Air of Importance. A Study of Air Distribution Systems in Manufactured Homes

Transcription

1 Air of Iportance A Study of Air Distribution Systes in Manufactured Hoes A research project sponsored by: Alternative Energy Corporation Carolina Power & Light Copany New York State Energy Research and Developent Authority U.S. Departent of Housing and Urban Developent Project Manager: Francis Conlin, Alternative Energy Corporation Heating Analysis Conducted by: Bob Davis, Ecotope, Inc. Cooling Analysis Conducted by Florida Solar Energy Center: Ji Tyson, Lixing Gu, Michael Anello, and Muthusay Swai Edited by: Eanuel Levy, The Levy Partnership, Inc. Final report printed May 1996 by Alternative Energy Corporation About Alternative Energy Corporation An independent nonprofit organization, Alternative Energy Corporation (AEC) was established in 1980 by the N.C. Utilities Coission in cooperation with the state's ajor electric utilities to proote energy efficiency. AEC develops, tests, and delivers energy innovations and efficiencies for eber electric utilities and their custoers. Meber utilities are Carolina Electric Cooperatives, Carolina Power & Light Copany, Duke Power Copany, Nantahala Power & Light Copany, and North Carolina Power. Alternative Energy Corporation After August 16, 1996: PO Box Capability Drive Research Triangle Park, North Carolina Raleigh, NC

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3 Acknowledgents There are any people who deserve thanks for their hard work on this project. I would like to thank Diana Woolley, without who this project would still be an idea. I would like to thank Eanuel Levy for his constancy and his willingness to coordinate the technical work of others. I would also like to thank AEC and its Board of Directors for allowing e to focus on this project. The Technical Design Coittee: Ed Salisbury, Dennis Jones, J.T. Willias, Allen Zieran, Bruce Davis, and Mark Modera, helped us keep the project on-target, practical and useful. Many retailers in North Carolina, Florida and New York and their state associations helped us find hoeowners willing to participate in the study, and any hoe owners repeatedly allowed us into their hoes for the testing. All of you deserve y heartfelt appreciation. Thanks to Jerry Bruner and the Fleetwood Plant in Roxboro, NC, who, because of their proxiity, I used to educate any contractors about anufactured hoes. Thanks to NCMHI and Stacey Cheathu who always answered y questions. A special thanks goes to Bob Davis of Ecotope Inc., who does take anufactured housing seriously. And, of course, this project would not have been possible without the support of our partners: Bill Freeborne of the United States Departent of Housing and Urban Developent, Bob Carver fro the New York State Energy Research and Developent Authority, and Russell Duncan fro Carolina Power & Light Copany. Disclaier The aterial contained in this publication was prepared by the Alternative Energy Corporation (AEC), a nonprofit corporation. Neither AEC, its eber organizations, the acknowledged individuals, nor any person acting on behalf of the: (a) akes any warranty, express or iplied, with respect to the use of any inforation, apparatus, ethod, or process disclosed in this publication that such use ay not infringe privately owned rights; or (b) assues any liability with respect to the use of, or for direct or consequential daages resulting fro the use of, any inforation, apparatus, ethod, or process disclosed in this publication; or (c) has any liability for daages that result fro any negligent act or oission involved in the preparation of this aterial. Any iplied warranty of erchantability of fitness for a particular use is specifically excluded.

4 Foreword One has only to look at the statistics to see how iportant it is to consider anufactured housing in any residential energy research. Twenty percent of existing single -faily hoes in the United States are anufactured, and 25 percent of new single -faily hoes built last year were factory -built. In North Carolina, the leading state for anufactured-hoe shipents, 40 percent of new hoes last year were anufactured. Sponsored residential energy research has advanced the understanding of building systes in general, but this research is not always transferable fro site-built to factorybuilt housing. The scarcity of articles in the literature dealing with new anufactured hoes deonstrates the disproportionate level of research investent being spent in this burgeoning hoe construction approach. The sall aount of anufactured housing research that does exist has recently focused ainly on ways to iprove the theral envelope. This led, in part, to an increase in the theral requireents for anufactured hoes in the recent changes to the HUD Standards (October, 1994). In the last several years, building scientists across the country have been quantifying the contribution ade by air distribution systes to building efficiency loss in site -built hoes. Estiates vary, but the average duct syste appears to reduce overall syste efficiency by 20 to 40 percent. This efficiency loss can have a ultiplying effect with air-flow sensitive, copressor-based space conditioning systes such as air conditioners and heat pups. Meanwhile, air distribution systes in new anufactured hoes have received very little attention. This study is a step forward in trying to better understand air distribution in anufactured hoes and their affect on overall syste perforance. An incentive for the anufactured housing industry to volunteer to iprove the quality of their product is found within the hoe buying arket. The industry has deonstrated its willingness to invest in change if such a change iproves ability to sell hoes or decreases probles that require on-site visits fro the retailer or factory to reedy. An inhouse survey of 50 anufacturers and 50 retailers showed that a callback cost of 10% was budgeted by the average retailer, and 12% of field visits had to do with a variety of air distribution related issues. A goal of this project was to suggest changes in the air distribution syste that will significantly affect these costs. Four technical bulletins were developed as part of this project to help educate retailers, anufacturers, and contractors about how to optiize air distribution perforance and at the sae tie reduce callback expenses for their housing product. This study analyzed the perforance of air distribution systes in 24 anufactured hoes in Alabaa, Florida, New York, and North Carolina, and copared the with the results of 9 hoes built to the ore stringent MAP specifications and tested previously in the state of Washington. One of the objectives in this study was to go beyond just describing the agnitude of air distribution syste loss and to uncover the source. Understanding the root cause of air distribution syste efficiency loss will help to identify the appropriate reedies. The anufactured housing industry has shown a increasing level of proactivity. For exaple, by the tie the new HUD regulations went into effect in October 1994, any anufacturers were already providing as a standard or, at least as an option, hoes with an equivalent level of theral insulation. The inforation in this report should help those innovators in the industry iprove the quality of their products. It is those in the industry who are proactive and who treat their hoes with building science in ind that I hope will benefit ost fro this report. ii

5 Table of contents 1. EXECUTIVE SUMMARY INTRODUCTION RESEARCH GOALS, APPROACH, AND STUDY LIMITATIONS SUMMARY OF THE PERFORMANCE OF ADS IN THE HEATING MODE SUMMARY OF THE PERFORMANCE OF ADS IN THE COOLING MODE RECOMMENDATIONS FOR FUTURE ADS-RELATED R&D AIR DISTRIBUTION SYSTEMS IN MANUFACTURED HOMES OVERVIEW HOW DUCTS IMPACT ENERGY USE Conductive losses fro the ducts Duct leakage Ducts and whole house infiltration Syste ibalances, register location, and cofort Equipent cycling, equipent sizing, and peak loads Off-cycle losses ENERGY PERFORMANCE OF DUCTED AIR SYSTEMS CURRENT CONSTRUCTION PRACTICES THE REGULATORY ENVIRONMENT PERFORMANCE OF AIR DISTRIBUTION SYSTEMS IN THE HEATING MODE OVERVIEW HEATING CLIMATE PROTOCOL DESCRIPTION FOR THE NEW HUD-CODE MANUFACTURED HOMES FIELD SURVEY OF NEW HUD-CODE HOMES House characteristics, North Carolina House characteristics, New York Energy features of the HUD-Code hoes Air leakage, air handler, and supply register data EFFICIENCY ANALYSIS AND RESULTS FOR NEW HUD-CODE HOMES Heat delivery efficiency testing and analysis procedure Measured efficiency results Heat delivery efficiency odeling RESULTS FROM THE NORTHWEST AND RECASTING OF THE EFFICIENCY ESTIMATES COST-EFFECTIVENESS OF THE MAP GUIDELINES REFERENCES PERFORMANCE OF AIR DISTRIBUTION SYSTEMS IN THE COOLING MODE OVERVIEW FIELD TESTS Description of hoes - Florida Description of hoes - Alabaa Protocols ANALYSIS Objectives Background Siulation Methodology Derived Results ALABAMA RESULTS Loads, Losses, penalties for five Alabaa Hoes Suary of efficiencies -- Alabaa Hoes FLORIDA RESULTS

6 Loads, Losses, penalties for five Florida Hoes Suary of efficiencies -- Florida Hoes NORTH CAROLINA RESULTS Loads, Losses, penalties for North Carolina Cliate Suary and Conclusions -- North Carolina DISCUSSION AND CONCLUSIONS ANNOTATED LITERATURE REVIEW

7 Index of figures and tables FIGURE 1-1 HEATING ENERGY COST BY END USE (NEW YORK)... 9 FIGURE 1-2 HEATING ENERGY COST BY END USE (NORTH CAROLINA) FIGURE 1-3 HEATING SEASON ADS EFFICIENCY LOSSES BY SOURCE FIGURE 1-4 COOLING SEASON TOTALSYSTEM LOSSES BY SOURCE FIGURE 1-5 COOLING SEASON ADS EFFICIENCY LOSSES BY SOURCE FIGURE 4-1 SEASONAL SENSIBLE SYSTEM EFFICIENCIES FIGURE 4-2 SEASONAL TOTAL SYSTEM EFFICIENCIES FIGURE 4-3 SCHEMATIC OF BUILDING SHOWING AIR PATHWAYS FIGURE 4-4 SCHEMATIC OF AIR FLOWS IN TYPICAL MANUFACTURED HOMES FIGURE 4-5 ALABAMA HOUSE 4 (AL-4) - TYPICAL SUMMER DAY, ACTUAL CONFIGURATION FIGURE 4-6 ALABAMA HOUSE 4 (AL-4) - TYPICAL SUMMER DAY, OPTIMUM CONFIGURATION FIGURE 4-7 FLORIDA HOUSE 3 (FL-3) - TYPICAL SUMMER DAY, ACTUAL CONFIGURATION FIGURE 4-8 FLORIDA HOUSE 3 (FL-3) - TYPICAL SUMMER DAY, OPTIMUM CONFIGURATION TABLE 2-1 SUMMARY OF ADS EFFICIENCY TABLE 3-1 PHYSICAL AUDIT DATA TABLE 3-2 WINDOW ASSEMBLY DESCRIPTION AND PERFORMANCE TABLE 3-3 DUCT CHARACTERISTICS TABLE 3-4 AIR LEAKAGE AND PRESSURE DIAGNOSTIC DATA TABLE 3-5 SERIES PRESSURE MEASUREMENT TABLE 3-6 PRESSURE PAN MEASUREMENTS TABLE 3-7 DUCT LEAKAGE AND AIR HANDLER RESULTS TABLE 3-8 STEADY-STATE HEAT DELIVERY EFFICIENCY MEASUREMENTS TABLE 3-9 MODELED STEADY -STATE HEAT DELIVERY EFFICIENCY RESULTS TABLE 3-10 PHYSICAL DATA FROM MAP COHEAT HOMES TABLE 3-11 EFFICIENCY RESULTS FROM MAP COHEAT TEST HOMES TABLE 3-12 STEADY -STATE HEAT DELIVERY EFFICIENCIES FOR HUD-CODE HOMES TABLE 3-13 ESTIMATES OF SYSTEM EFFICIENCY LOSSES BY SOURCE * TABLE 3-14 ENERGY COST COMPARISON IN RALEIGH, NC, VERSION TABLE 3-15 ENERGY COST COMPARISON IN RALEIGH, NC, VERSION TABLE 3-16 ENERGY COST COMPARISON IN SYRACUSE, NY TABLE 3-17 UPGRADES AND COSTS TABLE 3-18 CONSUMER ECONOMICS FOR SYSTEM UPGRADE TABLE 4-1 COOLING SEASON SYSTEM EFFICIENCY TABLE 4-2 ESTIMATE OF SYSTEM EFFICIENCIES TABLE 4-3 COMPONENT LOADS AND LOSSES FOR ALABAMA HOME 1 (AL-1) TABLE 4-4 COMPONENT LOSS ESTIMATES FOR ALABAMA HOME 1 (AL-1) TABLE 4-5 DELIVERY AND SYSTEM EFFICIENCIES FOR ALABAMA HOME 1 (AL-1) TABLE 4-6 COMPONENT LOADS AND LOSSES FOR ALABAMA HOME 2 (AL-2) TABLE 4-7 COMPONENT LOSS ESTIMATES FOR ALABAMA HOME 2 (AL-2) TABLE 4-8 DELIVERY AND SYSTEM EFFICIENCIES FOR ALABAMA HOME 2 (AL-2) TABLE 4-9 COMPONENT LOADS AND LOSSES FOR ALABAMA HOME 3 (AL-3) TABLE 4-10 COMPONENT LOSS ESTIMATES FOR ALABAMA HOME 3 (AL-3) TABLE 4-11 DELIVERY AND SYSTEM EFFICIENCIES FOR ALABAMA HOME 3 (AL-3) TABLE 4-12 COMPONENT LOADS AND LOSSES FOR ALABAMA HOME 4 (AL-4) TABLE 4-13 COMPONENT LOSS ESTIMATES FOR ALABAMA HOME 4 (AL-4) TABLE 4-14 DELIVERY AND SYSTEM EFFICIENCIES FOR ALABAMA HOME 4 (AL-4) TABLE 4-15 COMPONENT LOADS AND LOSSES FOR ALABAMA HOME 5 (AL-5) TABLE 4-16 COMPONENT LOSS ESTIMATES FOR ALABAMA HOME 5 (AL-5) TABLE 4-17 DELIVERY AND SYSTEM EFFICIENCIES FOR ALABAMA HOME 5 (AL-5) TABLE 4-18 SENSIBLE EFFICIENCIES FOR ALABAMA HOMES TABLE 4-19 TOTAL EFFICIENCIES FOR ALABAMA HOMES TABLE 4-20 COMPONENT LOADS AND LOSSES FOR FLORIDA HOME 1 (FL-1)

8 TABLE 4-21 COMPONENT LOSS ESTIMATES FOR FLORIDA HOME 1 (FL-1) TABLE 4-22 DELIVERY AND SYSTEM EFFICIENCIES FOR FLORIDA HOME 1 (FL-1) TABLE 4-23 COMPONENT LOADS AND LOSSES FOR FLORIDA HOME 2 (FL-2) TABLE 4-24 COMPONENT LOSS ESTIMATES FOR FLORIDA HOME 2 (FL-2) TABLE 4-25 DELIVERY AND SYSTEM EFFICIENCIES FOR FLORIDA HOME 2 (FL-2) TABLE 4-26 COMPONENT LOADS AND LOSSES FOR FLORIDA HOME 3 (FL-3) TABLE 4-27 COMPONENT LOSS ESTIMATES FOR FLORIDA HOME 3 (FL-3) TABLE 4-28 DELIVERY AND SYSTEM EFFICIENCIES FOR FLORIDA HOME 3 (FL-3) TABLE 4-29 COMPONENT LOADS AND LOSSES FOR FLORIDA HOME 4 (FL-4) TABLE 4-30 COMPONENT LOSS ESTIMATES FOR FLORIDA HOME 4 (FL-4) TABLE 4-31 DELIVERY AND SYSTEM EFFICIENCIES FOR FLORIDA HOME 4 (FL-4) TABLE 4-32 COMPONENT LOADS AND LOSSES FOR FLORIDA HOME 5 (FL-5) TABLE 4-33 COMPONENT LOSS ESTIMATES FOR FLORIDA HOME 5 (FL-5) TABLE 4-34 DELIVERY AND SYSTEM EFFICIENCIES FOR FLORIDA HOME 5 (FL-5) TABLE 4-35 SENSIBLE EFFICIENCIES FOR FLORIDA HOMES TABLE 4-36 TOTAL EFFICIENCIES FOR FLORIDA HOMES TABLE 4-37 COMPONENT LOADS AND LOSSES FOR NORTH CAROLINA HOME 1 (NC-1) TABLE 4-38 COMPONENT LOSS ESTIMATES FOR NORTH CAROLINA HOME 1 (NC-1) TABLE 4-39 DELIVERY AND SYSTEM EFFICIENCIES FOR NORTH CAROLINA HOME 1 (NC-1) TABLE 4-40 COMPONENT LOADS AND LOSSES FOR NORTH CAROLINA HOME 2 (NC-2) TABLE 4-41 COMPONENT LOSS ESTIMATES FOR NORTH CAROLINA HOME 2 (NC-2) TABLE 4-42 DELIVERY AND SYSTEM EFFICIENCIES FOR NORTH CAROLINA HOME 2 (NC-2) TABLE 4-43 SENSIBLE EFFICIENCIES FOR NORTH CAROLINA HOMES TABLE 4-44 TOTAL EFFICIENCIES FOR NORTH CAROLINA HOMES TABLE 4-45 SENSIBLE EFFICIENCIES FOR ALL HOMES TABLE 4-46 TOTAL EFFICIENCIES FOR ALL HOMES

9 1. Executive Suary 1.1. Introduction Most research relating to the energy use in anufactured housing has dealt with the perforance of theral envelope, space heating and cooling equipent, and ore recently, issues such as whole house ventilation and infiltration. While soe studies have looked at energy losses due to air distribution systes (ADS), this area is too often treated as a footnote to the overall perforance of the echanical syste. There are several reasons why this situation has developed. First, energy use associated with distribution systes is generally gauged solely by engineering analyses whose results are based on outdated or unsubstantiated assuptions. Manual J, for exaple, suggests that duct losses should be assued to degrade perforance by between zero and 15 percent, the latter figure being suggested for ducts placed outside the building s theral envelope in very cold cliates. Recent studies in the site-built area, and now this effort, shed soe light on the true perforance of distribution systes and suggest that these analysis tools are not particularly accurate predictors of actual syste perforance. Second, even with better predictive tools, the quality of installation too often leaves uch to be desired. Manufactured hoes are erected in a plant under the watchful eye of a quality control supervisor. The critical crossover duct connection is done in the field by contractors operating in a far less regulated environent and not subject to the sae rigorous third-party inspections. Third, exclusive of the anufacturers, there are only a few industry groups with vested interests in distribution systes and fewer advocates with the resources to conduct eaningful research. With the significant iproveents in theral envelope and equipent perforance, distribution systes have quickly becoe one of the critically weak links in aking further energy-efficiency iproveents. With these points in ind, this study was designed to ake inroads into our understanding of ADS in anufactured hoes. The following questions helped shape the design of the project: How large are the distribution losses in single- and ulti-section hoes and what are the principal variants -- in the areas of design, construction, aterials, installation -- that influence the agnitude of these losses? What practical and econoical steps can be taken to itigate distribution syste losses? How uch energy can be saved by such easures? What are the cost/benefits of and technical/ipleentation barriers to these easures? What kinds of new aterials, products, and/or technologies are needed in order to significantly iprove distribution syste energy perforance? 5

10 As part of the first phase of this effort, a literature search was conducted that noted a dearth of duct distribution studies generally, and specifically a near absence of research dealing with the perforance of theral distribution systes in anufactured housing (see Section 5). Several citations suggested that theral distribution syste inefficiencies ay degrade overall energy perforance by anywhere fro 15 to 40 percent. These figures are, for the ost part, derived fro field onitoring of site-built hoes. Even in these cases, however, there is no general agreeent on the conditions that cause a significant reduction in syste efficiency, the steps to take to iprove perforance, and the ipact that changes in construction practice have on the efficiency of the theral distribution syste. Syste perforance characteristics also appear to vary by cliate, as a result of the types of aterials used in fabricating the syste, and as a function of syste location (floor or attic) and layout. In short, there exists an acute gap in our basic understanding of the perforance of theral distribution systes that has two coponents: (1) how large an ipact theral distribution systes have on energy use in anufactured hoes; and (2) the specific conditions that influence when the losses occur. The need to easure the perforance of ADS through the field testing of hoes was underscored by a group of industry experts serving as advisors to the work Research goals, approach, and study liitations The study aied to contribute to an understanding of the perforance of air distribution systes (ADS) in anufactured hoes through field tests of actual, in situ operation. This poses a challenge for several reasons including the following: field tests are conducted over a short tie span and siulation tools are needed to extrapolate the results to entire heating and cooling seasons; and, since syste efficiency fluctuates by season, the construction of the hoe and its site location will influence the overall operating efficiency of the ADS. Relatively large perforance variations fro year to year and fro hoe to hoe are to be expected. The results of these investigations are displayed throughout the study in precise ters often depicted by graphic representations of ADS perforance. The reader should be circuspect in reviewing this aterial and recognize the liits of the study which include the following: Tools available for siulating ADS perforance are relatively new and have not been subject to broad use and validation by the engineering counity. Predicting ADS perforance is coplex and requires estiating several types of heat and air flow that change over tie and ay be occurring siultaneously. 1 The project was onitored by a tea of experts in the area of anufactured housing and/or air distribution systes. The tea consisted of the following people: Ed Salisbury of Fleetwood Enterprises, Mark Modera of Lawrence Berkeley Laboratory, Alan Zieran of Evcon Industries, Dennis Jones of R-Anell Hoes, J. T. Willias of Azalea Mobile Hoes. 6

11 Changes in the living environent, such as elevated huidity levels or syste ibalances that cause cold spots, were not considered as part of this study. These factors ipact overall syste perforance. The saple size is extreely sall (33 hoes 2 ), liiting our ability to generalize fro the results. Despite these liitations, this study suggests that using an ADS degrades energy perforance draatically, ainly as a result of poor installation and set up practices. In the heating ode, the average efficiency reduction was 40 percent (that is, for every 100 BTUs of heating energy entering the ADS, 60 arrived in the living spaces) and in cooling the loss was about 18 percent on average. In ost continental US cliates, annual energy use is split between heating and cooling. The efficiency of the ADS as a conditioned air delivery ethod varies by season, and it is the net ipact on energy use that is of ultiate interest in characterizing such systes. However, cobining heating and cooling perforance is a challenge beyond the scope of this odest effort. An ADS design that perfors fairly well in the cooling onths ay not be nearly as effective in the heating season and, therefore, tools used to easure perforance in the two seasons differ in any respects. In addition, soe cliatic and design factors, such as relative huidity, are iportant in easuring perforance in one season (cooling in this exaple) and not the other season. While a leaky duct syste is leaky all year round, its ipact on total annual energy use and operating efficiency depends on cliate and other site factors and often where exactly the leaks occur. Adding to the list of variables that influence seasonal perforance is the placeent of the ADS. In ost hoes, the ADS is priarily located in the interstitial space below the floor, referred to as the belly area. In Florida, however, the practice is to deliver conditioned air to the living spaces fro above through attic-ounted ducts. Consequently, the research applied different analytical ethods to predict heating and cooling seasonal perforance of the ADS and, as a result, there are soe differences in the data collection protocols. This is reflected in the structure of the report which is divided into heating and cooling chapters Suary of the perforance of ADS in the heating ode Estiates of ADS perforance in the heating ode are based on the results of field tests of 23 hoes in three cliatically distinct locations. Thirteen of the hoes were onitored expressly for this effort (six in New York state and eight in North Carolina). All hoes et or exceeded the new HUD energy standards of October 24, 1994 (a few were actually built prior to that date). Nine hoes were 2 Saple hoes include 6 fro New York, 8 fro North Carolina, 5 fro Alabaa, 5 fro Florida, and 9 hoes fro previous work sponsored by the Bonneville Power Adinistration Four of the hoes were single-section, the rest were double-section. 7

12 anufactured in the Northwest under the Bonneville Power Authority Manufacturers Acquisition Progra (MAP) to energy efficiency levels that exceed the new HUD standards. Indeed, the MAP hoes include energy conservation easures associated with iproved ADS perforance, such as insulated underfloor ducts, a fact reflected in the higher efficiency estiates for these hoes. The New York and North Carolina hoes are also typical of their respective regions in any ways (for exaple, the New York hoes have fossil fuel-fired furnaces and the North Carolina units are heated electrically, ainly with heat pups), and generally are representative of ADS construction and installation practices outside the Northwest. However, it s worth reiterating that the saple is too sall to suggest that the results are representative either of a location or of all anufactured hoes. Overall syste efficiency for the new HUD code hoes (the New York and North Carolina saples) averaged about 60 percent indicating a distribution syste loss of 40 percent. The MAP hoes tested earlier had a distribution syste loss of 15 percent during the heating season. To place the findings for the typical HUD code hoes in perspective, consider the profile of energy use for a hoe in the two study locations 3. In New York, the heating season space conditioning bill for the typical hoe would run about $893. As graphically illustrated in Figure 1-1, equipent losses would account for $223 (predicated on the equipent operating at the rated value of 75 AFUE), the ducts losses generate $268 (30%) of the total bill, and envelope-related heating costs (including infiltration) the reaining $402 (45%). The sae design in North Carolina (see Figure 1-2), in this case using electric resistance heating, would have space heating costs totaling $1,066 with the ADS responsible for $414 (39%) of the total and the envelope-related losses contributing $620 (58%) to the bill. 3 The exaples in Figures 1-1 and 1-2 are base on a 1400 square foot hoe. The trunk duct insulation on half of the hoes represented by the average is insulated with R-7 fiberglass insulation. The New York exaple assues a gas-heated hoe with a local fuel cost of $0.58 and an envelope U o -value of The North Carolina assuptions are electric costs of $0.075 per kwh and a U o -value of

13 9 Figure 1-1 Heating energy cost by end use (New York)

14 Figure 1-2 Heating energy cost by end use (North Carolina) 10

15 11 Figure 1-3 Heating season ADS efficiency losses by source

16 The ajor sources of energy loss attributable to ADS that were easured in this study, listed in descending order of ipact, are as follows: conduction through the duct walls, air leakage caused by gaps in the construction of the duct syste, and higher whole house infiltration as a result of pressure differences that arise when the duct syste is in operation. (See Figure 1-3) The conductive losses were surprisingly high and can be traced to two root causes. First, ost of the hoes in the study are double section (consisting of two boxes) with a trunk duct in each box. The two trunk ducts are connected by a crossover duct running underneath the hoe and outside of the insulated envelope. Typically, the exterior ducts are wrapped with an R-4 or R-5 insulation. The high teperature difference between the duct teperature and the abient, coupled with the relatively low insulation value, generates a portion of the conductive losses. The second, and in soe instances larger contributor to conductive losses is a result of holes in the underfloor insulation that allow abient air to coe in contact with the uninsulated trunk duct. Often, the last contractors to work on the hoe are the pluber or cable TV installer, trades that access the hoe through the floor cavity by cutting away part of the botto board and insulation. This air pathway is often not resealed after the work is coplete. Even a sall hole can result in substantial air igration. The cobination of uninsulated ducts and holes in the underfloor ebrane greatly increase conductive losses Suary of the perforance of ADS in the cooling ode ADS cooling perforance was gauged in twelve hoes in the southern tier; five hoes each in Florida and Alabaa, and two hoes in North Carolina. The Florida units reflected a statewide preference for delivering conditioned air into the living spaces via ceiling ounted registers, a practice not widely used outside the state. The Alabaa hoes were drawn fro a group of hoes built to the Good Cents standards, a voluntary energy efficiency progra offered by Alabaa Electric Cooperative. These hoes were anufactured prior to the revision of the HUD Energy Standards. However, they are of a relatively recent vintage and, while lacking a whole house ventilation syste, their level of theral integrity exceeds the current HUD standards. The North Carolina hoes were aong the units included in the heating analysis described in Section 1.3. The Alabaa and North Carolina hoes all have underfloor ducts for air distribution. Efficiency degradation in the cooling ode averaged about 18 percent for all hoes, considerably less than the heating result but a significant loss none the less. Data for overhead duct systes (Florida hoes) indicated an average perforance reduction of approxiately 24 percent and underfloor ducts (Alabaa and North Carolina) losing about 14 percent on average (see Figure 1-4). 12

17 13 Figure 1-4 Cooling season total syste losses by source

18 The superior perforance of the underfloor ducts is due to several factors, including the following: Any leakage that occurs in the underfloor ducts, which are located above the belly insulation, lowers the teperature in the floor cavity and reduces the rate of conductive losses fro the duct. Conversely, leakage losses fro attic ducts, which are located above the ceiling insulation, are ore easily vented to the outside and do not decrease conductive losses. The hot attic space will generate relatively high conductive losses fro the ducts, particularly those sections near the attic air ass. The floor tends to be a ore benevolent environent for ducts in the cooling season since the teperature in the crawl space is often below abient. The odeling also suggests that duct leakage in the attic ay create a positive pressure in the attic cavity relative to the living space. The pressure differential will drive attic air into the living spaces, which, even when blended with the air leaked fro the ducts, will be war enough to further increase the cooling load. Having easured and explained the echaniss behind the apparent superiority of underfloor ADS copared to overhead systes, it should be kept in ind that this analytical study did not attept to quantify the ipact of teperature stratification. Generally, in hoes with low ceiling heights or ceiling fans, stratification is not a ajor concern. Where stratification is a factor, the hoe owner often copensates for a perceptibly higher teperature by turning back the therostat. Ceiling ounted supplies will generally help ix the air. This factor ight favor overhead ducts and iniize the efficiency advantages associated with the underfloor configuration. Another challenge in estiating cooling season perforance of ADS is how to accurately account for the ipact of the latent coponent of the load on energy use. At present there is no consensus on this point, which is the subject of active debate within the engineering counity. The analytical process eployed here assues the equipent operates until the sensible load is satisfied. The huidity is allowed to float, although in reoving the sensible load oisture is extracted fro the air in the hoe. This odeling strategy has its liits too; if the sensible load is reoved and the relative huidity rises, the hoe owner ight copensate for the perceptual difference in cofort by lowering the therostat. This is an iportant question, and how the latent coponent of the load is assued to behave is a consequential issue because it ipacts the relative agnitude of ADS-related losses (see Figure 1-5). In predicting the cooling perforance of ADS, as in the heating analysis, losses are divided into conduction, leakage, and air infiltration coponents. Since the latent coponent does not lose energy through conduction, the relative agnitude of the losses changes depending on the odeling and hoe control assuptions. As shown on Figure 1-5, if only the sensible coponent of the load is considered, the efficiency reduction due to added whole building infiltration is about 5 percent out of a total 27 percent ADS-related perforance degradation (17 percent of the total loss). With latent included, the loss due to added air infiltration clibs to 14

19 15 Figure 1-5 Cooling season ADS efficiency losses by source

20 nearly 12 percent out of about 31 percent, or 38 percent of the total. How latent is handled in the analysis, therefore, will influence the kinds of easures considered to reduce ADS losses Recoendations for future ADS-related R&D The following two questions define the R&D needs in the area of anufactured housing ADS: how large an energy penalty is exacted when anufacturers use an ADS for theral transport?; and, if the penalty is large, what practical and cost-justifiable steps can be taken to reduce the losses? This study was a start at answering the first question and suggests soe directions for addressing the second. Below is an abbreviated list of high priority recoendations for future ADS-related R&D: Expand the saple size to iprove confidence in the results, particularly in cold cliates where ADS-related energy losses are the greatest. Use the results to validate siulation odels. Expand the field easureent to better identify specific sources and agnitudes of ADS losses. Include loss contributions due to crossover connections, trunk penetrations, perieter ducts, furnace to trunk connections and other likely leakage sites. ADS perforance varies greatly between hoes. Identify which factoryinstalled and field-installed sealing strategies are successful, and which fail. Evaluate through testing the ipact of siple, relatively inexpensive easures for iproving ADS perforance (such as wrapping the trunk duct with insulation). Use deonstration hoes to accurately easure ipact on energy use. Develop technologies designed to counter probles that often occur in field installation (such as snap-in, rigid crossover ducts). Explore design changes that reduce opportunities for ADS failures (such as reducing field penetrations of the botto board). Characterize the ipact of ADS-related theral phenoena, such as distribution ibalances, air flow across the supply grille, teperature stratification, huidity levels, outlet vent location, etc. Conduct a research effort exploring the ipact of ADS on other iportant energy-related areas, such as equipent operation, peak loads, and cofort. Conduct a field investigation of ADS in existing hoes to easure if, how, and by what aount perforance changes over tie and develop ethods for correcting coon probles in occupied hoes. Develop a siple test protocol that can identify ADS probles in the factory or during set-up. 16

21 2. Air distribution systes in anufactured hoes 2.1. Overview Up until the last few years, ost anufactured housing research has focused on ways to iprove the theral envelope of the building and, to a lesser extent, the echanical equipent. These are areas where it is easy to identify copanies or organizations with proprietary interests, such as the insulation and heat pup anufacturers. New products and aterials were developed that iproved the integrity of the theral envelope. Sensitized by a steady strea of consuer inforation, the arket responded by deanding higher insulation levels and iproved window products. The fixation with seeking higher R-values as a strategy for controlling energy use was forally sanctioned by the recent passage of changes to the HUD standards (October, 1994) that significantly raised the bar for andated energy efficiency. The attention of the scientific and hoe building counity and power suppliers is now shifting to the poorly understood area of air oveent. In this broad context, air flow issues fall into two subsets; ventilation designed to aintain a healthy living environent, and the transport of conditioned air for heating and cooling purposes. In nearly all new anufactured hoes, conditioned air transport is generally aided by a syste of ductwork designed to deliver heat and coolth to all areas of the hoe. Air is forced into the ductwork by a blower attached to the heating and/or cooling equipent and delivered to the living spaces via floor registers. A well-designed and constructed syste is balanced aintaining an even teperature throughout the hoe. The concept is siple yet far fro foolproof. Several anecdotal studies have hinted that the fabrication and installation of ductwork itself, and generally using air as a delivery echanis, ay exact a high energy penalty. Estiates vary but the average duct systes appears to reduce overall syste efficiency by between 20 and 40 percent. Despite the fact that duct systes are installed in virtually every new anufactured hoe rolling off assebly lines throughout the nation, research in this area has lagged. The current work is a ajor step in correcting this oission. The other iportant area related to air oveent is whole house ventilation. The oveent of air between the living spaces and outdoors is also not well understood but there is a growing consensus that anufactured hoes are on average very tight, particularly when copared to their site-built counterparts. Iproveents in building aterials, constructing hoes in cliate-controlled factories, and a high level of construction quality control are to be credited. The issue has now shifted fro building hoes that leaked, with associated energy penalties, to hoes that are tight with possible indoor air quality probles. HUD addressed this latter concern by requiring all new hoes to have continuous ventilation, but in reality the ventilation characteristics of these hoes are not well understood or quantified. Although ventilation and indoor air quality are not central to the current study, it is ipossible to delve into the delivery of conditioned air through ducts without touching upon the ventilation issue. 17

22 The coents that follow will attept to encapsulate what is know about ductbased theral distribution. The description is by necessity broad since it builds on a sall foundation of scientific inquiry. There are few conteporary studies dealing with ducts in anufactured hoes and uch of the data and observations related to duct syste perforance is, as noted earlier, anecdotal. (The project literature search, for exaple, turned up only three studies specifically addressing anufactured housing duct systes). There are plenty of opportunities to advance the state of knowledge; the challenge is to weed through the possible directions for the research and pursue those that exhibit the ost proise. Section 2.2 characterizes what is known about theral distribution in anufactured hoes; the report offers a synopsis of how ducts can ipact energy perforance. The reader should be aware of the fact that dividing areas of ADS-related energy loss into discrete categories is an oversiplification useful in structuring a research progra and understanding the therodynaics of the syste. The operation of the syste is such that any kinds of inefficiencies are occurring siultaneously. The relative ipact on energy use of each changes over tie, by location, as a function of hoe owner operation, and as a result of the physical characteristics of the hoe. Next, in Section 2.3, a suary of energy perforance of conteporary anufactured hoes using duct systes is provided based on the topical literature. As will be evident, the data base for this discussion is sall. In Section 2.4, the study offers a profile of the kinds of distribution systes used by the industry. This section describes the design configurations, products, aterials, and installation procedures coon aong anufacturers. The profile is a starting point for identifying iproveents in theral distribution systes. Section 2.5 briefly describes the HUD s energy standards for duct systes suarized fro the Manufactured Housing Construction and Safety Standards of October How ducts ipact energy use In concept, the theral distribution syste is quite siple. The echanical equipent heats or cools air that is fan forced into the ducts feeding the priary living spaces of the hoe. The air enters the living spaces through registers, generally located in either the floor or ceiling depending on the location of the duct syste. In ost installations, the return air supply enters through a grille on the face of the equipent closet. Few anufactured hoes have a separate ducted return air syste. Often, a relatively large proportion of the heating and cooling energy generated by the equipent is lost before it can provide useful 18

23 space conditioning. Soe of the ways energy is lost as a result of eploying 4 duct distribution are described in Sections through 2.2.6: Conductive losses fro the ducts Typically, ost of the duct run is located within the theral envelope. In ultisection designs, the duct runs in the boxes are coonly connected by an insulated cross-over duct located outside the theral envelope. This cross-over is subject to fairly high conductive losses, particularly at ties of peak heating and cooling. Interior duct runs are not, however, iune to conductive losses. The size of the loss is a function of the aount of insulation adjacent to the ducts, the tightness of the envelope, and the difference in teperature between the ducts and abient conditions. For exaple, ducts in hoes anufactured for the Florida arket are often placed in the attic, a location that experiences fairly high teperatures when cooling is needed the ost. In any cases, the shallow attic spaces afford little roo for insulating above the ducts Duct leakage Sealing the seas of the ducts to prevent conditioned air fro escaping into floor and ceiling cavities presents a challenge to the industry. Several sealing techniques are available, but the ost effective are often expensive or too difficult to easily integrate into the anufacturing process. This is an area where further study is clearly warranted, particularly with regard to sealing the juncture of the duct syste to the echanical equipent and the connection of the boot to the ain trunk run in floor systes. In addition, duct leakage ay change after the hoe is transported to the site and as a result of aterial degradation over tie. Soe duct tape sealants are particularly prone to this latter proble. However, it is not clear to what extent the leaks translate into energy penalties when the ducts are inside the theral envelope and soe of the heating and cooling energy lost through the leaks reain within the hoe Ducts and whole house infiltration When the blower fan switches on, the pressure within the hoe changes, often causing an increase in the rate of air oveent through leaks in the theral envelope. Several researchers have attepted to quantify the ipact of faninduced infiltration using site-built exaples. As noted earlier, the results fro site-built hoes often cannot be extrapolated to anufactured hoes where construction ethods typically provide a tighter envelope. Pressure ibalances in the syste can aggravate the leakage proble Syste ibalances, register location, and cofort Proper planning of theral distribution systes require that the ducts be sized according to the needs of each of the spaces serviced and that the registers be 4 A ore coprehensive categorization of air distribution loss echaniss is provided by Modera, et. al. (see reference 6 in the bibliography). 19

24 placed in areas where the air flow is not ipeded. This is difficult to achieve with current practices. Generally, duct runs are of a unifor cross-section construction, not graduated as would be dictated by the needs of the individual spaces. The result ay be noticeable roo to roo teperature variations. The air flow ibalance can be further exacerbated by poorly located registers and/or daaged grilles (e.g., bent blades). If cold spots result, the coon hoe owner response is to turn up the therostat, prolonging the operation of the space conditioning equipent and effectively wasting energy Equipent cycling, equipent sizing, and peak loads The decrease in syste efficiency due to the ducts ust be copensated for in the selection of the echanical equipent. The anufacturers and/or echanical contractors specifying the equipent explicitly or intuitively include in the sizing analysis a safety factor to assure that, even with the duct and other syste losses, the hoe owners will be cofortable. In ost instances, the capacity of the equipent far exceeds the design load. (This is true in the selection of both heating and cooling equipent although, except in the case of heat pups, cooling equipent is available in a wider range of capacities, allowing a closer atch to the actual load.) Oversizing has two priary disadvantages: increased equipent cycling, resulting in a lowering of the overall operating efficiency of the equipent; and an increase in the hoe s peak load. In a recent study of anufactured hoes in Alabaa, the ipact of a wide range of energy conservation options on peak load profiles was analyzed overall a three year period. The single ost effective strategy for saving energy and reducing 5 peak loads was properly sizing (i.e., downsizing) the echanical equipent Off-cycle losses The air distribution syste-related energy losses that occur when the blower fan is off, referred to as off-cycle losses, are not well understood and elude easy quantification. At ties when the echanical syste is not operating, the teperature within the ducts drifts toward abient through a cobination of heat flow due to conduction, radiation, and leakage. Exterior ducts exposed to higher teperature differentials are particularly prone to these kinds of losses. When the equipent switches on, the load to be satisfied now includes the ductwork itself. In addition, soe duct configurations lend theselves to off-cycle therosiphon losses. Air in the living space flows back into the ducts due to vertical teperature gradient (that is, convective air currents). This phenoenon effectively increases the envelope area of the hoe. Therosiphoning is ainly a danger in hoes with overhead ducts coon in any southern states, such as Florida. 5 Levy, Eanuel; Marisha Chilcott; et. al., 1994, Good Cents Manufactured Hoe Study, P , Washington, DC; National Rural Electric Cooperative Association 20

25 2.3. Energy perforance of ducted air systes As is evident fro the annotated literature review (Section 5), there is a dearth of anufactured housing-related air distribution citations. Nowhere is the lack of inforation ore noticeable than in the area of perforance data collection and analysis. The handful of studies that have sought to quantify the ipact of air distribution systes on anufactured housing energy perforance are odest in scope and fro a research perspective can only be characterized as anecdotal. Taken together they do not begin to reveal the agnitude nor coplexity of the energy use probles associated with the air distribution syste. Most of the data collected in regard to the reduction in energy efficiency caused by the distribution syste was extracted fro site-built housing studies. The table below suarizes the findings of a handful of such studies. Perforance degradation, as expressed as a percent of total energy use, ranged fro a low of 12 percent to a high of 40 percent. The lower value considered only the change in efficiency associated with the leakage fro the ducts and neglected the other kinds of loses described earlier. There is reason to believe that anufactured hoes would have values that are different fro those noted on the table based solely on the dissiilarities in construction practice. The agnitude of the differences and anner in which they are anifest are the subject of the accopanying research effort. Table 2-1 Suary of ADS efficiency Study (date, bibliographic reference) Estiated percent reduction in efficiency Field easureents of 24 electric hoes (1993,2) 29 Iproving the efficiency of air distribution systes 25 to 40 (1992,3) Theral distribution in sall buildings (1992, 5) 30 to 40 Electric appliance pilot project (1990, 11) 25 (cooling) 16 (heating) Residential infiltration and duct leakage (1989, 12) 12 Mobile hoe heating, cooling and fuel burning study (1979, 20) 15 single section 22 ulti-section In suary, there is every reason to believe that the distribution of the losses will vary between site-built and anufactured hoes. For exaple, the typical anufactured hoe has ost of the ducts within the conditioned envelope. This tends to iniize the conduction loses and allows other loses to be reclaied by the conditioned space. Conversely, when ducts are placed outside the hoe -- the ost coon exterior application is the cross-over duct in a ulti-section unit -- it is fully exposed to the eleents. Cross-over ducts experience a high conducive loss. Further, plant-applied aterials are subject to quality control checks and flaws are readily exposed. Unfortunately, the sae cannot be claied for the site-installed aterial. 21

26 The ducts in anufactured hoes are installed quickly and leaks in the duct work are not uncoon. Sall openings are prone to becoe larger openings if the sealing aterials have a short useful life. In addition, the hoe is subject to shaking and jarring as it is transported fro factory to retail lot and eventually to the site. The jostling ay take its toll on the overall air tightness of the duct syste. Another proble endeic to anufactured hoes is the inefficiency that results fro iproper placeent of duct registers or installation of the cross-over duct. When hoe owners coplain that the heating and/or cooling equipent is not providing sufficient space conditioning there ay be any of a nuber of root causes including floor registers covered by furniture, iproper syste layout and sizing, or a cross-over duct that is not securely connected to the ain trunk line. Other differences between site-built and anufactured hoes relate to geoetry and design. Manufactured hoes are typically long, thin structures. Ibalances in the duct design can easily translate into over-conditioning of spaces close to the equipent and under-conditioning of other living spaces. The hoe is alost always considered as one zone in planning the distribution syste. After all, a two-story anufactured hoe is a rare sight. As a result, stratification and therosiphoning are ore likely to be probles in site-built structures. Upon close inspection, the two hoes types share few coon denoinators in regard to theral distribution syste design, aterials, and installation. Extree care ust be exercised on attepting to apply the results of studies based on site-built hoes to anufactured designs. A handful of studies have sought to evaluate anufactured housing air distribution perforance specifically. Within the context of this discussion, one study of particular note was prepared by Ecotope for Bonneville Power Adinistration as part of the Super Good Cents progra. In that work, distribution systes in anufactured hoes were analyzed using a technique called coheating. Coheating allows the energy use of the hoe to be gauged with and without the duct syste. The difference between the two figures represents the duct losses. Typical construction was found to engender an average efficiency reduction of 30 percent. That is, 70 percent of the usable heating and cooling energy produced by the equipent was delivered to the spaces to be conditioned. This finding was based on testing of conventional underfloor duct systes. Systeatic duct sealing techniques reduced the loss by half to 15 percent. While the saple of hoes tested was sall, this study corroborated the growing body of evidence that energy loses due to the distribution syste can be significant. Quantifying the loses and searching for ways to reduce their severity are the subject of the other tasks of this progra Current construction practices The building block of anufactured housing architecture is the long, narrow wood-fraed box sitting atop a etal chassis. Most hoes are coposed of one or two boxes, but three or even four boxes are not uncoon. The box shape itself and the anner in which living spaces are grouped along the long axis of the box dictates the location and layout of the duct syste. Federal interstate transportation regulations liit the height of the box, assuring that the attic and 22