Lawrence Berkeley National Laboratory
Environmental Energy Technologies
Indoor Environment Department
Energy Performance of Buildings Group
Lawrence Berkeley 
Introduction
Low-Energy Cooling Systems are using alternatives
to the conventional motor-driven compressor cooling system to provide high
thermal comfort and indoor air quality. The compression chiller process
is very reliable and was improved within the past decades but it is still
using refrigerants which can harm the atmosphere and contribute to the greenhouse
effect. In non-residential buildings, the power to operate the compression
chiller at design conditions can amount to 2/3 of the electrical power requirement
for an all-air system and the annual primary energy use of such a system
can be as high as 50 % of the building’s primary energy consumption.
Therefore, replacing commonly used motor-driven compressors with a more
energy-efficient cooling strategy constitutes in a significant energy conservation
measure and peak-power reduction potential. Additionally, more advantageous
rates for electricity can be achieved due to the reduced power demand.
Only after steps have been taken to reduce internal and external loads, low-energy cooling sources can effectively perform their task to be a competitive alternative to compressor-driven cooling. Additional savings are possible if the building’s thermal distribution system is optimized by separating the tasks of ventilation and thermal conditioning.
In general, low-energy cooling is a result of combining architectural design with HVAC technology and selecting appropriate materials, equipment and the cooling sources.
The main general concern of this project is not the "energy use" itself, but the environmental impact, which is caused by the use of primary energy to operate the building, to produce the materials and the systems, by the building process, and also the use of other precious resources, e.g., water evaporated for cooling purposes.
Low-energy cooling systems generally result in a reduced primary energy consumption during operation, but often require an increased material input. It is therefore essential to make an integral assessment of the factors influencing the environmental impact of such alternative cooling systems. An assessment has got to be based on a life cycle inventory, concerning all relevant substances and effects, and should take care of the real configuration and of the annual performance of such systems including the human behavior.
For the proposed project the following will be considered:
(A limited number of) the following thermal distribution systems, cooling technologies, cooling sources and energy sources for heat-operated machines will be investigated:
These strategies will be compared with conventional reference cooling systems in order to make an integral assessment of cost, as well as energy environmental effects such as
The control behavior will be different for the alternative systems and the reference system. Therefore the evaluation in function of the time of the year must be considered in order to calculate the annual energy consumption and pollution. This requires the use of dynamic simulation for the thermal behavior of the building and the cooling system. The building energy tool DOE-2 is used for this purpose determining the loads, the power demand and the energy consumption of the building.
The study is using a well-designed new office building, which is investigated under different European and Californian climatic conditions. The design of this building is based on recently realized projects in California and Switzerland considering all relevant aspects of building construction and operation in practice.
The Research Project
The environmental impact of low-energy cooling will be investigated in a
project conducted by the Lawrence Berkeley National Laboratory (LBL), the
Intep AG, Zuerich and the Eidgenoessische Technische Hochschule Zuerich
(ETHZ). The building used for this investigation was created by Intep and
basic data was provided (part 1 of the project). The set-up of the alternative
cooling strategies, the simulation runs, the evaluation of the results regarding
energy use and demand is done by LBL (part two of the project). The ETHZ
will determine the environmental impact of the alternatives investigated
(part tree of the project).
Results of the Simulation Calculations
The following results are part of the project dealing with the energy use
of the building which is funded by the Deutsche Forschungsgemeinschaft (DFG)
and the U.S. Department of Energy (DOE). Five different climatic conditions
are used (Test-Reference-Year) for the simulation runs.
As a first step the building design is optimized in order to reduce the cooling loads. One important aspect is the control of the shading devices. Exterior blinds are used which are controlled by radiation sensors. Since the shadings influence the cooling loads and the illuminance in the spaces an optimization of the shading trigger value is required.
The following Figure 1 illustrates the building’s primary energy use influenced by the shading control. Independently of the climate investigated a shading trigger value between 200 and 400 W/m^2 represents the most advantageous setting.
A state-of-the-art cooling system with VAV ventilation serves as a reference case, against which the various alternative cooling systems will be evaluated. Figure 2 compares the climates investigated by presenting the building’s cooling load through the year.
Example Results
Night ventilation
Using the cooler outside air at night to pre-cool
a building requires a significant thermal storage capacity and appropriate
climatic conditions. The dry and hot climate of Red Bluff does not offer
advantages night air temperatures so that night ventilation is not investigated.
When a conventional VAV system is pre-cooling the building at night by supplying unconditioned outside air remarkable energy savings can be achieved. Figure 3 presents these savings. The motor-driven compression chiller can be downsized and the power demand gets reduced (see Table 1).
Table 1: Percentage of chiller size and power demand with additional night ventilation when compared with the reference VAV system
Germany |
Switzerland |
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Evaporative cooling
When water is evaporated into an air stream the
air temperature gets reduced. Evaporative cooling takes advantage of this
characteristic by using direct and indirect evaporative coolers. Depending
on the climatic conditions and the thermal loads this cooling strategy is
able to either support the compression chiller or even replace it. Table
2 presents the possible changes for the chiller size and the power demand
and Figure 4 depicts the primary energy savings achievable.
Germany |
Switzerland |
CA |
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Assessing the environmental impact
The environmental impact of the alternatives investigated
will be evaluated by the ETHZ after having finished the simulation runs.
Please find a link to the report of Dr. Martin Behne to the Deutsche Forschungsgesellschaft at the end of this page.
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Last update of this page: March 11, 2004
For more information please go to www.eere.energy.gov
Download the report on Alternatives
to Compressive Cooling in Non-Residential Buildings to Reduce Primary Energy
Consumption by Dr. Martin Behne to the Deutsche Forschungsgesellschaft.
Please note that this is NOT an LBNL-Report; it has not been peer-reviewed!