Unmet Hours

If you're using both Slab:GroundDomain and the pre-processor I think the answer is that you don't need to use both? My understanding was that the pre-processor was an older approach, and the GroundDomain model didn't need it - you feed in the 2m temperatures through Site:GroundTemperature:Shallow and Site:GroundTemperature:Undisturbed:KusudaAchenbach. Hence why the Slab:GroundDomain inputs ask for "Undisturbed" ground temperatures.

I've gotten reasonable alignment between GroundDomain and Kiva like this - the main point of disagreement is where Kiva predicts significant heat gains through the edge of the slab in summer, which can be reduced by edge insulation. Because of this Kiva tends to predict significantly higher overheating and cooling loads and significantly different effects from adding edge insulation. I've been running models with both ground models for sensitivity analysis because of this the past few years.

If you do try Kiva however you do need to update E+ beyond v9.4 though - there was a serious bug that resulted in Kiva estimating heating use to by like 40% lower than it should be. This was fixed in v22.1.0 iirc

If you're using both Slab:GroundDomain and the pre-processor I think the answer is that you don't need to use both? My understanding was that the pre-processor was an older approach, and the GroundDomain model didn't need it - you feed in the 2m temperatures through Site:GroundTemperature:Shallow and Site:GroundTemperature:Undisturbed:KusudaAchenbach. Hence why the Slab:GroundDomain inputs ask for "Undisturbed" ground temperatures.

I've gotten reasonable alignment between GroundDomain and Kiva like this - the main point of disagreement is where Kiva predicts significant heat gains through the edge of the slab in summer, which can be reduced by edge insulation. Because of this Kiva tends to predict significantly higher overheating and cooling loads and significantly different effects from adding edge insulation. I've been running models with both ground models for sensitivity analysis because of this the past few years.

If you do try Kiva however you do need to update E+ beyond v9.4 though - there was a serious bug that resulted in Kiva ~~estimating~~ underestimating heating use to by like ~~40% lower than it should be.~~ 40%. This was fixed in v22.1.0 iirc

If you're using both Slab:GroundDomain and the pre-processor I think the answer is that you don't need to use both? My understanding was that the pre-processor was an older approach, and the GroundDomain model didn't need it - you feed in the 2m temperatures through Site:GroundTemperature:Shallow and Site:GroundTemperature:Undisturbed:KusudaAchenbach. Hence why the Slab:GroundDomain inputs ask for "Undisturbed" ground temperatures.

I've gotten reasonable alignment between GroundDomain and Kiva like this - the main point of disagreement is where Kiva predicts significant heat gains through the edge of the slab in summer, which can be reduced by edge insulation. Because of this Kiva tends to predict significantly higher overheating and cooling loads and significantly different effects from adding edge insulation. I've been running models with both ground models for sensitivity analysis because of this the past few years.

If you do try Kiva however you do need to update E+ beyond v9.4 though - there was a serious bug that resulted in Kiva underestimating heating use by like 40%. This was fixed in v22.1.0 iirc

Edit: adding a couple of notes on GroundDomain defaults after looking at the idf:

Ground domain depth: the relationship of ground depth to heating use is vaguely U-shaped. In my experience, at least in my climates, the lowest heating use is found around 10m (the E+ default), while shallower depths will increase it and deeper ones will increase it more slowly. I'm not entirely sure this parameter is identical to the groundwater depth parameter in Kiva, but treating them as the same does seem to align their results decently. The Kiva documentation suggests using an approximation from an older paper to estimate the water table depth at ~0.1022 * elevation (though GroundDomain cannot go shallower than 2m). Anyway, 2m depth will produce higher slab heat loss, which may be interpreted as a worst estimate of heating use or an optimistic case of potential heating savings when looking at slab insulation. Sensitivity analysis of ground depth may be useful depending on what you are looking at.
Aspect ratio: this is an annoying parameter because it's not what we normally use to describe slabs (typically Area/Perimeter ratio). If I understand it correctly, the aspect ratio is instead the length/width ratio of an equivalent rectangle to your slab. The dimensions of an equivalent rectangle can be identified by solving a quadratic where a = 1, b = -perimeter/2, and c = area.

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