Prepared for: 1997 Energy Evaluation Conference - Chicago
Paper dated: November 5,1997
Prepared by Proctor Engineering Group
Contributor: Michael Blasnik
Some sources suggested that efficiency problems are common due to inadequate bleed rates set by water treatment companies attempting to reduce the amount of treatment chemical required. The potential impact of scaling is severe and can lead to failure to meet the required loads. Air cooled condensers can also degrade due to fouling and, in coastal areas, corrosion. We concluded that there is insufficient information to assess the relative degradation of evaporative cooled condensers. A research plan was needed to assess degradation.
While no relative degradation mechanisms were identified directly from the design differences, We did locate some measured data which indicated that refrigerators may suffer from significant performance degradation with usage increasing by 5-10% early in the life of newer units and perhaps much more over the life of older units.
We examined degradation mechanisms common to new efficient and baseline units in order to assess whether some mechanism may affect the two types of units differently. We performed a detailed analysis of insulation R-value degradation and gasket leakage as two potentially significant common degradation mechanisms which could explain the usage increases. That analysis indicated that degradation of foam insulation R-value may increase energy usage by 5%-10% over the first one or two years and perhaps by 20% over the life of a refrigerator. However, because the high efficiency units have more efficient compressors and motors, this degradation would lead to increasing energy savings over time when compared to baseline efficiency units ("negative" relative degradation). The same conclusion would hold for any factor which increased cabinet loads (e.g., gasket deterioration) because identical increases in cabinet loads lead to essentially equal percentage increases in energy usage for both units, which leads to a larger absolute difference in usage.
Based on the analysis of design differences and common degradation mechanisms, we concluded that efficient refrigerators will not experience relative degradation compared to the baseline efficiency units. Instead, the savings from high efficiency units are likely to increase over time due to degradation mechanisms which affect both units by an equal percentage.
These improved phosphors also provide for better lumen maintenance over time. Lamp manufacturers take advantage of this fact, along with the improved luminaire light output per lumen, to further reduce lamp wattage. The net result is that T8 lamps typically provide fewer initial lumens than comparable T12 lamps, and may even provide fewer mean lumens, but will tend to provide the same average level of illumination to the space. We concluded that T8 lamps with electronic ballasts will not suffer from relative performance degradation compared to standard T12 lamps with efficient magnetic ballasts.
We examined surface depreciation, dirt depreciation, and interactive effects as the key factors which may cause relative light output degradation. Both reflectors and standard luminaire surfaces may depreciate over time. The little data available (from one manufacturer performing a limited range of tests) suggests that their front-reflective silver film reflector surfaces do not significantly depreciate due to ultra-violet, moisture, temperature cycling, or dirt build-up. These tests did not examine potential depreciation caused by abrasion or chemical attack from improper cleaning. In summary, we concluded that, while existing data are encouraging, there is insufficient information available to determine whether reflector surfaces may experience a relative degradation in light output over time compared to standard luminaires. However, we did identify a potentially more important light output degradation mechanism. Much of the apparent ability of reflector retrofits to maintain pre-retrofit illumination levels is due to lens cleaning and installation of new lamps. The impacts of these actions will degrade over time as standard maintenance schedules are re-established.
Overall, we conclude that energy savings from reflector retrofits will not degrade over time. However, light output may experience relative degradation due to reflector surface depreciation and, perhaps more importantly, the short-lived benefits of lens cleaning and relamping performed during the retrofit. Light output issues need to be explored in retention studies.
The net effect of the increasing energy usage over time will be a modest reduction in average savings of about 4%. The values of specific degradation factors for use in adjusting annual savings estimates depend upon not only the actual rate of usage increase, but also the nature and timing of the first year impact evaluation, the annual lamp operating hours, the lamp life, and relamping strategies. A table showing degradation factors under a variety of assumptions was developed to aid in applying the results.
In terms of light output, metal halide systems have comparable initial and mean lumen ratings as the mercury vapor systems which they replace. Differences in rated lamp life, variations in lamp/ballast/fixture combinations and interactions, and differing shapes to the lumen depreciation curves provide a complex set of factors for comparing light output over time. However, manufacturers and lighting experts all consider the lumen maintenance characteristics of metal halide lamps superior to those of mercury vapor.
The only direct technical degradation mechanism identified was dust or dirt accumulation on the detection ports, leading to decreased sensitivity. While no data on this effect were found, reduced sensitivity would not reduce energy savings because the lights would turn off more often. But if this reduced sensitivity caused occupants to over-ride or tamper with the system, energy savings would be compromised. These potential occupant interaction problems need to be explored through retention studies.
Researchers and manufacturers agree that motors do not degrade in efficiency over time unless they are improperly rewound. Operational problems which reduce the efficiency of the motor (e.g., bearing and insulation failure) rapidly lead to motor failure, not continued operation at reduced efficiency. A key study which supports these conclusions measured actual in-field efficiency of older motors and found that there was no performance degradation in units that had never been rewound.
Manufacturers and researchers stated that high efficiency motors are more reliable and less prone to problems than standard efficiency units because of their design, materials, and lower operating temperatures. In one manufacturer's accelerated life and extreme operating tests, high efficiency units had double the expected life of standard efficiency units. These tests also found that high efficiency motors are better able to withstand overloads, frequent starting, voltage and frequency variations, high ambient temperatures, and high elevations.
Our analyses of relative and absolute performance degradation mechanisms and other operating factors which may influence energy savings from efficient motors all indicated that there will be no relative degradation in energy savings over time when compared to standard efficiency motors.
While system efficiency is unlikely to degrade over time, overall energy savings may decline due to changes in control settings (e.g., from sensor degradation or changes in set points). One study identified changes in pressure control settings as a key factor in reduced energy savings at some sites with ASD control of VAV systems. No other information on sensor problems or improper control settings was located, but significant savings degradation could occur if these events are common. We concluded that ASD savings may degrade over time due to control problems and that these issues would be best addressed in the context of measure retention studies.
In summary, the energy savings from infra-red fryers could degrade slightly due to some units experiencing problems with combustion air supply. However, other design advantages are at least as likely to create an offsetting amount of "negative" degradation. We concluded that infra-red fryers are unlikely to experience an overall average degradation in energy savings relative to standard atmospheric fryers.
A literature review and discussion with insulation contractors and weatherization practitioners identified human intervention as the primary potential cause for degraded performance of blown and batt fiberglass (the most common material used in the California programs). In particular, the use of attic space for storage and disturbances/removal of insulation from contractor activities (e.g., cable TV, alarm, electrical, and HVAC contractors) were identified as two common causes for performance degradation. Heat transfer calculations were used to assess a "worst case" insulation disturbance scenario involving these events. The calculations indicated that the absolute rate of heat loss will increase by about the same amount in attics with the higher and lower insulation levels. There fore, while disturbances to attic insulation caused by human intervention may have a large impact on heat loss, no significant relative degradation should occur from higher insulation levels.
The lack of savings degradation from attic insulation is also supported somewhat from the encouraging results of billing analysis-based persistence studies of residential weatherization (which typically have attic insulation as a key component). In particular, a carefully performed persistence study covering a seven year period found that net savings were stable or increasing over time. While the stability of these savings over time may be due to many factors, including comparison group usage increases, they tend to refute the idea that insulation savings are significantly degrading over time. In summary, no mechanisms for significant relative degradation were identified and available studies support this conclusion. Therefore we concluded that the energy savings from increased levels of attic insulation will not degrade over time compared to the standard levels.
The commercial package air conditioner plan involves two stages. In the first stage, laboratory testing will be used to simulate a variety of heat exchanger fouling scenarios and measure performance impacts. This testing may find that no relative degradation will occur, and the research will be complete. If the testing indicates that a small amount of relative degradation may occur, then the involved parties may be able to agree to default estimates of degradation factors, avoiding more costly research. If the testing indicates that large relative degradation may occur, then a model which relates measurable fouling parameters to system efficiency will be developed and field testing will be used to collect data needed to quantify the relative degradation rate.
The evaporative cooled condenser plan involves a relatively large number of brief site visits to characterize the population and typical field conditions (including a visual assessment of fouling/scaling) with more intensive site testing and modeling of a selected sub-sample of these sites. A combination of test data, population characteristics, and engineering simulations will be used to quantify relative degradation.
The scope of this study involved examining how performance may change over time after a measure is installed. Therefore, installation problems are only accounted for to the extent that they may lead to continuing performance changes over time. The immediate impacts of any initial installation defects are assumed to be accounted for in first year impact studies. For example, if an air conditioner is improperly installed, any reduction in its initial efficiency is not within the scope of this project but should instead be captured in a first year impact study. However, if installation defects lead to continuing declines in efficiency over time, then those effects are within the scope of this project.
The potential impacts and interactions of operation and maintenance practices with measure performance were also considered in the analysis. In most cases, the efficient and baseline measures are essentially two variations on the same equipment and therefore maintenance requirements are identical or very similar (e.g., lamps, ballasts, air conditioners, motors, refrigerators, fryers, insulation). The degradation analysis assumes that maintenance would be comparable for such comparable products. In a number of cases, the efficient version of the measure is believed to be more tolerant of poor practices or adverse conditions. However, for commercial package air conditioners, maintenance issues were identified as a key aspect of potential relative degradation.
For several measures, the efficient and baseline technologies are very different and require differing maintenance and operating procedures (e.g., evaporative vs. air cooled condensers, reflectors, occupancy sensors, adjustable speed drives). These differences were considered in the degradation analysis. In the case of evaporatively cooled condensers, maintenance is a key issue and a focus of the research plan. In the case of reflectors, maintenance issues may affect light output, but not energy savings. For occupancy detectors, dust build-up may lead to occupants changing control settings or over-riding the system. For adjustable speed drives, operators may over-ride the system or adjust settings which compromise savings. For each of these three measures, the CADMAC subcommittee determined that these issues should be addressed through retention studies.
The retention issues identified in this project need to be communicated to any parties performing retention studies on these measures. In particular, retention studies for reflectors need to measure light output, studies for occupancy detectors need to record control settings, and studies for adjustable speed drives need to examine control settings and sensor calibrations.
success, a follow-up study is currently being performed on another group of measures which should complete the analysis in terms of regulatory requirements (total resource value of covered measures equal to at least 50% of total resource value by sector and utility).
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