• Side By Side Study Of Energy Use And Moisture Control Comparing Standard Split System Air Conditioning And A Coleman® Prototype Heat Pump, Bousier City, LA

In 2001, the BAIHP team conducted research on two homes to define how tight ducts and a prototype Coleman® heat pump (proprietary technology) affect energy use and moisture control in a hot, humid climate. FSEC, in collaboration with Fleetwood Homes, York International Manufactured Housing Division (now Stylecrest Sales), and Coleman®, monitored two nearly identical side-by-side homes in Bossier City, Louisiana. The homes contained different air conditioning systems. House A used a standard split air conditioner, while House B used the Coleman® prototype unit (a more efficient, two-speed split air conditioner).

Figure 45 shows the reduced power draw of the two-speed compressor (green, dotted line) over a 24-hour period on September 2, 2000. With the unit operating at low-speed for most of the day, the cooling energy savings were 28% when compared to the energy use in House A. Average daily cooling energy was reduced by about 12% over the monitored period. An added benefit of the two-speed air conditioner was 20% greater moisture removal on days with an outdoor dewpoint above 60 F.

Figure 45 Power draw over a 24-hour period, September 2, 2000.

Savings from Duct Repair and POS Ventilation: In addition to comparing one house to the other, the BAIHP team also compared home performance before and after ductwork and ventilation system changes were made.

To make the comparison, duct and other leaks were sealed in both houses until the two were equally airtight. The ventilation method in each home also was changed from exhaust-only to a positive pressure system (POS). With exhaust-only ventilation, bathroom fans removed stale air from the home which caused fresh air to be pulled in through the building envelope. To simulate occupant use, two bath exhaust fans were operated by a timer for three hours in the morning and six hours in the evening.

In contrast to exhaust ventilation, the POS system introduced a small amount of fresh air on the return side of the air conditioning cooling coil. A POS system was installed in each home at the same time the ducts were repaired. Subsequent monitoring looked at the effects of this alternate ventilation system. Tightening the ducts and installing a POS ventilation system resulted in an 18% and 37% cooling savings in the two homes. Only about 2% of these savings were attributable to the ventilation system change, the remaining savings are a result of duct repair.

• WSU Energy House

Figure 45 WSU Energy House in Olympia, WA

This 2600 ft 2 home was built beyond SGC standards and incorporates Energy Star lighting and appliances. The home (Figure 45) has received significant national exposure through WSU campus and alumni newsletters, tours, the BAIHP website, and local and trade media including an article in the Automated Builder magazine and a feature by KING 5 News of Seattle.

WSU staff uses the house to try out innovative technologies and testing methods.

In the 5th budget period, BAIHP staff developed a moisture case study based on research at the WSU Energy House, published under a separate Building America project. The WSU Energy House has been monitored since 2000.  Collected monitoring data includes weather, temperature, humidity, CO 2, CO, and eight differential pressures.   Energy use data is being collected for water heating, laundry, fireplace and heating, ventilating, and air conditioning (HVAC).  Data from the house is available on the BAIHP web page (under Current Data) and has been presented to the building science, indoor air quality (IAQ) and HVAC research communities at conferences sponsored by ASHRAE, Air Infiltration and Ventilation Center (in the UK), HUD/NIST, NFPA, and BTECC. (See also Appendix D, WSU)

Working with Ecotope, ASHRAE, and the Energy Conservancy, BAIHP staff conducted “Delta Q” and “nulling” duct leakage tests in 2001.  Follow up pressure tests and analysis of test data conducted in 2002 indicate these tests are effective methods of measuring duct leakage in manufactured homes, and may be included in the upgrades to the National Fire Protection Association-501 standards for manufactured homes.

Blower door and duct leakage testing indicate very good whole house and duct airtightness (2.4 ACH50 and 61.6 CFM50 out). Tracer gas testing demonstrated that the use of a furnace-based intake damper does not change the leakage rate of the home.

• Zero Energy Manufactured Home (ZEMH)

Figure 46: 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 24.

The ZEMH (Figure 46) was built in Year 4 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 5th budget period 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.

• Manufactured Housing Indoor Air Quality Study

In the spring of 2003, BAIHP initiated a study with Palm Harbor Homes (PHH) to evaluate the energy savings from a Building America Manufactured Home, compared to a standard Palm Harbor Home.

These two homes were built in the fall and set up on PHH’s model center in Plant City, Florida.

The monitoring plan called for measurements of volatile organic chemical (VOCs) levels, air conditioning energy use and associated indicators such as indoor and outdoor conditions. Both homes have split system air conditioners, SEER 15 in the BA model, and SEER 10 in the Base Case model.

The two homes were instrumented in November, however, due to a PHH phone service conflict, no data was taken during this budget period. Data collection is expected to commence in May of 2004.

VOC measurements were conducted in collaboration with LBNL. The VOC data revealed significantly higher VOC levels in the Building America home than in nearby control models of a similar age. Normally, PHH would move furniture in from a previous model, but in an effort to ensure high quality in the BA model, PHH purchased all new, all wood furniture. This is believed to be the source of VOCs in the BA model. BAIHP and LBNL researchers will work to verify what caused the elevated VOC level in the next budget cycle.

• Manufactured Housing Laboratory – Ventilation Studies

Ventilation Study

The MHLab (Figure 47) 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

Figure 47 Manufactured Housing Laboratory at FSEC (above and below) was site for study of six residential ventilation systems.

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 25.

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.

Ventilation Rate: Researchers conducted whole house air tightness tests using sulfur hexafluoride as a tracer gas for a decay analysis (Figure 48) 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 48 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.

Interior temperature and relative humidity: A digital thermostat maintained interior temperature at 75 degrees Fahrenheit. Interior temperature and relative humidity sensors are located on the same wall as the thermostat, at approximately the same height from the floor. Dedicated interior relative humidity control was only available with the dehumidifier strategy, and was a byproduct of cooling coil operation in the other strategies.

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 26). A linear regression analysis was performed to compare energy use of the ventilation strategies as a function of temperature difference across the envelope (Table 27). 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 26 and Figure 49). 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 49.

Figure 49 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 26, in bold) with only a slight increase in energy usage – about 200 watts (Table 27). 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 27, 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.