Question

What is the most green and economical replacement A/C system for our 1969 South Florida home?

Asked by Alice Martinez
Hollywood, FL

We would like to balance what is green and what is the economical to use. We can do a lot of work ourselves. We live in Hollywood. Also will need to replace an existing shingle roof soon with an insulated attic. We have gas for our water heater, stove/oven & clothes dryer.

Answer

Edward Wright

Answered by Edward Wright

Cincinnati, Ohio

Wright Design, LLC

October 3, 2012

Alice,

Given your location in a cooling dominate climate and your goal to perform much of the work, I recommend replacing your roof with an Energy Star 'Cool Roof' to reflect the sun's energy before it enters and warms your attic.

  • An example of this would be GAF's Timberline Cool Series
  • The shingles and their installation should also meet the uplift resistance of the local High Velocity Hurricane Zone requirements.

Next the amount of insulation should be adjusted to reduce the remaining heat transfer into your living areas adding up to R-30 for an attic with 3-4 inches is recommended by Energy Star's retrofit insulation table. Using blown-in insulation would balance efficiency, cost and DIY.

Right-size your A/C

Most critically, then the HVAC system should be right-sized to account for the roof's reflectivity and additional insulation.

  • Just matching the existing condensing unit's size could result in reduced energy performance and not maximize dehumidification.
  • Dehumidifying is critical in your climate. 

These HVAC comments are based on your home having or installing a ducted cooling system.

Mini-split system

If your system is not ducted, a mini-split system may be an alternative.

However, each interior air device in each major room (kitchen, living, bedrooms, etc.) will require a condensate line to convey moisture to a drain.

  • This can be done with pumps, if a basement is not present.
  • However, the presence of pumps brings additional maintenance to avoid line clogs and pump failures that could lead to possible mold growth.

With the ducted A/C system, there is only one air-handler and thus a short run from the condensing coil to a drain.

I recommend installing a 14.5 SEER Heat Pump Energy Star system to balance efficiency and cost. This way you've got the cooling covered and have heat, should the need ever arise.

Best of luck with your projects!

Edward

 

For more information:

Read "I have an Arizona home built in 1997 with a swamp cooler and an A/C unit. What is the most Energy Efficient way to cool my house?" a Q&A answered by Elizabeth DiSalvo.

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