| 1. |
- Wallentén, Petter
(författare)
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Dynamic insulation : Analysis and field measurements
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A nonlinear least squares method for continuous measurement ofthe air flow in a 'dynamic insulation' was presented. The methodis called the gradient method to indicate that the temperature gradientsin the insulation are used. The method includes one dimensionaltransient and steady state calculations ofthe heat transfer inthe insulation. The model was verified by analytical and numericalsimulations. With the use of this method the air flow through aninsulation was continually measured in a single storey one familyhouse with a living area of 116 m2 during one year (1993). The housewas built at Dalby, Sweden which has a yearly average temperatureof 7.8 C. The exhaust ventilation was about 53 l/s. The air flowthrough the dynamic insulation as measured by the gradient methodwas 21 l/s or 4O % of t]ne total inlet air. The measurements showed aslightly higher air flow during the spring that during the autumn.This result corresponds well with laboratory measurements performedby Roots (1994) where 50 % of the inlet air passed throughthe insulation.
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| 2. |
- Wallentén, Petter
(författare)
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Heat Flow in Building Components, Experiment and Analysis
- 1998. - TABK 98/1016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three building components exposed to natural climate were studied: a dynamic insulation in the ceiling of a house, an outer wall and one window in the same wall. The term dynamic insulation implies that part of the inlet or exhaust air passes through the insulation of a house. A house with dynamic insulation was continuously measured for approximately a year and a half. The performance of the dynamic insulation was estimated by using hourly values of the temperature distribution inside the insulation. The air flow through the insulation was calculated as the air flow that best matched the measured temperature distribution. For the calculations both the transient and steady state heat transfer equations were used. The dynamic U-value for the insulation was about 0.05 W/m2°C for the ceiling. This corresponds to a dynamic energy efficiency for the insulation of 35%. Taking into account that only 40% of the total supply air passed through the insulation, the total efficiency became 14%. A heat exchanger for ventilation air have an efficiency above 60%. The general conclusion from the measurements was that dynamic insulation requires a house constructed to much higher standards, as far as air leakage is concerned, in order to work properly. An outer ambient wall with a window were studied with both theoretical analyses and measurements performed under conditions with natural climate. The method used was to estimate the heat flow through wall and window from measured temperatures and solar radiation. The longwave radiation was calculated from surface temperatures. The convective heat transfer was calculated as the difference between the heat flow through the building element and the longwave radiation. With the one-dimensional dynamic heat transfer model for the window which included shortwave radiation it was possible to measure the continuous heat flow through a window from temperature sensors and solar radiation measurements. With the one-dimensional finite difference model for the heat transfer through the wall it was possible to calculate the heat flow through a wall from temperature sensors. It was possible to continuously measure the convective heat transfer coefficient on the inner surface of a wall or a window. The accuracy was not very good: at best ±15% for the window and ± 20% for the wall. Even with this low accuracy the effect of different heating and ventilation strategies on the inside could clearly be detected. The results showed that the importance of the ventilation design and the position of the radiator is crucial. Local convective heat transfer coefficients may be more than 10 times the expected, due to ventilation or position of the radiator.
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| 3. |
- Wallentén, Petter
(författare)
-
Heat Flows in a Full Scale Room Exposed to Natural Climate
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An ambient wall with a window were studied with both theoretical analyses and measurements performedunder conditions with natural climate. The method used wes to estimate the heat flow through wall and windowfrom measured temperatures and solar radiation. The longwave radiation was calculated from surface temperatures. The convective heat transfer was caculated as the difference between the heat flow through the building element and the longwave radiation. With the one-dimensional dynamic heat transfer model for the window which included shortwave radiation it was possible to measure the continuous heat flow through a window from temperature sensors and solar radiation measurements. With the one-dimensional finite difference model for the heat transfer through the wall it was possible to calculate thre heat flow through a wall from temperature sensors. It was possible to continuously measure the convective heet transfer coeffìcient on the inner surface of a wall or a window, The accurary was not very good: at best +/- 15% for the window and, +/- 20% for the wall. Even with this low accuracy the effect of different heating and ventilation strategies on the inside could clearly be detected. The results showed that the importance of the ventiletion design and the position of the radiaton is crucial. Local convective heat transfer coefficients may be more than 10 times the expected, due to ventilation or position of the radiator.
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