Variable-Main Thread Parallel Configuration

this is shown in Figure 2.7, to save even more energy pumping (as a rule, approximately 15-20%).

Flow through coolers varies in response to the load of the system. Bypass valve opens to maintain a minimum flow, which is equivalent to about 30% of the flow through the largest hmm. This system has certain operational restrictions, with fast load fluctuations and changes in flow can lead to fluctuations in the cooling water inlet, but a viable option, where the critical temperature of chilled water control is not required.

The main criteria for the system are:

1. The flow through each chiller must be maintained in the range from 3 to 11 frames per second. Therefore, good quality flowmeters, which should have periodic recalibration required for each chiller.
2. If the rate of flow through the cooler changes too quickly, hmm control can't keep up. Therefore, load flucuations should be limited to not more than 30% per minute.

misconception about variable flow configuration is that chillers such a system will work more efficiently. With variable flow through the evaporator, LMTD evaporator remains constant but the convection heat transfer coefficient consumption decreases, thus reducing the heat transfer efficiency. With a constant flow through the evaporator, the CIRCULATION falls to the fall of temperature of input water, but the coefficient of convective heat transfer remains constant, as the flow remains constant. Thus, the power consumption of the refrigeration unit will be essentially the same whether the flow is constant or a variable.

Another misconception about these systems in terms of cost. Often in the literature would argue that the main variable flow system is less expensive than primary-secondary systems, because one set of pumps are eliminated. However, the cost of high-quality flowmeters (and additional pipeline to ensure that they are properly installed for accurate reading), by-pass relief valve, and more complex control systems, as a rule, will offset the pump-savings.

For larger systems with a high consumption and long distribution pipelines is done, additional savings in the process of transfer of energy generated by the configuration can be advantageous. But, it is much more complicated, and operating restrictions previously discussed. So, for most systems, more simple, primary-secondary system configuration remains the recommended approach for the majority of several cooling systems, although the variable main thread should be assessed on larger systems with long distribution uses more sophisticated operators...