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 Homestar Technical Clarification Rulings

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Technical Question Title Tool Version Date Released Credit Name Tool Category TC Link
Accounting for Energy Consumption from Mechanical Cooling v5, v5.1 June 2026 EF4 - Energy Use EF Link
Approved Ruling:

Where Pathway 4 in HC2: Summer Comfort is used, mechanical cooling energy is not automatically included in the annual electricity demand result in ECCHO. This is because the electrical energy required depends on the efficiency of the selected cooling system.

The ECCHO output provides the annual cooling demand for the dwelling. To calculate the cooling energy load for EF4 compliance:
1. Obtain the total cooling demand from ECCHO.
2. Determine the cooling Energy Efficiency Ratio (note that this is not the same as heating COP) of the proposed mechanical cooling system (e.g. heat pump or air conditioning unit).
3. Divide the total cooling demand by the cooling EER to determine the electrical energy load attributable to cooling.
4. Add this calculated cooling energy use to the total energy use reported by ECCHO.

This method assumes that:
• Mechanical cooling is available and operating for 100% of the predicted hours above 25°C; and
• The entire dwelling is served by the mechanical cooling system used in the calculation.

A single heat pump serving only one room does not comply with this method, as overheating may occur in other parts of the dwelling (for example, upstairs bedrooms).