1、Alex Lekov, Victor Franco, Steve Meyers, Lisa Thompson and Virginie Letschert are researchers at Lawrence Berkeley National Laboratory, Berkeley, CA Energy Efficiency Design Options for Residential Water Heaters: Economic Impacts on Consumers Alex Lekov, PhD Victor Franco Steve Meyers ASHRAE Member
2、Lisa Thompson Virginie Letschert ABSTRACT HEADING The U.S. Department of Energy (DOE) recently completed a rulemaking process in which it amended the existing energy efficiency standards for residential water heaters. A key factor in DOEs consideration of new standards is the economic impacts on con
3、sumers. Determining such impacts requires a comparison of the additional first cost of energy efficiency design options with the savings in operating costs. This paper describes the method used to conduct the life-cycle cost (LCC) and payback period analysis for gas and electric storage water heater
4、s. It presents the estimated change in LCC associated with more energy-efficient equipment, including heat pump electric water heaters and condensing gas water heaters, for a representative sample of U.S. homes. The study included a detailed accounting of installation costs for the considered design
5、 options, with a focus on approaches for accommodating the larger dimensions of more efficient water heaters. For heat pump water heaters, the study also considered airflow requirements, venting issues, and the impact of these products on the indoor environment. The results indicate that efficiency
6、improvement relative to the baseline design reduces the LCC in the majority of homes for both gas and electric storage water heaters, and heat pump electric water heaters and condensing gas water heaters provide a lower LCC for homes with large rated volume water heaters. INTRODUCTION Water heating
7、accounts for 14% of residential energy use in the U.S. (DOE EIA 2010) Most U.S. homes use either gas (52% of homes) or electricity (42% of homes) for water heating. (DOE EIA 2005) Water heaters have been subject to national energy conservation standards for over 20 years. Residential water heaters,
8、for statutory purposes, are defined as having a heat input of less than 75,000 Btu per hour (22.0 kW) and a storage volume between 20 to 100 gallons (76 to 379 liters) for gas storage water heaters and a maximum input rate of 41,000 Btu per hour (12 kW) and storage volume between 20 to 120 gallons (
9、76 to 454 liters) for electric storage water heaters.1Standards that required compliance beginning in 2004 set minimum energy factors (EFs) for gas and electric storage water heaters (SWHs) that vary based on the storage volume of the water heater. For the most common storage volumes - 40 gallons (1
10、51 liters) for gas SWH and 50 gallons (189 liters) for electric SWH), the minimum EFs were 0.59 for gas SWHs and 0.90 for electric SWHs. In the past several years, the Department of Energy (DOE) conducted a rulemaking to consider amended standards for 1Hereafter, the term “water heaters” is used to
11、refer to residential water heaters as defined above. LV-11-C013 2011 ASHRAE 1032011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, o
12、r transmission in either print or digital form is not permitted without ASHRAES prior written permission.water heaters. A key factor in DOEs consideration of new standards is the economic impacts on consumers. Determining such impacts requires a comparison of the additional first cost of energy effi
13、ciency design options with the savings in operating costs. The analytical approach and results reported here were part of DOEs rulemaking process for the final rule, which was issued on April 16, 2010. Complete details of the analysis may be found in the Technical Support Document (TSD) to the final
14、 rule.2DESIGN OPTIONS FOR WATER HEATERS The reference point for higher-efficiency designs is the baseline, which represents the most commonly-used type of water heater. DOE then considered a number of higher-efficiency designs, as shown in Table 1. The main designs considered are thicker insulation,
15、 electronic ignition, and power vent. Particularly noteworthy for water heaters is that technologies currently exist that provide much higher efficiency than the conventional designs that have been used in the past. These technologies are condensing designs for gas SWHs and heat pump designs for ele
16、ctric SWHs. Table 1. Efficiency Levels Considered for Gas-Fired and Electric Storage Water Heaters Efficiency Level (EF)* Technology Gas-Fired Storage* Baseline (EF = 0.59) Standing Pilot and 1” (2.5 cm) Insulation EF = 0.62 Standing Pilot and 1.5” (3.8 cm) Insulation EF = 0.63 Standing Pilot and 2.
17、0” (5.1 cm) Insulation EF = 0.64 Electronic Ignition, Power Vent and 1” (2.5 cm) Insulation EF = 0.65 Electronic Ignition, Power Vent and 1.5” (3.8 cm) Insulation EF = 0.67 Electronic Ignition, Power Vent and 2” (5.1 cm) Insulation EF = 0.77 Condensing, Power Vent, 2” (5.1 cm) Insulation Electric St
18、orage* Baseline (EF = 0.90) 1.5” (3.8 cm) Foam Insulation EF = 0.91 2” (5.1 cm) Foam Insulation EF = 0.92 2.25” (5.7 cm) Foam Insulation EF = 0.93 2.5” (6.4 cm) Foam Insulation EF = 0.94 3” (7.6 cm) Foam Insulation EF = 0.95 4” (10.2 cm) Foam Insulation EF = 2.00 Heat Pump Water Heater, 2” (5.1 cm)
19、Foam Insulation EF = 2.35 Heat Pump Water Heater, More-Efficient Compressor, 2.5” (6.4 cm) Foam Insulation * EF ratings are given for 40 gal (151 l) model for GSWHs and 50 gal (189 l) model for ESWHs. Condensing gas SWHs utilize a secondary heat exchanger to extract the heat from the moisture conten
20、t in the flue gases. Condensing gas SWHs are as yet only used in commercial sizes, but at least one condensing gas-fired storage water heater is actively marketed for residential applications. Heat pump water heaters (HPWHs)3are over twice as energy-efficient as conventional electric resistance wate
21、r heaters. A HPWH represents a merging of two technologies: (1) an electric resistance storage water heater with tank and controls; and (2) a refrigeration circuit similar to that found in a residential air-conditioner. Integrated HPWHs are currently being marketed by several manufacturers and now q
22、ualify for ENERGY STAR certification. Our analysis considered several issues that affect the consumer economics of HPWHs and condensing gas SWHs. First, HPWHs are slightly taller and wider than typical water heaters, so in some locations it might be difficult to fit the new water heater without some
23、 adjustments to the space. Second, because HPWHs extract heat from the surrounding air and exhaust air 2The DOE rulemaking considered and adopted standards for oil-fired SWHs and gas instantaneous water heaters in addition to standards for gas and electric SWHs. 3Throughout this paper, the term “hea
24、t pump water heater” refers to integrated units, not add-on products. 104 ASHRAE Transactionsat a colder temperature, they require adequate air flow. In indoor locations, providing adequate airflow may require special installation considerations. Further, the exhausting of cooled air affects the ind
25、oor environment. Depending on the location and the utilization of the water heater, its operation may significantly increase the homes heating load in the heating season (while decreasing the cooling load in the cooling season). Condensing water heaters are slightly wider than typical water heaters,
26、 so in some locations it might be difficult to fit the new water heater without some adjustments to the space. In addition, in replacement market a new plastic venting system is required. CONSUMER IMPACT ANALYSIS Analytical Method We conducted life-cycle cost (LCC) and payback period (PBP) analyses
27、to evaluate the economic impacts on consumers of potential amended energy conservation standards for water heaters. The LCC represents total consumer expenses during the life of an appliance, including equipment, installation, and operating costs (expenses for energy use, maintenance, and repair). T
28、o compute LCCs, we discounted future operating costs to the time of purchase, and then summed those costs over the life of the appliances. The PBP is calculated using the change in purchase cost (normally higher) at a higher efficiency level, divided by the change in annual operating cost (normally
29、lower). To conduct the consumer impact analysis, we developed nationally-representative samples of households that use gas or electric SWHs. The samples were drawn from the DOE Energy Information Administration (EIA) 2005 Residential Energy Consumption Survey (RECS 2005). The sample for gas SWHs was
30、 comprised of 2,166 records, representing 55.2 million homes, while the sample for electric SWHs was comprised of 1,523 records, representing 39.5 million homes. We assigned each household a water heater with a specific storage volume and determined the energy consumption for water heaters of varyin
31、g efficiency. We considered a range of storage volumes for each efficiency level. The LCC and PBP analysis models both the uncertainty and variability in the inputs using Monte Carlo simulation and probability distributions for several inputs. For each household, we measured the LCC change and the P
32、BP associated with a given efficiency level relative to the water heater assumed to be purchased in the base case. The base case reflects the future market in the absence of amended energy conservation standards, including the demand for products that exceed the current standards. Thus, the base-cas
33、e water heater for a given household is not necessarily the same as the baseline model. The analysis assumes that the water heaters are purchased in 2015, as this is the year in which compliance with amended standards is required. Consumer Product Cost Consumer product costs are based on U.S. DOE an
34、alysis that estimated the manufacturer selling price of baseline and higher-efficiency water heaters. DOEs engineering analysis develops cost-efficiency relationships that show the manufacturing costs of achieving increased efficiency. DOE used an efficiency level approach to identify incremental im
35、provements in efficiency for each product and a cost-assessment approach to develop the manufacturer production cost (MPC) at each efficiency level. DOE first identified the most common water heating products on the market and determined their corresponding efficiencies and the distinguishing techno
36、logy features. DOE then gathered information about these selected products using reverse-engineering methodologies, product information from manufacturer catalogs, and discussions with manufacturers and other experts of water heaters. This approach identified potential technology paths manufacturers
37、 use to increase energy efficiency. DOE used this information to generate bills of materials (BOMs), which is then converted into MPCs. By applying derived manufacturer markups to the MPCs, DOE calculated the manufacturer selling prices (MSPs). We applied markups to transform the manufacturer sellin
38、g prices into a consumer cost. In order to develop markups, we identified how the products are distributed from the manufacturer to the customer (the distribution channels). We derived separate markups for replacement and new construction applications. For each distribution channels, we used economi
39、c data from the U.S. Census Bureau and other sources to define how prices are marked up as the products pass to the customer. The 2011 ASHRAE 105price includes sales tax for replacement applications. The consumer price for the considered water heater efficiency levels are shown in Table 2. Since DOE
40、 analyzes efficiency levels as candidates for minimum efficiency standards, its analysis of manufacturer costs assumed a high level of production at each efficiency level. Table 2. Water Heater Prices Used in the Analysis Gas SWH Electric SWH Efficiency Level Consumer Price* (2009$) Efficiency Level
41、 (EF) Consumer Price* (2009$) Baseline, EF = 0.59 $450 Baseline, EF = 0.90 $281 EF = 0.62 $468 EF = 0.91 $291 EF = 0.63 $509 EF = 0.92 $301 EF = 0.64 $705 EF = 0.93 $304 EF = 0.65 $723 EF = 0.94 $325 EF = 0.67 $771 EF = 0.95 $362 EF = 0.77 $988 EF = 2.00 $1,039 EF = 2.35 $1,163 * Weighted average fo
42、r replacement and new construction applications Installation Costs The installation cost covers all labor and material costs associated with the replacement of an existing water heater or the installation of a water heater in a new home, as well as delivery, removal, and permit fees. The cost estima
43、tion was partly based on RSMeans cost estimates. Regional labor costs were applied to each RECS sample household to more accurately estimate installation costs. We included several installation costs to address the space constraints that water heaters having thicker insulation may face in some homes
44、. To estimate the fraction of households that would require various modifications, we considered the water heater location determined for each sample household. We determined the location using information from the 2005 RECS, which reports whether the house has a heated or unheated basement and the
45、presence or absence of a garage, crawlspace, or attic. For gas SWHs, we estimated that 813 percent and 1525 percent of all replacement installations would require significant modifications in order to install a design with 1.5-inch (3.8 cm) or 2-inch (5.1 cm) insulation, respectively. After consider
46、ing that some houses could choose a different dimension water heater, we assumed that major modifications would be necessary for 20 percent of replacement installations with 2-inch (5.1 cm) insulation and for 10 percent of replacement installations with 1.5-inch (3.8 cm) insulation. We estimated tha
47、t half of the cases would choose a smaller water heater with a higher setpoint and tempering valve or a smaller water heater with similar first hour rating as the existing unit. The other half would choose door jamb removal/replacement to fit a wider water heater through an indoor closet or attic. T
48、he incremental installation cost for the power vent design includes the cost of an electrical outlet and a single plastic pipe vent. The installation cost for the condensing design is the same as above, with the additional cost of the condensate disposal. One specific concern addressed by the analys
49、is is about the safety of atmospheric venting of 40 gallon (151 liter) gas SWHs at 0.63 EF. This concern relates to vent temperatures from water heaters with recovery efficiencies of 78 percent and higher that could encounter condensation and the resulting corrosive environment in vent connectors during water heater cycling. Although there are several currently available 40 gallon (151 liter) gas SWH models at 0.63 EF that utilize atmospheric venting and do not have any special venting requirement, we assumed that a stainless steel vent connector would be required for all models
