May 28, 2025
In air source heat pump renovation projects, most of the heating terminal equipment is traditional radiators. Radiators are one of the most common heating terminals in the north, and many old houses have them. Air source heat pumps can be used with radiators, which also provides a place for radiators in these old houses. From a short-term perspective, it saves initial investment, but high heating costs have to be invested in the later stage. Let's analyze the disadvantages of installing radiators at the end of air source heat pumps and what is the best heating method at present.
1. Using radiators as heating terminals requires high temperatures and reduces the energy efficiency of air source heat pumps.
Radiators are usually made of metal materials, and their heat transfer capacity is not particularly strong. At the same time, to give full play to the heating effect of radiators, it is necessary to ensure that the water temperature inside the radiator is high enough, usually reaching 60-90 degrees. This means that in order to ensure the heat dissipation effect of the radiator, its minimum water supply temperature must also reach 60 degrees. As we all know, the higher the outlet water temperature of the air source heat pump is set, the lower its energy efficiency ratio is, that is, the higher the outlet water temperature is set, the greater its power consumption is. Generally speaking, when the external ambient temperature is the same, the energy efficiency ratio at an outlet water temperature of 60 degrees is about 20% lower than that at an outlet water temperature of 45 degrees. In other words, its power consumption is increased by more than 20%.
2. Using radiators as heating terminals is troublesome to modify, and the indoor temperature is not ideal.
The influence of temperature on the heat dissipation capacity of radiators is very large. The decrease in the average water temperature of radiators will significantly reduce the heat dissipation capacity of radiators, and the number of radiators required will increase significantly. Taking cast iron radiators as an example, theoretically, when the supply and return water temperature of the radiator drops from 95/70℃ to 75/50℃, the number of radiators required will increase by about 70%; when it drops to 45/40℃, the number of radiators required will increase to 3.6 times the original. That is to say, if the air source heat pump is used instead of the boiler as the heat source, the cast iron radiator used needs to be increased by 2-3 times on the original basis. Moreover, in the actual transformation, even if the radiator is added, the heating effect is not ideal, and most indoor temperatures can only reach about 18 degrees.
3. Using radiators as the heating terminal will reduce the heating service life of the air source heat pump.
At present, the maximum outlet water temperature of most air source heat pumps is only 60 degrees, and a small number can reach 65 degrees in a short time. Using radiators for heating requires the outlet water temperature of the air source heat pump to be maintained at 60 degrees for a long time. In the operation of the air source heat pump, the higher the water temperature, the greater the work required by the compressor, the higher the exhaust temperature, the greater the pressure, and the pressure of the piping, especially the exhaust pipe, will also increase. If it is in this state for a long time, the life of the compressor and the piping will be correspondingly attenuated.
Therefore, in general, it is not recommended to use radiators as the heating terminal in air source heat pump heating projects. The water supply temperature of fan coil units only needs to be 45-55 degrees, and floor heating only needs to be 35-45 degrees, so it is best to use floor heating, which is the most suitable in terms of comfort and economy. In the project renovation, it is recommended to transform the original radiator into a fan coil unit.
