Article in ACHR news- comments please.

This is an extract of an article in the latest ACHR news.
‘…Often a receiver bypass will be used so the subcooled liquid will not sit in the receiver and lose it’s subcooling. This bypass simply bypasses liquid around the receiver and directly to the liquid line and filterdrier. A thermostat with a sensing bulb on the condenser outlet senses liquid temperature coming to the SV. If the liquid is pre-cooled to a predetermined temperature, it will be bypasses around the receiver..”’

My comment on this: ‘Often a bypass will be used…’ I never saw this in my life and read never of it in books. What will happen if the system has long lines and the TEV’s closes partially due to reduced load? The liquid will build up in the condenser.

Second comment: you can’t measure subcooling with only a thermostat. You need at least two thermostats or even better a press-stat and a thermostat.

What do you guys think of this?

Hi Peter,

I don't see what is the point in this bypass, Whats wrong with the liquid staying in the receiver?

I cant see any advantage in the idea apart from the extra cost and another thing that can go wrong.

Did you see in that article any names of users of this system?

Chemi :)

It was written by John Tomczyk, professor HVACR at the Ferris State University, Big Rapids, Mich.

I agree,a another device that can be a reason of faults and till the time you have saved so much energy with it (if it saves anyhow energy :confused: ) that the investment is paid, unit will be a long time on the scrapyard.

He mentioned it when the subcooled liquid is cooler than the receivers surrounding, that some subcooling will be lost. Ever seen an isolated liquid line in a standard refrigeration unit? You lose a lot more along these lines on warm days.

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It was written by John Tomczyk, professor HVACR at the Ferris State University, Big Rapids, Mich.

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How can he be sure to get 100% liquid 100% of the time?
If this system ever works I would bet that it`s got an over sized condensor, which will double up as a receiver, so then your back to square one! :confused:

Just another thought, on small systems up to 8hp, the receiver sits behind the cond so the hot air from the cond hits it. If you want to save energy move the cond. :)

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‘…Often a receiver bypass will be used so the subcooled liquid will not sit in the receiver and lose it’s subcooling.

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Hi Peter
This is a nonsense statement. Any liquid the passes through the saturated change level (vapour to liquid) will eventually increase the sub-cooling as heat is lost. If the liquid continues to stay in the receiver it is going to INCREASE it's sub-cooling as it loses heat ? Do you know of any receivers that increase in temperature?

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It was written by John Tomczyk, professor HVACR at the Ferris State University, Big Rapids, Mich.

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Hi Peter,

Good intentions will not help, I feel a bit sorry for the "professor"
It doesn't seen that he knows what he is talking about.

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the subcooled liquid is cooler than the receiver

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Thats in plain English is bullocks.

Chemi :)

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He mentioned it when the subcooled liquid is cooler than the receivers surrounding, that some subcooling will be lost.

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This is really a true statement Chemi. If you have sub-cooled liquid in the receiver and it's surroundings are warmer then the liquid will absorb that heat and lose sub-cooling.

Although like everyone else I have never seen this idea put into practice or have ever read it anywhere it may not be that bad an idea.

My original understanding of is if you select a condensing temperature, say 40'C the thermostat would then be set to say 36'C then when there was a bit of subcool the refrigerant would be diverted.

If the pressure inlet valve was set to open at a pressure above the condensing pressure if the expansion valve shut down the HP would rise and the valve would open to the receiver. If there was insufficient subcool the solenoid would de-energise raising the HP and opening the inlet regulator.

Obviously by removing the receiver when possible you can maximise the effect of subcool and increase the system capacity reducing the energy consumption.

The parts used are basic (cheap) so the payback time due to the running cost reduction could be relatively low.

David

Peter, see what you think of this scenerio:
The condition as described by the good professor seem to indicate that any condition other then (let us say) 10*F sub-cooling+- a small differential would be directed to the receiver.
For Example: Let us say we develop a short charge this would decrease sub-cooling and close the bypass, this in effect dould force the regulator to openand deliver refrigerant to the receiver, (where else can it go) on the other hand, if we have an over charge, we could have a situation where we have the bypass open and we could also have the pressure regulator feeding the receiver, Interesting, however refrigerant wanting to take the path of least resistance, I believe that the sub-cooled liquid would still be avialible to the TXV. Of course the setting on the pressure regulator is critical for this to work properly so I would set it for a condensing temperature of approxamately 105*F and counting on a sub-cooled temperature of say around 95*F. :)

Let me look at another aspect of this "revolutionary" system.

Lets assume that the receiver is full and the by pass will open,
if the temp in the receiver is higher' then so is the pressure, so the liquid from the receiver will feed theTXV even if the by pass valve is open.

And another thing, when the receiver is out of the game, and lets assume, it is full, there will be lack of refrigerant in the system.

My conclusion is that from any angle that I look, I don't like the idea.

Chemi :)

Me neither

Chemi, If the receiver is full and the temp/pressure is higher the reciever will empty when the bypass opens then the system should stabilize with the inlet valve shut down and the receiver will remain empty. I cannot imagine it happening but if the receiver did empty for whatever reason there would be insufficient subcool to keep the bypass valve open.

It is sort of like the Tyler Enviroguard system that was first introduced around 10 years ago.

If you look at the system why do we need the bypass solenoid, could it not all be controlled via the inlet regulator in a offset receiver setup. If the valves closed and the charge backed into the condenser the HP increases, the regulator opens and the system stabilizes, with a receiver drain line installed to empty the receiver.

I think someone should try it, but obviously someone other than me.

To increase COP of the compressor or decrease absorbed power, you have to apply for a HP as low as possible.

This mean you need a floating HP, related to the ambient temperature. So the subcooling temperature will also float.
You need an intelligent controller to achieve this.

Decreasing the HP is the biggest energy saving you can achieve with a compressor. The 'subcooling gains' with a condensor don't even come close when talking about saving energy.

Did a simulation with a Bitzer:
-10°C/45°C/0K SC --> COP: 2.09
-10°C/45°C/10K SC--> COP: 2.39
-10°C/40°C/0K SC --> COP: 2.44
-10°C/40°C/10K SC --> COP: 2.71

Throw away all those condensrs working with a DT of 15 to 20 K in summer.

Peter,

The Enviroguard system was based on what you detailed, drive the condensing temperature down as close to the ambient as possible. The receiver was offset via a T in the liquid line with a drain line to the suction.

I would agree that low condensing temperatures offer more energy saving features, however based on your original post do you think the system based on the original drawing would work. In my opinion I am sure it would.

David

The answer for low condensing temp is very large condensers with multiple fans.
I am working at the moment on a blast chiller and when it will be finished I will post some pictures.
it should work in crazy conditions, from 0°c in the winter to 42°c in the summer,
I 'm planning of 220 psi HP R-22

Chemi :)

David, it can work with 1 thermostat if you hold the HP pressure on a stable value and not a floating value.
What I often did it in the past was mounting a special subcooling coil in front of the condenser (vertical standing type) or underneath the condenser in case of a horizontal type.
Liquid out of receiver and then via the subcool battery to the TEV.

But it costs somem money and try once to convince a customer that this is better, changing a standard unit and where your competitors are saying that this isn't worth the efforts.

Same for bigger condensers, not easy to convince them to install a condenser with a DT of 8K instead of 15 K.

We installed a few times a plate HE water/***** between compressor and condenser. The water was the main water supply of a small factory. There was always some amount of water flowing, even it was only for the toilets, so the little warming up of the water couldn't harm anything.

The biggest savings we can achieve with compressors are:
lower that HP as low as possible
increase the LP as high as possible
subcool as much as possible.

These are the fundamental thermodynamic nature laws.

We had this winter a pack running for several weeks without any problems which ran on a LP of 4.4 bar and a HP of 8.5 bar (DP of only 4 bar) and 10 K, with TEV's which gave us a COP of 5.5

If we had let it run on the same LP but maintained a stable HP of 40°C like most are doing, the COP should have decreased to 2.9.

This is an enormous difference.

Peter, Just out of curiosity when the pack was operating with a DP of 4 bar what TEV were you using.

The small Danfoss TES2 valves.

"The biggest savings we can achieve with compressors are:
lower that HP as low as possible
increase the LP as high as possible
subcool as much as possible. "

adding " superheat as much as possible" (which help COP improve)

Hi Peter,
Would you pls copy the whole article about it? May we can understand more from the author.thx!

rgds
lichuan :)

While I have not seen the article I can comment on the receiver arrangment in general.

The receiver shown in the diagram is what we here in the USA ammonia industry call a "surge" receiver. Any liquid that does not flow to the system, backs up into the receiver. By the way, we do not use all of the contraptions shown in the drawing!

The normal receiver we see the most of is what I call a "flow-thru" receiver. The difference is the flow-thru receiver has a dip-tube. The surge type does not.

It is true that the surge type will allow any subcooling to remain in the liquid (as long as the liquid is flowing). The saturation temperature of the liquid is usually lower than the ambient dry bulb temp., so heat flows into the liquid. Very normal for ammonia systems using evaporative condensers.

Heat gain into the receiver does reduce the subcooling, and in some cases produces additional flash gas. In large ammonia systems this happens all of the time. This is why an external equalizing line is installed on the larger receivers. One, to equalize the pressure of the receiver, and two, to vent all of the flash gas plus the gas displaced by the incoming liquid from the condensers.

One important thing to consider: if you use the condenser heat transfer surface to subcool, you are stacking liquid up in the condenser (unless it has a separate subcooling coil). This can increase the discharge pressure at the expense of getting liquid subcooling.

Interesting topic.

Cheers.