Keep a Lid on Summer AC Heat Gain

Published on: July 4, 2013

As summer heat intensifies, people are asking how to lower utility bills and yet stay comfortable. Heat gain increases the load on air conditioners, making the unit work harder and run longer to cool the air and reduce humidity.

Heat gain occurs in several ways: as solar heat from sunlight, as radiant heat from surfaces, walls and furniture and as casual heat generated by lighting and appliances like clothes dryers and ovens. Even people generate heat. A sleeping adult emits 80 watts of heat energy; a person doing heavy work emits 570 watts.

When heat gain is evaluated in the context of heating, ventilation and air conditioning (HVAC) systems, AC contractors look at sources of sensible heat and latent heat. Sensible heat describes heat that causes a change in temperature. Sunlight on a glass window pane causes a change in temperature. Latent heat does not cause a change in temperature. Instead, it describes the energy used to change the state of a substance. The change in state from boiling water to steam maintains a temperature of 212 degrees F. Latent heat includes humidity or moisture.

Cooling load refers to the amount of energy required for an AC to remove heat to produce a comfortable indoor space. Reduction in temperature reduces sensible heat. Reduction in latent heat reduces humidity.Air conditioners must be properly sized to adequately cool and remove humidity. Oversized units may achieve the desired indoor temperature but without removing enough moisture for comfort. Undersized units run longer to remove heat and moisture, causing the compressor to work overtime.

A certified HVAC professional will conduct an energy assessment of your building to evaluate the cooling load and determine the proper size unit required for effective remediation by the AC from heat gain. AC Southeast® serves a five-state area in the southeastern United States. Our contractors are familiar with the climate and weather conditions of the region and are qualified to recommend products and treatments that can reduce energy usage while maintaining a comfortable indoor environment.

Sources of Heat Gain

When evaluating an AC’s heat gain removal capacity, our contractors will look at both the building and the building site to determine the overall effect of solar radiation, radiant heat and casual heat. One of the primary factors is the climate where you live. Southern states have longer periods of summer heat and higher humidity than northern states, so cooling load will be greater. Other factors include:

Building orientation. South-facing buildings in the Northern Hemisphere get more sunlight than north-facing structures. In southern regions, south-facing orientations increase cooling load because more solar radiation penetrates the building. In northern regions with longer winters and shorter summers, south-facing orientations reduce heat load.

Roofs and attics. Rooftops can be more than 50 degrees F hotter than the ambient air temperature during the summer, even reaching 195 degrees F, depending on the type and color of roofing material, amount of surface area exposed to sunlight and orientation of the building. Roofing materials transmit heat to surfaces and spaces below, adding heat to the building interior.

Number of windows and doors. Windows are a major source of solar gain. South-facing windows allow more light to enter a building but also transmit more heat. During winter months, this may reduce heating needs. During summer months, it increases cooling needs.

Insulation. The amount and type of insulation in roofs, walls and flooring affects cooling load. The Department of Energy recommends different levels of insulation for each of the climate zones of the U.S.

Placement of casual heat sources within a building. Utility rooms, kitchens and bathrooms can affect cooling load. Place heat-generating rooms like laundries and kitchens on the north or east sides of a building to shelter them from extra sunlight.

Ways to Reduce Heat Gain

There are several ways to reduce heat gain and save energy.

 Landscaping and vegetation. The type and placement of vegetation on a site can reduce heat gain. Trees can be used as wind breaks, for shade and to channel breezes toward the building.  Shade trees lower roof temperatures. Trees that lose their leaves in winter allow solar heat to penetrate the building and reduce heating needs. Shrubs and plants near a building can reduce ground temperatures by up to 9 degrees. Trellises shade walls and reduce radiant heat gain.

Use materials that reduce roof temperatures. Reflective or light-colored roofing materials help to reduce solar gain. Cool roofs can reduce energy usage by up to 15 percent.

Attic Solutions . Adequate attic insulation helps to lower indoor temperatures by forming a heat barrier between the attic and spaces below. Reflective barriers installed below the roof in the attic keep radiant heat from entering. Attic ventilation fans reduce temperature and humidity.

Use window treatments. Curtains, blinds and awnings keep sunlight from entering during hot months. Reflective coatings on window glass reduce heat gain. Double- or triple-pane glass also reduces heat gain.

Our Services

AC Southeast® serves residential and commercial customers in Alabama, Florida, Georgia, Mississippi and South Carolina. Our local contractors are Bryant and Carrier Factory Authorized Dealers trained in all aspects of HVAC installation, maintenance and repair. Contractors employ North American Technician Excellence (NATE) certified technicians to ensure that you receive the best service possible. We service all makes and models of furnaces, air conditioners and heat pumps. We can also help you select products to improve indoor air quality.