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Help with Carrier AC decision

Posted by kincade (My Page) on
Wed, May 15, 13 at 14:15

Hoping to solicit some advice from the pros here... We currently have a Carrier Infinity 96% efficiency furnace, variable speed blower, 2 stage gas valve, 80k btu furnace with the Infinity controller. The AC portion was an existing install, Kenmore 14SEEER. The compressor is making a very loud 'bang' every time it kicks off and we've had several techs from different companies give us bids to fix it. All bids have been what I consider to be too much in comparison to investing in a new system.

In any case, we are looking at the Carrier Infinity and Bryant Evolution communicating series of AC and heat pumps. I do know I'd like at least a dual stage compressor for comfort, but beyond that I don't know what to do. The sales guys are all trying to sell the highest seer available (obviously) and are pushing the heat pump as a good option saying that they'll both save us a ton of money. I'm not so sure and the information out there on money savings with a higher seer rating is mostly sales literature.

In AC, we are looking at the 24ANB6, 24ANB7, and 24ANB1 in a 3 ton with 3.5 ton coil. Manual J calculations have been performed by 2 of the bidders with the same results.

In heat pump, looking at the 25HNB6, 25HNB9, and 25VNA0 in a 3 ton with 3.5 ton coil.

Can anyone advise if there is any financial benefit to going with the higher SEER/EER rated units? I'd love to lower our utility bills but the higher units are significantly more expensive.

Live in Utah, where summers are hot 90-100*, winter is cold 10-40*, and spring and summer can be mild or any combination thereof. Rates for our power are as follows:

Summer:

1-400kw 8.6c/kw
401-1000kw 11.2c/kw
1001+kw 14c/kw

Winter:

1-400kw 8.6c/kw
400+kw 9.6c/kw

Rates for the gas as follows:

Summer:

1st 45dec 6.95/dec
45+dec 5.69

Winter:

1st 45dec 7.91/dec
45+dec 6.52/dec

Thanks for any help or advice you can give!


Follow-Up Postings:

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RE: Help with Carrier AC decision

The rates you listed are all inclusive costs both electric and nat gas?

Could you clarify your nat gas rate?

Your location please?

Post back.


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RE: Help with Carrier AC decision

Tigerdunes, the rates are the tiered rates by both the AC and natural gas; no other costs. Winter costs are written per decatherm, first 45 decatherms and after 45 decatherms. Does that answer your question?

Located in SLC, Utah.

Thanks for the help.


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RE: Help with Carrier AC decision

Thank you.

I plugged your numbers into a fuel comparison calculator that I like to use. I always tell the homeowner to take the results as a guide. But based on the results, nat gas on a BTU basis is less expensive than electric. Therefore I would not use a HP in a DF system. Stay high eff furnace with a high eff AC condenser.

Electric $.093 KWH with a COP of 3
Nat gas $.0075 cu ft with 95% eff

This is a conservative approach. Nat gas is quite cheap nationwide at the moment.

Cost per 100,000 btu of useable heat
Electric baseboard: $2.45
Heat pump: $0.91
Natural gas: $0.77

If you want to save a few bux, look at Carrier AC Condenser Mdl 24ACB7, Performance 17.

IMO


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RE: Help with Carrier AC decision

You have a low electric rate so it doesn't make sense to pay to for a high SEER rated condenser. A SEER rating of 15-16 would be fine. It also does not make sense to upgrade to a heat pump. The numbers show it is more economical for you to heat with natural gas.

Do you have high humidity in the summer? If yes, then spending the extra money on the 24ANB7 2-stage condenser would be a good choice. If not then the 24ANB6 or 24ACB7 which ever is the better deal after rebates.


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RE: Help with Carrier AC decision

"Make sure it has on and off fictions"

This is a well known feature of Goodman products.


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RE: Help with Carrier AC decision

If you have low humidity then I would not spend the extra money on a 2-stage condenser. The only other advantage is when the AC is running in the low stage it is very quiet and there are now drafts of cold air. The savings come when the lower humidity allows you to raise the thermostat setting 2-3 degrees. It does not appear you will be able to take advantage of this.

I forgot that you are only getting an AC condenser. In that case the rebates are low. The max rebate is $100 for the 2-stage Infinity, $75 for the single stage, and $50 for the performance series. Not all dealers participate in the rebate.

I think the Performance unit will communicate with the Infinity controller but it may require adding an interface module. Ask the contractor about this.


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RE: Help with Carrier AC decision

If you want lower energy bills install a smaller unit. They have smaller motors and therefore use less power. Most ductwork is undersized for the existing system, and downsizing the unit will allow you to better use the existing undersized ductwork. Most contractors are stuck on 500sqft per ton regardless of how well insulated the house is. A 2.5ton 13SEER will have about the same power bill as the 3ton 14 SEER or a 3.5ton 15 SEER. The 2.5ton 14-15SEER is about sweet spot for energy use vs. initial cost. I did a 2ton 14.5 SEER on my own 1600sqft Oklahoma house. Temps here get into the 100's most summers, last 2 summers we even hit the 110's a few times.

http://acrightsize.com/files/10_reasons_why_oversizing_persists.pdf


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RE: Help with Carrier AC decision

Thanks again for the helpful information Mike and Servicetech. This is great info. Is there any point in upgrading to a higher SEER like a 19-21 or is the payoff too long to be of any benefit?

Forgot to ask, all the contractors are recommending going with a 1/2 ton larger coil inside. Does this actually improve efficiency or just get the contractor more profit?

All contractors are saying it's ok to keep the lineset and flush for the new refrigerant.


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RE: Help with Carrier AC decision

Linesets must be sized to the manufacturer specification to achieve performance/efficiency capability of the system. I am not against flushing if done correctly and the lineset is correct size. Close does not count.if you don't know, then ask.

15-16 SEER is the sweet spot.

And I disagree with the previous poster. He suggests it's OK to downsize. It is not. You want to be sized correctly with the correct sizing of ductwork system to deliver the conditioned air.

IMO


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RE: Help with Carrier AC decision

At your electric rate the pay back for a high SEER (19-21) AC would be a long time and probably longer than the life of the system.

If you know your annual AC cooling costs then you can figure out your return on investment. Going from a 14 SEER to 16 SEER would saving about 13% in electricity costs, while a 14 to 19 SEER upgrade would be about 31%. The difference in savings in this case would be about 18%. If you annual cooling bill was $500, then you would be an additional savings of $90 per year by going to a higher SEER condenser. If it costs $1800 to upgrade then it would take 20 years to recoup your investment if you ignore interest rates.


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RE: Help with Carrier AC decision

Remember seer is rated at 82 outdoors/80 indoors. EER is a better indicator of power use. EER is rater at a much more realistic outdoor tempature of 95. I agree with the above poster, 15-16 seer is the sweet spot.


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RE: Help with Carrier AC decision

The EER would be a more accurate indicator of energy usage if you lived in an area where it was 95 degrees everyday of the cooling season. The SEER measurement tries to take into account that the temperature will vary. There are simple formulas to convert one value to the other.

The US Government only mandates a minimum SEER rating. There are no requirements for EER. The AC manufacturers tend to tout their SEER ratings to a point customers think they are buying a SEER rating and not an AC system.

When doing a comparison of two AC systems you can use either the SEER or EER rating to get a relative cost differential. Unfortunately you don't get the full percentage savings since a significant amount of cooling is lost through the duct work. You should only use the comparison as a rough guide.

The most important information you need in my opinion is the annual cooling costs. It seems most homeowners don't know how much it costs to cool and heat their houses. Once you know the energy costs then you can make a decision whether it makes financial sense to buy more efficient equipment, add more insulation, or both.


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RE: Help with Carrier AC decision

13 EER seems to be the sweet spot for premium systems that OP is considering for matching system...


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RE: Help with Carrier AC decision

If you REALLY want to understand your systems performance read the expanded performance data. You can see what EER is for any specific set of operating conditions. Keeps in mind these are steady state after the unit has been running at least 10 minutes. For the 1st 10 minutes of a cooling cycle EER is reduced significantly.


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