Heat load is the heat added or removed to maintain target temperature. Expressed in kW, BTU/hr or Tons of Refrigeration (TR). 1 TR = 3.517 kW = 12,000 BTU/hr.
Cp is heat energy needed to raise 1kg by 1°C. Water Cp=4.186 kJ/kg°C (high — excellent for heat transfer). Air Cp=1.005. Steel Cp=0.502.