Boilers and their piping (continued)
Mixing circuits for heat-carrier temperature decrease 31
Heat-carrier temperature decrease for low-temperature heat exchanger, including heating radiators aimed for low-temperature heat-carrier can be done by using a mixing circuit with controlled three-way distribution valve described above. The mixing system is connected to heat-accumulating tank and consists of independent circuit with its own pump, three-way distribution valve with heat regulator or servodrive, return valve, temperature transducer, expansion tank shown in diagram 31.
Mixing circuits shall be connected to heat-accumulating tanks, not to hard-fuel boiler.
The principle of operation of mixing system is the following. When the temperature of heat-carrier increases above specified value on sensing device a side pass through of the distribution valve opens and the direct pass through closes. Heat-carrier circulates (for example, along the warm floor circuit) without inflow of hot heat-carrier from the heat-accumulating tank. If the temperature decreases below the specified value, the side pass through slightly opens and direct opens a little, and the heat-carrier circulates through the heat-accumulating tank. Other solutions of «mixing system» are also available. On heating radiators, distribution collector of warm floor system separate thermostatic valves can be installed with thermostatic heads, which function is to change the consumption of heat-carrier through them, i.e. the function of temperature regulation. The warm floor surface temperature in living rooms shall not exceed 28оС. Besides, it shall be uniform over the whole floor surface. These limitations as well as limitations of temperature expansion of concrete bars of warm floor and pipes embedded has determined maximum temperature of heat-carrier supply to warm floor circuit. It is considered that temperature in the warm floor supply pipe shall not exceed 50оС. But, as a rule, it doesn’t exceed 45оС.
If the heating system consists only of warm floor it is required to decrease temperature of heat-carrier supplied to the warm floor; in t is case the heat-carrier temperature at the boiler output shall be maximum, i.e. the boiler shall be fired at full power. This is possible only in a variant when the heating system is provided with heat-accumulating tank. In case of using only low-temperature heat exchanges for heating the system shall contain heat-accumulating tank.
32 Heating system that is provided with heat exchangers with different temperature parameters shall also be designed with heat-accumulating tanks. The boiler always operates at full power and heats the heat-carrier in the tank. From the tank the heat-carrier is supplied for heating and to warm floor over its own independent circuit with its own pump having its own parameters.
It is possible to design hot water supply system from double-circuit boiler or use a mixing circuit of hot water supply boiler from the boiler which is parallel to heat –accumulating tank circuit. The temperature of heat-carrier in it shall not exceed 65оС.
Legend on the diagrams
I. V. Kuznetsov
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21/09/2017 © Igor Kuznetsov "Kuznetsov's stoves"