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This paper presents four ventilation controls for
variable-air-volume (VAV) systems. Their annual power
demand and indoor air quality (IAQ) simulation results
for an academic building as if it were situated in each
of six geographic locations are analyzed. The first
ventilation control satisfies the minimum system outdoor
air (OA) requirement accounting for the diversity of
ventilation-thermal load ratio of each zone. The other
three controls employ optimization techniques on one or
both of two air-side system variables: primary airflow
rate and supply air temperature (SAT). From an energy
perspective, ventilation controls using the optimization
techniques minimize the operating energy use of heating,
ventilating, and air-conditioning (HVAC) systems. The
savings from optimized primary airflow and/or SAT varies
in different geographic locations (or climatic zones).
This paper provides clear comparisons between optimized
ventilation controls in different climatic zones.
Compared with the non-optimization ventilation control,
the best control, optimizing both variables, saves up to
14% power in mild weather, while reducing power demand
only 2.1% in hot-humid weather.
This paper presents eight ventilation control
strategies and their annual energy and indoor air quality
simulation results for an academic building as if it were
situated in each of six geographic locations. The results
show that without tempering at the terminal boxes, no
ventilation strategy could satisfy the outdoor air
requirements when the thermal loads are low, and the
fixed outdoor air percentage method is the worst one.
From an economic perspective, strategies using
optimization techniques minimize the operation energy
demand and consumption. Supply air temperature and
primary airflow rate are the two proper optimizable
parameters on the air side of heating, ventilating, and
air-conditioning systems. In addition to control schemes,
geographic locations or weather patterns verify the
benefits of optimization. Generally, a mild-dry climate
signifies the advantages of the SAT reset and encourages
the primary airflow optimization. Inversely, hot-humid
weather minimizes the benefits.
Loss coefficient data for 9 ductwork fittings were
generated utilizing a commercially available
Computational Fluid Dynamics (CFD) code. A total of 159
unique coefficients were generated for the various flow
and geometry conditions. The computer code was used to
produce pressure field data necessary to compute the loss
coefficients, as well as to produce flowfield and static
pressure plots that offer insight into the physics of the
flow field.
The agreements between the published experimental and
representative computational results were well within the
15% error bounds, with 2 notable exceptions. The
exceptions were for the round die-stamped smooth radius
and the round 5-gore radius elbows, where the loss
coefficients obtained computationally were insensitive to
diameter change with r/D constant at 1.5. The reason for
the differences between the computational and published
results is shown to be due to absolute roughness
differences. The agreement has led to the conclusion that
computational techniques could be accurately utilized to
verify and expand duct fitting databases.
Results from the experimental phase of a much larger
research project are presented for three promising
ventilation controls capable of meeting the ventilation
requirements of ANSI/ASHRAE Standard
62-1989 with low energy use. Each control dynamically
adjusted the outdoor air (OA) requirement based upon
occupancy and measured building zone loads. Credit for
unvitiated air from overventilated spaces was also taken
in each control. Controls 2 and 3 used primary airflow
rate as an optimization variable to decrease the required
OA flow rate, thus reducing the energy needed to
condition OA. The supply air temperature in control 2 was
a constant, but was an additional optimization variable
in control 3.
The three ventilation controls were achieved by the
simulation/optimization algorithms resident in a stand
alone personal computer (PC) on site. A total of
twenty-four days of performance data were collected.
Typical day data sets for each control are presented in
some detail. The objective of the experimental phase was
to verify the reliability of the simulation/optimization
algorithms resident in the on site PC. That objective was
met for the each of the three controls since excellent
agreement was found between the measured data and the
control algorithm predictions.
The project objective was to control outdoor
ventilation airflow and distribution so that ASHRAE Standard
62-1989 was satisfied, while minimizing the impact of
energy utilization. The base system Direct Digital
Controls (DDC) are application specific, with
insufficient custom programming capacity to meet the
project objective by themselves. Three complex control
schemes were installed. In all cases the concept was to
continually reset the Outdoor Air (OA) fraction aspirated
into the Air-Handling Unit (AHU) as necessary to satisfy
ASHRAE Standard 62-1989. A personal computer based
system, independent from the DDC controls, was used to
collect data, perform the calculations, and send back new
control settings.
Based upon the perception that the world energy supply
is bounded, building mechanical system engineers have
taken many measures to reduce energy consumption since
the 1970's. Among the measures was a significant
reduction in the ventilation air provided to building
occupants. As a result, a host of building-induced
illnesses surfaced. In response, The American Society of
Heating, Refrigerating, and Air-conditioning Engineers
developed theANSI/ASHRAE
Standard 62-1989 "Ventilation for
Acceptable Indoor Air Quality," which set a
ventilation rate per person that was energy intensive.
Ever since, engineers and researchers have been seeking
the best ways to provide acceptable indoor air quality
(IAQ) with minimal energy consumption.
This thesis research provides a solution to ameliorate
the conflict between energy use and acceptable IAQ in
buildings served with variable-air-volume mechanical
systems. Eight ventilation controls were investigated,
and the resultant quantitative measure of IAQ and energy
consumption documented. Several of the controls employed
optimization techniques to achieve the desired results.
This research consists of two major portions, an
analytical portion and an experimental field evaluation
portion. In both the analytical and experimental
portions, a library building close to Harrisburg,
Pennsylvania, was used for evaluation. Detailed models of
the building and its mechanical systems were developed.
On an hourly basis for an entire year, the models were
used to simulate the building and its systems located in
six different geographic locations and operating under
each of the eight ventilation controls. Three of the best
controls were implemented into the library building and
data collected under various weather conditions to
confirm the analytical predictions.
The analytical simulations verified the necessity of
local tempering to ensure adequate outdoor air for a
zone. The simulations also revealed that the best
ventilation control, which simultaneously optimizes
primary airflow and supply air temperature, results in
the minimum energy consumption while providing acceptable
IAQ. The benefits of the best ventilation controls vary
with geographic locations (or climatic conditions). In
general, mild weather signifies the energy savings from
the supply air temperature optimization. The reduction in
the power demand is up to 15% in Los Angeles. Cold
weather is good for primary airflow optimization. The
reduction in the power demand is up to 7.9% in Chicago.
Conversely, hot-humid weather, such in Miami, flattens
the variations between different controls. In addition,
the field tests confirmed the reliability of the
simulation work and demonstrated the transformation of
the simulation code to optimization and control software
applied to a real system. Copyright © 1997 Yu-Pei Ke
This research, first, proposed a new method to
determine the dynamic zonal occupancy for ventilation
control based upon measured carbon dioxide (CO2)
concentrations in the supply and return airflows. The
central thesis of this proposed transient method was that
a fixed CO2 threshold based upon occupancy
alone is not possible under the current proposed BSR/ASHRAE Standard
62-1989R. Rather the actual dynamic occupancy
headcount must be known since the ventilation
requirements consist of two parts, the building component
and the occupancy component. The result is that the CO2
threshold must constantly be changed in time with
occupancy.
Based on the known occupancy, this research then
developed equations to determine the total unused outdoor
air (OA) flow rate in the discharge airflow. If the CO2
threshold is fixed, the quantity of unused OA can be
determined from CO2 concentration in the
return airflow; this is invalid for changing CO2
thresholds that differ from zone to zone. The scheme
developed in this research solved this difficulty and
determined the unused OA flow rate explicitly. Combined
with the transient occupancy-based ventilation scheme,
this algorithm is useful for real-time on-line
ventilation control and system optimization.
Finally, this research employed simulation results for
well-mixed office and conference rooms as the basis for
comparison of the proposed transient occupancy-based
ventilation with two other accepted methods: the CO2-based
ventilation and the constant airflow ventilation. The
simulation results show that calculated occupancy from
the transient equation follows the actual occupancy
precisely with a time lag equal to the measurement scan
interval. With the precise occupancy information, the
mechanical system can provide the exact ventilation
airflow required by standards. From a ventilation
perspective, the transient occupancy-based ventilation
scheme is better than the conventional CO2-based
ventilation, and without an energy penalty. Copyright
© 1997 Yu-Pei Ke
This paper proposes a new method to determine the
dynamic zonal occupancy for ventilation control based
upon measured carbon dioxide (CO2)
concentrations in the supply and return air. The central
thesis of this proposed transient method is that a fixed
CO2 threshold based upon occupancy alone is
not possible under the current proposed BSR/ASHRAE Standard
62-1989R. Rather the actual dynamic occupancy
headcount must be known since the ventilation
requirements consist of two parts, the building component
and the occupancy component. The result is that the CO2
threshold must constantly be changed in time with
occupancy. This paper employs simulation results for
well-mixed office and conference rooms as the basis for
comparison of the proposed transient occupancy-based
ventilation with two other accepted methods: the CO2-based
ventilation and the constant airflow ventilation. The
simulation results show that calculated occupancy from
the transient equation follows the actual occupancy
precisely with a time lag equal to the measurement scan
interval. With the precise occupancy information, the
mechanical system can provide the exact ventilation
airflow required by standards. From a ventilation
perspective, the transient occupancy-based ventilation
scheme is better than the conventional CO2-based
ventilation, and without an energy penalty. Furthermore,
this scheme is useful for real-time on-line ventilation
control and system optimization. Copyright © 1997 ASHRAE, Inc.
This paper presents eight ventilation control
strategies and their annual energy and indoor air quality
simulation results for an academic building. The results
show that without tempering at the terminal boxes, no
ventilation strategy could satisfy the outdoor air
requirements when the thermal loads are low, and the
fixed outdoor air percentage method is the worst one.
From an economic perspective, strategies using
optimization techniques minimize the operation energy
demand and consumption. Supply air temperature and
primary airflow rate are the two proper optimizable
parameters on the air side of heating, ventilating, and
air-conditioning systems. Copyright © 1997 ASHRAE, Inc.
Ultrasonic humidification has become increasingly
popular for both indoor air quality and energy related
reasons. The central thrust of this paper is to explore
these 2 reasons in depth. Application of ultrasonic
humidification, however, raises a number of design and
operational issues that are not important with steam
humidification. The 3 main issues, also emphasized in
this paper, are: heating coil requirements, supply air
temperature control sensor placement, and the impact of
the size and number of stages of humidification on supply
air temperature control hunting. Finally, the analytical
tools, currently missing from both private and large
public domain energy analysis software, are developed in
the paper and applied to a specific academic library
building located in central Pennsylvania. Copyright
© 1997 ASHRAE, Inc.
A criterion, based on optimization principles, for
determining the SAT setpoint in VAV systems is presented.
It is generally accepted that conventional SAT reset
controls (SATRC), bounded by either space humidity or
ductwork size, will save cooling and/or heating energy.
However, the ventilation consequences and penalty
resulting from increased fan power have generally been
overlooked. Ventilation is impacted since changes in the
SAT setpoint change the primary airflow rate and the
operation of economizer cycles, i.e. the distribution of
fresh outdoor air (OA). These changes may result in extra
energy demand and ventilation inefficiency if the reset
criterion is not appropriate. This optimization concept
simultaneously reduces energy consumption and meets
ventilation requirements. Simulation results illustrate
that the use of the optimized SATRC saves more energy
than a conventional one. Copyright © 1997 Elsevier Science Ltd.
The impact of close coupled ductwork fittings on
system pressure drop is the thrust of this paper. The
configuration was for a college library building. The
following research tools were employed: computational
fluid dynamic (CFD) analysis, scaled fitting and
arrangement testing in the laboratory, and full-scale
arrangement field testing. The research revealed that
close coupling of fittings can be either complementary or
detrimental, depending on the specific circumstance. For
the fittings investigated, close coupling resulted in an
approximately 27% higher pressure loss than predicted
using conventional procedures. Copyright © 1997 ASHRAE, Inc.
The multiple spaces equation of ASHRAE Standard
62-1989 makes it possible to bring in a
smaller fraction of outdoor air than that dictated by the
critical space. This paper develops an analytical proof
that increasing the primary airflow rate to the critical
space reduces the outdoor airflow rate required to meet
ventilation requirements. For systems employing
fan-powered boxes, where more than one box is critical, a
systematic procedure for incrementally increasing the
primary air is currently required. Also presented are
equations necessary to undertake such a systematic
procedure of incrementally increasing the primary air for
situations typically encountered in the operation of
fan-powered variable-air-volume systems. Copyright ©
1997 ASHRAE, Inc.
The central trust of this paper will be to derive a
generalized form of the multiple spaces Equation 6-1
which appears in ASHRAE
Standard 62-1989 (the Standard). The multiple spaces
equation currently in the Standard is for single duct
systems such as VAV systems using close-off boxes only.
In such systems all recirculated air is assumed to mix
with the outdoor air at a central air handling unit.
Since many VAV systems designed and installed today
employ fan-powered boxes, there was a sense of urgency
associated with deriving the generalization presented
here. The new generalized multiple spaces equation
extends the applicability of the multiple spaces concept
to include air distribution systems which can recirculate
a portion of the return air from well-mixed return
plenums directly back into the fan-powered terminal units
for mixing with primary supply air. Further, the work
illustrates that VAV systems employing fan-powered boxes
may often comply with the Standard while using less
outdoor air than would be required in a close-off VAV
system. Copyright © 1996 ASHRAE, Inc.
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, which also
provided valuable information on building thermal
performances especially during the design stage. (Content
in Chinese)
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. (Content in Chinese)
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)
Air enthalpy control strategy, or often known as free
cooling, has been very effective in conserving building
air-conditioning power consumption in moderate climatic
areas. However, it stands for a challenge in hot and
humid areas, such as in Taiwan, where outdoor air
enthalpies are constantly high.
Three control schemes, namely, temperature control
(economizer, or T-control) enthalpy control (H-control),
and the modified temperature control (MT-control), were
studied in this paper.
The MT-control method was actually applied on a
full-scale energy test house for experimental
investigation. Night ventilation in scavenging residual
heat gain through building envelope had successfully
introduced lower indoor temperature as expected in a
typical April day.
The simulation result of their annual performance was also validated that enthalpy control strategies have quite limited application potential in hot and humid areas, especially in the summer when cooling is most needed.
Send Comments to Yu-Pei Ke:
ypke@nkfust.edu.tw
Last : December 3,
2001
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