Quote:
Originally Posted by MEMPHIS91
Jeff, I am simply shooting for 12-15 subcooling temps. More than that I have no clue.
My best research says low subcooling (less than 12-15F) is a staved condenser and I am not keeping the condenser as full of liquid as I could be, therefore loosing efficiency. High subcooling (more than 12-15F) is a flooded condenser and I am just wasting power like you said.
As long as I am in the 12-15 range I should be as close to a correct charge as possible right?
I am not taking the gas temputure in, and am taking the pressure reading and convert to the saturation temp.
Or am I still WAY off on this whole idea?
I check out your thread.
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Ok, this conversation is quickly moving in the right direction. Your level of knowledge has progressed to the point where you can make accurate, measurable snapshots of what is happening inside the system, as it is happening. You have your system pretty closely charged to your assumed "normal" design conditions. If you were a fridgie tech setting up a factory unit to prescribed specs, you could simply tell the owner the unit is set up and working like it should. If the owner doubted your statement, you could point to gauges and verify values to something printed in a manual somewhere to prove it. You could be happily on your way to the next stop on your schedule.
This is not the situation at all. You have a system that is completely custom, with no factory specs to obey. This rig would be considered "abnormal" or "downright strange" by pro service techs in general. Without regard to the hydrocarbon refrigerant (you could lie and tell them it was filled with R22), none of them would want to lay a hand on it for any amount of money, at least not while they were on the clock. Knowing the unit was filled with propane, the daring techs would then not want to touch it, even on their own time. Its existence stands against their factory-taught premise for earning a decent living. To them, there is a righteous place in hell for people like us. The powers that be are not far behind in their positions on this subject.
Now that you know where you and your system stand, the time has come for you to leave the realm of the factory service manual and its limitations. For example, a 10 SEER air handler condenser, properly sized to the compressor and evap exchanger, would have 15 degrees of subcooling at a certain point on a chart in a manual, flowing a certain cfm, at a certain return air temperature, and you should see a certain pressure in the condenser. Changing any of these design conditions would put you at a different place in the chart, and interpreting this shift would give you a clue where to look in the system to find out how to eliminate the shift, for better or worse.
Looking at what you did this week, your system changes reflected this defined approach:
@210 psig, 97.7 degF condenser; 75 psig, 62.2 degF evaporator conditions:
5 degF subcool, 19 degF superheat, ? amps, ?btu/hr
Adding charge, the balance has now shifted to:
@250 psig, 103 degF condenser; 80 psig, 63 degF evaporator:
15 degF subcool, 23 degF superheat, ? amps, ?btu/hr
Since the dP across the compressor increased from 135 psi to 170 psi, we can assume the amp draw also increased. Since the superheat has risen, we can assume the txv is limiting maximum suction pressure. The added superheat is leading to additional de-superheating in the condenser, and its exit (liquid line) temperature is following this upward trend, indicating reduced effectiveness of the condenser. The extra superheat is being wasted as a rise in the liquid line temperature.
Whether or not any charge was added/recovered, the system found another balance point later:
@226 psig, 93 degF condenser; 78 psig, 64.3 degF evaporator:
17 degF subcool, 18 degF superheat, ? amps, ?btu/hr
The dP across the compressor has dropped from 170 to 150 psi, so we can assume the amp draw has decreased. The subcooling did not drop, so the liquid is exiting the condenser at a lower temperature, indicating a more effective condenser and less heating capacity being wasted.
Do you follow this analysis? Over the course of these readings, your evaporating pressure and temperature didn't change enough to count, which means the txv is doing a good job, and that your evaporator isn't working very hard. If your water tank was around 60 or 65 degF, your condenser is doing the best it can at trying to digest the hot gas you are feeding it. The condensing saturation temperature has risen and fallen from 105 to 118 to 111 degF, while the liquid line temperature changed from 97.7 to 103 to 93 degF. Assuming your tank temperature did not change significantly between readings, it seems to have been moving the most heat during the last reading.