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Ohlsson, K.E. Anders
Alternative names
Publications (10 of 14) Show all publications
Ohlsson, K. A., Fransson, Å. & Olofsson, T. (2018). Social wasp nests as source of bioinspired design of building skins: 1-2 October 2018, Bern, Switzerland. In: Advanced Building Skins: . Paper presented at 13th Conference on Advanced Building Skins, Bern, Switzerland, October 1-2, 2018. Advanced Building Skins GmbH
Open this publication in new window or tab >>Social wasp nests as source of bioinspired design of building skins: 1-2 October 2018, Bern, Switzerland
2018 (English)In: Advanced Building Skins, Advanced Building Skins GmbH , 2018Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Advanced Building Skins GmbH, 2018
Series
Conference Proceedings
National Category
Civil Engineering
Identifiers
urn:nbn:se:umu:diva-152730 (URN)
Conference
13th Conference on Advanced Building Skins, Bern, Switzerland, October 1-2, 2018
Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2019-06-19Bibliographically approved
Ohlsson, K. A., Östin, R. & Olofsson, T. (2018). Sol-air thermometer measurement of heat transfer coefficient at building outdoor surface. Energy Procedia, 132, 357-362
Open this publication in new window or tab >>Sol-air thermometer measurement of heat transfer coefficient at building outdoor surface
2018 (English)In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 132, p. 357-362Article in journal (Refereed) Published
Abstract [en]

Heat flow measurement with a heat flow meter is a standardized method (ISO 9869-1) to estimate thermal transmittance (U-value) of a building element. The heat flow meter is a thin plate mounted on top of the surface of the element, and measures the heat flux q through the plate. The measured q is the product of the difference in temperatures between exterior and interior environment, and the U-value. The heat transferred from the element is based on the radiant and the convective heat transfer.

ISO 9869-1 specifies that the environment temperature Te “is a notional temperature" and it "cannot be measured directly” (section A.3.1). The air temperature Ta is proposed as a reasonable approximation for the indoor environment, while overcast conditions and absence of significant solar radiation are specified conditions for replacing Te with Ta for the exterior environment.

The sol-air thermometer (SAT) measures the sol-air temperature Tsa, i.e. the equivalent temperature of the convective and the radiative environment. In the absence of solar radiation, Te = Tsa. SAT is a sensor consisting of a thin flat solid plate, of high thermal conductivity. The front side of the sensor is exposed to the environment, whose Tsa is to be measured, and the backside is thermally insulated. The temperature of the SAT-plate equals Tsa.

In this work we propose introduction of the measured Te in the existing standard (ISO 9869-1). The method for measurement of Tsa, using the SAT, has been demonstrated experimentally for different periods, without solar radiation present and under stable climatic conditions.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Environmental temperature, Sol-air thermometer, Heat transfer coefficient, Thermal transmittance
National Category
Civil Engineering
Identifiers
urn:nbn:se:umu:diva-152736 (URN)10.1016/j.egypro.2017.09.632 (DOI)
Funder
Swedish Energy AgencyThe Kempe Foundations
Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2018-11-09Bibliographically approved
Ohlsson, K. A., Östin, R. & Olofsson, T. (2018). Sol-air thermometer measurement of heat transfer coefficient at building outdoor surface. In: Cold Climate HVAC 2018: Sustainable Buildings in Cold Climates. Paper presented at CONFERENCE on 9th International Cold Climate HVAC 2018, Kiruna, Sweden, March 12-15, 2018 (pp. 329-338). Springer
Open this publication in new window or tab >>Sol-air thermometer measurement of heat transfer coefficient at building outdoor surface
2018 (English)In: Cold Climate HVAC 2018: Sustainable Buildings in Cold Climates, Springer, 2018, p. 329-338Conference paper, Published paper (Refereed)
Abstract [en]

There exists a building energy performance gap between theoretical simulations and the actual energy usage as measured. One potential reason for this gap might be a mismatch between predicted and measured values of the heat flux q through the building envelope. There is therefore a need to develop accurate and more cost-efficient methods for measurement of q. The standard ISO 9869-1 states that, at the outdoor surface, q = ho(Ts − Tenv), where ho is the overall heat transfer coefficient, including both convective and radiative components, Tenv is the environmental temperature, and Ts is the temperature of the building surface. It has previously been shown that the sol-air thermometer (SAT) could be used for convenient measurement of Tenv under dark conditions. In the present work, two SAT units, one heated and the other unheated, were employed for accurate outdoor measurements of ho in cold winter climate. Validation was performed by comparison of results from the new method against measurements, where previously established methodology was used. With current operating conditions, the measurement uncertainty was estimated to be 3.0 and 4.4%, for ho equal to 13 and 29 Wm−2K−1, respectively. The new SAT steady-state method is more cost-effective compared to previous methodology, in that the former involves fewer input quantities (surface emissivity and infrared radiation temperature are unnecessary) to be measured, while giving the same ho results, without any sacrifice in accuracy. SAT methodology thus enables measurement of both Tenv and ho, which characterizes the building thermal environment, and supports estimation of q.

Place, publisher, year, edition, pages
Springer, 2018
Series
Springer Proceedings in Energy
Keywords
Heat transfer coefficient, Sol-air thermometer, Environmental temperature, Building energy performance gap
National Category
Civil Engineering
Identifiers
urn:nbn:se:umu:diva-152725 (URN)10.1007/978-3-030-00662-4_28 (DOI)
Conference
CONFERENCE on 9th International Cold Climate HVAC 2018, Kiruna, Sweden, March 12-15, 2018
Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2019-06-19Bibliographically approved
Ohlsson, K. A., Östin, R. & Olofsson, T. (2018). Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer. Journal of Building Physics, 42(3), 373-387
Open this publication in new window or tab >>Step-transient method for measurement of the heat transfer coefficient at surfaces exposed to simulated building outdoor environments using the sol-air thermometer
2018 (English)In: Journal of Building Physics, ISSN 1744-2591, E-ISSN 1744-2583, Vol. 42, no 3, p. 373-387Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Sage Publications, 2018
National Category
Civil Engineering
Identifiers
urn:nbn:se:umu:diva-152733 (URN)10.1177/1744259118764823 (DOI)000450347200009 ()
Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2018-12-19Bibliographically approved
Metcalfe, D., Riccuito, D., Palmroth, S., Campbell, C., Hurry, V., Mao, J., . . . Oren, R. (2017). Informing climate models with rapid chamber measurements of forest carbon uptake. Global Change Biology, 23(5), 2130-2139
Open this publication in new window or tab >>Informing climate models with rapid chamber measurements of forest carbon uptake
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2017 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 5, p. 2130-2139Article in journal (Refereed) Published
Abstract [en]

Models predicting ecosystem carbon dioxide (CO2) exchange under future climate change rely on relatively few real-world tests of their assumptions and outputs. Here, we demonstrate a rapid and cost-effective method to estimateCO2exchange from intact vegetation patches under varying atmospheric CO2concentrations.We find that net ecosys-tem CO2uptake (NEE) in a boreal forest rose linearly by 4.7  0.2% of the current ambient rate for every 10 ppmCO2increase, with no detectable influence of foliar biomass, season, or nitrogen (N) fertilization. The lack of any clearshort-term NEE response to fertilization in such an N-limited system is inconsistent with the instantaneous downreg-ulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with consider-able empirical support – diversion of excess carbon to storage compounds – into an existing earth system modelbrings the model output into closer agreement with our field measurements. A global simulation incorporating thismodified model reduces a long-standing mismatch between the modeled and observed seasonal amplitude of atmo-spheric CO2. Wider application of this chamber approach would provide critical data needed to further improvemodeled projections of biosphere–atmosphere CO2exchange in a changing climate.

Keywords
boreal forest, earth system model, model-data integration, nutrient limitation, photosynthetic downregulation, Pinussylvestris
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-131516 (URN)10.1111/gcb.13451 (DOI)000397800600030 ()
Projects
Bio4Energy
Available from: 2017-02-16 Created: 2017-02-16 Last updated: 2019-09-06Bibliographically approved
Olofsson, T., Ohlsson, K. E. & Östin, R. (2017). Measurement of the environmental temperature using the sol-air thermometer. Paper presented at 11th Nordic Symposium on Building Physics, NSB2017, 11-14 June 2017, Trondheim, Norway. Energy Procedia, 132, 357-362
Open this publication in new window or tab >>Measurement of the environmental temperature using the sol-air thermometer
2017 (English)In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 132, p. 357-362Article in journal (Refereed) Published
Abstract [en]

Heat flow measurement with a heat flow meter is a standardized method (ISO 9869-1) to estimate thermal transmittance (U-value) of a building element. The heat flow meter is a thin plate mounted on top of the surface of the element, and measures the heat flux q through the plate. The measured q is the product of the difference in temperatures between exterior and interior environment, and the U-value. The heat transferred from the element is based on the radiant and the convective heat transfer.

ISO 9869-1 specifies that the environment temperature Te “is a notional temperature" and it "cannot be measured directly” (section A.3.1). The air temperature Ta is proposed as a reasonable approximation for the indoor environment, while overcast conditions and absence of significant solar radiation are specified conditions for replacing Te with Ta for the exterior environment.

The sol-air thermometer (SAT) measures the sol-air temperature Tsa, i.e. the equivalent temperature of the convective and the radiative environment. In the absence of solar radiation, Te = Tsa. SAT is a sensor consisting of a thin flat solid plate, of high thermal conductivity. The front side of the sensor is exposed to the environment, whose Tsa is to be measured, and the backside is thermally insulated. The temperature of the SAT-plate equals Tsa.

In this work we propose introduction of the measured Te in the existing standard (ISO 9869-1). The method for measurement of Tsa, using the SAT, has been demonstrated experimentally for different periods, without solar radiation present and under stable climatic conditions.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
environmental temperature, sol-air thermometer, heat transfer coefficient, thermal transmittance
National Category
Other Civil Engineering
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-142081 (URN)10.1016/j.egypro.2017.09.632 (DOI)000426435500060 ()2-s2.0-85033373961 (Scopus ID)
Conference
11th Nordic Symposium on Building Physics, NSB2017, 11-14 June 2017, Trondheim, Norway
Projects
E2B2 project 39699-1
Funder
Swedish Energy Agency, E2B2 39699-1
Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2018-06-25Bibliographically approved
Ohlsson, A., Yang, B., Ekblad, A., Boman, C., Nyström, R. & Olofsson, T. (2017). Stable carbon isotope labelled carbon dioxide as tracer gas for air change rate measurement in a ventilated single zone. Building and Environment, 115, 173-181
Open this publication in new window or tab >>Stable carbon isotope labelled carbon dioxide as tracer gas for air change rate measurement in a ventilated single zone
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2017 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 115, p. 173-181Article in journal (Refereed) Published
Abstract [en]

Carbon dioxide (CO2) has often been used as tracer gas for measurement of the air change rate l (h1 ) in buildings. In such measurements, a correction is required for the presence of indoor CO2, which commonly consists of atmospheric CO2 mixed with human respired CO2. Here, 13C isotope-labelled CO2 was employed as tracer gas, and cavity ring-down spectroscopy (CRDS) was used for simultaneous measurement of the two isotope analogues 12CO2 and 13CO2. This enabled the simultaneous measurement of the 13CO2 tracer gas, with correction for background 13CO2, and the concentration of indoor CO2, allowing for presence of occupants. The background correction procedure assumes that the isotope delta of the background indoor CO2 equals dB ¼ 19‰, based on the prior information that the carbon isotope ratio RB ¼ 13C/12C of all carbon in the bio-geosphere of earth is in the interval 0.010900 < RB < 0.011237. Evidence supported that l could be accurately measured, using the new 13CO2 tracer method, even when the background 13CO2 concentration varied during the measurement time interval, or when the actual dB value differed from the assumed value. The measurement uncertainty for l was estimated at 3%. Uncertainty in l due to uncertainty in RB, uRB(l), was estimated to increase with a decreasing amount of 13CO2 tracer. This indicated that at least 4 ppm tracer must be used, in order to obtain uRB(l)/l < 2%. The temporal resolution of the l measurement was 1.25/l h.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Air change rate, Ventilation efficiency, Tracer technique, Cavity ring-down spectroscopy, C-13-CO2, Isotope labelled carbon dioxide
National Category
Environmental Analysis and Construction Information Technology
Identifiers
urn:nbn:se:umu:diva-131522 (URN)10.1016/j.buildenv.2017.01.021 (DOI)000397363000015 ()
Projects
Bio4Energy
Available from: 2017-02-16 Created: 2017-02-16 Last updated: 2019-09-02Bibliographically approved
Ohlsson, A. K. E., Östin, R. & Olofsson, T. (2016). Accurate and robust measurement of the external convective heat transfer coefficient based on error analysis. Energy and Buildings, 117, 83-90
Open this publication in new window or tab >>Accurate and robust measurement of the external convective heat transfer coefficient based on error analysis
2016 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 117, p. 83-90Article in journal (Refereed) Published
Abstract [en]

Accurate measurement of the convective heat transfer coefficient hc at external surfaces, e.g. at building facades and roofs, is of fundamental importance for heat transfer studies of the built environment. There are two basic methods for measurement of hc, the Loveday and Ito methods, which use one and two heated sensor units, respectively. To guide in selection of method and operating conditions, and in design of the sensor, we performed an error analysis. This included estimation of systematic errors, comparison between methods, and to established Nusselt number correlations, sensitivity analysis, and an evaluation of the measurement uncertainty. The main conclusion was that both methods, at forced convection, yielded measurement uncertainties at the 4 % level, provided that the Ito method was operated under the new condition, where one of its sensors remained unheated. However, at natural convection conditions, the Ito method cannot be operated with one of its sensors unheated, since hc is then zero at that sensor surface, which violates the method assumption that hc is the same at both sensors. Sensitivity analysis showed that systematic errors will be reduced by decreasing the sensor surface emissivity. The major source of measurement uncertainty was the conductive heat flux estimate.

Keywords
Convective heat transfer coefficient, Energy balance method, Sensitivity analysis, Measurement uncertainty, Uncertainty analysis
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-119818 (URN)10.1016/j.enbuild.2016.01.040 (DOI)000373751300009 ()
Funder
Swedish Energy Agency, 39699-1The Kempe Foundations
Available from: 2016-04-28 Created: 2016-04-28 Last updated: 2018-06-07Bibliographically approved
Ohlsson, K. A., Östin, R., Staffan, G. & Olofsson, T. (2016). Dynamic model for measurement of convective heat transfer coefficient at external building surfaces. Journal of Building Engineering, 7, 239-245
Open this publication in new window or tab >>Dynamic model for measurement of convective heat transfer coefficient at external building surfaces
2016 (English)In: Journal of Building Engineering, ISSN 2352-7102, Vol. 7, p. 239-245Article in journal (Refereed) Published
Abstract [en]

Uncertainties in current empirical models for the convective heat transfer coefficient (CHTC) have large impact on the accuracy of building energy simulations (BES). These models are often based on measurements of the CHTC, using a heated gradient sensor, where steady-state convective air flow is assumed. If this requirement is not fulfilled there will be a dynamic measurement error. The objectives were to construct a validated dynamic model for the heated gradient sensor, and to use this model to improve accuracy by suggesting changes in sensor design and operating procedure. The linear thermal network model included three state-space variables, selected as the temperatures of the three layers of the heated gradient sensor. Predictions of the major time constant and temperature time evolution were in acceptable agreement with experimental results obtained from step-response experiments. Model simulations and experiments showed that the sensor time constant increases with decreasing CHTC value, which means that the sensor response time is at maximum under free convection conditions. Under free convection, the surface heat transfer resistance is at maximum, which cause enhanced heat loss through the sensor insulation layer. Guidelines are given for selection of sampling frequency, and for evaluation of dynamic measurement errors.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Convective heat transfer coefficient, Heat balance, Measurement uncertainty, Thermal network modelling, Dynamic sensor model
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-121735 (URN)10.1016/j.jobe.2016.06.005 (DOI)000397386000024 ()2-s2.0-84978427729 (Scopus ID)
Funder
The Kempe FoundationsSwedish Energy Agency, 39699-1
Available from: 2016-06-08 Created: 2016-06-08 Last updated: 2018-08-08Bibliographically approved
Ohlsson, K. E. & Olofsson, T. (2014). Quantitative infrared thermography imaging of the density of heat flow rate through a building element surface. Applied Energy, 134, 499-505
Open this publication in new window or tab >>Quantitative infrared thermography imaging of the density of heat flow rate through a building element surface
2014 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 134, p. 499-505Article in journal (Refereed) Published
Abstract [en]

Infrared thermography is often used to record an image of the building envelope surface temperature, and thereby acquire qualitative information on its thermal insulation performance. Recently, a thermography method has evolved, which enables quantitative measurement of the 2-dimensional pattern of the density of heat flow rate (q) across the building element surface. However, based on previous estimates of its measurement uncertainty, the capacity of the thermography method to yield accurate results has been questioned. We present here an improved procedure for measurement of q, with an evaluation of measurement errors. The main improvement consists of the simultaneous measurement of surface temperature, surrounding radiative temperature, and air temperature, based on information included in one single thermal camera image. This arrangement allows for accurate measurements of small temperatures differences, and thereby reduced uncertainty in the measurement of q. The measurement bias was evaluated experimentally by a comparison of thermography results against a reference method. Under natural convective conditions, there was a 2.6 W m(-2) constant difference between the two methods. The measurement uncertainty u(q) was estimated as a function of q. Based on this, the lower limit of the measurement working range was determined to be 6 W m(-2), which corresponds to less than 10% relative uncertainty. In the case of forced convection, the thermography method yielded less reliable results. The reason for this was the sensitivity of the results to the choice of model for the convective heat transfer coefficient, and the difficulty to select the position for measurement of the wind speed, which is appropriate for this model.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
infrared thermography, measurement uncertainty, thermal transmittance, density of heat flow rate
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-96489 (URN)10.1016/j.apenergy.2014.08.058 (DOI)000343336600048 ()
Available from: 2014-12-01 Created: 2014-11-21 Last updated: 2018-06-07Bibliographically approved
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