Better/Best HP's for Hot Dry Climate?

[Sand Penguin]

Any recommendations for better/best 4 ton all electric packaged HP's for Phoenix area? I presume they would be biased towards high sensible cooling capacity and not so much latent. Thanks!

[lynn comstock]

High airflow, good ductwork matters more than brand for the desert. Get an APS energy audit and find out your duct leakage (wasted cooling). Seal the ducts and do a Manual J heat load and retest the final duct leakage. Downsizing the AC will have the effect of enlarging the ducts and enabling high airflow.

Don't expect a correctly sized air conditioner to cool the house as fast as the old one. In the hottest weather, the correctly sized unit will run non-stop for 3 to 5 hours when the weather is 110°F or more. Don't expect to set stat warmer in the hottest weather and have the air conditioner recover quickly. If that is what you want, and most people think that the AC should work that way, you will need an oversized air conditioner.
See:
http://www.energystar.gov/ia/new_hom...dAC1-17-01.pdf
http://www.proctoreng.com/articles/bigger.html

[dunkman]

I'm not from the area, but I would think you should have demand defrost?

Of course, maybe the heating season is nill anyway, so who cares?

[Sand Penguin]

Thanks to you both. I had always worried that a near continuous run during the really hot days was a sign of an undersized HP and could expect a shorter unit life, higher electricity bills, etc. You are saying the frequent restarts for an over sized unit are what shortens life and heightens electricity bills. Thanks again.

[jimj]

Thanks to you both. I had always worried that a near continuous run during the really hot days was a sign of an undersized HP and could expect a shorter unit life, higher electricity bills, etc. You are saying the frequent restarts for an over sized unit are what shortens life and heightens electricity bills. Thanks again.

Exactly.

[sktn77a]

Well, you don't have the dehumidification issues that you would have elsewhere in the country so you won't have as large a downside in going to a slighly oversized unit. Depends if you want to size the equipment for the absolute worst case or 95% worst case scenario.

[acwizard]

Is this a changeout or new construction. In your climate zone there is very little if any dehumidification. Unit selection must be adjusted for outside ambient temperature greater than 95F design. Manual J will determine the needed capacity rating for the building. All a/c units perform below rated values at temperatures above 95F. I would caution in selecting a unit too small ( the article bigger is not better does not take into account that you are living in the desert) 115-120F are not out of the norm for Phoenix. A 4 ton unit may only deliver 2.5 tons of cooling at 120F. This has nothing to do with how good your home is insulated. The newer units operate with refrigerant R-410 and as temperatures peak above 120F there are issues that can arise that were not present with R-22 units.

[lynn comstock]

... All a/c units perform below rated values at temperatures above 95F....

That is why the manufacturers publish the performance data for a wide range of conditions above and below the ARI rating conditions (95/80/67). See: http://www.flaxentesting.com/atex/pu...12HEATPUMP.pdf for a sample extended performance data for a heat pump in both heating and cooling modes. See pages 11 to 16 based on design airflow of 400 cfm per ton. There are correction factors for other airflows.

These tables allow you to correctly match the Manual J building design load to the actural capacity of the chosen system at design conditions. The Pro Way.

[beenthere]

I'm not from the area, but I would think you should have demand defrost?

Of course, maybe the heating season is nill anyway, so who cares?

The OP has a short heating season, and low dew points in the heating season. So demand defrost is not as important as in other areas.

[aircooled53]

Is this a changeout or new construction. In your climate zone there is very little if any dehumidification. Unit selection must be adjusted for outside ambient temperature greater than 95F design. Manual J will determine the needed capacity rating for the building. All a/c units perform below rated values at temperatures above 95F. I would caution in selecting a unit too small ( the article bigger is not better does not take into account that you are living in the desert) 115-120F are not out of the norm for Phoenix. A 4 ton unit may only deliver 2.5 tons of cooling at 120F. This has nothing to do with how good your home is insulated. The newer units operate with refrigerant R-410 and as temperatures peak above 120F there are issues that can arise that were not present with R-22 units.

I agree same here in Texas, hot= falling btu's of cooling after 95* in 410A..

[Sand Penguin]

This is a Goettl replacement project. The old unit was probably designed specifically for the Phoenix area as I think Goettl was local and specialized in addressing the hot/dry conditions. The essence of my quandry is that I've had three licensed HVAC contractors give me proposals. They are all on my utility company (APS) preferred vendor list. They all ran Manual J's and came up with quite different size requirements ranging from 3.5 to 5.0 tons. They used ambient temps for summer loading of 110 stating the 36 annual hours that statistically exceed 110 were to few to design toward. That led to my original question here seeking a robust 4 ton recommendation hoping to identify one that came close to the ratings for the old Goettl. I've looked through extended rating info on the WEB and hadn't been able to locate a 4 ton as strong as the Goettl. I'm worried putting in a 5 ton,even with 2 stage compressor, would not only run afoul of all the warnings about over sizing but also require a new panel and feed to the HP based on required ampacity. Thanks again for all your expertise.

[lynn comstock]

I am inclined to believe the lowest heat calculation. All contractors want to size the equipment big enough. If the home was built in 1993, it probably has 2x6 R19 walls, R30 ceiling and double pane windows...Possibly LowE. If so, this construction with ducts in the attic typically works out to 650 sq. ft. per ton in Yuma.

The biggest weakness of a Manual J heat load is the data entry and assumptions of the one entering data. The tendancy of many companies is to end up with a heat load that somehow matches the 400 sq. ft. per ton rule of thumb. That kind of heat load is bogus, but it happens all of the time. You can do your own if you have a mind to. I can't remember the name, but the cost for one use is about $35. Enter the data carefully and you will get trustworthy results.

[acwizard]

This is a Goettl replacement project. The old unit was probably designed specifically for the Phoenix area as I think Goettl was local and specialized in addressing the hot/dry conditions. The essence of my quandry is that I've had three licensed HVAC contractors give me proposals. They are all on my utility company (APS) preferred vendor list. They all ran Manual J's and came up with quite different size requirements ranging from 3.5 to 5.0 tons. They used ambient temps for summer loading of 110 stating the 36 annual hours that statistically exceed 110 were to few to design toward. That led to my original question here seeking a robust 4 ton recommendation hoping to identify one that came close to the ratings for the old Goettl. I've looked through extended rating info on the WEB and hadn't been able to locate a 4 ton as strong as the Goettl. I'm worried putting in a 5 ton,even with 2 stage compressor, would not only run afoul of all the warnings about over sizing but also require a new panel and feed to the HP based on required ampacity. Thanks again for all your expertise.

Goettl were work horses, have put in a bunch of them over the years. I believe the a/c division has been gone for many years.The 36 annual hours had better be addressed , what is the point of cooling if the occupants are miserable. Another concern is that I believe the Goettl duct connections were reversed to all other makes. They also used over-under configurations as well.The equipment support more than likely will need to be modified.

[Sand Penguin]

The house was built in 1978 and is of block construction with asphalt/fiberglass shingled hip roof. The Continental Builder literature says the roof/ceilings were R30 & the walls R9 (internally firred out with 2 x 2's and bat insulation between them). It is still the original single pane glazing but generally all windows and much of the external wall surface is well shaded with mature trees, thick cat claw vines, and/or sun screens. You are correct that the old Goettl is an over-under but all the contractors told me there wouldn't be much loss caused by the twist adapter needed to convert to the new side by side. The old Goettl was/is also a "piggyback" with a 4500 cfm evap cooler tightly coupled to it. I was not planning to continue the evap cooler with the new HP due to higher efficiency (less cost to operate) of new HP's and concerns for mold, etc. in the duct work. However, I was thinking that the original piggyback Evap Cooler arrangement might mean the duct work was a little larger than that which the Goettl HP would have required on its own and therefore might be OK to handle larger CFM of a 5 ton's blower?