ENTREVISTA A JUAN EDUARDO SALDIVIA MEDINA

Energy intensive mechanical systems have been identified as those which address indoor environmental control and domestic hot water functions. However, the design process always starts by identifying the problem to be addressed which can be referred to as the design intent. For domestic hot water systems, the goal is clearly to provide potable hot water to designated spaces within each dwelling unit. In the context of indoor environmental control systems, the problem consists of maintaining an indoor environment which may be different

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than the local outdoor environment. Specifically, the goal is to maintain acceptable thermal comfort and indoor air quality within the interior space.

Thermal comfort is a broad term which refers to a handful of different criteria. It identifies conditions which satisfy a statistically acceptable portion of the population with respect to the air temperature, mean radiant temperature, humidity, and air velocity. It is a heavily studied research area, and consequently is addressed by dedicated standards such as ASHRAE Standard 55 (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2013).

Indoor air quality (IAQ) refers to the concentrations of particles and gaseous contaminants found in interior air. As such, acceptable indoor air quality implies these particles and contaminants are within established safe ranges for human occupancy. In building applications, the practical solution to provide acceptable IAQ involves reducing or eliminating pollutant sources, direct exhaust of pollutants, and dilution of remaining pollutants with clean air often from outdoors. These general strategies can include filtration, air cleaning, humidity control, and airflow control. ASHRAE Standard 62.1 is frequently referenced by North American building codes, and establishes minimum acceptable ventilation rates and contaminant ranges (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2016).

Design functions describe the tasks which must be accomplished by the design in order to solve the problem and thus meet the design intent. Unlike thermal comfort and indoor air quality, which are broad terms, design functions are specific and tangible requirements. Mechanical systems may be required to address up to seven functions in order to meet the design intent:

1. Heating 2. Cooling 3. Ventilation

4. Filtration and air cleaning

17 6. Air pressure and airflow control 7. Domestic hot water

Heating, or space heating, refers to the addition of heat to conditioned interior space in order to maintain an interior temperature setpoint. The temperature setpoint typically is based on occupant thermal comfort, but in special circumstances can also serve to satisfy thermal energy storage requirements for objects or building materials within conditioned space. In Canada, some form of heating is required in all occupied residential buildings.

Cooling refers to the removal of heat from conditioned interior space in order to maintain an interior temperature setpoint. As with heating, the temperature setpoint is based on occupant thermal comfort and material requirements. In Canada, cooling in high-rise MURBs is only common in certain locations such as Toronto, but its use is becoming more common.

Ventilation refers to the supply of clean air, and the exhaust of indoor air in order to remove or dilute contaminants generated within conditioned space. Typical contaminants include carbon dioxide and water vapour from human respiration and perspiration, cooking and waste odours, and off gassing of objects and building materials within the space. Ventilation can be provided passively, but often requires an active mechanical solution.

Filtration and air cleaning refers to the removal of particulates and gaseous contaminants from air within conditioned space in order to keep concentrations within acceptable levels. Some level of filtration is always required for equipment maintenance and the removal of dust and allergens, but more substantial filtration and air cleaning may be required by individuals suffering from respiratory illnesses, or if the outdoor air itself does not meet IAQ requirements.

Humidification and dehumidification may be required in order to maintain the interior relative humidity within an acceptable range for thermal comfort – typically 20-70% depending on activity levels and the time of year (McQuiston, Parker, & Spitler, 2005). As with heating and cooling, the need for humidity control is dependant on the climate, and thus is of varying

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importance across Canada. In a marine climate such as Vancouver, humidity control is not often required in summer whereas in a climate such as Toronto, both humidification and dehumidification are often desirable.

Air pressure and airflow control refers to the manipulation of relative pressure differentials across interior and exterior partitions to influence the passive flow of air. Some level of air pressure control is necessary to reliably provide ventilation, but often additional requirements are imposed in order to meet other practical needs such as acoustic requirements, odour isolation, fire and smoke control, and thermal comfort.

Domestic hot water refers to hot water which is provided for sanitary or cooking purposes within designated spaces such as bathrooms and kitchens. While viewed as an amenity, Canadian building codes require the provision of domestic hot water within dwelling units when available. In the context of high-rise MURBs in major Canadian cities, DHW will always be required.