Dynamic model for measurement of convective heat transfer coefficient at external building surfaces

Ohlsson, K. E. Anders; Östin, Ronny; Grundberg, Staffan; Olofsson, Thomas

doi:10.1016/j.jobe.2016.06.005

Cited by 15 publications

(7 citation statements)

References 15 publications

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“…This equality between q and p provided experimental evidence that conduction heat loss through the SAT insulation layer was negligible (cf. Ohlsson et al, 2016). In calculation of q, the thermal capacity of the heater foil (section ''Experimental'') was not included.…”

Section: Resultsmentioning

confidence: 99%

“…Table 1 for data). The R-model was evaluated by adding R ins in parallel to R c , while evaluation of the RCR-model step response (and τ ) was calculated as in Ohlsson et al (2016), with R = R ins / 2 . The evaluation was performed for the case where h r = h c = 5 W K −1 m −2 (where insulation effects should be highest), and the C -value was with and without a 10-fold reduction.…”

Section: Resultsmentioning

confidence: 99%

“…The sampling frequency was 0.02 Hz. Further details are given in Ohlsson et al (2016). The electrically supplied power P was estimated, based on measurement of U and R h , as…”

Section: Methodsmentioning

confidence: 99%

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Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer

Ohlsson

Östin

Olofsson

2018

Journal of Building Physics

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The environmental boundary conditions of the building exterior surface could be expressed in terms of the sol-air temperature T o and the heat transfer coefficient h o. This has previously been derived by applying Thevenin's theorem to the linear thermal network model of the convective and radiative environment. Here, the sol-air thermometer, previously used only for measurement of T o , was applied for accurate measurement of h o. The step-transient method was used, where the temperature of the sol-air thermometer was initially raised to above T o and then monitored during its transient return to thermal equilibrium. This method was validated by (1) comparison of h o results against values obtained with a steady-state method and (2) comparison of predicted heat flux against the electrical heater power, supplied for validation purpose. Accurate results were obtained, with 7.3% measurement uncertainty. The present solair thermometer time constant t was around 1 h. Based on predictions from dynamic modelling, the t could be reduced 10-fold, with only small effects on the accuracy from heat loss through the insulation layer.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer

Ohlsson

Östin

Olofsson

2018

Journal of Building Physics

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“…alone. Reflecting this, in transient measurements, the radiative resistance R r has been found to have only a minor influence on the thermal time constant [10]. However, other research into transient behaviour of walls has shown that the presence of internal shortwave radiant loads gives rise to a reduction in the decrement factor in terms of energy in winter, and an increase in summer [20].…”

Section: Radiative Coefficientmentioning

confidence: 92%

“…For external surfaces, according to BS EN ISO 6946:2007 [9], h c can be approximated as 4 + 4v, where v is the wind speed adjacent to the surface (m/s). Many empirical models exist that correlate h c and v in specific cases though there is a high uncertainty in the values predicted by such simplified empirical correlations [10]. Existing studies report widely different values for the influence of h c on the building energy consumption.…”

Section: External Convective Coefficientmentioning

confidence: 99%

Compact facility for testing steady and transient thermal performance of building walls

Byrne¹,

Byrne

Robinson

2017

Energy and Buildings

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Energy efficiency retrofit of buildings represents a key effort in reducing EU energy demand by 20% by 2020. However, predictions tend to overestimate savings by large percentages. The shortfall in savings can be attributed to incorrect predictive techniques, comfort takeback along with other behavioural and workmanship variables. Common predictive techniques related to heat loss tend to be based on the Uvalue of the building envelope. This paper presents the design of a more straightforward and compact version of the traditional Hot-Box apparatus (measures U-value) which instead determines the thermal resistance of samples of building envelope. U-value includes the need to measure/predict the effective surface resistances. In situ surface resistances, which include radiation and convection, are difficult to predict and vary depending on climatic conditions, exposure levels, surface emissivities among many other influences. The design of the test facility eliminates the need to incorporate these surface behaviour variables. This paper details the replicable apparatus and test methodology. The results of testing a hollow block wall of typical construction using the rig is then presented. The determined R-value is found to be within 1% of calculated values and the thermal time constant also matches closely with the most accurate predictive estimates.

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Sol-Air Thermometer Measurement of Heat Transfer Coefficient at Building Outdoor Surfaces

Ohlsson

Östin

Olofsson

2018

Springer Proceedings in Energy

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Dynamic model for measurement of convective heat transfer coefficient at external building surfaces

Cited by 15 publications

References 15 publications

Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer

Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer

Compact facility for testing steady and transient thermal performance of building walls

Sol-Air Thermometer Measurement of Heat Transfer Coefficient at Building Outdoor Surfaces

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