yaofeng wrote:

No. This guys has his business in our town and has been in business
for 35 years. He takes out about 1,000 permits a year. He did most of
the houses in my neighborhood. Actually one of my neighbors gave me
his number. He probably did the existing AC before I moved in the
house in 1990. We have had a couple of estimates for replacing the
system since late spring but kept procrastinating. His number is the
lowest, although not by very much.


What started it again was the AC
condenser went kaput a week ago. "The compressor heater went." (?) He sent
a guy to fixed it the same day coming to our house to give me the
estimate.

In addition to pricing, I am prejudiced because I like him. He
explains how things work to you.


If he puts that many A/C systems in two story homes the design should
have had them cooling both stories equitably!

I can explain to you how airconditioning systems work until hell freezes
over, and it means nothing if I don't design the systems I install in
two story homes to work properly for the occupants. I knew guys that
had been in the HVAC business for many decades and didn't do much right;
some keep doing it the way they had always done it and never learn to do
it right!

Running the returns up the walls should help some; have top and bottom
registers so you can close one off according to the season. (Use bottom
return for heating.)

Every home should have a manual J heatgain done by someone that will do
it right. You might be able to make some changes that would allow you to
drop down a half or full ton in unit sizing. A lot of 3.5ton systems are
only putting out 2 to 2.5-ton of cooling to the conditioned space.

For example I replied to this Tech: 35 ton 10 SEER system.

I'm at a loss for the 8 degree DT. HO has never said house doesn't cool
well just runs quite a bit when above 88 deg. Coils, ductwork, blower,
etc. checks OK. If I plug these numbers in my psychometric calculator
(which by the way works very well) I get these numbers

Here are my readings.

Ambient Temp= 78

Suction PSI= 70

Suction Temp= 61

Head PSI= 225

Liq. Line temp= 104

Entering DB= 74

Entering WB= 64.5

Leaving DB= 66

Leaving WB= 61

3.5-Ton equipment yielding:

17203 "total Btu/hr" Not even a 1.5-ton

13306 Btu/hr Sensible.

3717 Btu/hr Latent
What is up?
-----------------
The above tonnage loss is not as unusual as you would think; it is
rather common but not quite to that extent!
http://www.udarrell.com/ac-trouble-s...ubcooling.html
There is also probably a lot more wrong than just the charge and
airflow. - udarrell - Darrell
--

Factors in the Correct Sizing of Residential Air Conditioning Systems -
Recommended Procedures for Proper Duct Sizing of Residential Air Conditioning Systems
http://www.udarrell.com/proper_cfm_b...syste ms.html