Environmental Engineering Reference
In-Depth Information
by individual equipment across the facility and concentrating the data into a centralized loca-
tion. This information may serve to different purposes, such as determining where the efforts
need to be concentrated, comparing equipment efficiency, becoming aware of maintenance
requirements, and evaluating the efficacy of preventive maintenance.
Electricity is the most straight-forward form of energy to be monitored because devices
that detect energy flows are easy to install. When energy is contained in fluids, such as steam
or natural gas, installing a meter is not as simple as in the case of electricity, but it is possible.
Different methods to measure fluids flow are available, such as orifice plate, averaging pitot,
vortex flow meter, venturi tube, flow nozzles, coriolis, and ultrasonic. Each method has advan-
tages and disadvantages and different levels of accuracy.
Energy efficiency at the building's level
In buildings, the focus of efficiency improvements is primarily on the building's envelopes;
heating, ventilation, and air-conditioning systems; and lighting. Opportunities for energy
improvements are in processing buildings, warehouses, and office buildings.
A good starting point is to conduct an assessment of the energy intensity of buildings to
establish a baseline and track improvements or to benchmark with other facilities and
national averages. Energy intensity of a building is a metric that indicates how much energy
is used per unit of area in a year. In the United States, data from the Commercial Building
Energy Consumption Survey (CBECS) for the year 2003 indicates the average (1990-2003)
energy intensity of office buildings is 88.0 kBtu/ft
2
/yr and warehouses and storage buildings
33.3 kBtu/ft
2
/yr (1 kBtu/ft
2
/yr = 11.72 MJ/m
2
/yr). The same source indicates that significant
variations in energy efficiencies exist for buildings constructed with different exterior wall
materials:
Bricks or stucco are the least efficient materials with an intensity of 102.8 kBtu/ft
2
/yr.
●
Concrete, blocks or poured 85.5 kBtu/ft
2
/yr.
●
Concrete panels 83.4 kBtu/ft
2
/yr.
●
Siding 70.8 kBtu/ft
2
/yr.
●
Metal panels 56.8 kBtu/ft
2
/yr.
●
Roofing materials make a more significant difference than wall materials. On average,
buildings covered with synthetic membranes or rubber have an energy intensity of 122.3 kBtu/
ft
2
/yr; slate or tile 101.9 kBtu/ft
2
/yr; and metal 54.9 kBtu/ft
2
/yr (CBECS, 2006).
In most buildings, the energy used by the building throughout its useful life is normally
by far larger than the energy spent to build it. Therefore, the selection of the right materials
when constructing a new building can minimize energy loss during its use. In existing units,
energy lost through the building envelope can be reduced by application of insulation, which
is not an easy task in industrial or commercial buildings.
For heating, ventilation, and air conditioning (HVAC) systems, most of the ideas suggested
in the section “Refrigeration Systems” for refrigeration equipment apply to HVAC as well.
Also, HVAC is the right candidate for the application of off-peak cooling described previously.
The installation of energy monitoring and control systems assists in the optimization of the
HVAC system in terms of management and tracking energy consumption. Management of the
HVAC system includes practices such as set-back temperatures during nonuse hours and
variable air-volume based on demand of heating or cooling. What is more, the installation of
building automation systems allows the control of not only HVAC but also lighting systems
and the metering of water, electricity, gas, and fuel oil services.
