Vehicle air conditioning with forced ventilation Electric heater relevant criteria and design application of commonly used for vehicle air conditioner forced draft with Electric heater is iron standard TB/T2704-2016 standard of the Railway passenger cars and trains, Electric heaters, and for export to Europe for vehicle air conditioning forced ventilation in the Electric heater can be based on reference standard of France NF F 13-835 "Railway rolling stock - Electric air heaters shielded ele ments, with forced Ventilation.
Based on TB/T 2704-2005 Electric Heaters for Railway Passcars and EMU, TB/T 2704-2016 Electric Heaters for Railway Passcars and EMU mainly adds relevant contents of forced ventilation electric heaters, stipulates the noise and thermal inertia of forced ventilation electric heaters, and provides design, test and inspection standards for electric heaters for EMU. NF F 13-835 Railway Rolling Stock -Electric Air Heatersshielded Elements,with Forced Access provides for the performance, approval conditions, inspection and test conditions of the products for the forced ventilation tube type air heaters used in Railway vehicles. The two standards have their own emphases, which can be referred to each other in the design and verification to guide the design reasonably.
Electric heater design stage, can refer to the NF F 13-835 standard about power density ≤120 K W/m2 and unit load (light tube ≤ 2.2W /cm2;
Finned tube ≤ 3.6W /cm2), combined with the installation layout, the feasibility assessment of the electric heater power requirements;
For electric heater whose two parameters cannot meet the standard requirements, it is necessary to communicate with the manufacturer in time to modify the design scheme, so as to effectively control the risk in the scheme stage, avoid the safety risk of loading operation and the stability and reliability of operation.
Electric heater in detail design phase, must strictly enforce the TB/T 2704-2016 standard, the standard in terms of test and inspection request a NF F 13-835 standard in more detail, in some test items more method to the comprehensive, such as noise, starting current, deformation, water dielectric, high pressure, low temperature, damp and hot state circuit leakage measurement, flame retardant test, grounding resistance, leakage current and the function of overtemperature protection may be directly influences the use of safe and reliable test item points, etc.
Electric heater is mainly composed of installation frame, tubular heating element (finned tube or light tube), overtemperature protection element and so on.
The heater body protection components generally have a primary overtemperature protector and a secondary overtemperature protector. The primary overtemperature protector is an automatic reset type, and the secondary protector must be reset manually. Table 1 electric heater advices on the main design points and the serial number entry point or the reference 1 power design by NFF13835 or JB/T 4088-2012 standard calibration heater of the power density and the unit load, the reasonable design of heater design scheme (power density, accord with a standard unit load) 2 electric heater installation frame, and fasteners of heat-resisting stainless steel heating element according to JB/T 4088-2012, JB/T2379-1993 standards require 4 wire high temperature region using high temperature 200 ℃ flame retardant wire and cable, other areas with low smoke zero halogen lead wire connectors or terminals or according to customer technical requirement to meet customer technical requirement under consideration within the connection mode of easy to maintain air conditioning electric heater installation notices air flow evenly, waterproof insulation, etc.
The installation position of the electric heater in the air conditioning unit should first ensure that the heating element of the heater is in the ventilated unimpeded area. Local poor ventilation may lead to high local surface temperature of the heating pipe, which is a safety risk. The installation position of the main electric heater in the air conditioning unit is shown in Figure 1. It is generally installed in the downstream of the evaporator. At this time, attention should be paid to the relative relationship between the heater and the upper edge of the condensed water plate.
If conditions permit, make the heater bottom row above the height of the water tray;
When cannot meet, appropriately increasing the L size at the same time, to ensure uniform airflow blows bottom heating tube or through CFD simulation analysis of air flow field is relatively reasonable structural layout, to ensure uniform air flow through the evaporator and electric heater, consider the summer after a heater tube, at the same time in the development of prototype test, must be the necessary test.
