CHAPTER 7. ENERGY USE CHARACTERIZATION TABLE OF CONTENTS
7.1 INTRODUCTION

........................................................................................................... 7-1 7.2 WATER HEATERS

........................................................................................................ 7-1 7.2.1 Introduction

.................................................................................................... 7-1 7.2.2 Household Sample

......................................................................................... 7-1 7.2.3 Hot Water Use

................................................................................................ 7-2 7.2.3.1 Equation for Hot Water Use

.......................................................................... 7-3 7.2.3.2 Detailed Description of Key Variables Used in Draw Model

....................... 7-4 7.2.3.3 Impact on Hot Water Use of Technology Changes in Clothes Washers and Dishwashers

............................................................................................ 7-4 7.2.3.4 Assignment of Water Heater Tank Size

......................................................... 7-5 7.2.3.5 Determination of Hot Water Use for Instantaneous Water Heaters

............ 7-10 7.2.3.6 Calculations of Hot Water Use

.................................................................... 7-10 7.2.4 Annual Energy Consumption

....................................................................... 7-10 7.2.4.1 Approach to Calculating Water Heater Energy Use

.................................... 7-11 7.2.4.2 Description of Key Variables

....................................................................... 7-14 7.2.4.3 Derivation of Energy Parameters

................................................................. 7-15 7.2.4.4 Derivation of Temperatures

......................................................................... 7-19 7.2.4.5 Approach to Calculating Water Heater Energy Consumption

..................... 7-24 7.2.5 Average Annual Energy Consumption

........................................................ 7-25 7.2.5.1 Gas-Fired Storage Water Heaters

................................................................ 7-25 7.2.5.2 Electric Storage Water Heaters

.................................................................... 7-26 7.2.5.3 Oil-Fired Storage Water Heaters

................................................................. 7-26 7.2.5.4 Gas-Fired Instantaneous Water Heaters

....................................................... 7-27 7.3 DIRECT HEATING EQUIPMENT

.............................................................................. 7-27 7.3.1 Introduction

.................................................................................................. 7-27 7.3.2 Household Sample

....................................................................................... 7-28 7.3.3 Determining Annual House Heating Load

.................................................. 7-30 7.3.4 Assigning Direct Heating Equipment to Sample Households

..................... 7-31 7.3.4.1 Input Capacity of Existing Equipment

......................................................... 7-31 7.3.4.2 Efficiency of Existing Equipment

................................................................ 7-32 7.3.5 Calculations of Energy Consumption

.......................................................... 7-33 7.3.5.1 Fuel Consumption

........................................................................................ 7-33 7.3.5.2 Electricity Consumption

.............................................................................. 7-33 7.3.6 Average Annual Energy Consumption

........................................................ 7-34 7.4 POOL HEATERS

.......................................................................................................... 7-35 7.4.1 Household Sample

....................................................................................... 7-36 7.4.2 Input Capacity and Heating Load

................................................................ 7-36 7.4.3 Calculations of Energy Consumption

.......................................................... 7-37 7.4.4 Average Annual Energy Consumption

........................................................ 7-38

7-iLIST OF TABLES
Table 7.2.1 Selection of RECS 2001 Records for Water Heaters

........................................... 7-2 Table 7.2.2 Assignment of Water Heater Tank Sizes to Sample Households

........................ 7-6 Table 7.2.3 Water Heater Tank Sizes Selected for Sample Households

................................ 7-8 Table 7.2.4 Assignment of RE to Gas-Fired Storage Water Heaters

.................................... 7-16 Table 7.2.5 Assignment of RE for Electric Water Heaters

................................................... 7-16 Table 7.2.6 Distribution of RE for Oil-Fired Water Heaters

................................................ 7-17 Table 7.2.7 Assignment of RE for Gas-Fired Instantaneous Water Heaters

........................ 7-17 Table 7.2.8 Distribution of Input Capacity for Gas-Fired Storage Water Heaters

............... 7-18 Table 7.2.9 Distribution of Input Capacity for Electric Storage Water Heaters

................... 7-19 Table 7.2.10 Distribution of Input Capacity for Oil-Fired Water Heaters

.............................. 7-19 Table 7.2.11 Distribution of Input Capacity for Gas-Fired Instantaneous Water Heaters

...... 7-19 Table 7.2.12 Water Heater Location by Product Class

........................................................... 7-23 Table 7.2.13 Annual Energy Consumption for Gas-Fired Storage Water Heaters

................. 7-26 Table 7.2.14 Annual Energy Consumption for Electric Storage Water Heaters

.................... 7-26 Table 7.2.15 Annual Energy Consumption for Oil-Fired Storage Water Heaters

.................. 7-27 Table 7.2.16 Annual Energy Consumption for Gas-Fired Instantaneous Water Heaters

....... 7-27 Table 7.3.1 Summary of Direct Heating Equipment Household Sample (RECS 2001)

...... 7-29 Table 7.3.2 Distribution of Input Capacity for Representative Product Classes of Direct Heating Equipment

................................................................................. 7-32 Table 7.3.3 Energy Efficiency of Existing Direct Heating Equipment

................................ 7-32 Table 7.3.4 Annual Energy Consumption for Gas Wall Fan Direct Heating Equipment

..... 7-34 Table 7.3.5 Annual Energy Consumption for Gas Wall Gravity Direct Heating Equipment

.......................................................................................................... 7-34 Table 7.3.6 Annual Energy Consumption for Gas Floor Direct Heating Equipment

........... 7-35 Table 7.3.7 Annual Energy Consumption for Gas Room Direct Heating Equipment

.......... 7-35 Table 7.4.1 Criteria for Selecting Household Sample for Pool Heaters (RECS 2001)

......... 7-36 Table 7.4.2 Annual Energy Consumption for Gas Pool Heaters

.......................................... 7-38
LIST OF FIGURES Figure 7.2.1 Hot Water Draw Model Determination of Hot Water Use

.................................. 7-5 Figure 7.2.2 Assignment of Water Heater Tank Sizes

............................................................. 7-7 Figure 7.2.3 Range of Daily Hot Water Use in Sample Households for Each Water Heater Product Class

.......................................................................................... 7-10 Figure 7.2.4 Range of Annual Outdoor Air Temperature for Sample Households by Water Heater Product Class

............................................................................... 7-20 Figure 7.2.5 Range of Daily Average Annual Inlet Water Temperature for Sample Households by Water Heater Product Class

...................................................... 7-22 Figure 7.2.6 Range of Annual Ambient Air Temperature in Sample Households by Water Heater Product Class

............................................................................... 7-24 Figure 7.2.7 Calculating Water Heater Energy Use

............................................................... 7-25

7-iiCHAPTER 7. ENERGY USE CHARACTERIZATION 7.1 INTRODUCTION The U.S. Department of Energy (DOE) carried out the life-cycle cost (LCC) and payback period (PBP) calculations described in chapter 8 by determining the savings in operating cost consumers would realize from more energy efficient products. Energy costs are the most significant component of consumer operating costs, with maintenance and repair costs the other contributors. DOE uses annual energy use, along with energy prices, to establish energy costs at various energy efficiency levels. This chapter describes how DOE determined the annual energy use of residential gas-fired, electric, and oil-fired storage-type water heaters; gas-fired instantaneous water heaters; direct heating equipment; and pool heaters. 7.2 WATER HEATERS The following sections describe factors that determine the amount of hot water and energy water heaters use, the characteristics of water heater energy efficiency, and water heater operating conditions. 7.2.1 Introduction Water heaters may use gas, oil, or electric energy. In the engineering analysis, DOE used the DOE test procedure for each product to calculate the energy consumption of water heaters. For the LCC analysis, DOE estimated energy consumption of water heaters in actual housing units, as represented by the sample described in section 7.2.2. DOE calculated the energy use of residential water heaters in each of the four product classes: gas-fired storage water heaters, electric storage water heaters, oil-fired and liquefied petroleum gas (LPG) storage water heaters, and gas-fired instantaneous water heaters. The calculation considers the primary factors that determine energy use:

• hot water use per household,
• the energy efficiency characteristics of the water heater, and
• water heater operating conditions other than hot water draws.
DOE used a hot water draw model to determine hot water use for each household in the sample. The characteristics of each water heater’s energy efficiency were taken from the engineering analysis. DOE developed water heater operating conditions (other than hot water draws) from weather data and other relevant sources. Section 7.2.3 discusses hot water use; section 7.2.4 discusses the relevant characteristics of water heater energy efficiency and operating conditions to calculate the annual energy consumption for water heaters. 7.2.2 Household Sample DOE’s calculation of the annual energy use of residential water heaters relied on data 1 from the Residential Energy Consumption Survey 2001 (RECS 2001), which was conducted by
7-1DOE’s Energy Information Administration (EIA). RECS collects energy-related data for occupied primary housing units in the United States. The RECS 2001 collected data from 4,822 housing units that represent almost 107 million households. For the notice of proposed rulemaking stage of this rulemaking, DOE plans to update its analysis using the RECS 2005. The subset of RECS 2001 records used to study water heaters met all of the following criteria.

• A water heater served as the primary source of heated water.
• The water heater used one of four heating fuels (electricity, gas, LPG, or oil).
• The water heater provided heated water for only one housing unit.
• The RECS 2001 record included an indication of water heater size.
• The water heater’s energy consumption was greater than zero.
Table 7.2.1 Selection of RECS 2001 Records for Water Heaters
Fuel Type Algorithm No. of Records No. of U.S. Households Represented (million) Natural Gas Water Heater = Yes Fuel Type = Natural Gas 2167 49.4 Propane Water Heater = Yes Fuel Type = Propane 153 2.8
Fuel Oil Water Heater = Yes Fuel Type = Fuel Oil 107 1.7 Electricity Water Heater = Yes Fuel Type = Electricity 1638 36.8

DOE used EIA’s weightings for each RECS 2001 household. The weightings indicate how commonly each household configuration occurs in the general population. DOE believes that the household records, along with their weightings, are representative of housing nationwide (see appendix 7-A for details). 7.2.3 Hot Water Use Hot water use differs widely among households, because it depends on characteristics of the household and the water heater, such as the number and ages of the people who live in the household and the way they consume hot water, the presence of hot water-using appliances, the tank size and thermostat set point of the water heater, and the climate in which the residence is situated.

2 DOE developed the hot water draw model to improve on a previously used model. The hot water draw model accounts for the key characteristics described above to estimate the average daily volume of hot water various households use. 7-27.2.3.1 Equation for Hot Water Use The hot water draw model uses an equation expressed as follows.
vol = { sea
_ coef + ( per
_ coef × per ) + ( age 1

_ coef × age 1 ) + age 2

_ ceof × age 2 + [ age 34 _ coef *( age 3 + age 4 ) + ( T tank _ coef × T tank ) + ( Tanksz

_ coef × Tanksz ) + ( T

in _ coef × T in ) + ( T air _ coef × T air ) + (hom e
_ coef × athome )

− [( 0.692 × p er + 1 .335 × per ) * dw

_ adj

− [(1.1688 × per + 4.7737 × per ) × cw
_ a dj ]}* ( senior

_ mf

_ coef × s enior

_ m f ) × ( no
_ p ay
_ coef × no
_ p ay )
Where:
vol =	 hot water consumption, gallons per day, gal/day, per =	 total number of persons in household, age1 =	 number of preschool children, age 0–5 years, yr, age2 =	 number of school-age children, age 6-13, yr, age3 =	 number of adults, age 14–64, yr, age4 =	 number of adults, age 65 yr and above, yr, T

tank = thermostat setting of water heater, degrees Fahrenheit, o F, Tank sz =	 nominal tank size of water heater, gal, T

in =	 temperature of water heater inlet water, o F, T

air =	 outdoor air temperature, o F, athome = presence of adults at home during day, dw_adj =	 adjustment factor to account for the differences between the current energy conservation standard for dishwashers and the households that have no dishwasher, cw_adj = adjustment factor to account for the differences between the current energy conservation standard for clothes washers and the households that have no clothes washer, senior

_ mf =	 senior-only household in a multi-family building, no_pay =	 household that does not pay for hot water, T

tank _err =	 estimation error for the thermostat set point (normal distribution), sea_coef =	 coefficient for seasonal effects, per_coef =	 coefficient for total number of persons in household (normal distribution), age1_coef =	 coefficient for A age1" (normal distribution), age2_coef =	 coefficient for A age2" (normal distribution), age34_coef =	 coefficient for A age3" + A age4" (normal distribution), home_coef =	 coefficient for A athome @ (normal distribution), T

anksz_coef =	 coefficient for water heater tank size (normal distribution), T

tank _coef =	 coefficient for thermostat set point (normal distribution), T

inlet _coef =	 coefficient for water inlet temperature (normal distribution), T

air

_coef =	 coefficient for average outdoor temperature (normal distribution), senior_mf_coef = coefficient for senior-only household in a multi-family building (normal distribution), and 7-3no_pay_coef = coefficient for household that does not pay for hot water (normal distribution). 7.2.3.2 Detailed Description of Key Variables Used in Draw Model The following is a detailed description of the primary variables used in the hot water draw model.

• Number of Persons in Household (per) . The total number of household members.
• Number of Preschool Children 0–5 (age1) . The equation calls for the number of infants and young children ages 0–5. However, RECS 2001 bins ages of household members. The closest age bin was infants 0–1, so that is what was used. This will underestimate hot water usage due to this age category.
• Number of School-Age Children 6–13 (age2) . The equation calls for the number of children, ages 6–13. The closest age bin available in RECS 2001 was used, children 1– 12. Hot water usage due to this category will therefore be somewhat overestimated.
• Number of Adults 14–64 (age3) . The equation calls for the number of adults, ages 14 to 64. DOE used the closest RECS 2001 bin—ages 13–64.
• Number of Adults 65+ (age4). The equation calls for number of adults, age 65 or older. There is a RECS 2001 age category that corresponds to this.
• Number of Thermostat Set point (T tank) . The thermostat setting of the water heater.
• Water Heater Tank Size (Tanksz) . The nominal size of the water heater tank.
• Outdoor Air Temperature (T air) . The average annual outdoor air temperature.
• Inlet Water Temperature (T in ) . The temperature of the water entering the water heater.
• Household Member (athome). The presence of an adult household member at home during the day.
• Senior Only (senior_mf) . A senior-only (age 65 or above) household in a multi-family building.
• No-Pay Household (no_pay) . A household that does not pay to heat water.
• Coefficient for Seasonal Effects (sea_coef) . Variable that adjusts hot water use for winter, spring, summer, and fall seasons.
• Dishwasher (dw_adj) . Adjustment factor to account for the differences due to the current energy conservation standard for dishwasher and for the cases of households with no dishwasher.
• Clothes Washer (cw_adj) . Adjustment factor to account for the differences between the current energy conservation standard for clothes washers and households that have no clothes washers. 7.2.3.3 Impact on Hot Water Use of Technology Changes in Clothes Washers and Dishwashers The hot water draw model incorporates parameters that represent clothes washers and dishwashers as they existed in the 1990s. Since that time, the considerable changes made to clothes washer and dishwasher technologies have lowered hot water use. In particular, updated 3 Federal energy conservation standards for clothes washers that became effective in 2007 and for
7-44 dishwashers that will become effective in 2010 have a significant impact on hot water use by clothes washers and dishwashers. To account for changes in hot water use by clothes washers and dishwashers, DOE adjusted the parameters in the hot water draw model. See appendix 7-B, hot water draw model, for further discussion of the adjustment factors. Water Use Chart
. DOE applied the same equation for hot water use to all households, regardless of water heater fuel type. Figure 7.2.1 illustrates how the hot water draw model determines household hot water use.

RECS

Tank Size Age 0-5 Weather Data

T tank T in

Dishwasher Clothes washer Occupants

Other hot water using appliances Age 14-64 Age 65+ Age 6-13 Total T air
Temperature Parameters

Presence during the day Senior only Doesn’t pay for water Household Characteristics Hot Water Use

Figure 7.2.1 Hot Water Draw Model Determination of Hot Water Use 7.2.3.4 Assignment of Water Heater Tank Size Calculating hot water use for each sample household requires assigning the water heater a specific tank size (referred to as rated volume). For each household, RECS reports one of three water heater tank sizes, small, medium, or large, as well as giving the size range in gallons. Table 7.2.2 shows RECS data on water heater tank size and the fraction of households associated with each size. 7-5Table 7.2.2 Assignment of Water Heater Tank Sizes to Sample Households

Fuel Type RECS Data Standard Sizes Used

in LCC Analysis (gal) Percent of Historical Shipments* (%) Percent Assigned to Sample Households (%) Size Class Size Range

(gal) Percent of Sample Households (%) Small ≤ 30 12 30 17 12 Natural 45 Gas and Medium 31-49 61 40 41 42

LPG 50 40 Large ≥ 50 27 75 2 2 Small ≤ 30 17 30 22 17 40 33 36 Electric Medium 31-49 52 50 35 38 Large ≥ 50 31 66 3 75 10 6 Small ≤ 30 25 32 90 90 Oil Medium 31-49 44 Large ≥ 50 31 50 10 10 5 *Sources: Natural gas and LPG: 1988–1995 data from the Gas Appliance Manufacturers Association (GAMA) , 6 2004–2006 shipments data from the Air Conditioning, Heating, and Refrigeration Institute (AHRI). Electric: U.S. 7 8 Census Bureau data (2002–2006). Oil: 2001 DOE Water Heater Rulemaking. “Typical” water heater sizes, which are those most common for each fuel type, have the minimum energy factor allowed by current energy conservation standards. These “typical” units have the largest market share in their product class (50 gal/190 liter for electric, 40 gal/150 liter for natural gas and LPG, and 32 gal/120 liter for oil). In the LCC analysis, DOE expanded the range of sizes considered to include all those listed in Table 7.2.2 so that the analysis would accurately reflect the broad range of water heater sizes that consumers may encounter. The sizes in the expanded repertoire are referred to as “standard” sizes. DOE applied a two-step process to assign water heater sizes to the RECS households: (1) for each fuel type, a fraction of the RECS households was assigned to each standard size; and (2) water heater sizes were assigned to specific households based on RECS data on the number of bathrooms in the house. Figure 7.2.2 illustrates the process.

7-6Figure 7.2.2 Assignment of Water Heater Tank Sizes Step 1. Assignment of Water Heater Sizes
. Table 7.2.3 shows the percentage of each standard size that contained in recent shipments of water heaters. (See chapter 5, engineering analysis, for a discussion of how DOE chose standard sizes.) The percentages of standard sizes in shipments provide insight into the percentages one would expect to find in the housing stock. Lastly, the table shows the percentages of RECS households that were assigned to each standard size for the LCC analysis.

7-7Table 7.2.3 Water Heater Tank Sizes Selected for Sample Households Fuel Type RECS Size No. of Water Heater Percent Class Bathrooms Size (gal) Assigned to Size Class Small Any # BR 30 100% Any # BR 40 74% Natural Gas or LPG Medium Any # BR 50 26% 2 BR 50 100% 50 58% Large ≥ 3 BR 75 42% Small Any # BR 30 100% Any # BR 40 69% Electric Medium Any # BR 50 31% < 2 BR 50 100% 50 62% 66 22% 2 BR 75 16% Large ≥ 3 BR 75 100% Small Any # BR 32 100% Oil Medium Any # BR 32 100% Large Any # BR 32 69% Any # BR 50 31% The 1995 GAMA shipments data show that 17 percent of shipments of gas-fired water heaters were the 30-gallon size. Historical RECS data 1, 9, 10 show that households having a small 9 1 water heater declined from 20 percent in RECS 1993 to 12 percent in RECS 2001. Furthermore, only 4 percent of RECS 2001 “new construction households” (households built 1996–2001) have a small water heater. DOE assigned a 30-gallon water heater to all households having a small water heater (12 percent), and estimated that the rest of the shipments (5 percent) represented larger water heaters. DOE used the shipment data to assign 75-gallon water heaters to 2 percent of sample households. DOE assigned the remaining households that have a gas-fired water heater either a 40- or 6 a 50-gallon water heater. Based on the AHRI shipments data, DOE estimated that 52 percent of the that total are 40-gallon, and 48 percent are 50-gallon water heaters. Applying this 52/48 split to the remaining RECS 2001 households having medium and large water heaters resulted in assigning a 40-gallon size to 45 percent of households and a 50-gallon size to 42 percent. All RECS households having large water heater (after subtracting those assigned 75-gallon water heaters) were assigned a 50-gallon water heater. All RECS 2001 households having medium water heaters were assigned either a 40- or a 50-gallon water heater.
7-8U.S. Census shipments data show that 22 percent of shipments of electric water heaters were the 30-gallon size or smaller (including sizes smaller than 20 gallons and tabletop models, both of which are not subject of this rulemaking). Of RECS 2001 sample households, 16 percent have a small water heater. DOE assigned a 30-gallon water heater to all household having small water heaters, and estimated that the rest of the shipments (6 percent) consisted of water heaters having less than a 20-gallon volume and tabletop water heaters. DOE assigned 66- or 75-gallon water heaters to 10 percent of households, based on the U.S. Census shipments data. DOE estimated that 70 percent of those water heaters were 75 gallons, and 30 percent 66 gallon, based on AHRI’s shipments data for 1988–1995. DOE assigned the remaining households having electric water heaters either a 40- or a 50-gallon water heater. Based on U.S. Census shipments data, DOE estimated that 49 percent of the total are 40-gallon, and 51 percent are 50-gallon water heaters. Applying this 49/51 split to the remaining RECS 2001 households having medium and large water heaters resulted in assigning a 40-gallon size to 36 percent and a 50-gallon size to 38 percent. All RECS 2001 household having large water heaters (after subtracting those assigned 66- and 75-gallon sizes) were assigned a 50-gallon water heater, and all RECS 2001 households having medium water heaters were assigned either a 40- or a 50-gallon water heater. The distribution of sizes for oil-fired water heaters in the shipments data taken from the technical support document for DOE’s 2001 water heater rulemaking differs greatly from that in the RECS 2001 data. DOE believes the shipments data are likely to be more accurate than the RECS 2001 data, because the RECS sample is very small. Based on the shipments data, DOE assigned a 32-gallon water heater to 90 percent of the RECS 2001 households and a 50-gallon water heater to the remaining 10 percent. DOE assigned a 32-gallon water heater to all RECS 2001 households having small and medium water heaters, and split the RECS 2001 households having large water heater between 32- and 50-gallon sizes. DOE assigned a 50-gallon water heater to one-third of the households having a large water heater, and assigned a 32-gallon water heater to the remaining two-thirds of households that have a large water heater. Step 2. Assignment of Household-Specific Water Heater Sizes
. The preceding section described how DOE assigned standard water heater sizes to the households in each RECS water heater size class. In exploring the correlation between water heater size and several other variables, DOE found that the highest correlation with the number of bathrooms. DOE further therefore refined the assignment of water heater sizes to specific sample households by considering RECS data on the number of bathrooms per house. Table 7.2.3 shows how DOE combined the RECS data on water heater size and number of bathrooms to assign household specific standard water heater sizes. See appendix 7-B, hot water draw model, for further discussion of the assumptions used. A few sample houses reported an “unknown” water heater tank size. DOE randomly assigned tank sizes to those households based on the percentages assigned to households that reported a tank size.

7-97.2.3.5 Determination of Hot Water Use for Instantaneous Water Heaters DOE developed the hot water draw model for storage-type water heaters. Instantaneous water heaters have no “size” in terms of storage volume, so DOE did not explicitly model their hot water use. A feature of instantaneous water heaters is their potential to deliver “unlimited” hot water during times of high household demand. However, DOE did not find any usable data showing higher or lower hot water use for instantaneous water heaters, so it estimated that a household having an instantaneous water heater uses the same volume of hot water as it would with a storage-type water heater. 7.2.3.6 Calculations of Hot Water Use DOE calculated average daily hot water use to be 43.0 gallons for households having electric storage water heaters, 45.5 gallons for households having gas-fired storage water heaters, 43.0 gallons for households having oil-fired water heaters, and 45.8 gallons for households having gas-fired instantaneous water heaters. The variations primarily reflect differences in the average number of people in the households that use each type of fuel. Figure 7.2.3 shows the range in hot water use among sample households.
Hot Water Use (gallons) Ranges by Efficiency Level Median; Box 25%-75%; Whisker: 5%-95%

0 10 20 30 40 50 60 70 80 90 100

Gas WH Electric WH Oil WH Instantaneous Gas WH median Average

Figure 7.2.3	 Range of Daily Hot Water Use in Sample Households for Each Water Heater Product Class 7.2.4 Annual Energy Consumption DOE calculated the energy use of water heaters using a simplified energy equation, the 11 water heater analysis model (WHAM). WHAM accounts for a range of operating conditions and energy efficiency characteristics of water heaters. To describe energy efficiency
7-10characteristics of water heaters, WHAM uses three parameters that also are used in the DOE test 12 procedure: recovery efficiency ( RE ), standby heat-loss coefficient ( UA ), and rated input power ( P ON ). Water heater operating conditions are indicated by the daily hot water draw volume, inlet water temperature, thermostat setting, and air temperature around the water heater (ambient air temperature). The current version of WHAM is appropriate for calculating the energy use of electric resistance storage water heaters. To account for the characteristics of other types of water heaters, energy use must be calculated using modified versions of the WHAM equation. These modified versions are discussed below. 7.2.4.1 Approach to Calculating Water Heater Energy Use DOE utilizes the WHAM equation, which yields average daily water heater energy consumption ( Q in ) . The equation is expressed as follows. ⎛ ⎜ ⎝ ∗ 1

− ⎞ ⎟ ⎠ vo l × den C P ( T tank − T in ) UA ( T tank − T amb ) × × × Q in = + 24 × UA × ( T tank − T amb ) RE Pon
Where: Q in = total water heater energy consumption, British thermal units per day Btu/day, RE = recovery efficiency, %, P ON = rated input power, Btu/h, UA = standby heat-loss coefficient, Btu/h- o F, T

tank = thermostat set point temperature, o F, T

in = inlet water temperature, o F, T

amb = temperature of the ambient air, o F, vol = volume of hot water drawn in 24 hours, gal/day, den = density of stored water, set constant at 8.29 pounds per gallon, lb/gal, and C

P = specific heat of stored water, set constant at 1.000743, Btu/lb- o F. Additional details about the WHAM equation are provided in appendix 7-C, LCC energy use calculations. WHAM provides total water heater energy consumption ( Q in ). For gas-fired storage water heaters, gas-fired instantaneous water heaters, and oil-fired storage water heaters, the values for electricity and fuel consumption must be disaggregated. Q in is the sum of fuel and electricity consumption. DOE calculated electricity consumption as follows.

in Q electricity = Q × 

# (P aux − P standby 

# )

− P standby × 24 P

ON Where: 7-11Q electricity = electricity consumption, kWh/day, Q in = total water heater energy consumption, kWh/day, P ON = rated input power, kW, P aux = electricity demand when burner is on, kW, and P standby = electricity demand when burner is off, kW. DOE calculated gas consumption by subtracting electricity consumption from the total energy consumption for the water heater ( Q in ). For heat pump water heaters, energy efficiency and consumption are dependent on ambient temperature. To account for this factor, DOE expanded the WHAM to utilize the calculation approach used in the New York State Energy Research and Development Authority (NYSERDA) heat pump water heater site screening tool and DOE’s weatherization assistance program. 13, 14 The equation for determining the energy consumption of heat pump water heaters is similar to WHAM equation, but a performance adjustment factor that is a function of the average ambient temperature is applied to adjust RE . A heat pump water heater operates either in heat pump or in electric resistance mode. DOE assumed that the electric resistance mode of operation is used 100 percent of the time when the monthly ambient temperature is less than 32
o F. A heat pump water heater also operates in the electric resistance mode for part of the time even when the monthly ambient temperature exceeds 32 o F, because this product has a slower recovery rate than an electric resistance water heater. DOE determined that, depending on household hot water consumption patterns, the electric resistance mode of operation occurs for as much as 10 percent of the unit’s operating time. (See appendix 7-C for a full description of the method). The equation is: ⎡ HP frac ⎤ ⎛ ⎞ UA 

### (T tank − T amb 

### ) × ⎢ ⎢ ⎢ ⎢ ⎢ _

RE × P A HPWH (1

− HP

_ f rac ) ⎥ ⎥ ⎥ ⎥ ⎥ * 1

− + P

ON , HPWH ⎜ ⎜ ⎝ ⎟ ⎟ ⎠ hpwh 

### (T in 

### ) (T 

### ) * + 24 × UA × Q vol den C

− T

− T × × = in P tank tank amb ⎛ ⎜ ⎜ ⎞ ⎟ ⎟ U

A 

### (T tank − T amb 

### ) × * 1

− R E P ON , ER ⎝ ⎠ ⎣ ⎦ ER Where: Q in = total water heater energy consumption, Btu/day, vol = daily draw volume, gal/day, den = density of water, lb/gal, C

p = specific heat of water, Btu/lb- o F, T

tank = set point temperature for tank thermostat, o F, T

in = temperature of inlet water, o F, RE = recovery efficiency, %, UA = stand-by heat-loss coefficient, Btu/h- o F, T

amb = temperature of the ambient air, o F, P ON = rated input power, Btu/h, PA hwh = performance adjustment factor, and 7-12HP_frac = fraction of water heating load that is satisfied by heat pump mode. Heat pump water heaters draw heat from the space in which they are located. Thus, when such a water heater is located in a conditioned space, its use affects the heat load that the home’s space heating and air conditioning equipment must meet. When the home is being heated, use of the heat pump water heater increases the heating load, and when the house is being cooled, its use decreases the cooling load. To account for the indirect effects of heat pump water heaters on home energy use, DOE estimated the impact on space heating and air conditioning energy consumption for each home in the RECS subsample for electric water heaters that has the water heater in the conditioned space. For each such home, DOE estimated the impact on space heating in heating months only (when indoor temperature is 10 degrees greater than the average outdoor temperature), and the impact on air conditioning for cooling months only (when indoor temperature is 5 degrees less than the average outdoor temperature). DOE calculated the amount of cooling added (heat removed) by the heat pump water heater as follows:
CoolingInput = CoolingCap HPWH × vol × den × C p 

## ( T tan k − T in 

## ) P × RE × PA

ON , HPWH HPWH HPWH Where: CoolingInput = amount of cooling added by the heat pump water heater, Btu/h, vol = daily draw volume, gal/day, den = density of water, lb/gal, C

p = specific heat of water, Btu/lb- o F, T

tank = set point of tank thermostat, o F, T

in = indoor air temperature, o F, P ON,HPWH = rated input power, Btu/h, RE = recovery efficiency, %, PA HPWH = performance adjustment factor, and CoolingCap HPWH = cooling capacity of heat pump water heater.

14 P ON for heat pump water heaters is 500 watts (W) (1,704 Btu/h), and 13 Cooling_Cap_hpwh is 3,500 Btu/h. DOE used RECS data for each household to determine the primary heating system, fuel used to heat the house, and the type of cooling system. DOE then assigned an energy efficiency to each type of equipment to determine the energy loss (from heating) or gain (from cooling). DOE based the energy efficiency of the heating and air conditioning equipment on the stock-average values for 2015 given in EIA’s Annual Energy Outlook 2008. To account for the times during the summer months when the air conditioner is

7-13not operating, DOE reduced the estimated cooling benefits from the water heater by one-third. a See appendix 7-C for further details. For instantaneous water heaters, DOE utilized the approach used for storage water heaters to calculate the energy use, modified to account for the absence of storage tank. DOE applied a performance adjustment factor to account for evidence that the rated energy efficiency of instantaneous water heaters overstates actual performance. Preliminary results from a study of instantaneous water heater installations conducted for the California Energy Commission (CEC) 15 indicate a performance drop-off at small draw volumes. To account for this phenomenon, the study performed for the CEC recommends reducing the listed Energy Factor (EF) for gas-fired instantaneous water heaters by 8.8 percent. Thus a gas-fired instantaneous water heater rated at 0.82 EF would be treated as if rated at 0.748 EF. (Note that the study does not suggest that the CEC’s directory rate the instantaneous water heater at the lower EF). To incorporate this recommendation, DOE applied an adjustment factor by that effectively increases 8.8 percent the calculated energy use of a gas-fired instantaneous water heater at each EF. The resulting equation is: ⎛ ⎜ ⎜ ⎝
Where: Q in = total water heater energy consumption, Btu/day, vol = daily draw volume, gal/day, den = density of water, lb/gal, C

p = specific heat of water, Btu/lb- o F, T

tank = set point of tank thermostat, o F, T

in = inlet water temperature, o F, RE = recovery efficiency, %, PA iwh = performance adjustment factor, Q

p = pilot input rate, Btu/h, Q out = heat content of water drawn from the water heater, Btu/h, and P ON = rated input power, Btu/h.
7.2.4.2 Description of Key Variables The following is a description of the key variables for calculating energy use by gas-fired instantaneous water heaters:

a DOE believes it would be impractical for the occupants of the few households that use wood, coal, or kerosene as primary heating fuels to supplement heat produced by heat pump water heaters. Because DOE would find it difficult to quantify energy costs, DOE assumed that occupants would use an electric resistance heater to satisfy the additional heating requirements produced by the heat pump water heater. ⎞

⎟ ⎠

⎟ + 

## ( T in 

## ) Q P

ON vol den C

− T × × p P k 

## ( T amb 

## ) tan Q 1

− 24 × Q

− T × × = in Tank p RE PA hpwh ×

7-14• Recovery Efficiency (RE)

. The recovery efficiency ( RE ) is the ratio of energy added to the water compared to the energy input to the water heater. It represents how efficiently energy is transferred to the water when the heating element is on or the burner is firing. RE covers steady-state energy efficiency only. It accounts for the amount of energy lost through the water heater jacket, the flue, and fittings while the burner is firing.

• Rated Input Power (P ON ). Rated input power is the nominal power rating the manufacturer assigns to a particular design of water heater expressed in kW for electric water heaters and Btu/h for gas-fired or oil-fired water heaters. For gas-fired water heaters the rated input power includes the pilot light.

• Standby Heat-Loss Coefficient (UA). The standby heat loss coefficient ( UA ) indicates the water heater hourly standby energy losses, expressed in Btu/h-oF. UA, which is calculated by the DOE test procedure, is reported in terms of the energy input required to maintain the water at the set point temperature. It represents the rate at which energy must be added to the water heater when it is not heating water for delivery.

• Set Point of Thermostat (T tank ). The thermostat set point is the desired delivery temperature of the hot water.

• Inlet Water Temperature (T in

). The inlet water temperature is the temperature of the water supplied to the water heater.

• Temperature of the Air Surrounding the Water Heater (T amb). The temperature surrounding the water heater is the ambient air temperature of the space where the water heater is located.

• Volume of Hot Water Drawn in 24-Hour Period (vol). The estimated daily household use of hot water. This volume is calculated in the hot water draw model.

• Density of Water (den). The density of hot water at the average of the set point and inlet temperatures (8.29 lb/gal). The density is mass per unit volume, expressed as lb/gal (kg/l).

• Specific Heat of Water (C p

). The specific heat of water at the average of the set point and inlet temperatures (1.000743 Btu/lb- o F). The specific heat is the amount of heat needed to increase or decrease the temperature of 1 pound mass of water by 1 °F (1 kJ/kg - Kelvin). 7.2.4.3 Derivation of Energy Parameters Key parameters in DOE’s calculation of water heater energy consumption are the recovery efficiency ( RE), the standby heat loss coefficient ( UA ), and the rated input power ( P on ). 16 DOE’s test procedure for water heaters provided the definitions for these parameters. DOE developed the parameters for selected EF as described below. (See chapter 5, engineering analysis, for a discussion of DOE’s selection of EFs.)
7-15Determining RE. For each energy efficiency level used in the LCC analysis, DOE determined typical values of RE . For gas-fired and oil-fired storage water heaters, those values were based on the design features at each energy efficiency level and the distribution of models 17 at each EF, as given in the March 2007 GAMA Directory. This approach captures the variation of RE among models in the market.
Table 7.2.4 shows the RE values for gas-fired storage water heaters having a 40-gallon rated volume. The same RE values apply to the other three size categories (30, 50, and 75 gallons), because the design characteristics at each energy efficiency level are the same across the size categories. Table 7.2.4 Assignment of RE to Gas-Fired Storage Water Heaters

Efficiency Level EF (40 gallon) RE (%)
0 0.59 76 1 0.62 76 2 0.63 76 3 0.64 78 4 0.65 78 5 0.66 82 6 0.77 89

DOE estimated that the recovery efficiency for electric water heaters having immersed heating elements is 98 percent for most energy efficiency levels (Table 7.2.5). For heat pump water heaters, DOE calculated RE by using the UA value reported for the heat pump water 14 heater manufactured by ECR. Table 7.2.5 Assignment of RE for Electric Water Heaters

Efficiency Level EF (50 gallon) RE (%)
0 0.90 98 1 0.91 98 2 0.92 98 3 0.93 98 4 0.94 98 5 0.95 98 6 2.20 242

The RE values for 32-gallon size oil-fired water heaters also apply to the 50-gallon size (Table 7.2.6).

7-161 2 3 4 5 6 7

1 2 3 4 5 6 7 Table 7.2.6 Distribution of RE for Oil-Fired Water Heaters

Efficiency Level EF (32 gallon) RE (%) 0 0.53 76 0.54 76 0.56 76 0.58 76 0.60 76 0.62 78 0.66 80 0.68 82
DOE based RE values for instantaneous water heaters at each energy efficiency level on the design features at each level and on the distribution of models at each EF, as given in the 18 Federal Trade Commission (FTC) 2007 directory. This approach captures the variability of RE among the models in the market. The same RE values apply to all input capacities, because the design characteristics at each energy efficiency level are the same across the size categories. The RE for each energy efficiency level is shown in Table 7.2.7. Table 7.2.7 Assignment of RE for Gas-Fired Instantaneous Water Heaters

Efficiency Level EF RE (%)
0 0.62 72 0.69 78 0.78 78 0.80 80 0.82 82 0.84 84 0.85 85 0.92 93 Determining UA. DOE used the following equation to calculate values for stand-by heat loss coefficient ( UA ). ⎛ ⎜ ⎝ ⎞ ⎟ ⎠ 1 1

− EF RE UA = ⎛ ⎞ 24 1 ( T k − T amb )

− Q out RE × Pon × ⎜

⎜ ⎝ ⎟ ⎟ ⎠ tan

Where:
UA = standby heat loss coefficient, Btu/h- o F, EF = energy factor, RE = recovery efficiency; %. 7-17T tank = temperature of the air surrounding the water heater, o F; T

amb = thermostat set point temperature, o F; Q out = heat content of the water drawn from the water heater, Btu/h, and P ON = the rated input power, Btu/h. Appendix 7-C, LCC energy use calculations, describes the derivation of the above equation. For calculating UA , DOE used values for tank and ambient temperatures from the DOE test procedure. For heat pump water heaters, DOE estimated UA equals that of a 50-gallon electric storage water heater having a 0.95 EF. The additional heat losses due to the plumbing connections between the storage tank and the heat pump components are offset by the significantly higher RE of the heat pump water heater. Determining P ON. For each category of rated volume within each product class, DOE determined appropriate bins for rated input power ( P ON ) based on the models listed in the March 17 2007 GAMA Directory, then calculated the percentage of models in each bin. This approach captures the variability of input capacity among the products models in the market. The percentage of gas-fired water heaters in each volume category is shown in Table 7.2.8. Table 7.2.8 Distribution of Input Capacity for Gas-Fired Storage Water Heaters

Input Capacity Rated Volume (gallons) (P ON ) (kBtu/h) 30-gal (%) 40-gal (%) 50-gal (%) 75-gal (%) 26 3.59 0.00 0.00 0.00 30 58.08 5.92 1.45 0.00 35 23.35 37.06 15.55 0.00 40 14.97 48.90 47.02 0.00 50 0.00 8.12 17.72 1.37 60 0.00 0.00 6.33 9.59 65 0.00 0.00 11.93 9.59 70 0.00 0.00 0.00 54.79 75 0.00 0.00 0.00 24.66 The percentage of electric water heaters in each volume category are shown in Table 19 7.2.9. For heat pump water heaters, the P ON of 0.5 kW was based on ECR’s Watt Saver model.

7-18Table 7.2.9 Distribution of Input Capacity for Electric Storage Water Heaters Input Capacity Rated Volume (gallons) (P ON ) (kW) 30-gal (%) 40-gal (%) 50-gal (%) 66-gal (%) 75-gal (%) 3.0 5.74 0.54 0.97 0.00 2.06 3.8 27.05 22.04 16.91 10.67 12.37 4.5 65.57 74.73 77.78 86.67 79.38 5.5 1.64 2.69 4.35 2.67 6.19 Table 7.2.10 shows the percentage of oil-fired water heaters in each volume category. Table 7.2.10 Distribution of Input Capacity for Oil-Fired Water Heaters Input Capacity Rated Volume (gal) (P ON ) (kBtu/h) 32-gal (%) 50-gal (%) 90 50.0 0.0 105 50.0 100.0

For gas-fired instantaneous water heaters, which have no rated volume, DOE estimated the percentage of each of the three input capacities using RECS data on the size of gas-fired storage water heaters in households. To households having a small tank (<=30 gallon) DOE assigned a gas-fired instantaneous water heater having 140 kBbtu/h input capacity. To households having a large tank (>=50 gallon) tank DOE assigned a gas-fired instantaneous water heater having 199 kBtu/h input capacity. To households having a medium tank (31 to 49 gallons), DOE assigned some a gas-fired instantaneous water heater having 180 kBtu/h input capacity. DOE assigned the rest of the households a gas-fired instantaneous water heater having 199 kBtu/h input capacity (see Table 7.2.11). Table 7.2.11 Distribution of Input Capacity for Gas-Fired Instantaneous Water Heaters Range of Input Capacity (kBtu/h) * Assigned Input Capacity (kBtu/h) Percent Assigned to Sample Households (%) 140-169 140 11 170-185 180 16 186-199 199 73 * DOE did not include units having a capacity <140 kBtu/h, because such units are considered unsuitable for whole20 house water heating. 7.2.4.4 Derivation of Temperatures The temperatures for thermostat set point, inlet water, and the ambient air are derived from the average annual outdoor air temperature for each sample household. Outdoor Air Temperature. RECS 2001 provides data on heating and cooling degreedays, but not on air temperatures for each household in the sample. To each RECS 2001
7-19household DOE assigned a physical location from which outdoor air temperatures could be derived as follows:

• DOE assembled weather data from 282 weather stations that provide 30-year averages for 21, 22 annual average outdoor air temperatures. DOE also gathered the heating and cooling degree-days at a base temperature of 65 o F for 2004 for those weather stations. 23 The2004 heating and cooling degree-days match the period used to determine the degreedays in RECS 2001.
• RECS 2001 reports both heating and cooling degree-days to base temperature 65 o F for each housing record. DOE assigned each RECS 2001 household to one of the 282 weather stations by calculating which station (within the appropriate census region or large state) gave the best linear least-squares fit of RECS 2001 data to weather data. Details about the derivation of the annual average outdoor air temperature for the RECS 2001 water heater sample are provided in appendix 7-D, weather data and temperature parameters for LCC analysis. DOE’s analysis produced average outdoor temperatures of 59.1 o F for electric storage water heaters, 56.3 o F for gas-fired storage water heaters and gas-fired instantaneous water heaters, and 52.4 o F for oil-fired water heaters. Figure 7.2.4 shows the range of average annual outdoor air temperatures among sample households.

Average Annual Outdoor Temperature (° F) Ranges by Efficiency Level Median; Box 25%-75%; W hisker: 5%-95%

40 45 50 55 60 65 70 75 80

Gas WH Electric WH Oil WH Instantaneous Gas WH median Average

Figure 7.2.4	 Range of Annual Outdoor Air Temperature for Sample Households by Water Heater Product Class Inlet Water Temperature. Daily hot water and water heater energy use depend on average inlet water temperature. The inlet water comes to the water heater either from a municipal treatment plant or from ground well sources. DOE determined the water source using
7-20RECS 2001, which enables one to identify the households in the sample that have a water well. Households that don’t have a water well presumably use water from municipal treatment plants. DOE derived inlet water temperature using an approach developed by the National Renewable Energy Laboratory. 24, 25 This approach accounts for seasonal variations in inlet water temperature as a function of annual average outdoor air temperature. The monthly average inlet water temperature varies directly with the average annual outdoor air temperature corrected by an offset term. The equation for inlet water temperature has the following form:
T

IN = T air , avg + offset + lag The calculation details and the parameter definitions are described in appendix 7-D. 26 Institute to calculate the offset for the households that have water wells. This method suggests adding two degrees to the average annual outdoor air temperature to calculate the inlet water temperature for ground water sources. The offset for households using municipal treatment plants was calculated using typical average long-term water temperatures for households having 26 water that comes from municipal treatment plants. The derivation of those values is described in appendix 7-D. The analysis identified an average inlet water temperature of 62.6 o F for electric storage water heaters, 59.9 o F for gas-fired storage water heaters and gas-fired instantaneous water heaters, and 55.7 o F for oil-fired water heaters. Figure 7.2.5 shows the range of inlet water temperatures among sample households.

7-21Average Annual Inlet Water Temperature (° F) Ranges by Efficiency Level Median; Box 25%-75%; Whisker: 5%-95%

40 45 50 55 60 65 70 75 80 85

Gas WH Electric WH Oil WH Instantaneous Gas WH

median Average

Figure 7.2.5 Range of Daily Average Annual Inlet Water Temperature for Sample Households by Water Heater Product Class Water Heater Thermostat Settings. DOE assigned water heater thermostat settings to RECS 2001 households based on a 2006 survey commissioned by Plumbing & Mechanical 27 magazine. The information about thermostat settings reflects the results from a survey of 343 plumbing/hydronic heating contractor firms that install water heaters throughout the United States in new and replacement markets. The magazine survey indicated that 41 percent of responding contractors always install a water heater with a set point temperature of 120 o F; 20 percent always install the water heater with a set point temperature higher than 120 o F; and the other 39 percent that they usually install the water heater with a thermostat at 120 o F. Based on this information, DOE estimated that half of the latter water heater installations have a set point temperature of 120 o F, leading to a total of 61 percent of water heaters set to 120 o F, with 39 percent uniformly distributed between 121 o F and 140 o F. b This approach resulted in a mean temperature set point of 124.2 o F for the RECS 2001 water heater household sample. Although water heaters are shipped having the thermostat set to 120 °F, several factors may cause contractors and/or household occupants to increase the set-point temperature, such as:

• High hot water draws: Increasing the set point temperature decreases the likelihood of running out of hot water.

b 140 o F is the maximum allowed to avoid scalding. 7-22• Cold inlet water: Increasing the set point temperature can help compensate for the mixture produced by very cold water and hot water.
• Small water heaters: A smaller water heater might be set to a higher set-point temperature to be more responsive to hot water needs. Ambient Air Temperature. Ambient air temperature (the temperature of the air surrounding the water heater), which is used to calculate heat losses, differs based on where the water heater is installed. Water heaters most commonly are installed in garages, in basements, in crawlspaces, or inside the house. 8, 13 For single-family houses, RECS 2001 reports whether the house has a basement and whether the basement is heated or unheated. It also reports the presence or absence of a garage or crawlspace. For houses that have a basement only, DOE assumed that the water heater was located in the basement. For houses that have a basement and garage, DOE estimated that half the water heaters are in the basement and half in the garage. For houses that have a garage only, DOE assumed that the water heater was in the garage. For houses that have a crawlspace only, DOE assumed that half the water heaters were in the crawlspace and half inside the house. In the absence of a basement, garage, or crawlspace, DOE assumed that the water heater was inside the house (in a laundry room, kitchen, or utility closet). DOE further assumed that 50 percent of manufactured homes and 25 percent of multi-family houses in climates where the heating degree days are less than 4,000 would have the water heater installed in an outdoor closet. The rest of the manufactured houses and multi-family houses were assumed to have the water heater installed indoors. DOE assumed that oil-fired water heaters were not installed indoors. Therefore, if the above approach designated an oil-fired water heater as indoors, the water heater was assumed to be in a space similar to a garage or crawlspace. Table 7.2.12 shows the percentages of the various water heater locations as well as the ambient air temperature derivation for each installation location. Table 7.2.12 Water Heater Location by Product Class Location Temperature Derivation GasFired (%) Electric (%) Oil-Fired (%) Heated basement Avg. Indoor Temperature 24.3 13.6 53.2 Unheated Basement (Avg. Indoor Temp + Avg. Outdoor Temp) / 2 8.5 8.1 21.5
Garage, Crawlspace,

or Outdoor closet Avg. outdoor Temp + 5 °F 36.9 37.0 25.3

Inside house Avg. Indoor Temperature 30.3 41.3 0.0 Total 100 100 100

7-23DOE determined ambient air temperatures based on information about typical locations of water heaters as follows:

• For houses having heated basements, DOE assumed the ambient temperature equaled the home’s average house indoor temperature given by RECS 2001.
• For houses having unheated basements, DOE calculated the ambient temperature as the mean of the average house outdoor and indoor temperatures.
• For houses having a garage, crawlspace, or outside closets, DOE assigned an ambient temperature that was 5 o F (2.8 o Celsius) higher than the outdoor air temperature for that 8 location.
• For inside-the-house installations, DOE assumed the ambient temperature equaled the home’s average house indoor temperature given by RECS 2001. This analysis identified in average annual ambient temperatures of 68.7 o F for electric storage water heaters, 67.0 o F for gas-fired storage water heaters and gas-fired instantaneous water heaters, and 64.5 o F for oil-fired water heaters. Figure 7.2.6 shows the range of annual ambient air temperature among sample households.

Average Annual Ambient Air Temperature (° F) Ranges by Efficiency Level Median; Box 25%-75%; W hisker: 5%-95%

50 55 60 65 70 75 80

Gas WH Electric WH Oil WH Instantaneous Gas WH median Average

Figure 7.2.6	 Range of Annual Ambient Air Temperature in Sample Households by Water Heater Product Class 7.2.4.5 Approach to Calculating Water Heater Energy Consumption Figure 7.2.7 provides an overview of DOE’s approach to calculating water heater energy use for each sample household.

7-24RECS Sample

Energy Use WHAM Water Use Draw Model T amb Engineering Analysis Contractor

Survey Weather Data

T tank T in RE

UA EF
Operating Conditions Efficiency Characteristics

Figure 7.2.7 Calculating Water Heater Energy Use 7.2.5 Average Annual Energy Consumption The following sections describe the derivation of average annual energy use and the average energy savings for each considered energy efficiency level compared to the baseline energy efficiency for gas-fired storage, electric storage, oil-fired storage, and gas-fired instantaneous water heaters. 7.2.5.1 Gas-Fired Storage Water Heaters Table 7.2.13 lists the average annual energy use for gas-fired storage water heaters and the average energy savings for each considered energy efficiency level compared to the associated baseline water heater. The energy savings include the higher use of electricity at an EF of 0.64 and above.

7-25Table 7.2.13 Annual Energy Consumption for Gas-Fired Storage Water Heaters Energy Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (EF) Gas (MMBtu/yr) Electricity (kWh/yr) 0.59 (baseline) 16.7 0

-- 0.62 15.6 0 1.1 0.63 15.3 0 1.4 0.64 14.8 69 1.8 0.65 14.5 68 2.2 0.66 14.2 67 2.5 0.77 12.1 61 4.6
7.2.5.2 Electric Storage Water Heaters Table 7.2.14 lists average annual energy use for electric storage water heaters and average energy savings for each energy efficiency level evaluated in the LCC analysis, compared to the baseline water heater. Table 7.2.14 Annual Energy Consumption for Electric Storage Water Heaters Energy Efficiency Level (EF) Average Energy Consumption (kWh/yr) Average Energy Savings (kWh/yr) 0.90 (baseline) 2,703

- 0.91 2,657 46 0.92 2,612 91 0.93 2,568 135 0.94 2,525 177 0.95 2,483 220 2.20 1,342 1,361
7.2.5.3 Oil-Fired Storage Water Heaters Table 7.2.15 shows the average annual energy use for oil-fired water heaters and the average energy savings for each energy efficiency level compared to the baseline. The energy savings include the lower use of electricity at an EF of 0.54 and above.

7-26Table 7.2.15 Annual Energy Consumption for Oil-Fired Storage Water Heaters Energy Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (EF) Fuel Oil (MMBtu/yr) Electricity (kWh/yr) 0.53 (baseline) 19.4 56

-- 0.54 18.9 55 0.5 0.56 18.0 53 1.4 0.58 17.2 50 2.2 0.60 16.4 48 2.9 0.62 15.7 46 3.7 0.66 14.7 43 4.7 0.68 14.2 41 5.2
7.2.5.4 Gas-Fired Instantaneous Water Heaters Table 7.2.16 lists the average annual energy use for gas-fired instantaneous water heaters and the average energy savings for each energy efficiency level compared to the baseline water heater. Table 7.2.16 Annual Energy Consumption for Gas-Fired Instantaneous Water Heaters Energy Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (EF) Gas (MMBtu/yr) Electricity (kWh/yr) 0.62 (baseline) 17.0 0

-- 0.69 16.0 0 1.0 0.78 12.5 26 4.5 0.80 12.2 29 4.8 0.82 11.9 29 5.1 0.84 11.6 29 5.4 0.85 11.5 29 5.6 0.92 10.6 29 6.4
7.3 DIRECT HEATING EQUIPMENT The following sections describe DOE’s analysis of energy consumption for direct heating equipment. 7.3.1 Introduction Direct heating equipment utilizes both gas and electric energy. In the engineering analysis, DOE calculated energy consumption of baseline direct heating equipment using the

7-27DOE test procedure for those products. For the LCC analysis, DOE estimated energy consumption of direct heating equipment in actual housing units. To represent actual households likely to purchase and use direct heating equipment, DOE 1 developed a household sample from RECS 2001. For each household in the sample, DOE used RECS 2001 reported heating energy consumption (based on the existing heating system) to calculate the heating load of each household. The heating load represents the amount of heating required to keep a housing unit comfortable throughout an average year. DOE estimated the heating loads from the reported heating energy consumption and the estimated energy efficiency of the direct heating equipment in each sample housing unit. DOE assigned the energy efficiency of existing systems based on the distribution of energy efficiencies for direct heating equipment 17 provided in the 2007 GAMA directory. The estimation of heating loads also required calculating the electricity consumption of the blower (when applicable), because heat from the blower contributes to heating the housing unit. To complete the analysis, DOE calculated the energy consumption of alternative (more energy efficient) products if they replaced existing systems in each housing unit. 7.3.2 Household Sample The subset of RECS 2001 households used for evaluating the energy use of direct heating equipment met all of the following criteria:

• The household employed a pipeless floor or wall furnace, fireplace, or heater as the primary or secondary source of heat.
• The heating fuel was natural gas or LPG.
• The equipment heated only one housing unit.
• Primary fireplace equipment had a thermostat or secondary fireplace equipment had a flue vent.
• The equipment had energy consumption greater than zero. The subset of household using direct heating equipment represents 578 housing records, representing 12.3 million households (11.5 percent of the total weighted RECS sample). Table 7.3.1 lists the criteria used to develop the household sample and shows the number of households included in the analysis. Appendix 7-A, RECS 2001 values and variables, describes the subset of households.

7-28Table 7.3.1 Summary of Direct Heating Equipment Household Sample (RECS 2001)
Category Selection Criteria Fuel Type No. of Records No. of US Households Represented (million ) Primary Equipment Floor/Wall

Furnace Primary Equipment Type = Floor/Wall Pipeless Furnace Number of Housing Units Heated = 1 Natural Gas 134 3.1 LPG 11 0.2 Room Heater Primary Equipment Type = Heater Number of Housing Units Heated = 1 Natural Gas 136 2.8 LPG 53 1.1 Fireplace Primary Equipment Type = Fireplace Number of Housing Units Heated = 1 Fireplace has Thermostat = Yes Natural Gas 5 0.1 LPG 3 0.0 Secondary Equipment Floor/Wall

Furnace Secondary Equipment Type = Floor/Wall Furnace Natural Gas 7 0.1 LPG 9 0.1 Room Heater Secondary Equipment Type = Heater Natural Gas 47 0.9 LPG 46 0.9 Fireplace Secondary Equipment Type = Fireplace Fireplace is vented = Yes Natural Gas 106 2.6 LPG 21 0.4 Each RECS heating equipment category is matched to the direct heating equipment product classes using several assumptions. For gas wall fan direct heating equipment, DOE used a household sample that includes the RECS 2001 categories of floor/wall furnace and fireplaces. 17 Based on the percentage of fireplace models in the GAMA directory and GAMA’s shipments 28 data, DOE sampled 80 percent from the RECS 2001 floor/wall furnace category and 20 percent from the fireplace category. For gas wall gravity direct heating equipment, DOE used a household sample that includes only the RECS 2001 floor/wall furnace categories. For gas floor direct heating equipment, DOE used a household sample that includes only the RECS 2001 category for primary floor/wall furnaces. c For gas room direct heating equipment, DOE used a household sample that includes the RECS 2001 room heater and fireplace categories. Based on 17 28 the percentage of fireplace models in the GAMA directory and GAMA’s shipments data, DOE sampled 20 percent from the RECS 2001 room heater categories and 80 percent from the RECS fireplace categories.

RECS 2001 does not distinguish between wall and floor furnaces. Thus the samples for wall furnace, gravity furnace, and floor furnace direct heating equipment utilize the same household sample (not including fireplaces). 7-29 c7.3.3 Determining Annual House Heating Load The annual house heating load (HHL) is the total amount of heat output from the direct heating equipment during the heating season. This amount includes heat from both the burner and the blower. DOE determined the HHL for each sampled housing unit based on the household heating fuel consumption and the characteristics of the systems. DOE used the following 12 calculations, which are based on the DOE test procedure. Details are presented in appendix 7­ C. Q YR , RECS − 8760 × Q P HHL = + 4160 × Q P × η

U A × ( Q IN − Q P )
Where: Q YR,RECS = annual fuel consumption for heating the housing unit, from RECS 2001, kBtu/yr, Q P = pilot input rate, Btu/h, Q IN = rated input capacity of direct heating equipment, Btu/h, 8,760 = hours in a year, h, 4,160 = average heating season hours according to test procedure, h, A = TP factor, h/kBtu, 100,000
= , 341,000 × PE + 

## ( Q in − Q P 

## ) × η

U PE = power consumption of the direct heating equipment while the burner is on, W, and η U = efficiency of part-load utilization (%). The average pilot input rate for the above calculation is 400 Btu/h for gas wall fan and gas wall gravity direct heating equipment, 450 Btu/h for gas floor direct heating equipment, and 29 350 Btu/h for gas room direct heating equipment. Section 7.3.4.1 describes the values for input capacity ( Q IN )

. The PE value reflects a design that incorporates a draft inducer, electronic ignition, and air circulation fan components. To calculate PE , DOE used values given in the 1993 technical 29 support document. For room heaters that operate at higher energy efficiency levels, PE also includes the power consumption of the air circulation fan. Note that the efficiency of part-load utilization ( η U) depends on AFUE, the assignment of which is explained in Section 7.3.4.2. For households for which the natural gas use for heating clearly is associated solely with use of the direct heating equipment as primary or secondary heating equipment, DOE used the annual fuel consumption for heating the housing unit, from RECS 2001. DOE adjusted the house heating load for households that used a gas furnace as the primary heating equipment and the direct heating equipment as secondary heating equipment. RECS 2001 reports the percentage of heating energy consumption attributable to secondary products. DOE reduced the house heating
7-30load applicable to the direct heating equipment by subtracting the estimated amount of heat provided by the secondary system. Details are presented in appendix 7-E, derivation of heating load for pool heaters and direct heating equipment, for details. 7.3.4 Assigning Direct Heating Equipment to Sample Households As explained in the framework document, DOE proposes to maintain the sixteen product classes for direct heating equipment established in the Energy Policy and Conservation Act of 1975 (EPCA). DOE, however, performed the LCC analysis using a single representative product class for each product category ( i.e., for gas wall fan, gas wall gravity, gas floor, and gas room equipment). DOE extrapolated to the other classes the analytical results for the representative product class in each category of direct heating equipment. DOE selected the class having the greatest percentage of shipments to serve as the representative product class. Based on shipment data from the 1993 technical support 29 document for gas wall fan, gas wall gravity, gas floor, and gas room direct heating equipment, and the number of available models listed in GAMA March 30, 2007, Residential Direct Heating Directory, DOE chose the following product classes to represent each direct heating equipment category:

• gas wall fan direct heating equipment using more than 42,000 Btu/h;
• gas wall gravity direct heating equipment using more than 27,000 and up to 46,000 Btu/h;
• gas floor direct heating equipment using more than 37,000 Btu/h; and
• gas room direct heating equipment using more than 27,000 and up to 46,000 Btu/hour. 7.3.4.1 Input Capacity of Existing Equipment Table 7.3.2 shows the distribution of input capacities for the representative product classes listed above, based on GAMA March 30, 2007, Residential Direct Heating Directory. Gas wall fan direct heating equipment includes vented gas fireplace heaters that are listed as fan wall heaters. Gas room direct heating equipment includes the rest of the vented gas fireplace heaters as well as gas stoves and other hearth heaters.

7-31Table 7.3.2 Distribution of Input Capacity for Representative Product Classes of Direct Heating Equipment Input Capacity Percentage of Models (kBtu/h) Gas Wall Fan Gas Wall Gravity Gas Floor Gas Room 27.5 0.0% 1.8% 28 8.3% 0.0% 30 16.7% 52.7% 31 0.0% 1.8% 31.5 0.0% 3.6% 32 16.7% 0.0% 33 20.8% 1.8% 35 33.3% 16.4% 36 0.0% 1.8% 37 0.0% 7.3% 38 4.2% 10.9% 40 0.0% 1.8% 45 0.0% 0.0% 16.7% 0.0% 50 14.3% 22.2% 55 45.2% 0.0% 60 4.8% 11.1% 62 0.0% 22.2% 62.5 19.0% 0.0% 65 16.7% 5.6% 75 0.0% 22.2% Average (kBtu/h) 57.6 32.8 59.3 32.6 7.3.4.2 Efficiency of Existing Equipment To represent the energy efficiency of existing direct heating equipment, DOE used the current Federal minimum energy conservation standards for such equipment that took effect in 30 1990. This choice was based on product ages from RECS 2001 and the belief that energy efficiency changed little during the 1980s and 1990s. DOE assumed that existing direct heating equipment is equipped with a continuous pilot light. Table 7.3.3 shows the energy efficiency levels for the representative product classes. Table 7.3.3 Energy Efficiency of Existing Direct Heating Equipment Representative Product Class Efficiency (AFUE) Gas Wall Fan More Than 42,000 Btu/h 74% Gas Wall Gravity More Than 27,000 up to 46,000 Btu/h 64% Gas Floor Product Classes More Than 37,000 Btu/h 57%

Gas Room More Than 27,000 up to 46,000 Btu/h 64%

7-327.3.5 Calculations of Energy Consumption Knowing the heating load of each sample housing unit, one can estimate the energy consumption if more energy efficient products, rather than the existing baseline products, were used in each household. 7.3.5.1 Fuel Consumption DOE calculated the fuel consumption ( FuelUse ) for single-stage direct heating equipment 31 using the following formula, which is taken from the current revision of DOE’s test procedure.
FuelUse = B OH × ( Q IN − Q P ) + 8760 × Q P Where:
FuelUse = fuel consumption, kBtu/year, BOH = burner operating hours, h, Q in = input capacity, kBtu/h (at the max input rate), 8,760 = hours per year, and Q

p = pilot light input rate, kBtu/h. The value assigned to burner operating hours (BOH) is a function of the heating load, average heating season hours, efficiency of part-load utilization, and pilot light input rate. The BOH accounts for the contribution the electrical components make to heating the house. For each considered energy efficiency level, BOH has a different value. Calculating energy consumption is described in detail in appendix 7-C. 7.3.5.2 Electricity Consumption DOE calculated the electricity consumed by direct heating equipment for the draft inducer, igniter, and air circulation fan and during stand-by mode. e The current DOE test procedure accounts for only the total electricity demand when the product is firing ( PE), but some components consume electricity when the unit is not firing. This standby consumption includes use by the ignition device, by the controls when the unit is off, and when the circulationfan is operating while the burner is off. DOE calculated the electricity consumption for singlestage direct heating equipment as follows.
ElecUse = B OH × PE + (8760

− BOH ) × P stby Where:
ElecUse = electricity consumed by direct heating equipment, kWh/year; BOH = burner operating hours, h;

e The DOE test procedures do not measure the electricity used by controls when the direct heating equipment is not firing. 7-33PE = electricity demand when the equipment is firing, kW; and P stb y = stand-by power consumption (when the burner is off), kW. The details for calculating electricity consumption are described in appendix 7-C. 7.3.6 Average Annual Energy Consumption The average annual energy use and energy savings for each considered energy efficiency level are shown in Tables 7.3.4 through 7.3.7 for each representative product class. The energy savings reflect the changes in electricity use for different efficiency levels. Table 7.3.4 Annual Energy Consumption for Gas Wall Fan Direct Heating Equipment Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (AFUE) Gas (MMBtu/yr) Electricity (kWh/yr) 74 (baseline) 27.1 35

-- 75 25.6 42 1.5 76 25.2 42 1.9 77 24.9 42 2.2 80 23.9 61 3.2 Table 7.3.5 Annual Energy Consumption for Gas Wall Gravity Direct Heating Equipment Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (AFUE) Gas (MMBtu/yr) Electricity (kWh/yr) 64 (baseline) 29.6 0

-- 66 28.7 0 0.8 68 27.9 0 1.6 71 26.8 0 2.7 72 25.6 18 4.0 75 24.4 58 5.2

7-34Table 7.3.6 Annual Energy Consumption for Gas Floor Direct Heating Equipment Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (AFUE) Gas (MMBtu/yr) Electricity (kWh/yr) 57 (baseline) 30.4 0

-- 58 29.9 0 0.5 61 28.5 0 1.9 62 28.1 0 2.3 65 25.5 12 4.9 78 21.0 54 9.3 Table 7.3.7 Annual Energy Consumption for Gas Room Direct Heating Equipment Efficiency Level Average Energy Consumption Average Energy Savings (MMBtu/yr) (AFUE) Gas (MMBtu/yr) Electricity (kWh/yr) 64 (baseline) 22.0 0

-- 65 21.7 0 0.3 66 21.4 0 0.6 67 21.1 0 0.9 68 20.8 0 1.2 70 19.4 12 2.6 78 17.2 75 4.9 93 14.4 65 7.6
7.4 POOL HEATERS In the engineering analysis, DOE calculated energy consumption of pool heaters using the DOE test procedure for those products. For the LCC analysis, DOE estimated energy consumption of pool heaters in actual housing units. To represent actual households likely to 1 purchase and use pool heaters, DOE used a household sample from RECS 2001. For each household, DOE used RECS-reported energy consumption for pool heating (based on existing systems) to calculate the pool-heating load of each sample household. The pool heater heating load represents the amount of heating required for a pool throughout a year. DOE estimated the pool-heating load from the reported pool-heating energy consumption and the estimated energy efficiency of the existing pool heater in each sample housing unit. To complete the analysis, DOE calculated the energy consumption of alternative (more energy efficient) products if they were installed in each housing unit in place of existing products.

7-357.4.1 Household Sample The subset of records used to select a RECS 2001 household sample for pool heaters met all of the following criteria (see appendix 7-A, RECS 2001, values and variables, for details).

• The household had a swimming pool.
• A pool heater was used to heat pool water.
• The pool heater used natural gas or liquefied petroleum gas (LPG) as a heating fuel.
• The heater heated pool water for only one housing unit. Table 7.4.1 Criteria for Selecting Household Sample for Pool Heaters (RECS 2001)

Fuel Type Algorithm No. of Records No. of US Households Represented (million) Natural Gas Have Swimming Pool? = Yes Is it heated? = Yes Fuel Type = natural gas 30 0.8

Propane Have Swimming Pool? = Yes Is it heated? = Yes Fuel Type = propane 11 0.2

7.4.2 Input Capacity and Heating Load DOE assigned all sample households a 250-kBtu/h pool heater, the most common rating 32 for all covered models listed in the May 2007 FTC pool heater directory. The annual pool heater heating load ( PHHL ) is the total heat output from the pool heater during a year. DOE used the following equation to determine PHHL for each sampled household.
PHHL = ( Q RECS − Q p × POH ) × E t Where: Q RECS = pool heater annual fuel consumption (kBtu/yr); Q

p = pilot light input rate (kBtu/yr); POH = average number of pool operating hours (h/yr); and Et = thermal efficiency of the existing pool heater associated with the household (%). The annual fuel consumption for the pool heater ( Q RECS ) for each household having a pool heater was taken from RECS 2001. For units that have a pilot light, DOE assigned a pilot light input rate of 1,000 Btu/h. 29, 33 DOE assigned pilot lights to 29 percent of the households that have pool heaters based on the
7-36percentage of such models in the 2007 FTC directory. DOE assumed the remaining 71 percent were equipped with electronic ignition. The DOE test procedure uses an average value for pool heater operating hours (when the pilot light is on) of 4,464 hours per year. DOE used a distribution around this average to assign values for pool heater operating hours to the sample households. The distribution ranges from 235 h/yr to 8,760 h/yr, where the upper limit represents a year-around operation. The value of 235 h/yr is the minimum value of the triangular distribution used to calculate pool operating hours. DOE assigned all sample households a pool heater having a 78 percent thermal efficiency. This efficiency was selected based on a maximum lifetime for pool heaters of 12 years. Thus all pool heaters associated with RECS 2001 households were installed after 1989, which was after EPCA mandated the 78-percent energy conservation standard. 7.4.3 Calculations of Energy Consumption Knowing the pool heater heating load for each sample housing unit, one can estimate what the energy consumption would be if more energy efficient products, rather than the existing products, were used in each household. DOE used the method stipulated in the DOE test procedure to calculate the fuel consumption at the considered energy efficiency levels for each household.
E F = BOH × Q IN + ( POH

− BOH ) × Q p Where:
E

F = average annual fuel energy for pool heater, kBtu/yr, BOH = burner operating hours, h/yr, Q in = pool heater input rate, kBtu/h, POH = pool operating hours, h/yr, and Q

p = pilot light input rate, kBtu/h. DOE calculated the electricity consumption at the considered energy efficiency levels for each household using the method provided in the DOE test procedure and adding stand-by electricity consumption.
E AE = BOH × PE

− ( POH

− BOH ) × PE standby Where:
E

AE = average annual auxiliary electrical energy for pool heater (including standby electrical consumption), kWh/yr; PE = electrical power when the burner is on, kW; and PE standby = electrical power when the burner is off, kW.
7-37The calculations for fuel and electricity consumption are detailed in appendix 7-C. 7.4.4 Average Annual Energy Consumption The average annual energy consumption for each considered energy efficiency level for pool heaters is shown in Table 7.4.2. Table 7.4.2 Annual Energy Consumption for Gas Pool Heaters Efficiency Level (Thermal Efficiency in Percent) Average Energy Consumption (MMBtu/year) Average Energy Savings (MMBtu/year) 78 (baseline) 53.6

-- 79 52.9 0.7 81 51.6 1.9 82 51.0 2.5 83 49.2 4.4 84 48.6 5.0 86 47.5 6.1 90 45.4 8.2 95 43.0 10.6

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