32 kW caliber binding diagram

Power Adjustment Units for Plenum Air Heaters

(explanatory note)

In this design there are power control units for water air heaters of plenum ventilation plants, which serve as actuating units of the system for automatic maintenance of plenum air temperature. Calculated water parameters at the entrance to the calorifer power adjustment units (hereinafter - "binding units"): a) on the supply line - temperature + 120 0С, pressure 0.410 atm (bar); b) on the return line - temperature + 70 0С, pressure 0-8 atm (bar), c) pressure drop 9 between the supply and return lines) 0.71.5 atm (bar). It is necessary to pay attention to another mandatory requirement for water pressure in the supply network: the pressure in the supply line directly at the water piping should always exceed the water pressure in the return line by at least 0.4 atm (40 kPa). This requirement is related to normal operation of the binding unit. In addition, all tie-in units shall be mounted in close proximity to the heaters they serve (not further than 8 m). This requirement is associated with a certain response time of the system to the control effect. Control and protection are performed from Vento Control VCB (or VCX) Remak (Czech Republic) control units with smooth (analog) adjustment. All binding nodes are of the same type, so it is enough to consider the work of any of them.

The proposed diagram of the binding unit complete with this equipment provides an equal percentage control characteristic (due to the special profile of the cone of the saddle control valve) and 100% calorifer protection against freezing (including the so-called active protection).

The control valve (with a certain coefficient Kvs) is selected on the condition that its resistance at the calculated coolant flow rate through the calorifer is at least 1.3 times more than the resistance of the controlled circuit (and for piping units with a small Kvs, the valve resistance is 3-4 times more). This provides better loop control and increases valve seat life.

The diagram of the piping unit, when correctly configured, always keeps the calculated value of the coolant flow through the heater (~ constant) when the pressure drop in the supply network fluctuates and the outside air temperature changes. This, in turn, contributes to the accurate maintenance of the temperature of the supply air and guarantees the complete heating of the heater, as well as increases the level of protection against freezing of individual parts of it (the so-called coolers).

Further consideration will have references to the items of the subassembly in the layout attached to the project. The diagram of the piping unit is based on the principle of no overflow of hot coolant (bypassing the heater) from the supply to the return line. This comment applies both to the proposed units with 2-way, and to binding units with 3-way control valves. The explanation of this limitation in the case of a 2-way valve is the simplest - there are no ways except for the heater itself to flow water from the supply to the reverse. The single bypass route is equipped with a check valve (pos.11 on the diagram of the piping unit), which prevents this. The explanation in the case of a 3-way valve circuit is somewhat more complicated. In the proposed scheme, a 3-way mixing valve is used. In its extreme positions, the overflow of the coolant is not possible, since either the bypass (lower inlet "B" of the valve) or the supply line (inlet "A" of the water to the valve) is completely closed. The possibility of overflow can only be considered when the control valve is in the middle intermediate position. During normal operation of the circulation pump (item 7 on the diagram), overflow is excluded due to a certain pressure drop in the supply channels of the valve created by the pump (item 7), or possibly in a small volume with a significant pressure drop in the supply heating system, and when the pump (item 7) is not able to compensate for this difference with its difference of another sign, i.e. - countercurrent movement of the coolant in the bypass. A significant water bypass is possible in the considered version of the piping unit (with a 3-way valve) only when the circulation pump is stopped (position 7) and the control valve is in the middle position. However, this is not the operational state of the linkage assembly. In the diagram of the connection unit with a 3-way valve, as well as in the previous diagram, there is a bypass line. It is also, as in the scheme with a 2-way control valve, equipped with a check valve preventing bypass from the supply line to the reverse. In this scheme, a bypass is needed to close the small loop in the emergency state of the system to implement active protection of the heater from freezing. To achieve the required value of resistance of the bypass line, a balancing valve is placed on it (pos.10). With correct adjustment, the resistance of the bypass line and the heater in total is equal to the pressure developed by the circulation pump (pos.7) at the calculated water flow rate. This ensures the normal controllability of the control system (including maintaining the specified supply air temperature) with a minimum decrease in the pressure drop in the supply supply lines (so that the pump does not supply too much cooled water from the return).

Such a restriction guarantees that the water temperature in the return line does not exceed 70 0С (subject to normal operation of the control unit and correct selection of the heater). A prerequisite for this is the availability of permanent power on the Vento Control ventilation control units. The same prerequisite is imposed on the power supply of the circulation pump of the heater. Moreover, the last two conditions are mandatory for the normal operation of automatic defrosting protection of the heater, and they must be performed in the cold period of the year always, around the clock, regardless of the state in which the ventilation system itself is (working or turned off).

Three thermomanometers are provided in the piping unit to control the pressure drop and temperature of the coolant: before and after the control valve before the calorifer, if moving in the direction of water movement, and one immediately at the calorifer outlet, before the pump. They are selected so that they allow you to control the pressure in the system during pressure testing. To prevent mechanical mashing and premature wear of sliding parts, a coarse water filter (mud bar) is provided in the circuit. Automatic air vents are provided in the system at the upper points to remove air from the mains. Some types of heat exchangers (such as Vento VO Remak ventilation units) provide for the installation of Mayevsky cranes, in particular TACO Remak, on their headers. If necessary, they must be installed. To perform preventive works and replace the elements, the binding unit has two valves (2) at the inlet, and a drain valve at the lower point. For quick and convenient installation, the pump and control valve have a connection of the type with a swivel nut at the points of connection to the lines.

To ensure the constant design value of coolant flow through the calorifer (~ constant), as well as to close the small circuit in order to operate active defrost protection, there is a bypass line with a check valve (pos. 11) and balance valve (item 10). The latter must be adjusted so that when the control valve is closed (pos.5) and the pump is operating, no more than the estimated amount of coolant flows through the heater. With correct adjustment, the resistance of the bypass line and the heater in total is equal to the pressure developed by the circulation pump (pos.7) at the calculated water flow rate. This ensures the normal controllability of the control system (including maintaining the specified supply air temperature) with a minimum decrease in the pressure drop in the supply supply lines. The balancing valve at the outlet of the piping unit (pos.13) is required to limit the coolant flow through the heater with the control valve fully open (pos.6) not higher than the calculated value. Balancing valves (pos.10 and 13) are equipped with sockets (measuring input), which allow connecting the BALLOREX electronic flowmeter for measurements. Water can also be released through these measuring inlets during preventive work.

At the outlet of the heater in the immediate vicinity of it, a submersible temperature sensor must be installed to monitor the water condition in the return line by the system. The sensor is part of the automatic defrost protection system. To duplicate protection along the air path, a capillary thermostat must be installed on the calorifer. This is also due to the fact that the performance of the protection system embedded in the Vento Control Remak control unit is about 1520 seconds (after passing the signal about the threat of freezing of the heater). Actuation of the set of calorifer protection measures associated with the capillary thermostat takes no more than 5-6 seconds after switching the latter. On the thermostat, stop the fan engine of the plenum ventilation unit and de-energize the air damper at the external air inlet to the latter. This is accomplished by connecting the thermostat limit switch in series to the power supply circuit of the fan motor starter coil.

As mentioned above, balancing valves (pos. 10 and 13) are adjusted at operating pressure drop in the network and operating circulation pump (position 7) using an electronic flowmeter. In the absence of the latter, you can make an approximate adjustment by setting the required values on the balancing valves in accordance with the BALLOREX valve differential diagram available in the instructions from the supplier. Preliminary values of control at operating parameters in a heating system (T = 120/70 0C; pressure drop P = 0.61.5 bar) and the calculated coolant flow rate through the calorifer are given in the characteristics of the balancing valves in the specification to the diagram of each piping unit. On the circulation pump (pos.7) it is necessary to set the speed in accordance with the specific parameters of the supply heating system. With correct selection, the calculated point of dependence "flow pressure" of the circulation pump should be in the working zone of changing its parameters..