Heating, Ventilation and Air Conditioning (HVAC)

HVAC systems contribute significantly to energy expenses and are indispensable in part because of comfort concerns for the occupants. In Alberta, heating your building is the most energy intensive part of your HVAC system.

Most small commercial buildings use natural gas fired hot air furnaces either free standing or as part of roof top heat/cool units. The most energy efficiency heating system for small commercial facilities is a condensing furnace, which utilizes a direct current (DC) electronically commutated motor (ECM) to operate the circulating fan. This system can save energy costs up to 40 per cent.

Important issues to consider in choosing a natural gas furnace are size, number of units and efficiency. The size refers to the input rating, in BTUs/hour, of your furnace and is determined by the heat loss of your building. A qualified contractor can supply a heat loss calculation.

Natural gas furnaces are rated by their Annual Fuel Utilization Efficiency (AFUE), which is the ratio of the energy output to the total energy input (BTUs/hr) by the furnace. All new furnaces have a label on the cabinet indicating the AFUE. In Alberta there are three types of gas furnaces:

Standard efficiency (50 to 79 per cent AFUE) These exist in many small commercial buildings, but are no longer available to purchase. They use a standing pilot light, single heat exchanger and indoor air for combustion.
Mid efficiency (80 to 85 per cent AFUE) These also use a single stage heat exchanger with electronic ignition, indoor air for combustion and a power controlled vent fan. These reduce the indoor air that is lost up the chimney, although some heat is lost even when the furnace is off.
High efficiency (90 to 97 per cent AFUE) The high efficiency is achieved through the addition of a secondary heat exchanger that recovers an additional 10 to 17 per cent of the heat produced by the burning gas. The cooler exhaust gases are vented through a plastic pipe to an outside wall instead of up a chimney.

There is no pilot light in high efficiency furnaces as burner ignition is achieved electrically. In the secondary heat exchanger, the combustion gases are cooled to a point where the water vapour condenses, releasing additional heat into the building. The condensate then runs into a floor drain. The exhaust gas is cool enough to be vented through a plastic (PVC) pipe, usually out the side wall of the building.

High efficiency furnaces have induced draft room sealed burners. These burners take the combustion air through a second PVC pipe from outside the building, which eliminates any loss of heated indoor air for combustion. In addition to the natural gas savings, a 20 to 30 per cent reduction of electricity used by the furnace blower fan can be realized by selecting the brushless DC ECM (Direct Current Electronically Commutated Motor) blower motor as an alternative to the AC induction motor.

Also available are Energy Star air conditioners, and depending on the buildings’ operating hours, should be considered if buying new or replacing older systems. Energy Star room units are at least 10 per cent more efficient than standard models and central systems are approximately 20 per cent more efficient.

Proper temperature control is an inexpensive method of saving heating and cooling energy. The thermostat setting determines how long a furnace or air conditioner runs and how much natural gas or electricity is used.

For heating, a general rule of thumb is for every 1° C you set back your thermostat for a minimum of eight hours, you will save up to two per cent. This can be particularly beneficial for businesses that close on weekends.

A programmable thermostat will automatically control the temperature to suit daily routines. It has multiple program settings that provide options for different settings for weekdays and weekends.

Temperature set-back works because the fuel required to re-heat a building to a comfortable temperature after a period of set-back is less than the fuel that would have been used to maintain the higher temperature through the same period. The greater the degree of set-back and the longer the period of set-back, the more energy and money is saved.

A common misconception is that the higher you raise a thermostat setting, the faster the building will heat up. Setting the thermostat to 21^o C will ensure the building space achieves that temperature quickly and with more comfort than setting it to a higher setting.