Transcribe NRG

Recommended HVAC Tasks

N-now HVAC tasks
Control Air Leakage
Seal/Insulate Ducts
Install/Increase Attic Insulation
Install Programmable Thermostats

R-research HVAC tasks
Shade Windows
Upgrade/Replace Windows/Doors
Increase Roof/Wall/Floor Insulation
Replace HVAC Equipment/System

G-green HVAC tasks
Install Solar Powered / Solar Assisted Air Conditioner
Install Solar Powered / Solar Assisted Heat Pump

HVAC - Overview

HVAC (Heating, Ventilation and Air-Conditioning) energy costs can be reduced by making improvements to the house envelope (walls, floor and roof), air distribution system and HVAC equipment. Since HVAC energy is the largest energy use category in most houses, reducing air leakage through the house envelope and within the HVAC distribution system is one of the most practical, cost-effective energy conservation measures.

HVAC - Air Movement

Air movement into a house (called infiltration) is influenced by air leakage. Air leakage occurs when there are openings (holes, gaps) within the structure and a driving force (wind, mechanical fan) to push the air through the opening. Wind is usually the primary driving force for air leakage in mild climates. When the wind blows against a house, it creates a high pressure zone on the windward surfaces of your house. This causes outdoor air to enter your house from the windward side and forces conditioned air to exit your house (called exfiltration) on the leeward side. In addition to excessive heating and cooling bills, air infiltration can cause other problems including: high humidity levels in summer and dry air in winter; allergy problems; radon entry via leaks in the floor system; mold growth; drafts and window fogging or frosting. Air leakage control is a simple concept that involves sealing all leaks between conditioned and unconditioned spaces with durable materials. Examples include: caulking or otherwise seal penetrations for plumbing, electrical wiring, and other utilities (note: use caulks and sealants which will remain pliable and will stick to the surface to which they are applied); sealing junctions between building components; and utilizing air sealing insulating materials like cellulose or plastic foam. The first step for minimizing air leakage is to seal as many holes (around windows, doors, and through walls) as possible. Additional effort should be given to finding and sealing other key sources of air leakage that are hidden from view (behind cabinets, around bath fixtures, within dropped ceilings, within chases for flues and ductwork, through insulation and attic access openings). While there are many well-known sources of air leakage, virtually all homes have unexpected air leakage sites that may require diagnostic testing to locate. Energy efficient house builders are striving for less than 0.3 air changes per hour under natural conditions. Older, drafty houses often have natural air leakage rates greater than 1.0 air change per hour. Energy professionals can perform blower-door tests to determine existing air leakage rates. However, it can be assumed that most houses (except for new, tightly-constructed houses) will benefit from efforts to reduce air leakage. While all houses need ventilation to remove stale interior air and excessive moisture and to provide oxygen for the inhabitants, the amount of needed ventilation varies based on the number of occupants and the design features of the home. Concerns about indoor air quality are leading some owners of tightly-constructed homes to install controlled ventilation systems to provide a reliable source of fresh air. When needed, the simplest approach to controlled ventilation is to provide spot ventilation of bathrooms and kitchens. For tightly-constructed homes, a good energy efficient option of adding outside air into the home is to install an air-to-air heat exchanger, or heat recovery ventilator (HRV). These systems typically have separate duct systems that draw in outside air for ventilation and distribute fresh air throughout the house. For most older homes, you can significantly reduce air leakage and still obtain sufficient fresh air through natural infiltration to maintain good indoor air quality. When in doubt, contact an energy professional to access your air leakage rates.

HVAC - Insulation

An energy efficient house should have a continuous layer of insulation around the entire building envelope. Insulation materials come in a variety of forms but the commonly used are fiber and foam. Fiber insulation includes fiberglass, cellulose and rock/mineral wool. Fiberglass comes in batt, roll, board and loose-fill form. Cellulose (made from recycled material) and rock/mineral wool (often contains a percentage of recycled material) are primarily available in loose-fill form so they are mostly used in attic insulation, however, with netting or binders these types of loose-fill insulation can be used for walls and floors. Foam insulations include extruded polystyrene, polyisocyanurate, polyurethane and polyicynene. The effectiveness of insulation is expressed as R-value per inch of material thickness. A larger R-value indicates that the material is a better insulator.

Most floors in conventional homes are constructed with 2x10 or 2x12 wood joists, wood I-beams, or trusses over unconditioned crawl spaces or basements. Generally, insulation is installed underneath the subfloor between the framing members. Typically R-19 fiberglass batts are used for insulating framed floors. These batts are installed flush against the subfloor. Recent studies have found that insulating the walls in crawl spaces can be an effective alternative to underfloor insulation. Note: to be effective the crawl space must be leak-free, remain dry and have a ventilation system to provide a controlled amount of air-exchange.

Attics over flat ceilings are one of the easiest parts of a home’s exterior envelope to insulate and provide a good opportunity for energy savings. In addition, some home builders are beginning to insulate the roof deck to create a conditioned attic space. Note: additional research and/or professional guidance may be required when insulating a roof deck to ensure that condensation will not form on the insulation surface during cold weather. Roof vents, or other attic ventilation systems, are commonly used to remove moisture from the attic that could potentially deteriorate insulation or other building materials. Attic ventilation also reduces roof and ceiling temperatures, thus saving on cooling costs and lengthening the roof's life. Note: building science experts are currently researching the benefits of attic ventilation. The combination of continuous ridge vents along the peak of the roof and continuous soffit vents at the eave provides the most effective ventilation. Electrically powered roof ventilators can consume more electricity to operate than they save on air conditioning costs and therefore are not typically recommended. Radiant heat barriers are reflective materials that can reduce summer heat gain in attics and walls. While not a substitute for insulation, they can be used in warm climates to lower air conditioning costs during the summer. Note: radiant heat barriers have a controversial history because some manufacturers have oversold their benefits.

HVAC - Windows and Doors

Windows and doors connect the interior of a house to the outdoors and provide ventilation and daylight. They also have relatively low insulating values. Although the efficiency of windows has improved markedly, they still represent a major energy liability in the home. The type, size, and location of windows greatly affect heating and cooling costs. Select good quality windows, but shop wisely for the best combination of price and performance. In general, double-paned units with low-emissivity coatings are a cost effective window choice. In summer, unshaded windows can significantly affect the cost of keeping your house cool. Energy efficient windows have a low U-factor, high transmission rates of visible light, low air leakage rates and low transmission rates of invisible radiation (ultraviolet and infrared light energy). Many improvements have occurred in recent years including: thermal breaks (to reduce heat losses through metal frames); inert gas fills between glass panes (to reduce heat transfer through the glass); tighter weatherstripping (to lower air leakage rates); and low-emissivity coatings (to reduce radiant heat flow).

U-factor (also called U-value) is the rate at which a window, door, or skylight conducts non-solar heat flow. It is usually expressed in units of Btu/hr-ft²-^oF. U-factor typically represents the entire window performance, including the frame. A lower U-factor means that the window, or door, is more energy efficient.

The Solar Heat Gain Coefficient (SHGC) is the fraction of solar radiation admitted through a window or door. Therefore, product with a higher SHGC rating is more effective at collecting solar heat gain during the winter and a product with a lower SHGC rating is more effective at reducing cooling loads during the summer by blocking heat gained from the sun. Window shading is a cost-effective way to reduce air-conditioning costs. Effective window shading options include overhangs, exterior shades or shutters and interior shades or shutters. Overhangs are effective on south-facing windows whereas shades and shutters are effective for east, south and west window orientation. Exterior window shading treatments are effective cooling measures because they block sunlight before it enters windows. The screens absorb sunlight so they should be used on the outside of the windows. These screens should be removed in winter to allow full sunlight through the windows. Shades or shutters located inside the house include curtains, roll-down shades and adjustable shuttles and blinds. Interior shutters and shades are generally less effective than exterior shading because they attempt to block sunlight that has already entered the room. However, if east, south, or west-facing windows do not have exterior shading, interior measures are beneficial. The most effective interior treatments are solid shades with a reflective surface facing outside.

Exterior wood doors have low insulating values. Adding a storm door to a wooden exterior door will slightly increase the overall R-value and reduce air infiltration. The best energy-conserving alternative is a metal or fiberglass insulated door. Metal doors have a foam insulation core, which can significantly increase the insulating value of the door.

HVAC - Ductwork

Poorly sealed ductwork is a very common problem that is often easy and cheap to fix. You could easily be wasting 10% to 30% of your heating and cooling energy because of duct leakage. In addition, duct leakage can lessen comfort and even be a health or safety risk. The best way to minimize duct leakage is to install the entire duct system within the conditioned space. However, ductwork is often located in unconditioned crawl spaces and attics and needs to be sealed using materials specifically designed for this purpose. Forced-air heating and cooling systems should be balanced so that the amount of air delivered through the supply ducts should be equal to the amount of air drawn through the return ducts. If these two airflows are unequal, then the pressure within the house will be affected. Pressure imbalances can increase air leakage into or out of your home. Pressure imbalances can create air quality problems in homes including: increasing air leakage from the crawl space to the home (note this air may contain dust, radon or mold). Homes with central returns can have pressure imbalances when the interior doors to individual rooms are closed. In addition, homes with kitchen vent hoods, clothes dryers, and/or attic ventilation fans, may experience negative pressures when these ventilation devices are operated. Many HVAC ductwork seams are not sealed properly during installation. When ineffective materials, including cloth duct tape, unrated aluminum tape, or similar products, using lower quality adhesives are used they will not provide an airtight seal over the life of the home. When applied properly, duct sealing mastic with fiberglass mesh tape, high quality caulking or foam sealant, and/or aluminum UL-181 tape will properly seal ductwork.

HVAC - Systems

When thinking about energy efficiency, the type and efficiency of the heating and cooling system is very important. Note: the operating efficiency of a heating and cooling system depends as much on proper installation as it does on the performance rating of the equipment. The two most common types of heating systems are forced-air and radiant. Forced-air heating systems are the most common in the United States. The heat source is typically either a furnace or an electric heat pump. Furnaces are generally installed with central air conditioners while heat pumps provide both heating and cooling. Furnaces burn fuels such as natural gas, propane, or fuel oil to produce heat and warm air. The efficiency of a furnace is measured by the Annual Fuel Utilization Efficiency (AFUE) rating. The minimum AFUE for most furnaces is now about 78%, with efficiencies of over 97% for furnaces that have condensing heat exchangers. The most common type of heat pump is the air-source heat pump. The heating efficiency of a heat pump is measured by its Heating Season Performance Factor (HSPF), which is the ratio of heat provided to energy used so the larger HSPF the more energy efficient the equipment is. Unlike an air-source heat pump, which has an outside air heat exchanger, a geothermal heat pump relies on fluid-filled pipes, buried beneath the earth, as a source of heating in winter and cooling in summer. Although more expensive, geothermal heat pumps are more energy efficient and are gaining in popularity. Another heat pump option is the dual-fuel heat pump. These heat pumps combine the high-efficiencies of using an electric heat pump in mild weather with the use of a furnace in colder temperatures when furnace operation is more economical than a heat pump.

Safety Note: unvented heaters that burn natural gas, propane, kerosene, or other fuels are not recommended. While these devices can operate without problems, the consequences of a malfunction may be life threatening as they can exhaust carbon monoxide directly into household air. Unvented heaters also can cause serious moisture problems inside the home. An example of an unvented unit to avoid is a vent-free gas fireplace note: use a sealed combustion, direct vent unit instead.

In the summer, air conditioners and heat pumps work the same way to provide cooling and dehumidification. They extract heat from inside the home and transfer it outside. Both systems typically use a vapor compression cycle. This cycle circulates a refrigerant, a material that increases in temperature significantly when compressed and cools rapidly when expanded. The exterior portion of a typical air conditioner is called the condensing unit and houses the compressor (Note: the compressor is the noisy part of the system that consumes the most energy) and the condensing coil. The air-handling unit, which is either located inside the house or packaged with condenser into a single exterior unit, houses the evaporator coil, the blower, and the expansion (or throttling) valve. The controls and ductwork for circulating cooled air to the house complete the system. The cooling efficiency of a heat pump or an air conditioner is rated by the Seasonal Energy Efficiency Ratio (SEER), a ratio of the average amount of cooling provided during the cooling season to the amount of electricity used so a higher SEER indicates more efficient equipment.

The most basic type of control system is a heating and cooling thermostat. Programmable thermostats, also called setback thermostats, can be big energy savers for homes. These programmable thermostats automatically adjust the temperature setting when people are sleeping or are not at home. Be certain that the programmable thermostat selected is designed for the particular heating and cooling equipment it will be controlling. This is especially important for heat pumps, as an improper programmable thermostat can actually increase energy bills. Larger homes often use two or more separate heating and air conditioning units for different floors or areas. Multiple systems can maintain greater comfort throughout the house while saving energy by allowing different zones of the house to be at different temperatures. The greatest savings come when a unit serving an unoccupied zone can be turned off. Rather than install two separate systems, automatic zoning systems that operate with a single HVAC system can be used. However, these systems must be carefully designed and installed to ensure that energy savings can be realized.

Solar Powered Air Conditioner (or Solar Powered Heat Pump)

Solar powered air conditioners get some or all of their power from solar. Solar photovoltaic panels are installed to produce DC power for these units. 100% DC solar air conditioners use the DC power from photovoltaic panels directly while hybrid AC-DC solar air conditioners are powered partial through solar power (either using DC power directly or using an inverter to obtain AC power) and require an AC power connection when solar power is not sufficient to power the unit. A third type of solar powered air conditioners is referred to as solar ready. These units connect to AC power that has been inverted from solar panels and connected to the AC grid.