The electric heating power is generally based on the actual heating requirements, and the climatic conditions of the project location as well as the building thermal insulation properties should also be taken into account. The power is the result of thermal load calculation. According to the present regulations of MOC (Ministry of Construction), the civil residential buildings should meet the energy saving standard of 65 %, and public buildings should reach 50 %. If have good thermal insulation properties, the building projects with electric heating centralized control system are encouraged to choose 65~80 w/㎡ installed power and 18 w/m heating cable. Corresponding adjustments can be made according to different building and user requirements. For instance, if the installed power is increased to 90-180 w/㎡, the heating speed is faster and the temperature control range is wider from 16 to 35 ℃, which ensures higher level of comfort. Of course, the initial investment on power grid will increase accordingly. The alternative air conditioning load in summer and electric heating load in winter will also affect the total load of the project.
The supply voltage of the power distribution system for electric heating in the building should use 220/380V three phase four wire when the power supply load is greater than 12 kW, according to JGJ142-2004 Floor Radiant Heating Technical Regulations. In accordance with the section 10.7.8 of the JGJ16-2008 Code for Electrical Design for Civil Building that single phase distribution current of the lighting circuit shall not be greater than 16 A, the power load of each single phase distribution branch circuit for electric heating should not exceed 3 kW. Because the distribution branch circuit of the electric heating system is usually single phase distribution, please pay attention to balanced distribution. Actually, the load current of the maximum phase should not be 15 % higher than the average, and the load current of the minimum phase shall not be15% lower than the average.