Hi all,
My wife thinks I’m crazy, but I swear the new (and “better”) AC unit doesn’t cool as well as the old one.
We went from an old Coleman Unit (part outside and part in the attic) both about 15 years old. It was a 3.5 ton unit that was replaced because of a leak somewhere. Living in Houston TX, I think it did pretty well since we get 100+ F weather and could get it down to 74* without any issues.
The new unit is a 4 ton RUDD unit and was put in Aug of last year (2007). In the same weather, this thing is lucky to get us to 78* inside and runs all day…. I mean ALL DAY without stopping until after 8 PM.
This happened immediately after it was installed and was not a progressive issue, I just haven’t done anything about it until now. I don’t know why this would happen, anyone able to shed some light on it for me?
Houston, TX summer design is 95-dry bulb, 77-wet bulb or around 45% Relative Humidity. Humidity can vary big-time & cause less temp pull-down. You need to always keep track of the indoor & outside percent relative humidity.
Ruud is good equipment, the install & setup might have issues?
If there are setup issues that could explain the difference in performance
Did they change out the indoor coil with a matched coil?
However, the laws of physics explains some of the reasons why a higher 4-ton SEER matched system, might not perform as well as a 15-year old half a ton smaller 3.5-ton system.
All performance issues would have to be resolved before such a conclusion could be made
Your system may have been on the low end of CFM airflow for the 3.5-ton equipment. When they increased the tonnage of the equipment there would be insufficient airflow.
The higher SEER design engineering requires oversized coils & a smaller compressor Rated below the BTUH of the coils & thus that equipment.
The (SEER) Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80°F inside and 82°F outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER will NOT represent the actual seasonal energy efficiency of an air conditioner in your climate and your other environmental and system factors.
What happens in high temp climates or other extra heavy loads is that the refrigerant boils off in the evaporator faster than the volumetric capacity of the smaller compressor.
The suction pressure & the temperature of the evaporator rises, whereby, the lager compressor of the old design continues to handle the increased boil off vapor at a lower pressure & temp for the evaporator coil.
Under similar heavy load conditions the old better compressor capacity ratio will keep the coil much colder than the new lesser capacity ratio to coil & load ratios.
Many contractors appear to be up sizing by a half to a full ton to get the compressor capacity higher & then go to a lower 350-CFM per/ton airflow to help keep the evaporator operating at a lower temperature.
They should never have outlawed the production of 10 & 12-seer units, they did a good job cooling & the customer could more easily afford them.
The Supply Air & the Entering Return Air delta-T, – tends towards less & less as the EER/seer goes higher, therefore, dehumidification could become more difficult at the highest EER/seer levels.
Also, the EER & SEER levels widen, as SEER goes up. I have a table chart elsewhere illustrating the differences in three categories between from 7-EER to 13-EER,[/b]but cannot post a table here.
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