Energy equivalent R-value

Transcription

1 Mechanical & Aerospace Engineering Energy equivalent R-value Part 1: Integrated evaluation methodology for BE Mark Bomberg and Thomas Thorsell,, Syracuse University,

2 Outline Objective: measure simultaneously H, A& M 1. Factors affecting energy performance of assembly under field conditions 2. Why verification of HAM models on both material and system levels are required 3. Proposed methodology for testing and verification of HAM models

3 Factors affecting the R-value of low sloped roofs (Bomberg & Pazera 2006) Mean temperature of insulation varies Aging of gas-filled foams Thermal bridges = mechanical fasteners used for insulation boards Air gaps & air flow between boards Moisture contained in the roof Moisture carried by air or condensation caused by air movement Reflective coatings may lower surface temperature (cool roofs)

4 To measure heat, air and moisture at the same time with calibrated box we need: (a) the quantity of heat produced inside the box, (b) the quantity of heat lost through the sides of the calibrated box, (c) the quantity of heat carried by air flowing through the wall, (d) the quantity of heat carried in or out of the box by air flows (e) the quantity of air entering to the calibrated box,

5 We need to measure HAM simultaneously we need : (f) Mass of air leaving the calibrated box, (g) Mass of air transmitted across the wall, (h) Air borne moisture delivered to the box (i) Air borne moisture leaving the box (k) Mass of moisture transmitted through the wall by the air infiltration (l) Mass of moisture transmitted through the wall through diffusion

6 Measurement contradictions 10 or 11 individual measurements is needed Air flows are affected by a perimeter so air-box box- larger than the test wall To calibrate flanking heat loss the box must be - smaller than the wall Even if moisture effects were tested in the lab, the field effect need to be calculated for the actual field climate

7 Integrated testing and computer modeling must have three objectives 1. Characterize effect of air flow on R-R value through the assembly as built 2. R-value under reference conditions of air flow through the assembly 3. Method for verification of HAM models for a given assembly under reference conditions that involve simultaneous ingress of air and moisture

8 Proposed approach involve a sequence of 4 steps Step 1: measure nominal and several local R-values, R no air or moisture effects We measure temperature differences across the assembly and heat fluxes: minimum (insulation), maximum (thermal bridge) and intermediate on three levels (9 local measurements) We use 2-D 2 D heat flow model to calculate mean R-value R for the test wall

9 Understanding air flow measurements To evaluate the effect of air flows on R-R value when air pressure fields outside and inside the wall interact each with other, we need to measure separately: 1. Connectivity between wall and environment 2. Resistance to air flow inside the wall In the latter case: (a) what is the internal path, (b) what is caused by construction workmanship and moisture effects?

10 Step 2: Add 50 Pa on the weather side We measure on the wall as built: (1)isothermal conditions, connectivity (2)Under Under thermal and pressure gradients we characterize the assembly. To this end we use calibrated inlet and outlets and 2 levels of flow to examine air flow - pressure relations Two points permit estimating variation in results measured for only one case of connectivity.

11 Step 3: HAM verification - moisture carried by air enters the test wall We apply hot and humid conditions for 3 days. Moist air is driven into the wall by (1) air pressure and (2) thermal gradient Initially, a longer period was used but some walls even though protected with WRB got so wet that drywall was soaked and thermal tests on inner surface had to be stopped.

12 Step 4: HAM verification, reverse to standard conditions of step 2 Stages 3 and 4 are used for only for verification of HAM models. At this stage energy equivalent R-R value expands the R-value R concept only to standardized measurements of thermal bridges and air ingress.

13 Application of the proposed methodology Having developed integrated testing and modeling methodology we will apply it to different residential and commercial wall assemblies to see how far the field performance can be from the laboratory R-valueR

14 Syracuse University - Building Energy & Environmental Systems Laboratory Integrated methodology for evaluation of energy equivalent R- value for BE, 2: Application to residential walls Thomas Thorsell PhD student Mark Bomberg Research Professor 14

15 Wall 1 (reference wall) with MFI, R13 batt ) 15

16 in series 1 before drywall placement 16

17 3% unfilled corners spacer s for MFI batt, facer stapled on side of studs a) For full sized cavity 2 x 2 inch triangle (b) For narrow cavity 1.5 x 1.5 inch triangle 17

18 Details of test wall preparation RH, T and air pressure sensors at different locations WRB has an overlap made in accordance with mfg instructions 18

19 Air pressure taps on the inner side of the batt 19

20 Climatic chambers at SU are used for H, A, M, and Pollutant tests 20

21 8 different residential walls were tested but only 2 are reported Results obtained during test method development are not reported Published results represent typical and best achievable on market place energy equivalent R-values R with a small modifications Wall 4 has continuous, permeable air barrier on inner side and dense pack CFI. There is a small air gap between drywall and AB material. 21

22 Definitions R-value R in this paper R-value in this paper represents the air to air resistance to heat flow. It is an inverse of the U-value. U This definition is different from one used in ASHRAE to avoid several measurements on the wall surface to establish the mean surface temperature when multi - dimensional heat transfer causes large temperature differences. 22

23 Definitions = Nominal and Local R-values Nominal R-value R = thermal resistance under steady-state, state, unidirectional heat flow through the center section of the insulation. Local R-value R = a ratio between temperature difference between indoor and outdoor air and heat flux measured at this point (The R-valueR of calibrated boundary layer is already subtracted). 23

24 Energy equivalent R-value R-value that includes effect of multidirectional heat flow and air flow measured under specified ΔT T, T m and ΔP P conditions. Effect of moisture is not included as it requires performing a HAM model calculations. 24

25 Wall location Cold side, air o C Reference wall, step 1, nominal R-value Warm side, air o C Temp. differe nce o C Heat flux W/m 2 App. Rsivalue, (m 2 K)/W Local Rsivalue, (m 2 K)/W Local R-value (IP units) Top bottom Avg This agrees well with R15.0 h o Fft 2 /Btu obtained as the sum of R13 batt, OSB, drywall and surface film resistance values. 25

26 Calculation of multidimensional heat flow effect This calculation is performed with the heat flow model (we( use two different 2-D D models to eliminate calculation errors) With 14.3% effect for this geometry (see introductory paper to session 4) one obtains R12.9 h o Fft 2 /Btu 26

27 Measurements in stage 2 (50 Pa) Wall locat. Temp differ. o C Heat flux W/ m 2 App. Rsi, (m 2 K)/W Nominal Rsi, (m 2 K)/W Nominal R-value (IP units) Refer. R-value (IP units) Reduced R-value by % Top Bott Avg % From nominal R-value multi-dimensional flow 14.3% and air flow 14.5 % total 28.8%. Energy equivalent R-value is 15.0 ( ) = 10.7 h o Fft 2 /Btu 27

28 Wall 4, step 1, measured nominal R-value Wall location Cold side, air o C Warm side, air o C Temp. difference o C Heat flux W/m 2 Apparent Rsi-value, (m 2 K)/W Local Rsi-value, (m 2 K)/W Local value R- (IP units) top middle bottom Average Repeated test top middle bottom Average

29 Heat flux measured in C518 apparatus on sealed, wet specimen vs calculated one For moisture characteristics used as input consult other papers 29

30 Calculated heat flux during the test in climatic chamber caused by moisture Heat flux (conduction) in [W/m2] g 50 HFT_stud HF_whole HFT Time in [h] Maximum, minimum and mean values of heat flux vs testing time 30

31 The test as above but AB material on inner side is also a water vapor retarder Heat flux (conduction) in [W/m2] HF_whole HFT1 HFT_stud Time in [h] With the mean heat flux calculated here, the nominal R-value is 15.9 and the one expected from material testing is 15.8 h o Fft 2 /Btu 31

32 Effect of air flow and energy equivalent R-value Wall location Temp. differ, C Heat flux W/ m 2 Apparent Rsi-value, (m 2 K)/W Nominal Rsivalue, (m 2 K)/W Wall R-value (IP units) R-value measured in Step 1 Reduction R-value, percent top mid bott Avg For wall 4 combined effects of thermal bridges and air flows is 18.8 i.e.10% less than for wall 1. Energy equivalent R-value is 15.9 ( ) = 12.8 h o Fft 2 /Btu 32

33 Conclusions Demonstration of the proposed test method show a reduction from the nominal R15 to energy equivalent R10.7 h o Fft 2 /Btu Furthermore, different air flow effect causes a difference about 10% in the energy equivalent R-valueR value. The proposed test method identified transient effect of moisture, an important issue in verification of HAM models. 33

34 Comments: compare published R-valuesR -values for 2x4 walls measured with a Hot Box Wall # no ΔP 15 mph wind % reduction % % % Walls: #1 = R13 batt,, #2 = 3 ¼ open cell foam, #3 = 3 ¼ SPF (cc), #4# 4 = ½ PIR and cc foam (SPF) 34

35 Energy equivalent R-value Part 3: Application to metal assemblies Thomas Thorsell and Mark Bomberg Energy and Environmental Systems Lab

36 Wall tested in this project Reference wall multi-component (MC) glass fiber in the steel frame system nominal R23 Selected panel system (PS) exterior insulation with sheet metal protection nominal R15.6

37 Assembly 1, MC Multi Component (MC) Wall System

38 Assembly 2, PS Selected Panel System (PS)

39 2D Modeling results, MC Horizontal section Vertical section

40 2D Modeling results, MC C h=20 W/(m²K) 20 C h=7.7 W/(m²K) R18.9 ft²hr F/BTU

41 2D Modeling results, MC Horizontal section 20 C h=7.7 W/(m²K) -20 C h=20 W/(m²K) R10.4 ft²hr F/BTU (nominal R23)

42 2D Modeling results, MC Horizontal section Temperature on inside surface Lowest surface temperature 11.3 C 20 C, h=7.7 W/(m²K) -20 C, h=20 W/(m²K)

43 2D Modeling results, PS Horizontal section Vertical section

44 2-D Modeling results, PS 20 C h=7.7 W/(m²K) Horizontal section C h=20 W/(m²K) R13.6 ft²hr F/BTU

45 2D Modeling results, PS C h=20 W/(m²K) 20 C h=7.7 W/(m²K) R11.5 ft²hr F/BTU R13.4 ft²hr F/BTU

46 Experimental data from climatic chambers 46

47 Measurements, implementation Front side Rear side On the wall Temperature profile on Vertical Thermal Bridge Heat Flux Transducer is built in the CBL

48 Step Duration Test procedure Air Flow/Pressure [cfm or Pa] Edges Temp [ C] Chamber 0 1 day Wall characterization RH [%] Lab Temp [ C] 1 a 3 days 0 Pa Normal -16 C Dry room 1 b 3 days 0 Pa Sealed -16 C Dry room 2 a 3 days 50 Pa Normal -16 C Dry room 2 b 3 days 50 Pa Sealed -16 C Dry room 3 3 or5 days 50 Pa Normal 40 C 80 % room or 5 days Transition + period of drying 4 2 day test 50 Pa As is -16 C Dry room

49 Surface temperatures, under CBL on drywall in inches from the stud Multi-component wall Exterior insulating panel

50 Test results, MC STEP 1 Chamber Room -16 C 20 C Tested nominal R=14.7 ft²hr F/BTU + 0 Pa 50% RH Agrees with the model RH results ( )/2= Uncontrolled 14.8 ft²hr F/BTU

51 Effect of air pressure on MC STEP 2 Chamber Room -16 C? 20 C Measured R-value + 50 Pa U ncon t r o l le d RH 50% RH 12.4 ft²hr F/BTU ( )/14.7 = 15.6%?

52 Measured results, SPS STEP 1 Chamber Room -16 C 20 C + 0 Pa 50% RH Uncontrolled RH Nominal R-value 10.1 ft²hr F/BTU i.e. much less than expected, let us go back to the model and check the effect of stainless steel chamber on flanking loss from the metal wall

53 Effect of flanking loss from the metal panel in stainless chamber Mounting strip above the wall Middle part s R= 13.3 ft 2 hr o F/ Btu 26.3% reduction Average wall R= 9.8 ft 2 hr o F/ Btu

54 Measured results, SPS STEP 1 Chamber Room -16 C 20 C Nominal R-value 10.1 ft²hr F/Btu + 0 Pa 50% RH Compare to Uncontrolled RH 14.7*0.737 = 10.8 ft²hr F/Btu

55 STEP 2 Chamber Effect of air flow on PS? Room -16 C 20 C Measured R-value + 50 Pa 50% RH 9.3 ft²hr F/BTU Uncontrolled RH so the effect of air flow is 0.8/10.1 about 8%?

56 Measured temperature profile on the wall surfaces, no air pressure Top level of the wall, vertical thermal bridge PS MC

57 Measured temperature profile on the wall surfaces, no air pressure Middle level PS MC

58 Measured temperature profile on the wall surfaces, no air pressure -3 Bottom level PS MC

59 Effect of air infiltration Top position MC PS

60 Effect of air infiltration Middle position MC PS

61 Effect of air infiltration Lowest position MC PS

62 Measured temperature profile on the wall surfaces -conclusions Surface temperature in deg C : Without air infiltration - with ΔP=50 Pa Top Middle Bottom So, with the inflow of cold air into the assembly we draw warm air into the insulation or air cavity in the wall

63 Interim concluding remarks Exterior insulated panel is superior to MC in the following ways: 1) Calculated temperature depression is from 20 deg C in air to 11.3 deg C on the surface (much lower in the corner) 2) Under CBL (uniform layer with R3) measured temperature depression is about 13 deg C while the corresponding value for SPS is only 2 deg

64 General discussion: instrumented plates

65 General discussion continue : effect of hot & humid conditioning

66 General discussion: mold as the effect of hot and humid exposure

67 Conclusions PS is more reliable in avoiding condensation than MC The impact of sealed and unsealed drywall is significant. In case of sealed drywall % of the pressure drop was across the drywall. The pressure drop was more than 80 % when the drywall was not sealed.

68 Conclusions 3-3 (1) Nominal R-values R ft²hr hr F/BTU (2) multi-dimensional heat transfer (3) air flow (1) (2) (3) air % total % MC R % 46% PS R * 12.5* 8 % 21% */ correcting for effect of flanking loss in stainless steel climatic chamber

69 Different start but at the end there is the same Ree - value MC nominal R23 energy equivalent 12.4 (46% reduction) PS nominal R16 energy equivalent 12.5 (21% reduction)

70 Acknowledgment This research was supported entirely by the following companies For 3 years: Centria Corporation Greenfiber Corporation Huber Engineered Wood For 2 years: Fortifiber Corp Jeld-wen Corp