Condenser capacity

[reggie]

Sporlan where are u?


Ive just repaired a condenser coil on a Mitsi which had a leak on the ends due to rubbing on the metal holding plate. Anyhow due to it being a pain i crimped and isolated that part of the coil.
Theres a distributor that has 6 pipes which feed from each section of the coil and feed the liquid line before going through an accurator to the evaporator.
How much condenser capacity will i lose will it be 16%? and what difference will it make to the head pressure.
Also is it true that Japanese equipment is designed to run at higher head pressures due to the difference in ambient design.

[herefishy]

16% loss in condenser capacity seems pretty hefty to me. for every 10degF in ambient temperature you lose/gain 6% of capacity, by rule of thumb. With 16% loss in condenser coil area, you theoretically could have increased the condensing temperature 20 degrees.

Would anyone agree with that? Maybe the loss in capacity is not proportional due to the increase in rate of heat transfer due to a higher TD.

A better repair would be to find the next pass that circuits in the same direction as the pass being abandoned, and pipe around the affected area.

If the equipment is not under warranty, under which the condenser coil would be replaced, perhaps this failure is an indication of "the beginning of the end" of the equipment, and replacement would be best considered.

[superheat]

Heat transfer is area times DT. 16% loss in area would give a 16% rise in DT. Then I would round up. I would guess a 30* DT would now be a 35* - 40* DT.
(I guess DT should really be LMT difference.)

I do not think the DT would be nearly double Fishy.

[herefishy]

HUH???


I didn't say anything about DT. I'm talking about TD. I think my point was that the SCT would be 20 degrees higher than before the elimination of 16% of the condenser coil circuit, under similar conditions.

[superheat]

I get DT and TD backwards all the time, so I call the difference in air temp over the coil "split". They will be close to the same number. Sorry about any confusion over this. Gary can tell us the right term for what we are discussing.

A 30* DT/(TD) plus the 20* you assumed due to the lack of condenser space seems a bit high to me. Look at the high SEER AC condensing units. They are up to 50% bigger than 10 SEER. The DT is up to 50% less. That is my reasoning.

[Gary]

The thing to ask yourself is whether you are looking at a single flow as it changes or are you looking at two different flows and comparing them.

If you are measuring the temperature change in the air (a single flow) as it goes through the coil it is a delta-T.

If you are comparing the temperature difference between the refrigerant and the air (two different flows) then it is a TD.

Split = temp change = delta-T aka dT

[herefishy]

On an evaporator, with changing space humidities, we can expect to see, with respect to time, a d-LMTD. That is a "delta Log Mean Temperature Difference"

You can also have a coil to air dTD which is related to the return air temperature change between stat on and off settings (differential).

Okay, so you're associating a "before and after" scenario with the term "Temperature Difference".

Thank you for that A change in the TD. Very impressive

I think the math speaks for itself. However for clarification, are you suggesting that the observation regarding the 16% decrease of the volume of the condenser circuit results in a proportinal loss in the heat exchange, as expressed by your factor of 1.19?

[Dan]

I think the math speaks for itself. However for clarification, are you suggesting that the observation regarding the 16% decrease of the volume of the condenser circuit results in a proportinal loss in the heat exchange, as expressed by your factor of 1.19?

The heat exchange remains the same. the condition for the heat exchange is what changes. I suppose a point could be made that the heat exchange actually increases as a result of the higher discharge pressure and temperature, but then, oh, never mind.

[superheat]

That is what I was thinking Dan. A 2 ton compressor and 2 ton valve would try to give 2 tons of capacity. Since the head pressure would go up, compressor capacity would go down due to an increase in compression ratio. My current guess is a 5 - 10% loss in capacity with lower compressor life due to the higher head.

[frank]

Since the head pressure would go up, compressor capacity would go down due to an increase in compression ratio.

I think you meant to say a decrease in compression ration

Frank

[herefishy]

I don't think so.....

if you have 200/50, ratio = 4......
if you have 250/50, ratio = 5.

The number gets "bigger" (therefore the word increase) and results in.....

....decrease in the volumetric efficiency.

[frank]

if you increase the head pressure, surely on the PH chart the cop decreases and the efficiency of the system comes down

[frank]

Sorry,

Just read the original post and it clicked! must stop reading these threads after a few beers!