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: December 3,
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The concern over the perception that the US energy
supply is bounded led building mechanical system
engineers to take many measures to reduce energy
consumption in buildings since the 1970's. Among the
measures was a significant reduction in the ventilation
air provided to building occupants. As a result a whole
host of building induced illnesses surfaced. In response,
ASHRAE developed Standard
62-1989 "ventilation for acceptable indoor air
quality". The standard set a ventilation rate per
person which went counter to the energy concerns of the
day. Ever since engineers and researchers have been
seeking the best ways to provide acceptable IAQ with
minimal energy consumption.
The piece of research presented in this report
provides an automatic control approach to ameliorating
the conflict between energy use and acceptable IAQ in
buildings served with variable air volume mechanical
systems. Eight control strategies are investigated, and
the resultant quantitative measure of IAQ and energy
consumption documented. Several of the controls employ
optimization techniques in real time to achieve the
desired results. The research consists of 2 major
portions, an analytical piece and an experimental field
evaluation piece.
In both the analytical and experimental pieces of the
research, a Central Pennsylvania library building was
used as the focus of the work. Detailed models of the
building and its mechanical systems were developed. The
models were used to simulate, on an hourly basis for an
entire year, the building and its systems located in 6
different geographic locations and operating under each
of the 8 control approaches. Three of the best control
approaches, each able to meet the ventilation
requirements at acceptable energy consumption levels, was
implemented into the library building and data collected
under various weather conditions to confirm the
analytical predictions.
The analytical results reveal that the control which
optimizes outdoor air flow and supply air temperature
resulted in minimum energy consumption and energy demand
while providing acceptable IAQ. The analytical work was
confirmed by the field study.
This energy improvement research project explored the
potential to simplify the real-time on-line optimization
control for building variable air volume (VAV) mechanical
systems. The research was undertaken in the context of
the AMP Headquarters building located in Harrisburg, PA.
The research revealed that in the AMP building 27% of the
zones were never critical and could thus reduce the
complications of the control. It was further found that
by forcing some critical zones to be non-critical
(accomplished by elevating the VAV box minimum primary
airflow rate settings) the system could be further
simplified with 39% of the zones now non-critical without
an increased energy penalty or indoor air quality (IAQ)
problem. Forcing more zones to never be critical rapidly
caused the energy advantages the real-time on-line
optimization control to decrease. The team is interested
in continuing this research by moving from the analytical
to experimental phase.
A complete implementation of the real-time on-line
optimization control in commercial buildings employing
VAV air-conditioning systems, to minimize energy demand
and consumption while meeting the strict IAQ standards
required by ASHRAE Standard
62-1989, is estimated to result in Pennsylvania
energy savings in excess of $40 million per year when
compared to other possible ways of meeting the standard.
An incalculable improvement in worker productivity and a
reduction in costly litigation from sick building
syndrome is also expected.
After the worldwide energy crisis in the 1970's,
building energy conservation attracted a lot of attention
and research efforts. In 1975, the first energy code was
established in the US, which utilized the Overall Thermal
Transfer Value (or abbreviated as OTTV) as an energy
efficient criteria and design guide in evaluating the
thermal performance of building envelopes. The OTTV
standard was again widely applied in ASEAN countries,
especially Singapore and Thailand with success.
In adapting the OTTV standard and probing its
applicability in Taiwan, a thorough parametric analysis
was performed in this study. Ten years of weather data in
Taiwan were compiled into an Average Weather Year, and 46
typical existing buildings in major cities of the country
were analyzed. Followed by applying the orthogonal array
analysis, the reference OTTV values in Taiwan to be
adapted in energy codes were completed.
A new index Envelope Cooling Load Value, or ECLV, was
originated during this research, which is based on a more
profound dynamic air-conditioning load theory. It was
justified to be more reliable in reflecting building
thermal performances, after carrying out the same
analytical methodology as in OTTV.
Finally, the Perimeter Annual Load, or PAL, initiated
and applied in Japan, was studied with results compared
OTTV and ECLV. The comparison among these 3 indexes was
performed to justify their applicabilities in Taiwan, and
this also provided valuable information on building
thermal performances especially during the design stage.
(Content in Chinese)
This project is the third phase of a long-term project
on building conservation study sponsored by the Energy
Committee of Taiwan. In this year, the topics are the
analysis of energy savings of (1) a passive design
strategy--internal shading, and (2) an active
system--chemical dehumidification encoupled hybrid
cooling system.
The study was first focused on "internal
shading." Through the dynamic air-conditioning load
calculation via program HASP8001, the theoretical energy
savings of internal shading on buildings in Kaohsiung
area can be analyzed. The experiment was then set up on
the Energy Test House, room A and room B. Actual tests
were conducted in October, June, and July to obtain the
actual weather data and air-conditioning power
consumption under internal shading, with and without
internal loads. It was found that, theoretically, in the
3 months of year, the internal shading would provide
24.0%, 24.6%, and 31.9% energy savings, respectively,
under no internal load condition. These values only
deviated from the experimental results by 13.5%, 5.1%,
and 8.8%, respectively. This result is within engineering
tolerances and thus quite satisfactory. The validation of
the mathematical model can only be performed under the
same operation conditions as stated above. After the HASP
validation was completed, the AYWD (Average Year Weather
Data) of the 6 large cities in Taiwan, namely, Taipei,
Taichung, Tainan, Kaohsiung, Taitung, and Hualien,
compiled during 1987's project, were then input into HASP
to evaluate the energy savings.
It was found that, under normal air-conditioning
system operation conditions, the annual energy savings in
imposing internal shading are 2.3%~3.7% only. This is
quite insignificant, especially when compared with the
"external" shading that was evaluated in an
earlier phase of this long-term project. It is also
concluded that, in Taiwan area, more efforts should be
emphasized on external shading design, instead of
internal shading.
On the other hand, in analyzing the chemical
dehumidification system, the study was conducted through
computer simulations and experimental investigations by
manufacturing a prototype system. The verification was
successful, which warrants further long-term research on
this system in the future.
The mass and heat transfer phenomenon involved during
the chemical dehumidification process was theoretically
formulated into a mathematical model. The model was then
numerically analyzed through Runge-Kutta scheme. The
analysis indicated that the predominant factors in
affecting the performance of a chemical dehumidifier are
the outdoor air conditions, rotational speed, air face
velocity, and silica-gel regeneration temperature. The
theoretical analysis was validated by actually
manufacturing a prototype desiccant drum using
silica-gel. The experimental results yielded only a low
10% deviation, compared with theoretical results. The
other components of the system were also analyzed, such
as the thermal wheel, which showed that 83% effectiveness
can be achieved. This condition occurred with an optimal
rotational speed at 12~16 RPH, while the evaporative
cooler was having an average outlet air wet bulb
temperature of 23 C because of the high humid weather in
Taiwan.
According to the original plan stated in the proposal,
only the chemical dehumidification system, composed of a
desiccant drum with evaporative cooler and thermal wheel
heat exchanger, would be studied. However, following the
successful theoretical and experimental analysis of such
a system, which yielded 8%~10% deviation only, the
research team was encouraged to extend the study of
another hybrid system, whose evaporative cooler was
replaced with a conventional vapor-compression
air-conditioner. The result was more successful. The
comparison of the experimental and theoretical results
indicated 5% deviation only.
The successfully validated simulation model developed
in this research was then utilized to generate the
energy, especially electrical energy, savings in Taiwan
area. An average 20.5%~25.3% electrical energy savings
can be experienced. The system can be even more effective
if the strategy of return and/or fresh air by-pass mixing
is utilized in design, which warrants further long-term
research in this area. (Content in Chinese)
Send Comments to Yu-Pei Ke:
ypke@nkfust.edu.tw
Last : December 3,
2001
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