Integrated Collector Storage Systems

Integrated collector storage (ICS) systems use the hot water storage as part of the collector, i.e., the surface of the storage tank is used also as the collector

Mantle heat exchanger

Insulated pipe ■

Mantle heat exchanger

Insulated pipe ■

Hot water OUT Insulated pipe

FIGURE 5.4 Mantle heat exchanger concept.

absorber. As in all other systems, to improve stratification, the hot water is drawn from the top of the tank and cold make-up water enters the bottom of the tank on the opposite side. Usually, the storage tank surface is selectively coated to minimize heat loss.

The main disadvantage of the ICS systems is the high thermal losses from the storage tank to the surroundings, since most of the surface area of the storage tank cannot be thermally insulated, because it is intentionally exposed to be able to absorb solar radiation. In particular, the thermal losses are greatest during the night and overcast days with low ambient temperatures. Due to these losses, the water temperature drops substantially during nighttime, especially during the winter. Various techniques have been used to keep this from happening. Tripanagnostopoulos et al. (2002) present a number of experimental units in which a reduction in thermal losses was achieved by considering single and double cylindrical horizontal tanks properly placed in truncated symmetric and asymmetric CPC reflector troughs. Alternatively, if a 24 h hot water supply is required, these systems can be used only for preheating and, in such a case, must be connected in series with a conventional water heater.

Details of an ICS unit developed by the author are presented here (Kalogirou, 1997). The system employs a non-imaging CPC cusp-type collector. A fully developed cusp concentrator for a cylindrical receiver is shown in Figure 5.5. The particular curve illustrated has an acceptance half angle, 0c, of 60° or a full acceptance angle, 29c, of 120°. Each side of the cusp has two mathematically distinct segments, smoothly joined at a point P related to 0c. The first segment, from the bottom of the receiver to point P, is the involute of the receiver's circular cross-section. The second segment is from point P to the top of the curve, where the curve becomes parallel to the y-axis (Mclntire, 1979).

With reference to Figure 5.6, for a cylindrical receiver, the radius, R, and the acceptance half angle, 0c, the distance, p, along a tangent from the receiver to the curve, are related to the angle 9 between the radius to the bottom of the

FIGURE 5.5 Fully developed cusp.

Cpc Concentrator

FIGURE 5.6 Mirror coordinates for ideal non-imaging cusp concentrator.

FIGURE 5.6 Mirror coordinates for ideal non-imaging cusp concentrator.

receiver and the radius to the point of tangency, T, by the following expressions for the two sections of the curve (McIntire, 1979):

p(e) = Re, e < ec + n/2 (this involute part of the curve)

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  • crystal
    How to make integrated collector storage?
    8 years ago

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