SummarySeven homes from the Pacific Northwest were selected to evaluate the differences between estimated and actual energy savings achieved from deep energy retrofits. The energy savings resulting from these retrofits were estimated, using energy modeling software, to save at least 30% on a whole-house basis. Modeled pre-retrofit energy use was trued against monthly utility bills. After retrofits were completed, each of the homes was extensively monitored, with the exception of one home that was only monitored pre-retrofit. This work is being conducted by Pacific Northwest National Laboratory (PNNL) for the U.S. Department of Energy Building Technologies Program as part of the Building America Program.Previous research has shown that realized savings from retrofit measures may not be consistent with energy savings estimates produced by modeling software (Lancaster et al. 2012;Parker et al. 2012;Polly et al. 2011). In previous studies, research has generally shown models to over-predict energy savings and energy use, especially in older, less efficient homes (Polly et al. 2011). Modeling occupant behavior has proved to be especially important for improved model accuracy and have found that detailed audit inputs, including operational behavior, can successfully increase the accuracy of models to within ±25% on a whole house basis ).However, this study found that by truing models based on whole-house energy consumption and utility bills, offsetting errors can give the illusion of accuracy when in fact individual end-uses are substantially different than the model predicts. This can make determining the fundamental accuracy of the model (e.g., how well model predicts energy use at the component level) and identifying the root cause of inaccuracies difficult because sources of error can act simultaneously and confound one another (Polly et al. 2011). Sub-metered energy usage data are required for robust calibration of individualized models of a single home and homeowner . In this research project, seven homes in the Pacific Northwest that have undergone extensive energy retrofits and were sub-metered. For six homes the monitored post-retrofit energy usage was compared to energy models that were trued based on preretrofit utility bills. The seventh home was monitored pre-retrofit, however, post-retrofit analysis was not completed because the retrofits were not completed in time for this report. With sub-metered data, the accuracy of the overall whole-house model as well as the accuracy of specific equipment profiles can be examined.This work found many discrepancies between actual and estimated energy savings and identified the potential causes for the discrepancies. The differences between actual energy use and modeled energy use also suggest improvements that could be made to enhance model accuracy. The difference between whole-house actual and estimated energy savings on a monthly basis ranged from 75% more energy saved than predicted by the model to 16% less energy saved for all the monitored homes. Similarly, th...
SummaryIncreasing penetration of heat pump water heaters (HPWHs) in the residential sector will offer an important opportunity for energy savings, with a theoretical energy savings of up to 63% per water heater 1 and up to 11% of residential energy use (EIA 2009). However, significant barriers must be overcome before this technology will reach widespread adoption in the Pacific Northwest region and nationwide. One barrier is that the demand response (DR) performance and characteristics of HPWHs is unknown. Previous research has demonstrated the potential of electric resistance water heaters (ERWHs) to provide significant grid stability and control benefits through demand-side management, or DR, strategies (Diao et al. 2012). However, if ERWHs are to be replaced with HPWHs to improve residential energy efficiency, it is important to understand the DR characteristics of HPWHs and how these characteristics will impact DR programs and overall grid stability now and in the future.This project evaluates and documents the DR performance of an HPWH as compared to an ERWH for two primary types of DR events: peak curtailments and balancing reserves. The experiments were conducted with General Electric (GE) second-generation "Brillion™"-enabled GeoSpring™ hybrid water heaters in the Pacific Northwest National Laboratory (PNNL) Lab Homes 2 , with one GE GeoSpring water heater operating in "Standard" electric resistance mode to represent the baseline and one GE GeoSpring water heater operating in "Heat Pump" mode to provide the comparison to heat pump-only DR. Signals were sent simultaneously to the two water heaters in the side-by-side PNNL Lab Homes under highly controlled, simulated occupancy conditions. It is expected that "Hybrid" DR performance, which would engage both the heat pump and electric elements, could be interpolated from these two experimental extremes.Based on the data collected in these DR experiments, both ERWHs and HPWHs are capable of performing peak curtailment and regulation services. However, their characteristics differ, as can be seen in Table 5.1, which shows the average impact on power use during the DR event, energy use during the DR event, and daily energy use for ERWH and HPWH for peak curtailment, 1-2 hour balancing events when generation and load are mismatched either due to higher load than generated power (INC events) or greater power generation than available load (DEC events). In general, the HPWH has much lower power use than the ERWH (587 Watts [W] versus 4,650 W) and provides approximately 38% of the potential to reduce load for peak curtailment or INC balancing events of the ERWH. The ERWH provides more dynamic response with a high magnitude of power increase or decrease per water heater. However, the HPWH has longer and more frequent operating times, which means the HPWH has a higher likelihood of being able to respond when an INC event or peak curtailment is called for. In addition, the inherent efficiency savings of HPWHs (61.7 ± 1.7%, as measured in the PNNL Lab Homes) will resul...
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