NEW TECHNOLOGIES FOR ENERGY SAVINGS IN BUILDINGS
The energy auditor may consider the potential of implementing and integrating new technologies within the facility. It is, therefore, important that the energy auditor understands these new technologies and knows how to apply them. Among the new technologies that can be considered for commercial and industrial buildings include:
1. Building Envelope Technologies
Recently, several materials and systems have been proposed to improve the energy efficiency of the building envelope, especially windows, including:
• Spectrally selective glasses which can optimize solar gains and shading effects
• Chromogenic glazing which change their properties automatically depending on temperature and/or light-level conditions (similar to sunglasses that become dark in sunlight)
• Building integrated photovoltaic panels that can generate electricity while absorbing solar radiation and reducing heat gain through the building envelope (typically roofs)
Fig.1: Window Films Fig.2: Shading Technologies.
2. Light Pipe Technologies
While the use of day lighting is straightforward for perimeter zones that are near windows, it is not usually feasible for interior spaces, particularly those without skylights. Recent but still emerging technologies allow one to “pipe” light from roof or wall-mounted collectors to interior spaces that are not close to windows or skylights.
3. HVAC Systems and Controls
Several strategies can be considered for energy retrofits, including:
• Heat recovery technologies such as rotary heat wheels and heat pipes can recover 50 to 80% of the energy used to heat or cool ventilation air supplied to the building
• Desiccant-based cooling systems are now available and can be used in buildings with large dehumidification loads during long periods (such as hospitals, swimming pools, and supermarket fresh produce areas)
• Geothermal heat pumps can provide an opportunity to take advantage of the heat stored underground to condition building spaces
• Thermal energy storage (TES) systems offer a mean of using less-expensive off-peak power to produce cooling or heating to condition the building during on-peak periods; several optimal control strategies have been developed in recent years to maximize the cost savings of using TES systems
This is not really a new technology. However, recent improvements in its combined thermal and electrical efficiency have made cogeneration cost effective in several applications including institutional buildings such as hospitals and universities.
VERIFICATION METHODS OF ENERGY SAVINGS
Energy conservation retrofits are deemed cost-effective based on predictions of the amount of energy and money a retrofit will save. However, several studies have found that large discrepancies exist between actual and predicted energy savings. Due to the significant increase in the activities of energy service companies (ESCOs), the need became evident for standardized methods for measurement and verification of energy savings. This interest has led to the development of the North American Energy Measurement and Verification Protocol published in 1996 and later expanded and revised under the International Performance Measurement and Verification Protocol.
In principle, the measurement of the retrofit energy savings can be obtained by simply comparing the energy use during pre- and post-retrofit periods. Unfortunately, the change in energy use between the pre- and post-retrofit periods is not only due to the retrofit itself but also to other factors such as changes in weather conditions, levels of occupancy, and HVAC operating procedures. It is important to account for all these changes to accurately determine the retrofit energy savings. Several methods have been proposed to measure and verify savings of implemented energy conservation measures in commercial and industrial buildings. Some of these techniques are briefly described below.
- Regression Models
The early regression models used to measure savings adapted the Variable-Base Degree Day (VBDD) method. Among these early regression models, the Princeton Scorekeeping Method (PRISM) which uses measured monthly energy consumption data and daily average temperatures to calibrate a linear regression model and determine the best values for non weather-dependent consumption, the temperature at which the energy consumption began to increase due to heating or cooling (the change-point or base temperature), and the rate at which the energy consumption increased. Several studies have indicated that the simple linear regression model is suitable for estimating energy savings for residential buildings. However, subsequent work has shown that the PRISM model does not provide accurate estimates for energy savings for most commercial buildings. Single-variable (temperature) regression models require the use of at least four-parameter segmented linear or change-point regressions to be suitable for commercial buildings. , Katipamula proposed multiple linear regression models to include as independent variables internal gain, solar radiation, wind, and humidity ratio, in addition to the outdoor temperature. For the buildings considered in their analysis, Katipamula et al. found that wind and solar radiation have small effects on the energy consumption. They also found that internal gains have generally modest impact on energy consumption. Katipamula et al. (1998) discuss in more detail the advantages and the limitations of multivariate regression modeling.
- Time Variant Models
Several techniques have been proposed to include the effect of time variation of several independent variables on estimating the energy savings due to retrofits of building energy systems. Among these techniques are the artificial neural networks, Fourier series, and non intrusive load monitoring. These techniques are very involved and require a high level of expertise and training.
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