HVAC

Heating, ventilation, and air conditioning represents almost half (47% according to the chart) of the energy usage of a typical home. Most, but not all homes, utilize natural gas for heating and electricity for air conditioning. If the heating and cooling system is a "forced air" system, the conditioned air (heated or cooled) is blown or ventilated throughout the house.

An important consideration when remodeling you home if you are going to replace the HVAC system and do other energy efficiency improvements is to "right-size" the heating and cooling system. "Right-sizing" means to reevaluate the energy needs of the whole home and size the heating and air conditioning appropriately. Typically heating and air conditioning systems were sized by "rules of thumb" based on the square footage of the house. Right sizing looks at the actually heating and cooling needs of the house based on the amount of insulation, efficiency of the windows and doors, appliances, occupants, orientation, and a number of different factor which attribute to the comfort of the home and size the system appropriately.

Heating

Heating in the Xtreme Energy Makeover house was provided by a natural gas-fired furnace located in a hall closet on the bottom floor. Combustion air was drawn in from the living area, which will cause unconditioned air to be drawn in from the exterior. The replacement furnace was installed in a vented attic space to use outdoor air and save energy from not using condition air in the furnace.

Air Conditioning

The Xtreme Energy Makeover house was cooled by a 3-ton air conditioning system. The condenser was located on the exterior on the north side of the house and was well shaded. The system was of unknown age and the nameplate information (manufacturer, size, serial number, etc,) was removed so little information was know about the unit prior to replacing it with an energy-efficient condenser and compressor.

Ventilation

Conditioned air was ducted throughout the house from the up-draft, forced-air furnace located in a hall closet on the bottom floor. Return air was drawn in from around the base of the furnace closet in the hall and living room and forced upward into a duct system that supplied both floors.

The most critical component of the HVAC's ventilation system is the ductwork. Ducts channel conditioned air to where it is needed. Leaky, bent, uninsulated, or compromised ducts reduce the amount of conditioned air getting to where it is needed, wastes critical energy, reduces indoor air quality, and makes residents uncomfortable. A complete duct inspection is a good idea, especially by pressure testing the ductwork to check for leaks.

Programmable Thermostats

One of the keys in energy management is with a programmable thermostat. These thermostats can be set to match the household comfort patterns.

The Replacement HVAC System

The Xtreme Energy Makeover house was analyzed and an HVAC system sized to meet the needs of the occupants after all the energy efficiency improvements are made.

Not only did the system include a state-of-the-art, high-efficiency (90% AFUE) furnace and a 2.5 ton air conditioning compressor, but it also included an efficient air filtration system and an air-to-air heat exchanger to recover heating or cooling from air brought in from the outdoors.

The new system was relocated into the attic so that the air needed for combustion in the furnace would come from outside and not use conditioned air from the inside. The duct system in the attic was replaced where needed and resealed to tighten up the duct system to improve indoor air quality and save energy.

Low Cost Cooling

A low-cost and energy-efficient way to provide cooling in a home is through "compressorless" cooling, that is cooling without using a typical refrigerant-based "air conditioner". The most common ways to do this is through passive ventilation, ceiling fans, whole-house fans, and evaporative cooling. Because of the climatic conditions of the location of the Xtreme Energy Makeover home an evaporative cooler was not included.

Passive Ventilation

Passive ventilation is using windows and doors to provide cooling and to keep a home from heating up. Doors and windows are opened in the evening allowing the home to "air out", bringing in cooler outside air for indoor air. In a two-story house this is assisted by a process called the "stack effect". Warm air rises and exhausts the air out of the second story windows, as this warm air leaves the building it is replaced by air that is drawn through lower floor windows and doors.

The second step to this process is to close the doors and windows in the morning to keep air that is being warmed by the sun out. This can keep the interior of a home much cooler and then the air conditioning system doesn't have to work as long or as hard to cool the house.

Shading

Keeping the sun off of the walls and windows keeps it cooler. Shade trees, awnings, overhangs, patio covers, etc. all act to keep your house cool by keeping it from being heated in the first place.

Whole House Fans

To assist the stack effect, especially in single-story homes, whole-house fans can be installed to physically pull warm air out of a home during the evening and night time when the outdoor air temperature is cooler. The air that is drawn out is then replaced by cooler outdoor air and the house cools down. The recommended way to use a whole-house fan is to operate it for 10 to 15 minutes and turn it off and let the air warm up inside the house and then operate the fan again. In this fashion the house is cooled down. Unfortunately, most whole house fans are operated in a continuous fashion and therefore use more energy than is necessary.

At the Xtreme Energy Makeover house another option was used, a two-speed, enrgy efficient, low-flow, whole house fan was installed. These fans are very quiet, and run it continuously while the outside air temperature is cool provides a quiet comfortable cooling effect throughout the night.

Ceiling Fans

Ceiling fans do nothing more than move air. Moving air has a cooling effect on our skin as it evaporates the moisture that accumulates on it. This is a relative cooling effect as the air itself is not cooled by the movement of the fan blades. By using a ceiling fan a comfortable temperature can be achieved at higher temperatures, instead of running an air conditioner at 76 degrees, the set point temperature can be increased to 80 or 82 degrees and occupants can feel the same cooling effect at a lowered energy cost.

Not all ceiling fans are energy-efficient. EnergyStar fans come equipped with compact fluorescent or circline fluorescent lamps that can't be exchanged for incandescent lamps. Even better fans are being made with special fan blades that move air easier and require less energy to do it.