def recalc_dhw_vol_to_energy(vol, delta_t=35, c_p_water=4182, rho_water=995):
    """
    Calculates hot water energy in kWh/a from input hot water volume in
    liters/apartment*day

    Parameters
    ----------
    vol : float
        Input hot water volume in liters/apartment*day
    delta_t : float, optional
        Temperature split of heated up water in Kelvin (default: 35)
    c_p_water : float, optional
        Specific heat capacity of water in J/kgK (default: 4182)
    rho_water : float, optional
        Density of water in kg/m3 (default: 995)

    Returns
    -------
    dhw_annual_kwh : float
        Annual hot water energy demand in kWh/a
    """

    en_per_day = vol / 1000 * rho_water * c_p_water * delta_t \
                 / (3600 * 1000)  # in kWh
    dhw_annual_kwh = en_per_day * 365

    return dhw_annual_kwh