Homeowner question: Comparing cost vs efficiency

[bmilam]

I hope it is ok to post this.. I'm not asking for pricing advice from anyone.. but for reference, I want to post some relative figures for what I'm looking at.

Someone please tell me if this is not ok, and I'll pull this right away.

Ok... First off... I'm not rich, so money is definetly an object. I currently have a 5-ton Goodman 10seer (Straight-A/C) unit manufactured in '99 I with a Bristol Scroll compressor. The compressor has a pin-hole in it on the side at an internal weld.

New compressor installed - (**Edited: about twice the price of a 5-ton compressor)
(I have no problem with this figure.. I know they don't give out free 5-ton compressors)

Or I could get a new outside unit installed for about the same price and use the same evap coil/AH that is in place now, I'm guessing this would still put me somewhere in the 10 seer range.

Or I could get a new 13 seer Heatpump inside/outside installed for roughly twice this. (I don't believe this has variable speed fan)

Or.... I could go with a 16 seer unit with 2-stage compressor and variable speed fan for just a little more than 3x as much.

I am in the deep south, the temps in the summer months are in the mid 90's and humidity runs very high. May-Aug are the big summer cooling months here. Winter's are relatively mild. I may have 1 month where the power bill gets up a bit in January, but nothing like the stretch we see in the Summer months. For heat it is just using the Internal coil heater, no air pump at this point. My summer cooling costs is prob $250-300 a month in the hottest months.

I'm very confused on what to do here... the people I have talked with have all been straightforward, and I know it's probably impossible to determine what savings I would see from going with the higher seer units, but I'm just looking for an idea of how much more efficient would the higher priced units be over what I have installed now. I have to do something anyways.. with a hole in the compressor

[gary_g]

If you edit out the price of the compressor, the post should be OK.

I just read somewhere that replacing a 10 SEER system with a 13 SEER system would provide a 30% savings in operating costs. 14 SEER would be 40%, etc. I would take this as a ballpark estimate.

If you replace the whole system, I would step up from the 13 SEER to the Goodman 14 SEER. Make sure you get the optional TXV (thermostatic expansion valve) for the air handler coil. It provides maximum cooling efficiency under all operating conditions.

In my opinion, a 14 SEER offers the best combination of purchase price and true operating costs.

A good installation is critical for a properly performing, long lasting system.

Good luck.

[bmilam]

Done...
I like the idea of the variable speed fan, I do have some issues with humidity in the house. It is 2400sq ft of living space with single pane windows. The tech recommended to stay with a 5-ton... he said that the variable fan would help with the humidity. It is a Carrier Infinity system BTW.
But... that's a lot of money... One good point is I could get a low interest loan from the local power company, the other options I'm just going to have to put it on the Credit card which is not low interest.

I hope I'm not being too much of a goober by asking these questions, but I've been reading these forums for a long time.

[gary_g]

Done...
I like the idea of the variable speed fan, I do have some issues with humidity in the house. It is 2400sq ft of living space with single pane windows. The tech recommended to stay with a 5-ton... he said that the variable fan would help with the humidity. It is a Carrier Infinity system BTW.
But... that's a lot of money... One good point is I could get a low interest loan from the local power company, the other options I'm just going to have to put it on the Credit card which is not low interest.

I hope I'm not being too much of a goober by asking these questions, but I've been reading these forums for a long time.

Goodman makes a variable speed air handler - the model# starts with AEPF. It can be used with any Goodman heat pump from 13 SEER to 18 SEER. Model# ARUF is the 3-speed air handler, ASPF is the 5-speed air handler.

www.GoodmanMFG.com

Carrier Infinity is the Cadillac of the line. Carrier also makes a mid-level Performance series which has excellent efficiencies when paired with the right air handler.

[beenthere]

Hot and humid.
A single stage with VS will make it feel better then what your old system did.
A 2 stage with VS will be able to lower the humidity more yet. Possibily allowing you to set the stat a degree or 2 higher, and still feel as comfortable.

Not sure how cold your area gets, or how long your heating season is. But a heat pump does help to lower the bill compared to strip heaters.

[bmilam]

Another thing I just thought about
The tech said there wasn't any real reason to replace the evap coil.... (currently 10 seer) if I replaced the outside unit... I'm guessing it would be a 13 seer unit since thats the minimum. He explained that I certainly would not be seeing 13 seer.

I understand that it would not be as efficient , but would I have anything close to my current 10 seer performance if doing this?

I've been browsing/searching the forums for hours now... and have read some scary stuff now on mismatches. Should I be worried about this option?? Would it make sense to go ahead and replace the inside unit ?

Sorry for the stupid homeowner querstions

[beenthere]

If you reuse your old indoor coil. You could have anything from a 9 SEER to a 12 SEER.

If your compressor fails, and the distributor or manufacturer ask for the mod and serial of the indoor coil, and it doesn't match, they will void the compressor warranty.

Read the mismatch performance.

[bmilam]

Thanks Beenthere! That is a heck of a lot of difference.

[beenthere]

Yep.

And if they can't get it to work right in a lab. How is anyone gonna make it work right in the field.

[RyanHughes]

Your indoor humidity problems could be a result of an oversized system. 5 tons is a lot for 2400 sq. ft., but your climate might just warrant that. I have a smaller system (3.5 tons) for my house (around than 3500 sq. ft. including conditioned finished basement) and it cools to 72* on the hottest 90*+ days with fine humidity control; however, I am in Maryland, not Alabama. My home has shade, and yours may not. Insulation, windows, etc. also vary, so it's possible that you may need 5 tons (my point is to make sure! ). How often does (did) your system cycle on an average day? Oversized systems use more electricity. 2-stage systems help with humidity removal and longer cycles, but they still need to be sized properly. If any contractor wants your job, I would ask him to perform a load calculation to be sure of sizing.

[RyanHughes]

If you reuse your old indoor coil. You could have anything from a 9 SEER to a 12 SEER.

If your compressor fails, and the distributor or manufacturer ask for the mod and serial of the indoor coil, and it doesn't match, they will void the compressor warranty.

Read the mismatch performance.

Why didn't they do a test with a 10 SEER outdoor unit and 13 SEER indoor unit mismatched? Don't they anticipate any problems with a setup like this? Interesting read nonetheless.

[beenthere]

Why didn't they do a test with a 10 SEER outdoor unit and 13 SEER indoor unit mismatched? Don't they anticipate any problems with a setup like this? Interesting read nonetheless.

You can get the BTUs from the larger then needed coil.
So all it would do is prove you lose latent BTUs with that match up.

[RyanHughes]

You can get the BTUs from the larger then needed coil.
So all it would do is prove you lose latent BTUs with that match up.

Along with charge issues and efficiency issues, correct? I'm just checking because I thought even a 13 SEER mismatched coil on a 10 SEER heat pump was bad. I guess it's a gamble still.

[beenthere]

Heat pump is a whole other animal.
You could have charge imbalance that way also.

[bmilam]

Your indoor humidity problems could be a result of an oversized system. 5 tons is a lot for 2400 sq. ft., but your climate might just warrant that.

I'm thinking the same thing Ryan. Temperatures in May-Aug/Sep run in the 90's and avg humidity is 87% at night and 61% in the daytime. The unit didn't seem to cycle on all that much really, but my power bill is still pretty high in the summer months. kwh is only $7.262, but my power bill has seen > $400 for jun-july

One reason I think he is saying 5-ton is it is an older home built in '75. It has good insulation in the attic and below the floors, but the windows are single pane aluminum channel windows, I know I have to be losing a lot of cool air from them... but a couple of grand cheaper a/c would buy a lot of windows... Argh!... decisions, decisions...

I'm gonna go back to renting... it was much simpler when I was younger and renting an apartment and didn't have to worry with this stuff

I'm going to get some more estimates tomorrow , maybe that will help my decision.

The old unit when I moved into here was rated at 4.7 tons but it was in the crawlspace with a duct running into the attic for distribution. That unit was replaced with a 5-ton unit in a closet.

[DanW13]

If I were you I would think about upgrading windows, sealing doors and other holes like ceiling boxes in your upstairs ceiling, adding insulation in the attic, and any other areas before having a heat load calc done to see what your sizing requirements are for new equipment will be. paying for new windows and insulation will be alot cheaper and greater payback than a new system without is going to be alot more beneifical to you in the long run and will yeild you a better ROI on the new equipment once you go ahead with the purchase. There's alot you as a HO can do to to increase your over all bottom line on the items I suggested, and even more so if your a alittle bit of a DIY'er where you could do most of that work yourself, as liek insulation and maybe the windows, and definately doing the sealing of door's and other penertration thru out the home.

[pstu]

I am a homeowner in a hot-humid climate too. I have a 2-stage AC but it is strictly a luxury, when money is a sizable concern you will get better use of your dollars by buying a 1-stage unit. They are available up to 15-16 SEER, although the 5-ton size usually drops a point or two in efficiency.

However... infiltration of outside air is a big enemy in climates like yours and mine. It will add serious humidity load to your AC and generally just run up your bills. Back in 1975 almost nobody built tight houses so I would assume there are many opportunities for improvement. The good news is sealing up air gaps is cheap to do. The bad news is it is labor intensive and very difficult to find people to do it for you. There exist some sophisticated methods for measuring your house tightness but they may not be widely available in your area. When you get tight enough, there is a need to pay attention to explicit ventilation systems, but that is probably academic when you start with a 1975 house.

For the subject of windows (also mucho expensive), let me observe that so much of the time the temperature difference between indoors and outdoors is 10-15F or so. That is the basis for some saying double pane is not so important. The real reason for double pane windows in the South these days is the anti-heat-ray coating is fragile and needs to reside on the *inner* surface of a double pane where it cannot be scratched off. I suggest you look into solar screens as a cost effective thing to do first.

Sales people always say "more insulation". Well insulation is usually good but if it is applied over a leaky ceiling with many cannister lights, I think it is the wrong answer to the problem. If you don't have radiant barrier in a ventilated attic, you should get some unless your house is nearly always shaded. Radiant barrier can reliably save 8-12% of your AC usage in our climate, it will make your attic cooler in a way you can really feel.

A high efficiency AC will save *some* money, but the way to make sure your house is not an energy hog is to get better sealing. I would not feel ashamed of 13 SEER but the money saved should go into making your house tighter, if you can.

Hope this helps -- Pstu

[BigJon3475]

Or heck use HVAC Calc and do the figuring yourself....then you can instantly see what upgrading insulation or windows may do for you. With that info you might be able to choose the best option where you get a more efficient system and were also able to choose the best envelope upgrades to compliment that for your money.

[bmilam]

Thanks so much guys... I have learned a ton in the last two days by pouring over the archives. I never knew how important some things were that my house is lacking.

I know there are some areas in the ceiling lights that are not sealed properly. I didn't know how important this was before. I've replaced 7-8 recessed fixtures already and will replace them all now. I know that anytime in the past when I've had a fixture removed, I could feel a lot of hot air coming out of the hole into the living space. So.. I'm going to get to work on fixing those items. I also need a vapor barrier in the crawl space.. that can't be helping Also think I want to install a radiant barrier on the joists to try and keep the attic a little cooler. The Duct-work is in the attic, so that might help. I think I could stand to save a good bit of money with some diy grunt work to make my house tighter.

I think I've pretty much decided on the Bryant System, just not sure on which one yet.

It's either a 13 seer Bryant heat-pump unit
or the 16-seer Bryant Evolution (W/ 2stage compressor & Var Spd Fan) heat pump system for 2grand more (after rebate).

[BigJon3475]

Attic access doors can be pretty bad also.


Hopefully this works....it's some good reading material about the humidity and comfort in the south. It's from 2002 but still worth reading.
http://www.fileden.com/files/2008/6/18/1965139/DOE%20Building%20Science%20Case%20Study.pdf