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  • How Energy Efficient Upgrades Impact your HVAC System

    Many homeowners and business owners have added energy efficient upgrades to reduce their environmental impact. Double-paned windows and high quality insulation can decrease the amount that owners spend on heating and cooling costs. These efforts are also more environmentally friendly because energy is not lost due to leaks. However, many owners don't take into consideration the impact that these improvement have on the HVAC system of the home or business.

    Energy efficient improvements change the heat load of the house. In fact, the US Department of Energy calculated how much the heat load of a 2000 square foot house in North Carolina would change with energy efficient improvements. The hypothetical house improved the insulation in the ceiling and walls, upgraded to double-paned glass, increased the window overhangs and eliminated duct leakage by moving the ducts into the conditioned space. Before the updates, the house's heat load would have been 46,100 Btu/hr by the Manual J calculation. After the updates, it would have been only 21,300 Btu/hr. The energy efficient upgrades cut the heat load in half!

    Unfortunately, many people don't realize the impact that this heat load reduction has on the HVAC system. In the original home, a 4 - 5 ton HVAC system would have been installed. This large HVAC system would have been appropriately sized for the home. However, HVACs are sized based on the heat load. Therefore, after improvements, the proper HVAC sizing would be 2 tons. If the HVAC system is not upgraded with the rest of the house, it will not be properly sized for maximum efficiency.

    The Department of Energy evaluated how much energy savings would result if the HVAC system was upgraded with the rest of the house. With a new 2 ton HVAC system, the homeowners would save 63 percent on heating energy and 53 percent on cooling energy. If the homeowners did the rest of the upgrades but did not upgrade the HVAC system, they would save 54 percent on heating and 47 percent on cooling. It does save energy to do the other upgrades, but homeowners that match the HVAC system to the current heat load gain an extra 10 percent increase in energy efficiency.

    Long lasting HVAC systems are often not included in home and business energy efficiency upgrades. However, they should be. As the heat load of the home or business changes, the HVAC system should be matched to the needs. A right-sized HVAC system could boost the energy efficiency of the home by 10 percent.

  • A Checklist for Heat Load Calculations

    To have an HVAC (heating, ventilation and air conditioning) system run at optimal efficiency, homeowners and business owners need to know the heat load of the building. This metric, measured in tonnage, determines which size of HVAC system to purchase. Selecting the right size system is important for efficiency. For example, over-sized systems don't properly de-humidify the air during the summer. Under-sized systems may not be able to effectively heat or cool a building. Homeowners and business owners want the right size to have efficient heating and cooling.

    The most common way to determine the heat load of a building is a Manual J calculation. A licensed HVAC contractor can complete this calculation for a fee. However, there are some online Manual J calculators that allow home and business owners to complete their own calculations. The key piece is not the calculation, however, but the inputs. Owners must know many details about the building in order to complete a Manual J calculation. The checklist below contains the inputs required to do a Manual J heat load calculation.

    Materials for Walls, Ceiling and Floors

    A heat load calculation takes into account the insulation properties of the house. For this reason, it's not enough to know that a home is “brick.” Homes with brick walls also may or may not have insulation. The insulation can be various types. The same principle applies to ceilings and floors. A building plan or an HVAC contractor may be required to find out this information.

    Window Type

    The insulating properties of windows can also vary, depending on whether the window is single or double paned. Even the frame type (usually metal, wood or vinyl) has an impact on the heat load calculation.

    Door Type

    Surprisingly, there are differences in insulation properties between wood doors. In fact, there are multiple types of wooden doors in the heat load calculation. The insulation depends on whether the door is hollow or solid. Metal doors also have drastically different heat properties.

    Ceiling and Window Height

    The ceiling height helps to determine how much air needs to be warmed or cooled. Window height also has an impact on the heat load calculation.

    Length x Width x Height of Walls, Windows and Doors

    This information helps determine the size of the home or business and how much air needs to flow through the building for proper heating and cooling.

    Orientation of the Building

    The orientation of the front door and windows can be north, south, east or west. Southern exposure tends to be warmer in the northern hemisphere, since the sun hits that surface year-round.

    With this checklist, home and business owners can begin to complete a heat load calculation. There are online resources available to assist. However, it's important to note whether the calculation assumes the house is a “block” or it asks for the inputs for “room-by-room.” Block calculations are simpler to complete, but they don't tell owners how much heating and cooling is required for each room. To properly size ductwork and maximize efficiency, a room-by-room heat load calculation is preferred.

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