Background: In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ/yr) of the energy used in commercial buildings and nearly 50% (10.1 EJ/yr) of the energy used in residential buildings. Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.
Question: What can be used to balance out a portion of the energy used by HVAC systems?
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<extra_id_0> Solar heating, cooling and ventilation technologies<extra_id_1>