Methodology for the Evaluation of Natural Ventilation in ... - Cham

2.4.5 Short-Term MeasurementsThough long-term measurements are important for overall performance of a building, shorterterm and spot measurements can enhance these data. The short-term measurements can be usedto further explain the data collected over the long-term. Spot measurements at specific locationscan help in determining what is occurring within a building for a given set of parameters. Theseinsights can include the impact of solar gain on internal temperatures and airflow circulation onsunny days or impact of ventilation on internal conditions.Short-term measurements include detailed vertical temperature distribution, air velocitymeasurements and visualization. The introduction of air into the space and exhaust out of thespace is difficult to monitor over the long-term. Short-term measurements provide informationthat can be integrated into the long-term data to obtain the full picture of the building operation.2.4.6 Building BenchmarksMonitoring can provide important insight in to the operation of a building, and be used incomparing a building to other similar buildings. Often this technique can provide the impetus tofine-tune a building to further reduce its operating costs, or determine areas where there is roomfor improvement. Ventilation and thermal comfort requirements, and energy consumption, byeither annual usage by fuel type or by sub-system, can be measured to establish several keyperformance indicators, standards and benchmarks for building comparisons. The relativeperformance of the subject building can be obtained by comparing these measurements tocomfort scales. For both mechanically and naturally ventilated buildings, there are comfortscales, such as the American Society of Heating Refrigeration and Air-conditioning Engineers(ASHRAE) comfort charts; ASHRAE Standard 55 (ASHRAE 2004) provides separate comfortzones for mechanically and naturally ventilated buildings. Additionally for both ventilationtypes, carbon dioxide levels can be a key indicator for indoor environment and air quality. Healthand safety organizations (Environmental Monitoring Services, Bureau of Environmental HealthAssessment, ASHRAE) have published data for recommended exposure levels of carbon dioxidefor the working environment.Several factors should be quantified to determine a building‘s performance: occupancy andtemperature schedules, mechanical systems, other equipment, building size, any control systems,building envelope, lighting systems, and weather data (MacDonald 1989). Comparisons of theenergy used to condition the space (heating, cooling and ventilation) as well as lighting andequipment data (internal electric loads) can be used to determine relative performance inmechanically conditioned buildings, whereas for naturally ventilated buildings the primarycomparisons are to internal electric loads and heating energy usage. The energy usage values arebased more on the occupant and equipment density within the building, rather than its layout inmechanically ventilated buildings (air-conditioned standard and air-conditioned prestige), sincethere is a prescribed amount of ventilation that is delivered uniformly to all conditioned spaces ofa building. For natural ventilation however, the amount of energy used can be dependent on theconfiguration of the building, whether the office layout is open floor or cellular, and the numberof people within the space. For example, open floor plans tend to make better use of naturaldaylight throughout the space and have broader controls, whereas cellular offices restrict thepenetration of daylight into the core of the building, and normally have controls for eachindividual space.39