Heating and Cooling

Space cooling

Unlike the residential sector in which air conditioning is almost totally powered by electricity, air conditioning in Canada’s commercial and institutional sector is 84.8 per cent powered by electricity and 15.2 per cent powered by natural gas.

Common space cooling systems

Chillers, air conditioners and rooftop cooling units use what engineers call a vapour compression cycle to chill air. In these systems, a refrigerant is forced through a cooling loop, which includes an evaporator, a compressor, a condensor and an expansion valve. Within the evaporator, the liquid refrigerant gains heat from the building causing the refrigerant to vapourize; the compressor then pumps the refrigerant to a higher temperature and pressure. Within the condensor, heat is released from the refrigerant and it condenses back into liquid form; the refrigerant then passes through an expansion valve where its pressure is reduced and the cycle begins again.

Cooling towers are generally located on the roof of a commercial building, where outdoor air helps the heat from the building dissipate through evaporation. This technology creates a spray of water that is cooled with either a fan or natural wind currents; the water condenses and is returned at a cooler temperature to the building.

Evaporative coolers use the same principles of evaporation as do cooling towers, except they cool ventilation air. In this system, water is sprayed into incoming outdoor air and as the water evaporates, it cools the air. An additional form of cooling occurs when a secondary air stream is chilled by direct evaporative cooling; this air stream is used to cool incoming outdoor air through an air-to-air heat exchanger.

New space cooling technologies

High-efficiency air conditioning shares many of the same technologies as traditional air conditioning, but is designed to use up to 25 per cent less electricity. Condensors are larger to reduce condensing temperatures and compression ratios; air filters and cooling coils are also larger to improve heat transfer and reduce airflow velocity.

Radiant cooling systems rely on chilled water pipes rather than a conventional system of chilled air and ductwork to distribute cooling throughout a building. Based on the principle of radiative heat transfer, this system relies on cool water pipes to absorb heat generated by people inside the building. There are three methods of delivering chilled water in this system: through aluminum panels mounted on walls, floors or ceilings; through a capillary tube system which comprises a mat of small tubes encased in plastic; or through a concrete core with embedded tubes and thermal storage capacity for a cooling system.

Solar air conditioning refers to air conditioning that uses solar power. Passive solar building design slows the rate of heat transfer into a building in the summer; one of the more popular forms of passive design is green roof technology. As its name implies, a green roof is a lightweight engineered roofing system that incorporates rooftop vegetation while protecting the integrity of the underlying roof. Green roofs can help to reduce air conditioning use in small commercial buildings by absorbing heat; a reduction in one per cent of the temperature of a roofing surface removes five per cent of the demand for air conditioning electricity. Solar collectors may be used to provide energy for a building’s cooling system. This form of solar energy incorporates a glazed panel, a heat transfer circuit and a storage system including a heat exchanger. Hot water collected during the collection process makes steam, which is conducted into a turbine; the turbine drives a compressor that compresses the steam at a low pressure, which cools the air.

Energy Management Control Systems (EMCS) incorporate a sophisticated system of computers, sensors and communications links that monitors energy usage within a building at all times. An EMCS is designed to automatically control temperature and humidity in a building, and to turn off air cooling equipment temporarily during lower load conditions (i.e., late night/early morning hours when commercial buildings are usually unoccupied.)