Heatpump Calcs in Beopt

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The upcoming version of BEopt (3.1.0), expected next month, will include a number of new heat pump inputs, including heating capacity retention for both mini-split and central air source heat pumps. It will also have some updated performance curves and assumptions, particularly for variable speed heat pumps.

It will look something like this:

The default heating capacity retention fractions in BEopt 3.0.1 are:

• ASHP, 1-speed: 0.45
• ASHP, 2-speed: 0.4
• ASHP, var-speed: 0.5
• MSHP, var-speed: 0.4

They will change a bit in BEopt 3.1.0.

That said, note that for a given rated HSPF, the heating capacity retention fraction will generally not have a significant effect on annual energy consumption because a higher fraction will result in a lower heat pump COP in order to achieve the specified rated performance. However, a higher retention fraction can result in a significantly smaller heat pump capacity, and therefore cost, for simulations with autosized equipment.