Klems, J.H.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleMEASUREMENT OF FENESTRATION PERFORMANCE UNDER REALISTIC CONDITIONSPermalinkhttps://escholarship.org/uc/item/7tn6v7dhAuthorKlems, J.H.Publication Date1984-02-01eScholarship.org Powered by the California Digital LibraryUniversity of Californiar,,:, . . t \--1-:,1 • LBL-17429 c--J-. Lawrence Berkeley Laboratory RECEIVED UNIVERSITY OF CALIFORNIA LAWRENCE BERf<I'"U::v I_AB0r?AT APPLI ED SCI ENCE DIVISION JUL % 4 1984 LIBRARY AND DOCUMENTS SECTIOl'-l To be presented at Windows in Building Design and Maintenance, Gothenburg, Sweden, June 13-15, 1984 MEASUREMENT OF FENESTRATION PERFORMANCE UNDER REALISTIC CONDITIONS J.H. Klems February 1984 " TWO-WEEK LOAN COpy, { This is a Library Circulating Copy which m~y be borrowed for two -k'lo.., ....... ________ ............. _~~l.# ..... ~ ..• -" ..... ~ t,·.,. ~ • .:..x .... ~~ ...... ~,~~j. ... ~ .. .,.:tdIlU'J~:: -'CJ;~1"'. ~~:(~,:l~}1 - ';'" 'i ~~~~~~~:l:;T, I ~ , 'of ",~ . ,;;M(./lW-~~i!:~~" APPLIED SCIENCE DIVISION Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098 DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. LBL-17429 EEB-W 84-02 W-158 Paper to be presented at Windows in Building Design and Maintenance, Gothenburg, Sweden, June 13-15, 1984 MEASUREMENT OF FENESTRATION PERFORMANCE UNDER REALISTIC CONDITIONS J. H. Klems Applied Science Division Lawrence Berkeley Laboratory University of California Berkeley CA 94720, U.S.A. February 1984 This work was supported by the Assis~ant Secretary for Conservation and Renewable Energy, Office of Energy Research and Development, Building Systems Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. MEASUREMENT OF FENESTRATION PERFORlIANCE mmER REALISTIC CONDITIONS ABSTRACT J.H. Klems Applied Science Division Lawrence Berkeley Laboratory University of California Berkeley CA 94720, U.S.A. The need for fenestration performance measurements under realistic conditions is noted, and the Mobile Window Thermal Test facility (l-loWiTT), newly constructed at LBL to make these measurements, is· described. A key feature of the MoWiTT is the direct measurement of instantaneous net energy flow in the presence of sunlight. Ongoing calibration to establish the accuracy of this facility is described, and calibration data 80 far obtained are presented. Estimates from these data indicate that the facility will have sufficient accuracy for most fenestl'ation measurements of interest. Keywords: Fenestration thermal performance, field measurement, calorimeter, fenestration U-value, and shading coeffi-cient. -iii-INTRODUCTION Fenestration systems are unique among building envelope components in that they experience instantaneous net heat flows which (a) may be directed inward under winter conditions, and (b) may change by 100% or more over a short time period, due to changes in sky or wind conditions. The impact of these heat flows on building energy consumption is a long-term average of the net energy flow. Accurate calculation of the average value of a rapidly varying quantity requires very good knowledge of that quantity's behavior; however, numerous authors (e.g., Yellott, Schuyler, and Timmons, 1979; Fracastoro, Masoero, and Cali, 1983) have suggested ways in which fenestration systems under realistic conditions may be expected to depart from the assumptions generally made in calcu-lating their performance and have pointed to the need for realis-tic performance measurements (Klems and Selkowitz, 1981). A FENESTRATION PERFORMANCE MEASUREMENT FACILITY In Klems, Selkowitz, and Horowitz (1982) it was shown that a surprisingly high degree of measurement accuracy is necessary for .. determining fenestration performance moderately well. The refer-ence then described a facility designed to have the necessary accuracy, the Mobile Window Thermal Test facility (MoWiTT), on which work was underway at Lawrence Berkeley Laboratory. The MoWiTT, one module of which has now been completed, is shown in Fig. 1. Realistic measurement conditions are achieved by using roomlike interior chamber dimensions, especially height (2.4 m), and by exposing the fenestration systems (which may include skylights) to actual weather; commensurability of results is achieved by simultaneous, side-by-side comparison of a given sys-tem with a simple reference system (such as unshaded single glaz-ing), the behavior of which is relatively predictable. The air inside the calorimeters may be either electrically heated or cooled by a liquid-to-air heat exchanger. Extracted heat is determined by temperature and flow measurements on the ·fluid; electrical inputs (including fans) are monitored using accurate watt-hour meters. The interior air temperature may be either tightly controlled or allowed to "float" within a set range. The key measurement made by the MoWiTT facility is the direct, calorimetric determination of the net heat-flow rate through the fenestration, including solar gain if any, as a function of time and with a short time constant. This is accomplished by almost completely covering (approximately 90%) the interior surfaces of each calorimeter with larg~area heat-flow sensors [see Fig. 1(c)] of a type developed especially for this application (Klems and DiBartolom'eo, 1982; Klema, 1983). These, together with measure-ment of the heat added to or extracted from the air, allow the fenestration net heat transfer to be inferred from the net heat balance of the air in the calorimeter. The dominant time con-stants will be (1) that of the heat-flow sensors (approximately 3 minutes) and (2) that associated with the distribution by convec-tion of heat within the air. Both of these are much shorter than -1-(a) Identical test chambers with removable parly wall ChonQ80ble windows and mounfino systems VOrloble thermol moss in floor system Active Quord· air insulation in exterior walls (b) Control and dota 98m I Skylight ~ ~~~:~ ~~~~~"====:IJ_~ dotted ~ __ ~ .. , Test cell Test cell Supply air plenum PLAN VIEW Possible skylights Window Window test pane I fest ponel Guard air channel Structural envelope Return oir SECTION - ELEVATION VIEW Chiller (c) ~6~ fr~~'~~h .(;;;;';':_:_=_=_~~~1SkYh9hf sample fiberglass insulolio~ , Removable plugs 3.0m--i-----I"" 2.4m (d) XBL 811-125A Figure 1. The Mobile Window Thermal Test facility (MoIU TT). (a) Planned field configuration, showing two mobile test modules, each containing a pair of room-sized, air-guarded calorimeters. (b) Layout of a test module, showing the controlled-temperature guard plenunI surrounding the calorimeters, together with its air-handling system. The guard air temperature, which plays no direct part in the net heat balance, is normally at the same temperature .s the calorimeter air, but can be varied for specific experiments. (c) Cross section through the center of a test chamber, showing mounting of various window or skylight systems. (d) The first test module ciuring calibration at LaH'rence Berkeley Laboratory. -2-/" / , the time constant of any real building, so the net heat-flow meas-urement is effectively instantaneous. In addition to the basic net heat-flow measurement, the MoWiTT facility records weather data such as wind speed and direction, barometric pressure, ambient temperature, humidity, and direct and diffuse solar intensity. Up to 200 channels of additional data may be recorded per chamber in order to provide sufficient physi-cal information to explain the net heat-flow measurement. MOWITT CALIBRATION Klems, Selkowitz, and Horowitz (1982) demonstrated that not only is it possible for the fenestration heat flow to be obliterated by random experimental errors, but it is also possible to make sys-tematic errors much larger than one would expect based on the quoted accuracy of the instruments used. Accordingly, it is important to establish the accuracy of the MoWiTT by direct meas-urement. Each subsystem entering into the net heat balance measurement has been calibrated individually. The results of the calibrations for two critical subsystems are shown in Fig. 2. In each case the calibration measurements are consistent with the expected result, represented by a straight line. From the scatter of the points about the line we can estimate the reproducability of the measure-ment system, provided we make the pessimistic assumption that all the scatter is due to intrinsic errors. (In fact, most of the scatter is due to known sources of uncertainty in the calibration experiments; however, this procedure fairly represents the limits of our current knowledge about the system accuracy.) By this method ~e derive an RMS error of 10 W for the cooling system, and 0.13 W/m for the heat-flow sensor. The latter figure implies an overall error of 5 W in th~ envelope heat flow. In a similar manner, accuracy estimates have been made from meas-urements on each subsystem of the first calorimeter chamber. Similar measurements will be made on the second chamber when its instrumentation is completed. The results for the first calorime-ter chamber are shown in Table 1. The next step in the calibration will be a system-level test of the assembly. The wall holding a window [shown in Fig. l(c)] will be replaced by a blank double wall covered with heat-flow sensors; guard air will flow between the parts of the double wall just as it does on the other surfaces of the calorimeter (except the com-mon wall between the two chambers). ThiS "closed-box" test will provide a redundant measurement of changes in the air heat con-tent, and thus a check on the accuracy of the complete measurement system. Response of the heat-flow sensors to inhomogeneous radia-tive fluxes will be checked by using a light source inside the closed chamber. The estimates in Table 1 allow us to. explor2 the limitations of the facility. If we wished to measure aIm window having 7 times the thermal resistance of single glazing, achieving 20% accuracy -3-would require an inside~outside temperature difference of about 30 °C. A north-facing 1 m window would admit approximately 100 W of diffuse solar energy during most parts of the year and during most daylight hours. If we neglect thermal losses, the cooling system uncertainty would imply that one could achieve 20% accuracy when measuring a system having a 0.5 shading coefficient. This is ade-quate resolution for spring, summer, and fall measurements on sys-tems of moderate thermal resistance; better resolution may be desirable for high-thermal-resistance, north-facing systems during winter, when thermal losses and solar gains offset one another. 200 300 -15 -10 -5 o 5 10 15 Applied watts Heat flux (watts/m2) 20 X~L 842 lOG75 XBL 842·10075 Figure 2. Calibration of two critical measurement subsystems in the MoWiTT. (a) Calibration of system measuring the energy extracted by the cooling system, using an electric heater to inject a known wattage into the heat-transfer fluid. (b) Guarded hotplate calibration of one of the large heat-flow sensors (0.55 m x 1.10 m) lining the calorimeter interior. Table 1. Error sources in MoWiTT determination of fenestration net energy flows. Source Magnitude (Watts) Heat Added to Air 0.1 Heat Removed from Air 10 Envelope Heat Flow 5 Air Infiltration <1 Air Heat Capacity <2 -4-'-', \ l ~/ {J / ; CONCLUSIONS A mobile facility for measuring fenestration performance under realistic conditions has been constructed, and calibration, still in progress, has demonstrated that the facility provides high measurement accuracy. This accuracy is both necessary and ade-quate for measuring most fenestration systems of current interest. However, for very high-therma1-resistance fenestration systems (7 to 10 times the resistance of single glazing), especially in north-facing orientations, accuracy may have to be improved. ACKNOWLEDGEMENT Supported by Assistant Secretary for Conservation· and Renewable Energy, Office Energy Research and Development, Building Systems· Division, U.S. Department of Energy - Contract DE-AC03-76SF00098. REFERENCES G. Fracastoro, M. Masoero, and M. Cali, 1983,"Surface Heat Transfer in Building Components," American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Proceedings of the ASHRAE/DOE Conference on the Thermal Performance of the EXterIOr Envelopes-of Buildings II, P:-180, Atlanta, GA. -- ---J. H. K1ems and S. E. Se1kowitz, 1981, "The Mobile Window Thermal Test Facility," American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., Proceedings of the . ASHRAE/DOE Conference on the Thermal Performance of the EXterIOr Envelope of Buildings, 930, New York. -- ---J. H. K1ems and D. DiBartolomeo, 1982, Sensitivity Heat Flow Sensor," American Review of Scientific Instruments~: 10, p. "Large-Area, High-Institute of Phj.ics~ 1609, New York. J. H. K1ems, S. Se1kowitz, and S. Horowitz, 1982, "A Mobile Facil-ity for Skylights," Environment sium:), Vol. Measuring Net Energy Performance of Windows and An Foras Forbartha, Energy Conservation in the Built (Proceedings of CIB W67 Third International Sympo-III, p. 3.1, Dublin, Ireland. J. H. Klems, 1983, "Use of Large-Area Heat Flow Sensors to Measure Building Heat Flows," American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Proceedings of the ASHRAE/DOE Conference on the Thermal Performance of the Exterior Envelopes-of Buildings II, P:-734, Atlanta, GA. -----J. I. Ye110tt, P. V. R. Schuyler, III, and R. D. Timmons, 1979, "The Phoenix Fenestration Tests of 1977--Therma1 Aspects," Ameri-can Society of Heating, Refrigerating, and Air Conditioning Eneineers, Inc., ASHRAE Transactions, 85, pt. 2, p. 651, New York. -5-'f ,~ This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable. ."'" ...... TECHNICAL INFORMATION DEPARTMENT LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 ~.r - ,Q, 

MEASUREMENT OF FENESTRATION PERFORMANCE UNDER REALISTIC CONDITIONS

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California