Measured Results in Redding, California
The following is an excerpted chapter of the book, Measured Home Performance—A Guide to Best Practices for Home Energy Retrofits in California, by Rick Chitwood and Lew Harriman. This material is reprinted with the permission of the Gas Technology Institute, Davis, California.
Laws Help, But Measured Results Are Better
Californians have a lot to be proud of. We use less energy per capita than residents of 46 other states in the U.S. In part, that’s because we build under Title 24, our California energy code. On the other hand, although the code is necessary—it does not ensure all the results we need.
Measured Home Performance results from Redding, California
Measured installation improvements that partly contributed to energy savings
Selling Comprehensive Measured Home Performance Retrofits
For example, in 2009 and 2010, as part of the regular assessment of the effectiveness of Title 24 code provisions, 80 single-family homes were selected for on-site-measurement of the actual performance of their energy features. The homes were located in a representative sample of California’s 16 distinct climate zones, and all were both occupied and new (completed after January 2007). The results suggest that there is considerable room for improvement in the messy, real world of design and installation, even when the energy code is strong. Measurements showed that:
- The average maximum sensible cooling effect from the AC systems was 55% of the equipment’s rated capacity.
- The delivered air volumes averaged less than 66% of what they should deliver in our climates.
- Fewer than 25% of supply air grilles provided the 500 to 700 fpm air velocities needed for good air mixing and thermal comfort.
- Air leakage (wasted air) from the HVAC systems averaged 10%.
- Of the 80 systems measured, not even one met the HVAC equipment manufacturers’ requirement to limit system pressure drop to less than 0.5” WC to deliver the equipment’s rated efficiency.
It remains a bit of a mystery that public outcry does not force our HVAC industry to improve. Surely, if cars were only delivering 55% of necessary highway speeds the public would complain.
On the other hand, there’s a more positive side to this state of affairs—these houses—and hundreds of thousands of other houses throughout the State—represent golden opportunities for Measured Home Performance Contractors.
Measured Home Performance In Redding
In 2009, the municipally-owned Redding Electric Utility decided to implement a demand reduction program based on the principles of Measured Home Performance. But it was not an easy decision. The money allocated for reducing electrical demand was fixed. Utility managers could have decided to make small changes in many houses, rather than large improvements in fewer houses. Politically, helping a larger number of homeowners was an attractive option. But program managers decided to make big improvements in fewer houses for very good reasons:
- It was not clear that small improvements would make any measurable reduction in peak demand, even if the improvements made modest reductions in annual consumption.
- The target homes often had many problems other than high electrical consumption. Some of those problems had life safety implications. Those would not even be discovered, much less eliminated, by just replacing HVAC equipment or other minor improvements.
- Training local contractors in Measured Home Performance practices could help transition the local construction infrastructure from a culture of lowest dollar towards a culture of superior measured results. Any transition in that direction could reduce the local growth in electrical demand, which would in turn pay big cash benefits to the utility for decades to come.
The cost of electricity during periods of peak demand is a major problem for all electrical utility companies. For example, in many parts of California their cost to buy electricity at 2:00 am is often less than $2.00 per megawatt hour. ($0.002 per kWh) In contrast, electrical demand often peaks at 7:00 p.m. when everybody is home watching TV, playing video games, cooking dinner and turning on oversized air conditioners. By 6:00-7:00 p.m. the wholesale market cost of electricity skyrockets to more than $2,000 per megawatt hour. ($2.00 per kWh). Buying electricity at $2.00/kWh and selling it for less than $0.15/kWh is a really big problem for any utility company.
Results in Redding
By any standard the Redding program has been very successful. In the upgraded homes, the measured results to date include:
- Average 35% peak demand reduction
- 25% average monthly cooling energy reduction.
- 65% average monthly heating energy reduction.
- All safety issues fixed and documented.
- Trained 18 local general contractors, 18 HVAC contractors and 5 “HERS rater” consulting firms that provide 3rd-party verification of Measured Home Performance improvements.
Figures 2 and 3 show more results from this program. Figure 2 shows the measured energy reductions based on at least six months of data compared to the three-year average of energy consumption in those same homes during previous years.
Figure 3 shows the improvements in two aspects of the building’s HVAC systems that (in part) made those saving possible, namely the reduction of air leakage between indoors and outdoors, and the reduction in leakage of conditioned air out of the HVAC systems’ duct connections.
Why Peak Demand Reductions Have Persisted Over Time
The reductions in electrical demand have been persistent because the replacement HVAC equipment is in all cases, much smaller. It’s not the rated energy efficiency of the equipment that matters—it’s the maximum possible power draw. Smaller maximum amperage equals smaller peak electrical demand, period. There’s no need to model this fact with computers. This characteristic of the retrofits in Redding may be the most important test for any contractor (or utility Program Manager) who believes they have accomplished retrofits that will reduce peak demand: is the HVAC equipment smaller than it was before the retrofit—or not?
If the equipment is smaller, then its peak demand will be smaller. If not... you’re stuck in the uncertain world of hopeful speculation called computer energy modeling.
Why Everything Must be Done at the Same Time
These projects cost quite a bit of money; typically between $15,000 and $40,000. That’s usually between 7 and 10% of the cost of the houses that are involved, or roughly the cost to retrofit a kitchen. Given the cost, it’s reasonable to question whether all these components need to be installed at the same time.
They do. Unless all of the energy features of the home are upgraded at the same time in a truly interdependent design with measured installation quality, either the big energy savings don’t occur, or comfort is compromised, or the project creates problems that did not exist before, or the project is not large enough to provide a sustainable business for the multi-skilled contractors who are capable of doing the work. Experience of the last 10 years shows this fact, which has been confirmed (yet again) by the projects in Redding. In short, large-scale integrated design and installation succeeds, and small-scale, disintegrated design and installation does not. Here are some of the many reasons why:
- Air tightening the building without also measuring and ensuring combustion safety of natural draft combustion appliances can increase risks, as documented by the pioneering Canadian experiences of the 1980s. When the structure is tight but the HVAC supply ducts are leaky, air pressures inside the tight enclosure can create negative pressure in the combustion appliance zone. Excessive negative pressure would pull products of combustion back into the home. Natural draft appliances must have adequate draft under worst-case depressurization conditions.
- Attic insulation seems like a good idea all by itself, but it’s not. Before any insulation is installed, it’s very important to air seal the penetrations and joints in the attic-to-upper floor assembly (the “attic plane”). If the attic plane leaks air during cooler months, moisture and later mold will accumulate in the attic as warm, humid indoor air drifts upward into that space.
- Changing older HVAC equipment for “higher efficiency” models does not save energy when the air distribution system is poor. There’s not much point in installing “high efficiency” HVAC equipment if the rest of the system throws away 45% of that equipment’s capacity (as documented by the 80-home field measurement project referenced earlier).
So to get big results, one needs to do big projects, redesigning and reinstalling each energy feature of the home in an integrated way and in a logical sequence.
The Importance of Check Numbers
The mantra of Measured Home Performance Contractors is to “measure before the project, measure during the project and measure at the end of the project.” Figure 4 shows some of the check numbers, which have been used in Measured Home Performance projects.
Those who work in commercial buildings may be startled by values shown in Figure 4. It would be unusual (to say the least) to have a limit for air leakage of less than 20 CFM in an entire single-zone commercial HVAC system or a maximum cooling capacity of no more than 1 ton per 1,000 ft2 of occupied space. But those are indeed the post-project values typical of the retrofitted houses described in Figure 2.
For an example, consider house number 7. Before the project, its HVAC system leaked 895 CFM at test pressure. After the equipment was downsized and the air distribution redesigned and reinstalled, the total HVAC system air leakage was measured at 18 CFM.
The check numbers in Figure 4 also help explain why the houses described by Figure 2 were able to so greatly reduce their peak demand. Smaller HVAC equipment means lower peak electrical demand. From an energy perspective as in fashion, “extra capacity” is not better (see Figure 5).
The importance of HVAC Knowledge For 3rd-Party Verifiers
One of the lessons learned in the Redding project is the immense importance of training in HVAC equipment and systems for all consultants who check that the work has been done correctly.
The experts trained as “Energy Raters” are likely to be most knowledgeable about the big picture; the overall energy aspects of homes and their systems. They may have less detailed experience of operational characteristics of specific HVAC equipment and the critical details of its installation and commissioning. If the quality assurance inspector has authority—but does not actually understand equipment operational variations—that person can misguide the HVAC technician into illogical practices that damage equipment and eliminate savings.
For example, in the Redding project a common problem was 3rd-party verifiers (fully trained and certified to audit houses in California) who, armed with digital pressure gauges, instructed HVAC technicians to add or remove refrigerant from AC systems to achieve target values. But the target numbers for subcooling and superheat change with load. Baseline numbers cannot be reached without adjusting for the actual running load conditions at time of test. Installer ignorance combined with verifier ignorance resulted in severely overcharged and undercharged equipment. In some cases they did not understand the behavior of AC equipment when operating at less than full load conditions. In other cases they did not understand that the test values obtained indicated faulty equipment rather than faulty installation. HVAC equipment has such a wide variety of configurations that it’s really impractical for an energy auditor to be an expert in all types. So training on the specific models of HVAC equipment used in the program is critical, not only for installers, but also for verifiers.
In the case of the Redding projects, both the HERS Raters and the HVAC techs were guided and mentored as part of the program. They were trained (and monitored) by a knowledgeable HVAC and Measured Home performance consultant, to make sure they did not accidentally add problems during the installation process.
HVAC redesign is often the most difficult aspect of projects
Compared to other aspects of Measured Home Performance such as lighting replacement and air sealing, HVAC redesign and installation is pretty complicated for existing homes.
It’s not that the principles are had to grasp—it’s that existing buildings make it difficult to design and install systems the way we know they have to be done to save energy. And it’s usually even more difficult to convince the owner that his system is so hopeless and horrible that it must be torn out entirely, redesigned, downsized and reinstalled in order to achieve comfort and save energy. But that’s what has to happen.
The big difference from past practice is to simply design and install these systems the way we all know they should be done, rather than using equipment oversizing and energy waste to compensate for installation shortcomings. A few of the many design and installation imperatives include:
U.S. Energy Consumption by State. 2009. U.S. Energy Information Agency.
“Efficiency Characteristics and Opportunities for New California Homes” Final Report of Project Number PIR-08-019 2011. Proctor , Chitwood & Wilcox, California Energy Commission
Home Performance Program Evaluation 2011, David Jackson & Kim Hein, P.E, Redding Electric Utility, Redding, CA
“Just right and air-tight.” Joseph Lstiburek, ASHRAE Journal May 2011 pp. 58-66.
ANSI/ACCA Manual J - 2006 “Residential Load Calculations” (8th Edition).
- Room-by-room load calculations. The “Manual J” procedures established by the Air Conditioning Contractors Association (ACCA) are the basis of the room-by-room calculations that provide the crew with the air flow numbers they will need to ensure correct flows and therefore comfort.
- Air-tight systems. Air tightness is taken very seriously. The limit of 20 CFM leakage includes the entire system and the air handler cabinet, not just the duct joints. (Note: the actual goal is always ”leakage too-low-to-measure.”)
- Return air paths large enough to allow adequate air flow. The retrofit designer is both creative and ruthless about gaining adequate space for return air ducts that will bring all of the supply air back to the air handler.
- Short, straight duct runs. The longer and more twisted the path of the air, the more fan energy is needed to push and pull it through the house. This often means the air handler must be relocated from its distant location in the garage, to a central location in a closet inside the home, or to a central location in the attic. Then the duct runs can be shortened and straightened in a radial layout, as opposed to the all-too-common spaghetti configuration.
- Flow-setting dampers placed at the supply outlet plenum near the air handler, rather than at the supply grilles in the rooms. Keeping the air velocity high and the air flow straight as it leaves the supply grille is important for good air mixing. These projects use flow-setting dampers back at a supply air plenum box at the end of the air handler. Without dampers at the grille, the supply air flow is straight, fast and quiet as it enters the room. Excellent air mixing provides the constant comfort that keeps occupants content. Constant comfort eliminates the counterproductive and energy-wasting fiddling that desperate owners often are forced into when systems are poorly designed and installed.
- Air flows to each space measured and set with flow hoods. With a real, honest-to-goodness room-by-room load calculation, the air flows for each room can be established with certainty. This is accomplished by the installing crew, using their digital flow hood.
- High evaporator air flows. In warm and dry California, dehumidification is a problem rather than a virtue in the summer. So for these dry-climate systems, air flows of 500 to 550 CFM/ton are ideal. Using a flow plate to measure and set supply air flow to ensure those air flows is part of the installation crews’ responsibilities.
- Insulated ducts, buried under attic insulation. Conductive losses from duct work become nearly negligible.
The results obtained in Redding are consistent with results obtained in other Measured Home Performance retrofits in California. These results all far exceed the hoped-for-but-never-measured energy savings of low-budget, equipment-only retrofits.
The fundamental principle of Measured Home Performance is consistent with the advice of a widely known 20th century statesman; Winston Churchill. He achieved success later in life after many disastrous early career mistakes. Churchill suggested: “However beautiful the strategy, one should occasionally look at the results.” We always need to measure our results rather than just hope for them to be successful.
This chapter could not have been written without the assistance of Mike MacFarland of EnergyDocs in Redding, California, and the data provided by the Home Performance Program Managers at Redding Electric Utility.
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