AC replacment

[never_retreat]

So I think the AC in my house is getting a little old, Its a 21 year old 2.5 ton lenox system with a direct vent propane unit in the basement.
I think the efficiency increasing alone might warrant he replacement. How many seer is worth it? Is there a point on diminishing returns?
I'm actually really hopping that the current almost consistent 2 week long brown out will kill this thing so the homeowners insurance covers it.
My supply house is a big crown/goodman dealer, so any great deal I can get will be with those brands. (I get wholesale prices) So unless there is a reason not to buy those brands it would most likely go with them for the price issue. But how efficient should I go?

[AZRedhawk44]

I just went from a 17 year old 6 seer to a Goodman 14 seer system.

Keep in mind my home has 3 total AC units:  1 for the front of the house, 1 for the back of the house, and a separate one for a 400sq ft workshop out back.  The workshop stays off most of the summer and I stay out of it during the hot months.  All 3 of the units are 16+ years old.

Last July 2012, my home consumed about 78 kWh per day.  I was not working from home that summer, I had taken a job where I had to go into the office every day that summer.  Both 6 seer systems were set to keep the house at 79 degrees.

This July 2013, my home consumed about 75 kWh per day.  I am working from home this summer 4 days a week (this increases overall use).  I also had my AC on out in my workshop for 2 weeks straight, to intermittently go out and work on my motorcycle as various parts came in.  It was lazy of me to just leave it on, but there were recommendations in the instructions to perform the clutch maintenance work under 90 degrees, and my workshop gets into the mid-100's without turning the AC on.  So I had it set anywhere from 80 to 88 degrees depending on my activity out there.

Going back to my July 2011 bill, my home consumed about 85 kWh per day.  I was also working from home back that summer, and had both 6 seer units.  I did not use the AC out in the workshop that summer enough to matter much.

Realistically, I expect my peak summer bills here in AZ to average 65-70 kWh per day when I am not using the AC out in the workshop, now that I have replaced one unit.  My August bill should shed more light on this since I'm done doing any temperature sensitive work out in the workshop and only turn on the AC for a few hours at a time as I work on particular tasks on an as-needed basis out there. 

If all goes according to plan I will be replacing the second house unit next spring.  That one, I will be going for something a bit more high-end than my new Goodman.  I don't like how loud the Goodman is.  It's a variable speed blower but a fixed speed compressor.  The back one feeds my office and bedroom and I'll be wanting variable speed blower and compressor for peak quietness, which brings me up closer to 16 or 17 seer rating as well.  Should drop the house summer average energy consumption to 50-55 kWh per day.

My 2011 July bill was $331.  Worked from home that summer.  2629 kWh used.

My 2012 July bill was $323.  Did not work from home that summer.  2426 kWh used.

My 2013 July bill was $297.  Worked from home this summer and had the 3rd unit running half the month.  2312 kWh used.

I'm unable to find cost per kWh.  In AZ we have multiple plans for electricity, then on/off peak rates for each of those plans.

[Azrael256]

In my experience...

Go with the best one you can afford from a quality brand, if you plan to live there another 20 years.  If you plan to move in 2015, buy the cheapest.  Adjust for anything in between as needed.

If you buy the 25SEER American Standard, it will be a great unit, but it will take quite a while to pay off.
If you buy the 13SEER Goodman, you'll save in the short run on install cost, and eat it when it doesn't last so long if you're the one to replace it.

The 5-year difference between 10 and 20 based on 'the national average' is under a grand.  What was the price difference for the unit?  Texas or Minnesota?

http://www.lennox.com/resources/energycalculator.asp

So buy on desired features and reliability.  The fancy unit with the better reputation and warranty is probably the more efficient one anyway.

[never_retreat]

I did not even know they went to 25 sear. I was just looking at the 14,16 vs 18.
I have know idea of the sear of the current unit.
My other dilemma is about making it bigger. Its currently 2.5 tons on about 12-1,300 sq foot ranch house.
I'm finishing the basement so I plan on tapping in a few vents. So I think I should make it a little bit bigger.

[Triphammer]

Talk to your electric company. Oft times they'll do a survey & infra-red imaging of the house & make recommendations.

[AZRedhawk44]

Beware making it bigger.

Often not a good idea.

The biggest expense to an AC unit's operation is the electrical pulse that starts it.  It wears out switches, solenoids, capacitors and motors, and is the highest amperage draw of the whole system.  "Running" doesn't cost nearly as much.

Far better for it to run for one 15 minute period per hour, than to run for 4 separate 3.75 minute periods per hour.  Runtime is the same, but on/off wear is much higher.




I was recently told by my AC installer that did my Goodman, that American Standard / Trane used to be the last firm that actually manufactured their own compressors and they finally caved to market pressure last year.  ALL COMPRESSORS are now made by one company, from Goodman to Trane to Lennox to York. 

As such, I went Goodman and got a better warranty on paper than what American Standard was offering.  We'll see if it holds up.  AZ is a great place to test that warranty.

So far the only complaint I have is noise of the air handler.  And that's more a function of the old ductwork than the air handler itself.  Once I get my brother (a noob journeyman AC graduate from RSI) to get in my attic and extend my plenum and ductwork up there, the air flow should distribute across far more channels and reduce overall velocity, resulting in far less noise and much moar happiness on my part.  The previous air handler didn't have nearly as strong a blower as this one.

[280plus]

16 SEER is about max in the optimum cost vs efficiency tale. Any higher SEER and you're paying too much vs the return on efficiency. A/S and Goodman are both good units. Heat pumps are much more efficient than they used to be and are not a bad way to go if you're already doing the A/C the added cost is payed off in just a few years.

[Jim147]

I've used a few Goodman dryship units without any problems. I've worked on several of the systems and most of the problems are the same as I see on any other brand. Poor quality installation and or lack of maintenance. I like the looks of their 14 SEER heatpumps.

As 280 said, you have to watch upsizing. Most systems have iffy duct work to start with. You're not really adding to the load by cooling the basement. Unless you plan on growing a bunch of personal use product down there. You are gaining efficiency with the new unit and there is nothing you can do to help the system that tops sealing up the house.

jim

[geronimotwo]

the last I new goodman was identical to carrier, they just swap out the nameplate.

So far the only complaint I have is noise of the air handler.  And that's more a function of the old ductwork than the air handler itself.  Once I get my brother (a noob journeyman AC graduate from RSI) to get in my attic and extend my plenum and ductwork up there, the air flow should distribute across far more channels and reduce overall velocity, resulting in far less noise and much moar happiness on my part.  The previous air handler didn't have nearly as strong a blower as this one.

 new units use the theory that they want all the energy out of the unit and into the house, hence the faster fan.  most of them are adjustable by changing a jumper on the main board.  otherwise you may need to install some softer ductwork.

[AZRedhawk44]

the last I new goodman was identical to carrier, they just swap out the nameplate.

 new units use the theory that they want all the energy out of the unit and into the house, hence the faster fan.  most of them are adjustable by changing a jumper on the main board.  otherwise you may need to install some softer ductwork.

Yeah, I currently have no plenum at all.  It's a hard right angle out of the fan box into some square ductwork just above the ceiling, and the highest velocity air is shot out into my living room.  I find myself turning the TV volume up when the AC kicks on, then down when the AC kicks off.

Ideally I'd rip out all of the prior ductwork entirely and go with an attic plenum and duct system.  As-is, gonna extend to a plenum in the attic and probably run 4 x 10" softducts to far corners of the house, furthest from the thermostat but still served by this unit.  That will cut the volume and velocity of the air in the legacy ductwork by a good 75%, resulting in almost no noise from it.

The actual fan box air handler is quite quiet.  It's just the sharp edges and right angles and small volume of the current ductwork that is the problem.

[280plus]

There may be dampers in the supply branches that you can dial down? There should be anyways. They should be right where the branch comes off the trunkline.If not maybe install some?

[AZRedhawk44]

There may be dampers in the supply branches that you can dial down? There should be anyways. They should be right where the branch comes off the trunkline.If not maybe install some?

That just increases the whistling.

Basically, I have (estimated, haven't measured) a single output from the fan that is about 5" tall by a foot wide.  It shoots out so fast from the strongest register that I can feel the wind when I stand about 15 feet away from the main output.

There's a small deflector/damper between the main output and a couple of offshoot ducts that maybe moves 1/3 of the total air to those offshoot ducts.  But 2/3 of the force of the fan comes out of 1 register.

I figure a plenum and 4 more offshoot runs that are 10" diameter each will basically take me from a 60" output path and add 124" total potential flow for a total of 184" output.  Three times the flow, 1/3 the velocity, less than 1/3 the noise.

[280plus]

Whaaaat? I can't hear you over all the whistling...

Sounds like somebody winged it when they put it in.

[never_retreat]

The duct work does not seem to be undersized on the current system. No noise or anything like that. It leaves the unit at 8x24 half way down the 40 some foot trunk it goes to 8x18. It used to go down again to 8x12 but I bumped that up during some of the basement work. I did not want the trunk passing at the bottom of the steps so I had to rearrange the last 2 6" supplies.

I think the system is a little small anyway. If its hot out and for some reason the ac was off and the house got hot, it takes almost 2 hours of solid running to drop 1 degree.

[280plus]

Could be a dirty condenser, low charge or a combination. Just because a condenser looks clean on the surface doesn't mean it is. Depending on the unit you may have two coils sandwiched together that need to be separated to be properly cleaned. I see lots of cases where the condenser is clogged and once I clean it the charge is low. Why? Because some numb nuts hooked his gauges up to it, saw the high discharge pressure and misdiagnosed it as an overcharge rather than a dirty condenser. So they let freon out to lower the pressure. Neat huh? I'd make sure it was up to snuff before I would say it was too small.

[Nick1911]

Could be a dirty condenser, low charge or a combination. Just because a condenser looks clean on the surface doesn't mean it is. Depending on the unit you may have two coils sandwiched together that need to be separated to be properly cleaned. I see lots of cases where the condenser is clogged and once I clean it the charge is low. Why? Because some numb nuts hooked his gauges up to it, saw the high discharge pressure and misdiagnosed it as an overcharge rather than a dirty condenser. So they let freon out to lower the pressure. Neat huh? I'd make sure it was up to snuff before I would say it was too small.

<thread drift>

A condensing unit the customer reported didn't work well, after I got the covers off:


To determine what size system you need, a proper manual J load calculation should be preformed.  They do take a little bit of time, but I've had good luck with the calculation if you give it accurate data.  Like 280 said, your current system may just need maintenance/cleaning.

[AZRedhawk44]

Is that spider web, cotton, dryer lint or what?

[Nick1911]

Is that spider web, cotton, dryer lint or what?

Cottony crap from trees, I believe.

[280plus]

"tree fur" It's been a particularly bad season for it.

[geronimotwo]

save it for tinder!

[never_retreat]

Ok the condenser does not look dirty. What is the best method to clean it? Pressure washer?
Since I have almost every tool under the sun, but not those magical test gauges for air conditioning I think I should get a set.
Any recommendations?

[Nick1911]

I'll be interested in what Ron, 280 and Jim have to say on this, but personally I like Nu-Calgon Nu-Brite Coil Cleaner.  It is a foaming lye based cleaner that seems to do a really nice job dissolving crud and allowing it to be washed free with a garden hose.

Do not use a pressure washer on your condenser coils.  The fin material is much to weak to withstand that kind of pressure without folding over.  I use a garden hose with a fairly standard variable-cone-shaped sprayer attachment.

For gauge sets, I like Yellow Jacket stuff.  However I believe that they would be of limited usefulness for charging without a decently accurate clamp thermometer and pretty good understanding of vapor-compression refrigeration.

[never_retreat]

I'll be interested in what Ron, 280 and Jim have to say on this, but personally I like Nu-Calgon Nu-Brite Coil Cleaner.  It is a foaming lye based cleaner that seems to do a really nice job dissolving crud and allowing it to be washed free with a garden hose.

Do not use a pressure washer on your condenser coils.  The fin material is much to weak to withstand that kind of pressure without folding over.  I use a garden hose with a fairly standard variable-cone-shaped sprayer attachment.

For gauge sets, I like Yellow Jacket stuff.  However I believe that they would be of limited usefulness for charging without a decently accurate clamp thermometer and pretty good understanding of vapor-compression refrigeration.

Ah I think I have seen that cleaner stuff used before. I will pick some up at the supply house.
I don't have a pressure washer so thats good.
What is this clamp on thermometer you speak of? I have an IR thermometer.

[Jim147]

I'll agree with everything Nick said. I have used a soft brush and then a hose when I got caught without my cleaner. don't foget what 280 said about some coils being doubled. The crap gets caught in between.

The clamp thermometer is a standard K type in a spring clamp to read the temp of the lines. I've never had any luck with the IR type but if you have a standard K type wire you can wrap and insulate it to the line.

You use the line temp along with your pressures, PT chart and dry bulb/wet bulb temps to find the required super heat/subcooling for the metering device your unit uses. Beer can cold, sweating back to the compressor and ambient plus some number are not proper ways to charge a unit.

jim

[280plus]

I like "Re-Nuz" myself and yes be careful with pressure, do not damage the fins! Take the cover off the unit and get a look at the ends of the condenser (tube sheet) if you have 1 column of u bends it's single, if you have two (or more) columns of U bends you have a "split coil" and those must be carefully dismantled, spread apart as far as possible without damaging the tubes and you must clean each coil separately as best you can. I spray them all down both sides with cleaner, let it cook for a while (15 minutes?) and then use a medium pressure spray cone pattern just backed off of a straight stream. I like the straight brass screw type nozzle better than the handgrip type. Then I rinse with it up close between the tubes and watch the water and dirt come out the other side. When I find no more spots where the water is coming out dirty the coil is clean. This can take a while but is worth it in the long run. I can usually knock one off like Nick posted in about an hour.