The classic CALMAC Energy Storage Model A tank became the industry's informal benchmark soon after its 1979 introduction – and remains so today. The Model A was among the first thermal storage tank to be incorporated into a full chiller plant, which quickly made it the industry "gold standard." This proven solution has stood the test of time and remains a popular approach for engineers and buildings owners.

The model A tank features two-inch flanges. Unlike the CALMAC Model C tanks, each A model tank needs to be connected individually to distribution piping, so this solution works best for smaller installations.