**4-i** CHAPTER 4. ENERGY USE CHARACTERIZATION

TABLE OF CONTENTS

**4.1 INTRODUCTION ........................................................................................................... 4-1**  **4.2 DEVELOPMENT OF FLEOH ESTIMATES BY BUILDING TYPE AND**  **GEOGRAPHIC REGIONS ............................................................................................. 4-1 4.3**  **DEVELOPMENT OF ENERGY USE ESTIMATES FROM FLEOHS ......................... 4-3 4.3.1**  **Rated Thermal Efficiency for Energy Use Estimates ....................................... 4-3 4.3.2**  **Calculation of Seasonal Energy Consumption ................................................. 4-6 4.3.3**  **Estimated Boiler Usage Weights by State and Building Type ......................... 4-6 4.4**  **ENERGY ANALYSIS SUMMARY RESULTS ............................................................ 4-7 REFERENCES ............................................................................................................................ 4-8** **4-ii** LIST OF TABLES

**Table 4.2.1 Boiler Full Load Equivalent Operating Hours by 11 Sub-Census Divisions by**

**Building Type ...................................................................................................... 4-2**

**Table 4.2.2 Augmented Census Division and Component States ............................................... 4-3**

**Table 4.3.1 Large Gas-Fired Hot-Water Commercial Packaged Boiler Efficiency Levels ......... 4-4**

**Table 4.3.2 Large Oil-Fired Hot-Water Commercial Packaged Boiler Efficiency Levels .......... 4-4**

**Table 4.3.3 Fraction of Floorspace Using Boilers by Region and Building Type ....................... 4-7**

**Table 4.4.1 National Average Site Energy Consumption Estimates by Boiler Class and**

**Efficiency Level ................................................................................................... 4-7 4-1**  CHAPTER 4. ENERGY USE CHARACTERIZATION

4.1 INTRODUCTION

**The engineering analysis in TSD chapter 3 provides estimates of contractor costs for commercial packaged boilers that meet the rated thermal or combustion efficiency levels as**  **required by American Society of Heating, Refrigerating and Air-Conditioning (ASHRAE) Standard 90.1-2007**  **1 (the baseline level 0 for the life-cycle cost [LCC] analysis) or higher**  **standard levels under consideration by U.S. Department of Energy (DOE) and as would be determined under the relevant test procedure, Hydronics Institute (HI) Boiler Testing Standard**  **(BTS) 2000. 2**  **However, to perform the LCC analysis as discussed in chapter 5 of the TSD and the national impacts analyses discussed in chapter 7 of the TSD, DOE must develop estimates of**  **annual energy consumption for users of commercial packaged boilers that correspond to the baseline and subsequent higher-efficiency levels as possible standards.** 

**DOE estimated the energy consumption for the 10 commercial packaged boiler equipment classes analyzed in the engineering analysis (TSD chapter 3). For the Notice of**  **Proposed Rulemaking analyses, these energy consumption estimates were based on the use of Full Load Equivalent Operating Hour (FLEOH) estimates developed for 7 types of commercial**  **buildings and 11 geographic regions of the continental United States, and the rated thermal efficiency of the boilers as estimated by DOE. For high-efficiency condensing boilers, where the**  **rated efficiency depends on the return-water temperature, DOE developed a simplified model of the annual efficiency of a condensing boiler used to serve a typical hydronic coil supplying heat**  **to a building heating, ventilation, and air-conditioning (HVAC) air distribution system. This chapter describes the development of annual energy use estimates for the selected equipment for**  **analysis from TSD chapter 3.**

**DOE examined various standard levels for each class of equipment, including the baseline level (current Energy Policy and Conservation Act of 1975 level), the ASHRAE**  **Standard 90.1-2007 efficiency level, and up to four efficiency levels above the ASHRAE Standard 90.1-2007. For equipment classes where ASHRAE Standard 90.1-2007 defines**  **combustion efficiency and where chapter 3 identifies higher efficiency standard levels using combustion efficiency, DOE developed corresponding estimates for thermal efficiency for each**  **combustion efficiency level identified. From the thermal efficiency estimates and the FLEOH data, DOE developed annual energy consumption estimates for each efficiency level by State and**  **building type. Finally using building stock estimates developed from the DOE Commercial Building Energy Consumption Survey (CBECS)**  **3 , DOE was able to generate national energy use**  **estimates by boiler class and efficiency level.**

4.2 DEVELOPMENT OF FLEOH ESTIMATES BY BUILDING TYPE AND GEOGRAPHIC REGIONS

**DOE uses the energy use characterization analysis to assess the per-unit energy savings potential of commercial boilers at different efficiency levels. This analysis estimates the energy**  **use of commercial boilers at specified efficiency levels by using previously calculated FLEOH metrics by building type and by climate across the United States. FLEOHs are effectively the**  **number of hours that a system would have to run at full capacity to serve a total heating load 4-2** 

**equal to the annual heating load on the equipment. Boiler FLEOHs are calculated as the annual heating load divided by the equipment capacity. In the case of the FLEOHs used in this analysis,**  **the FLEOH values were based on simulations documented for the “Screening Analysis for EPACT-Covered Commercial HVAC and Water-Heating Equipment” (hereafter called the 2000**  **Screening Analysis) 4**  **and used 7 different building types and 11 different U.S. climates. This resulted in 77 unique FLEOH values defined for commercial boilers.** 

**In the 2000 Screening Analysis, these 11 U.S. climates were in turn mapped to 11 geographic regions of the United States using defined weighting factors for each climate**  **developed for each region. These regions consist of seven of the nine U.S. Census divisions, each composed of groups of States with no overlap, and four sub-census divisions. The sub**  **census divisions were developed by breaking the Pacific Census division into northern and southern geographic regions, approximately at the Oregon-California border, and breaking the**  **Mountain Census division similarly into northern and southern geographic regions. The separation into sub-census divisions is done to reflect climate and energy cost differences**  **characteristic of the northern and southern regions of the Pacific and Mountain Census divisions. For the purposes of this chapter, the set of 11 geographic regions is referred to as the sub-census**  **divisions.**

**Table 4.2.1 shows the commercial boiler FLEOHs by these sub-census divisions as developed under the 2000 Screening Analysis.** 

Table 4.2.1 Boiler Full Load Equivalent Operating Hours by 11 Sub-Census Divisions by

Building Type

Building Type Augmented Census Division Assembly Education Food Service Lodging Office Retail Warehouse **New England 2042.1 939.8 1591.5 1713.6 739.0 605.3 1094.1**  **Middle Atlantic 2011.2 939.4 1525.3 1642.2 767.9 681.5 993.8 East North Central 2176.8 1137.3 1833.4 1988.4 1101.6 1201.1 2111.6**  **West North Central 2156.6 1067.1 1705.8 1917.7 1075.5 1005.1 1484.0 South Atlantic 1151.7 531.0 898.4 735.4 376.3 342.9 1024.4**  **East South Central 1443.2 650.7 1048.0 912.2 388.2 314.5 342.1 West South Central 1172.2 556.5 978.0 750.3 368.4 257.8 331.5**  **Mountain North 1968.1 924.2 1453.2 1474.2 577.5 577.6 698.6 Mountain South 1001.8 349.0 788.5 373.3 205.8 40.9 36.0**  **Pacific North 2640.9 1357.0 1995.3 2202.4 968.6 1234.2 1855.5**  **Pacific South 1402.1 642.3 979.7 655.8 320.9 187.1 36.7** 
**DOE had no further geographic resolution for the FLEOH analysis, but presumed that the FLEOHs shown in Table 4.2.1 effectively represent average values for the defined region and**  **could be used to represent the typical FLEOHs for States within each region. Each region was defined by the group of States composing it. The mapping of States to regions used for this**  **analysis is shown in Table 4.2.2. Each mapped State is assigned the characteristic FLEOH shown in Table 4.2.1 for the corresponding augmented census division in Table 4.2.2.** **4-3**

Table 4.2.2 Augmented Census Division and Component States

New England Middle Atlantic East North Central West North

Central South Atlantic East South Central
**Connecticut Maine**  **Massachusetts New Hampshire**  **Rhode Island Vermont**  **New Jersey**

**New York Pennsylvania**  **Illinois**

**Indiana Michigan**  **Ohio Wisconsin**  **Iowa**

**Kansas Minnesota**  **Missouri Nebraska**  **North Dakota South Dakota**  **Delaware**

**Dist. of Columbia Florida**  **Georgia Maryland**  **North Carolina South Carolina**  **Virginia West Virginia**  **Alabama**

**Kentucky Mississippi**  **Tennessee**

West South Central Mountain North Mountain South Pacific North Pacific South
**Arkansas Louisiana**  **Oklahoma Texas**  **Colorado**

**Idaho Montana**  **Wyoming Arizona** 

**Nevada New Mexico**  **Utah Oregon** 

**Washington Alaska** * **California**

**Hawaii***

***** **Alaska and Hawaii are technically not part of the defined U.S. Census divisions, but have been included with the nearest augmented census divisions for the purpose of assigning FLEOHs.** 

4.3 DEVELOPMENT OF ENERGY USE ESTIMATES FROM FLEOHS

**For each equipment class, DOE estimated the energy usage of a given piece of equipment by multiplying the characteristic equipment output capacity by the FLEOHs appropriate to each**  **combination of representative building type and climate location. The product is effectively the total annual heat output from the boiler. The input energy is then determined by dividing the**  **annual heat output by the thermal efficiency of the equipment at each efficiency level. The thermal efficiency is used here for all equipment classes because it defines the relationship**  **between energy input and useful output of a commercial packaged boiler.**

4.3.1 Rated Thermal Efficiency for Energy Use Estimates

**For the two equipment classes where a thermal efficiency (E t**  **) metric was not specified by ASHRAE Standard 90.1-2007, and subsequently not indicated for higher efficiency levels in**  **TSD chapter 3, an estimate of the thermal efficiency of equipment meeting the combustion efficiencies (E**  **c ) specified in TSD chapter 3 was developed based on DOE’s market analysis. For**  **these two equipment classes, DOE developed estimates of the rated thermal efficiency based on an estimated 1.5 average percentage point difference (or delta (∆)) between thermal and**  **combustion efficiency for large, gas-fired hot-water boilers (see Table 4.3.1) and an estimated 2 average percentage point difference between thermal and combustion efficiency for large, oil**  **fired hot-water boilers (see Table 4.3.2). These efficiency deltas correspond to approximately the average differences between thermal and combustion efficiencies for these classes of equipment**  **in the DOE boiler database discussed in chapter 2 of the TSD.**

**In addition, for condensing hot-water boilers, it is recognized that the thermal efficiency of a commercial packaged boiler in actual use depends on the return-water conditions. This is**  **particularly true in the case of condensing boilers, where most condensing boilers will not condense unless the return-water temperature is lower than some threshold or they are operating**  **in a low-fire regime, or both. In turn, the return-water conditions are dependent upon the hydronic system design and control. For DOE’s analysis, the rated thermal efficiencies for fully** **4-4**

Table 4.3.1 Large Gas-Fired Hot-Water Commercial Packaged Boiler Efficiency Levels

Efficiency Level Combustion Efficiency (E C ) Levels (%) Estimated Rated Thermal

Efficiency (E t ) Levels (%) **Baseline Efficiency Level 0 82**  **80.5 Level 1**  **83 81.5**  **Level 2 84**  **82.5 Level 3**  **85 83.5**  **Level 4 (Condensing) 95**  **93.5**

Table 4.3.2 Large Oil-Fired Hot-Water Commercial Packaged Boiler Efficiency Levels

Efficiency Level Combustion Efficiency (E C ) Levels (%) Estimated Rated Thermal

Efficiency (E t ) Levels (%) **Baseline Efficiency Level 0 84**  **82 Level 1**  **86 84**  **Level 2 87**  **85 Level 3**  **88 86** 

**condensing equipment were further adjusted to reflect return-water conditions based on installation in existing buildings with conventional hydronic heating coils. In this analysis, DOE**  **assumed that most boilers will go into typical hydronic or steam system applications serving heating coils in air handlers (either centrally or via fan coils or unit ventilators). Furthermore,**  **DOE assumed that most of the installations at the time the energy conservation standards would go into place are retrofit (approximately two-thirds of the market). DOE assumed that most of**  **the existing systems using hot-water boilers have been designed for typical hydronic system design conditions of 180 °F supply water and 160 °F return water (20 °F ∆T) to meet peak**  **heating loads, and that most systems have some type of hot-water reset control already or the reset control can be easily added.** 

**DOE also assumed that new condensing hot-water boilers going into place would at a minimum be fitted with existing or new hot-water reset capability, which would allow the**  **supply-water temperature to be reset lower than that used for design conditions to provide for higher-efficiency boiler operation when building loads permit.** 

**In a conventional gas-fired boiler, condensation in the flue will occur with flue gas temperatures below approximately 130 °F, and supply-water temperature reset control can at best**  **bring the boiler-water delivery temperature down to approximately 135 °F, but below that it would cause raining (condensation) to occur in a conventional boiler. So in practice, the**  **conventional hydronic system isn’t designed to supply-water temperature below 140 °F and supply-water temperature is not reset below 140 °F to avoid problems with condensation.** 

**At a 140 °F supply-water temperature, the temperature difference between the return air at approximately 60 °F is 80 °F. At 180 °F supply-water temperature the temperature difference**  **between the supply-water and return air is 120 °F. So under the 140 °F supply-water temperature condition, the overall total temperature difference between air stream and supply-water stream is**  **reduced to 67 percent of what it is at design conditions, with a corresponding decrease in coil capacity. This simple analysis allows one to estimate the outdoor temperature suitable for the** **4-5**

**reset schedule. In this example, the reset schedule is to deliver design supply-water temperature at the outdoor design conditions of 0 °F or below, and to deliver 140 °F water temperature at an**  **outdoor air temperature corresponding to 67 percent of the system load or at any higher outdoor air temperature. Assuming that the heating load is linear from some building balance point of**  **zero load (~50 °F for a typical commercial building application) and 100 percent load (based on an outdoor design temperature of 0 °F.), the 67-percent load point occurs at an outdoor air**  **temperature of approximately 16 °F.**

**A reset schedule in this conventional boiler should provide that the supply-water temperature at an outdoor condition of 16 °F or higher would be at least 140 °F. In practice,**  **many reset schedules are not this aggressive because peak building loads may depend on building pickup or other conditions. Nevertheless, for outdoor air temperatures above a defined**  **set point (16 °F) the conventional boiler supply temperature remains fixed at no less than 140 °F.**

**For outdoor air temperatures below 16 °F, the load on the system is such that the supply water temperature must be above 140 °F to allow the hydronic coils to meet the load, and no**  **condensing can occur in the system regardless of boiler design (condensing or non-condensing boiler). Above an outdoor temperature of 16 °F, the reset controls are fixed in the conventional**  **boiler system to prevent condensation from occurring. The return-water condition in this example is calculated, based on the 67-percent load on the coil, to have approximately 67 percent**  **of the design coil delta T, or to be 13.4 °F below the supply-water temperature, or 123.6 °F. In practice, this temperature may be too low for proper boiler operation for the non-condensing**  **boiler and the supply-water temperature would be raised to compensate for the low return-water temperature.** 

**It is not necessary for a condensing boiler hold the supply-water temperature artificially high (to prevent flue corrosion) when a high supply-water temperature it is not needed to satisfy**  **the coil loads. A condensing boiler is designed to allow for condensation to occur in the boiler and consequently delivers cooler flue gases to the flue system. Determination of whether**  **condensation occurs is based on the return-water temperature. Condensing boilers commonly use a counter flow heat exchange design where the flue temperature gases are exposed to the**  **lowest water temperature (i.e., the return-water temperature) a**  **to maximize heat exchange before being exhausted to the flue. The reset schedule for the condensing boiler is modified to allow for** **even lower supply-water temperatures at higher outdoor air temperatures. These lower supply water temperatures can continue to meet the expected building load, but because condensation is**  **allowed to occur in the system, the operating efficiency of the boiler is higher under these low load conditions than with the conventional boiler. The seasonal efficiency of the condensing**  **boiler is determined by the fraction of the building heating load being served while operating in a non-condensing mode (typically with supply-water temperatures above approximately 135 to**  **140 °F) and operating in a condensing mode (supply-water temperatures below approximately 135 °F).** 

**a Cooke, J. 2005. “Condensing Boiler Technology.” Powerpoint presentation by Jim Cooke, Mechancial Systems**  **N.W. to Puget Sound ASHRAE Chapter. <www.pugetsoundashrae.org/PDF_files/AshraeCondensingtechnology.ppt**  > **(Accessed on September 12, 2008). 4-6** 

**DOE estimated that in a typical commercial application where a boiler that serves an existing air handler is being replaced and where there is no modification of the hydronic coils,**  **but allowing for a revised reset strategy, a seasonal average thermal efficiency for a condensing boiler would be approximately 88 percent (see TSD Appendix 4-A for calculations). DOE**  **recognized that more expansive system retrofits that included coil replacement or applications to other types of hydronic systems (**  e.g., **heated slab) could result in significantly higher seasonal efficiencies, but at increased cost, and such retrofits were not assumed to occur under DOE’s**  **high-efficiency standards scenario. Based on this estimate, the seasonal thermal efficiencies for small and large gas-fired hot-water boilers at efficiency Level 4 were modified to be 88 percent**  **for the purposes of the annual energy calculations. The seasonal efficiencies for the other boiler classes were assumed to be represented by the rated thermal efficiencies.** 

4.3.2 Calculation of Seasonal Energy Consumption

**DOE calculated annual energy consumption as follows:**

AEC = 1000 x BOILCAP x FLEOH / EFFseas Eq. 4.1

**where**

**AEC = Annual Energy Consumption (million Btu/yr) BOILCAP = Boiler output capacity (kBtu/hr)**  **FLEOH = Full Load Equivalent Operating Hours for Location and Building Type EFF**  **seas = Seasonal Thermal Efficiency** 

**DOE calculated annual energy consumption for each market segment defined by the FLEOH for each combination of State and building type for each efficiency level.** 

4.3.3 Estimated Boiler Usage Weights by State and Building Type

**DOE developed estimated weights by State and building type for commercial boiler sales based on data found in the CBECS and data reported in the DOE Energy Information**  **Administration’s (EIA’s) National Energy Modeling System (NEMS). First, DOE developed estimates for the fraction of building stock by each census region for 2014 based on data from**  **the EIA NEMS as developed for the** Annual Energy Outlook 2008 5 **, which provides floorspace projections for each of the seven building types and for each census division of the country. The** **floorspace for the Mountain and Pacific Census divisions were then disaggregated into the sub census divisions (mountain-north, mountain-south, pacific-north, pacific-south) using the**  **identical fraction of floorspace allocated to each region as determined in the 2000 Screening Analysis (64 percent of the Mountain Census division is allocated to mountain north, 36 percent**  **to mountain south; 18 percent of Pacific Census floorspace is allocated to pacific north, 82 percent to pacific south).** 

**The fraction of commercial floorspace using commercial packaged boilers differs by region of the country and by building type. DOE used the equipment shares matrix for**  **commercial packaged boilers developed for the 2000 Screening Analysis, which provided the estimated fraction of commercial building floorspace using boilers for each of the 11 sub-census**  **divisions (see Table 4.3.3).** **4-7**

Table 4.3.3 Fraction of Floorspace Using Boilers by Region and Building Type
Building Type Sub-Census Division Assembly Education Food Service Lodging Office Retail Warehouse **New England 0.36 0.76 0.07 0.41 0.42 0.25 0.14 Mid-Atlantic 0.36 0.76 0.07 0.41 0.42 0.25 0.14**  **East N. Central 0.36 0.76 0.07 0.41 0.42 0.25 0.14 West N. Central 0.36 0.76 0.07 0.41 0.42 0.25 0.14**  **South Atlantic 0.35 0.46 0.06 0.24 0.21 0.05 0.04 East S. Central 0.35 0.46 0.06 0.24 0.21 0.05 0.04**  **West S. Central 0.35 0.46 0.06 0.24 0.21 0.05 0.04 Mountain-North 0.42 0.62 0.18 0.31 0.29 0.18 0.08**  **Mountain-South 0.27 0.40 0.02 0.50 0.31 0.03 0.04 Pacific-North 0.42 0.62 0.18 0.31 0.29 0.18 0.08**  **Pacific-South 0.27 0.40 0.02 0.50 0.31 0.03 0.04**
**The product of the floorspace projections by building type and sub-census division and the fraction of the floorspace using boilers results in an estimate of the total floorspace using**  **boilers in 2014 by building type and sub-census division. This value is then normalized to provide the fraction of floorspace using boilers to 1,000 ft**  **2 of total floorspace in the nation.** 

**Finally, within each sub-census division, the allocated floorspace using boilers was further disaggregated between States using relative population data from the 2000 Census. The**  **result is an estimate of, for each 1,000 ft 2**  **of floorspace using commercial boilers in the nation, the relative fraction of that floorspace that would be allocated to each State and each of the 7**  **building types. This estimate was then used as a proxy for the relative shipments of boilers to market segment (**  i.e., **each State and building type combination) for which it derived FLEOH estimates as discussed previously.** 

4.4 ENERGY ANALYSIS SUMMARY RESULTS

**Table 4.4.1 shows summary results for national average energy consumption estimates by efficiency level and boiler class.**  Table 4.4.1 National Average Site Energy Consumption Estimates by Boiler Class and

Efficiency Level

Equipment Class National Average Site Energy Consumption (Million Btu/yr) Baseline Level 0 Level 1 Level 2 Level 3 Level 4* **Small Gas-Fired Hot Water 1077 1051 1026 1002 979**  **Small Gas-Fired Steam All Except Natural Draft 1091 1077 1064 1051 1038**  **Small Gas-Fired Steam Natural Draft 1119 1105 1091 1077 na**  **Small Oil-Fired Hot Water 1051 1026 1002 979 na**  **Small Oil-Fired Steam 1064 1051 1038 1014 na**  **Large Gas-Fired Hot Water 4013 3964 3916 3869 3671**  **Large Gas-Fired Steam All Except Natural Draft 4090 4039 3989 3940 3893**  **Large Gas-Fired Steam Natural Draft 4196 4142 4090 4039 3989**  **Large Oil-Fired Hot Water 3940 3846 3801 3757 na**  **Large Oil-Fired Steam 3989 3940 3893 3846 3757** 

***** **na means that no efficiency level was designated for analysis. 4-8** 

REFERENCES

**1. American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). 2008.**  Energy Standard for Buildings Except Low-Rise Residential Buildings

**. ANSI/ASHRAE 90.1-2007, ASHRAE, Atlanta, Georgia.** 

**2. Hydronics Institute of GAMA. Testing Standard BTS-2000 (Rev06.07) – Method to**  **Determine Efficiency of Commercial Space Heating Boilers. 2007.**

**3. U.S. Department of Energy/Energy Information Administration (DOE/EIA). 2003.** Commercial Buildings Energy Consumption Survey **. Available at: http://www.eia.doe.gov/emeu/cbecs/**  **(Accessed September 2008).**

**4 U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (DOE EERE). 2000.**  Energy Conservation Program for Consumer Products: Screening Analysis for EPACT-Covered Commercial HVAC and Water-Heating Equipment Screening Analysis

**. DOE-EERE, Washington, D.C.** 

**5. U.S. Department of Energy/Energy Information Administration (DOE/EIA). 2006.** Annual Energy Outlook 2006 **. DOE/EIA-0383(2006), DOE/EIA, Washington D.C. 4-1**  ABBREVIATIONS AND ACRONYMS
**ASHRAE American Society of Heating, Refrigerating and Air-Conditioning**

**BTS Boiler Testing Standard**

**DOE U.S. Department of Energy**

**EIA (DOE) Energy Information Administration**

**FLEOH Full Load Equivalent Operating Hour**

**HI Hydronics Institute HVAC heating, ventilation, and air-conditioning** 

**LCC life-cycle cost**

**NEMS National Energy Modeling System**