1、4736 Thermal Performance Characteristics of an Energy-Efficient, Healthy House E.A. Ibrahim, Ph.D., P.E. H. Aglan, Ph.D., P.E. M. Khan, PhB. M. Bhuyan R. Wendt S. Livengood ABSTRACT A collaborative effort between Oak Ridge National Labo- ratory and Tuskegee University has resulted in an energy-efi-
2、cient, healthy house that is built on Tuskegee Ls experiment station farm to conduct various energy eficiency and indoor air quality studies. The house is well insulated and possesses other energy-eficient features, such as airtight construction, reflective roofing, and unventilated crawlspace. The
3、energy eficiency and thermal performance of the house are investi- gated in view of electric power consumption as well as indoor and outdoor temperature and relative humidity data. The data were collected over three periods during the heating season of 2002. The ventilation fan was continuously turn
4、ed offfor the firstperiod and turned on ai the rates of 60 cfm (28.3 L/s) and 115 cfm (54.3 Us) during thesecond and thrdperiods, respec- tively, to facilitate comparisons of indoor conditions and energy consumption at various ventilation levels. A blower- door test was performed to evaluate the air
5、tightness of the house. A heating load analysis was employed to assess the thermal performance of the house. Indoor relative humidity data indicated that forced air ventilation contributed to an improved indoor air quality. Independent house air leakage estimates obtained through infiltration load c
6、alculations and blower-door measurements agreed that the house was fairly airtight, requiring mechanical ventilation. INTRODUCTION In light of the need to address energy efficiency and indoor air quality in residential buildings, a team of research- ers from Oak Ridge National Laboratorys Building T
7、echnol- ogy Center and Tuskegee Universitys College of Engineering, Architecture and Physical Sciences, Tuskegee, Alabama, have designed and constructed a “health house.” The teams goal was to develop a prototypical house that balanced the oAen competing values of affordability, energy efficiency, a
8、nd indoor air quality. The result is a 24 x 32 ft (7.32 x 9.75) or 768 ft2 (71 m2) house located at Tuskegees exper- iment farm. The floor-to-ceiling height is 8 feet (2.44 m) and therefore the house volume is about 6,144 fi3 (174 m3). The house has two bedrooms, one bath, a dine-in kitchen, a livin
9、g room, and small utility areas. The house construction cost totaled about $35,000 or $45.57/ft2. A schematic of the house floor plan is shown in Figure 1. The HVAC system is an optimally sized, conventional split package, 1.5-ton heat pump system that is centrally located to minimize ductwork. Inst
10、alling a heat pump elimi- nates potential combustion by-products. The house has averti- UVING ROOM tV-T x 144“ 17-lO“x tl-* BEDROOM 2 iv-2- x il*” 1 . FRESH AIR IN PRofONpe FLOOR PUN EXMUST 7s8 Squat0 Foot Figure I Floor plan of the house. - - E.A. Ibrahim is a professor, H. Aglan is an associate de
11、an and professor, and M. Bhuyan is a graduate student in the Mechanical Engineering Department, at Tuskegee University, Tuskegee, Ala. M. Khan is an associate professor in the Aerospace Science Engineering Department, Tuskegee University. R. Wendt is an architect and S. Livengood is a research engin
12、eer in the Building Technology Center, Oak Ridge National Laboratory, Oak Ridge, Tenn. 432 02004 ASHRAE. - cal air handledventilation system with a 1/6 hp (1/8 kW) motor, 1 15 cfm (54.3 L/s) rated fan and a 0.3-micron filter, and spot ventilation units in the bathroom. All appliances are elec- tric,
13、 which also helps to eliminate combustion byproducts. It is recognized that there are few large bodies of data on building energy performance, and those that exist often express that performance in incompatible ways. Typical expressions of energy performance have been: site energy without regard for
14、 energy form, source energy without regard for type of energy resource, etc. Each of these is often “normalized” by dividing by building floor areas, ignoring the significant differences between large and small buildings. ASHRAE Standard 105-1999, Standard Methods of Measur- ing and Expressing Build
15、ing Energy PerSormance (ASHRAE 1999), provides a uniform basis for reporting energy use by requiring the reporting of the “raw” normally measured data for each form of energy used as delivered to the building. Compliance with ASHRAE Standard 105-1 999 also requires the reporting of sufficient inform
16、ation about the building, its use, the local climate, and the calculation or measurement method used so that those receiving the data can apply their own desired analysis and comparison. In the present work, data of the house energy efficiency and thermal performance characteristics are presented an
17、d analyzed. These data include measurements of temperature and relative humidity as well as power consumption. The data were collected for three periods over the months of November and December during the heating season of 2002. The first, second, and third periods ran from 1 1/22 to 12/3, 1213 to 1
18、2/ 11, and 124 1 to 12/1$, respectively. Each of the three periods had a different amount of fresh air supply to allow for compar- ing the influence of ventilation on the house thermal perfor- mance and indoor air quality. During the first period, the fresh air supply (ventilation fan) was turned of
19、f. The fresh air supply was set at 60 cfm (28.3 L/s) and 115 cfm (54.3 Ws) during the second and third periods, respectively. A blower-door auto- matedperformance testing (APT) technique was conducted on 2/12/2003 to assess the airtightness of the house. All windows were closed during the entire mon
20、itoring period. The house has never been occupied or furnished, but appliances, such as refiigerator, water heater, and range, are installed. One or two investigators entered the house briefly during daytime hours to check on data collection. The measurements were obtained with the house unoccupied
21、and all lights and appliances shut off. Therefore, electric energy is only consumed in providing the air-conditioning system heat pump, ventilation fan, and data acquisition system demands. The data are examined and conclusions regarding the house thermal performance and airtightness are drawn. ENER
22、GY EFFICIENCY FEATURES in the house construction are: I. Good insulation 2. Airtightness The most important energy efficiency features considered 3. Unventilated crawlspace The house is sheathed with R-5 insulated foam sheathing to provide a continuous layer of insulation as well as some air and moi
23、sture barrier. An R-19 fiberglass batt is compacted between the wood studs that frame the exterior walls. The sheathing and framing techniques are designed to minimize thermal shorts and improve energy efficiency. The foam sheathing joints are not sealed. The attic has two layers of R- 19 fiberglass
24、 insulation, for a total R-value of 38. One layer of insulation is placed between the bottom chords of the trusses and the second layer is laid perpendicular to the first layer. The roofing material selected is relatively low-cost white metal roofing called 5-V Crimp. This roofing material does not
25、off- gas as much as petroleum roofing products and it requires little maintenance over a 40-50 year life span. A continuous soffit and ridge vent system was installed to control the temperature in the attic. The selected insulation materials and techniques are geared toward decreasing heat losses fr
26、om the house. Several airtightness features are employed in the house construction to diminish leakage. The concrete masonry unit (CMU) foundation wall has an enclosed crawlspace with concrete footings under the exterior wall, filled with cement concrete mixture. The house sheathing and framing prov
27、ide a barrier to air and moisture. Off-the-shelf wall-mounted light fixtures are used to reduce penetrations through the ceiling. The house has only one plumbing wall with one floor pene- tration. All ductwork and penetrations through the building envelope are sealed. The implemented air-tightening
28、tech- niques are believed to maintain air leakage through the house to a minimum. Anis (2001) notes that minimizing air leakage is impor- tant to maintaining comfort, enabling the mechanical system to meet loads and maintaining pressurization in the case of a fire, in addition to the benefits of red
29、uced energy bills. Air pressure acting on building envelopes can wreak havoc with building performance if not properly understood and adequately designed. Uncontrolled air pressure across the building envelope can cause infiltration and exfiltration that overpower HVAC systems. Exfiltrating air carr
30、ies with it water vapor and lost energy. The water vapor may condense and cause problems such as wetting that lead to deterioration of the building envelope. Water vapor is carried in with infil- trating air, causing condensation, mold, and bacterial growth. Although it is usually assumed that air l
31、eakage is a result of poorly weather-stripped windows and doors, 80% or more of air leakage is due to the many imperfections that are designed or built into exterior envelopes (Anis 2001). U.S. Department of Energy (DOE) and Oak Ridge National Labo- ratory (ORNL) sponsored three symposia in 1999-200
32、1 to draw national attention to the problem of air leakage in build- ings and how to take care of it using air barrier technology. Anis (2001) notes that both ASHRAE Standard 90.2-2001, Energy Eficient Design of Low-Rise Residential Buildings (ASHRAE 200 1) and the International Energy Conservation
33、Code requirements “are extremely vague when it comes to air ASHRAE Transactions: Research 433 tightening the building envelope. Air tightening is typically called for by requiring caulking, gasketing, weather stripping and stuffing crevices and cracks. That seems to be an outdated and nave approach
34、to a major problem in buildings today.“ The crawlspace is not ventilated to prevent air and mois- ture leakage and reduce energy loss through the house floor. The crawlspace floor is covered with 2 in. (0.05 m) of fine sand on top of a full-ground polyethylene vapor-retarding membrane. The crawlspac
35、e is enclosed to minimize migration ofmoisture from the ground to the living area ofthe house. The present measurements show that the crawlspace temperature was only about 4.5“F (2.5“C) below the living room temper- ature, on average, during the monitoring period. This small temperature difference a
36、cross the house floor significantly reduces the heat transmission load of the entire house since the floor has a large area and very small thermal resistance, as will be discussed later. EXPERIMENTAL TECHNIQUE To monitor the indoor conditions, dual temperaturerela- tive humidity sensors are placed i
37、n the living room, attic, and crawlspace. A dual sensor is used in each area. The living room sensor is placed at a central location on a table about 3 ft (0.92 m) above the floor. The attic sensor is installed 2 ft (0.61 m) above the attic insulation, while the crawlspace sensor was located in the
38、joist. The temperature measurement accuracy ofthe sensor is lt0.9“F (k0.5“C) fora range of-23“F to + 13 1 “F (-5C to + 55OC) with linearity better than O. 18F (0.1OC). The relative humidity measurement accuracy for the sensor is f 3% over the range of O to 95% and has a tempera- ture dependence betw
39、een 50F and 104F (10C and 40C) for a variation of the relative humidity less than 0.5%. The outdoor temperature and relative humidity are downloaded from a weather station located about 200 yards (183 m) away from the house. The output voltages from the dual temperaturerelative humidity sensors are
40、scanned by a 0.7 kW data acquisition/ switch unit. This unit has a storage capacity of 50,000 scans with programmable scanning rates. Data from the data acqui- sition unit are periodically downloaded to a notebook computer for processing. The electric power consumption is measured using a house mete
41、r that is provided by the power company. Since there are no occupants and all lights and appliances are turned off, the registered electric power consumption is totally spent in supplying the air-conditioning system heat pump, ventila- tion fan, and data acquisition system demands. An automated-perf
42、ormance-testing (APT) blower-door test is conducted to assess the overall airtightness of the house. The blower door consists of a powerful, % hp (0.56 kW), cali- brated fan that is temporarily sealed into the exterior doorway of the building using an adjustable aluminum door frame. An airtight nylo
43、n tarp is fitted around the adjustable frame. The tarp contains a large hole near the bottom into which the fan is fitted. Elastic around the perimeter of the large hole keeps air from flowing around the outside of the fan. A long flexible plastic tube fits tightly through an opening in the tarp and
44、 is used to measure the pressure difference between the building and outdoor. The fan blows air out of the building to create a negative pressure difference in the house relative to outside. This nega- tive pressure induces air to enter the house through cracks, penetrations, or holes in the buildin
45、g exterior surface. By simultaneously measuring the airflow through the fan and its effect on the air pressure in the building, the blower-door system measures the airtightness of the building envelope. The tighter the building, the less air is needed from the blower-door fan to create a change in b
46、uilding pressure. During the automated testing, a notebook computer is used to adjust the speed of the blower-door fan while simul- taneously monitoring the building pressure and fan flow using two differential pressure channels built into a data acquisition box powered by a 12 V power supply. The A
47、PT system has a computerized door fan speed control and data collection, which improves the accuracy and repeatability of test results by reducing wind and operator errors. The automated operation also eliminates time spent zeroing gauges and adjusting fan speed. The APT system auto- matically recor
48、ds the offset pressures due to wind and stack effects. Cruise control allows for maintaining a constant build- ing pressure during diagnostic procedures. RESULTS AND DISCUSSION Thermal Performance During the first period of monitoring (November 22 to December 3, 2002), indoor and outdoor measurement
49、s of temperature and relative humidity were taken with all windows closed and without running the ventilation fan- there was no fresh air makeup. The electrical power consump- tion meter gave an average reading of 13 kWh/day for the i 1 - day monitoring period. Figures 2 and 3 display the tempera- ture and relative humidity data, respectively, for outdoor, attic, living room, and crawlspace. The maximum, minimum, and average temperature and relative humidity are also computed and listed in Table 1. During the second period of monitoring (December 3
