during normal operation are shown for each of the five networks in Table 8. These figures are based on the intermediate system size (4608 collectors). The last column of Table 8 is an estimate of the energy required to heat up the heat transport network from ambient to operating temperature. This startup energy is expressed in terms of time of operation of the collector field at average capability. The magnitude of the operating network heat leak compared to the IEI indicates that systems 2 and 3 lose enough heat that during a 13 hour overnight down time, all of the initial energy investment IEI is lost. The two systems must be heated to operating temperature every morning, and a rough guide to the warmup time is estimated in the last column. System 1 will have some residual energy left after an overnight down time of about 13 hours. Approximately 20% of the initial energy investment will remain. The warmup time will be approximately 0.42 hours rather than the initial warmup time of 0.52 hours. The hot helium system (system 4) has such a large IEI due to thick pipes of large diameter that even though its average heat loss is greater than any other system, it will have some heat left at the end of a night. Approximately 30% of the IEI will remain after 13 hours. The warmup time will be about 1.7 hours, which is somewhat less than the 2.44 hours indicated as the initial startup time. The energy required during the warmup is about 15% of the total daily energy collected and is a further liability for system 4. System 2 (steam-water) has a small IEI and only a 9 minute initial startup time. Even though all this energy is lost overnight, it represents only a 1 to 2% energy loss per day. System 5 (chemical) has negligible amounts of energy lost each day even after a 13 hour shutdown time since there was almost no IEI.
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