched the subject of flooded coils was a long time ago back at college. Since then i never actually came into contact with one untill recently.

Peter_1
02-01-2005, 10:44 PM
If I may Rog....sure, it excists even in freezer applications.
In plants I have seen, the HP form the compressors goes straight in the LP vessel. A compound set-up, is this correct?

The instalaltions i've seen had a only a SV for the liquid feed but pressure regulations valve to control defrost.

You can see it also simplified as a big heating plant with panel radiators: a pump or more pumps are feeding warm water to the different radiators. As soon a room is on the preset etmpertaure, supply is shut off.
You can use pressure regulators to balance the system (those regulators, don't know the name anymore... those you turn in certain rotations for a precalculated DP)

Have also a look at one of our suplpiers - a Dutch company - http://www.wijbenga.nl/nfwittuk.htm where we buy certain components. Many of the info is in English.

and http://www.th-witt.de/englisch/start_en.htm from which we use their pumps via Wijbenga

dormy
06-01-2005, 08:44 PM
Cheers for that Peter. Them sites were interesting reads...

Lc_shi
07-01-2005, 02:08 AM
Hi peter,
It's good websites and products.
How about the q-plate HX compared with alfalaval plate HX?
Have you used the flooded system?

eggs
07-01-2005, 02:51 AM
i am not a technical man, but my understanding of these systems, in the plain english you ask for is!

imagine your toilet at home,
the cistern is the evaporator
the cold water(refrigerant) in that cistern is absorbing heat from the room
even when the toilet is not being flushed, it is absorbing heat, hence the ecconomy of these systems.
eventually some of the water will evaporate as it comes up to room temperature.
You flush the bog (start the compressor), ball**** drops, float needle opens, freash cold water (refrigerant) floods in and the cycle starts again.

i amaze myself sometimes


cheers

eggs

Lc_shi
10-01-2005, 09:43 AM
eggs,
Make sense!
Flooded system can increase the chiller COP for the higher evapration temp with same condensing temp.
It's reasonable to apply for large volume chiller to balance the cost for oil return system adding. No benefit for small ones.
ASHRAE 1998 refrigeration handbook has a good description.