535 research outputs found
Information Technology for Energy and Maintenance Management
We describe the design of a tenant interface for energy and maintenance systems (TIEMS) in commercial
buildings. TIEMS is designed for use by occupants (tenants) of commercial buildings. Our hypothesis is that by
allowing tenants access to information from the energy and maintenance systems and by giving them some control
over these systems, energy and maintenance performance can be improved. We used interviews with potential users
and existing energy and maintenance databases to guide the design. Results of a field trial demonstrate the utility of
TIEMS.
We also describe the design of a maintenance and operations recommender (MORE). MORE uses information
from computerized maintenance management systems (CMMS) and energy management and control systems
(EMCS) to recommend what maintenance personnel should do in response to a maintenance service request. MORE
integrates text descriptions of problems with sensor information related to the problem. After work orders are
closed, MORE uses the information about what was actually done to solve the problem to learn how to improve its
recommendations
A Thermal Sensation Index for Real-Time Tuning and Energy-Optimal Control of HVAC Systems
In this paper we discuss and develop a thermal comfort index that addresses the limitations of applying thermal comfort indices to control applications. The derivation closely follows the derivation of PMV, but certain changes and simplifications make the index an explicit, linearly parameterized function of environmental variables. We show that the differences between the derivation of this index and the derivation of PMV do not reduce the accuracy of the index in comparison to PMV. Since this index is linearly parameterized, the parameters can be quickly and efficiently tuned in real time to reflect the thermal sensation of the specific occupant. Parameter tuning makes it possible to accurately predict the thermal sensation of the occupant without exact knowledge of the activity level or clothing insulation of the occupant when these two quantities are known to be constant. Additionally, the tuning process makes the thermal sensation prediction relatively insensitive to sensor location because biases and scaling errors are absorbed by the estimated parameters. Real-time parameter tuning is demonstrated experimentally for a seated, stationary occupant. The feasibility of using variable air flow and variable heat flow to regulate the thermal sensation index in a way that minimizes power consumption is investigated. The simplified index provides a quantitative means for determining the most energy efficient comfortable conditions. The analysis demonstrates that for low to moderate outdoor relative humidity there is an energy optimal combination of air flow and heat flow
Multi-Sensor Single-Actuator Control of HVAC Systems
It is common to control several rooms in a
building with a single sensor in one of the rooms and a
single actuator driving just one control element such
as an air damper. New, low-cost, wireless sensor
technology now offers the opportunity to replace the
single sensor in one room with a network of sensors
having at least one sensor per room. This paper
addresses this multi-sensor, single-actuator control
problem. We used computer simulations and
optimization to study the problem. We designed a
computer simulation of the heat transfer behavior of a
section of a building that accounted for the effects of
weather, building materials, ventilation, and loads
from occupants and equipment. We considered ad hoc
methods (such as averaging) of using information
from multiple sensors. We also developed a new,
model-free method of using information from multiple
sensors that is based on a simple optimization
procedure. The optimization procedure can be
configured to optimize comfort or to optimize energy
under comfort constraints. We compared the
performance of the single-sensor strategy with the ad
hoc strategies and optimized strategies using annual
simulations of a four-room, perimeter section of a
building and weather data from Sacramento,
California. We report heating and cooling energy
performance along with two comfort metrics, the
average number of rooms within the ASHRAE
comfort zone and the Predicted Percentage
Dissatisfied (PDD). The results show that most of the
multi-sensor control strategies do better than the
single-sensor strategy on the basis of both energy
performance and comfort. The energy-optimal
strategy reduces energy consumption by 17% while
reducing PDD from 30% to 24%. The
comfort-optimal strategy reduces energy consumption
by 4% while reducing PPD from 30% to 20%. The
performance improvements occur primarily when the
average load among all rooms is nearly zero, with
some rooms requiring heating while others require
cooling. Under these conditions, the single-sensor
strategy either overcools or overheats, whereas the
multi-sensor strategies use almost no energy
Opportunities to Save Energy and Improve Comfort by Using Wireless Sensor Networks in Buildings
This paper discusses how intensive information
technology can affect future building operation.
Recent breakthroughs in wireless sensor network
technology will permit 1) highly flexible location of
sensors, 2) increased sensing density and variety of
sensor types informing more comprehensive control
systems, 3) occupants' involvement in control loops,
4) demand responsive electricity management, 5)
integration among now-separate building systems,
and 6) the adoption of mixed-mode and other new
types of air conditioning systems. The paper
describes the capabilities of the new sensor networks,
assesses how some applications can increase the
quality of control and improve energy efficiency, and
suggests opportunities for future development
Recalibration of the Complaint Prediction Model
This paper describes the evaluation and recalibration of the complaint prediction model developed by Federspiel (2000). We collected temperature time-series data and complaint data from six buildings ranging in size from 60,000 ft2 to 800,000 ft2 from three different geographical locations. Using these data, we found a low correlation between the observed number of complaint events and the Predicted Average Complaint Events (PACE) for the monitoring intervals and systematic underprediction of hot complaints. We recalibrated the model, increasing the correlation coefficient between observed number of complaint events and PACE to r = 0.49. This degree of correlation, though still not high, is statistically significant (p = 0.044). The recalibrated model predicts that the temperature corresponding to the minimum number of complaints is lower than that of the original model. The recalibrated model also predicts that the minimum number of complaints is greater than that of the original model. Finally, the recalibrated model is not symmetrical. The recalibrated model predicts that hot complaints will increase faster as the average temperature rises than will cold complaints as the average temperature decreases. We used complaint temperatures and an observed setup in building-wide mean temperature to validate the recalibration. From observed complaint temperatures, we constructed six hypothesis tests on predicted values of the mean and standard deviation of complaint temperatures. The differences between the predicted and computed complaint temperature statistics were not statistically significant in all six cases. We compared the observed effect of raising the mean temperature 3°F with the predicted effect. The observed hot complaint rate during the high-temperature period was 2.4 times higher than during the low-temperature period. The predicted ratio was 5.3 times. The difference was explained by underreporting observed by the chief engineer. We expected a dependence of the mean complaint levels on mean outdoor temperature because correlations between mean outdoor temperature, clothing insulation, and indoor air velocity have been established. However, we did not find such an influence. The complaint model predicts that the mean temperature for minimizing complaint rate on arrival is lower than for minimizing complaint rate during the occupied period of the day. This can be explained by a higher metabolic rate on arrival
Coordinated Control of HVAC Systems
This paper describes the development of new control logic for starting and stopping energy-intensive
equipment in buildings such as staged air-conditioning units. The concept is to use pulse-width
modulation (PWM) instead of level-crossing logic. A finite state machine is used to handle the case where
a single unit has multiple stages of operation. An optimized coordinator determines the phase of the PWM
signals of each unit so that peak demand for power is minimized over each PWM period. Control logic
for the PWM function was developed so that the phase could be manipulated by the coordinator.
Computer simulations were used to assess the performance of the new strategy and to compare it to levelcrossing
logic. The following five metrics were used to assess the performance: 1) magnitude of the
control error, 2) start/stop frequency, 3) average power consumption, 4) standard deviation of the power
consumption, 5) peak power consumption. The computer simulations showed that the new strategy could
reduce peak power consumption by 20% relative to level-crossing logic. The computer simulations also
showed that the new strategy increased the magnitude of the space temperature control error by 11% and
increased the number of start/stop operations by 27% relative to level-crossing logic
Cepheid Calibration of the Peak Brightness of SNe Ia -- IX. SN 1989B in NGC 3627
(Abridged) Repeated imaging observations have been made of NGC 3627 with the
HST in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs
in the F555W band and on five epochs in the F814W band. The galaxy hosted the
prototypical, `Branch normal', type Ia supernova SN 1989B. A total of 83
variables have been found, of which 68 are definite Cepheid variables with
periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is
determined to be (m-M)_0= 30.22+/-0.12 (internal uncertainty) using a subset of
the Cepheid data whose reddening and error parameters are secure.
The photometric data of Wells et al. (1994), combined with the Cepheid data
for NGC 3627 give M_B(max)= -19.36+/-0.18 and M_V(max)= -19.34+/-0.16 for SN
1989B. Combined with the previous six calibrations in this program, plus two
additional calibrations determined by others gives the mean absolute magnitudes
at maximum of = -19.48+/-0.07 and = -19.48 +/-0.07 for `Branch
normal' SNe Ia at this interim stage in the calibration program.
The second parameter correlations of M(max) of blue SNe Ia with decay rate,
color at maximum, and Hubble type are re-investigated. The dependence of
on decay rate is non-linear, showing a minimum for decay rates between
1.0< Delta m_15 <1.6. Magnitudes corrected for decay rate show no dependence on
Hubble type, but a dependence on color remains. Correcting both the fiducial
sample of 34 SNe Ia with decay-rate data and the current 8 calibrating SNe Ia
for the correlation with decay rate as well as color gives H_0= 60+/-2
(internal) km/s/Mpc, in both B and V. The same value to within 4% is obtained
if only the SNe Ia in spirals (without second parameter corrections) are
considered.Comment: 32 pages (with 7 tables and 14 figures) LaTeX, uses emulateapj.sty; a
full-resolution version with complete figs. 4 and 5 is available at
http://www.astro.unibas.ch/cosmology/papers.html ; accepted for publication
in Ap
Striatal responsiveness to reward under threat-of-shock and working memory load: A preliminary study.
Reward and stress are important determinants of motivated behaviors. Striatal regions play a crucial role in both motivation and hedonic processes. So far, little is known on how cognitive effort interacts with stress to modulate reward processes. This study examines how cognitive effort (load) interacts with an unpredictable acute stressor (threat-of-shock) to modulate motivational and hedonic processes in healthy adults.
A reward task, involving stress with unpredictable mild electric shocks, was conducted in 23 healthy adults aged 20-37 (mean age: 24.7 ± 0.9; 14 females) during functional magnetic resonance imaging (fMRI). Manipulation included the use of (a) monetary reward for reinforcement, (b) threat-of-shock as the stressor, and (c) a spatial working memory task with two levels of difficulty (low and high load) for cognitive load. Reward-related activation was investigated in a priori three regions of interest, the nucleus accumbens (NAcc), caudate nucleus, and putamen.
During anticipation, threat-of-shock or cognitive load did not affect striatal responsiveness to reward. Anticipated reward increased activation in the ventral and dorsal striatum. During feedback delivery, both threat-of-shock and cognitive effort modulated striatal activation. Higher working memory load blunted NAcc responsiveness to reward delivery, while stress strengthened caudate nucleus reactivity regardless reinforcement or load.
These findings provide initial evidence that both stress and cognitive load modulate striatal responsiveness during feedback delivery but not during anticipation in healthy adults. Of clinical importance, sustained stress exposure might go along with dysregulated arousal, increasing therefore the risk for the development of maladaptive incentive-triggered motivation. This study brings new insight that might help to build a framework to understand common stress-related disorders, given that these psychiatric disorders involve disturbances of the reward system, cognitive deficits, and abnormal stress reactivity
Observation of a critical pressure gradient for the stabilization of interchange modes in simple magnetized toroidal plasmas
The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. This gradient is reached during a scan in the neutral gas pressure pn. Around a critical value for pn, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure profile is locally flattened, stabilizing the interchange mode observed at lower neutral gas densities. The measured value for the critical gradient is close to the linear theory estimate
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