• Air Handler Air Tightness Study

To determine the impact of air handler location on heating and cooling energy use, researchers measured the amount of air leakage in air handler cabinets, and between the air handler cabinet and the return and supply plenums. To assess this leakage, testing was performed on 69 air conditioning systems. Thirty systems were tested in the 2001 and 39 in 2002. The 69 systems were tested in 63 Florida houses (in six cases, two air handlers were tested in a single house) located in seven counties across the state - four in Leon County in or near Tallahassee, 17 in Polk County, three in Lake County, 13 in Orange County, one in Osceola County, two in Sumter County, and 29 in Brevard County. All except those in Leon County are located in central Florida. Construction on all houses was completed after January 1, 2001, and most homes were tested within four months of occupancy.

In each case, air leakage (Q 25) at the air handler and two adjacent connections was measured. Q 25 is the amount of air leakage which occurs when the ductwork or air handler is placed under 25 Pa of pressure with respect to its surrounding environment. Q 25 also can be considered a measurement of ductwork perforation.

To obtain actual air leakage while the system operated, it was necessary to measure the operating pressure differential between the inside and outside of the air handler and adjacent connections. In other words, it was necessary to know the perforation or hole size and the pressure differential operating across that hole. By determining both Q 25 and operating pressure differentials, actual air leakage into or out of the system was calculated.

Field Testing Leakage Parameters

Testing was performed on 69 air conditioning systems to determine the extent of air leakage from air handlers and adjacent connections. Testing and inspection was performed to obtain:

• Q 25 in the air handler, Q 25 at the connection to the return plenum, and Q 25 at the connection to the supply plenum.
• Operating pressure at four locations - the return plenum connection, in the air handler before the coil, in the air handler after the coil, and at the supply plenum connection.
• Return and supply air flows were measured with a flow hood. Air handler flow rates were measured with an air handler flow plate device (per ASHRAE Standard 152P methodology).
• Overall duct system and house airtightness in 20 of the 69 homes.
• Cooling and heating system capacity based on air handler and outdoor unit model numbers.
• The location and type of filter.
• Dimensions and surface area of the air handler cabinet.
• The fractions of the air handler under negative pressure and under positive pressure.
• The types of sealants used at air handler connections.
• Estimated portion of the air handler leak area that was sealed “as found.”

Air Handler Leakage

Figure 64 Thermograph of air being drawn from the attic to the air handler in a Florida house

Leakage in the air handler cabinet averaged 20.4 Q 25 in 69 air conditioning systems. Leakage at the return and supply plenum connections averaged 3.9 and 1.6 Q 25, respectively. Using the operating pressures in the air handler and at the plenum connections, these Q 25 results convert to actual air leakage of 58.8 CFM on the return side (negative pressure side) and 9.3 CFM on the supply side (positive pressure side). The combined return and supply air leakage in the air handler and adjacent connections represents 5.3% of the system air flow (4.6% on the return side and 0.7% on the supply side). This is a concern, when considering that a 4.6% return leak from a hot attic (peak conditions; 120 oF and 30% RH) can produce a 16% reduction in cooling output and 20% increase in cooling energy use (Cummings and Tooley, 1989), and this was only from the air handler and adjacent connections. (Figure 64)

“Total” Duct Leakage

Some important observations were made from the extended test data in 20 houses. Total leakage on the return side of the system (including the air handler and return connection) was 53 cfm with weighted operating pressure on the return side of about -100 Pa (including the air handler), operating return leakage was calculated to be 122 CFM, or 9.7% of the rated system air flow.

Total leakage on the supply side of the system (Q 25s,total) was very large, at 134. The ASHRAE 152P method suggests using half of the supply plenum pressure as an estimate of the overall supply ductwork operating pressure, if the actual duct pressures are not known. For the 20 systems with extended testing, supply plenum pressure was 73.3 Pa. Based on a pressure of 37 Pa, actual leakage should be 167 CFM or about 13.3% of the rated air flow. To test the ASHRAE divide-by-two method, supply duct operating pressure measurements were taken from 14 representative systems. These averaged 35.9 Pa, compared to 65.7 Pa for the supply plenums for those same 14 systems. For these systems, the duct pressure was 55% of the supply plenum pressure - making the ASHRAE method a reasonable method for estimating central Florida home’s supply ductwork operating pressures.

However, the ASHRAE method wasn’t reasonable for estimating central Florida home’s return ductwork operating pressures. For these 20 systems, 38% of the Q 25r,total was in the air handler and 62% of the Q 25r,total was in the return ductwork. Given an air handler pressure of -133 Pa, a return plenum pressure of -81.5 Pa, and return duct pressure of approximately -70 Pa, the weighted return side pressure was approximately -95 Pa. By contrast, the ASHRAE method predicted -41 Pa. Clearly, in systems with a single, short return duct plenum like those commonly found in Florida, the actual operating pressure should be greater than the return plenum, maybe by as much as 1.2 times the plenum pressure.

Return side leakage is available on 58 of the 69 systems. Return leak air flow (Q r,total) combined for the air handler, return connection, and the return ductwork was found to be 152.4 CFM, or 11.8% of total rated system air flow for this group. For this larger sample, Q r,total is considerably greater than for the 20 houses with extended testing. These alarming results show that even in these newly constructed homes about 12% of return air and 13% of supply air duct systems are leaking.

Duct Leakage to “Out”:

In 20 homes, duct leakage to “out” was measured. (Table 38) On average, 56% of the leakage of the return ductwork and supply ductwork was to “out.” “Out” is defined as outside the conditioned space, including buffer spaces like an attic or garage. The fraction of leakage that was to “out” varied by air handler location. For return ductwork, the proportion of total leakage to “out” is 81.4% for attic systems, 67.6% for garage, and 28.0% for indoors. For supply ductwork, the proportion of total leakage to “out” was in the range of 52% to 56% for all three locations.

The attic return ductwork was the most predictive variable to “out” leakage findings. All of the return ductwork for attic units was located in the attic. Much of the return ductwork for other units was located in the house. As a consequence, the energy penalty associated with locating the air handler in the attic was greater than indicated in the computer modeling results in Table 39, since the modeling only considered the leakage of the air handler cabinet and the adjacent connections, and not the return ductwork leakage.

Table 39 shows that the operating supply leakage to “out” was large for all three air handler locations, averaging 89 CFM. The average operating return leakage to “out” was slightly larger, at 90 CFM. However, there was a large variation between air handler locations; 96 CFM for attic systems, 131 CFM for garage systems, but only 38 CFM for indoor systems. From an energy perspective, the attic systems experienced the greatest “real” energy penalties, because all of the return ductwork and air handlers were located in the attic. (Table 38) By contrast, a majority of the return leakage for the garage systems likely came from the garage (which is considerably cooler than the attic). For indoor systems, the return leakage to “out” most likely originated from the attic. However, since the return leakage was so much smaller, the energy impact was likely considerably less than both the attic and the garage systems.

Figure 65 Supply CFM25 “total” leakage versus the number of supply registers.

Figure 66 Supply CFM25 “out” leakage versus the number of supply registers.

Correlation of Supply Duct Leaks with Number of Registers: When analyzing the supply leakage in the extended test data, a surprising correlation was observed. This correlation indicated a systematic and consistent duct fabrication problem across a wide range of air conditioning contractors. Figure 65 illustrates this correlation, showing that each supply duct has a remarkably predictable total duct leakage. The coefficient of determination is 0.86, indicating that 86% of the variability in total supply duct leakage was explainable by the number of supply registers. Figure 66 shows a similar relationship between supply leakage to “out” and the number of supply registers. In this case the coefficient of determination was 0.69, indicating that 69% of the variability in total supply duct leakage was explainable by the number of supply registers. Note that one of the two houses with 13 registers showed considerably less leakage than expected. In this case, supply ducts were located in the interstitial space between floors. When the house was taken to -25 Pa, it is probable (though not measured) that the interstitial spaces were substantially depressurized as well, so leaks in those supply ducts would show less air flow (i.e., less pressure differential = less leakage air flow) and therefore be under-represented.

The data suggest that a duct leakage problem occurs in nearly all new homes. Researchers identified three issues that create most of the leakage: (1) the connection of the supply register or return grill (Figure 68), (2) the boot (supply box) to sheet rock connection (Figure 67), and (3) the flex duct to collar connection. The supply register or return grill leakage typically shows as supply leakage in the “total” test. It usually occurs when the register or grill does not fit snugly to the ceiling or wallboard. Issues two and three show up as leakage to both “out” and “total.”

Figure 67 Flexible duct to metal collar connection.

Figure 68 Gaps at the supply register to drywall joint

Figure 67 shows how flexible duct connections typically are made. In some cases metal tape is used, but the tape wrinkles when applied to complex angles and over bumps associated with these connection types. Although small in size, these cumulative wrinkles at each connection allow air to pass through.

Computer Modeling for Florida Energy Code Air Handler Multipliers:

FSEC researchers performed simulations and developed air handler multipliers for the Florida Energy Code using this study’s simulation results. Researcher used the FSEC 3.0 model, a general building simulation program developed in 1992. This program provided simultaneous detailed simulations of a whole building system, including energy, moisture, multi-zone air flows, and air distribution systems.

In 2001, modeling had been performed to develop initial air handler multipliers. These multipliers were based on estimated Q 25 and duct operating pressures. At the time of the 2001 modeling, there was essentially no data on air handler and connection leakage. Modeling for this project was performed again, but this time using the results of the 69 field tested homes.

The modeling inputs used in 2001 and those from the current study are shown below. (Table 40) Note that the same Q 25 and operating depressurization (dP) values was used for all air handler locations, since there was essentially no difference between the Q 25 values for attic, garage, and indoor air handler locations when gas furnace units were removed from the analysis.

While the Q 25 leakage for the air handler and connections was about 65% less than earlier estimates, operating pressures were much higher. The air handler multipliers based on the current computer modeling results are presented in Tables 41, 42, and 43. Modeling of air handler energy use also was performed for the air handlers located outdoors, despite the fact that no field data was collected for outdoor units. The modeling input parameters were the same as the other air handler locations as shown in Table 40. Note also that the air handler multipliers for the attic, indoors, and outdoors are normalized to the garage, since this location was considered the baseline. The final report for this study can be viewed online at: http://www.fsec.ucf.edu/bldg/pubs/cr1357/index.htm.

• Air Conditioning Condenser Fan Efficiency

Purpose

The purpose of this study is to develop an air conditioner condenser fan that reduces the electric energy use of the condensing unit (Figure 69). To accomplish this, researchers are designing and producing more aerodynamic fan blades and substituting smaller horsepower (HP) motors which achieve the same air flow rates as the larger, less efficient motors typically used.

4th Budget Period

Figure 69 Air conditioning condenser fan and diffuser.

During the 4th budget period, researchers developed baseline data for the fan power use in a standard condensing unit (Trane 2TTR2036) and tested a new prototype design: “Design A5” with five asymmetrical blades

Baseline data included condenser airflow, motor power, sound levels, and condenser cabinet pressures. Test results favorably compared with the manufacturer’s test data. An experimental set of fan blades, “Design-A5,” designed for a 1/8 hp motor at 850 rpm was numerically created and then successfully produced using rapid prototyping. These prototype blades were substituted on the original condenser, and all test measuredments were redone. Design-A5 was found to reduce power use by 20% (40 watts) with approximately equivalent airflow to the original condensing blade design.

5th Budget Period

During the 5th budget period, activities included re-calibration and improvement of the test equipment configuration, refinement of various designs, and patent filing.

Re-calibration and Improvement of Test Equipment Configuration

The air flow measurement equipment was re-calibrated by the Energy Conservatory in Minneapolis in accordance with ANSI/ASHRAE 51-1985 ("Laboratory Methods of Testing Fans for Rating."). Testing determined that the "flow cube" could be modified with settling screens and a flow straightener to yield a 5% absolute flow accuracy and a 2% relative accuracy from the test equipment. Also, the test configuration was moved indoors in order to better measure sound and also to reduce test variability from wind-related effects. Noise measurement protocol improved to comply with procedures used by the air conditioning industry.

Continued Testing to Refine the Identified Condenser Fan and Condenser Top Design

All fans were re-evaluated after bringing the test apparatus into compliance with ANSI/ASHRAE 51-1985 ("Laboratory Methods of Testing Fans for Rating.") New fan prototypes “Design-D” and “Design E” were tested as well as a diffuser for a 27" fan and a specially prepared Electronically Commutated Motor (ECM) provided by General Electric.

All designs were also tested with the conical diffuser with 20-27% increases in measured flow from the low rpm designs, which use 8-pole motors. Sound measurements (Table 44) also showed large advantages with as much as a 4 dB reduction in fan sound level over the standard fan. The final test prototype with diffuser and fan is shown in Figure 70.

Presentation and Commercialization

In January, BAIHP researcher Danny Parker made a presentation at the DOE Expert meeting on HVAC and Fans in Anaheim, California and participated in productive meetings with Trane Corporation in May 2004 to discuss licensing of the technology under an existing non-disclosure agreement.

Patents Pending

U.S. Application Serial No. 10/400,888, Provisional applications 60/369,050 / 60/438,035 & UCF-449CIP; WhisperGuard (UCF-Docket No. UCF-458)

Key Improvements from WhisperGuard Technology

Figure 70 Final test prototype with diffuser and fan.

Tested Performance with Trane TTR2036 Condenser:

• Provides 46 Watt reduction in fan power (144 W vs. 190 Watts)
• Increases condenser air flow by 130 cfm (6% increase in fan flow)
• Provides 102 W power reduction with ECM 142 motor
• Reduce ambient fan-only sound level by 4-5 dB
• ECM motor allows lower fan speeds for ultra-quiet night operation, higher flows for maximum capacity during very hot periods (temperature based control)
• Attractive hi-tech diffuser appearance

Key Technologies Employed

• High efficiency 5-bladed asymmetrical fan moves air quietly at lower fan speeds
• Diffuser top for effective pressure recovery increasing air flow at slow speed ranges
• Conical center body reduces exhaust swirl
• Acoustic sound control strip to reduce tip losses and control tip vortex shedding
  
  
• Fenestration Research

American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Technical Committee :

In 2002, BAIHP researchers wrote a statement of work for the development of a methodology to calculate solar spectral distributions incident on windows for various sun positions and atmospheric conditions. ASHRAE approved the project and sent it out for bid. Completion of this work project should make it much easier to determine the true solar heat gain through spectrally selective fenestration systems for varying atmospheric conditions and solar altitude angles.

Calorimetric Measurements of Complex Fenestration Systems

FSEC’s research calorimeter will be used both indoors with the FSEC Vortek solar simulator and outside under natural solar radiation, on its Sagebrush solar tracker, for window solar heat gain experiments. The results of this testing will offer a way to test the solar gain properties of complex and other non-standard fenestration options for industrialized housing, such as exterior and interior shades and shutters, and those placed between the panes of double pane windows.

Sagebrush Solar Tracker

The computer program running the calorimeter, the Sagebrush tracker, and both together is complete. It contains a user-friendly graphic interface and offers a wide variety of experimental opportunities. There are many channels for adding additional temperature sensors and the calorimeter/tracker can be operated with either the sun as a source - in a variety of tracking modes - or with FSEC’s Vortek solar simulator.

To conduct outdoor testing, the Neslab chiller must be connected to the flow meter, the temperature sensors to the calorimeter, and the calorimeter mounted on the tracker. The Sagebrush tracker now is functional, responding properly to commands sent from the computer, rotating in altitude, and azimuth and stopping when the limit switches are encountered. A telescopic sight and level for positioning it outdoors in the proper orientation for accurate solar tracking has been designed and is near fabrication completion.

Figure 71 Side view of calorimeter before it was mounted on the Sagebrush Tracker.

The Neslab chiller and remote controller have been connected to a Gateway laptop computer and a RS-485 serial interface card necessary to operate the calorimeter has been installed. Researchers can now send commands and receive data from the chiller. Although the calorimeter is designed to work directly with the existing FSEC hydronic loop used for testing solar collectors, the Neslab will give an independent, standalone capability to the calorimeter. (Figure 71)

The water flow meter purchased for measuring the flow into the calorimeter has been successfully connected to the Agilent (HP) 34970A data acquisition system and its measurements were incorporated into the calorimeter operating program. Temperature sensors also successfully connected to the data acquisition system, are reading properly, and have been incorporated into the calorimeter program. The program has coding to include a number of additional temperature channels once the temperature probes have been received and installed in the calorimeter. Another 20-channel input card is being purchased for the Agilent, to permit additional temperature readings. Knowing the flow rate and temperature difference, the heat delivered to the water by the calorimeter can now be accurately determined.

Now that all portions of the system are operational, researchers will configure the outdoor system, verify, and begin testing in Year 5.

Vortek Solar Simulator

In 2003, the Vortek Simulator was fired up and operated reliably on the calorimeter testing with FSEC’s solar collector test apparatus. As expected, a few computer and other problems delayed initial data collection by a couple of days. However, these problems were corrected and testing proceeded normally.

During testing, the calorimeter was connected to the existing facility’s hydronic loop, which was developed over a period of years to a temperature stability of 0.01 degrees centigrade. The irradiance level measured about 820 watts per square meter over an aperture of 0.557 square meters. The calorimeter was tested as though it were a flat plate collector, to obtain its efficiency curve. This was used to infer the thermal losses and solar heat gain coefficient of the eighth inch clear single pane of glass used for the test. The nominal wind speed was set by the laminar blower to five miles per hour. The coolant flow was run at levels of 0.2, 0.5, and 1.0 gallons per minute (GPM), and at varying inlet temperatures.

For all test runs, steady state conditions were established by observing the outlet temperature in a real-time plot as equilibrium was approached. During periods of non-equilibrium, the recorded data was used to measure the first-order system time constant, a function of the flow rate. The calorimeter time constant varied from 1.5 minutes at 1.0 GPM to 6.9 minutes at 0.2 GPM. These time constants were obtained by blocking the incident beam and watching the decay in outlet temperature.

Skylight Dome Transmittance

Researchers completed work on the skylight dome transmittance, adding a spherical shape to the cylindrical one previously used. The ray tracing programming was changed to eliminate reflection of rays approaching the dome from the inside, for comparison with the analytical model, which does not yet include internal reflections. The difference between the two computational approaches, at a 30 E solar zenith angle is 1.7%, considered acceptable for rating skylight performance.

With both cylindrical and spherical dome models, transmittance at large solar zenith angles above 60 is substantially greater than for a horizontal flat plate. This is because most of the rays incident on the dome and entering the skylight are incident on the dome close to perpendicular, where dome transmittance is highest.

Energy Gauge USA and Energy Gauge FlaRes

BAIHP mapped a table of window and shade characteristic simulations that could be run with these two programs. These runs will be used to determine the energy use of various fenestration options for Florida residences and to guide the preparation of instructional materials.

Florida Market Transformation

From the beginning of the BAIHP program, researchers have provided technical background information and support to the Alliance to Save Energy and the Efficient Windows Collaborative to promote the sale and installation of energy efficient fenestration in hot climates (such as Florida) and other areas for both conventional and industrialized homes. BAIHP also provides advice, technical information, and educational information to energy companies regarding window energy performance.

National Fenestration Rating Council (NFRC) Technical Committee

In 2002, BAIHP presented a final report at a Task Group meeting in Houston, on the NFRC- funded work to develop a draft standard practice for the rating of tubular daylighting devices. That project is now complete.

In 2001, BAIHP researchers performed a number of ray traces on a highly reflective cylinder of varying lengths, using the trace results to determine the cylinder’s transmittances for different interior surface reflectivities (from 90% to 100%). These results generated a “default table” for determining the transmittance of this tubular daylighting component. Using simplified assumptions, and then multiplying the tube transmittance by the top and bottom dome transmittance results, researchers determined the total transmittance for a chosen sun angle. Based on the findings, BAIHP provided NFRC and the industry with a list of suggested research projects to test and develop this methodology further. One of these submitted projects was sent out for bid by ASHRAE in Year 4 and is expected to begin in Year 5.

Tubular Daylighting Device SHGC and VT Value Calculations

Following a request from the TDD industry, a sequence of operations and a new computer program were written to access the Window 5 glazing database and obtain from it the spectral transmittance and front and back reflectance data for any sheet of glazing in that database which might be used in making the top dome of a tubular daylighting device. This permits determination of the input parameters needed to run TDDTrans. The computer program was posted for free download and is available by clicking on http://fsec.ucf.edu/download/br/fenestration/software/TddTrans-Beta/TDDTrans.exe.

Access sequence:

• Download and run the Optics 5 program.
• Select the glazing to be used in the tubular daylighting device.
• Export its spectral data file as a standard ASCII text file.