BAIHP Research: A. Manufactured Housing Research Cont'd

• Zero Energy Manufactured Home (ZEMH)
  Nez Perce Fish Hatchery, Idaho
  Category A, 1 home

Figure 57 Zero Energy Manufactured Home, on site at the Nez Perce Fish Hatchery

BPA, working with BAIHP staff in Idaho and Washington, provided funding for the most energy efficient manufactured home in the country. The RFP was sent to 18 Northwest manufacturers; Kit HomeBuilders West of Caldwell, Idaho was selected as the manufacturer of the home. BAIHP staff solicited 24 industry partners to provide energy efficient building components, including Icynene wall, floor and roof insulation, a low-cost HUD-approved solar system, sun-tempered solar design, and Energy Star© windows, appliances and lighting. Partners include Building America Team members such as Flexible Technologies, Icynene and LaSalle. Complete list of specifications provided in Table 29.

The ZEMH (Figure 57) was built in the Fall of 2002 along with a control home. The ZEMH was displayed at the 2002 Spokane County Interstate Fair before siting at the Nez Perce tribal fish facility near Lewiston Idaho. Blower door and duct leakage tests at the plant and on-site indicate that this is the tightest home ever tested by BAIHP staff.

Working with FSEC and BPA, BAIHP staff installed monitoring equipment for the ZEMH. Monitoring began in the 2003 and includes the following:

• Total electric use from grid
• Resistance elements in heat pump
• Heat pump compressor and fan motors
• Water heating equipment, including gallons used
• PV energy production (ZEMH)

Data logger collects 15 minute data from wired sensors and transmits daily to the host computer at FSEC via modem. Summary data reports are available at www.baihp.org under “Current Data.” Plug-type loggers were installed in mid March 2003 to sub-meter the energy use of the refrigerator, freezer and clothes washer in each home, as well as the radiant heat panel and HRV in the ZEMH. Data from these loggers was collected by occupant readings in mid-December 2003.

Preliminary findings

Measured net energy use of the ZEMH 6% is lower than the base home, not normalized for occupant behavior. This also does not take into account the fact that the ZEMH’s PV system was only fully operational for one month.

The ZEMH required 45% less space heating energy, possibly due to improved building envelope measures, and the lack of consistent HRV operation.

The measured envelope leakage in the ZEMH was 2.0 ACH50, much lower than the base home (indeed, lower than any other NEEM home tested in the field) and substantially tighter than typical HUD code homes.

The ZEMH total duct leakage was 46% lower than the base home; leakage to the outside was 405% lower than the base home. The BAIHP staff speculates that the unprecedented low leakage to the outside value is the result of the ducts in the ZEMH being located within the conditioned space, and effectively within the pressure envelope of the home, surrounded as they are by foam insulation.

The solar water heating system in the ZEMH provides most, if not all of the hot water needed during the summer months, and roughly 45% of the total hot water demand. The PV system with net metering provides 38% of the total ZEMH energy use.

The project highlights the importance of occupant choices and behavior on the performance of energy efficient housing. Based on the preliminary monitoring data and occupant surveys, the behavior patterns of the ZEMH occupants are not themselves “energy efficient”. These patterns create the appearance of a less efficient home. On the other hand, the behavior of the ZEMH occupants may shorten the payback for the innovative technologies of the ZEMH.

BAIHP staff also performed a benchmarking analysis on the ZEMH, as part of the overall benchmarking effort. The ZEMH reached a level of 60% above the NREL prototype, which indicates the difficulty of obtaining a high benchmarking score.

In December of 2004, a research paper was presented at BTECC which provided a preliminary evaluation of the ZEMH performance without the full operation of the PV net metering system. By the spring of 2006, there will be a full year of ZEMH data, with the PV system operational.

• Manufactured Housing Indoor Air Quality Study
  Plant City, Florida, and FSEC MHLab
  Papers: Hodgson, A.T., Apte, M.G., Shendell, D.G., Beal, D. and McIlvaine, J.E.R. (2002a). Implementation of VOC source reduction practices in a manufactured house and in school classrooms. In Levin, H. (Ed.), Proceedings of the 9th International Conference on Indoor Air Quality and Climate. Indoor Air 2002, Santa Cruz, CA, Vol. 3. pp. 576-581.
  Hodgson, A.T., D. Beal and J.E.R. McIlvaine. 2002b. Sources of formaldehyde, other aldehydes and terpenes in a new manufactured house. Indoor Air12: 235-242.
  Hodgson, A.T., A.F. Rudd, D. Beal and S. Chandra. 2000. Volatile organic compound concentrations and emission rates in new manufactured and site-built houses. Indoor Air10: 178-192.

This is a summary of several indoor air quality (IAQ) projects designed to improve the IAQ of manufactured homes; specifically to find ways to reduce the formaldehyde levels found in manufactured homes. This was a collaborative effort of the Florida Solar Energy Center (FSEC), Lawrence Berkeley National Laboratory (LBNL) and Palm Harbor Homes, Inc. (PHH), a leading nationwide producer of multi-section, high-end, manufactured houses with corporate offices in Addison, TX.

In 1999 – 2000 a study was conducted to identify and verify the major sources of formaldehyde, aldehydes, and terpene HCs in a new manufactured house. Laboratory emission tests were conducted with a number of wood and engineered wood products and aldehyde and volatile organic chemical (VOC) measurements were made in the house. Although only a single house was studied, the information on sources is anticipated to have broad application to residential construction due to the widespread use of similar materials and building practices.

The manufactured house was typical of better quality two-section houses produced in Florida. It was completed in November 1999. Within three weeks of manufacture, it was installed at a nearby site. The house was used daily as a sales model. It was decorated, fully furnished, but unoccupied. There were three bedrooms and two bathrooms.

The manufacturer supplied a detailed list of materials used in the house. Between December 1999 and January 2000, ~30 specimens of the major materials were collected from the production facility. These were cataloged, packaged in aluminum foil, and shipped to the laboratory by airfreight. The specimens were stored at room conditions in their original packages until they were tested. Most materials were tested within three months of collection. Measurements were made after about a 3-week exposure, and area-specific emission rates (i.e., emission factors) were calculated.

Air sampling in the house and outdoors was conducted in March 2000. The house ventilation rate was quantified concurrently by tracer gas decay. The ventilation rate measurement and the VOC air sampling and analytical methods for field and chamber work have been described previously (Hodgson et al., 2000)

Whole-house emission rates for combined materials were predicted based on the emission factors and the corresponding material quantities. These predicted values were compared to whole-house emission rates derived from measurements of VOC concentrations and ventilation rates. For 10 of the 14 target compounds, including formaldehyde, the predicted and derived rates agreed within a factor of two, which considering the uncertainties involved is considered good agreement. The predominant sources of formaldehyde in the house were bare particleboard (PB) and medium density fiberboard (MDF) surfaces in the cabinetry casework and molded high-density fiberboard doors. The plywood subfloor under the carpet was a smaller source of formaldehyde and the major source of higher molecular weight aldehydes and terpene hydrocarbons.

As the result of this study, recommendations were developed for reducing concentrations of formaldehyde and other VOCs in new house construction (Hodgson et al., 2002a). These are reproduced here in Table 30. The first five recommendations are aimed at controlling or eliminating important sources of formaldehyde. Other potential sources of formaldehyde not addressed in the house study or in the table include tack strips used for the installation of wall-to-wall carpet and fiberglass insulation used in wall, floor and ceiling cavities. Use of barrier materials on the floor may result in moisture condensation problems in hot-humid climates and possibly other situations and, therefore, should be used with caution.

In 2004 a pilot demonstration project was conducted at PHH’s production facility and sales office in Plant City, FL. The project was originally conceived in 2002 as a side-by-side demonstration of simultaneous improvements in energy performance and IAQ to be achieved using existing technologies. The concept was to build two houses, essentially identical with respect to their size, floor plan, and major materials. One house would have added features to improve energy performance and IAQ. The other house would have no special modifications and would serve as the control. They would be sited in a residential community on adjacent, identical lots. Both would have computer-simulated occupancy (i.e., controlled use of lights, appliances, heating and cooling). Monitoring of energy usage and performance and IAQ metrics would be conducted over at least a one-year period. Finding the appropriate residential site and the funds needed to cover the costs associated with maintaining the houses at the site for a year proved difficult. Consequently, the study plan was modified in 2003 to reduce costs and take advantage of PHH’s model home sales office in Plant City.

Approximately on an annual cycle, PHH builds examples of their new houses for display at their sales office. The houses present PHH’s range of models and features. They are decorated and furnished, but unoccupied. The houses are open to the public during normal business hours seven days a week and their heating and cooling systems are operated accordingly. The use of these houses as study houses has some limitations. The houses generally vary somewhat with respect to size and floor plan, interior finishes and furnishings may vary, orientation with respect to sun and wind may vary, monitoring instrumentation must be kept out of sight, and sampling can only be conducted outside of normal business hours. In addition, computer controlled simulations of occupancy are not possible.

To the extent possible, the study plan was revised to accommodate these factors.

In June 2003, two model houses, then in the planning stage, were selected for use in the project. A 1,440-ft2, double-wide house designated as “Monte Carlo” was selected to receive the energy and IAQ modifications. A 1,540-ft2 double-wide house designated as “Edison 2” was selected to serve as the primary control house. The houses were to be installed on nearby lots in the sales center in approximately the same orientation.

The project participants early on developed specifications for enhanced IAQ. These specifications were reviewed and revised in June 2003 to reflect those energy and IAQ modifications determined by PHH management to be relatively easily installed on the production line and/or during installation. The revised IAQ specifications are listed in Table 31.

The two houses were produced in late July and early August 2003. Installation of the two houses was completed and the heating and air conditioning (HAC) systems were operational by the end of September. Not all of the originally planned IAQ modifications (Table 2) were installed in the Study house. Standard molded high-density fiberboard, passage doors were used, as the door manufacturer no longer produces vinyl-coated doors. Medium-density fiberboard (MDF) was used for the face frames of the cabinets because PHH did not have sufficient stock of the plywood material. Standard tack strips with unquantified emissions of formaldehyde were used for the carpet installation, as LBNL was unable to identify an alternate with low formaldehyde emissions.

Energy Gauge ratings of the experimental house (Monte Carlo) and the control (Edison) showed that the control house was an Energy Star home, scoring 86.5, while the experimental house was a Building America house, scoring 91.1. There were many obstacles to successfully retrieving data from the houses, but available results show that the BA house saved about 50% more air conditioning energy than the control house. Figure 58 illustrates this. The plot normalizes the data by plotting the daily air conditioner energy use pre ft 2 of conditioned space versus the average daily temperature difference between the inside and the outside (Average Daily )T).

Figure 58

IAQ work started with an initial set of active air samples for VOCs and aldehydes collected outdoors and in the Study and Control houses on December 11, 2003, approximately 2.5 months after the houses were fully operational. The second set of active samples was collected three months later on March 2, 2004. Passive aldehyde samples were obtained in the Study and Control houses and in an additional triple-wide house of the same age over four one-week intervals between these dates.

Based on previous laboratory measurements of formaldehyde emissions from interior components, we anticipated a minimum 25% reduction in the formaldehyde emission rate in the Study house relative to the Control house. This was anticipated due to the use of fully encapsulated particleboard for the cabinetry casework, a diffusion barrier on the undersurface of the particleboard countertops, and the weatherization barrier applied over the plywood subfloor (Hodgson et al., 2002b). We additionally expected the difference to persist over the course of a year. The two-fold higher formaldehyde emissions in the Study house prompted us to abandon our original plan of quarterly measurements and instead to focus on identifying the unexpected source of formaldehyde emissions in this house. Firstly, FSEC and PHH staff jointly inspected the houses. This inspection confirmed that the intended formaldehyde source reduction measures had been implemented in the Study house.

Two other potentially relevant differences between the houses were known at the time. Due to the energy efficiency specifications for the Study house, a different manufacturer than the HAC system in the Control house produced the HAC mechanical system in the house. Secondly, some furniture believed to be solid wood had been newly purchased for decoration of the Study house. Older furniture taken from PHH’s stock was used to decorate the Control house.

In July 2004, the potential for the HAC systems to emit formaldehyde was investigated. Each system is located in a closet near the central living area. Active sampling for formaldehyde was conducted in each house. The differences between the return and supply measurements were small, about plus 3% for the study house and about minus 8% for the control house. These differences are within the uncertainties of the measurements and, therefore, are not significant.

Another inspection revealed that some of the backsides and undersurfaces of the new wood furniture were fabricated from particleboard, a typically high formaldehyde emission source (Kelly et al., 1999; Hodgson et al., 2002b). Due to delays imposed by PHH model center needs and 2004’s hurricane season, in December 2004, approximately 14 months after the furniture was first delivered, we located the furniture pieces in a storage garage. From one accessible piece, we obtained 4.4-cm diameter specimens of 3-mm thick particleboard using a hole-saw. Specimens of 13-mm thick particleboard were similarly collected from a furniture piece that was several years old and was used in the sunroom of the house.

The emissions of formaldehyde from the two specimens of furniture particleboard individually were measured in the laboratory using small-scale environmental chambers as described by Hodgson et al. (2002b).

From the purchase requisition and the company’s sales literature it was determined there were eight new pieces of living room and master bedroom/retreat furniture that likely contained some particleboard. The total exposed surface area (one side) of particleboard in these pieces was estimated to be 8.5 m2. Thus, the estimated formaldehyde emission rate attributable to the new furniture was about 80% of the total formaldehyde emission rate derived for the house in December 2003. Based on the formaldehyde emissions from the particleboard from the older furniture, it is likely that the formaldehyde emissions attributable to furniture would have been substantially lower if older furniture pieces had been used.

This study did not progress as originally intended, and the results did not conclusively show the efficacy of low-cost measures intended to reduce the sources of formaldehyde in the Study house. However, it is likely that the source of the elevated formaldehyde emissions was correctly identified to be a component of the new wood furniture installed in this house and not in the Control house. If one-half the estimated formaldehyde emission rate from the new furniture (i.e., approximately the difference between the emissions from new and old furniture particleboard) is subtracted from the whole-house emission rate, the formaldehyde emission rate in the Study house is nearly equivalent to the rate in the Control house.

A formaldehyde concentration of 50 ppb and below has been suggested as a reasonable target for new houses (Sherman and Hodgson, 2004). The source reduction measures directed toward other VOCs were successfully demonstrated. The use of the weatherization barrier applied over the plywood subfloor in the Study house appeared to function as predicted to reduce the emissions of higher molecular weight aldehydes and terpene hydrocarbons from this source, and the use of the low VOC interior paint reduced the emissions of a major VOC component associated with latex paints.

Data collection was curtailed by the onset of 2004’s hurricanes, three of which impacted Plant City, and sales activity resulting in houses moving. The collected data did show that the energy goals established for the house were met, with a 50% reduction of energy use for air conditioning compared to the control house.

• Manufactured Housing Laboratory - Ventilation Studies
  FSEC, Manufactured Home Laboratory
  Paper: Moyer, Neil, Chasar, Dave, Hoak, Dave, Chandra, Subrato, "Assessing Six Residential Ventilation Techniques in Hot and Humid Climates," Proceedings of ACEEE 2004 Summer Study on Energy Efficiency in Buildings, American Council for an Energy Efficient Economy, Washington, DC, August 2004. (Also available online at www.baihp.org under Current Data and Publications)

Ventilation Study

Figure 59 Manufactured Housing Laboratory at FSEC (above and below) was site for study of six residential ventilation systems.

The MHLab (Figure 59) is a research and training facility of 1600 ft 2. This Energy Star® manufactured home has two separate heating and cooling systems:

1. An overhead duct system connected to a package unit air conditioner with electric resistance heating.
2. A floor-mounted duct system connected to a split system air conditioner, also with electric resistance heating.

Only the floor mounted duct system was used in these ventilation experiments.

Introduction

Ventilation is a HUD code requirement. The goal of ventilation is to add fresh air to the home. This may be accomplished by supplying outside air to the house or mechanical system, exhausting air from the house (which consequently pulls air into the house through joints in the walls, floor, and ceiling), or a combination of the two.

Supply based ventilation tends to slightly pressurize the home whereas exhaust based ventilation does the opposite slightly depressurizing the house. The disadvantage of supply based ventilation is that it forces conditioned air into the floor, wall, and ceiling cavities, possibly leading to condensation or mold growth in cold climates and during the heating season. Likewise the disadvantage of exhaust systems is that they pull unconditioned outside through the floor, wall, and ceiling cavities into the conditioned space, possibly leading to condensation, mold growth, or uncomfortably high indoor humidity levels in hot and hot-humid climates and during the cooling season. The six residential ventilation strategies evaluated are described in Table 32.

House Operation and Experimental Procedure

Occupancy Simulation: Automated, computer controlled devices, such as appliances, showers, and lighting, simulate the sensible/latent heat generation and carbon dioxide (CO 2) production of a family of four persons with periodic showers, cooking and cleaning.

The simulated latent occupancy load from breathing, bathing, cooking, and laundry was achieved by adding 14 to 15 pounds of water per day based on documentation of "average" household operation based on ORNL research conducted by Jeff Christian. Water vapor was injected into the space using a vaporizer at a rate of approximately 0.4 lbs per hour continuous and an additional 0.4 lbs per hour during the evening hours.

Ventilation Rate: Researchers conducted whole house air tightness tests using sulfur hexafluoride as a tracer gas for a decay analysis (Figure 60) to determine if each ventilation strategy met the ASHRAE 62-2 Ventilation Standard during the test period. The spot ventilation strategy (#2) did not meet the standard on a daily basis as the runtime was not long enough. The outside air method (#3) was marginal in meeting the standard. Strategies #4-#7 met the standard.

Figure 60 Results of tracer gas decay testing indicating operational infiltration
(house not under test pressure) rates measured for each ventilation strategy.
ASHRAE Standard 62.2 was the target ventilation rate, not met by Spot or OA
strategies. Note: Wind speed averaged over 2 hour infiltration test.

Whole House and Duct Air Tightness: The average whole house air leakage (CFM50) was 1224 (ACH50 of 5.4). The target normalized duct leakage is Qn #6%, where Qn=CFM25/conditioned area, this is the same as the duct leakage target in the Manufactured Home Energy Star program. The total duct system leakage in the MHLab Qn total=5% (CFM25 total = 75) with leakage to the outside measured to be Qn (out)=3% (CFM25 out = 45), well under the leakage target.

Cooling/ventilation power usage

With all mechanical ventilation systems, additional energy use from both increased conditioning loads and fan (if present) power is expected. The split system with the floor duct system is a 12 SEER system with a rated cooling capacity of 30.2 kBtu. The ventilation strategies that required the use of the air handler fan, an energy recovery ventilator, or the dehumidifier had the energy use added to the cooling energy. The dehumidifier strategy did use the most energy for cooling; however, it should be noted that this test occurred during the hottest ambient conditions.

Findings

The cooling energy required to maintain the 75°F interior set-point appeared to vary as a result of the temperature difference across the envelope (Table 33). A linear regression analysis was performed to compare energy use of the ventilation strategies as a function of temperature difference across the envelope (Table 34). The power use at the average temperature difference of five degrees Fahrenheit is shown in bold.

• Case 4, the dehumidifier system, has the highest average power at 1592 watts.
• Case 7 (humidistat controlled fan speed or Hstat) is second highest at 1485 watts.
• Case 5 (10/20 cycle controller) used the least power at 1315 watts.

As might be expected, interior relative humidity had the least variance with the dehumidification system with a low of 46% and a high of 51% (Table 33 and Figure 61). The best performing system, Case 4 (10/20 cycle plus dehumidifier), was able to maintain the relative humidity at a nearly constant level for almost 80% of the test period. The next best performer was Case 2 (spot ventilation). Humidity levels during the test period are graphed in Figure 61.

Figure 61 Average hourly relative humidity profiles for each strategy

Conclusions

The operation of a correctly sized air conditioning system with a supplemental dehumidification system to pre-condition the outside air and provide additional dehumidification of the space appears to provide the best interior humidity control (Table 33, in bold) with only a slight increase in energy usage – about 200 watts (Table 34). This is represented by Case 4 of this study. Only this strategy was able to maintain the interior humidity conditions in a range of less than 5% (Table 34, in italics).

Though all of the strategies did provide some humidity control over the test period, it is most likely a result of the run time afforded by the correctly sized air conditioning system and the consistent simulated interior sensible load. When an air conditioning system operates for extended periods of time, the removal of moisture from the air stream is enhanced (Khattar, Swami & Ramanan 1987).

Additional testing with other ventilation strategies in the MHLab will be undertaken in the next budget period.

• Manufactured Housing Energy Use Study, North Carolina A&T
  Paper: W. Mark McGinley, Alaina Jones, Carolyn Turner, Subrato Chandra, David Beal, Danny Parker, Neil Moyer, and Janet McIlvaine. Optimizing Manufactured Housing Energy Use. Symposium on Improving Building Systems in Hot and Humid Climates, Richardson, Texas, May 17-19, 2004.

Side-by-side monitoring of two manufactured homes at North Carolina Agricultural and Technical State University (NCA&TSU), evaluated the value of a variety of energy saving technologies and techniques. (Figure 62 and Table 35) Home instrumentation measured energy consumption as well as interior and exterior climatic conditions. The “standard home,” designed and built to basic HUD code requirements, represented the control home. Modified to use at least 50% less energy, the “energy home” met Building America standards. Cooperating researchers at NCA&TSU and FSEC investigated energy feature performance and compared actual energy used to energy modeling program predictions. In-situ energy performance data provided researchers with interesting information on both issues.

Figure 62 Side-by-side monitoring of manufactured homes at NCA&TSU.

Each model contained 1,528 ft 2 of living area with nearly identical floor plans. Though the homes were unoccupied during the testing, home lighting and water heating use was simulated with timers. A datalogger in each home recorded: (1) the interior and exterior temperature and humidity along with solar radiation and wind speed, (2) the home’s total power consumption, (3) the air conditioning/heat pump compressor, air handler fan, and electric resistance heater use (primary heater in the standard house, backup or emergency heater for the energy house), and (4) water heating and water usage data.

The energy house features combined higher insulation values, improved windows, centralized and airtight duct design, high efficiency heat pump, and a solar water heater. Feature-by-feature construction differences are highlighted in Table 35.

Data collection on the two homes began in early January 2001 and continued through this reporting period. Palm Harbor Homes in Siler City manufactured both homes, the results for program year three and four are detailed below.

Year 4 Side-by-Side Monitoring Results

During Phase 2, modifications were made to the solar water heating system in the energy efficient housing unit to help improve the performance this system. Further, a number of the incandescent light bulbs in the energy unit were replaced with compact fluorescent bulbs. These changes were staged to allow an evaluation of the effect of each measure on the home’s energy use.

Based on investigative results, it can be concluded that:

• Changes in the building envelope, HVAC and duct systems, and fenestrations in the energy home met researchers’ 50% energy use reduction goal. Measured annual energy savings for heating and cooling energy was 58%, and 53% for heating, cooling, and hot water production.
• Care should be exercised in the manufactured housing unit setup or relatively minor construction deficiencies can significantly reduce a home’s energy efficiency. Many of these items are invisible to the homeowner; therefore procedures must be developed to ensure that deficiencies do not occur during setup.
• The Energy Gauge energy analysis program appears to give a reasonably accurate prediction for expected energy use reduction in a typical manufactured housing configuration. The predicted energy savings for the housing units evaluated in this investigation ranged from 54% to 63%, while the measured values ranged from 53% to 58%. Version 2.0 of the Energy Gauge Program provided a more accurate energy savings prediction than the older software versions.
• An increase in pipe and tank insulation can increase not only the energy efficiency of a solar water heater by reducing stand-by losses, but also can reduce the cooling load in a manufactured housing unit and increase the overall energy efficiency of the water heating unit. Even small amounts of exposed piping can significantly affect the energy efficiency of the water heating system.
• While providing essentially the same lighting levels, replacing incandescent lamps with compact fluorescent bulbs not only reduces lighting energy use, but also reduces the home cooling load.

The total measured energy used by each of the housing units for cooling and heating are shown in tables below. Table 36 shows the energy used for heating and cooling the standard housing unit from January through August of 2002. The standard home datalogger was struck by lighting in mid-August 2002. Data after this point was not included since only partial data is available and performance comparisons were not possible. Table 37 shows a summary of the cooling and heating energy used by the energy housing unit. Tables 38 and 39 list the energy use for hot water production for the standard and energy units, respectively.

Also listed in each table are the monthly energy use values measured during the first phase of this investigation, January through August 2001. Please note that the energy housing unit data prior to August 2001 is suspect due to duct and HVAC system problems later corrected. The entire data set, including, temperature, relative humidity, solar radiation, and power use is listed on the FSEC web site www.infomonitors.com .

The total energy used for water heating and central cooling over the period of August 1 through August 15 was 363.5 kWh for the energy home and 596 kWh for the standard home. This represents a 40 % reduction in energy use between the two homes.

The total energy used over the period of August 1 through August 15 for water heating was 27.13 kWh for the energy house and 85.18 kWh for the standard home. This represents a 68% reduction in energy use with the solar water heating system and compares well with the June and July reductions of 63% and 60%, respectively. Consistent findings indicate that the tank and piping insulation has reduced the standby tank losses and improved the solar water system efficiency.

In the energy housing unit, three of the 100 watt incandescent lamps that were on the evening four-hour timed duration were exchanged for 25 watt compact fluorescent lamps on June 4th. This change did appear to have a small effect on the cooling load in the energy housing unit. The relative cooling energy used by each of the housing units from June, 2002 through August 2002 showed a small change. The percentage reduction in cooling energy used by the energy housing unit increased from about 30% to 38%. However, it is difficult to isolate the effects of the improvements in the solar water heating system insulation and the effects of the compact fluorescent bulbs. In any event, these effects appear to be much smaller than that produced by the hot water system changes.

Year 3 Side-by-Side Monitoring Results :

Figure 63 Heating season consumption and savings for side by side study of Energy Star Manufactured Housing.

Heating system savings (2001 to 2002) were a remarkable 70% during Phase 1. Cooling energy season savings were 36%, less than heating but still very substantial. The combined heating, cooling, and water heating savings were 52% for a 9-month period. (Figure 63)

In addition to the energy monitoring effort, NCA&TSU researchers investigated the feasibility of replacing the conventional framing/envelope used in manufactured/industrial housing with alternative systems. Included in this evaluation, was an analysis of the energy impact of using aerated autoclaved concrete (AAC) flooring systems and structural insulated panels (SIP) to supplant traditional wall and roofing systems. The economic viability of using AAC blocks for structural skirting/foundation around the model units also was evaluated.

Analysis’ results determined:

• The best manufactured home energy performance can be achieved using the SIP wall and roof systems with the AAC plank. This performance can be further enhanced with an R-8 unvented crawl space. Though a manufactured home performs best with these alternative systems, the cost to include them may not make economic sense.
• AAC planks can be designed to replace both the steel frame and flooring systems for HUD code manufactured housing units and modular units. These planks also can be modified to incorporate built-in insulated ducts.
• AAC planks are pre-manufactured and require less assembly labor than a typical stick framed unit, but including the plank flooring would increase framing costs by 28%. The heavier weight of an AAC system might exacerbate high framing costs. Similarly, comparative analysis results found that replacing a conventional framing system with a SIP system would increase framing costs by 66%.
• At the current prices for energy and wood products, neither the AAC plank system nor the SIP systems are as economically effective as improvements in the current conventional HVAC systems, steel and wood framing, sheathing systems, and air barriers with respect to improving energy performance.
• The use of AAC planks has the potential to be economically viable in the modular housing market, especially if used with sealed crawl space foundation systems, where their improved resistance to moisture degradation would be very important.
• SIP wall and roof systems also could prove to be economically viable if the price of wood energy increases, and the SIP manufacturing costs decrease through large volume purchases.
• The proposed AAC planking system presents a system that is significantly less affected by water and moisture degradation and may be effective in reducing manufactured housing units’ susceptibility to flood damage. These systems also are not susceptible to termite attack.
• The savings from reduced transportation damage from greater durability and increased floor system stiffness were not addressed in this investigation. It wouldn’t take many days of damage repair (at about $300/person-day for personnel costs related to transportation) to vastly improve the economics of these alternative systems.