Within about 2 weeks, I expect construction to be started on my new 2 story custom home here in Albuquereque. The normal high in July typically exceeds 90 degrees F. The house will have radiant floor heat with conventional air conditioning. The plans are for 1 unit for the 1st floor and 1 unit for the 2nd floor. However, according to the contractor, central a/c is not available without hot air heat, so he expects me to have 2 units which provide both heating and cooling, even though there will be radiant floor heating, but that I won't have to use the hot air heat. Both of the 2 units will be about 2 tons. To me, that sounds like nonsense. I see no good reason that I should be unable to get air conditioning without also having hot air heat when there will be radiant floor heating. I plan to meet the a/c contractor next week and tell him that it is unacceptable to install hot air heat which will not even be used. Also, they are thinking about putting both units on the (flat) roof and insist that heat from the sun will have no effect, which I also see as nonsense. Perhaps having the sun shine on the units would not have too great an effect, but with the entire roof hot from the sun and the air provided to the condenser being hot, surely the high side pressure would be greater causing the compressor to draw more power. Can anyone advise me?

I'd advise you to talk to another HVAC guy and explain to him what you are trying to accomplish. 

It may be that your current guy can get heat pumps at a lower price than he can get straight AC units which are almost one in the same.  Yes, you will need an air handler and ducting to distribute the cool air just as you would for the heating side. 

One thing that I would caution you on is that any AC unit mounted on the roof (I have one at 5,000' in AZ) will sound like you are in a drum when it comes on and you are in the house.  We have a Trane 1600 on our roof and it is great, other than it is noisy in the AC mode, but not in the gas heat mode.

Good luck with your project!

Thank you for the reply.

It was the GENERAL contractor that said that straight AC units would not be available and that the AC would have to be combined with gas - hot air heat. Air source heat pumps are not efficient here because the temperature often drops below freezing at night during winter.

I shall try to get an appointment to talk to the AC contractor next week and emphasize that it must be QUIET, almost to the point of being inaudible. I have written a list of specifications that clearly state that the AC must be quiet. If the one for the 2nd floor combines the compressor with the air handler, making it quiet could be more difficult. Considering that central AC is common in Hawaii where heat is not required, it must be that AC is available without heat. I may have to be very assertive and do some of the research myself. I had hoped that someone could recommend a source.

hopefully your general knows more about structural issues than he does about hvac
look at www,sanyo.com
they have dealers in the us.
when we travel in the far east it is all you see--you do not hear them as they are quiet

Thank you - I shall visit their site.

Because I lived in Fiji for 10 years, I am familar with Sanyo AC. However, I don't yet know whether they have central systems that can be used with a good electronic air filter. I may be able to find out from their site.

From visiting the site for Sanyo, it appears that they don't market AC units in the U.S. Also, it appears that they manufacturer only ductless systems, and it would not be possible to combine ductless systems with a good electronic air filter. However, it is possible that they have units available which I could not see on their web site.

www.minisplitsystems.com

Well, I guess that they do sell then in the U.S. then. Their main web site could be improved because I couldn't get that info on it. I might consider a system like that, but I do have problems with it. The filters on those wall-hung evaporator units could not possibly be as good as an electronic filter on a central system, and they could not incorporate a heat recovery ventillation system. Having those features while using ductless split systems would require adding something completely separate, but perhaps that should be considered. Each floor will be about 1200 square feet, with a total of about 2400 square feet. Presumably a micro air handler could be used to incorporate an electronic air cleaner and heat recovery ventilator which would be separate from the ductless split systems, but I don't know whether that would be a reasonable thing to do. There are also mini split split systems which have the evaporator unit in a closet or above the ceiling and use short ducts, but I don't know how quiet those would be. The ducts are very small for the volume of air moved, and that could cause noise.

FRE
I suggest you also check into www.unicosystem.com which is one of the High-velocity type AC systems. Basically an air handler with an AC coil. You can add heat backup if necessary.

As to the heat-pump comment, I know efficiency changes somewhat as temp drops, but then again, I also thought they installed a heat coil for the extremes when it gets too cool to provide proper temps?

you can also check int www.hvac-talk.com and should find a lot of info in some of the forums.

Jim,
I checked out their web site. I can see that for certain situations, the Unico system could be reasonable. For example, it could be used to circulate air through a good filter system or distribute air from a heat recovery ventilation system independently of an AC system. However, for actual air conditioning, it would be very inefficient and in certain areas of the country, would even fall short of code requirements.

Unico did not provide effeciency numbers, and it's no wonder. They state that their system moves only half as much air per ton of cooling as other systems do. The problem with that is that the air that is moved would have to be considerably colder which would reduce efficiency. The recording stated that the Unico system is far more effective at removing humidity because it operates at a lower temperature, but I had already figured that out before I got to that part of the recording.

To increase cooling efficiency (SEER or COP), modern AC systems move a higher volume of air at a higher temperature than older systems did. The higher the temperature at which the evaporater can operate, the greater the efficiency, ceteris paribus, the drawbacks being poorer humidity control and, because of the higher volume of air, possibly noiser operation. So again, if the Unico system were used for cooling, its efficiency would be significantly lower than that of a system that delivered air at a higher temperature.

The above criticism of the Unico system applies only if the size is selected per their recommendation. However, if the size of their air handler were selected so as to move the more usual amount of air per ton of AC, then efficiency should not be a problem.