The Florida Solar Energy Center Logo
 
 
 
Home > Research > Photovoltaics > Virgin Islands Energy Office > Building Energy Audits > General AC Recommendations

Stylized Text: General Air Conditioning Recommendations.

Where air conditioning is used in tropical climates, it normally represents the largest single energy user in a building. Any efficiency gains that are made here have the greatest impact on the overall energy bill. The following strategies are recommended:

Reduce cooling load by focusing on:

Roof - Paint with light color, use radiant barrier or insulate
Windows - Use interior or exterior shading
Ducts - If ducts are present, test for leakage and repair
Other Areas - Reduce infiltration, lighting and equipment loads

Install Correctly Sized, Efficient Air Conditioning

Replace multiple AC units with a single unit where possible


Reduce Cooling Loads:

The heat that enters or is generated within a building is collectively called the cooling load, and this is where the focus must initially be placed. Reducing these loads will reduce the size and first cost of installing or upgrading any cooling equipment.

Roof

One of the largest sources of heat an air conditioner must remove comes through the roof. Since the primary mechanism of heat transfer is radiation, roof reflectance is a key concern. Fortunately, two very cost-effective options exist in light colored roofing and attic radiant barriers. White metal or white tile are the best choices in reflective roofing but if those are not practical an attic radiant barrier works well on almost any roof design. Both of these options also reduce heat gain to attic-installed ducts since attic temperatures are reduced by up to 25-30 degrees F. When insulating the attic space, install R-19 on buildings with white roofs and R-30 otherwise.

References:
White Roofs

Radiant Barrier (FSEC-CR-1231-01)

Windows

Another large contributor to heat gain, windows should have exterior or interior shading to reduce direct solar radiation. New windows are available that restrict solar gains while permitting visible light to enter but these are expensive. Exterior overhangs are best at reducing gains while allowing natural daylighting. Interior blinds operated by occupants can also keep radiation heat gain to a minimum.

References: - (www.efficientwindows.org), FSEC Windows Guide

Ducts

Ductwork, when present, can have a significant impact on air conditioning efficiency and occupant health, especially when installed in hot attic spaces. Ducts should be carefully inspected and when integrity is in doubt, a leakage test should be performed ideally with a Duct Blaster fan. Duct repairs should be made with mastic and fab-glas versus duct tape or other adhesives that tend to be short-term fixes.

Reference: Duct Repair (http://www.baihp.org/casestud/Bossier/index.htm)

Other Load Reduction Measures

Infiltration of hot and humid outside air should be reduced as much as possible. Penetrations in ceilings that allows hot attic air into the space should be targeted first since temperatures are greatest there (up to 140 degrees F).

Lighting heat must also be removed by the air conditioner. For every 3.5 kW of interior lighting, 1 ton of air conditioning is required. With the year-round cooling season of the Caribbean, efficient lighting saves energy both on its own and in smaller installed air conditioner capacity.

Office equipment constitutes the fastest growing portion of electrical loads in buildings. However, much of this energy is wasted because equipment is left on when not in use throughout the workday, at night, and on weekends. ENERGY STAR Office equipment uses about half the electricity of conventional equipment by powering down and entering "sleep" mode or off mode when not in use.

Install Correctly Sized, Efficient Air Conditioning

Using the measures above to reduce cooling load translates into smaller air conditioner equipment selection. In fact, a large portion of the cost of load reduction can be paid for by savings from downsized AC equipment. Once the cooling load is reduced, correct air conditioner sizing is essential for efficiency and indoor humidity control. An accurate load calculation should be performed to determine proper size.

The best efficiency in a central split unit is achieved with a 13 or higher SEER model with a variable speed air handler. This type of air conditioner will also remove more moisture than one with a constant speed blower. Packaged window units and mini-split ductless models come with an EER rating instead of SEER. The best models today have ratings of 10 EER or higher and save about 20% over older 8 EER models.

Other References:

Home Design Priorities