Zone Radiant Exchange : Difference between ScriptF and CarrollMRT E+ (V9.3)

asked 2020-09-07 02:21:10 -0600

Ttthomas
71 ●2

updated 2020-09-08 08:20:07 -0600

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

Hello

I have a building including many differents surfaces in each zone. To avoid long simulation time i'm using the new object PerformancePrecisionTradeoffs of EnergyPlus (9.3) which allow to chose the Zone Radiant Exchange Algorithm between ScriptF which is a quadratic radiant exchange algorithm and a linear one called CarrollMRT.

When I compare the consumption of my building using the ScriptF algorithm and the CarrollMRT algorithm I notice a difference of 1% on the total consumption but at the hourly time step I sometime have differences of up to 80 kW or -70 kW corresponding to a difference of approximatly 12% on the whole consumption of my building.

I would like to know what is the difference between those two algorithm when there is a radiant floor heating in the zone ? Does it change a lot compared to a fan coil heating ?

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answered 2020-09-08 12:31:52 -0600

Neal Kruis

4735 ●10 ●17 http://bigladdersoftware.com/

The difference will depend a lot on the geometry of your model and whether you are defining view factors between surfaces when using ScriptF.

The two methods should be identical (or close to identical) for six sided rectangular prisms. If you are not defining view factors the biggest difference between the default view factors and what is assumed in the CarrollMRT method is that ScriptF will assume that surfaces facing the same direction (or within 10 degrees of the same direction) cannot see each other. With the Carroll method, surfaces can exchange radiant heat with other surfaces facing the same direction through the mean radiant temperature node. Differences in results will be exacerbated when surfaces facing the same direction are very different temperatures.

If you can share a visualization of your geometry and/or hourly time step data, that might help better understanding why there you are seeing differences in your specific case.

Hope that helps!