The heat loss from a tank with a volumetric capacity > 700 L can be estimated in three steps. First, the heat loss from a tank with the insulation covering the entire tank surface area is calculated. In the second step the heat loss is increased to allow for imperfections and heat bridges in the tank insulation. In the final third step the heat loss is further corrected for extra heat losses from openings in the insulation (e.g. from attached pipes and valves). Figure 1 shows an idealised cylindrical tank with flat top and base that is covered with insulation of thickness and thermal conductivity. The tank with flat top and bottom may approximately represent an actual tank with curved dome (see Appendix 1 for a drawing) when the insulation thickness for the tank top and bottom is set to the average insulation thickness of the actual tank (see Appendix 2 for calculation). Note the values for and may be different for the various tank surfaces (cylinder, top and base). The heat loss from the tank can be estimated by assuming the insulation material provides the only significant resistance to heat flow, i.e. by neglecting the relatively small convective resistances on the inside and outside tank surface and the minor conductive resistances provided by the tank wall and the tank cladding. Figure 1. Cross sectional view through an idealised cylindrical tank of inner diameter and height covered with insulation of thickness ∆x. Step 1 Using the tank insulation mid diameter and mid height for the calculation of the heat loss area (dashed line in Figure1), the steady-state heat loss rate from the tank cylinder wall (index 1 in eq 1), the tank top (index 2 in eq 1) and the tank base (index 3 in eq 1) can be expressed with of conduction as: Fourier’s law [W] (1) = Heat loss or heat flow rate where [m2] [m2] [m] [m] [m] [m] [K] In the above equation denotes the temperature difference between the inside tank water and the outside ambient air (55 K for the standing tank heat loss of AS/NZS 4692.1:2005). Note in the
The heat loss from a tank with a volumetric capacity > 700 L can be estimated in three steps. First, the heat loss from a tank with the insulation covering the entire tank surface area is calculated. In the second step the heat loss is increased to allow for imperfections and heat bridges in the tank insulation. In the final third step the heat loss is further corrected for extra heat losses from openings in the insulation (e.g. from attached pipes and valves). Figure 1 shows an idealised cylindrical tank with flat top and base that is covered with insulation of thickness and thermal conductivity. The tank with flat top and bottom may approximately represent an actual tank with curved dome (see Appendix 1 for a drawing) when the insulation thickness for the tank top and bottom is set to the average insulation thickness of the actual tank (see Appendix 2 for calculation). Note the values for and may be different for the various tank surfaces (cylinder, top and base). The heat loss from the tank can be estimated by assuming the insulation material provides the only significant resistance to heat flow, i.e. by neglecting the relatively small convective resistances on the inside and outside tank surface and the minor conductive resistances provided by the tank wall and the tank cladding. Figure 1. Cross sectional view through an idealised cylindrical tank of inner diameter and height covered with insulation of thickness ∆x. Step 1 Using the tank insulation mid diameter and mid height for the calculation of the heat loss area (dashed line in Figure1), the steady-state heat loss rate from the tank cylinder wall (index 1 in eq 1), the tank top (index 2 in eq 1) and the tank base (index 3 in eq 1) can be expressed with Fourier’s law of conduction as: [W] (1) = Heat loss or heat flow rate where [m2] [m2] [m] [m] [m] [m] [K] In the above equation denotes the temperature difference between the inside tank water and the outside ambient air (55 K for the standing tank heat loss of AS/NZS 4692.1:2005). Note in the
Heat%20loss%20test%20procedure%20for%20solar%20water%20heaters%20with%20a%20hot%20water%20storage%20tank%20greater%20than%20700%20L.docx