- Convincing proof of energy savings and performance in a
specific building and occupant context
If direct proof of savings is desired, the only feasible method of obtaining it is full
installation of the system in question in a building, together with appropriate measuring
equipment capable of determining the energy savings and performance level achieved.
Lighting and daylighting system tests sometimes take this approach. For window systems
this would entail installation of the window technology in question in all of the windows
of the building. Although expensive, such an approach might make sense for a large
institution planning to implement a well-defined and engineered fenestration strategy in a
large number of buildings, where initial implementation in an instrumented trial building
might provide a check on whether the strategy pays off.
However, it is very common that such tests at least initially discover unanticipated
aspects of the building that interfere with measurement or the intended operation. Even
when carried through to a successful conclusion, the information obtained in such a
measurement is usually very dependent on the building, its systems and occupants. That,
after all, is the information desired; but it also makes it difficult to extract
information from the tests that bears specifically on the window systems and how they
might perform in a different context.
- Impact on and acceptablity to occupants
A frequent use of field testing (e.g., the "full-scale mockup" in an
architectural design project) focuses on the interaction between the technology and the
occupants, without attempting to measure energy flows accurately. An example might me
installation of a one or more test windows in an occupied building. This can often yield
important information about unanticipated advantages, disadvantages or problems from the
user perspective, but information about energy flows (e.g., from IR thermography) is at
best qualitative.
- Quantitative
energy performance under a realistic range of physical conditions
The complementary approach is to concentrate on energy flows and generic information about
the window system, while excluding the interactions with the occupants and unrelated
building systems. This requires a specialized measurement facility. To prevent the
measurements from becoming comparably costly to the first case above, the facility must be
capable of sufficiently accurate measurements so that the energy flows through one or a
small number of windows can be used to provide useful information. The measurements must
be carried out under conditions that faithfully represent the variety of interior and
exterior conditions that a window might be exposed to in its normal functioning.
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