Wednesday, January 9, 2008

Energy Efficient Housing Construction: Ventilation and Conservation


Air Leakage

Older homes rarely suffered from a lack of fresh air. Air leaking in through cracks and holes in older homes and poorly built new homes can allow the entire house air volume to change more than once every hour. Air also leaks in to replacing air which is used by the chimneys and exhaust appliances or through upper storey windows (because hot air rises). Energy efficient homes do not have such air leakage problems. Homes today can be built so airtight that the entire volume of the home would take many days to be replaced. This would, however, lead to poor indoor air quality causing stuffiness, indoor pollution, odour buildup and high humidity problems.

Natural Ventilation

Although energy efficient homes stay cooler in summer because of high insulation levels, natural ventilation should be provided with opening windows or screened doors. On one and one-half or two-storey homes, windows opening on different levels will promote natural ventilation by convection on warm summer days and nights. Openings on different sides of one-level homes will permit cross-ventilation. There are times ventilation may be required in the winter as well. Sunny warm winter days (with a low sun angle) may cause short overheating problems in a well-insulated, properly oriented home - a fast and easy solution is to simply open a window or two for a short period of time.

Mechanical Ventilation Systems

A much more reliable and effective approach to use in today's world of well insulated and air
sealed homes is some type of controlled mechanical ventilation system. With a mechanical ventilation system occupants are able to control the ventilation rate, and have the ability to keep air pollutant levels as low as possible while increasing oxygen levels and avoiding the problems associated with uncontrolled air leakage. There are a variety of systems available, from exhaust only types to continuous, balanced mechanical ventilation systems.

Balanced ventilation systems are recommended because they exhaust stale indoor air and replace it with an equal amount of fresh outside air, thereby preventing any pressure differences from occurring. These systems should be designed to exhaust warm, stale air from major pollutant sources, such as bathrooms, kitchens, hallways and laundry rooms, while distributing fresh incoming air equally throughout the rest of the house.

Balanced Mechanical Ventilation Systems

Balanced Ventilation Systems

Non-Heat Recovery Systems are one type of balanced mechanical ventilation system. These systems use separate fans to exhaust stale house air and supply an equal amount of fresh outside air. This maintains the pressure balance within the house. It should be a system which exhausts and supplies air all over the home with separate ductwork or through a forced air system. Ventilation rates should be maintained between one quarter to one third air changes per hour (ACH).

Heat Recovery Ventilation Systems

Heat Recovery Ventilation Systems

Heat Recovery Systems are another example of a balanced mechanical ventilation system. They exhaust stale air and supply an equal amount of fresh air. The two streams of air are passed through the core of the heat exchanger, where heat from the exhaust air is passed to the cooler incoming air. Fresh air supplied to the rooms of the house has already been pre-heated, reducing the problems with cold drafts and the extra expense of pre-heating cold incoming air.

Since the stale, humid air that has to be exhausted contains heat, reclaiming some of that heat can reduce the energy loss while pre-heating cold incoming air. An air to air heat exchanger (also called a Heat Recovery Ventilator or HRV) is commonly used in energy efficient housing to extract heat from the outgoing air.

Currently available units are capable of extracting 70% to 80% of the heat from the exhausting air. Tying a heat exchanger into the return air duct of a forced-air heating system works well. The incoming fresh air is distributed evenly to all living spaces by the heating system duct work. An alternative for housing using non-forced air heating systems is to have the air-to-air heat exchanger separately ducted into each room. Either way the fresh air will mix well and, if a ventilation rate of one quarter to one third the total house volume is maintained each hour, humidity, odours and indoor air pollution will not be problems.

Heat Recovery Ventilator

Drawing air from bathrooms through a heat exchanger instead of exhausting it outdoors also saves heating energy in winter months. As mentioned in the construction section 'Roofs and Ceilings', exhaust ducts should be vented down interior walls to the floor joist space where they could easily be attached to a heat exchanger. Excessively humid air can cause an ice buildup in a heat exchanger but most commercially made models have a defrost cycle to control ice buildup.

Because of potential grease and lint problems, range hoods or clothes dryers should not be exhausted through an air-to-air heat exchanger. Recirculating range hoods with good quality filters will eliminate having to exhaust air from that source.

Water Conservation

Water Use

The importance of conserving water relates in two ways to energy efficient housing. Energy is used to heat water so lowering hot water use saves energy. Energy is also used to gather, treat and supply water, so lowering total consumption will also save energy. Rates paid for urban water and sewage services are rapidly escalating to meet the energy costs of processing, supply and disposal. In a rural situation, lowering total water use means less wear and tear on pumping equipment, lower electrical costs, lower treatment costs and fewer sewage capacity problems.

Water Volume Conservation

Although a lot of energy is used to heat water, the bulk of the total water volume a home requires is used for flushing toilets. In the typical household the toilet accounts for 43% of water usage, showers and bathing use 29%, laundry and dishwashing 19%, drinking and cooking 5% and 4% for other (car washing, lawn watering, etc.) New 1.6 gallon (6 litre) toilets can reduce toilet water usage by 60 to 80% . Composting toilets are also available which use hardly any water at all. Water reduction devices such as tap aerators, flow restrictors and low volume showerheads also help reduce water usage when washing or showering. Common sense can be applied to find other ways of lowering water usage - habits changed, wastage reduced, etc. In areas where water shortages may occur through drought or an unpredictable (or expensive) supply, conservation is doubly important.

Domestic Water Heating

In an average home, a large percentage of the energy purchased is used for domestic hot water heating. Domestic water heaters can use electricity, natural gas, propane, wood, coal and even solar energy as a heat source/fuel. Gas burning and electric hot water tanks are available in tank (storage) types and tankless (demand) types. Standard gas-fired water heaters have seasonal efficiencies of 50% to 60%. More efficient gas units with electronic ignition, induced draft fans and improved heat exchangers offer efficiencies of 75 to 80% but cost more. Electric units are more efficient but electricity is more expensive than gas so on going operating costs are higher. Locating water heaters close to the points of use and insulating supply lines will help improve efficiency. Point-of-use electric and fuel fired units which are installed directly in the kitchen or bathrooms work well but flow rates (2 to 4 gallons per minute) are low. Some hot water heating systems (usually boilers or combined systems) can also be used to produce domestic hot water in companion hot water tanks.

Using hot water efficiently also relates to efficient appliance operation. The hot water tank temperature need only be set at 120° (50°). Most new dishwashers have electric heating elements to boost water temperatures. Only full loads of laundry or dishes should be washed. Water level controls in clothes washers should be utilized for smaller loads and cold or warm water can be used for many cycles. Hot water use can further be reduced by installing flow restricting devices such as tap aerators, flow restrictors and low volume showerheads.

Preheating the cold water supplied to the hot water heater is another way of lowering energy consumption. Preheating can be done with a dark coloured tank placed so as to be solar heated in a sunspace, greenhouse or in front of a south-facing window.

Solar Water Preheating

Gray water heat recovery systems which can preheat incoming cool water are also available but are not approved for usage in all areas.

Domestic solar water heating systems are a proven technology which can make a significant contribution to the hot water requirements of the average family. A wide variety of solar domestic hot water systems are available. Modern solar water heaters will now work when the outside temperature is well below freezing and are protected from overheating on hot, sunny days. Many models also have their own built-in, back-up heater which can meet all of a consumer's hot water needs - even when there is no sunshine.


Electrical Energy Use

Electricity can account for one-third of the energy dollars a homeowner spends. The amount of energy may only be one-tenth of the total but, because electrical energy is more expensive per unit, it can be a significant part of your energy bill. Appliance operation and lighting accounts for most of the electrical consumption in the average home.


The use of electric lighting is a necessity in cold climates because natural light is in short supply in the winter. However, lighting can be designed for efficiency. Matching light output to requirements, locating light sources properly and using efficient fixtures are all points to consider in lighting design and layout.

When planning the layout of spaces and rooms, consider the functions and place the lighting accordingly. Work areas require more intense light levels than relaxation areas. Individual lamps may work better than a single ceiling source in bedrooms. Use highly efficient fluorescent light sources in task areas (like the kitchen, laundry or workshop). Use timers, sensors and dimmer switches to add flexibility, safety and security to your system. When available, natural light should be utilized through proper window layout.

Exterior lighting should be carefully planned as well. Avoid an excess - but do maintain a safe level. The lighting intensity (and positioning) should be at an adequate level to prevent accidents. Motion detectors or timers can be used to turn lights on and off as required and can substantially reduce energy usage and operating costs.

Appliance Selection and Use

Appliances such as refrigerators, freezers, washers, dryers and stoves consume a large portion of the electricity you buy. Buyers of new major appliances should check for energy usage labels to help choose products which use less energy. Look for labels which state in kilowatt hours per month the amount of energy an appliance will consume under normal usage. Potential buyers can save money by checking energy consumption totals when comparing similar models of appliances.


Regular maintenance of the systems in an energy efficient home is the most important point in keeping that home energy efficient. All appliances and heating equipment will operate longer, have less problems, and use less energy if properly cared for. On a notepad, or in a small scribbler-type book, routine maintenance or service (as pointed out in appliance manuals) can be recorded. The date, type of service, costs involved, time taken, or any number of points can be noted. It then becomes a good reference and convenient reminder for routine maintenance. Some major maintenance points include:

  • Heat distribution systems rely on an unimpeded movement of air. Keep duct work, fans and filters clean and make sure grilles, registers or convectors are not blocked by furniture or drapes.

  • The heat source should be serviced frequently during the heating season. Furnace units require filter cleaning monthly, motor lubrication twice yearly and regular visual checks on the blower drive belt condition, tightness and alignment. Hot water systems, using a boiler, rely on a circulating pump which should be lubricated twice yearly. The venting pipes and chimney connections should also be checked periodically for tightness or any signs of leakage or rust spots.

  • Wood space heaters or stoves should be checked periodically for tightness of connections and joints. As well, a thorough chimney cleaning is required periodically to reduce creosote deposit buildup. The frequency will depend on the type of wood burned and amount of use. You can monitor creosote deposits by occasionally looking in the chimney.

  • If your home utilizes solar energy, keep south-facing glass clean, absorbing surfaces dusted and mass floors uncluttered. If any ducts, fans, vents or thermostats are incorporated to move passively heated air then keeping those parts clean and air flow unimpeded is important.

  • Some energy efficient homes rely on window insulation to lower heat loss at night. Keep the edge seals clean on interior window insulation units. Regular lubrication of hinges, latches and operators may be required for exterior movable panels.

  • The domestic hot water heater should be drained every two or three months to remove sediment from the tank. Proper water treatment and filtering, if the water supply is questionable, will help prevent scale or sediment formation in the hot water tank.

  • Duct work used in ventilating the home should be kept clean. Dampers on exterior outlets should be adjusted so that closure is positive. Air-to-air heat exchangers should be cleaned regularly as should any auxiliary air filters installed in the system.

  • Major cooking, storage and cleaning appliances will operate more efficiently and last much longer if regularly maintained and operated as specified in service manuals. Clean reflective surfaces on stoves, heat exchanger coils on fridges and freezers, and replace filters on a regular basis.

  • Before purchasing major appliances or heating and ventilating equipment, consider some basic questions and facts that may affect your decisions. Buy from a reputable manufacturer or dealer, understand any warranties supplied, and find out about service, installation, and part availability. If possible compare each units efficiency and energy usage to insure the best overall performance. Be sure electrical, gas, and other hook-ups in your home will be adequate to handle the appliance load.

  • Read and make sure you understand installation, operating, and maintenance instructions. Establish whether the dealer will be installing and testing the device. Confirm a delivery date with the supplier and be on hand to supervise installation and testing. Remember to fill out any warranty forms, and to read, understand, and safely store all operating manuals.


mikesac said...

Appliance operation is expensive, but it can be less so when you buy energy star rated air conditioners .

Anonymous said...

great stuff man !!!! i never had this much knowledge on this topic..!!!