SERI/Tp·254·3629

UC Category: 350

DE90000323

Testing the Effectiveness

of Mobile Home Weatherization

Measures in a Controlled

Environment: The SERI

CMFERT Project

R.D. Judkoff

C.E. Hancock

E. Franconl

March 1990

Prepared under Task No. 00011041

Solar Energy Research Institute

A Division of Midwest Research Institute

1617 Cole Boulevard

Golden, Colorado 80401-3393

Prepared for the

U.S. Department of Energy

Contract No. DE-AC02-83CH10093
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any

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Reference herein to any specific commercial product. process. or service by trade name. trademark, manufacturer. or otherwise does not necessarily constitute or imply its endorsement. recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

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can be found in the current issue of the following publications which are generally available in most libraries: Energy Research Abstracts (ERA); Government Reports Announcements and Index (GRA and I); Scientific and Technical Abstract Reports (STAR); and publication NTIS-PR-360 available from NTIS

at the above address.
TP-3629

PREFACE

This report is an account of work conducted by the Solar Energy Research Institute in 1988 and 1989

on the weatherization of mobile homes as part of the SERI CMFERT (Collaborative Manufactured

Buildings Facility for Energy Research and Training) Project. The report describes the results from

testing three mobile homes within a warehouse modified to allow tight control of environmental

variables. Reference is also made to two mobile homes that were tested in other, unmodified

warehouses.

The report is intended for weatherization professionals and researchers. The executive summary and

Appendix B, which describes the weatherization measures and installation techniques, will be of greatest

interest to the weatherization practitioner. The sections describing testing and analysis methods and

detailed results will be of most interest to the researcher.

iii
TP-3629

EXECUTIVE SUMMARY

Mobile homes constructed before the U.S. Department of Housing and Urban Development (HUD)

enacted thermal standards in 1976 use from 1.25 to 2 times the energy per square foot of comparable

site-built houses. Their unique construction detailing makes them difficult for weatherization agencies

to treat effectively using the measures and techniques developed for site-constructed dwellings. A study

conducted by the Meridian Corporation (1988) for the U.S. Department of Energy indicated that average

energy savings in mobile homes nationally were about 5% after a weatherization expenditure of $1,012,

resulting in a simple payback of about 21 years. For site-builts, energy savings were about 14% with

an expenditure of $1,463, yielding a payback of about 11 years. Although mobile homes are less than

5% of the total residential building stock, they represent about 25% of the buildings that qualify for

low-income weatherization. This poses both a problem and an opportunity.

A major impediment to weatherizing mobile homes more effectively has been the .lack of hard data

on the thermal effectiveness of various weatherization techniques. In response to this problem, the

Buildings Research Branch at the Solar Energy Research Institute (SERI) developed a short-term testing

method that allows mobile homes to be monitored inside an environmentally controlled warehouse.

The method consists of three tests. The first is a coheating test to measure the building loss coefficient.

A constant temperature difference between the warehouse and test building is created by maintaining

constant temperatures in the warehouse and the building until quasi-steady-state is attained. Generally,

the warehouse and building are kept at about 40° and 800F, respectively, so that work can be done in

relative comfort. However, the signal-to-noise ratio can be improved by increasing the temperature

difference. Electric resistance heaters are installed in the test building to maintain the desired

temperatures. The building's own heating system is turned off. The electric heater power in the test

building is measured under the quasi-steady-state condition to extract the building loss coefficient.

The building loss coefficient has both a conduction component and an infiltration component. To

separate these components, a tracer gas test is conducted using the same temperature difference as in

the coheating test. In the tracer gas test an inert, nontoxic gas, sulfur hexafluoride, is introduced into

the test building until it is well mixed with the air in the unit. A gas chromatograph or an infrared

specific vapor analyzer measures the decay in gas concentration over time to extract the air exchange

rate, which is used to derive the conduction and infiltration components.

Some weatherization (thermal) improvements affect delivered heat efficiency as well as the building

heat loss. Therefore, a third test is conducted in which the building's own heating system is used to

maintain the conditions of the coheating test. We define the ratio of the electric heater power to the

furnace fuel and fan energy as the delivered heat efficiency for a given temperature difference.

With these three tests, the changes in conduction, infiltration, and delivered heat efficiency caused by

any single thermal improvement, or by a given combination of thermal improvements, can be

determined rapidly as follows.

A mobile home is moved into the warehouse and tested in its initial condition to determine the heat

losses from infiltration and conduction, and to determine the delivered heat efficiency of the furnace

and duct system. A single weatherization measure is then installed, and the testing is repeated to

determine the changes in conduction and infiltration losses and delivered heat efficiency caused by that

measure. This process is repeated until the individual effects of an entire set of weatherization measures

have been determined. The warehouse allows each measure to be tested under equivalent conditions.

Each test usually takes only one or two nights, so it has been possible to combine testing with

weatherization training workshops. The trainees install a measure one day and find out how effective

their work has been 12 to 36 hours later.

iv
TP-3629

To date SERI has tested five mobile homes using the warehouse technique. Figure 1 shows the building

heat loss coefficient associated with a series of weatherization measures installed on unit #1, a

12 ft x 60 ft 1971 Champion, which is typical of mobile homes treated in the federal low-income

weatherization program. The bottom and top portions of each bar represent the conduction and

infiltration portions of the heat loss, respectively. The installation of this weatherization package resulted

in a total reduction of 44% in the heat loss coefficient; the measures in the package were blowerdoor-directed air sealing, duct repair, furnace tune-up, interior storm panels, belly blow, and roof blow.

The belly wrap was removed before proceeding with the belly blow.

Figure 2 shows the overall reduction in heat loss coefficient for each weatherization measure in the

three mobile homes that were tested in the environmentally controlled warehouse.

Figure 3 shows the change in delivered heat efficiency caused by each weatherization measure installed

on mobile home #1. Sealing holes in the ducts. belly wrap, belly blow, and furnace tune-up all

increase the efficiency. The roof blow shows a decrease in efficiency. We hypothesize that this decrease

is because as the mobile home becomes better insulated the furnace becomes relatively oversized for

the load, and thus furnace cycling losses increase. The floor insulation measures more than compensate

for this effect by also insulating the heat distribution duct.

Figure 4 shows the overall increase in delivered heat efficiency for three of the mobile homes. Units

#2 and #3 showed larger efficiency increases than unit #1, primarily because they had larger leaks in

their duct systems.

Storms Belly Belly Roof

Wrap Blow Blow

26 26 25 24

326 292 291 230

352 318 316 254

35

362

397

96

362

458

Base Heat

Waste

Infiltration

Conduction

Total

UA (Btu/h F) 500 ,---------------------------,

400··· .

300

200

100

a

_ Conduction Infiltration

Total Reduction = 44.5% (204 Btu/h F)

Belly wrap removed before belly blow

Figure 1. Mobile HOOle #1: Measured VA Overall, Conduction and Infiltration

v
S-

="111[ :!!tl ·lall TP-3629

Btu/h F

Belly

Blow

Belly

Wrap

Roof

Blow

Roof

Cap

Heat

Waste

Storm

70 r-----------

60

50

40

30

20

10

o

Unit 1

Unit 2

Unit 3

45

24

37

61

43

55 25

62

47

34

25

36

46

_ Unit 1 fZ:Z} Unit 2 ffimI Unit 3

Figure 2. Mobile Homes #1, #2, and #3: Measured VA Savings, Conduction and Infiltration

UA(Tin-Tout)/(Qgas+Qelec) 0.1 ,..,..-------------------------------,

0.08

0.06

0.04

0.02

o

-0.02

-0.04

-0.06 L--_--l..- ..L-- ----1 --.1- -.l-- -'--_~

Seal

Ducts

Belly

Wrap

Belly

Blow

Roof

Blow

Furnace

Tune Up

All

Measures

0.03 0.04 0.01 -0.05 0.08 0.07

Figure 3. Mobile Home #1: Change in Furnace Efficiency due to Weatherization Measures

vi
TP-3629

Post-weath e11 minus Pre-weath etf

0.3 r------------------------,

0.25 - ······················..················1)':2"4··········· .

0.2 ---- - .

0.16 .

0.1 " -

0.06 ....

o

Champion

*1

E.fftdenc:y-Ocot:eQV{Cgaa+01an)

Central Detroltar

If'3

Figure 4. Mobile Homes #1, #2, and #3: Increase in Measured Combined Furnace and

Duct Efficiency

The information shown in Figures 1 through 4 is based on data directly measured in the controlled

warehouse environment. To project savings in the outside environment, we used SUNCODE, the

microcomputer version of SERlRES1 an hourly building energy analysis simulation program developed

at SERI (Palmiter et al. 1983). The program uses statistical weather data known as typical

meteorological years to model the thermal response of the building to weather and occupant behavior

hour by hour throughout the year. The weather inputs include temperature, wind speed. solar radiation,

and moisture. Occupant behavior inputs include thermostat control, window and door openings, use of

curtains, and use of appliances and lights. The data collected in the warehouse help us model the

mobile home and its associated weatherization measures more accurately by allowing us to calibrate

the model to the data.

Figure 5 is based on the results of the simulation model. It shows the simple and discounted payback

that might be expected for mobile home #1 in several locations, assuming local fuel costs. The analysis

is based on blower-door-directed air sealing and duct repair. furnace tune-up, interior storm panels, and

belly blow (the roof blow was included for the Denver location only). These four measures were

estimated to cost $1,162 in the Denver area (roof blow = $420). Costs will differ somewhat by locale.

To generalize these results to locations for which simulations had not been run, we investigated the

relationship between degree-days(base 65) (DD65) and energy savings from the four weatherization

measures installed on mobile home #1. Figure 6 demonstrates that the relationship is quite linear; it

can be represented by

SAVINGS(million Btu) = (DD65 X 0.0081) -0.2467 .

The points on Figure 6 represent some typical climates, from warmest to coldest: Memphis 1 Tenn.;

Denver, Colo.; Concord, N.H.; Madison. Wis.; and Fairbanks, Alaska.

vii
TP-3629

Years

10 -----------~------------..-~ -.-----..----------... -----------------.~--------- ...

8.4

MEMPHIS TN

$4.96

DENVER CO

$5.11

MADISON WI

$6.39

CONCORD NH FAIRBANKS AL

$~26 $~87

_ SIMPLE PAYBACK t222d DISCOUNTED PAYBACK

Roof blow only in Denver

Fuel cost in $/million Btu

Figure s. Mobile Home #1: Payback of Measures Package in Several Cities

Million Btu

4 6 8 10 12 14 16

Thousand, Degree Days

2

140 r--------------------------------,

120

100

80

60

40

20

O~----.L-------l-.--_.l....._______L ....L.... .L._______l...._______'

o

Unear Regression

RSQ=.996 St.Dev=2.71

Slope=.0081 Yint=-.2467

-- Regression Line Simulation Results

Figure 6. Energy Savings versus Degree Days (Base 65)

viii
TP-3629

The simple payback (PByrS> for any location can then be determined, given the degree-days, fuel cost

per million Btu ($FC), and retrofit cost ($RC), by

PByrs ::::; $RC/(O.0081 x 0065 x $FC) .

If we assume that the cost of the package of four retrofit options is $1,162, then we can generate

Figure 7, which allows graphic determination of the payback any place in the United States where

degree-day and fuel cost data are available.

Over the past two winters we tested these 10 weatherization measures:

• blower-door-directed air sealing and duct repair

• furnace tune-up

• interior storm panels

• window repairs and replacements

• belly blow (fiberglass and cellulose)

• belly wrap

• skirting

• roof blow (fiberglass and cellulose)

• roof cap

• wall insulation

In general, we find the most cost-effective measures for colder climates to be blower-door-directed

air sealing and duct repair, furnace tune-up, interior storm panels, belly blow, and roof blow. The roof

blow may result in moisture damage if used in humid climates, and it should probably be studied

further before being applied widely.

The blower door has shown itself to be an essential tool in weatherizing mobile homes. Not only

does it help crews tighten the units more effectively, it also prevents overtightening, which can be

especially dangerous in low-volume buildings.

Fuel Cost ($/million Btu)

F

Payback-ct yr

12 13 14 15 16

F=Fairbanks AK

M=Madison WI

D=Denver CO

T=Memphis TN

M

Payba k=1yr

6 7 8 9 10 11

DO X 1000 (base 65)

2 3 4 5

4

6

7

8

5

T

Payback>8yr

20 .----------------------------------,

18

16

14

12

10

8

6

4

2

OL.-_L-_..l....-..-_--L-_---L.-_~_.......l...__ ___L.__ __l__ __L_ _____.J.._ ___'__L___..l____.....L..__________J

1

Enter fuel cost ($/million Btu) & degree days

Package cost = $1,162

Figure 7. Simple Payback USA, Mobile Home Weatherization Package

ix
TP-3629

Our tests to date have shown skirting, insulated skirting, and roof caps to be less cost-effective.

However, more research is needed on those measures. Our research also indicates that window and door

replacements should be used only when repair would be more expensive than replacement. Even for

jalousie and awning windows, money is better spent on interior storm panels than on window

replacement.

Finally, the research indicates that cost-effective energy savings are possible if we apply weatherization

measures adapted to the unique construction details in mobile homes.

The study by Meridian Corporation established that application of traditional weatherization techniques

in mobile homes had resulted in average energy savings of only 5% per home at a cost of more than

$1,000. A growing number of states are beginning to improve on this by applying the techniques

suggested here for cold climate weatherization. Through proper training and testing, an agency can

easily increase the average heating energy savings to about 20% to 50% at the same cost per home.

Agencies wanting to quantify the effectiveness of their current mobile home weatherization practices

should consider using these testing techniques to improve their programs.

References

Meridian Corporation. (August 1988). Weatherization Evaluation Findings: A Comparative Analysis

(Draft). Alexandria, VA: Meridian Corporation.

Palmiter, L. S.: Wheeling. T.; Judkoff, R.; Wortman, D. N.; Simms, D. A.; O'Doherty, R. J.

(June 1983). SERf-RES: Solar Energy Research Institute Residential Energy Simulator Version 1.0.

Argonne, IL: National Energy Software Center. Argonne National Laboratory.

x
- II Ii ..::.-s- - ~"'~

TABLE OF CONTENTS

TP-3629

1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1

1.2

1.3

Background .

Objective .

General Teclmical Approach .

1

2

3

2.0 Methodology . 4

2.1

2.2

2.3

2.4

2.5

Test Facility .

Mobile Home Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description of Weatherization Measures .

Test Method .

2.4.1 Instrumentation, Data Acquisition, and Control .

2.4.2 Measurement of Air Leakage .

2.4.3 Electric Heating Tests .

2.4.4 Heating System Efficiency Tests .

Data Analysis .

4

4

5

6

8

8

9

9

10

3.0 Test Results . 12

3.1

3.2

3.3

3.4

3.5

Infiltration Test Results .

Electric Heating Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Delivered Heat Efficiency Test Results ..

Special Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Test Results Summary: Mobile Homes #1, #2, #3 .

12

13

13

15

16

4.0 Generalization of Measured Results for Other Climates . 19

4.1

4.2

4.3

4.4

Calculated Building Conductance .

Computer Simulation of Performance: Mobile Home #1 . . . . . . . . . . . .

4.2.1 Infiltration .

4.2.2 Heating, Cooling, and Ventilation Control Strategies .

4.2.3 Calculating the Natural Ventilation Capacity .

4.2.4 Internal Gains .

4.2.5 Orientation and Windows .

Simulation Results .

Retrofit Economics .

19

25

25

25

26

26

26

26

27

5.0 Mobile Home Retrofit Analysis Tool . 33

5.1

5.2

Description .

The Mobile Home Tool's Analysis Method . . . . . . . . . . . . . . . . . . . .

5.2.1 Mobile Home Load Coefficient .

5.2.2 Mobile Home Heating Energy Load .

33

34

34

34

6.0

7.0

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References .

37

38

Appendix A - Audit Summary: Mobile Homes #1, #2, #3 40

Appendix B - The Weatherization Measures . . . . . . . . . . . 41

xi
LIST OF FIGURES

TP-3629

2.1.

2.2.

3.1.

3.2.

3.3.

3.4.

3.5.

3.6.

3.7.

3.8.

4.1.

4.2.

4.3.

4.4.

4.5.

4.6.

4.7.

4.8.

Environmentally Controlled Warehouse used in Weatherization Experiments ....

Mobile Home #1: Measured VA Values, Quasi Steady State (0:00-7:00) .

Mobile Home #1: Measured VA Overall, Conduction and Infiltration .

Mobile Home #1: Reduction in Measured VA due to Weatherization Measures

Mobile Home #1: Change in Delivered Heat Efficiency due to Weatherization

Measures .

Mobile Home #1: Variations on Window Savings . . . . . . . . . . . . . . . . . . . .

Mobile Homes #1, #2, and #3: Initial and Final UA Overall .

Mobile Homes #1, #2, and #3: Measured VA Savings, Conduction and

Infiltration .

Mobile Homes #1. #2, and #3: Measured UA Savings Percentage, Conduction and

Infiltration .

Mobile Homes #1, #2, and #3: Increase in Measured Delivered Heat

Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mobile Home #1: Heating Energy Use in Denver .

Mobile Home #1: Heating Energy Use in Madison .

Mobile Home # 1: Purchased Energy Savings, Denver and Madison . . . . . . . . .

Mobile Home #1: Retrofit Payback, Denver . . . . . . . . . . . . . . . . . . . . . . ..

Mobile Home #1: Retrofit Payback, Madison . . . . . . . . . . . . . . . . . . . . ...

Mobile Home #1: Retrofit Payback, Memphis

Mobile Home #1: Retrofit Payback, Fairbanks

Mobile Home #1: Retrofit Payback, Concord .

xii

4

7

14

14

15

16

17

17

18

18

27

28

28

30

30

31

31

32
- ~ .;o:;~ -- '{I"

~~~,

LIST OF TABLES

TP-3629

2.1

2.2

3.1

3.2

4.1

4.2

4.3

5.1

5.2

Mobile Home Description .

Weatherization Measures Implemented .

Infiltration Summary for Mobile Home #1 .

Electric Coheating Summary for Mobile Home #1 .

Material Conductance Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ASHRAE VA Calculation - Mobile Home #1 Base Condition

ASHRAE VA Calculation - Mobile Home #1 Final Condition

Simple Model Calculation .

Simple Model versus SUNCODE Analysis .

xiii

5

6

12

13

20

21

23

35

36
TP-3629

1.0 INTRODUCTION

Between 3 million and 5 million mobile homes built before the U.S. Department of Housing and Urban

Development (HUD) enacted thermal standards in 1976 (U.S. Department of Commerce 1983~ Quick

Facts 1980, 1985) are in use in the United States today. These homes consume from 1.25 to 2 times

the energy per square foot of comparable conventional single-family detached houses. Currently,

weatherization services spend about $1,000 to $1,500 retrofitting each of these units. However, very

little information exists on the effectiveness of retrofit measures in mobile homes. Most weatherization

services and programs freely admit a need for additional knowledge about retrofitting mobile homes.

Many weatherization services simply apply those measures considered cost-effective in site-built

housing. This is usually ineffective because the construction details in manufactured buildings are quite

different from those in site-builts. With a potential national cost of approximately $5 billion to

weatherize qualifying units, the U.S. Department of Energy (DOE) is supporting a research effort to

evaluate and further improve the effectiveness of weatherizing mobile homes.

1.1 Background

In 1979, the Solar Energy Research Institute (SERI) was asked by DOE to manage its Manufactured

Buildings Program. Through this program, SERI gained considerable experience working with the

manufactured buildings industry, which produces new mobile homes.

In 1985, SERI began studying weatherization problems related to mobile homes constructed before

1976, when the HUD thermal standards went into effect. This was under the auspices of the DOE

Building Energy Retrofit Research Program. The findings from that effort were used by DOE for

multiyear planning (Dekeiffer and Edwards 1985). The multiyear plan identified three areas of research

that related specifically to mobile homes built before 1976:

• Option-specific monitoring to ascertain the contribution of retrofit measures being used or considered

for use in weatherization delivery programs

• Evaluation of new materials and retrofit techniques

• Evaluation of innovative energy equipment options.

The work described in this report concentrated on the first area, which had been deemed of highest

priority by state and local weatherization field organizations.

SERI began the project, which came to be known as the CMFERT (Collaborative Manufactured

Buildings Facility for Energy Research and Training) project, in 1987 by informally surveying state and

local weatherization agencies, subcontractors, and suppliers to determine what retrofit measures were

commonly being used on qualifying mobile homes. Most weatherization programs were emphasizing

retrofit measures intended to reduce infiltration (called "general heat waste" by many weatherization

services). The air-sealing strategies were essentially identical to those used for conventional, site-built

houses, i.e., caulking and weatherstripping around doors, windows, and joints. A few weatherization

programs had tried or considered using retrofit procedures specially adapted to the construction details

common in mobile homes. These included floor, wall, and roof insulating techniques and improved airleakage reduction methods. The weatherization services expressed a need for hard data on the thermal

effectiveness of these various retrofit options. Based on the results of this survey, SERI designed a

research program to focus on infiltration-reducing retrofits in 1987 and conduction-reducing retrofits

starting in 1988.

For the infiltration portion of the project, SERI collaborated with Sunpower Consumer Association, a

nonprofit cooperative with an excellent reputation in Colorado for conducting furnace tune-up and

"House-Nurse" programs. The Westside Energy Association, which provides weatherization services to

Denver County, paid Sunpower to retrofit 20 mobile home units in accordance with Colorado Division
TP-3629

of Housing guidelines. SERI collected data on the 20 units, which included a complete physical

description of the mobile home units; blower door test results taken before, during, and after installation

of the retrofits; and complete retrofit cost data.

Sunpower completed its work in April 1987, and SERI then analyzed the data. The results from that

study were documented in Mobile Home Weatherization Measures: A Study of Their Effectiveness

(Judkoff et a1. 1988). Major conclusions from that project were the following.

• The primary infiltration sites are different in mobile homes than in site-built residences.

• Primary leakage sites were

- heating ducts

- furnace closets

- envelope penetrations for ducts, flues, plumbing, wiring, and vents

- water heater closets

- broken windows and operator mechanisms

- swamp cooler chases (for units having these evaporative coolers).

• Air-sealing weatherization measures typically used for site-built houses are ineffective in mobile

homes.

• A blower door is an excellent tool for locating infiltration sites, and an essential tool to prevent

overtightening of these low-volume buildings.

• The average reduction in infiltration rate was about 40%, resulting in about 15% heating energy

savings in the Denver climate.

In late 1987, SERI began working on measuring the effect of conduction-reducing weatherization

options. A short-term monitoring technique was developed that involved moving a mobile home into

a warehouse and maintaining quasi-steady-state conditions for the test (Judkoff et a1. 1988). Heater

power in the mobile home was measured, as was the temperature difference between the mobile home

and the warehouse, to extract the effective overall conductance of the unit. Theory indicated that this

could be done on consecutive single nights of testing, with the different weatherization measures

installed during the daytime. Two series of tests were conducted to try the method. The first was done

in Jackson, Wyo., in conjunction with a Wyoming State Weatherization Workshop. The second set of

tests was done in Glenwood Springs, Colo., in conjunction with the Colorado Division of Housing's

Weatherization Program and Colorado Mountain College. The test results suggested several improvements to the technique, including

• tighter control of warehouse environment

• greater warehouse-to-mobile-home temperature difference

• longer testing period (12-36 h) instead of 8-12 h.

In the summer of 1988, a warehouse near SERI was instrumented and modified to incorporate these

improvements. Three mobile homes were tested during the winter of 1988-1989. Two of the three

were tested in conjunction with a weatherization training workshop held in April 1989.

1.2 Objective

The primary objective of this research was to directly monitor the effect of individual weatherization

measures on infiltration losses, conduction losses, and furnace and duct-delivered heat efficiency. The

purpose was to provide weatherization services with thermal data on the measures so that costeffectiveness could also be determined, A secondary objective was to combine testing and training to

provide feedback to trainers on the effectiveness of various measures and installation techniques.

2
S -- ' I ·C_CII "'- l><.), - .l\!_!r

1.3 General Technical Approach

TP-3629

Our general approach involves a combination of direct measurement and calculational models. The

direct measurements taken in the warehouse under controlled, repeatable conditions allow us to calibrate

our models of the mobile homes and the weatherization measures. We can then use these models to

simulate the energy use of the mobile homes and the savings associated with each weatherization

option in any climate for which hourly typical meteorological year (TMY) weather data exist.

An alternative method for determining the energy impact of the retrofits would have been to use the

Princeton Scorekeeping Method (PRISM) to analyze utility bill data from occupied homes (Fels,

Reynolds, and Stram 1986). This kind of testing seems to be attractive because the conditions are

completely realistic. However, this approach would have required a much larger sample size (preferably

about 100 per retrofit) and several years to establish the baseline performance of the units, install the

weatherization measures, and track post-weatherization energy performance. The large sample size

would have been necessary because new tenants, lifestyle, or operational changes can strongly affect

the energy performance of the units, thereby masking the effects of the retrofits. In the PRISM type

of testing, the measured results apply only to the climate or climates where the testing was done. If

we wished to extrapolate the results to other climates we would have had, again, to rely on

calculational models.

Our warehouse format allows application of classic, controlled experimental techniques where all conditions are held constant while only one parameter is changed at a time, a technique very different

from statistically based approaches such as PRISM. We judged that a short-term, highly controlled

testing approach had several advantages. First, testing could be accomplished in days rather than years.

Second, the warehouse allowed close inspection of the appropriateness of a given weatherization

measure for the special construction details in mobile homes. This enabled us to better understand the

energy flows in the homes, and thus to better adapt the weatherization measures to the construction

type. Third, we could use the warehouse to train weatherization personnel.

The approach used here, a combination of short-term direct measurements and modeling, was designed

to be accurate in measuring energy differences. Because our primary interest is the energy savings from

various retrofit options, we believe that the approach is the most cost-effective for evaluating individual

measures and improving mobile home weatherization techniques. However, this approach cannot account

for the effect of individual human behavior patterns. In this sense, our results are analogous to an

Environmental Protection Agency gas mileage test. They indicate the savings owing to weatherization

measures under a set of assumed standard operating conditions. As such they are more indicative of

the overall efficiency of the "fleet" than of a given home with given occupants.

More details on the monitoring technique are provided in Section 2.0 of this report.

3
TP-3629

2.0 METHODOLOGY

2.1 Test Facility

Because a mobile home can be easily moved, it is a particularly good candidate for testing in an

environmentally controlled chamber. For our purposes, an insulated warehouse with an adequate heating

system is a sufficient environmental chamber. Figure 2.1 is a photograph of the warehouse used in

these experiments. The warehouse has approximately 5000 ft2 of floor area and a ceiling height of

24 ft. It has no windows and is reasonably well insulated, with approximately R-I0 walls and R-5 roof.

One overhead door. 18 ft wide x 14 ft high, is large enough to accommodate almost any mobile home.

The warehouse is heated with two gas-fired unit heaters suspended from the ceiling. No cooling

equipment is available, so some restrictions on temperature control in the facility are unavoidable and

tests can be conducted only during the winter months. The testing season lasts for about 5 months in

the Denver climate. Additional features of the site include adequate outdoor space for storing or testing

one or two mobile homes and an adjacent building with classroom facilities.

2.2 Mobile Home Description

In accordance with this study's goals, the mobile homes selected for analysis were built before the 1976

HUD thermal standards. Three mobile homes were tested: (1) a 1971 Champion, 12 ft x 60 ft; (2) a

1972 Central, 14 ft x 53 ft: and (3) a 1974 Detroiter, 14 ft x 65 ft.

Figure 2.1. Environmentally Controlled Warehouse used in Weatherization Experiments

4
TP-3629

The most extensive tests were conducted on mobile home #1. It was tested and retested in each

weatherization condition, providing many data sets for evaluation. Mobile homes #2 and #3 were

weatherized during a weatherization workshop held in April 1989. Thus, although mobile homes #2

and #3 were tested repeatedly in their initial and final conditions, they were tested only once or twice

per retrofit during the 5-day workshop. Also, the delivered heat efficiency could be tested only before

and after the workshop because of insufficient time between installation of measures during the

workshop.

These homes were selected for testing because their construction characteristics represented typical pre1976 units. For more information concerning the defmition of a typical unit, refer to Mobile Home

Weatherization Measures: A Study of Their Effectiveness (Judkoff et al. 1988).

A brief description of the mobile homes is given in Table 2.1. The conduction and infiltration values

are for the homes in their initial preweatherization condition. The dimensions listed are interior

measurements. More detailed construction characteristics are given in Appendix A.

Table 2.1 Mobile Home Description

#1 #2 #3

Cond UA (Btu/h OF) 362 327 358

ELA-Clliladian (in.2

) 330 418 688

Inside length (ft) 56.6 49 61

Inside width (ft) 11.2 13.5 13

Wall insulation (R-value) 8.0 4.8 4.8

Roof insulation (R-value) 4.8 4.8 6.4

Floor insulation (R-value) 4.8 4.8 6.4

Furnace type downdraft downdraft downdraft

Cold air return closet closet belly

2.3 Description of Weatherization Measures

The three mobile homes were tested in their initial condition and after the implementation of retrofits.

Quantifying the thermal condition of the home before and after installation of a weatherization measure

permits thermal evaluation of the retrofit by a simple subtractive approach. A brief description of each

weatherization measure investigated in this study is given below. For detailed descriptions of the

retrofits, see Appendix B.

General Heat Waste is the implementation of general infiltration-reducing measures. These measures

generally differ from the infiltration-reducing measures performed on site-built houses. For this reason

it is strongly recommended that a blower door be used during infiltration reduction work on mobile

homes. The blower door permits quick identification of leakage sites and helps avoid overtightening.

Air tightening for mobile homes includes sealing holes in ducts, sealing around plumbing and electrical

penetrations, installing ludwig clips on loose awning and jalousie primary windows, tightening the wall

between the water heater closet and the unit, filling gaps around combustion air intakes and flues,

repairing kitchen and vent fan dampers, sealing swamp cooler chases, and tightening doors.

Furnace Tune-Up includes cleaning the blower, replacing the filter, adjusting or replacing fan switches,

adjusting the thermostat anticipator, clearing duct blockages, and performing basic health and safety

checks.

5
TP-3629

Storms is installing. storm windows on the inside of existing windows. An interior installation is

recommended because it cuts an infiltration path passing through the wall cavity and window frame.

An exterior storm panel will not interrupt this infiltration path.

Belly Wrap involves wrapping the underside of the mobile home with 6-in. batts of vinyl-backed

fiberglass insulation. A wire grid system attached to the rim joists of the mobile home provides support

for the batts. Field conditions may prohibit this retrofit because it requires full access to the underside

of the mobile home. This retrofit should not be performed on mobile homes that will be moved. Longterm durability of this retrofit is currently unknown, but it is considered doubtful.

Belly Insulation is blowing insulation into the area between the underside of the floor and the rodent

barrier. This area is often called the belly cavity. The effectiveness of this retrofit depends on the

depth of the cavity.

Roof Insulation involves blowing insulation into the bow-string truss area of the mobile home. This

can be done from inside or outside the home. The effectiveness of this retrofit depends on the depth

of the cavity. This retrofit is currently recommended only in mobile homes located in dry climates. In

humid climates this retrofit may exacerbate moisture buildup in the ceiling because of condensation

from the underside of the metal roof. Further research is needed to determine under what conditions

this will actually occur.

Roof Cap is installing rigid-board roofing insulation on top of the existing roof. The rigid-board

insulation is then covered with a continuous and seamless elastomeric membrane such as Hypalon or

EPDM. This retrofit requires that the existing plumbing, heating, and exhaust vents be extended above

the new roof level. This method of roof insulation will not cause moisture problems; however, it is

expensive.

Table 2.2 shows which retrofits were performed on which mobile homes.

Table 2.2 Weatherization Measures Implemented

Mobile Home

Retrofit #1 #2' #3

. General heat waste X X X

Furnace tune-up X X X

Storms X X X

Belly wrap X X

Belly blow X X

Roof blow X X X

Roof cap X

2.4 Test Method

The objective of our tests on mobile homes is to determine the effectiveness of certain weatherization

measures. To do this, total thermal losses from a mobile home are carefully measured both before and

after a particular weatherization measure is applied. Because the tests are done under carefully

controlled environmental conditions, changes in the total loss coefficient as little as about 5% can be

adequately measured. Figure 2.2, a plot of measured building load coefficient (VA) versus time,

indicates excellent repeatability. Although field test methods are available (pels, Reynolds, and Stram

6
TP-3629

UA (BtUlhr F)

............................................................................................

_..............................................................................................................................

_...............................................-...................... ~: .................................. ........ a .......

..

_.............................................................................................................................. - - - .... ...... .......... ................ ~.- ............... ... ........ ......... y

- -

f-............................................................................................................................. _

IL

, 7 "7

400

320

280

240

0:00 1:00 2:00 3:00 4:00 6:00 6:00 7:00

BaM

-+- Belly Wrap

--- Heat Wale -s-- Storm.

-.9r- Belly Blow --- Roof Blow

Figure 2.2. Mobile Home #1: Measured VA Values, Quasi Steady Steady State (O:()()~7:00)

1986; Lee and Hadley 1988; Subbarao 1988), a test of this type is thought to be essential for

evaluating individual weatherization measures that produce changes of 10% or less. In addition, the test

results are expected to provide enough information to estimate weatherization performance for a wide

range of real environmental conditions. To accomplish this, four experimental procedures are required:

steady-state electric heating to determine total heat loss, tracer gas infiltration measurement to separate

infiltration heat flow from conduction heat flow, blower door measurement of equivalent leakage area

for use in extrapolation models, and calorimetric measurement of heating system efficiency.

The building thermal load coefficient (BLC) is the essential parameter that is measured during the

steady-state test. The BLC is defined by

where

Q = energy required to maintain inside temperature

Tin = mobile home average air temperature

Tout = warehouse average air temperature.

For the purposes of the present work, thermal losses from a building are considered to be caused by

two different mechanisms that should be measured separately. These are conduction losses through

the shell of the building and infiltration losses caused by air exchange between the mobile home and

the warehouse. The thermal conduction occurs because of the difference in temperature between the

inside and outside environments. Air flow through cracks in a building is caused by pressure differences

between the inside and outside that, in turn, can be caused by both wind and temperature differences.

The heat flow caused by infiltration occurs because the inside air and outside air are at different

temperatures. However, it is not entirely straightforward to determine heat flow for a given air flow

because some of the heat can be "recovered" as air flows through cracks, depending on the characteristics of the cracks (Claridge and Bhattacharyya 1989). The main reason for separately measuring

7
TP-3629

conduction and infiltration is that they must be treated differently when using a simulation or other

simplified model to predict the effects of the weatherizaton measures under a wide range of climatic

conditions.

2.4.1 Instrumentation, Data Acquisition, and Control

The steady-state heat loss tests performed on the mobile homes are fundamentally simple in concept,

and the measurements required are not particularly complex. However, care must be taken in making

these measurements because accuracy is also required.

The principal data acquisition and control hardware includes a Keithley Series 500 motherboard with

a lti-bit analog-to-digital converter, 48 channels of analog inputs with thermocouple compensation

available, and 32 channels of digital input/output. The Keithley system is connected to and controlled

by an IBM-cornpatible personal computer with an 80286 processor and a 20-megabyte hard disk. A

relatively simple program written in BASIC samples the sensors, processes the data to convert to

engineering units, stores data, and controls the heaters that maintain temperatures in the mobile home

and the warehouse. Data from the analog inputs are processed and stored every 30 s. The instrument

reading for each channel is sampled 20 times and averaged to minimize the effects of electromagnetic

noise. Hourly average values of important quantities are printed on paper as well as stored

electronically.

Temperature and electric power are the principal quantities measured in these experiments. To measure

the BLC, air temperatures inside and outside the mobile home are measured, and the energy required

to maintain the inside temperature is measured. All temperatures are measured using type T thermocouples. Multiple-point measurements are made inside and outside to sample the vertical and horizontal

distribution and to obtain an average bulk temperature. Each temperature sensor is placed in a concentric cylinder of relatively low emissivity material to shield the sensor from radiative exchange with

the surfaces of the mobile homes and the warehouse. Temperatures of the inside surfaces of the warehouse are also measured so that radiative exchange with the mobile home can be calculated, and the

BLC results can be corrected if necessary.

Electric power is measured with a Hall-effect watt transducer mounted at the breaker panel of each

mobile home. The accuracy of this instrument is approximately 0.5%.

2.4.2 Measurement of Air Leakage

Two different measurements are made of the infiltration characteristics of each building. A blower

door (Sherman and Grimsrud 1980) is used to measure the equivalent leakage area (ELA) of cracks

in the mobile home, and a tracer gas test measures the air infiltration rate during a steady-state test.

The ELA is used in a mathematical model (Shennan and Modera 1986) to predict air leakage under

various weather conditions. The results of the tracer gas test are used to partition the total heat loss

into conduction and infiltration components.

The blower door used in all our mobile home tests is manufactured by the Minneapolis Blower Door

Company, and the computer programs used to process the data were written at SERI (Judkoff 1988).

At least two blower door tests were done for each retrofit measure of the mobile home, and the results

of each two tests were compared. If the results did not agree to within less than 5%, more tests were

done until this criterion was met. The conditions inside the warehouse are particularly favorable for

blower door testing because there is no wind.

Tracer gas tests used sulfur hexafluoride (SF6) as the tracer, and tracer concentrations were measured

with either a Sentex Scentograph gas chromatograph, with a 60/80 molecular sieve column and an

electron capture detector, or a Foxboro Miran 101 infrared specific vapor analyzer. SF6 was injected

into the air inside the mobile home and allowed to mix for about 15 min. The decay in SF6

concentration was measured over a period of about 1 h, and the air flow rate was calculated as follows:

8
1_' *

V(dc/dt) = F, - QlCl

C = CC-CQ/Y)l l 1

QN = I

where

C, == initial concentration for each interval

C,= concentration at time (t)

Q = volumetric flow rate (ff/h)

V = volume of mobile home (fr')

t = time (h)

Ft = tracer gas injection rate at time (t): this term is 0 for decay method

dc/dt = time rate of change of concentration (h-l)

TP-3629

The sample period is relatively short because mobile home air is being exchanged with warehouse

air (not outside air as in a normal tracer test) so even though the warehouse volume is about 20 times

greater than the volume of a mobile home, warehouse air might eventually become significantly

contaminated. The contamination problem can be minimized by alternately sampling the mobile home

and the warehouse tracer concentration. However, a computer-controlled alternate sampling device

would have to be built and tested. Tracer gas tests are only begun after thermal steady-state conditions

have been reached; therefore, a short sample period does not appear to be a limitation because

infiltration should be a constant under these conditions.

2.4.3 Electric Heating Tests

Portable electric convective heaters are placed inside the mobile home and controlled by the data

acquisition computer to maintain a constant average temperature. The readings of the nine interior

thermocouples are averaged and compared to a programmed set-point temperature. Typically, only one

of the three or four heaters is controlled, and the others are on constantly. An attempt is made to

distribute the heaters so that all parts of the home are heated to a uniform temperature in the horizontal

direction. A vertical temperature stratification of approximately 5°P is typically observed during electric

heating. Excellent control of the interior temperature can normally be achieved with hourly variances

of less than O.02°F observed.

2.4.4 Heating System Efficiency Tests

Combustion efficiency of furnaces can be measured relatively simply in the field as a diagnostic test;

however, this test alone does not provide adequate information for estimating actual energy requirements

of mobile homes. The efficiency of the entire heating system, including heat losses from distribution

ducts, must be measured to obtain useful estimates of annual energy savings. This measurement can

be made with relative ease for steady-state conditions inside the warehouse. The mobile home furnace,

controlled by its normal thermostat, is operated to maintain a constant temperature, and the warehouse

temperature is also controlled to be constant. This test is best performed at temperatures close to those

used for measuring the BLC so that the radiative environment and infiltration conditions will be the

same. Gas consumption of the furnace is measured by recording the length of time the gas valve is

open. Heating system efficiency can then be calculated as follows:

efficiency = BLC x (Tin - TouJ/(Qgas + QrarJ '

where

Qgas = energy content of natural gas consumed

Qfm = electrical energy consumed by distribution fan.

9
TP-3629

where

The test provides a measure of the net change in system efficiency because of installation of a

particular weatherization retrofit, but it does not determine the cause of the change within the heating

system.

The heating system efficiency is typically measured after each weatherization measure has been

installed. Some measures such as repair of leaky ducts are intended to directly reduce duct losses.

Other measures such as insulation of the belly are primarily intended to reduce conduction through

the shell but also will usually reduce conduction losses from the ducts to the outside and may reduce

air leakage in the ducts. Sometimes changes in heating system efficiency are observed when

weatherization measures such as roof insulation are installed that appear to be completely unrelated to

the furnace or ducts. The explanation for this appears to be that because the total heating requirement

is reduced, the existing furnace becomes relatively more oversized and thus less efficient because of

cycling losses. Although this effect seems obscure, it is important to recognize that the furnace, ducts,

and thermostat interact with the rest of the building in complex ways, and that a whole system test is

the most reliable way to determine the effect.

2.5 Data Analysis

To determine whether steady-state BLC values have been achieved, average heating energy required,

mobile home air temperature, and warehouse air temperature are calculated for each hour. Each quantity

must be constant within strict limits for several hours before data are accepted as steady state. In a

typical test, the air temperatures reach their set points rather quickly, but the heat flow required to

maintain the internal temperature requires several more hours to reach steady state as the massive

elements of the structure reach their final temperatures. Because outside ambient temperatures are most

constant between midnight and 6 a.m., the steady-state period usually occurs then. Daytime tests are

not usually possible, especially on sunny days, because the balance-point temperature of the warehouse

rises above the ambient temperature. Thus, the warehouse temperature becomes too wann for testing

and also uncontrollable because there is no cooling system. The test hours selected exhibit a maximum

difference of less than ±1% for at least 4 to 6 h. Data for all other test hours are discarded. A tracer

gas infiltration measurement must also be made during the steady-state period.

The total BLC is calculated for the above steady-state data as

BLCtotal = Qtow!(Tin - Tou~ •

The tracer gas measurement is used to calculate the heat flow caused by infiltration:

Qinf = mCiTin - TouJ '

Qinf =infiltration heat flow

m = mass flow rate of air leakage

Cp = heat capacity of air.

Then the so-called conduction portion of the total BLC can be calculated by subtracting infiltration

from the total:

The most accurate comparisons between different weatherization measures are achieved if the temperatures in both tests are exactly the same. It is also important that the difference between the mobile

home and warehouse air temperatures is the same to provide the best comparability for infiltration.

Several options are available for checking the consistency of repeated tests. For each mobile home,

repeated tests were done under essentially identical conditions. These tests demonstrated that essentially

identical results could be achieved for the repeated tests. For some retrofit measures, such as general

heat waste. only the infiltration part of the total BLe was changed, and the calculated conduction value

is expected to remain constant. Essentially this is a thermal measurement of the change in infiltration

10
TP-3629

heat flow, which can be compared to the tracer gas measurement. There is also the potential for

measuring the infiltration heat recovery effect using this method; however, this was not pursued because

of time constraints.

Another consistency check is possible because storm windows can be easily removed and reinstalled

in combination with each of the other weatherization measures. Results indicate that applying storm

windows to what amounts to different base cases produces results that can differ by 20%, or about

6 Btu/h. The results are inconclusive as to whether the difference is caused by interactions with

different base cases or is an indication of the expected uncertainty in the measurement. However, in

a second test where storm windows were applied to the mobile home in its initial condition and then

in its final condition, the difference was only 3 Btu/h. This implies that the differences are due to

measurement uncertainty rather than order dependence. Discussion of the complete results follows in

Section 3.0.

Additional information on the monitoring methods is available in Judkoff et al. (1988).

11
TP-3629

3.0 TEST RESULTS

Three mobile homes were tested in a controlled environment to determine the effectiveness of

implemented retrofits. The tests performed, described in detail in Section 2.0, led to the collection of

data needed to quantify retrofit effectiveness. The test results for mobile home #1 are presented in

detail, and a summary of the results for the three mobile homes is given.

3.1 Infiltration Test Results

Blower door and tracer gas tests were performed to quantify the air infiltration rate. The tracer gas

tests were performed to directly measure the air changes per hour (ACH) occurring during the electric

coheating tests. The electric coheating test measures the combined losses caused by infiltration and

shell conduction. Performing the tracer gas test permitted these two separate heat transfer paths to be

quantified.

The tracer gas test measures ACH over the test period. The testing data do not supply information

about what infiltration rate would occur if the mobile home is placed in a different environment. To

obtain this type of data, a blower door test is conducted. A blower door test measures the ELA in

the building for a particular pressure difference. Models have been developed that use this measured

ELA value to determine the ACH that would occur under different climatic conditions (Shennan and

Modera 1986).

Table 3.1 summarizes the measured infiltration data for mobile home #1. Tracer gas and blower door

tests were performed on the mobile home for six different weatherization measures. From the blower

door tests, the average measured ELA Canadian at 10 pa for each measure is listed. The tracer gas

tests measured ACH occurring during the electric coheating tests. The ACH measurement needs to

be taken with the same temperature difference that was maintained under the coheat test so that

accurate VA conduction values can be determined.

As shown in the table, the infiltration VA for the base case varies slightly from the value calculated

from the tracer gas test. The infiltration VA for the base case was determined by using the conduction

VA value established for the heat waste retrofit. This conduction VA value was subtracted from the

measured overall VA for the base case to find the infiltration VA for the base case. The conduction

VA of the heat waste case is the same as the base case because the heat waste retrofit changes only

infiltration. Although the VA conduction determined from the base case could have been used for the

two cases, it was believed that the VA conduction determined from the heat waste case was more

accurate. This is assumed because the heat waste condition has a smaller infiltration component

resulting in less error in the tracer gas measurement and higher confidence in the determination of the

conduction VA.

Table 3.1 Infiltration Summary for Mobile Home #1

Tracer Gas Test Infiltration

Weatherization ELA Delta T ACH VA VA

Measure Canadian eF) (Btu/h OF) (Btu/h OF)

Base 330 32.0 1.24 91 96

Heat waste 178 38.0 0.51 35 35

Storms 145 37.6 0.38 26 26

Belly wrap 145 38.6 0.35 24 26

Belly blow 142 37.7 0.34 23 24

Roof blow 133 38.5 0.35 24 24

12
TP-3629

3.2 Electric Heating Test Results

The electric heating tests were performed to determine an overall BLe for the mobile home in each

weatherization condition. The BLC includes the effects of conduction and infiltration. Subtracting the

infiltration VA component from the BLC gives the conduction component.

Table 3.2 summarizes the measured coheating test data for mobile home #1. Figures 3.1 and 3.2 present

the coheating test results in graphic form, The second and third columns in Table 3.2 are the mobile

home-warehouse temperature difference and the measured BLC from the electric heating tests. Values

are given for the mobile home with the six different weatherization measures.

In the second set of columns, the BLC values are separated into their infiltration and conduction

components. The conduction component is found by subtracting the infiltration VA from the BLC.

The last column in Table 3.2 lists the actual conduction UA used in the evaluation of the retrofit.

The measured VA conduction for storms differs slightly from the assumed VA conduction value for

storms. This adjustment was made to reflect the measured results of other tests involving storm

installation on mobile home #1. These tests are not based on the mobile home in the general heat

waste condition with and without storrns but rather on the mobile home in the belly wrap condition

with stonns and without storms, The effect storms had on the mobile home in the belly wrap conditon

resulted in a change in UA conduction of 33 Btu/h OF compared to a change of 39 Btu/h OF for the

general heat waste condition. Based on these two different tests, an average reduction in conduction

VA of 36 Btu/h OF was assumed.

Although the difference between the two measurements is relatively small, the possibility of an

implementation order dependence on retrofit effectiveness exists. To investigate the matter, storm

window effectiveness was evaluated for mobile home #3 in two different weatherization stages. With

mobile home #3 in its initial condition, storms were found to decrease the BLC by 37 Btu!h "F. With

mobile home #3 in its final weatherization condition, the decrease was measured to be 40 Btu/h OF.

These test results show that the decrease in storm effectiveness measured in mobile home #1 was not

repeatable in mobile home #3. Therefore, the two tests do not support order dependence, because the

differences were from larger to smaller for home #1, and smaller to larger for home #3.

Based on the implementation of four retrofits--heat waste, storms, belly blow, and roof blow-the

BLC for mobile home #1 was reduced from 458 Btu/h OF to 254 Btu/h OF, a reduction of 44.5%. For

a breakdown of the reduction in the BLC for each retrofit, see Figure 3.2.

Table 3.2 Electric Coheating Summary for Mobile Home #1

Weatherization

Measure

Electric Heating Test

Delta T BLC

COP) (Btu/h OF)

Test

VA Inftl UA Cond

Actual

Conduction

UA

Base

Heat waste

Storms

Belly wrap

Belly blow

Roof blow

38.4

38.1

37.7

37.3

39.2

38.0

458

397

349

318

316

254

96

35

26

26

25

24

362

362

323

292

291

230

362

362

327

292

291

230

3.3 Delivered Heat Efficiency Test Results

Besides reducing air infiltration rate and shell conduction, retrofits may also affect the delivered heat

efficiency. Changing the delivered heat efficiency affects the energy that must be purchased to meet

the building load.

13
TP-3629

UA (Btulhr F)

400

300

200

100

o

Infiltration 98

Conduction 382

Total 458

He..t Storm. Betl)' Bell)' Roof

Wale Wrap Blow Blow

35 28 28 25 24

382 327 292 291 230

397 353 318 318 254

_ Conduction Infiltration

Total ReduCClon - 44.5% (204 btuhl F)

BeUy·wrap removed before bell)' blown

Figure 3.1. Mobile Home #1: Measured UA Overall, Conduction and Infiltration

Change In UA (Stulhr F) 250 ---=-----..;;.---..:...------------,

..................................................................................................

....................................................................................................

..............................................................- .

60

100

160

200

0

He Bell)' Roof All ..t Starma BeUy

Wale Wrap Blow Blow Mea.urea

Total 81 44 35 37 82 204

Infiltration 81 9 0 1 1 72

Conduction 0 36 35 38 81 132

_ Conduction Inflltrallon

Figure 3.2. Mobile Home #1: Reduction in Measured VA due to Weatherization Measures

14
-- 11_"

.~

TP-3629

Figure 3.3 shows the change in efficiency resulting from the retrofits. The delivered heat efficiency

appears to decrease when the roof blow retrofit is implemented. Yet, realistically, the roof blow

retrofit has no effect on the heating ducts or the furnace settings. A possible explanation for the

decrease in efficiency is the heat load decrease. As the heat load gets smaller, the furnace becomes

more oversized, and cycling efficiency decreases. Therefore, although it appears that the roof blow

is causing a decrease in delivered heat efficiency, it is really a result of all the retrofits causing a

decrease in the heating load. The six retrofits implemented on mobile home #1 and the furnace tuneup produced a net increase of 7% in delivered heat efficiency. Had there been no loss in cycling

efficiency, then the gross increase would have been at least 12%. This suggests that developing a

procedure for downsizing the furnace may be worthwhile.

3.4 Special Studies

Besides testing the effectiveness of the six retrofits, the study also investigated variations on retrofit

implementation. Mobile home #1 was tested to evaluate the effect of tightening primary windows with

and without storms installed. Leaky primary windows were simulated by placing a 16-penny nail

between the window glass and the metal window frame. Electric coheating tests were conducted, and

the effective BLC evaluated for the following conditions: (1) leaky primary windows, (2) tight primary

windows, (3) tight primary windows with storms, and (4) loose primary windows with storms. The

results of the study are presented in Figure 3.4. In the figure, the change in the measured BLC is

presented for three cases. The tight primes case is the change in the BLC resulting from tightening the

primary windows (removing the nails and installing ludwig clips). The tight primes with storms case

is the change in the BLC resulting from storms being added to the tight primary windows. The loose

primes with storms case is the change in the BLC resulting from the primary windows' becoming leaky

(ludwig clips removed and nails in place) with the storm still in place. With stack-driven infiltration

it appears that the tightness of the primary windows has little effect on the load coefficient when

UA(Tln-Tout)l(Ogas+Oelee) 0.1 ,...--....:.-----:..-------------------,

0.08 .

0.08 , .

0.04

0.02

o

-0.02 .

-0.04 .

-0.06 1...----L -L.-__-.1- oL....-__--'- ""'-----'

Heat

Waate

Batly

Wrap

Belly

Blow

Roof Furnace All

Blow Tune Up Measure.

0.03 0.04 0.01 -0.06 0.08 0.07

Figure 3.3. Mobile Home #1: Change in Delivered Heat Efficiency due to Weatherization

Measures

15
TP-3629

50 .C_h_an_g_8_'n_B_L_C....;:(_Bt_Ul_h_r_F..;.> ----.

40 .

30 .

20 ......l77"~,..,.,..,.,..,__

10 ......

20 o

Figure 3.4. Mobile Home #1: Variations on Window Savings

storms are in place. Therefore, it is not recommended that expensive repairs to tighten primary

windows be made if storm windows are installed. Further work under typical wind conditions is

necessary to fully support this recommendation.

3.5 Test Results Summary - Mobile Homes #1, #2, #3

The same tests conducted on mobile home #1 were also completed for mobile homes #2 and #3 except

that in homes #2 and #3, delivered heat efficiency tests were performed only under the initial and final

conditions. Figure 3.5 presents the measured VA overall for the three mobile homes in their initial

and final conditions.

The testing for mobile homes #2 and #3 was conducted during a 2-week period in April, and the

testing for mobile home # 1 was conducted from December through March. Because of the wanner

temperatures in April, the testing of mobile homes #2 and #3 was conducted with a 28°P temperature

difference, in comparison to the 38°F temperature difference maintained during the testing of mobile

home #1. The test temperature difference affects the infiltration VA. Therefore, a direct comparison

between each home's infiltration VA and overall VA should not be made.

Figure 3.6 shows the measured change in the overall VA that resulted from implementing a retrofit.

Variations within the retrofit measured savings can be attributed to many factors. Much of the

difference is a result of the heat transfer areas associated with the retrofit being different from home

to home. Also, for the retrofits involving insulation blown into a cavity, the blown insulation density,

consistency, and cavity depth also have an effect on the measured savings. Figure 3.7 shows the

measured savings in VA resulting from the retrofits as a percentage of the initial overall VA.

The measured change in delivered heat efficiency varied significantly in mobile homes #2 and #3 from

that measured in mobile home #1. Figure 3.8 presents the measured change in efficiency experienced

in each mobile home. As shown in the figure, mobile homes #2 and #3 both experienced large

improvements in furnace efficiency. Both of these mobile homes had very large holes in their duct

systems initially. Mobile home #3 also had a below-floor return air system. Repair of these items

resulted in the vast improvements in delivered heat efficiency.

16
(Btulhr F)

600.--------------

400

300

200

100

0

MBH.l MBH.1 MBH.2 MBH'112 MBH .3 MBH If3

sa.. Final sa•• Final Ba.. Final

lnflhratlon 98 24 72 18 117 42

Conduction 362 230 313 209 340 273

TotaJ 458 254 385 225 457 315

_ Conduction Inflhratlon

Figure 3.5. Mobile Homes #1, #2, and #3: Initial and Final UA Overall

BTU'h F

70 ,..-----------------------,

80 .

_ Unit 1

Storm H.at

Wale

60

40

30

20

10

o

Unh 1

Unh2

Unit 3

44

24

37

81

43

55

Roof Roof Belly Belly

Cap Blow Wrap Blow

82 35 38

47 48

25 25

Unit 2 wm Unh3

Figure 3.6. Mobile Homes #1, #2, and #3: Measured UA Savings, Conduction and Infiltration

17
TP-3629

% savings 14 ,.---....;;......--------------------.

_ Unit 1

Ihorm He.t

W.te

12

10

8

8

2

o

Unh 1

Unit 2

Unh3

0.8

8.2

8.1

13.3

11.1

12

Roof Roo' Belly Belly

Oap Blow Wrap Blow

13.6 7.4 7.0

12.2 11.0

5.5 5.5

~Unh2 511 Unh 3

Figure 3.7. Mobile Homes #1, #2, and #3: Measured VA Savings Percentage,

Conduction and Infiltration

Post-weath ef1 minus Pre-weath e11

0.3 ,.------------------------,

0.26 •··..·..··..····..···..···········0..214···········..·..

0.2 .

0.15 .

0,,1 .

0.06 ....

o

Champion

111

Efftciency-Qcoheatl(Qgaa+Cfan)

Central Detrolter

tl'3

Figure 3.8. Mobile Homes #1, #2, and #3: Increase in Measured Delivered

Heat Efficiency

18
TP-3629

4.0 GENERALIZATION OF MEASURED RESULTS FOR

OTHER CLIMATES

From the mobile home tests, the effect of the retrofits on the BLC and air infiltration rate was

measured. To determine the cost-effectiveness of the retrofits, these data must be translated into

expected energy savings in various climates. This analysis was completed using the test data collected

for mobile home #1, because these were thought to be the most reliable data of the three mobile homes

tested. An explanation of the analysis process for determining energy use from infiltration rate and

building conductance is given below.

The infiltration rates measured with tracer gas during the electric coheating tests were not the same

rates that would be experienced with the mobile home placed in the real environment. Unfortunately,

there is no direct way to extrapolate tracer gas results to different environmental conditions. Therefore,

we used the Lawrence Berkeley Laboratory (LBL) infiltration model (Sherman and Madera 1986),

which, given leakage area as measured with a blower door, and crack distribution, can predict infiltration rates for any location for which long-term temperature and wind data are available. Once infiltration rate is determined, the energy associated with air infiltration is simply the heat needed to warm

the incoming air from the outdoor temperature to the indoor temperature.

The building conductance is the heat transfer coefficient of the mobile home envelope. The energy

associated with the conduction losses can be estimated by multiplying the building conduction load

coefficient by the indoor-outdoor temperature difference. This simplified calculation does not account

for internal gains generated within the home, solar gains, and thermal capacitance of the building. To

accurately calculate the change in the heating load associated with implementing a retrofit, a more

detailed analysis was done. To achieve this, a computer simulation program was used to model the

dynamic thermal response of a mobile home. The program uses hourly weather data depicting a typical

meteorological year for a specified location. Heat flows within the building are calculated for each

hour in the year, and the heating and cooling loads for the building are determined.

4.1 Calculated Building Conductance

The thermal model of the mobile home in the computer program is based on the collected audit data

for mobile home #1 and the thermal characteristics of the construction materials. To ensure that the

model accurately represents the measured building conduction UA, the building conduction UA was

calculated and compared to the measured VA conduction determined from the infiltration and electric

coheating tests. In calculating the building conductance, standard methods outlined in the 1985

ASHRAE Handbook of Fundamentals (ASHRAE 1985) were used.

In performing the audit calculations, some uncertainty exists as to the exact values to use for material

properties and for some dimensions of materials such as insulation thickness. To obtain the best

comparison of measured and predicted heat flows for all conditions of the mobile home, an iterative

process of adjusting the audit parameters was used. The best judgment of the auditor led to an initial

audit description that was within about 5% of the measured heat loss coefficient for the base case

condition. However, as measured changes were compared to calculated changes for the various retrofits,

it was apparent that the initial audit probably contained offsetting errors. Changes were made in the

audit description to best reconcile the results of the entire series of tests. These changes are not

arbitrary and capricious but are made to reasonably represent the expected uncertainty in material

properties and dimensions. The validity of this method of extrapolating results depends to a significant

extent on obtaining a good estimate of the initial condition for each component (walls, floor, etc.).

Therefore it was worth making this effort to get the best possible estimate of the initial state of the

mobile home.

The audit observations led the initial American Society of Heating, Refrigerating, and Air-Conditioning

Engineers (ASHRAE) calculation to a close match with the measured UA of mobile home #1 in its

base condition. For the base condition, the calculation anticipated that the VA conduction value would

19
TP-3629

be 381 Btu/h of; the measured value was 362 Btu/h of. By changing the wall insulation R-value

from 6.4 to 7.8, the discrepancy was eliminated. This adjustment was well within the uncertainty in

measuring the wall insulation thickness and the uncertainty in R-value per inch reported by ASHRAE.

Comparing the measured changes in the VA conduction with the anticipated changes based on the

calculation resulted in a few other adjustments to the heat transfer calculation. These adjustments are

discussed below.

An additional heat transfer path was added to the floor and to the roof. The heat flows through the

perimeter of the floor cavity and the roof cavity were added to the ASHRAE conductance analysis.

This resulted in a better correlation with the measured data. The fmal heat transfer model used to

represent the mobile home in its six weatherization conditions agreed with the measured data. That

is, the model's calculated ASHRAE conduction values were the same as the conduction values measured in the study. The material R-values used in the ASHRAE conduction calculation are listed in

Table 4.1. Conduction calculations characterizing the mobile home in its initial and final conditions

are given in Table 4.2 and 4.3.

Comparing the ASHRAE heat transfer calculated value with the measured coefficient resulted in some

interesting observations. The belly wrap and the belly blow retrofits performed less well than expected,

and the roof blow performed better than expected.

Table 4.1 Material Conductance Values

Material

carpet thin

carpet thick

foam rubber

linoleum

mineral fiberboard

metal window

metal window w/storm

wood stud 2

wood stud 3

wood joist 5

wood panel

particleboard

fiberglass blanket 10

fiberglass blanket 15

fiberglass blanket 25

fiberglass batt 60

fiberglass blown 4.25

fiberglass blown 4.5

fiberglass blown 10

Thickness

(in.)

0.13

0.50

0.25

0.50

1.62

2.62

4.62

0.25

0.63

1.00

1.50

2.45

4.25

4.25

3.00

3.50

11K

(h ft2 °F/Btu in.)

2.46

2.46

5.00

2.64

1.23

1.23

1.23

1.23

1.06

3.20

3.20

3.20

3.20

3.86

3.50

3.50

0.31

1.23

1.25

0.05

1.32

1.35

2.22

1.99

3.22

5.68

0.31

0.66

3.20

4.80

7.84

13.60

16.41

10.50

12.25

air film coefficients

horizontal-flow down

horizontal-flow up

vertical-flow horizontal

surface coefficients

3.5 horizontal down

3.5 horizontal up

1.5 horizontal up

0.75 horizontal down

20

0.92

0.61

0.68

1.15

0.91

0.83

1.02
S=~II.1 TP-3629

Table 4.2 ASHRAE VA Calculation - Mobile Home #1 Base Condition

ROOF (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4

air film-hor up 0.61 0.61 0.61 0.68

fiberglass blnkt 1" 3.20

truss/joist 16"OC 7.07 2.76

fiberglass blown 0 0 0

air space >4" hor up

film coef-hor up 0.61

film coef-hor up 0.61

air space - hor up 0.91 0.83

mineral fiberbrd 0.5" 1.32 1.32 1.32 1.32

air film-hor up 0.61 0.61 0.61 0.61

R-path 9.61 6.21 6.96 3.44

Area 38.92 38.92 544.88 22.00

VA-path 4.05 6.27 78.29 6.40

VAtot 95.00

WALLS (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4

air film-vert hor 0.68 0.68

metal window 1.35

metal window w/storm 2.22

stud 2"x3" 3.22

fiberglass blnkt 2.5" 7.84

paneling 1/4" 0.31 0.31

air film-vert hor 0.68 0.68

R-path 4.89 9.51 1.35 2.22

Area 109.63 767.38 125.00 0.00

VA-path 22.42 80.71 92.59 0.00

VAtot 195.72

21
S=~II_I TP-3629

Table 4.2 ASH RAE VA Calculation - Mobile Home #1 Base Condition

(Concluded)

FLOOR (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4 Path 5

air film-hor down 0.92 0.92 0.92 0.92 0.92

carpet 0.54 0.54 0.54 0.54 0.54

particle board 5/8" 0.66 0.66 0.66 0.66 0.66

air space 0.75" 1.02 1.02

joist 2"x5" 5.68 5.68 1.99

air space> 4"

film coef-hor dwn 0.92 0.92 0.92 0.92

film coef-hor dwn 0.92 0.92 0.92

fiberglass blnkt 1.5" 4.80 4.80 4.80

fiberglass added 0 0 0 0 0

rodent barrier 1/16"

air film - hor down 0.92 0.92 0.92 0.92

air film - vert 0.68

R-path 9.74 9.68 16.38 9.68 5.71

Area 25.02 225.18 37.25 335.27 51.21

VA-path 2.57 23.27 2.27 34.64 8.97

UAtot 71.72

Total MBH

UAcond 362.4

22
S=~II'II TP-3629

Table 4.3 ASHRAE VA Calculation - Mobile Home #1 Final Condition

ROOF (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4

air film-hor up 0.61 0.61 0.61 0.68

fiberglass blnkt 1" 3.20

truss/joist l6"OC 7.07 2.76

fiberglass blown 13.51 16.405 3.86

air space >4" hor up

film coef-hor up 0

film coef-hor up 0

air space - hor up 0 0

mineral fiberbrd .5" 1.32 1.32 1.32 1.32

air film-hor up 0.61 0.61 0.61 0.61

R-path 9.61 18.81 22.15 6.47

Area 38.92 38.92 544.88 22.00

VA-path 4.05 2.07 24.61 3.40

DAtot 34.12

WALLS (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4

air film-vert hor 0.68 0.68

metal window 1.35

metal window w/storm 2.22

stud 2"x3" 3.22

fiberglass blnkt 2.5" 7.84

paneling 1/4" 0.31 0.31

air film-vert hor 0.68 0.68

R-path 4.89 9.51 1.35 2.22

Area 109.63 767.38 0.00 125.00

VA-path 22.42 80.71 0.00 56.31

VAtot 159.44

23
S-~I_ TP-3629 -- II I,

,~-~/

Table 4.3 ASHRAE UA Calculation' - Mobile Home #1 Final Condition

(Concluded)

FLOOR (ASHRAE heat transfer coefficient calculation)

R-Values Path 1 Path 2 Path 3 Path 4 Path 5

air film-hor down 0.92 0.92 0.92 0.92 0.92

carpet 0.54 0.54 0.54 0.54 0.54

particle board 5/8" 0.66 0.66 0.66 0.66 0.66

air space 0.75" 1.02 1.02

joist 2"x5" 5.68 5.68 1.99

air space > 4"

film coef-hor dwn 0 0 0 0

film coef-hor dwn 0 0 0

fiberglass blnkt 1.5" 4.80 4.80 4.80

fiberglass added 0 10.5 12.25 12.25 7.875

rodent barrier 1/16"

air film - hor down 0.92 0.92 0.92 0.92

air film - vert 0.68

R-path 9.74 18.34 26.79 20.09 12.67

Area 25.02 225.18 37.25 335.27 51.21

UA-path 2.57 12.28 1.39 16.69 4.04

UAtot 36.97

Total MBR

UAcond 230.5

The belly wrap retrofit consists of suspending 6-in. fiberglass batts against the underside of the mobile

home. The added R-value for this retrofit is 19.2, but the measured effect the insulation had on the

mobile home was equivalent to adding an R-value of 13.6. It was observed that the batts were not

properly in place against the belly. When the belly wrap, wire grid, and insulation were dropped from

mobile home #1, it was seen that in some places the batts overlapped, and in other places there were

gaps where no insulation was present. The irregularity of the batt covering is a result of the difficulty

in installing this retrofit.

The belly blow and roof blow retrofits involve blowing insulation into the belly and roof cavities. It

is difficult to accurately calculate savings for any retrofit using blown insulation because it is difficult

to determine the density and uniformity of blown insulation. The blown insulation density affects the

insulation's R-value per inch, which, of course, affects the retrofit's effectiveness. Also in blown

insulation installations, it is difficult to determine if the cavity has been completely filled. For this

study, the lower than expected performance of the belly blow retrofit was attributed to the pan cavity's

not being completely filled. It was anticipated that mobile home #1 's pan cavity would be filled with

8.5 in. of insulation, and the wing cavity filled with 3 in. of insulation. Yet, assuming the insulation

was blown at the manufacturer's recommended density with an R-value of 3.5jin., there was effectively 3.5 in. of insulation in the pan and 3 in. of insulation in the wings. Thus, the performance of

the belly blow retrofit would have been better if the pan cavity had been completely filled with

insulation.

For the roof blow retrofit, observations led to the opposite conclusion as for the belly blow retrofit

During the roof blow installation, the force from the blowing insulation actually pushed the roof up

to increase the depth of the roof cavity. This retrofit was expected to add an R-14.9 to the roof,

assuming the blown insulation R-value/in. is 3.5 and the average roof cavity is 4.25 in. The measured

24
TP-3629

results reveal that an R-16,4 was added to the roof. This is equivalent to adding 4.75 in. of insulation

to the roof cavity.

4.2 Computer Simulation of Performance: Mobile Home #1

The computer simulation used to determine the thermal performance of the retrofits was SUNCODE

(palmiter, Wheeling, and DeLaHunt 1981). SUNCODE, the PC version of SERIRES, is a detailed

dynamic thermal analysis program using time steps of less than 1 h (Palmiter et al. 1983). The

mathematical representation of the building is a thermal network with nonlinear temperature-dependent

controls. The mathematical solution techniques used in the program include forward finite differencing,

Jacobian iteration, and constrained optimization.

All building energy simulation programs require certain input data for characterizing the thermal

behavior of the building. For mobile home #1, the heat flow paths and the materials' R-values defined

in the ASHRAE UA calculation and based on the measured results were modeled in the SUNCODE

program. Each of the six weatherization conditions of mobile home #1 were evaluated: base, heat

waste, storms, belly wrap, belly blow, and roof blow. The input data reflect the results of the mobile

home testing.

Other program inputs reflect assumptions about the behavior of the mobile home occupants (i.e.,

operating thermostats, and opening and closing windows). For these types of inputs, commonly accepted

references were used to defme average behavior (Pels, Rachlin, and Socolow 1986; Krieder 1982). The

assumptions used in creating the SUNCODE input file are presented below. A copy of the input files

is available on request.

4.2.1 Infiltration

The equivalent and effective leakage areas (ELA-Canadian and ELA-LBL) were determined before and

after each implemented retrofit. The ELA values are calculated from data collected from the blower

door tests. These two measures are similiar in that they represent the equivalent amount of open area

that would have the same air flow as the actual leakage area. The main difference between them is

that the ELA-LBL assumes that the equivalent open area has a rounded edge, and ELA-Canadian

assumes a sharp edge. Also, the reference pressure difference for ELA-LBL is 4 pa, and for ELACanadian it is 10 pa.

An infiltration model developed by Shennan and Grimsrud (1986) was used to determine the climatedependent air infiltration rates from the measured ELA-LBL values. Average air infiltration rates were

determined for each month for each weatherization condition of the mobile home. To use the model,

the values of the ELA-LBL, the monthly average wind speed, the monthly average indoor-outdoor

temperature difference, and the relative location of the measured leakage areas must be known. The

climate variables are easily obtained from TMY weather data, but there is no direct practical method

for determining crack distribution. We used the method described by Judkoff et al. (1988) to define

the crack distribution for each case. This analysis was completed for each climatic location in which

SUNCODE was run. The monthly infiltration values calculated using the model were used as input to

the SUNCODE program.

4.2.2 Heating, Cooling, and Ventilation Control Strategies

The control strategies and schedules developed for heating, cooling, and ventilation were designed to

reflect normal occupant behavior in controlling comfort conditions. The heating and cooling set points

were assumed to be 69°F (20.5°C) and 79°F (26°C), respectively, as recommended by ASHRAE

(1985).

Many occupants will open windows under overheated conditions. However, no consistent pattern has

been determined to characterize this behavior. To assume that windows were never opened would

25
/._;;;~

-- II II.~-~

TP-3629

show unjustifiably large savings for some retrofits. Therefore, assumptions were made concerning this

effect.

To simulate the occupants' opening and closing the windows, the ventilation set point was scheduled

seasonally. In September and October, and March through May, it was assumed that the occupants

would open the windows when the indoor temperature equaled or exceeded 75°F. In November through

February, it was assumed that occupants would open windows if the indoor temperature equaled or

exceeded 79°F. In June through August, it was assumed that occupants would open the windows if

the indoor temperature equaled or exceeded 71°F. These assumptions are conservative in the sense that

failure to adhere to this strategy would result in greater heating savings.

4.2.3 Calculating the Natural Ventilation Capacity

The capacity for natural ventilation is limited by the available open window area, indoor-outdoor

temperature difference, and wind speed and direction. Several different techniques for calculating this

effect exist. One of the more detailed methods was developed by Aynsley, Vickery, and Melbourne

(1977), and one of the more simplified approaches was developed by Olgyay (1963). In previous work

Judkoff (1981) demonstrated close agreement between these two methods for simple building

geometries. Thus, the simplified method of calculation was used to determine monthly average natural

ventilation from window openings in the different analysis locations. The equation used is

ACH = 60 x E x A x V ,

where

E = factor-dependent inlet area to outlet area ratio

A = inlet window area (ft2)

V =onsite wind velocity normal to the open face (mph)

ACH = ventilation capacity per hour.

For the calculation it was assumed that half the window area was available for ventilation. Half this

area carried air flowing in and half carried air flowing out. The yearly average ventilation rate was

used in the SUNCODE input file.

4.2.4 Internal Gains

Internal gains are heat contributions to a space from such activities as cooking, hot water use,

appliances, and lighting. Internal gains occurring in the winter contribute to heating the unit. The

amount of internal gains used in the mobile home model are 2400 Btu/h. This gain is based on the

average daily nonheating energy consumption for homes in the Denver area (Fels, Rachlin, and Scolow

1986) and is considered realistic for mobile homes in other areas.

4.2.5 Orientation and Windows

In the SUNCODE program, the orientation of the mobile home was specified such that one short wall

faced 45° from south. Thus, one long wall was also 45° from south. The window areas were set

equal on each long wall and each short wall. The total window area still equaled the window area

measured in mobile home #1. These specifications were made to eliminate the bias in retrofit savings

that could result from variation in solar orientation. (If there is a choice of orientation, however, it is

recommended that the maximum window area be toward the south in heating-dominated climates.)

4.3 Simulation Results

The SUNCODE simulations were run for the mobile home in five different climates. The selected

climates were Denver, Colo.; Madison, Wis.; Memphis, Tenn,; Fairbanks, Alaska; and Concord, N.H.

The simulation outputs state the yearly heating load for the mobile home in the different weatherization

26
'•.~~'. - II II

- TP-3629

conditions. The roof blow condition was analyzed only for Denver because more research is needed

to determine if this retrofit will cause ceiling moisture problems in morc humid climates.

The amount of fuel needed to heat the home can be found by dividing the heating load by the

measured delivered heat efficiency. Figures 4.1 and 4.2 present load data for the mobile home in

Denver and Madison. The tables in the figures report the determined loads, furnace efficiencies, and

calculated purchased energy requirements.

Figure 4.3 presents the purchased energy savings caused by the implementation of retrofits in Denver

and Madison. In comparing the results, it is helpful to know that Denver has 6545 degree days and

total horizontal solar radiation equaling 581,000 Btu/tt2

, and Madison has 7572 degree days and total

horizontal solar radiation equaling 434,000 Btu/ft2. The total purchased energy savings for Denver

excluding the belly wrap retrofit is 57 million Btu/yr. representing a 58% reduction in energy use. The

total purchased energy savings for Madison excluding the belly wrap and the roof blow retrofits is

65 million Btu/yr, representing a 47% reduction in energy use.

4.4 Retrofit Economics i

The simple and discounted payback periods were calculated for the retrofits in the five different

locations. The belly wrap retrofit was not considered in this economic analysis. The durability of the

belly wrap retrofit needs to be investigated further before its implementation is recommended.

Purchased Energy (MMBtulyear) 120 r--------..,;;..;;.....;-----'--~---.....,

20

0

Baae Heat Slorma Belly Belly Roof Tune

Waate Wrap Blow Blow Up

Purchased Energy 98.5 79.7 67.7 58.6 58.4 46.7 41.7

Heating Efficiency 0.68 0.71 0.71 0.75 0.72 0.67 0.75

Heat Load 67 58.8 48.1 42.5 42.1 31.3 31.3

_ Purchased Energy

Figure 4.1. Mobile Home #1: Heating Energy Use in Denver

27
S=~II'.I' TP-3629

Purchased Energy (MMBtulyear) 1eo ,.-------..;;.;;..-.;....--....:....._~ .....

140 .

120

100

80

eo

40

20

o

BaH Heat Stofnw Belly Belly Tune

Waate Wrap Blow Up

Purchased Energy 138.8 109.4 92.8 78.9 81.2 74

Heating EffJciency 0.88 0.71 0.71 0.76 0.72 0.79 Heat Load 94.4 77.7 86.9 69.2 68.6 68.6

_ Purchased Energy

Figure 4.2. Mobile Home #1: Heating Energy Use in Madison

;.M::B:::t::UI~y~e=ar=- .., as .

Denver Madison

6

16 ..

10 .

20

30 .

26 .

HeatW...

c:::J Belly Blow

8Iorrrw

E3 Root Blow

B88S Belly Wrap

OIl] F~naC8 Tun.

Figure 4.3. Mobile Home #1: Purchased Energy Savings, Denver and Madison

28
The simple payback is calculated by dividing the retrofit cost by its energy cost savings. The

discounted payback is a more complicated calculation, taking into consideration the time value of

money. Three economic factors are used in this calculation: the discount rate 0), the general inflation

rate (j), ~U1d the fuel inflation rate Ue). The discount rate is the interest rate or the expected fate of

return on a potential investment. IL'i upper limit is the cost of borrowing money, and its lower limit

is the foregone return on the homeowner's next best alternative investment. The general inflation rate

is used to calculate the real discount rate i', where

i' = (i - j)/(l + j) .

This formula modifies the discount rate with the inflation rate. The fuel inflation rate includes the

general inflation rate plus the anticipated energy rate increase beyondinflation. This rate is used

to calculate the inflation-adjusted discount rate for energy, i", where

i"= (i - je)/O + je) .

The discounted payback is the time required for the initial investment to equal the future energy

savings. This relationship is represented by

I .. I C N*Y 1 E S· *[CRF,i',Nl, nina ost = ear y nergy avmgs [CRF,i",N]

where N = years, CRF = the capital recovery factor, and CRF(i,N) = i/[l - (l + i)-N].

The retrofit costs assumed in the economic evaluation are listed below. They are based on figures

provided by the State of Colorado Weatherization Office.

Heat waste

Storms

Belly blow

Roof blow

Furnace tune-up

$200

$450

$400

$420

$112

The discounted and simple paybacks for the retrofits are presented for each of the five locations in

Figures 4.4 through 4.8.

The particular values for i, j, and je are those recommended by Kreider (1982). The calculated time

for payback is somewhat sensitive to the values chosen, and there is no consensus as to what values

are correct. However, the particular values of i, j, and je do not have any influence on the relative

paybacks among the various weatherization measures.

29
Years

10 r--------------------------,

8 .

TP-3629

Simple Discounted

B883 Belly Blow

[[l]]J All

Ga. OO.t "'5.11IMMBtu

DtllCOuntrate -.08 Inllallon r" -.07

FUIII 1ntI.llon rate -.13

Figure 4.4. Mobile Home #1: Retrofit Payback, Denver

Years 6,...:....:...:...:...::..-.---..---------------------,

6

3

2

o

Simple

HeatWaste

E3 FurnTuna

Stornw

OIID All

Discounted

Belly Blow

Gaa Cost c$6.39/MMBtu

Discount rate -.09 IntlaUon rate -.07

Fuel Inflation rate -.13

Figure 4.5. Mobile Home #1: Retrofit Payback, Madison

30
TP-3629

Years

I-......................... ........................................................ ........................., ............

1-- .............. ........................................................."'" .'" .............................

~,~

~,~

I-.•............~,~ .. -...................................................... -..........................

::-.:" ~,~

1- .............. ~,,," ........................ ~~ ...........................

"..... ~'" f- .............. ......................~'" t--.."'~ ..... r-..................... :--...."...... ~,

1- .............. ..................... .................. ..

l'............

ro" ....." ..........v/// ."..... .....

~"' 1"/"././/ro-..."............ '/././/l",

16

14

12

10

8

6

4

2

o

Simple Discounted

HeatWaste

E3 Fum Tune

Storms

lIIID All

gggj Bully Blow

Gas Cost ~$4.96JMMBtu

Discount rate -.09 Inflation rate -.07

Fuel Inflation rate ...13

Figure 4.6. Mobile Home #1: Retrofit Payback, Memphis

Years

2.5 r--------------------------.

..................... ~~

...........................................

2 f- ~~ ~~~........................................... ..............•......•..•..

I-.:~,,~,'#,~;<>Q'l

1.5 fSimple

.......... ......

Wj:r-.., ~l'-....""""'~

Discounted

E2Zd Heal Waste

FumTune

StormB

rrrrn All

Belly Blow

Fuel Coat -$7.87/MMBtu

Discount rate -.09 Inflation rate -.07

Fuel Inflation rate -.13

Figure 4.7. Mobile Home #1: Retrofit Payback, Fairbanks

31
TP-3629

Years

sr---------------------------.

4

3

II···························

o

Simple Discounted

HeatWasle

E3 Fum Tune

Storms

llII] AU

BellyBlow

Gas Cost -$7.261MMBtu

Discount rate •.09 Infladon rate •.07

Fuel Infladon rate ...13

Figure 4.8. Mobile Home #1: Retrofit Payback, Concord

32
TP-3629

5.0 MOBILE HOME RETROFIT ANALYSIS TOOL

5.1 Description

The retrofit energy savings predicted by the SUNCODE analysis arc valid for mobile homes that have

initial conditions identical to those of mobile home #1. To provide an analysis technique for mobile

homes with different initial conditions, the Mobile Home Retrofit Analysis Tool was developed.

The tool helps the user to determine the mobile home load coefficient from audit data. The computer

tool is designed to be used by state weatherization personnel or individual auditors. The analysis is

based on a particular mobile home's dimensions, construction materials, and location. The program

output is retrofit energy savings and payback periods.

The aim of the Mobile Home Retrofit Analysis Tool is to couple the calculation power of a personal

computer with the knowledge of experienced mobile home auditors. The program combines

conventional programming techniques with innovative expert system programming methods. Expert

system programming is quite different from conventional programming. Conventional programs involve

the processing of data by algorithms. Expert system programs are based on processing logical

statements. Experts' rules of thumb are encoded into the program. These rules are accessed during

the program execution and are used to help an inexperienced person solve a complicated problem.

In the case of the Mobile Home Retrofit Analysis Tool, the lessons learned from the mobile home

study and some rules of experienced auditors are contained in the program. This built-in guidance

helps the user to input accurate audit data. The program also provides helpful hints for the successful

implementation of recommended retrofits. Currently, the program serves to demonstrate the capabilities

of a knowledge-based mobile home audit tool. Further development needs to be completed before the

program can have widespread use.

The program comprises four major components, each addressing different aspects of mobile home

retrofit analysis. These four sections are (1) a presentation of the mobile home weatherization research

conducted at SERI, (2) a mobile home audit analysis, (3) an evaluation of the energy savings of six

mobile home retrofits, and (4) an economic evaluation of the six retrofits. A brief description of each

program component is given below.

The weatherization research conducted at SERI is presented in the program to provide background

information to the user. The research results are the basis for the analysis used in the program to

predict expected retrofit energy savings. Described in the program are SERI's mobile home

weatherization test procedures, the results of the tests, and a discussion of the mobile home retrofit

workshop held at the testing facility.

The mobile home audit analysis guides the user in the thermal characterization of the mobile home.

The goal of the audit is to deterimine the BLC for the mobile home in its present condition. The

program requires the user to enter structural and material data into the computer. The data may be

typed in or selected from a menu of possible responses. Based on the data and accepted methods of

calculating heat transfer coefficients, the conduction component of the BLC is determined. The

infiltration component of the load coefficient is determined from a one-point blower door measurement.

An average natural infiltration rate is calculated from air changes per hour measured at 50 pa and

a location-dependent factor (Meier 1986).

To evaluate the retrofit energy savings, the heating load is calculated for the mobile home in a

specified location. Although the calculation could be performed using SUNCODE or other simulation

programs, the program uses a simplified load model. A simulation program was not used to pcrfonn

the calculation because it would take too long to run. The simple model adapted from Mitchell (1983)

provides results instantaneously to the audit tool. The results from the simple model are comparable

to those predicted by SUNCODE. Comparison results are provided in Section 5.2.

33
";;; il<- -- II"

~-~'

TP-3629

The program evaluates the six mobile home retrofits: general heat waste, storm windows, insulation

wrapped around the belly, insulation blown into the belly cavity, insulation blown into the roof cavity,

and furnace tune-up. The evaluation is performed by determining the heating energy use of the mobile

home before and after retrofit implementation.

The economic evaluation section of the program translates the energy savings anticipated by the retrofit

analysis into dollar savings. Based on default or user-specified cost data and economic factors, the

simple payback and discounted payback are presented for each retrofit.

Currently, the program can determine retrofit savings for mobile homes in four different locations. In

order for the tool to analyze other locations, more weather data files must be made. Because the

temperature data used in the simple model are monthly averaged values, it is feasible to have many

locations available for analysis.

5.2 The Mobile Home Tool's Analysis Method

5.2.1 Mobile Home Load Coefficient

The mobile home tool uses accepted analysis methods to determine the BLC. The methods outlined

by ASHRAE and described in Section 4.0 were used to determine the conduction component of the

BLC. To determine the infiltration component, the results of a one-time blower door pressurization

test are used. The method is a refmement of Persily's 1982 infiltration research in which natural air

changes per hour were found by dividing the air changes at 50 pa by 20. Refmements to Persily's

method were made by Sherman to customize the formula to include factors correcting for different

climate conditions, stack effects, wind shielding, and crack characteristics (Meier 1986). The factor

values are derived from the most commonly accepted infiltration model used for estimating infiltration

rates (Shennan and Modera 1986).

5.2.2 Mobile Home Heating Energy Load

The simple load model used to determine the mobile home's heating energy load is a steady-state heat

loss analysis based on variable degree days. This method is described by Mitchell (1983). In the

method the building's energy loss is determined from the BLC and monthly heating degree days at a

particular base temperature. A sample calculation using the simple load model is given in Table 5.1.

The values listed are based on mobile home #1 in its initial condition located in Denver.

As shown in the table, the simple model predicts a yearly load of 62.4 million Btu for the mobile

home. The SUNCODE detailed simulation determined the load to be 67.0 million Btu. As can be

seen, the absolute load values from the two methods are quite close. The more important comparison

is the measured effect that retrofits have on the load. The simple model predicts a load decrease of

35.7 million Btu if all weatherization measures are implemented. SUNCODE sets this value at

34.6 million Btu.

The simple model results were compared to SUNCODE results for other locations. Table 5.2 lists

the locations and their respective loads. For Madison and Memphis the final weatherization condition

is after the general heat waste, storms, and belly blow retrofits have been implemented. For Denver,

the final weatherization condition is after the general heat waste, storms, belly blow, and roof blow

retrofits have been implemented.

Although the simple model does appear to underestimate the heating load for sunny climates, overall

it comes very close to matching the SUNCODE load. The simple model does succeed in accurately

determining energy savings from retrofit implementation. Therefore, the simple load model appears

to be an acceptable, abbreviated calculation method for determining retrofit energy savings in mobile

homes for the climates studied to date.

34
Table 5.1 Simple Model Calculation In

III

--U

-

•

I I:

Parameter Units Name Value ~--~

Temperature Data

Room temperature of Ted 69

Shell UA Data

Conduction VA Btu/h of VAshell 399.0

Infiltration VA Btu/h of VAinf 141.0

Total VA Btu/h of VAtotal 540.0

Annual Heat Loss Calculation Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

days in month days 31 28 31 30 31 30 31 31 30 31 30 31

monthly avg temp of Tm 29.0 30.9 38.4 48.8 57.3 64.7 72.8 70.1 62.3 49.1 38.3 30.7

VA shell Inf Btu/h OF VAt 540 540 540 540 540 540 540 540 540 540 540 540

daylength h hda 9 11 12 13 14 15 15 14 12 11 10 9

Windows an!a Insolation through Window (Btu/ttl day)

SW 45 884 851 919 835 813 799 791 835 950 979 809 840

SE 22 848 844 1035 946 914 868 916 926 998 1000 835 800

NW 22 161 247 412 535 659 719 662 566 443 291 186 139

NE 45 157 241 429 578 7W 762 741 599 452 289 184 136

U.)

Vl total window gain Btu/day Gwd 69023 73155 92442 96171 103610 105175 103629 97346 94784 85437 67141 74579

Btu/h Gwh 7343 6574 5899 5269 4861 4664 4728 5075 5612 6332 7116 7502

internal gain Btu/h Gl 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400

net day gain Btu/h Gtd 9743 8974 8299 7669 7261 7064 7128 7475 8012 8732 9516 9902 net night gain Btu/h Gtn 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400 2400

b. temp day OF Tbd 51 52 54 55 56 56 56 55 54 53 51 51

b. temp night OF 100 65 65 65 65 65 65 65 65 65 65 65 65

Degree day calculations

std dev 21.2 19.8 19.5 17.2 15.9 14.3 13.0 13.5 14.7 17.5 19.2 20.9

Hd 1.034 1.083 0.782 0348 -0.110 -0.614 -1.307 -1.l06 -0.552 0.214 0.682 0.955

Hn 1.675 1.697 1.344 0.915 0.456 -0.010 -0.634 -0.410 0.153 0.885 1.370 1.6i9

Fd 0.003 0.002 0.008 0.056 0.249 0.632 1.307 1.l07 0.575 0.096 0.013 0.004

Fn 0.000 0.000 0.001 0.005 0.036 0.196 0.650 0.454 0.120 0.005 0.001 0.000

DObd 682 603 4n 209 69 8 0 1 10 168 400 621

DDbn 1102 942 811 475 243 80 7 18 121 482 788 1050

Monthly Heat Loss

day Qd 3.46 3.42 3.01 1.48 0.53 0.06 0.00 0.01 0.07 0.99 2.09 3.09

night Qn 8.69 6.87 539 2.80 1.28 0.40 0.03 0.10 0.76 3.41 6.08 839

total Qtot 12.15 10.29 8.40 4.27 1.81 0.46 0.04 0.11 0.83 4.40 8.18 11.+8

Qtotyear 62.4

...,

""0I

U.)

0'\

tv

\0
S-~I. TP-3629 - II Ii - "=-~

Table 5.2 Simple Model versus SUNCODE Analysis

Load Denver Madison Memphis

(million Btu)

Initial

Simple 62.4 93.7 37.5

SUNCODE 67.0 94.4 38.6

Final

Simple 27.8 57.6 21.4

SUNCODE 31.3 58.5 22.7

Delta

Simple 34.6 36.1 16.1

SUNCODE 35.7 35.9 17.2

36
TP-3629

6.0 CONCLUSIONS

Over the past two winters we tested a number of weatherization measures, including the following:

• blower-door-directed air sealing and duct repair

• furnace tunc-ups

• interior storm panels

• window repairs and replacements

• bell y blow (fiberglass and cellulose)

• belly wrap

• skirting

• roof blow (fiberglass and cellulose)

• roof cap

• wall insulation.

In general for colder climates we fmd the most cost-effective measures to be blower-door-directed air

sealing and duct repair, furnace tune-up, interior storm panels, belly blow, and roof blow. The roof

blow may result in moisture damage if used in humid climates, and it should probably be studied

further before it is widely applied.

The blower door has shown itself to be an essential tool in the weatherization of mobile homes. Not

only does it help crews tighten the units more effectively, but it also prevents overtightening, which

can be especially dangerous in low-volume buildings.

Our tests to date have shown skirting, insulated skirting, and roof caps to be less cost-effective.

However, more research needs to be done on those measures. Our research also indicates that window

and door replacements should only be used when repair would be more expensive than replacement.

Even for jalousie and awning windows, money is better spent on interior storm panels than on window

replacement.

Finally, the research indicates that cost-effective energy savings are possible if we apply weatherization

measures adapted to the unique construction details in mobile homes.

37
TP-3629

7.0 REFERENCES

American Society of Heating, Refrigerating, and Air-Conditioning Engineers. (1985). ASHRAE

Handbook; 1985 Fundamentals. Atlanta, GA: American Society of Heating, Refrigerating, and AirConditioning Engineers.

Aynsley, R. M.; Vickery, B. J.; Melbourne, W. H. (1977). Architectural Aerodynamics. London:

Applied Science Publishers.

Claridge, D. E.; Bhattacharyya, S. (1989). "Measured Energy Impact of Infiltration in a Test Cell."

Solar Engineering 1989 - Proceedings of the Eleventh Annual ASME Solar Energy Conference; San

Diego, California; April 2-5, 1989. New York: American Society of Mechanical Engineers.

Dekeiffer, R.; Edwards, B. (November 1985). Mobile Home Retrofit (Draft). Golden, CO: Solar

Energy Research Institute.

Fels, M. F.; Reynolds, C. L.; Stram, D. O. (October 1986). PRISMonPC Version 4.0 Users Manual.

PU/CEES Report #213A. Princeton, NJ: Princeton University.

Fels, M. F.; Rachlin, 1.; Socolow, R. H. (1986). "Seasonality of Non-heating Consumption and Its

Effect on PRISM Results." Energy and Buildings; Vol. 9, pp. 139-148.

Judkoff, R. (May 1988). BLOWDOR Version 1.0 (SERI internal model).

Judkoff, R. (1981). "Physiological Cooling by Natural Ventilation." Passive/Hybrid Cooling in

Commercial Buildings; Proceedings of a Workshop presented at the Passive'81 6th National Passive

Solar Conference; Portland, Oregon; September 8-12, 1981. San Antonio, TX: Trinity University.

Judkoff, R.; Hancock, E.; Franconi, E.; Hanger, R.; Weiger, 1. (December 1988). Mobile Home

Weatherization Measures: A Study of Their Effectiveness. SERI/fR-254-3440. Golden, CO: Solar

Energy Research Institute.

Kreider, J. F. (1982). The Solar Heating Design Process. New York: McGraw Hill Book Company.

Lee, A. D.; Hadley, D. L. (October 1988). A Proposed Method for Improving Residential Heating

Energy Estimates Based on Billing Data. PNL-SA-15600. Richland, WA: Pacific Northwest

Laboratory.

Meier, A. (July/August 1986). "Infiltration: Just ACHso Divided by 20?" Energy Auditor &

Retrofiiter; pp. 16-19.

Mitchell, J. (1983). Energy Engineering. New York: John Wiley & Sons.

Olgyay, V. (1963). Design with Climate: Bioclimaiic Approach to Architectural Regionalism.

Princeton, NJ: Princeton University Press.

Palmiter, L. S.; Wheeling, T.; DeLaHunt, M. (1981). SUNCODE-PC Version 5.5. Seattle, WA:

Ecotope Inc.

Palmiter, L. S.; Wheeling, T.; Judkoff, R.; Wortman, D. N.; Simms, D. A.; O'Doherty, R. 1. (June

1983). SERI-RES: Solar Energy Research Institute Residential Energy Simulator Version 1.0. Argonne,

IL: National Energy Software Center, Argonne National Laboratory.

Quick Facts about the Manufactured Housing Industry. (1985). Arlington, VA: Manufactured Housing

Institute.

38
TP-3629

Quick Facts about the Manufactured Housing Industry. (1980). Arlington, VA: Manufactured Housing

Institute.

Sherman, M. H.; Grimsrud, D. T. (October 1980). Measurement of Infiltration Using Fan

Pressurization and Weather Data. LBL #10852. Berkeley, CA: Lawrence Berkeley Laboratory.

Sherman, M. H.; Modera, M. P. (1986). "Comparison of Measured and Predicted Infiltration Using

the LBL Infiltration Model." Measured Air Leakage of Buildings; Philadelphia, Pennsylvania; 2-3

April, 1984. Treschel, H. R. and Lagus, P. L., eds. Philadelphia, PA: American Society for Testing

and Materials.

Subbarao, K. (September 1988). PSTAR - Primary and Secondary Terms Analysis and

Renormalization; A Unified Approach to Building Energy Simulations and Short Term Monitoring.

SERIffR-254-3175. Golden, CO: Solar Energy Research Institute.

U. S. Department of Commerce. (1983). 1980 Census of Housing, Volume 1: Characteristics of

Housing Units; Chapter A, General Housing Characteristics. Washington, DC: U.S. Department of

Commerce, Bureau of the Census.

39
APPENDIX A

AUDIT SUMMARY - MOBILE HOMES #1, #2, #3

TP-3629

Champion Central Detroiter

#1 #2 #3

Dimensions - Interior

length (ft) 56.6 49 61

width (ft) ]1.2 13.5 13

height (ft) 7.5 7 7.5

floor area (ft2) 624 662 793

volume (ft3

) 4753 4590 5948

window area (ft2

) 129 64 70

opaque wall area (ft2

) 877 811 1060

floor wing area (ft?') 250 282 293

floor pan area (ft2

) 374 385 500

Wall Section

interior material 1/4" paneling 1/4" paneling 1/4" paneling

studs 2x3 16"OC 2x216"OC 2x2 16"OC

cavity 2.5" 1.5" IS'

insulation 2.5" batt 1.5" batt 1.5" batt

lath 1x224"OC lx2 24"OC 1x224"OC

exterior material metal siding metal siding metal siding

Floor Section

interior floor 1 1/2" carpet 3/4" carpet 1/4" carpet

1/2" foam rubber 1/2" foam rubber 1/2" foam rubber

interior floor 2 1/4" carpet 1/2" carpet 1/4" carpet

linoleum linoleum linoleum

subfloor 5/8" particleboard 1/2" particleboard 1/2" particleboard

joists 2x520"OC 2x5 16"OC 2x620"OC

pan cavity 10" 13" 10"

wing cavity 4.5" 4.5" 5.5"

insulation 1.5" batt 1.5" batt 2" batt

exterior material 1/16" rodent barrier 1/16" rodent barrier 1/16" rodent barrier

Roof Section

interior material 1/2" mineral board 1/2" mineral board 1/2" mineral board

6 mil polyethylene 6 mil polyethylene 6 mil polyethylene

truss bowstring 16"OC solid 16"OC bowstring 20"OC

cavity depth 3.5" avg 5.5" avg 7" avg

insulation 1" batt 1.5" batt 1.5" batt

exterior material galvanized metal galvanized metal galvanized metal

40
TP-3629

APPENDIX B

THE WEATHERIZATION MEASURES

The weatherization techniques described here are those we observed being used by Region VIII

weatherization personnel and subcontractors, and those that were taught at the National Training

Workshop conducted by SERI and the Colorado Division of Housing in April 1989. They may not be

representative of methods used by other weatherization groups. The description of the methods provided

below does not represent an endorsement by SERI for any specific method or material. Occasionally,

we mention alternative methods and materials. However, this section is not intended to be a

comprehensive treatment of different methods. The primary purpose of this section is to describe what

was done to weatherize the mobile homes tested during the project and what was taught at the

weatherization training workshop.

Blower-Door-Directed General Heat Waste

Plumbing and Electrical Penetrations

These penetrations commonly occurred through the floor or wall. Frequently, a 2-3-in.-diameter hole

had been drilled at the factory for a 1/2-in.-O.D. or smaller pipe. Much larger openings were sometimes

found where sloppy plumbing or electrical repairs had been made. Weatherization consisted of plugging

these openings with expanding foam, silicone with backerod, 6-mil polyethylene sheet and construction

adhesive, or insulating aluminized foil and silicone.

Furnace Closet and Heating System

Leakage areas were found where the flue penetrates the ceiling, and where the combustion air duct

penetrates the floor and rodent barrier. The flue penetration was sealed with sheet metal, hightemperature caulk, or silicone. The combustion air duct penetration was sealed with silicone, opencell foam, sheet metal, or expanding foam depending on the size, shape, and accessibility of the

opening.

Mobile homes typically use a furnace with a sealed combustion chamber. Combustion air is supplied

from under the mobile home through ductwork, or from above through a downdraft air channel fabricated as part of the furnace flue. Other combustion air sources are not necessary as long as the sealed

combustion path is operating properly and there are no cracks in the heat exchanger. Nevertheless, a

carbon monoxide test should always be conducted after any work on the furnace or furnace closet.

Also, with these repairs care should be taken to respect furnace and flue clearances, to use sealing

materials with proper fire retardancy ratings, and to inspect for appliance backdrafting and spillage.

Most mobile home furnaces use a register in the furnace closet door as the cold air return. In some

mobile homes a separate return air system was found between the floor and the rodent barrier. Such

systems are extremely leaky and unnecessary because of the small volume of single-wide units.

Weatherization consisted of sealing the return air floor registers and the return air chase at the base

of the furnace. A large register was then installed in the furnace closet door to accommodate the cold

air return. Finally, a clearance of about 1 to 1 in. was assured between the top of the floor or carpet

and the bottom of interior doors by trimming the door bottom if necessary.

Another important source of air leakage in the heating system was at the junction of the hot air

delivery plenum and the floor heating register sleeves. These vertical sleeves were often poorly

connected to the longitudinal plenum via a loose friction fit. They are also usually poorly fitted to the

opening in the subfloor, allowing leakage between the belly and the living space. These and other holes

in the heat distribution ducts can best be observed with a mirror and a flashlight aimed from a floor

register. Such leaks were sealed with aluminum tape, silicone, or expanding foam. Access to these

leaks is sometimes difficult. However, a blower door can help to isolate duct leak locations by

41
TP-3629

successively sealing off sections of duct with temporary air blocks inserted through the floor registers.

semi-rigid tape measure inserted in the end registers can identify holes at the duct ends.

Leaks in the heating distribution ducts have two very different effects depending on whether the furnace

fan is on or off. With the fan off, extra infiltration leakage paths exist from the underfloor area through

the ducts and up through the floor registers into the living space. With the fan on, the heated

distribution air leaks out into the underfioor space and then to the outside environment. Thus the

overall efficiency of the heating distribution system is decreased.

Gas Water Heater Closet

In most of the mobile homes in our study the gas water heater was in a separate closet outside the

intentionally heated space of the unit. The water heater is located so that combustion air is supplied

from outside the living area. This closet area proved to be a major source of air leakage. Leakage sites

in the hot water closet were also among the least accessible for correction. Several of these closets

opened directly into bathroom cabinets, built-in drawers, or under-sink or under-tub areas. Where

possible, these points were best sealed with lI8-in. hardboard and silicone. For less accessible areas,

6-mil polyethylene sheet or insulating aluminized foil and construction adhesive sometimes worked.

For smaller penetrations, expanding foam or silicone and backerod were effective. Others have tried

stuffing large openings with batt insulation, then sealing them off with an insulating foil membrane.

Generally, the approach should be to air seal between the closet and the living space, and to insulate

wherever possible including the common wall. the outside wall, and the door of the closet. Make sure

adequate combustion air is available from outside.

Occasionally, we find a gas water heater drawing combustion air from inside the mobile home. In such

cases we recommend isolating the closet from the interior of the mobile home, and installing an outside

combustion air opening in the closet. Such appliances should be carefully checked for carbon monoxide,

backdrafting, and spillage.

These kinds of problems are not generally found in units using electric water heaters. where the heater

can safely be located within the conditioned space.

Evaporative Cooler

Many mobile homes have rooftop evaporative coolers, sometimes called swamp coolers. The cooler

chase is a major source of air leakage. Cooler covers made of reinforced vinyl and fastened with screw

clips are commercially available. However, an easier, less expensive, and more effective method is to

use a commercially available interior plastic cover on the chase itself. These are easily accessible on

the ceiling, allowing the occupant the option of removing the cover in summer without having to climb

on the roof.

Windows, Repairs, Replacements and Interior Storm Panels

Most older mobile homes have some air leakage from the windows. The mobile homes in our study

frequently had awning or jalousie windows. Although these windows are by nature less tight than a

sliding window, they did not constitute a major air leakage problem unless they were damaged. The

most common failure of this type of window was malfunctioning of the operator mechanism, rendering

tight closure impossible. The second most common problem was degradation of the seals between

panes. Additionally, cracked, broken, and missing panes were frequently found. Occasionally, cable TV

lines, antennae wire, and antifreeze tapes were routed through the windows, preventing tight closure

of the assembly.

There are several ways to weatherize windows. The general approach should be to mmnmze

expenditures on the primary windows in order to preserve budget for installation of interior storm

panels. Replacement windows should only be used when the cost of repair would exceed the cost of

replacement. This is because primary windows do not reduce the air leakage path through ventilated

42
TP-3629

walls into the window frames. Inexpensive repairs to primary windows included ludwig clips, operating

mechanisms, and pane replacement. Damaged seals at awning and jalousie pane edges were repaired

or replaced with weatherstripping. TV lines and antennae wires were rerouted through the floor or wall.

Cracks between the window trim and interior wall were sealed with siliconizcd acrylic caulk.

Stann windows reduce energy consumption by reducing infiltration and by reducing conduction losses.

Several vinyl interior storm panel systems are available commercially, which can reduce the installed

cost to about $1.5O/fe. The durability of these systems should be further investigated, but reports from

the field indicate that some vinyl systems have not significantly degraded after as long as five years.

Conventional glass interior panels at $3.00-$4.50/fe are still cost-effective in many cold climates.

Doors

Doors were not usually major sources of air leakage in these mobile homes. For those doors that did

show significant air leakage, conventional weatherizing devices such as jamb seals and door-sweeps

were not appropriate because mobile home doors open outward. They rely on a seal created by

weatherstripping on a flange that surrounds the door perimeter. The flange is pressed against the outer

wall at the door frame when the door is closed. Some weatherization personnel have tried attaching

door weatherstripping "jamb-up" kits to the mobile home door itself.

Common problems and appropriate repairs for mobile horne doors were:

• Damaged, missing, or degraded weatherstripping on door flanges. Replace.

• Damaged latch or lock mechanisms, which prevent tight sealing of the door. Repair or adjust latch

plates.

• Damaged door flange, preventing a pressure fit of the weatherstripping upon closure. Replace the

door.

• Damaged window in the door. Remove the window and replace with rigid insulation sheathed in

mobile home siding.

• Door does not fit properly in the door frame. This can be corrected by leveling with jacks and

installing supplementary support pylons. However, leveling often creates as many problems as it

solves. Doors and windows that previously sealed may cease to do so. Leveling is a last-resort

solution.

Kitchen Vent Fans

When in proper working condition, the vent dampers provide a sufficient seal. However, the fans are

prone to certain failures over time. Broken pull-chain fan operators cause the fan damper to remain

open and the fan to run continuously. This is a straightforward repair. Damaged dampers require

replacement of the fan unit. Degraded damper seals can be corrected by replacing the seals.

Rodent Barrier

Rodent barriers are commonly constructed of relatively fragile fiberboard-type materials. Holes and

loose seams in the rodent barrier allow additional infiltration through the floor and unwanted cold air

circulation around the heating distribution ducts. This air flow also short circuits whatever insulation

may be in the underfloor area. Openings in the rodent barrier were sealed with insulating aluminized

foil, silicone adhesive, and stitch staples.

43
TP-3629

Exterior Walls

Exterior walls of a mobile home tend to be vented because of the vertical ridges in the aluminum skin.

Air leakage past the exterior skin penetrates the interior finish materials via seams, joints, and electrical

outlets. None of these individual leakage sites are great, but their cumulative effect is fairly significant.

This was generally the lowest priority area for the weatherization crews because of the diffuse nature

of the leakage problem. In general, unless an occupant identified a drafty spot, or a large leak source

was found with the blower door, these sites were not sealed. These cracks should not be sealed from

the exterior because of the potential for moisture buildup in the walls. A certain amount of diffuse air

leakage is beneficial to meet ASHRAE minimum fresh air standards. The blower door is essential to

prevent overtightening.

Belly Insulation

Most methods involve blowing loose fill insulation in the cavity between the rodent barrier and the

floor. An alternative method called a belly wrap was also tested in this project. A contractor, Sunpower,

installed 6 in. of 5-ft-wide, vinyl-backed, glass-fiber roll insulation below the rodent barrier. To do this

a grid of 16-gauge wire was formed below the main steel support beams of the mobile home. Nails

were driven into the rim joists 16-in. D.C. Wires were secured to the nails and pulled tight across the

width of the unit. The grid hangs 6 to 8 in. below the rodent barrier and supports the insulation. The

insulation was cut to appropriate sizes and fit between the structural supports of the steel framing

member. The pieces were oversized by 8 to 12 in. in both dimensions to achieve a tight fit and less

leakage past the vinyl vapor barrier at the seams. After the insulation was installed, additional wires

were strung the length of the unit for extra support.

This method has some minor thermal advantages over blown-in insulation. However, problems with the

durability of such installations have been observed in the field, especially when the units are moved.

Roof Blow

On average, blowing the bow-string truss area full of insulation will save about 12% of the heating

bill. However, more research is needed to determine if this retrofit may eventually cause moisture

damage to the ceiling from condensation in humid climates. This measure has been successfully applied

with no long-term problems in arid areas like Colorado.

Insulation can be blown into the bow-string truss area from either inside or outside the home. For

the interior application, holes must be drilled neatly to accommodate plastic filler plugs. Holes are

drilled in each truss cavity either down the center or at the "third" points, depending on the

characteristics of the blowing equipment and the fill material. The goal is to get a complete fill out

to the perimeter. A fill tube can help achieve a uniform fill to the perimeter. An occasional hole drilled

at the perimeter in a closet or cabinet can be used to check that insulation is reaching the perimeter.

Insulation should be directed away from furnace flues and other potential fire hazards. This can be done

by drilling extra holes close to the flue and blowing in the direction away from the flue on each side

of it. When carefully done, the finished job is hardly noticeable from the inside. Both chopped

fiberglass and cellulose are commonly used for roof blow applications. Cellulose is generally easier to

blow than fiberglass. However, cellulose is heavier than fiberglass and will absorb more water than

fiberglass if exposed to moisture.

For an exterior roof blow, holes are cut in the roof over the roof trusses at the peak so that only a

minimum number of holes are needed, and drainage is away from the holes. The roof is then filled

in the usual manner, and special care is taken around the furnace and hot water flues to allow adequate

clearance. A jointed fill tube will minimize the number of holes that must be cut in the roof for a

uniform fill. Batt material can be used to "dam" a clearance area around flues before blowing starts.

Careful watertight repair of the holes is crucial. First, a square of galvanized sheet metal is beaded

with roofing caulk and secured to the roof with a tight pattern of self-tapping screws. Then the patch

is covered with high-quality roofing compound. Reinforcing mesh is placed over the patch and covered

44
TP-3629

with a second coat of roofing compound. When properly applied, the patches will be leakproof for the

life of the roof.

Furnace Efficiency Improvements

The furnace efficiency procedures suggested here are fairly simple. However, they should not be

attempted by untrained personnel because of the potential health hazards associated with an improperly

operating furnace. Mobile home furnaces are commonly fueled by gas, propane, oil, or electricity, and

should always be of the sealed combustion type for safety. The procedures emphasize increasing

efficiency on the air delivery side of the furnace, and simple safety checks with respect to furnace

combustion and exhaust. A 5-min heat rise test is conducted by measuring temperatures at the return

air intake and the closest heating register. The temperature difference, fan-on temperature, and fanoff temperature help diagnose potential problems. For example, excessive heat rise usually indicates

insufficient air flow because of a dirty or faulty blower, a clogged filter, duct blockage, or an oversized

fuel jet. Low heat rise usually indicates a clogged fuel line, faulty gas valve, duct leaks, or undersized

fuel orifice. Service procedures consist of cleaning out duct blockages, repairing duct leaks, cleaning

the blower, replacing the filter, replacing or adjusting fan on and off switches, and adjusting the

thermostat anticipator. All furnace work should include basic safety checks for carbon monoxide,

spillage, backdrafting, flame color, and cracked heat exchangers.

45
Document Control 11. SERI Report No.

Page SERI/TP-254-3629 1

2. NTIS Accession No.

DE90000323

3. Recipient's Accession No.

4. Title and Subtitle

Testing the Effectiveness of Mobile Home Weatherization

Measures in a Controlled Environment: The SERI CMFERT

Project

7. Autnorts)

R.D. Judkoff, C.E. Hancock, E. Franconi

9. Pertorming Organization Name and Address

Solar Energy Research Institute

1617 Cole Blvd.

Golden, CO 80401-3393

12. Sponsoring Organization Name and Address

15. Supplementary Notes

5. Publication Date

March 1990

6.

8. Performing Organization Rept. No.

10. Project/Task/Work Unit No.

11. Contract (C) or Grant (G) No.

(C) DE-AC02-83CH10093

(G)

13 Type of Report & Period Covered

Technical Report

14.

56

16. Abstract (Limit 200 words) For several years the Solar Energy Research Institute has been

testing the effectiveness of mobile home weatherization measures, with the support

of the U.s. DOE Office of State and Local Assistance Programs Weatherization Assistance Program, the DOE Office of Buildings and Community Systefls, the seven states

within the federal Weatherization Region VII, the Colorado Division of Housing, and

the DOE Denver Support Office. During the winter of 1988-89, several weatherization

measures were thermally tested on three mobile homes under controlled conditions inside a large environmental enclosure. The effects of each weatherization measure on

conduction losses, infiltration losses, and combined furnace and duct-delivered heat

efficiency were monitored. The retrofit options included air sealing, duct repair,

furnace tune-up, inteFior storm panels, floor insulation, and roof insulation. The

study demonstrated that cost-effective heating energy savings of about 20% to 50%

are possible if weatherization techniques adapted to the special construction details in mobile homes are applied.

17. Document Analysis

a. Descriptors conservation, weatherization, mobile homes, retrofit

b. Identifiers/Open-Ended Terms

C. UC Categories 323

1a. Availability Statement 19. No. of Pages

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

20. Price

A04

Form No. 0069 (3-25-82)