Mass Flow Rate with Big Condenser

[US Iceman]

What is the difference between upwards and downwards?

You must be kidding? Up means up and down means down. (sorry, couldn't resist)

The difference is what you call a liquid seal. If you drain downwards the liquid may not stay in the condenser to achieve any subcooling.

If you provide a liquid seal, the liquid has a place to collect so that it can subcool.

Condenser manufacturers handle this differently in their designs.

[david2008]

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You must be kidding? Up means up and down means down. (sorry, couldn't resist)

The difference is what you call a liquid seal. If you drain downwards the liquid may not stay in the condenser to achieve any subcooling.

If you provide a liquid seal, the liquid has a place to collect so that it can subcool.

Condenser manufacturers handle this differently in their designs.

Thank you.

[wambat]

A bigger condenser could have all of the following positive effects on a refrigeration system because it would have a lower condensing temperature.
1. A better refrigeration effect
2. A lower mass flow rate
3. A lower volume flow rate
4. A higher COP
5. A lower condenser heat of rejection
6. A lower condenser temp difference
7. A lower condenser split
8. A lower KW/ton
9. higher efficiency and a happy compressor and it's components

[jwasir]

A bigger condenser could have all of the following positive effects on a refrigeration system because it would have a lower condensing temperature.
1. A better refrigeration effect
2. A lower mass flow rate
3. A lower volume flow rate
4. A higher COP
5. A lower condenser heat of rejection
6. A lower condenser temp difference
7. A lower condenser split
8. A lower KW/ton
9. higher efficiency and a happy compressor and it's components

If Bigger Cond is a WIN-Win situation, then why we dont design all the systems with BIGGER cond.

The initial cost will be high but system efficieny, COP, etc will increase drastically.

There must be some disadvantages......

[US Iceman]

...off they immediately start hunting.

Hhhmmm, usually hunting only occurs when the components are not balanced or going through some severe/strange transients.

If the equipment is balanced at 60Hz, the same should be expected at 50Hz with the only exception being the rated duty should be compensated for to achieve the desired results while operating at 50 Hz.

[US Iceman]

You need indeed a certain minimum Dp over the TEV but 4 bar is also given by Danfoss themselves.
And we have the proof it works (even 3.5 bar)
Look ones in the Danfoss tables and you will see that the capacity doesn't decrease that much with decreasing pressures.
You say that SC increases during winter which is true but this increases also the capacity of the TEV and compensates a little for the lower DP.
In theory, you can only have full liquid after the valve if you SC liquid to evaporating temperature.
But I think this won't give any problem.

These comments offer so much information that you do not typically learn in school. It would be well worth the time of other members to try to understand what Peter is describing and how it applies to refrigeration systems.

Refrigeration systems do NOT have to have high discharge pressures to work.

The only time you should see higher discharge pressures on air-cooled condensers (or evaporative condensers) is in the summer time (or during the hottest temperatures of you location).

[US Iceman]

There must be some disadvantages......

Well, there could be if the system is not designed to work under the lower discharge pressures. The refrigerant charge may increase a little, but the biggest problem is the additional cost of the condenser heat rejection capacity.

From my experience... the smallest condensers are used so that the installing contractor can have the lowest price.

[GXMPLX]

Hhhmmm, usually hunting only occurs when the components are not balanced or going through some severe/strange transients.

Not necessarily. You get TEV instability if the valve tries to operate below a curve called MSS (Minimum Stable Superheat) that graphs capacity versus valve superheat. By increasing subcooling you are moving this curve to higher superheat and will produce instability more often with TEVs that have fast acting charges.

TEV stability problems are the ones I find less understood in these posts, not an easy subject that needs some drawings and I'll post something on this when I'm ready.

If the equipment is balanced at 60Hz, the same should be expected at 50Hz with the only exception being the rated duty should be compensated for to achieve the desired results while operating at 50 Hz.

Though the equipment remains in balance due to the fact that TEV works fine at 20% off nominal capacity, the compressor capacity is 20%less.

The evaporator and condenser are different because it depends if the manufacturer changed blade´s attack angle to compensate for lower RPMs or not.

The problem arises when you have low thermal loads the system becomes completely unstable and out of balance. The TEV is oversized and perform VERY poorly if thermal load drops 20% to 30% below the 50Hz value! Except for balanced port valves or absorber charges, that can control well as low as 20% off their rated capacity.

This is worse in some equipment that already had the TEV oversized for the 60Hz capacity (It was correctly chosen but a little oversized).

[wambat]

If Bigger Cond is a WIN-Win situation, then why we dont design all the systems with BIGGER cond.

The initial cost will be high but system efficieny, COP, etc will increase drastically.

There must be some disadvantages......

They do make bigger condensers that is why the SEeR is going up every year, 15 years ago the seer was about 8 now it's 18 /19

[GXMPLX]

If Bigger Cond is a WIN-Win situation, then why we dont design all the systems with BIGGER cond.

Cost is a BIG disadvantage.

The initial cost will be high but system efficieny, COP, etc will increase drastically.

There must be some disadvantages......

No! Some compressor are optimized for high condensing other for low condensing, if you use the wrong compressor with a large condenser you will get less COP.

Consider that with this line of thought all condensers should be water cooled! Go ask Chemi_cool if this is possible!

Every application has some optimizing to be done. Little larger condensers ok, too large will cause problems and probably lower system COP.

[Peter_1]

[The difference is what you call a liquid seal. If you drain downwards the liquid may not stay in the condenser to achieve any subcooling.

Indeed, that's the correct expression, liquid seal

We had - perhaps 20 years ago - some condensing units running (Copeland with hermetic piston DCRQ's running), evaporating at 5°C.
The compressor could handle this perfectly but the condensers were ways too small. So we installed in line a second condenser and this decreased HP almost nothing. Only if we placed one in parallel, then it resulted in a serious HP decrease.
In line, what we made was a huge subcooler which didn't increase the condenser area, so HP remained almost unchanged.