Research of system performance of sewage-source heat pump with fouling effect

In order to ensure successful sewage treatment with biological method in cold climate, a sewage-source heat pump system using disposed sewage as heat source to heat raw sewage was presented according to the status of sewage treatment in one medicine factory in Harbin, China. The problem of fouling is critical and difficult in designing and popularizing sewage-source heat pumps. The relationship between fouling and heat exchanging was discussed, and the performance of this system with the change of fouling thermal resistance was simulated. The results show that spray heat exchanger is suitable for sewage-source heat pump, and fouling impact on heat transfer is not only decided by fouling thermal resistance, but also related to heat transfer coefficient. It can be simulated that with the increase of fouling thermal resistance, system energy efficiency ratio and mass flow rate of refrigerant will reduce, and the sewage temperature of condenser outlet will decrease. It is necessary to remove fouling when this temperature is lower than 30°C. When fouling thermal resistance increases from 0 to 5.28 × 10^-4 m²·K/W, the input power of compressor will increase by 18.02%. The analytical results also indicate that less the fouling thermal resistance is, lower average temperature refrigerant can heat up sewage with.