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Berkeley Comfort Model

Model of the Month: April 2009Model of the Month: April 2009

The Berkeley Comfort Model provides localized comfort results for each body segment computed from temperatures predicted by our Human Thermal Module. The Berkeley Comfort Model was developed at University of California-Berkeley's Center for the Built Environment. It is an advanced design tool for assessment of thermal comfort designs and functions as a separately-licensed feature within our software. An overview of the Berkeley Comfort Model can be viewed here.

Air Conditioning Source Temperature Curves

Figure 1. AC source air temperature curves for two AC pul down casesFigure 1. AC source air temperature curves for two AC pull down cases

This sample demonstrates an evaluation of AC pull-down using two different source air temperature profiles and the resulting effects on localized passenger comfort. The two profiles are shown in Figure 1 and the more powerful AC system delivers colder airflow faster.

 

 

 

Figure 2: AC pull-down results for systems with high and low power and responseFigure 2: AC pull-down results for systems with high and low power and response

The human thermal manikin is seated in a rather fancy 4-door sedan in Arizona during the month of August. The air in the cabin is segmented into 3 air nodes, top, middle and bottom. The AC flow of 18,000 liter/minute is divided equally into these nodes and they are connected to surfaces of the cabin interior and the human model. We can see in Figure 2 the resulting temperatures for the cabin air nodes, dash board, and floor panel. The faster pull down of the higher-powered AC system is evident in the lowest set of air node curves. The thermal mass of the dash board, floor pan and other surfaces creates a slow downward trend that would continue past the 15-minute solution end time.

Higher Powered AC System Case: Thermal Sensation and Thermal Comfort

Figure 3. Berkeley Thermal Sensation by body segment and overall for the higher powered AC source air.Figure 3. Berkeley Thermal Sensation by body segment and overall for the higher powered AC source air.

For the higher-powered, but less fuel-efficient, AC system, we can see in Figure 3 that our manikin undergoes very hot sensation for all body segments, followed by some segments being cooled below neutral comfort levels.

 

 

 

 

Figure 4: Berkeley Thermal Comfort by body segment and overall for the higher powered AC source airFigure 4: Berkeley Thermal Comfort by body segment and overall for the higher powered AC source air

The intensity of the discomfort is visible in Figure 4, where overall comfort is restored (passing 0) at about T=5 minutes. Note that the Berkeley Comfort Model shows us that the head is very thermally sensitive, reaching a max 4.0 hot sensation quickly but then responding very quickly to the AC pull down and experiencing cold (below 0) sensation within 3 minutes.

Lower Powered AC System Case

For the lower-powered, more fuel efficient AC system, we recognize the longer period of hot thermal sensation and discomfort in Figures 5 and 6. The lower-powered AC system in this case results in a restoration of overall thermal comfort at about T=12 minutes. Note the local sensation of the head in Figure 5 shows the head crossing into the cool sensation region at T=5 minutes, two minutes longer than in the higher powered AC case (Figure 3).

Results: Comparison of High VS Low Powered AC Source

It can be argued that the second case, with energy savings through the reduced power load required by the AC, still provides a reasonable response to a hot startup under very hot conditions. The manikin achieves overall comfort in 12 minutes, rather than the 5 minutes delivered by the more consumptive but powerful AC system. The Berkeley Comfort Model thus demonstrates the value of decoupling the metrics of thermal comfort from thermal sensation and provides a means of optimizing the design of cooling on a body-segment level.

To learn how the ThermoAnalytics Human Comfort Module with the integrated Berkeley Comfort Model can be used to improve human effectiveness, comfort, and safety, contact us.


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