To discuss in a systemic way all what has been said above about different decentralized systems, we present the main principle schemes in one illustration (see Figure 75).
Which system is better, with forced circulation or with natural? with classical collector distribution or with primary-secondary rings?
A natural circulation system cannot be regulated automatically; it requires the installation of large diameter pipes which are more expensive and not very aesthetic in the house. Regulation of such a system can be done only manually: to decrease the height of the fire in the burner of the boiler if it is too hot in the rooms, and if it becomes cold, to increase the flame again. If in your house, the electricity goes off often and for a long time, then the gravity system is for you. Such a system doesn’t require any automatic heating devices: air purgers, safety group devices, pressure relief valves and other equipment. But it demands a higher quantity of fuel than systems with pump circulation. Sometimes, one hears from contractors that gravity systems are too «last century»; it is better, if you have an unreliable electric supply, to purchase a back-up generator, and use it with the pump circulation. In advising this, they completely forget that generators as well as circulating pumps also need money, service, and fuel for their work. Besides that, more complicated pump systems need periodical service: replacement of the pumps and automatic devices. It is obvious that the more engineered units there are in the scheme, the more likely some of them will break. The system with natural circulation is extremely reliable. Properly installed at the beginning, it can serve up to forty years without any maintenance. In it, except for the boiler, there is simply nothing to break, because it consists only of the boiler, pipes, and radiators.
If you prefer convenient and comfortable heating, but you don’t mind that it will require service, then choose a forced circulational system. The system with forced circulation is more comfortable — the warmth using such a system can be controlled: you can set the desired temperature in each room and it will be automatically maintained. The quality of such a system is higher than that of the gravity system. But it requires an uninterruptable power supply. Our contractors are more familiar with the systems made according to classical schemes, but they require balancing of heating contours and a large quantity of flow metres, valves, air purgers. Systems made on the principle of primary-secondary rings do not need so many devices, but in contrast with the classical scheme, they require the installation of circulating pumps on each heating ring. Systems with hydraulic «arrows» (hydro-aligners) are made mainly for heating schemes with powerful boilers and a large number of consumers.