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Replace air conditioner first or last?

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1 hour ago, 3STTW said:

The inverter part of the equation is about the cost of running the fan in the head unit, old AC’s used to run until the thermostat told them to stop - and start again when it got hot again. This is extremely inefficient because hot air rises and the thermostat is high up in the head unit. Plus they had clunky old motors which were expansive to run.

 

The inverter is an electronic method of running the fan on a tiny amount of electricity so that it can keep circulating the air (even when the condenser is not running) and diminishes the effect of hot air rising. 
 

They have also replaced the old thermostats with PID temperature sensors. PID (proportional integral derivative) electronics is much better at controlling temperature than an on/off thermostat because they monitor the rate of change and anticipate the target temperature.

 

Therefore the ultimate cost saving is significant due to the maximised efficiency.

 

If you get quoted high prices for replacement electronics, get online - the reputable dealers make these by the 100k’s so they should never be more than $100. Unless the boards get wet or get zapped by the electricity supply, they should be good for 20 years+.

 

In our last house we replaced the living room AC with a ‘dual inverter’ unit, we overestimated the BTU requirement and It dropped the electricity bill by 30%.

The compressor in the outdoor unit is the power hungry device not the fans. The compressor compresses the refrigerant and pumps it to the indoor unit where it reaches the evaporator (radiator) where the refrigerant "flashes" off in the and, due to the laws of thermodynamics, cools the air passing through the evaporator which is provided by the fan. The heated refrigerant is returned to the outdoor unit where it passes through the condenser (another radiator) and another fan blows air over the condenser and removes the heat removed from the room and the cycle is repeated.

 

Old style ACs the compressor cuts in and out as you mention. The inverter type has the electronics to change the speed of the compressor and thus the refrigeration cycle keeping a more constant temperature control. If the AC unit is undersized and the compressor runs at full speed and thus does not save power. A 2 horsepower compressor uses the same power in an inverter or non inverter if running at full speed. An inverter does not magically produce power.

 

The earlier inverter electronic boards were very susceptible to vermin such as mice and ghekos. They would run on the boards and short them out. That has been pretty well overcome now.

 

Another downside to an inverter type is heat. Electronicsare susceptible to heat and there is enough "smarts" built into the ACs to prevent damage to the components from excess heat. This is done by de-rating the output of the AC which defeats its purpose on a very hot day. It is especially important with inverters to shade the outdoor unit if possible especially if the unit does not have much excess capacity as required by the area cooled.

 

 

 

 

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4 hours ago, 3STTW said:

The inverter part of the equation is about the cost of running the fan in the head unit, old AC’s used to run until the thermostat told them to stop - and start again when it got hot again. This is extremely inefficient because hot air rises and the thermostat is high up in the head unit. Plus they had clunky old motors which were expansive to run.

 

The inverter is an electronic method of running the fan on a tiny amount of electricity so that it can keep circulating the air (even when the condenser is not running) and diminishes the effect of hot air rising. 
 

They have also replaced the old thermostats with PID temperature sensors. PID (proportional integral derivative) electronics is much better at controlling temperature than an on/off thermostat because they monitor the rate of change and anticipate the target temperature.

The indoor fan motor of my non inverter office AC is far from clunky and has smart electronic speed control. The ambient temperature sensor is constantly monitored by a microprocessor which appears to be quite good at working with the rising thermals.

 

Non inverter AC's also use PID control to help hold the set point. Duty cycle is used instead of proportional control of the output.

 

It is of course possible to make savings by installing inverter controlled AC's especially if they replace conventional units that have become very inefficient. 

 

A few moons back we moved the office inverter AC to another location and replaced it with a conventional unit of same capacity. The difference in energy consumption is not worth screaming about even though the capacity is slightly above what is required and perfect for proportional control.

 

The guys at our electronics bench repair AC and refrigerator inverter controls as a side line to make extra cash. Many of the failures are from installers not grounding the inverter board and unwanted guests in the outdoor enclosure.
 

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Posted (edited)
On 6/3/2020 at 7:02 AM, OneMoreFarang said:

Is the current air-conditioner in the perfect position? Would the new one be in another location?

I am renting. I had a new air-con installed in another position, a lot nearer to the compressor outside. Now my electricity bill is less than half. I don't know how much is about the new inverter technology and how much about the position. But the air-con technician told me since years that long lines make is less efficient. 

In the pipes is only gas. The cooling happens at the inside unit where the compressed gas gets decompressed. There is a minimum and maximum length for the pipes in the specifications. Too short is not good too. 

 

 

 

Edited by Oldie

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Posted (edited)
4 hours ago, Oldie said:

In the pipes is only gas. The cooling happens at the inside unit where the compressed gas gets decompressed. There is a minimum and maximum length for the pipes in the specifications. Too short is not good too. 

 

 

 

Home slit type ACs are supplied with sufficient refrigerant to use around 3 to 5 metres of piping. The instructions nearly always gives a table (see attached for a Daiken unit) on how much extra refrigerant of the same class, eg R22 or R410A, etc per extra metre of pipe run. I haven't seen where to remove refrigerant for short runs so I think the design caters for that. The minimum length is usually to prevent noise/vibration travelling to from the outdoor unit to the indoor unit. Having said that too much refrigerant will cause pressure problems. I had that issue with a reverse cycle AC back home in Oz. I added a bit too much refrigerant and it kept tripping out on pressure in the heating mode.

 

NOTE: piping distance is measured as a pair of pipes (supply and return) not total pipe length, ie a 3 meter run is classed as 3 meters not 6 meters as there is 6 meters pipe.

 

Screen Shot 2020-06-05 at 8.29.47 am.png

Edited by Dazinoz
Extra info.
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I would use the old AC until the renovation is almost complete. Then I would pull it out, patch and paint and then have the new one installed.

 

I did this in my home. Had the new AC unit quoted, completed the renovation using the old AC, had the AC guy pull the old unit, patched and painted, had the AC guy come back and install the new unit.

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