1、NA-04-6-1 Field Observations of Room Air Distribution Performance in a High-Performance Home Keith A. Temple, Ph.D., P.E. Member ASHRAE ABSTRACT The objective of the current investigation was to evaluate thejeldperformance of room air distribution in two rooms of a high-performance (low heating and
2、cooling load) home. The two rooms had similar exterior exposures but had direrent supply register locations (high sidewall andfloor). The impact of normal equipment cycling on the room air distribution pe rformance was also investigated. The performance was evaluated based on room air temperature me
3、asurements and the requirements of ASHRAE Standard 55 (ASHRAE 1992). Measurements were made in a test home in Pittsburgh, Penn- sylvania (cold climate), during both heating and coolingperi- ods. The room with the high sidewall register (bedroom) had approximately 50% of the design airflow based on l
4、oad calcu- lations, and the room with thefloor register (dining room) had approximately 140% of the design airflow. Acceptable temper- ature conditions were maintained at most times in the room with high sidewall supply with approximately 50% of the design airflow. Based on this observation, a concl
5、usion of this investigation is that the heating and cooling loads associated with the thermal envelope of a high-performance home create a rather forgiving situation for a space-conditioning system with high sidewall supply. A preliminary conclusion, based on stratijcation and temperature cycling pe
6、rformance, is that high sidewall supply with a non-spreading register is efective for both heating and cooling operation in a cold climate. This requires further investigation because it is not clear how the low supply airfow impacted the vertical temperature stratifi- cation in this room. Another p
7、reliminary conclusion from this investigation is that floor supply with a spreading register provides marginal heating operation in a high-performance home, as indicated by higher vertical temperature stratijica- tion and unacceptable temperature cycling. All the conclu- sions from this investigatio
8、n are limited to the conditions of the room air distribution methods studied and are worthy of further investigation. Future workwill include balancing of the test home system and continued investigation of the room air temperatures. INTRODUCTION Residential spaces that are heated and cooled with a
9、forced air system depend on room air distribution to satisfy the thermal load conditions and maintain acceptable thermal comfort. This room air distribution is typically accomplished with dimisers or registers located in the space. Current design and installation practices, however, often result in
10、unsatisfac- tory results from both a comfort and energy consumption perspective. Poor system performance is often a result of several of the following factors: poor air outlet location, improper selection of diffuser or register, varying airflow rates, and outlet obstruction. Existing room air distr
11、ibution methods were developed primarily for commercial applica- tions. Current residential applications impose different design constraints, including reduced internal loads and space occu- pancy issues (furniture location, etc.). A high-performance home also has reduced envelope loads. The reduced
12、 load densities usually result in lower airflow rates. All of these factors contribute to the need for careful design and selection of supply and return registers to provide good room air distri- bution. The objective of the current investigation was to eval- uate the performance of the room air dis
13、tribution in two rooms of a high-performance home. Keith Temple is a research and design consultant in Pittsburgh, Penn. 02004 ASHRAE. 699 BACKGROUND The effectiveness of room air distribution is a subject that has received much attention related to commercial applica- tions; however, room air distr
14、ibution related to residential applications is rarely addressed. The ASHRAE Handbook- Fundamentals (ASHRAE 2001) chapter entitled “Space Air Diffusion“ presents general information and guidelines for room air distribution, but the information is most applicable to commercial spaces and does not cove
15、r the low load densities associated with high-performance homes. The ASHRAE Handbook-HVAC Systems and Equipment (ASHRAE 2000) Cooling Systems“ presents selection criteria for supply outlets cations. The Air Conditioning Contractors of America Manual T (ACCA 1992) provides guidelines for selecting su
16、pply outlets and return inlets for residential applications; however, there is some disagreement with the information presented by ASHRAE. There is limited design guidance for room air distribution systems that are to be used in residential applications for both heating and cooling. Thermal comfort
17、is a focus of room air distribution inves- tigations and evaluation. ASHRAE Standard 55 (ASHRAE 1992) specifies a number of criteria that must be met in order to maintain acceptable thermal comfort in occupied spaces. Several of these relate directly to room air distribution for spaces heated and co
18、oled by forced-air systems. The floor temperature must be between 65F and 84F (1 8C to 29OC). To minimize drafts, local air speed must be controlled based on space temperature, e.g., at 74F (23.3“C) and 10% turbu- lence intensity, the maximum air speed is 50 fpm (0.25 ds) in the occupied zone. The v
19、ertical air temperature difference from 4 to 67 in. (O. 1 to 1.7 m) above the floor should not exceed 5 .O“F (3OC). When temperature fluctuations are involved- which is usually the case for residential applications due to equipment cycling-the rate of temperature change should not exceed 4.0F/h (2.2
20、“C/h) when the temperature variation exceeds 2.O“F (1 .l“C), peak-to-peak in a 15-minute period. The standard also provides test procedures for evaluating ther- mal comfort. Much of the previous research related to room air distri- bution has focused on commercial applications (Rock 2001, 2002; Stra
21、ub and Cooper 1991); however, there has been significant work recently related to residential applications. Saunders et al. (1 992) investigated thermal stratification and comfort in four unoccupied, heated residences. Tempera- ture measurements were made at the center of rooms, and stratification w
22、as computed based on the temperature differ- ence from 43 to 4 in. (1.1 to O. 1 m). Thermal stratification was found to be affected by many factors, including supply air temperature, room air temperature, room geometry, duty- cycle, and register locations. The dominating influence was air delivery t
23、emperature, with hotter supply air temperatures resulting in greater stratification; however, the influence was not as significant for second-floor rooms. The supply register locations for this study were not indicated in the paper. I chapter entitled “Design of Small Forced-Air Heating and that are
24、 appropriate for residential and light commercial appli- I Room air distribution using ceiling diffusers was demon- strated at IBACOS Lab House B in Pittsburgh, Pennsylvania (cold climate). Air was supplied to rooms by high-perfor- mance (commercial) ceiling difisers located at the rear of each room
25、 (away from the exterior wall). Initial comfort measurements, as reported by Rudd et al. (1994), consisted of local air velocity, temperature, and relative humidity measured at the center of rooms. Holton (1996a) presented additional comfort data, including temperature stability and temperature stra
26、tification data. The temperature stratification from head to foot was a maximum of 4F during the heating season. Additional comfort data are presented by Holton (1 996b). Overall, the Lab House B application was considered to be very successful at maintaining thermal comfort. Additional performance
27、testing related to residential applications was reported by Holton and Beggs (1 997). The objective of the testing was to study the performance of rear room ceiling and high wall diffusers in residential scale rooms. Testing was completed for three difisers in a ceiling config- uration and one diffu
28、ser in a high sidewall configuration, all at isothermal conditions. The two residential ceiling diffusers had unacceptable performance compared to the commercial diffuser that performed acceptably. One residential diffuser had sufficient throw but had almost twice the pressure drop of the commercial
29、 diffuser. The high sidewall configuration was found to have significant pressure drop at the approach fitting and required further investigation. Holton (2002) presented observations on changing design conditions for room air distribution in residential applications. The discussion includes the ide
30、ntification of a number of factors that must be addressed when investigating room air distribution, including supply location, supply register type, airflow rate, and supply air temperature. Baskin and Vineyard (2003) investigated thermal comfort for a conventional forced-air system and a high-veloc
31、ity forced-air system for cooling operation. They performed some limited investigation of the impact of register location (floor, ceiling, high wall, low wall) for the conventional system. The register location was found to affect thermal comfort, with the floor register having the lowest comfort le
32、vel. There are limited data available in the published literature on the performance of room air distribution systems used for both heating and cooling of high-performance homes. Addi- tional information is needed to develop appropriate design guidance for these applications. This paper will present
33、 the results of an investigation focusing on room air distribution performance in two rooms of a house located in a cold climate. FIELD INVESTIGATION In April 2002, a field investigation of room air distribution performance was initiated at a new home in Pittsburgh, Pennsyl- vania. The two-story tes
34、t home has three bedrooms and a total conditioned floor area of 2,700 ft (25 1 m2). The wall construc- tion includes nominal R-16 ft?.h.“F/Btu (R-2.8 m2.K/W) insu- 700 ASHRAE Transactions: Symposia lation and windows with U-0.32 Btu/(ft2.h.“F) (U-1.8 W/m2.W W) and SHGC-0.34. The roof has nominal R-3
35、8 (R-6.7 m2.W W) insulation. The house is heated and cooled by a central forced-air system with a gas-fired furnace and split system air-condition- ing system. The system thermostat is located in a hallway on the first floor near a return register. The house is currently being used as a model house
36、and has intermittent occupancy during the day, primarily on the weekends. Analysis and testing were completed to determine the house performance. The airtightness was determined to be 2.5 air changes per hour at 50 pascals based on a blower door test. The home obtained a Home Energy Rating System (H
37、ERS) score of 87. The calculated heating load is 5 1,000 Btuk (14.9 kw and the cooling load is 27,000 Btuk (7.9 kW) for outdoor design conditions of 1 “F (-1 7C) for winter (99%) and 89F (32C) for summer (1%). Two rooms were investigated-the dining room and one of the bedrooms. Partial floor plans a
38、re presented in Figure I, showing the location ofthe two test rooms. The rooms have the same compass orientation and similar wall exposures, with the exception of the dining room being longer. The dining room is located on the first floor above a conditioned crawlspace. The supply air outlet is a fl
39、oor regis- ter with vanes oriented perpendicular to the wall that provide some horizontal spread of the airflow. The ceiling height for the first floor is 10 ft (3.1 m). The return air path is through a 5 ft (1.5 m) wide opening that connects the room to a central hallway. Because of the low air spe
40、ed at the opening, the return air path is not expected to have a significant impact on the room air distribution. The bedroom is located on the second floor directly above the dining room. The supply air outlet in the bedroom is a high sidewall register with horizontal and vertical vanes. The verti-
41、 cal vanes are aligned (non-spreading) and provide some deflection toward the exterior wall with the window. The hori- zontal vanes are also aligned and direct the air parallel to the ceiling. The ceiling height is 9 ft (2.7 m), and the register is located 9 in. (229 mm) below the ceiling (to the to
42、p of the register core). A return air transfer opening is provided low on the wall near the door; however, the door is always open to the hallway. Because of the low air speed at the opening, the return air path is not expected to have a significant impact on the room air distribution. Room data are
43、 summarized in Table 1 and include the room dimensions and register type. The table includes a load fraction defined as the ratio of the room load to the total house load (heating or cooling). The load densities are also included for reference. Table 1. Test Home Room Data ASHRAE Transactions: Sympo
44、sia 701 - Floor Suppiy Register DINING ROOM mately 50% of the design airflow based on load calculations. The dining room (floor register) had a measured airflow of approximately 140% of the design airflow. The improper room airflows represent the system as it was installed and are due to a lack of s
45、ystem balancing. Approximate throw values are also reported in Table 1. The bedroom high sidewall register has an approximate throw of 5.3 ft (1.6 m) compared to a recommended value of 10 to 16 ft (3.0 to 4.8 m) based on ASHRAE (2000). The low throw is due primarily to the low airflow rate. The appr
46、oximate throw for the dining room floor register exceeds the recommended value of 4 to 6 ft (1.2 to 1.8 m) for a spreading floor register based on ASHRAE (2000). The results of this investigation are dependent on the register type and performance. Room air temperatures were monitored in each room wi
47、th Type-T thermocouples. Temperatures were measured at two horizontal locations and four elevations (8 points). The temperature sensors were located at elevations of4 in. (O. 1 m), 24 in. (0.6 m), and 67 in. (1.7 m) above the floor and 4 in. (O. 1 m) below the ceiling to comply with the requirements
48、 of ASHRAE Standard 55 (ASHRAE 1992) on thermal comfort measurements. The horizontal locations with the highest potential stratification in each room were selected for moni- for sedentary occupants. Temperatures at 43 in. (1.1 m) above the floor could be approximated by interpolating between the tem
49、peratures at 67 in. (1.7 m) and 24 in. (0.6 m). Additional short-term temperature measurements were made at several I RESULTS Data were collected for one cooling and one heating season during the period from June 2002 through January 2003. The data were analyzed in order to evaluate the room air distribution for both cooling and heating operation. A warm day (August 1,2002) and cold day (January 27, 2003) were selected for detailed analysis. Cooling A detailed analysis of cooling data for August 1, 2002, was completed. This was one of the warmest days in Pitts- burgh for th
