Deep Energy Retrofit X10 Part 3: Gathering Data
This is the last article in a series of three that have summarized the design, construction, and performance of ten Northern California deep energy retrofits (DERs) that have been monitored by Lawrence Berkeley National Lab (LBNL). In the prior two articles, the projects were identified as either remodels or retrofits, depending on the extent of the intervention and aesthetic changes. The first article (“Deep Energy Retrofit X10,” HE May/June ’12, p. 38) summarized the remodels. The second article (“Deep Energy Retrofit: Part 2,” HE Mar/Apr ’13, p. 36) summarized the retrofits. Both articles provided very basic summaries of annual post-retrofit energy use. In this article, we will briefly review all the projects. We will then present detailed results of the monitoring, and key findings of this research and offer a list of recommendations.
Review of the Projects
The ten DERs (P1-P10) reduced energy use by a variety of means, eschewing any single approach (see Table 1). This is likely to be true of DERs as they reach a wider audience, due to wide variability in existing homes. DER solutions will be creative, partial, mixed, and flexible.
Airtightness and Ventilation
Airtightness averaged 4.8 ACH50, but varied from relatively loose (10.8 ACH50 in P7) to extremely airtight (0.48 ACH50 in P3). Consistent with the Passive House emphasis on superinsulation and airtightness, the projects inspired by the Passive House standard (P1, P3, and P5) were substantially more airtight, averaging 1.3 ACH50 compared to 6.3 ACH50 for the other houses. Deep retrofits should set specific goals for airtightness, and should plan specific ways to achieve those goals. Finally, we measured mechanical ventilation airflows in each home and assessed the ventilation provided using airflow requirements from ASHRAE 62.2-2010. Only 4 of the 10 homes provided continuous mechanical ventilation, though all homes provided some form of kitchen and bathroom venting. It was common for fans to provide airflow below required levels. For example, 10 of 20 bathroom fans failed to deliver the required 50 CFM. This suggests that a greater focus on indoor air quality, mechanical ventilation, and commissioning is needed in deeply retrofitted homes.
Post-Retrofit Net-Energy Usage and CO2e Emissions
Percentage Reductions in Net-Energy and CO2e Emissions
Table 1. Retrofit Measure Comparisons
Absolute Reductions in Net-Energy and CO2e Emissions
End-Use Contributions of All Project Homes
Combined HVAC-DHW and Combined Plugs-Lights-Appliances
Comparison of Hourly Average Winter Temperatures in DER Homes
Whole-House Energy Performance
We calculated post-retrofit net-site energy, net source energy, and CO2 equivalent emissions (CO2e) for each project home (see Figure 1). Percentage and absolute reductions were calculated for the five projects with pre-retrofit energy data (see Figures 2 and 3). We calculated source energy using Building America conversion factors of 3.16 and 1.02 for electricity and natural gas, respectively. CO2e factors were from the local utility (0.575 and 0.399 lb/kWhsite, respectively). In order to achieve net zero energy, the average required PV array size was 6.3 and 3.8 kW for site and source energy, respectively.
We noted in part 2 of the series that projects with high preretrofit usage achieved the largest absolute energy and carbon reductions. Homes with preretrofit net site usage < 15,000 kWh had average absolute reductions of 6,546 kWh; homes with preretrofit net site usage > 30,000 kWh had average absolute reductions of 22,246 kWh. High-usage preretrofit homes were much more successful at achieving large absolute net site reductions, despite having higher average postretrofit usage (13,797 versus 6,314 kWh for low-usage preretrofit homes).
We have used three metrics—net site energy, net source energy, and carbon emissions—because performance can change dramatically depending on how it is assessed and reported. For example, site and source energy savings were dramatically different depending on changes in the home’s fuel mix. The impact on net source energy performance of switching from natural gas to electricity for heating and/or cooking can be seen when P2 and P4 are compared (see Figures 2 and 3). Despite similar percentage net site energy reductions, P4 achieved 14.4 times the percentage net source energy reduction that P2 did. The reason for this is that both homes began as users of natural gas for space and water heating. Then P2 shifted to an all-electric home and added mechanical cooling and numerous miscellaneous electronics, while P4 maintained its original fuel mix. Note that CO2e reductions were less affected by electricity use than by fuel mix. This was because CO2e emissions of electricity provided by the local electric and gas utility (Pacific Gas & Electric) in 2009 were lower in California than they were in most other states—approximately 44% of the national average. In states where carbon intensity is particularly high, carbon emissions would be even worse than the source energy performance we have reported. For example, P1 achieved a 19% carbon savings in this study, but if the home were located in the Central Plains states and had the exact same electricity and gas usage, the retrofit would have increased carbon emissions by 28%. Similarly, P2 would go from a 47% reduction in emissions to a 15% increase in emissions. Fuel choices should be made with care in all deep retrofits in light of these effects, and projects should be evaluated in terms of source energy and carbon intensity.
Energy End Uses
We also monitored the energy end uses for each project home (see Figure 4). All values are in site kWh consumption. Some end uses were combined in this research (for example, heating and hot water were combined in P2, P8, and P10) due to limitations in end use disaggregation. To overcome this limitation, end uses were combined as “HVAC and DHW” and “plugs-lights-appliances,” which we compared across all homes (see Figure 5).
For those homes where heating and hot water were disaggregated, usage averaged 2,088 kWh and 2,031 kWh, respectively. Average appliance usage (2,446 kWh) was greater than either disaggregated heating or hot water, and plug loads were of a similar magnitude (1,717 kWh). Lighting was on average 916 kWh. Combined HVAC-hot water usage averaged 6,444 kWh (54% of total consumption), and plugs-lights-appliances accounted for 4,856 kWh (46% of total consumption).
The 24/7 electrical base load averaged 203 watts. Annually, base load accounted for an average of 1,778 kWh (16% of total consumption), which was similar to annual heating energy. Base load reductions were an obvious opportunity for deeper, low-cost energy savings in almost all project homes, even those that had already pursued reductions. Solutions such as whole-house off switches or smart home energy management tools should be considered in future projects.
We used preretrofit data to estimate preretrofit heating energy use, and absolute heating energy reductions averaged 12,937 kWh (76%), with reductions per square foot averaging 5.9 kWh/ft2 (80%). Yet total net site reductions were only 58% for the same homes. Homes that achieved heating energy savings greater than total net savings (P1 and P2) increased energy usage in other end use areas, which offset their impressive heating reductions. This highlights the importance of including all energy end uses in analysis of deep retrofits. It is also important to be aware of increases in other end uses that can offset heating energy savings.
“Highly” or “super” insulated projects used substantially less heating energy than code-style retrofits (see Table 1). These projects averaged 1,089 kWh (0.7 kWh/ft2) in annual heating energy, as compared to 3,753 kWh (1.3 kWh/ft2) for code-style retrofits. Yet low heating energy use did not guarantee whole-house performance. In fact, P9 was the largest single reducer of net source energy, despite having the highest postretrofit heating energy use of any project home.
Among the many nonenergy-related benefits of deep retrofits, improvements in thermal comfort may be the most important for homeowners investing in improvements. We compared the hourly temperature profiles in these projects for the months of December and January (see Figure 6). Thermal comfort is highly variable in these homes, with indoor average hourly temperatures varying by up to 10°F between homes. Winter temperatures were lower than those suggested by the ASHRAE thermal comfort standard 55-2010.
Enhanced insulation did not necessarily lead to higher interior temperatures, though it was clearly related to very low heating energy use. Retrofits that are targeting consistently high heating-season temperatures and very low heating energy use will need to employ very high-performance—that is, highly insulated and airtight—envelopes and HVAC equipment. Code-style homes can still be comfortable and achieve large whole-house energy reductions (P2, P4, and P9), but their heating energy use will remain high, and must be balanced by reductions in other end uses.
Get information about the California Residential Appliance Saturation Survey.
Learn more about this study.
We have developed a number of general recommendations based on the results and observations of this research:
- Establish goals early on (energy reduction, cost reduction, comfort, and so on) and choose performance measures that assess goals directly (for example, energy reduction does not equal cost reduction).
- Design with occupant needs, wants, and current patterns of consumption as guides to achieving real-world reductions. Make “good” behavior the default, providing easy control and feedback for those who want it, and automatic controls for others.
- Comprehensively target all end uses.
- Be cautious when switching from gas to electricity for heating end uses. To avoid increasing emissions and environmental impact, assess projects in terms of source energy and/or carbon emissions.
- Super insulation and airtightness are not required for success. Rather, target International Energy Conservation Code (IECC) 2012, unless superior thermal comfort and very low heating energy are project goals.
- Use high-efficiency, off-the-shelf solutions. Complex, custom systems often cost more and perform poorly. Comply with current ASHRAE Standard 62.2, even when this is not required by code, and commission all ventilation equipment.
- Think twice before adding energy-consuming items, such as cooling, structured wiring, and home entertainment systems unless superior thermal comfort and very low heating energy are project requirements/goals.
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