Air Conditioning

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27th September 2016, 03:38 PM
rrich

Air Conditioning

I know that your Air Conditioning or Refrigeration season is about to start. I also know that our electricity distribution is a bit different than your. As I understand it, yours goes from the hot lead to neutral or ground for all residential amperages. Ours uses the center tap of a transformer for neutral or ground. High wattage appliances pull the current from across the transformer while small appliances pull the current from one side of the transformer (or phase) to neutral. Our phases are 0° and 180° and not to be confused with three phase distribution which is industrial.

Long story, short version is that I reduced the current draw of our Air Conditioner by 15% by cleaning the heat exchanger coils with a garden hose. See excruciating details below.

The A/C guy was out for a variety of reasons. One of the things that he did was to put an inductive ampere meter on one of the 230 volt phases. While the A/C was running it showed about 20.4 amperes. Not too big of a surprise as the A/C is on 40 ampere breakers in series with 35 ampere fuses. (It's code. Don't ask me why.)

Then we cleaned the heat exchanger by spraying it with the hose. Nothing drastic, just a gentle spray. The A/C unit has been installed for about 10 years and this was the first cleaning. After about 5 minutes we restarted the A/C. The ampere meter was still attached. Initially the reading on the ampere meter was about 16.4 and rose to 17.3 after 5 minutes of running.

Most of you are saying something like BFD or SO right now. Well just by cleaning the heat exchanger we are using 15% less electricity. The A/C guy said to clean the heat exchanger at the beginning of summer and just about the start of fall. Our really hot season is just starting and should continue through most of October.

If your cooling causes a rise in the electricity bill by $100 then cleaning the heat exchanger could save you $15 monthly.
27th September 2016, 05:03 PM
Bohdan

I'm sorry but your version of the drop in current flow to you AC doesn't follow the rules of physics.

The AC is powered by a compressor which runs at a relatively constant load and therefore fixed current. The coolling is achieved by dumping the heat in the gas at the exchanger and cleaning it will not reduce the current but it will reduce the length of time that it runs for to achieve the desired temperature drop. This will save you money with a shorter duty cycle.

Cleaning the heat exchanger will in fact increase the air flow and that will increase the current draw but this will result in faster cooling.

Your conclusion that cleaning the heat exchanger will save you money is correct albeit for the wrong reason.

The cause of the current drop in the wiring is a mystery but it is definitely not due to cleaning the coil.
27th September 2016, 06:55 PM
q9

Quote:

Originally Posted by Bohdan

I'm sorry but your version of the drop in current flow to you AC doesn't follow the rules of physics.

Unless it is one of the inverter systems where the motor runs more or less constantly but with varied speed...
28th September 2016, 04:03 PM
rrich

Quote:

Originally Posted by Bohdan

I'm sorry but your version of the drop in current flow to you AC doesn't follow the rules of physics.

The AC is powered by a compressor which runs at a relatively constant load and therefore fixed current. The coolling is achieved by dumping the heat in the gas at the exchanger and cleaning it will not reduce the current but it will reduce the length of time that it runs for to achieve the desired temperature drop. This will save you money with a shorter duty cycle.

Cleaning the heat exchanger will in fact increase the air flow and that will increase the current draw but this will result in faster cooling.

Your conclusion that cleaning the heat exchanger will save you money is correct albeit for the wrong reason.

The cause of the current drop in the wiring is a mystery but it is definitely not due to cleaning the coil.

I'm sure you're correct. I can only report what I saw.

My theory is that by more efficiently removing the heat. the compressor was reducing less gas to a liquid state.

I guess we file this one under another great mystery of life.
28th September 2016, 09:18 PM
Pearo

Quote:

Originally Posted by Bohdan

I'm sorry but your version of the drop in current flow to you AC doesn't follow the rules of physics.

The AC is powered by a compressor which runs at a relatively constant load and therefore fixed current. The coolling is achieved by dumping the heat in the gas at the exchanger and cleaning it will not reduce the current but it will reduce the length of time that it runs for to achieve the desired temperature drop. This will save you money with a shorter duty cycle.

Cleaning the heat exchanger will in fact increase the air flow and that will increase the current draw but this will result in faster cooling.

Your conclusion that cleaning the heat exchanger will save you money is correct albeit for the wrong reason.

The cause of the current drop in the wiring is a mystery but it is definitely not due to cleaning the coil.

I dont think this is quite right, but I will fess up here and say that I am falling back on common core engineering stuff from uni.

A dirty condenser means a higher temp difference. higher temp difference means increase gas pressure, increase pressure means motor works harder.

Might I also add, I though this is why aircon compressors are always supposed to be located where they get good airflow as it increases efficiency.
29th September 2016, 09:54 PM
Chief Tiff

Quote:

Originally Posted by Bohdan

I'm sorry but your version of the drop in current flow to you AC doesn't follow the rules of physics.

The AC is powered by a compressor which runs at a relatively constant load and therefore fixed current.

Sorry Bohdan; but your source of information regarding how compression refrigeration systems operate is incorrect. The motor load is governed by the gas pressure required to condense the gas into a liquid, this pressure is directly related to the temperature of the cooling medium across the condenser and its efficiency. From memory the standard designed temperature differential for a fan cooled condenser is about 14 degrees K, if it is dirty that differential effectively rises meaning that the gas pressure has to rise higher to reach the vapour condensing point. Obviously this load will also increase as the ambient air temperature rises.

Having a clean condenser reduces the running load of the motor by lowering the compressor discharge pressure, additionally the whole process becomes more efficient as the liquid refrigerant is now at a lower temperature before it enters the expansion phase in the evaporator.

Rrich's advice and the reasoning behind it is sound; one addition I would add is to use a PH-neutral surfactant coil cleaner. This is available from most engineering suppliers such as Blackwoods, or dedicated refrigeration suppliers like Actrol.

Lastly; this also applies to refrigerators. The older style convection coils at the back need to be kept clean and have adequate airflow, more modern fridges use fans but again the air intakes must be kept clean.
30th September 2016, 02:07 PM
rob streeper

I've been told by a friend who teaches AC that cleaning the coils with water is something that should be done regularly. The other day the cat got a bird and some of the down ended up in our mini-split coils.