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The ten sentence summary
Residential air conditioning is the single biggest contributor to the peak electricity load in California.
A California duct system wastes about 40% of the power it consumes on hot days. About half of this peak loss can be saved by sealing the air leaks in ducts. The other half can be saved by insulating ducts and tuning-up the home's cooling system. Additional peak power reductions can be achieved by using smaller capacity high efficiency equipment.
A program that insulated and sealed ducts to improve the efficiency of all residential central air conditioning systems would:
A duct program would cost about $1 billion. This would be an investment in increased California home values and employment for California contractors, rather than payments to out-of-state power producers
Why improve the energy efficiency of heating and cooling ducts?
The answer is that we should save energy when and wherever we can because electricity supply in California is too limited to meet peak electrical loads and because customers’ utility bills are skyrocketing because the cost of energy is driven higher when demand is greatest.
Home heating and cooling systems are prime candidates for reducing peak load through energy-efficiency improvements because these systems contribute more heavily to peak loads than to overall energy consumption. For example, residential air conditioner use is about 20% of total peak electrical load but only about 7% of total statewide electricity use.
Over the past twenty or so years there have been significant improvements in residential buildings to reduce energy waste, and almost all new houses are well insulated and have good windows. However, the heating and cooling systems in houses have not kept pace with the improvements in these areas, and in some situations may even have got worse. In the past, the relatively mild climate in California, combined with low energy costs, meant that there was little penalty for wasting energy when heating or cooling a house. This picture has changed with the recent California power crisis and the rising cost of natural gas. In addition, the population increases in California's inland climates with their associated air conditioner use have led to greater peak demand.
Given that most parts of the building are already about as good as we could reasonably expect, the only significant place we can save some energy is in the heating and cooling system. Of the twelve million residences in California, about eight million have some sort of forced air heating and/or cooling system. These systems blow heated or cooled air through ducts to the different parts of the house. Studies funded by the U.S. Department of Energy (DOE) and the California Institute for Energy Efficiency (CIEE) through Lawrence Berkeley National Laboratory (LBNL) have therefore concentrated on forced air distribution systems. These studies have found that typically a quarter of the energy used for heating and cooling is wasted becasue of duct leaks and poor duct insulation for ducts that are often installed outside the conditioned space (often in attics or crawlspaces). This means that homeowners are inadvertently paying to heat and cool these unoccupied spaces and wasting energy, money and precious natural resources while polluting the environment.
Duct system performance is even worse under peak conditions when house loads are highest and the ducts and cooling equipment are exposed to the harshest conditions (attic temperatures can reach 150 degrees F on a summer day). A typical system under these conditions wastes about 40% of the energy it consumes. About half of this peak loss can be saved by sealing the air leaks in ducts. The other half can be saved by insulating ducts.
This problem has been recognized by utility programs that target the reduction of duct losses (SMUD Duct Program, SMUD Advantage Homes and PG&E Duct Program), and by the state energy code (Title 24). Title 24 currently has an optional duct sealing credit, and recent revisions to Title 24 have made duct sealing almost imperative. In new houses that participate in utility energy efficiency programs the duct leakage has been reduced by about a factor of four. These savings have been achieved using existing technologies and installation methods, that require no extensive retraining of heating and cooling equipment installers, and that there are no technological barriers to implementation.
Although the performance of duct systems in new houses is improving thanks to utility programs, only about 100,000 new houses are built each year in California. This leaves eight million existing homes with forced-air heating/cooling, most of whose duct systems need efficiency improvements.
How much peak load energy is wasted by air-conditioning ducts?
Residential air conditioning is the biggest contributor (roughly one fifth) to peak load in California. Although electricity alerts and blackouts were common during the winter of 2000-2001, the greatest electricity demand in California occurs in the summer as a result of air conditioning. The utilities call this the "load from hell" because maximum air conditioner use tends to coincide with an increase in other residential electricity use when people return home from work in the late afternoon.
How can we fix this problem?
We can save the energy lost through duct systems by expanding existing initiatives to upgrade all residential duct systems in California. Benefits to individual homeowners would include reduced utility bills, improved comfort, less chance of blackouts and an increase in home value. Utilities would benfit from reduced peak demand. The public would benefit from reduced state expenditures to purchase electricity (particularly at expensive peak times), reduced need for new power plants, reduced pollution (both in California and the other states that are paid to burn coal for California) and keeping money in the state in stead of being paid to out of state power generators.
Fixing the leaks for a typical California house will reduce peak demand
by about 20% for both heating and cooling. A program of residential duct
sealing would:
Save about 1 GW during peak summer cooling.
Save about 1 GW plus 60 Billion Btu/h of gas consumption during peak
winter heating.
Save at least $400 Million per year, every year. From a combination
of 90 million therms of natural gas and 650 GWh of electricity.
Additional peak power and energy savings can be made by adding insulation
to duct systems, performing a system tune-up (e.g., checking the amount
of refrigerant in an air conditioner) and replacing old, oversized and
inefficient equipment. These additional changes could approximately double
the savings estimates.
How to save a GigaWatt
A program that targeted all central air conditioner systems would save between One and two GW of peak power on the summer peak.
A Watt is a measure of power consumption. A GigaWatt (GW) is a thousand million (1,000,000,000) Watts. For some perspective, a lightbulb is typically about 70W, an air conditioner consumes several thousand Watts, and the peak consumption for all buildings in the state is about 37 GW. So, one GW is a lot of air conditioners, but only a small fraction of the total peak load for the whole state. One more perspective is that a typical power plant produces about half a GW. Therefore, we are proposing to reduce the state peak electricity requirements by two whole power plants.
A program that targeted all forced air heating systems would save about one GW of peak electrical power and 80 Million kBtu/h during the winter peak. If only houses with central air conditioning were targeted, then these winter savings would be reduced by a factor of three.
How to save a billion dollars
A program to seal ducts should address both heating any cooling systems because the high cost of gas in the current market has the greatest impact on consumers (electricity rates are currently fixed although this may change in the near future). Another reason to address systems that use gas is that new most new electricity generating capacity will be gas-fired, which will increase future gas demand and thus its price.
Sealing ducts in California's three million air-conditioned homes will save about $0.4 Billion a year in combined electricity and natural gas costs. The electricity estimate is highly volatile and was chosen to be conservative (30 cents/kWh) given that most of the avoided cost is at peak (that reached 250 cents/kWh in January 2001).
Another important consideration is the overall reduction in electricity prices due to reducing peak load by a few percent. Electric Power Research Institute (EPRI) studies (recently reported in the Economist) show that a 2.5% drop in peak demand reduces wholesale prices by up to 24%. Saving one GW out of the peak building load of 37 GW would therefore have a significant effect on the cost of electricity to all consumers, not just the residences targeted.
How much will sealing ducts cost?
Studies have shown that the cost to repair duct systems is about $250 to $500 per house, so the investment required to fix all the duct leaks in centrally air conditioned homes would be about $1 billion. To put this figure in perspective, the state has already spent 5 Billion dollars to purchase electricity over about a three month period (winter 2000-2001). The $1 billion invested in ducts would have an approximately 40% rate of return ($0.4 billion in saved energy costs) per year. The investment in California houses is retained as added value to these homes and spending on labor and materials will be mostly within the state.
How quickly can we seal all the ducts?
Because all the technology currently exists to seal duct systems, work could begin immediately. The projected 1 GW peak reduction in peak energy use would be realized when all systems have been fixed. Therefore, the faster we fix, the faster we reap the peak power savings. There are about 1700 active HVAC contractors in California. If we assume that each contractor has at least two work crews, it should be possible to easily find the approximately 3000 work crews required to fix 3 million systems over a period of two years.
Sealing all ducts in centrally air-conditioned homes in a single year would take more than 6,000 work crews, which might require labor from out of state. (Note that it is not possible to plan, approve, build, commission and bring on-line a 1 GW power plant in one year).
Ducts in commercial buildings
Small commercial buildings (less than 10,000 square feet) have heating and cooling systems that are similar to those in the residential sector. Sealing ducts in these commercial buildings would also save about 20% of peak demand, with 10% total energy savings over a year. In California there are about 350,000 of these buildings with average floor areas of about 3,000 square feet. They have heating and cooling systems of similar size to those in residences; a typical 3,000-square-foot space is served by two four-ton air-conditioning units. The peak savings per system are about 1.1 kW. Assuming that half of the systems operate at peak (slightly more than for residential systems), there is the potential to save about 0.4 GW at peak by sealing the ducts in these systems. The cost to fix duct leakage in these systems is the same as for residential systems although costs could be lower and the number of systems sealed per day could be increased because many of these systems are located close together.
Large commercial buildings could also reap large savings from
duct repairs. However, research is still required to quantify the
potential savings and ascertain the best ways to achieve them in these
large systems.
Other improvements in energy efficiency that can be made at the same time as sealing ducts
Studies have shown that, in addition to the losses from the duct system, air conditioners have several other problems that lead to poor performance (and increased peak demand and energy consumption). Fixing these items has the potential to double the peak savings estimates described above (this additional work would also increase repair costs).
System Refrigerant Charge. Many cooling systems do not contain the correct amount of refrigerant ("charge"), which, in most cases, reduces cooling capacity. With reduced capacity, the system runs longer, use more energy and often is not able to supply enough cooling to some or all of the house, which makes the house less comfortable. Air conditioning equipmnet can also be damaged and may stop working as a result of incorrect charge. Most people call an HVAC contractor only after an air conditioner is no longer operating. However, the problem of incorrect charge can be fixed if an HVAC contractor tests the system and puts in the correct amount of refrigerant.
Replace Furnace Filters. Clogged filters reduce system air flow, which can increase energy consumption. Bad filtration fouls cooling coils, which can reduce their capacity and efficiency. Dirty filters also create indoor air quality problems. Filters are inexpensive ($10 for a good pleated filter, or much less if purchased in bulk as would be the case with a duct-sealaing program) and very easy to install, so they would be an effective addition to a duct sealing program.
Air Flow. Many systems do not have enough air flow because there is too much resistance in the duct system. Too little air flow reduces an air-conditioning system’s capacity and efficiency and means that some rooms may not get enough heating or cooling air and thus may be uncomfortable. Sometimes air flow can be increased by replacing dirty or plugged filters with new ones. This job that can easily be done by a homeowner. However, if changing the filter does not solve the problem, an HVAC contractor may need to clean the indoor air conditioner coil, replace ducts, or install extra ducts.
Replacing Air Handler Fans. Air handler fans and motors
in residential HVAC equipment are typically not very efficient. More efficient
fans and motors are used by all major HVAC manufacturers in premium quality
equipment. The limited application of high-efficiency motors in residential
settings is probably because the added cost is about $100 to $150 off the
shelf for a single unit (much cheaper for manufacturers buying in bulk).
Replacing existing inefficient electric motors with electronically commutated
motors could save about 300 Watts of energy per house during heating and
cooling seasons. In cooling season, there is the added bonus that the air
conditioner no longer has to remove this 300 Watts of heat from the air
stream, which means that about 400 Watts of air conditioner power reduction
is achieved. During heating season, the furnace must provide the
lost 300 W loss of heat instead. There are some power factor issues
related to the operation of these motors, which are of concern to
utilities (rather than customers), but appropriate power-line conditioning
can address these issues.
The statewide peak demand savings for replacing air handler fan motors
would be:
Cooling Season: 400 W x 8 million houses x 1/3 x 1/3 = 0.35
GW.
Heating Season: 300 W x 8 Million/1.7 (furnace oversizing and
diversity factor) = 1.4 GW.
Replace Equipment. Several current market schemes encourage the
purchase of more efficient heating and cooling equipment. If efficient
equipment is installed when ducts are sealed, the savings are attractive
because duct sealing reduces HVAC system losses, which means that the size
of the furnace or air conditioner can be reduced. The money saved by purchasing
a small-capacity unit offsets the increased cost of purchasing a higher-efficiency
device. Better equipment results in additional peak demand savings on top
of those achieved by reducing duct losses. The additional peak demand savings
may be realized by reduced operating time (e.g., a 90% AFUE furnace operates
for 13% less time than a standard 78% AFUE furnace) or reduction in equipment
capacity (a 90% AFUE furnace operating for the same amount of time as a
78% AFUE furnace can have 13% smaller capacity and meet the same building
load).
Oversizing. Almost all heating and cooling systems are "oversized". This means that they have more capacity than they need. The idea behind installing higher capacity systems is to ensure that no matter how cold or hot it gets (or how bad the ducts are) the house can be kept at a comfortable temperature. However, a bigger system requires less time to heat or cool the house. These shorter "cycles" mean that energy is lost because it is left behind in the ducts at the end of each cycle. Also, the furnace or air conditioning equipment takes some time to reach its optimum operating temperature and shorter cycles mean that the equipment is operating less efficiently. Lastly, oversized equipment uses more power (or gas) whilst it is operating, and this creates a bigger peak demand for the electricity or gas utility.