In order to feel comfortable in the cooling season conditioned air has to be at the right air temperature AND relative humidity. Conventional AC dehumidifies when it is running but it is thermostatically controlled by air temperature only. Which means that when air temperature is reached the AC turns off and stops dehumidifying. Not a big problem if you live in an arid climate such as Pheonix but if you live in New England where the summers are very humid and not THAT hot then you most likely will never get that perfect comfort combination of cool and dry air.

To exacerbate the problem further a recent North East utility study determined that 100% of AC systems are over designed and that more than 50% are over designed by more than 100%. Which is why summer AC in Connecticut (my home state) is typically cold and dank, (I hate it). Why does this happen? For example; let's take a typical July day, 86 degrees and 95% relative humidity, put the AC on and the system blasts on at 100% capacity and quickly lowers the air temperature and doesn't cycle long enough to dehumidify. Now the air temperature is OK but the occupant is still not comfortable because the air is too humid, so what do they do? Right, they lower the thermostat some more to make the air even colder but it is still too humid. It is actually impossible for the conventional AC system to achieve comfortable conditions.

Bottom line on conventional AC is that is works poorly most of the time. Primarily because it cannot load match and therefor can't cycle properly to control air temperature AND humidity at the same time. My recommendation is to switch to an inverter driven air source heat pump that can modulate to always match the load and actively dehumidify (many actually have a dry mode). This type of operation not only optimizes comfort but greatly contributes to overall system efficiency that is not reflected in the outdated SEER rating system that only measures systems at full capacity working only to lower air temperature. An added bonus is that inverter heat pumps also work amazingly well in heating mode too. Let's stop trying to even make conventional AC work and move on to the next generation of HVAC equipment that does the job right.

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Tags: AC, air, comfort, dehumidification, heat, indoor, pump


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Comment by Steven Lewis on May 25, 2012 at 11:25am

MIni splits work fine as spot cooling/heating and inverter tech is great but has a long way to go to meet loads in Kansas. 

Even the manufacturers say their product in not designed to handle whole house loads or conditions.  (Meeting last month with the sales tech rep)    how do you move air from your two rooms to the other 4 to 6 rooms and have any comfort or temp control?  I have installed minisplits and they work in their application but they will not replace whole house central systems  especially at our high elect rates vs low gas prices.  

Just because something is a solution to a problem does not mean it THE solution to all problems. 

Comment by Joseph Novella on May 24, 2012 at 1:14pm

Actually you could install a 3-ton Fujitsu or Daikin mini split inverter heat pump system with two indoor wall mounted air handlers for about $6,500 in a day or so. Also I would not emulate "what the AC pros do" in their homes, thats how we got into our current poor state of affairs regarding horrible system design and deplorable efficiency. 


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