VINDICATION is Sweet!  I have been railing for months that changing an outdoor unit to a 13- seer while leaving a 10-seer air handler was a mean, awful, nasty, unethical thing to do. I didn’t have the “run test” data to back up such a claim, just the number crunching of the engineering data.  That was then.

Now, the good folks at a local power company have done the research that has been so desperately needed to show the actual effect of this MIS-Match situation, and I applaud them for it.

• Up to 40% reduced capacity in cooling which means system may not be able to keep up with the thermostat.
• Up to 48% reduced capacity in heating resulting in heat strip coming on earlier.
• Up to 40% reduced efficiency in cooling resulting in higher power bills. Not only is it going to run longer, but also dollar per cooling will be more as well.
• Up to 60% reduced efficiency in heating resulting in higher power bills.
• System charging becomes critical since the charge might seem correct for one season but not another.
• TXV will not solve the charge problem for all cases since the Super Heat and Sub Cooling can change dramatically with condition.

All of these situations will result in numerous service calls and most likely the only way to resolve it is to replace the indoor coil with a larger coil anyway. 

In Florida the Energy TAC has produced a “DEC” statement that requires install at or above the SEER from the last time the system was inspected when changing component parts.  The data shows that unless both indoor and outdoor pieces or changed, it is a violation of the Florida Energy Code.

The real problem is that our state only has so much electrical energy available.   Since several hundred thousand of these change outs per year are being installed there will be a significant impact on peak energy consumption.  The amount of power required to run all these new units will dramatically increase and possible surpass that which the power companies are capable of supplying.

Governor Charlie Crist has recently issued and Executive Order that makes bold statements requiring significant mandatory increases in energy efficiency in new construction houses, and the appliances in them. This is a positive move, though the change-out market of A/C dwarfs the size of the new construction market.  All the efforts in new construction would be squandered if these inefficient mis-matched installations continue to be allowed in the market 12 + million existing systems that will most likely need replacement over the next ten years and not just new construction.

The hidden problem is that these mis-matched systems will require refrigerant charge modification twice per year.  In the Power Company scenario, that was the removal of approximately four plus pounds of refrigerant to allow the unit to operate in heating, only to have it reinstalled in the cooling mode.  The test results also clearly show that the application of a TXV does not eliminate the problem. 

Written by Bob Cochell, a FRACCA Board member and member of the Energy Technical Advisory Committee of the Florida Building Commission

Year after year, manufactures produce “higher efficiency equipment”, but will these new products truly deliver the savings you are looking for?  The short answer is “yes”, but it’s not only about the equipment.   In my experience, when customers are looking to purchase an HVAC system, they’re fixated on just the equipment and what SEER rating it delivers.  However, what they don’t realize is that when an HVAC contractor does a Manual J heat load on the house to determine the size of the system for the house, the ductwork must match the size of the system.  So if you need a 3-Ton unit for your house, you will need a duct system that delivers 1200 CFM, which is the amount of air a 3-Ton unit delivers.   If not, you could be wasting money on that new, expensive high efficiency unit you’re thinking of buying.  An inadequate duct system can cost you up to 40 % of the system’s efficiency.

I like to use the straw analogy. Take a straw from McDonalds.  If you ever grab a straw from McDonalds and blow through it, you’ll notice that there is no resistance. You probably didn’t have to work very hard to feel air come out the other end.  Now take a coffee straw and blow through it.  I’ll bet you’re huffing and puffing to notice a little bit of air coming out the other end.  It’s the same concept with your air conditioner and duct system. You’re the air conditioner and the straw is the duct system.  It has to work harder to produce the amount of air it is moving… which, in return, means higher electric bills, possible repair problems, and performance issues because it’s unable to deliver the air it needs to cool your house.

The key is to make sure you ask your contractor about the ductwork, how big your duct system is, and if the air conditioning system he is proposing will match your duct system.  Remember, when most people change out their heating and cooling systems, they have a low efficiency unit and are looking to upgrade to a higher efficiency unit.  Don’t spend thousands of dollars for a high efficiency unit if your ductwork isn’t correct.  If it’s not in the budget to do both, then go with a lower efficiency unit and get the ductwork fixed.  You’ll be much happier with your system from an energy and comfort standpoint.

Amount Of Air Put Out By Each System Size:

• 1.5 Ton system delivers 600 CFMs of air
• 2.0 Ton system delivers 800 CFMs of air
• 2.5 Ton system delivers 1000 CFMs of air
• 3.0 Ton system delivers 1200 CFMs of air
• 3.5 Ton system delivers 1400 CFMs of air
• 4.0 Ton system delivers 1600 CFMs of air
• 5.0 Ton system delivers 2000 CFMs of air