home a/c efficiency

If it’s the efficiency you’re going after every degree you raise the temperature it gets a little more efficient runs less but you may be a little uncomfortable sometimes .
I myself personally don’t care about efficiency if I’m going to be uncomfortable I just put it at the temperature that keeps me comfortable during a hot spell.
But then I spent 4 1/2 years taking three major simultaneously when was for commercial and refrigeration HVAC. The other was for residential air conditioning. And other was for building automation. All three majored in emphasized about building envelope sealing for Air tightness and insulation. With a heavy major towards mechanical equipment efficiency. The endgame comes down to are you comfortable or not. Then you think about the money which one is your prime consideration.
Good example 2 houses next-door neighbors one built in the 1950s or 60s in Texas 1700 ft.² may take a 5 ton air conditioner running all day long to try to keep it at 78° . Second house built 2019 to be a self-sufficient net zero house and only needs a 2 ton air conditioner that just barely runs off and on or variable frequency idling along with keeping the house at 78° only consuming about 1/8 of the amount of electricity of the old 5 ton in the same size house

 

This is why a Manual J sizing calc is done, to determine the heat gain on the structure and size the HVAC unit appropriately. In the newer houses, it is common to have a much more air-tight envelope and typically this is confirmed with a blower door test. In older homes, that test was never performed at construction.

 

Forget ducts, it takes energy to push the weight of air against the friction of all the pipes and elbows and grill. On top of that you’re paying to either heat the entire house in every room or cool the entire house every room when you only occupy one or two rooms a day. Ductless is the way to go. Instead of a 5 ton condensing unit running to cool the entire house through all the ducts you could have one tiny 4000 BTU mini split head just cooling one isolated room. On top of that you can do heat recovery all the energy you use to cool your house in the summer gets dumped into a water heat exchanger to heat your hot water needs for your house or your swimming pool without spending extra money for energy because you already paid for it the first time to do the cooling you’re just transferring it over to a different medium instead of blasting it out into the atmosphere and wasting it.

 

Yes, mini-splits are the latest and greatest development, extremely efficient, but are not the do-all, be-all answer to all problems. Everything has it's own set of unique problems. Mini's have been and are always a topic of discussion on the HVAC forum.

If I were purchasing a new construction, mini's are probably the direction I would go. As always, the installing contractor is the #1 most important piece of that equation, ESPECIALLY with mini's.

 

Motel and Hotel owner and operators have known for years that the best option is not even mini-splits but self contained or window units.

My husband's friend, who have serviced HVAC units for over 40 years, replaced his 20 years old failed heating and cooling furnaces with heat only furnaces and window units.

Window units have lesser SEER ratings than central air units but efficiency is not lost through heat transfer loss through ducts going through a hot 120 degrees hot attic.

There is no corrosion built up from condensate through an evaporator coil in the air handler or any restriction from the coil as the furnace is operated in the winter. The furnace fan is not operated in the warm and hot seasons, so it will last much longer.

Any service call will likely cost as much as a brand new window unit. A window unit can be replaced by a homeowner within minutes.

There is little or no corrosion of the coils in a window unit, since it either drains or evaporates within a short period of time.

Central air is generally oversized to maintain a constant temperature setting. Under sizing a window unit results in better humidity control. A gradual rise in temperature during the day and a lowering in the evening is easily tolerated by individuals living in the dwelling.

That's why I went to window units, even when I have central air in my house.

 

This only applies in your ducts go through an attic. Where I live, all the homes have basements and the ductwork is all internal to the home. On a one story, the ducts don't go far to get from the basement to the floor of the next level.

 

With central air, most windows are closed anyway. Window units can easily be framed through the wall, if blocking the window bothers you.

Newer window units are much quieter than older ones.

 

Most all new homes in the South are built on slabs without basements. Attics seem to be the only option. The South is where air conditioning is most needed.

In the future, even happening now, a basement can make ones house more vulnerable to flooding than they were in the past.

 

Mini splits are nowhere near the latest and greatest thing they’ve been around for over 40 years just lack of education in this country about them it’s become the new great thing. They have them now where are you direct drop in replacement of your standard size furnace or HVAC system the upright or vertical connected outside to a mini split condenser or heat pump. You can even replace the guts out of the existing old Train or Carrier unit on the rooftop slip in a Mitsubishi or a FUJITSU or an LG throw in one of their control boards and evaporator and run it off there condensing or heat pump without changing the entire system so now they are a direct replacement for even the old systems at a fraction of the price you can use with existing ducting and have Adjustable control unmanageable with the old systems. Any of the problems the old-timers are having with the new systems is all due to lack of education, correct training and inability to keep up with the times. All the American manufacturers have been becoming partners with the Asian markets Japanese Korean and China because they all owned the patents and have perfected the electronics to run the new compressors so they are borrowing that technology having it manufactured to for them and dropping it into the American brand-name units because Americans have dropped the ball and let technology pass them bye. Good example have you ever seen that advertisement years ago on a billboard . “ A brain is a terrible thing to waste” it’s a good explanation of the American education system. And why all the highest tech components most advanced reliable and energy-efficient are coming from every other country around the world except the United States.

 

That's a bit of a stretch. A lot of top technology comes out of the US every day. And where are foreign students coming to get their PhDs? Stanford and MIT PhD programs are crawling with non-US students. If the foreign tech was so advanced, they would be studying at home, wouldn't you expect?

 

The US might develop the technology, but it is the foreign manufacturing systems that brings the goods to the world at an inexpensive price.

My husband's friend states that he remembers paying $150 (1969 dollars) discounted for a 5,000 btu basic Westinghouse window unit. The same more efficient can be had for $136 today at Walmart even with the tariffs on Chinese goods.

The US technology developed the VCR and the DVD player. The East Asians made them affordable.

 

That’s exactly right and they go home take what they learned here and beat us at our own game. Most every advanced product or medicine from United States came from a foreigner who came to this country but with the education they brought with them. The majority of the new top 100 traded companies of recent came from foreigners from other countries and opened and expand their business in this country it did not come from the blood sweat and tears of American born students. Like my wife from Shanghai says (“it’s so easy to take American jobs in management positions and take over their companies they’re so lazy and uneducated and they don’t know what competition is.

 

We'll have to disagree on this. It appears you have a very limited perspective on this issue.

 

With HVAC knowledgeable people here, I'd appreciate a discussion of what refrigerants are currently used in what parts of this industry.

 

Absolutely,

For a thousand years and even with the Roman Empire, metropole countries have subjugated the colonial assets to live in subsistence, so that the metropole citizens can live in luxury.

The corporate controllers of industry, money and political influence in this country transfers the blame effectively to the efficient and harder working offshore workers, while they are the perpetrators of off shore manufacturing as their own profit.

Domestic workers are led to believe that the offshore manufacturers degrade the quality of life with the inexpensive goods that they could not afford, if they were manufactured domestically and the workers paid the prevailing wage.

They cannot have it both ways in a world market.

 

I am an advocate of more environmentally refrigerants, but I will not purchase small appliances with R600A. since the refrigerant if flammable.

 

More like that, please. Was not aware of use of R600a and R290. I'm baffled about why they cannot simply be called isobutane and propane. Among chemical names, those seem not nerdy at all.

 

It's called marketing to ameliorate fears from general knowledge that propane and isobutane are flammable and dangerous. The informed consumer will look for the flammable symbol on the appliance's carton. But, the majority will not.