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Energy modelling

Energy Model- What is it?

An energy model estimates how much energy a building will use based on its specific design and construction selections.

The energy modelling software used on this project, REM/Rate, uses specific inputs to generate its estimate such as:

​>  Where is the building brick or siding? 

>  Where are the windows, how large are they and how efficient? 

>  What kind of heating and cooling system? 

>  How much insulation is there and where? how air tight is the home?...and much more...

As a builder, we use this modelling to compare different construction choices affects on performance and their associated cost.

What is a HERS Score and why does it matter?

LEED requires a HERS score.  A HERS score compares that estimated energy use of the designed building to a reference building. The reference building is the same building that instead of being designed to be energy efficient, is built to the current building code.  A HERS score of 100 predicts the proposed construction will use the same energy as a code built home.  A HERS score of 0 is a net zero home.

311 Varnum's HERS score is to be determined as the final third party testing of duct tightness and envelope tightness have not been completed.  However, it is modeled at approximately HERS score of 60.  Which means it is modeled to use roughly 40% less energy than a code built home.

What happens if house has renewable energy added to it?

Because of the low amount of initial load adding a renewable energy source to this house has an enormous impact on it's overall energy use.  For example, if a 8kW PV system (which is currently the approximate maximum that will fit on the roof) were added at a later date, the HERS score drops to being in the 5-10 range. That is within striking distance of being net zero.


Although we as builders would love to say that what is predicted or modeled will come to pass, we cannot.  Energy use is utterly personal.  Some people use a lot, some use a little.  A couple could buy this house, or a large family.  With such unknown factors controlling actual energy performance, True Turtle LLC and CAT Consulting offer no guarantees whatsoever on energy performance or the ability of this building to be net zero. 

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