Deep Energy Retrofit X10 Part 2
This article is part 2 in a series on deep energy retrofits (DERs). The series describes in-depth end-use monitoring in ten DERs in Northern California. The Lawrence Berkeley National Laboratory (LBNL) conducted the monitoring. In part 1 of this series (May/June ’12, p. 38), we characterized ten DER projects as either “remodels” or “retrofits.” The six remodels were described in detail. In addition to exhaustive energy upgrades, these homes underwent the most structural and aesthetic intervention, and most of them did not resemble the home in its preretrofit condition. In this article, we will describe the four retrofits. In general, these projects kept the same look and feel as the preretrofit home, but made thorough upgrades to all systems and to most elements of the building enclosure. Renewable energy installations were added in several homes. In some cases, the homeowners chose this approach for purposes of historic preservation. In other cases, the home was new enough that it was not necessary or desirable to make major aesthetic or functional changes.
The Retrofits (P2, P7, P8, P9)
Retrofits are less extensive than remodels. As a result, they are less disruptive for occupants, cost less, and use fewer resources during construction. P2 is a house in Palo Alto whose look and feel have remained faithful to its English Tudor Revival style, but whose performance has been substantially improved. P7 is a house in San Mateo whose Craftsman detailing, decorative plaster, and historic windows were maintained during the retrofit. In an attempt to balance historic detailing, energy use, and comfort, the owners decided to create a house-within-a-house. This inner “house” comprised the kitchen, a bathroom, and a multipurpose room. It is fully insulated and air tightened on all six sides, whereas the rest of the home was improved where possible and otherwise left intact. P8 is a compact bungalow in the Rockridge district of Oakland. This home has maintained its consistency with the historical character of the neighborhood while achieving LEED Platinum certification. P9 was a tract home built in the 1990s in Folsom, a Central Valley community known for hotter summers and harsher winters than the Bay Area. P9 did not need aesthetic upgrades, nor was it historically significant, but the occupants were able to carry out an extensive home performance retrofit, upgrading nearly all the building systems, enhancing insulation and air sealing, and solving numerous comfort, noise, and indoor air quality (IAQ) problems.
Whereas most of the remodels we described in part 1 of this series had added exterior insulation and extensive air sealing, the retrofits were constrained by the need to preserve either the building exterior or interior finishes. Most, but not all, of the above-grade walls in P2, P7, and P8 were insulated with either blown fiberglass or cellulose. Historic windows, wood paneling, or other details often made some walls impractical to drill and fill. In all three of these retrofits, the attic and HVAC equipment were brought into conditioned space. This was done by sealing the attic and insulating the roof with spray foam in P2 and P8; and by sealing the attic and insulating the roof with fiberglass and foam board in P7. The ductwork was partially buried in extra blown cellulose attic insulation in P9. The slab-on-grade floor of P9 was not improved during the retrofit, but the basements or crawl spaces of P2, P7, and P8 were insulated with spray foam, polyisocyanurate foam board, and fiberglass batts, respectively.
Some window improvements were more extensive than others. P2 was retrofitted with double-glazed, low-e interior storm windows throughout. P7 used high-performance windows in the house within a house but left the original windows untouched elsewhere. In P8 most, but not all, windows were replaced with double-glazed, low-e units. The windows in P9 were relatively new and were replaced only in the kitchen, where other remodeling was being done.
According to the latest figures in the LBNL Residential Diagnostics Database, California homes built from 2001 to 2011 had a mean ACH50 of 3.9, and California homes built from 1990 to 2000 averaged 6.7 ACH50. P9 was the only project to achieve good airtightness within this context, with 2.4 ACH50 postretrofit. P2 achieved 5.7 ACH50, and P7 and P8 were both greater than 9 ACH50. Since these retrofits did not include removal of exterior cladding or interior drywall, it was difficult to make the house airtight under these conditions. Airtightness was also not sufficiently prioritized or specified by the project teams.
The mechanical systems in these retrofits resemble traditional systems, but their energy sources and modes of operation are designed for maximum efficiency and low energy use. P2 uses forced-air heating and cooling distribution, but an air-to-water heat pump generates heated and chilled water for domestic hot water (DHW) and space heating and cooling. The two air handlers both have hydronic heat exchangers and integrated heat recovery ventilators (HRVs), which operate 24/7 on low speed and ventilate at higher rates during system operation for heating or cooling. P7 uses two traditional, high-efficiency gas forced-air furnaces, which are zoned in such a way as to allow for the house-within-a-house approach; the inner house is the main comfort zone, and the temperature of the rest of the house is allowed to “float.” P8 uses a solar combisystem for DHW, as well as space heating with hydronic radiators. P9 uses a traditional-looking forced-air heating and cooling system, but cooling efficiency is increased by the use of an evaporatively cooled condenser, as well as a Night Breeze system that uses the air handler to distribute 100% outside air at night for precooling. These advanced traditional systems are well suited to retrofits, which often already have system infrastructure in place, and cannot achieve the extreme insulation and airtightness levels required of low-load systems, such as point source heating.
Retrofits still focus on reducing all sources of energy use in the home, and most lighting and appliances are replaced as part of the upgrade. P2, P8, and P9 undertook full lighting retrofits. In P9, LED can lights were installed in the ceilings throughout, and LEDs and CFLs were installed elsewhere. The lighting in P2 was replaced with CFLs, halogen, and LEDs, and in P8 old, inefficient lighting was replaced with CFLs and LEDs. P7 already used low-energy lighting. All appliances were replaced with Energy Star units in P2 and P8, but P7 and P9 kept most of their existing appliances. A historic gas stove turned out to be a major energy hog in P7. With six pilot lights, this antique burned 1 cubic foot of gas every 40 minutes. (This adds up to approximately ~3,950 kWh per year, on standby—with no actual cooking.) The occupants turned off all but the oven pilot, and the unit still uses 1 cubic foot every hour and 40 minutes. We estimate this to be equivalent to 1,580 kWh per year on standby; the occupants have installed a CO monitor due to fears that even the one pilot may be producing potentially dangerous levels of CO and other pollutants.
Occupants in P7 and P9 have reduced their miscellaneous electric loads (MELS) use very aggressively. Occupants in P2 and P8 have not reduced their MELS, which are among the highest in the study.
Because further envelope improvements would have been prohibitively expensive in these retrofits, renewable energy technologies were employed to reduce energy consumption. P2 and P8 both installed PV panels, and occupants in P7 plan to do so in the near future. P8 used a solar combisystem to meet its space heating and DHW needs, in addition to PV panels for electricity.
The following is a more detailed description of the four retrofits, giving the reader a sense of each home’s unique “personality,” both pre- and postretrofit. (See Tables 1–4 for a summary of each home’s features.)
P2 Palo Alto Green
P2 was originally constructed in 1936, using a wealth of locally made artisan materials, and it was retrofitted in 2006. The home has two full-time occupants and five part-time occupants. It has three bedrooms, three bathrooms, and a home office. The DER was initially designed and constructed to act as a home and place of business for the owner and developer of the property, but it has ended up as a high-end rental.
During the retrofit, the floor area of the home remained unchanged at 2,780 square feet. A 4.3 kW PV system was installed, and all remaining power is purchased from the Palo Alto Green renewable electricity program. (Palo Alto is on the Peninsula south of San Francisco.) The home experiences approximately 2,563 base 65 heating degree-days (HDD65) and 486 base 80 cooling degree-days (CDD80) per year. The owners took a five-pronged approach to retrofitting this home. Energy reductions constituted just one prong; health, historic preservation, comfort, and water conservation were considered equally important. The home was intended to be net zero energy and carbon neutral, but it has not yet achieved this goal in operation. It has, however, achieved a net-site energy reduction of 61%, for a total reduction of 24,492 kWh.
Feedback from the designer and the contractor included reservations about the costs and liabilities of the fully custom air-to-water heat pump combisystem they installed. The system had a bewildering array of controls, pumps, relays, and regulators. The result was what we considered an unnecessarily complex system that could be serviced only by the installer or the original designer. In fact, this system failed and had to be replaced in the winter of 2011, at cost to the contractor. Complexity was reduced slightly, by eliminating the chilled water storage, as well as some pumps and controls.
P7 San Mateo House-Within-A-House
P7 was originally constructed in 1910 in the Craftsman style, and it underwent an extensive retrofit in 2011–12 to meet the ACI Thousand Home Challenge. The home has two full-time occupants, three bedrooms, two bathrooms, and a home office. The floor area was not expanded during the DER, remaining at 3,136 square feet. No renewable energy was added to the home, but the roof was reinforced, so that solar panels could be installed in the future. Located in San Mateo, the home experiences approximately 3,042 HDD65 and 108 CDD80 per year. P7 has achieved a whole-house ACH50 reduction from 17.1 to 10.8 (house-within-a-house leakage to outside was 5.0 ACH50); and it has reduced energy use by 72%, for a total reduction of 22,653 kWh.
The key features of the P7 retrofit are the house-within-a-house approach and the occupants’ efforts at energy conservation. With extensive areas of historic features, it was not practical for the occupants to insulate and fully air seal the home. Instead they’ve pursued a strategy with HVAC zoning based on occupancy patterns, levels of insulation, and airtightness. The house-within-a-house is approximately 700 square feet and is well insulated and air sealed. To reduce heating energy, the occupants use minimal heating throughout the home, with somewhat warmer temperatures in the house-within-a-house. P7 currently uses a hybrid gas water heater with tankless technology that includes a 2-gallon buffer tank. The unit is switched off entirely when there is no hot water draw, to avoid conductive losses from the buffer tank, which is located outside. Cold water is used for most hand and dish washing, with the water heater remaining off. Timely delivery of hot water has also been an ongoing problem for the occupants with the hybrid water heater. Cooking gas usage is the largest load in the home, equaling or exceeding energy use for space heating and water heating combined. The occupants have experimented with alternative cooking methods, including slow cooking and solar, and they are considering a stand-alone electric induction burner as a gas alternative.
P8 Oakland Ultragreen
P8 was originally constructed in 1915 and was retrofitted in 2008 with the intention of making it one of the greenest homes in the country. The family of four who occupied P8 and performed the DER sold the home in the winter of 2011–12, so occupancy changed to two new occupants partway through our study. The compact three-bedroom, two-bathroom home went from 1,440 to 1,627 square feet with the addition of a conditioned ground level laundry room. A modern office pod, separate from the rest of the house, was also added at that time. The retrofit included the installation of both a 2.7 kW solar PV system and a solar-thermal combisystem. This home experiences an average 2,909 HDD65 and 128 CDD80 per year. In the interests of sustainability, P8 included numerous design features in addition to those intended to increase energy efficiency. These included a graywater system, rainwater catchment tanks used for toilet flushing, and the use of low-VOC and recycled materials. Preretrofit data were not available, so we compare P8 to the average single-family residence in California, which uses 20,061 kWh per year. P8’s annual net energy use of 17,086 kWh is only a 15% reduction from the California average.
P8’s space heating and DHW usage is notably high. It accounts for just under 75% of total annual energy consumption, despite P8’s high-efficiency gas boiler with solar-thermal preheat. We believe this is caused by extensive hot-water distribution losses. Pipe runs begin at the storage tank in a detached garage, proceed underground, and are carried up through an unconditioned crawl space. The piping is insulated; however, the R-value of the insulation is minimal. Combined with the significant length of the piping, this leads to large losses. The home’s 9.3 ACH50 air leakage contributes to the high space-heating usage.
P9 Folsom Home Performance Superstar
P9 was originally constructed as a tract home in 1996 under the Sacramento Municipal Utility District’s (SMUD) Advantage program, and it underwent an extensive home performance retrofit in 2006, as a demonstration project intended to get home performance off the ground in California. A family of four lives in this three-bedroom, two-and-a-half-bathroom, 3,114 ft2 home. P9 did not include any renewable-energy technologies in its retrofit. The home is located in Folsom, in California’s Central Valley, where it experiences an average 2,702 HDD65 and 1,470 CDD80 per year. P9 has reduced its energy use by 54%, for a total reduction of 19,592 kWh.
P9 is notable for its low cost, limited disruption to the occupants, and dramatic savings. Yet, the owners may value the improvements to indoor environmental quality most highly. Prior to the retrofit, they experienced numerous problems. These included excessive air handler noise, extreme temperature stratification between floors, forced-air registers dumping air on occupants at high velocity, and extreme room pressure imbalances during air handler operation (>40 Pa measured across bedroom doors). IAQ was poor; the house was often damp; and there were major leakage pathways from the garage to the child’s bedroom. All of these problems were remedied as part of the retrofit, the cost of which was rolled into the mortgage when it was signed. The occupants were very pleased that the project was nearly cost neutral, with only a $15 net increase in their monthly cost of home ownership.
These California DERs prove that homeowners can substantially reduce energy and increase comfort in a relatively mild climate, without seriously disrupting the look and feel of the home. Total net-site energy reductions ranged from 19,592 kWh at P9 to 24,492 kWh at P2, averaging 22,246 kWh for all four houses. These reductions equal or exceed the total average household energy use of a California single-family detached home (20,061 kWh). (Data on household energy use is from the California Residential Appliance Saturation Survey, 2009.) Each of these retrofits effectively removed 1 to 1.2 average California homes from the electric and gas grid. In contrast, reductions in the remodels featured in part 1 of this series averaged only 6,546 kWh, because those homes used less energy in pre-retrofit condition. These retrofits illustrate the importance of retrofitting high-energy-use homes, where the greatest impact can be achieved.
Get information about the California Residential Appliance Saturation Survey.
With the exception of P7, which has reduced interior heating to achieve deep energy cuts, all projects have resulted in homes that are dramatically more comfortable. These projects show that historical preservation and drastic energy reductions can be fully compatible with each other. Exceptional airtightness and above-code insulation have not proven necessary to achieve dramatic energy reductions in existing California homes. This is mostly because the mild climate reduces the need for heating energy use, and because the occupants can control nonheating energy use.
In part 3 of this series we will explore the energy performance in more detail for all ten homes. We will discuss end use disaggregation, which enables us to identify where more energy can be saved, and to illustrate the effects of occupant behavior.
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