1、4751 Field Observations of Room Air Distribution Performance in Two Rooms of a Cold-Climate Home Keith A. Temple, PhD, PE Member ASHRAE ABSTRACT The objective of this investigation was to evaluate thefield performance of room air distribution in two rooms ofa high- performance (low heating and cooli
2、ng load) home. The two rooms had similar exterior exposures but had diferent supply register locations (high sidewall and floor). The impact of normal equipment cycling on the room air distributionperfor- mance was also investigated. The performance was evaluated based on room air temperature measur
3、ements and the require- ments of ASHRAE Standard 55 (ASHAE 1992). Measure- ments were made in a test home in Pittsburgh, Pennsylvania (cold climate), during both heating and cooling periods, after the air distribution system had been balanced. The room with the high sidewall register (bedroom) had a
4、pproximately 75% of the design airflow based on load calculations, and the room with the jloor register (dining room) had approximately 100% ofthe design airflow. A conclusion of the study, based on strat- $cation and temperature cycling performance, is that high sidewall supply with a nonspreading
5、register at an interior wall is efective for both heating and cooling operation in a cold climate. Another conclusion from this investigation is that jloor supply with a spreading register at an exterior wall provides marginal heating operation in a high-performance home, as indicated by higher vert
6、ical temperature stratijica- tion and unacceptable temperature cycling. All of the conclu- sions from this investigation are limited to the conditions of the room air distribution methods studied and are worthy of further investigation. Additional research is recommended to investigate the effect of
7、supply air temperature, register throw, alternate equipment control, and outlet location on room air distribution performance in residential applications. INTRODUCTION Residential spaces that are heated and cooled with a forced air system depend on room air distribution to satisfy the thermal load c
8、onditions and maintain acceptable thermal comfort. This room air distribution is typically accomplished with diffusers or registers located in the space. Current design and installation practices, however, often result in unsatisfac- tory results from both a comfort and energy consumption perspectiv
9、e. 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 distribution methods were developed primarily for commercial applica- tions. Curren
10、t 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, resulting in reduced load densities and usually lower airflow rates. All of these factors
11、contribute to the need for careful design and selection of supply and return registers to provide good room air distri- bution. The objective of this investigation was to evaluate the field performance of the room air distribution in two rooms of a high-performance home after the air distribution sy
12、stem was balanced. BACKGROUND The effectiveness of room air distribution is a subject that has received much attention related to commercial applica- tions; however, room air distribution related to residential applications is rarely addressed. The ASHME Handbook- Fundamentals (ASHRAE 200 i), “Space
13、 Air Diffusion” chap- ter, presents general information and guidelines for room air Keith A. Temple is with KAT Consulting, Langhome, Pa. 02005 ASHRAE. 1 o1 distribution, but the information is most applicable to commercial spaces, focuses on cooling performance, and does not cover the low load dens
14、ities associated with high-perfor- mance homes. The ASHRAE Handbook-HVAC Systems and Equipment (ASHRAE 2000), “Design of Small Forced-Air Heating and Cooling Systems“ chapter, presents selection criteria for supply outlets that are appropriate for residential and light commercial applications. The A
15、ir Conditioning Contractors of America Manual T (ACCA 1992) provides guidelines for selecting supply 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 method
16、s that are appropriate for use in residential applications for both heating and cooling. Thermal comfort 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 to main- tain acceptable thermal comfort in o
17、ccupied spaces. Several of these relate directly to room air distribution for spaces heated and cooled by forced-air systems. The floor temperature must be between 65F and 84F (18C and 29C). To minimize drafts, local air speed must be controlled based on space temperature; e.g., at 74F (23.3OC) and
18、10% turbulence inten- sity, the maximum air speed is 50 fpm (0.25 ds) in the occu- pied zone. The vertical air temperature difference from 4 in. (0.1 m) to 67 in. (1.7 m) above the floor should not exceed 5.O“F (3C). When temperature fluctuations are involved, which is usually the case for residenti
19、al applications due to equipment cycling, the rate of temperature change should not exceed 4.0F/h (2.2“Ch) when the temperature variation exceeds 2.O“F (1.1 OC) peak-to-peak in a 15-minute period. The standard also provides test procedures for evaluating ther- mal comfort. Much of the previous resea
20、rch related to room air distri- bution has focused on commercial applications (Rock and Zhu 2002a, 2002b; Straub and Cooper 1991); however, there has been work recently related to residential applications. Saunders et al. (1 992) investigated thermal stratification and comfort in four unoccupied, he
21、ated residences. Tempera- ture measurements were made at the center of rooms, and stratification was computed based on the temperature differ- ence from 43 in. (1,l m) to 4 in. (O. 1 m). Thermal stratification was found to be affected by many factors, including supply air temperature, room air tempe
22、rature, room geometry, duty cycle, and register locations. The dominating influence was air delivery temperature, 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 stud
23、y were not indicated in the paper. Room air distribution using ceiling dimisers was demon- strated at a laboratory house (Lab House B) in Pittsburgh, Pennsylvania (cold climate). Air was supplied to rooms by high-performance (commercial) ceiling diffusers located at the rear of each room (away from
24、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 ccnter of rooms. Holton (1996a) presented additional comfort data including temperature stability and temperature stratification da
25、ta. The temperature stratification from head to foot was a maximum of 4F (2.2“F) during the heating season. Additional comfort data were presented by Holton (1 996b). Overall the Lab House B appli- cation was considered to be very successful at maintaining thermal comfort. Additional performance tes
26、ting 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 diffuser
27、 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 d
28、iffuser. 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 ident
29、ification 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-velocit
30、y 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 leve
31、l. Temple (2004) reported on field measurements of room air distribution in two rooms of a home located in Pittsburgh, Pennsylvania. Room air temperatures were measured during a cooling season and a heating season and the room air distri- bution was evaluated based on the criteria in ASHRAE Stan- da
32、rd 55 (ASHRAE 1992). There were several preliminary conclusions from the study. High sidewall supply (nonspread- ing) was found to be effective for both heating and cooling operation in a cold climate in the configuration of the test room. The vertical stratification was less than 3F (1.7“C) for 99.
33、5% of the time during the peak heating and cooling months, and temperature cycling was at acceptable levels. Floor supply (spreading) at an exterior wall provided marginal heating operation in a cold climate in the configuration of the test room. This was indicated by the higher vertical temperature
34、 stratification and temperature cycling that exceeds the limit of ASHRAE Standard 55 (ASHRAE 1992). The stratification exceeded 3F (1.7“C) for 32% of the time during the peak heating month of January. The maximum vertical stratification 1 02 ASHRAE Transactions: Research High Sidewall Siipply Regist
35、es Re utes il Secoiid Floor Taliperahire SellSOrs M m 00s Supply Re however, supply air temperature was not varied during the tests. Further investigation was recommended to investigate the impact of system balancing issues. (The high sidewall supply had 50% of the design airflow rate and the floor
36、supply had 140% of the design airflow rate.) 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 the
37、se applications. This paper will present additional results of an investiga- tion 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 distribu- tion performance was initiated at a new ho
38、me in Pittsburgh, Pennsylvania. The two-story test home has three bedrooms and a total conditioned floor area of 2,700 ft2 (25 1 m2). The wall construction includes nominal R- 16 ft2.h.“F/Btu (R-2.8 m2.K/W) insulation and windows with U-0.32 Btu/(ft2.h.“F) (U-1.8 W/m2.K/W) and SHGC-0.34. The roof ha
39、s nominal R-38 (R-6.7 m2.K/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. The system thermostat is located in a hallway on the first floor, near a return register. The house was being used as a model house an
40、d had 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 (ach) at 50 pascals (Pa) based on a blower door test. The house obtained a home energy rating
41、 system (HERS) score of 87, determined in accordance with the National Home Energy Rating Technical Guidelines (NASE0 2000). The calculated heating load is 5 1,000 Btu/h (14.9 kW) and the cooling load is 27,000 Btu/h (7.9 kW) for outdoor design conditions of 1F (-17C) for winter (99%) and 89F (32C)
42、for summer (1%). Two rooms were investigated, the dining room and one of the bedrooms. Partial floor plans are presented in Figure 1 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. T
43、he dining room is located on the first floor above a conditioned crawlspace. The supply air outlet is a floor regis- ter, located near an exterior wall, with vanes oriented perpen- dicular to the wall that provide some horizontal spread of the airflow. The ceiling height for the first floor is 10 fi
44、 (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 speed 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 dir
45、ectly above the dining room. The supply air outlet in the bedroom is a high sidewall register, located at an interior wall, with horizontal and vertical vanes. The vertical vanes are aligned (nonspread- ing) and provide some deflection toward the exterior wall with the window. The horizontal vanes a
46、re 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 top of the register core). A return air transfer opening is provided low on the wall near the door; however, the door was open to the ha
47、llway during the test period. 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 summarized in Table i and include the room dimensions and register type. The table includes a load fraction defined
48、as the ratio of the room load to the total house load (heating or cooling). The predicted heating and cooling load densities are also included for reference. Room airflow rates were measured using a flow-measur- ing hood with a range of 10 to 500 cfm (5 to 235 l/s) and an accuracy of 3% of reading.
49、The data are reported in Table 1 for flow rates before balancing and after balancing in February 2003. The airflow fraction is the ratio of the room airflow to ASHRAE Transactions: Research 103 Table 1. Test Home Room Data Room Supply register, in. (mm) Ceiling height, ft (m) ft (ml ft (ml Room length, Room width, Load fraction Room Data Bedroom Dining Room 1 O x 4 high sidewall (254 x 102) 4 x 12 floor (102 x 305) 9 10 (2.7) (3.1) (4.0) (5 .2) (4.0) (4.0) 13 17 13 13 0.063 0.098 Heating Data Load density, Btu/hft2 (W/m2) cfin (Us) Prebalanced approximate register velocity,
