Search

This paper describes a dynamic test method for determining transfer function coefficients (TFCs) for a wall specimen using a calibrated hot box (CHB). In this method, a wall specimen is installed between the climatic and metering chambers of a CHB. After a steady specimen heat transfer rate is attained, the air temperature in the climatic chamber is quickly ramped from an initial to a final temperature level in a linear manner. The final temperature level is maintained until a new steady specimen heat transfer rate is attained. The metering chamber is maintained at a steady indoor condition and is used as a calorimeter. The transient heat transfer rate at the inside surface of the wall specimen is determined at hourly time steps from an energy balance of the metering chamber. The poles and residues for a ramp analytical solution are derived by analyzing the measured specimen heat transfer response. The ramp analytical solution is subsequently used to form a triangular pulse from which TFCs are derived. The dynamic test method was conducted on a masonry wall. Empirical TFCs derived by the test method predicted the diurnal performance of the wall specimen with good agreement. In fact, the results predicted by empirical TFCs tracked the measured results as closely as an analytical model.

A detailed computer analysis is conducted to investigate whether moisture problems occur in the roof cavity of manufactured homes constructed in compliance with the current Department of Housing and Urban Development (HUD) Standards for manufactured housing. The current HUD Standards require a ceiling vapor retarder, but do not require outdoor ventilation of the roof cavity. In cold climates, the analysis revealed that moisture accumulates at lower roof surface and poses a risk of material degradation. The analysis found the following combination of passive measures to be effective in preventing detrimental winter moisture accumulation at lower surface of the roof: (1) providing a ceiling vapor retarder; (2) sealing penetrations and openings in the ceiling construction, and (3) providing natural ventilation openings in the roof cavity. In addition, the performance of a roof cavity exposed to a hot and humid climate is investigated. The analysis revealed that outdoor ventilation of the roof cavity causes the monthly mean relative humidity at the upper surface of the vapor retarder to exceed 80%. This condition is conducive to mold and mildew growth.

This paper experimentally verifies and compares two dynamic test methods for a calibrated hot box to characterize the transient thermal performance of complex walls. In these methods, a wall specimen is sandwiched between the two conditioning chambers of a calibrated hot box. The exterior surface of the wall specimen is subjected to a time-varying excitation function in air temperature. At the interior surface, the air temperature is maintained steady, and the heat transfer response is measured. Conduction transfer function coefficients that relate the measured heat transfer response to the excitation function are derived. The two dynamic test methods were applied to an insulated hollow concrete block wall that contained significant thermal bridges and lateral heat flows. Empirical transfer function coefficients derived by the test methods predicted with good agreement the heat transfer response of this wall specimen when its exterior surface was subjected to excitation functions that differed markedly from those used to derive the coefficients.

We used the MOIST Computer Model to conduct a detailed analysis of the moisture performance of one wall typical of current construction practice in manufactured housing, and two new alternative wall designs with potential for better moisture performance in a wider variety of climates. The analysis showed that the current-practice wall with an interior vapor retarder performed acceptably in a cold climate (Madison, WI), but poorly in a hot and humid climate (Miami, FL). The alternative wall designs both exhibited satisfactory moisture performance in the cold climate and the hot and humid climate, even with moderately severe indoor conditions. The alternative wall designs also performed satisfactorily in a mixed climate (Little Rock, AR). These alternative wall designs should be of interest to the manufactured housing industry, which distributes homes to all climatic regions of the United States.

This paper investigates the transient temperature distribution within packed beds after being subjected to single blow heating. Numerical solutions are derived for the fluid and solid temperatures that include the effect of forced convection heat transfer at the fluid-exit surface. An inlet-face heat transfer coefficient is specified that includes both the effect of small scale inlet-face convective heat transfer and heat conduction in the oncoming transpirant. The boundary conditions do not require fluid or solid temperatures to be specified at the bounding surfaces. Charts are presented for predicting the response times for packed bed heat exchangers and chemical reactors covering a wide range of parameters.

Thermal resistance measurements of two highly insulated residential walls are made using a calibrated hot box operated under winter and summer climatic condi tions. The well-insulated wall consists of two insulated wood-frame sections with staggered framing, having a nominal thermal resistance of R-27 F·ft2·h/Btu (4.8 K· m2/W). The superinsulated wall is identical in construction, except for additional in sulation placed between the two wood-frame sections increasing the wall thermal re sistance to a nominal value of R-39 F·ft2·h/Btu (6.9 K·m2/W). The measured thermal resistance for both walls is examined as a function of mean wall temperature and compared with predictions using the ASHRAE parallel-path method, the ASHRAE isothermal-plane method, and a finite-difference model with temperature-dependent thermal conductivities. Good agreement between measured and predicted values is obtained using both ASHRAE methods and the finite- difference model. At mean wall temperatures above 40°F (4.4°C), the ASHRAE parallel-path method tends to overpredict, while the ASHRAE isothermal-plane method tends to underpredict the overall thermal resistance. The effects of the com pression of glass-fiber blanket insulation and nail penetrations on the overall thermal resistance are investigated.

This paper investigates the transient temperature distribution in transpiration-cooled porous matrices, after sudden initiation of uniform internal heat generation. Analytic solutions are derived for the tube and plate geometries that include the effect of forced convection heat transfer at the gas-exit surface where the conventional heat-transfer coefficient is used to define the boundary condition.

This paper investigates the transient temperature distribution within transpiration-heated and -cooled porous tubes that occur after a step increase in the rate of convective heat transfer at one of the tube surfaces. Analytic solutions are presented for transpiration cooling, catalytic chemical reactor, and tubular regenerator applications. These solutions include the effect of forced convective heat transfer at both tube surfaces where conventional heat-transfer coefficients are used to define the boundary conditions.

The effect of wall mass on the peak sensible heating and cooling loads of a single-family residence was investigated using a sophisticated computer program called the Thermal Analysis Research Program (TARP). The computer simulation accuracy was verified by comparing its predicted sensible heating and cooling loads to measured values for six test buildings each having different wall constructions at the National Bureau of Standards. Good agreement was obtained for the load comparisons. The computer program subsequently was used to simulate the performance of identical houses each having the following three insulated-wall constructions: wood frame, conventional masonry (outside wall mass), and innovative masonry (inside wall mass). When the house was operated with fixed thermostat settings, the effect of wall mass on the peak sensible heating and cooling loads was found to be less than 11% for the climatic regions analyzed. Operating the typical house with a 10/sup 0/F (5.6/sup 0/C) night temperature setback during an 8-hour night period caused the daily peak sensible heating loads to be approximately twice those without setback.

Hourly sensible heating and cooling loads for six test buildings were predicted using two computer programs, called TARP and EMPS. The predicted loads were compared to corresponding measured loads for winter heating, spring heating, and summer cooling periods. Both computer programs predicted the general trends of the measured data.

A field study was carried out to investigate the accuracy of using high-resolution radiometers to determine the in situ thermal resistance of building components having conventional residential construction. Two different types of radiometers were used to determine the thermal resistances of the walls of six test buildings located at the National Bureau of Standards. These radiometer thermal resistance measurements were compared to reference thermal resistance values determined from steady-state series resistance predictions, time-averaged heat-flow-sensor measurements, and guarded-hot-box measurements. When measurements were carried out 5 hours after sunset when the outdoor temperature was relatively steady and the heating plant was operated in a typical cyclic fashion, the following results were obtained: for lightweight wood-frame cavity walls, the radiometer procedures were found to distinguish wall thermal resistance 4.4 h.ft2- A‚°F/Btu (0.77 m2•K/W) systematically higher than corresponding reference values. Such a discrimination will per-mit insulated and uninsulated walls to be distinguished. However, in the case of walls having large heat capacity (e.g., masonry and log), thermal storage effects produced large time lags between the outdoor diurnal temperature variation and the heat-flow response at the inside surface. This phenomenon caused radiometer thermal resistances to deviate substantially from corresponding reference values. This study recommends that the ANSI/ASHRAE Standard 101-1981 be modified requiring the heating plant to be operated in a typical cyclic fashion instead of being turned off prior to and during radiometer measurements.