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LCC Optimisation Results Not Reproduced Manually
Posted by Andy Tindale on 02-May-23 04:20 PM
Important Advice for using the Life Cycle Cost (LCC) KPI in parametric simulations (optimisations, parametric analysis and UA/SA):

1. The LCC total present value KPI requires the Detailed HVAC model option to be used as it uses settings on the Economics model data tab which is only available for Detailed HVAC.

The LCC total present value values calculated in optimisation and other parametric simulations will only correspond with the value calculated directly by EnergyPlus if the basis for calculation is the same. In practice this means that the following 2 further requirements must be met:

2. Any additional "Adjustment" costs on the "Component cost" dialog should be removed. To do this set all costs to zero and the "Regional adjustment factor "to 1.

3. The 1-BeginningOfYear Discounting convention on the "Life cycle cost" dialog must be used. This should be the case for models created in v7.

Additional Background Information

DesignBuilder calculates building LCC during parametric simulations by adding

a) the sum of the base construction cost line items (as calculated on the Cost and Carbon tab) to

b) the LCC value calculated by E+ without the line item construction costs.

The addition is done by DesignBuilder at the time of generating the result for the LCC KPI, after the E+ optimisation simulation has been completed.

This simplification in the calculation of the LCC KPI is necessary because it is not currently possible for DesignBuilder to feed in parametrically varied cost results to the E+ inputs for the corresponding parametric variant.

The rationale behind the approximation used by DesignBuilder in the calculation of the optimisation LCC KPI is that the base cost calculated on the cost and carbon tab is close to the more correct Present Value base construction cost used by E+ and so it can be added to the LCC present value calculated in E+ with no construction costs included. I.e. the “Present Value Factor” for Construction Costs (reported in the “Present Value for Recurring, Nonrecurring and Energy Costs” Summary report table) is close to 1.

Unless conditions 2 and 3 above are met, this simplified approach generates different results from the case where the base construction costs are fed into E+ for a full LCC calculation taking into account the Present Value of the construction costs and a range of other adjustments and factors included in the full E+ financial calculation method, which is based on NIST.
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