Should I replace my A/C

[Brian Steele]

Hi Everyone:

I've got a Miller NHX-018 / MDX-01 split system A/C that serves the master bedroom in my house (2,400 cu.ft.). I live in the tropics, and ambient temperature outside during the day can hover around 29~31 degrees celsius for most of the year, except when it's raining. Electricity here costs approximately US$0.33/kWh.

My electricity bills are horrendous. My daily consumption hovers around

39kWh, and most of that seems to be caused by the A/C unit.

Are there more efficient A/C systems available, and will it be worth my while (e.g. payback in 3~5 years) if I swap out the Miller unit for one of those more efficient systems? A bit more about the Miller A/C unit I have can be seen at

but as they don't mention EER or SEER ratings, perhaps it's something they don't want to advertise :-).

Also, is there anything that I can do to increase the efficiency of my current system? I read somewhere that for best efficiency, the compressor unit should not be located where it will hit by direct sunlight - is this correct? The location of my compressor unit can be seen at the following URL:

From 10:30 in the morning to about 4:30 in the afternoon, it's exposed to the sun.

Regards, Brian Steele

[Travis Jordan]

Brian Steele wrote: > they don't mention EER or SEER ratings, perhaps it's something they don't want

SEER = BTU OUTPUT / WATTS INPUT Your system 18,000 / (2190 + 50) = 8.0 SEER.

There are higher SEER systems available but you'd have to do the math to see if they would save enough money over their expected lifetime to pay for themselves.

Research shows that shading of the condenser from direct sunlight doesn't cause significant energy reduction - unless you shade it enough so that you can change the ambient inlet air temperature.

[Stormin Mormon]

From what I read on the web page, sounds like that's about as modern as you'll get. There is a difference of opinion, if it matters that the outdoor unit is in the sun. I believe it does matter.

I'd suggest you call an AC company, and have them dissemble and clean the outdoor unit. Dust and dirt will increase your energy bill. Also check the freon level. Check the filters for the inside unit, make sure there is enough air flow.

[Brian Steele]

Thanks. So it looks like my unit is a fairly low-efficiency one, as they've got units with much higher SEER ratings available at the moment.

Based on some of my meter readings, my current A/C consumes about 15kWh/day at least.

At my current utilitity rates (US$0.33/kWh), that works out to US$4.95 a day, or roughly US$1,800 / year.

Given the SEER definition, for comparison purposes a SEER 13 system with the same BTU rating would likely consume 15*8/13 = 9.2 kWh/day under the same conditions. That works out to US$3.04 / day, or roughly US$1100 / year.

So, I should save about US$700/year or US$3,500 over 5 years if I go with a SEER 13 A/C.

Likewise, if I go with a SEER 16 system, I should save about US$4,500 over 5 years if I go with a SEER 16 system.

Am I on the right track here?

Great - thanks. This seems to make sense, as the ability of the unit to dissipate heat will depend a lot on the temperature of the heat "sink" (air in this case).

Hmm... maybe I should look into water-cooled A/Cs, LOL. I've got this huge water tank below the house...

Thanks for the feedback, Brian

[Brian Steele]

Hi Christopher:

Have a look at the unit in the picture below:

It's rusting on the bottom and the sides. I think it's likely to fall apart completely if someone tries to take it apart to clean it, LOL.

I check the filters on the inside unit on a monthly basis to ensure that they're clean.

Thanks, Brian Steele

[Bubba]

But then we all know how stupid and "udderly" clueless you are in anything related to this industry. Stormy, You should really just sit back on your half blind fat ass and Shut the Fuck up! Bubba

[Travis Jordan]

Your system's total power input is approximately 2240W, so 15KW would be the equivalent of roughly 7 hours of run time. Sound right?

Do you run it 7 hours every day, even during the winter? If not, recalculate using your expected annual run hours.

A 13 SEER system would use approximately 18000/13 = 1385W input. Another way of getting to the same number (9.3kWh/day).

I come up with $687.

Yes you are.

[Stormin Mormon]

Higher effiency. Chance to put it in the shade. Not rotted out.

Sounds like we're leaning towards a replacement unit. Or, minimally a replacement outdoor part of the unit.

[[SPICEISLE.COM] Brian Steele]

Well, I leave the A/C on almost 24 hours a day, but the condenser does cycle off for much longer times at night...

No winter here. I live on an island in the tropics (11 degrees North). Ambient temperature typically varies from 26 to 30 degrees Celsius (79 to 86 degrees Farenheit). I've got the A/C usually set at either 24 or 25 degrees Celsius (75 or 77 degrees Farenheit).

Thanks for your help, Brian

[Bubba]

OK, that does it. Take yourself and your island in the tropics and go. You Suck! :-) Bubba

[Oscar_Lives]

You can get a more efficient unit, but the payback won't be there unless your electricity is over $0.28 a kilowatt hour.

Sure, there are lots of things you can do: You can install a booster fan on the condensor unit to help it get better airflow without the existing motor drawing excessive amperage. A garden hose spraying cold water on the coils will also save lots of money by keeping them more cool. A booster fan on the indoor unit will also relieve some of the load and amp draw of the indoor unit. Miller is known for using the smallest wires and tubing it can get by with; if you replace all the wiring and tubing with at least one size bigger, you can save at least 20% on efficiency.

Cover it with heavy black plastic or a dark colored tarp to reduce its sun exposure. Reflective aluminum foil is good, too.