Solving heat calculation problems?

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May I ask, our factory’s direct-fired refrigeration units require 3.5 million kcal of heat. We plan to switch to hot water for heating; we need to determine by how much the amount of gas required will increase (from using gas for direct heating to using gas to generate steam first before heating). The values I obtained through theoretical calculations are shown in the figure below. But there is one problem: our leader said that the steam generator with a capacity of 4 T/H was sufficient in the past, so why does the calculation indicate that 7 T/H is needed? ? Moreover, the heat output of 600,000 calories per ton of steam generated by the boiler remains constant; 3.5 million calories would require around 6 tons of steam. Even with 4 tons, it’s not enough – so why was it sufficient before? Is it a calculation error or is there some other problem? ? Thank you all in advance; I hope you’ll feel free to share your advice! ! !