Daily Maintenance and Cleaning Protocols for Commercial Solar Thermal Water Heating Systems

This section outlines the maintenance and servicing protocols for commercial solar water heating systems, with emphasis on routine maintenance practices to ensure sustained, reliable system performance, as well as systematic cleaning and descaling procedures for key components.  

Following commissioning, solar water heating systems typically exhibit stable operation during the initial operational phase. However, prolonged use inevitably leads to performance degradation due to scale accumulation, sediment deposition, and component wear. Consequently, a structured maintenance regime—comprising periodic inspections, preventive maintenance, and scheduled deep cleaning—is essential to preserve system efficiency, longevity, and safety.  

Cleaning and Descaling Protocols for Solar Water Heating Systems  

1. Scale Removal Methods  

Two principal approaches are employed: mechanical (physical) removal and chemical cleaning. Mechanical methods—including brushing, scraping, or ultrasonic treatment—are preferred where accessible and effective, particularly for external surfaces and non-critical components. However, internal piping, heat exchangers, and collector manifolds often harbor adherent, hard-to-reach scale deposits that resist mechanical intervention. In such cases, chemical cleaning is necessary. The scale formed within solar thermal systems is typically porous and loosely adhered, rendering it highly responsive to appropriately selected acidic agents.  

2. Selection of Cleaning Agents  

Commonly used cleaning agents include organic acids (e.g., citric acid, acetic acid), inorganic acids (e.g., diluted hydrochloric acid), and phosphate-based formulations. From both potable water safety and materials compatibility perspectives, food-grade organic acids—such as citric acid and diluted acetic acid (e.g., 5–8% vinegar essence)—are strongly recommended. These agents offer sufficient chelating and dissolving capacity while minimizing corrosion risk to stainless steel tanks (particularly those containing chromium and nickel). When hydrochloric acid is employed, it must be used only in conjunction with an approved corrosion inhibitor—preferably an imidazoline-type inhibitor—to protect metallic components.  

Cleaning agents are available in solid and liquid forms. Liquid formulations require no dilution and facilitate uniform dosing and circulation; solid agents must be dissolved in water at a mass-to-volume ratio of approximately 1:5 (e.g., 1 kg solid per 5 L water) prior to introduction into the system.  

3. Standardized Cleaning and Descaling Procedure  

The following procedure ensures thorough, safe, and repeatable cleaning:  

(1) Open the cold water inlet valve to fill the storage tank partially;  

(2) Introduce the pre-diluted or ready-to-use cleaning agent into the tank;  

(3) Activate the system’s circulation pump to initiate thermal circulation for 20–30 minutes, ensuring full contact between the cleaning solution and all wetted surfaces;  

(4) Drain the cleaning solution completely via the designated drain outlet;  

(5) Refill the tank with clean water and circulate for two minutes to rinse residual chemicals;  

(6) Drain the rinse water—completion of the cleaning and descaling process.  

4. Critical Safety and Operational Precautions  

(1) System configurations vary significantly across manufacturers and models. Always consult the original equipment manufacturer’s (OEM) technical manual before initiating any maintenance activity. Execution by certified solar thermal technicians is strongly advised.  

(2) Optimal cleaning efficacy is achieved at solution temperatures between 40 °C and 60 °C. While elevated temperature accelerates reaction kinetics, temperatures exceeding 70 °C may compromise seal integrity, degrade elastomeric components, or induce thermal stress in glass vacuum tubes.  

(3) For evacuated tube collectors exhibiting severe internal scaling, individual tube disassembly and targeted cleaning are recommended. This approach enhances cleaning efficacy, reduces chemical consumption, and minimizes environmental impact. Such operations must be performed exclusively by trained personnel to prevent vacuum loss, tube fracture, or injury.  

The maintenance of solar water heating systems mainly includes three aspects: maintenance of solar collectors, maintenance of the piping system, and maintenance of the heat storage system. 

I. Maintenance and Care of Solar Collectors

1. Try to avoid the solar collector system from experiencing excessive exposure to the sun during operation. 

The key points in the operation and management of solar collectors are to prevent the collectors from being exposed to direct sunlight for too long, especially for vacuum tube type collectors. At the same time, it is also necessary to avoid the "stagnant sun exposure" caused by the lack of flow of the heat transfer medium. 

2. Anti-freezing Issues of Solar Collectors

For systems using antifreeze as the heat transfer medium, it is necessary to check the composition of the antifreeze before the arrival of each winter to determine whether it affects the antifreeze performance and whether a replacement is needed. 

For systems that use water as the heat transfer medium, anti-freezing measures such as draining, recirculation, circulation, and heating tapes can be adopted. 

3. Prevention of overheating in solar collectors 

When the system is no longer in use or when the water temperature in the summer water tank is too high, a sunshade net or other items can be used to cover the collector to reduce the sunlight exposure and prevent the collector from overheating. 

4. Cleaning and descaling of solar collectors 

For flat-type collectors, it is necessary to keep the transparent cover plate clean. Regularly remove the accumulated dust to ensure a high degree of transparency. Generally, it is recommended to clean it once every half a year to one year. 

For vacuum tube type collectors, if conditions permit, it is best to regularly clean or rinse the dust off the surface of the collector. Because the dust will adhere to the vacuum tubes, over time it will affect the transmission rate of light and the reflectivity of the reflector. Therefore, the outer surface of the vacuum tubes can be wiped clean every half a year to one year. When wiping, first use soap water or washing powder water to clean the vacuum tubes, and then rinse the surface of the vacuum tubes with clean water. 

The water temperature in the heat collection system is relatively high, which easily leads to the formation of scale. This seriously affects the heat absorption efficiency of the collector and requires regular cleaning. Generally, it is necessary to clean it once every half a year to one year. 

II. Maintenance and Care of the Pipeline System

Due to the high temperature of the pipeline in the solar hot water system, the daily maintenance and care of the pipeline is particularly important. The daily maintenance and care of the pipeline mainly include the following aspects: 

1. Ensure that the insulation layer of the pipeline and the moisture-proof layer on the surface are free from any damage or detachment, to prevent the occurrence of thermal bridges and condensation dripping. 

2. Ensure that there is no air in the pipeline to prevent the hot water from being unable to reach the various water distribution points due to air blockage. 

3. Ensure that the system pipes are unobstructed. Regularly flush the entire system to prevent accumulated rust and dirt from blocking the pipes.

III. Maintenance and Care of the Heat Storage System

The heat storage system mainly refers to the water tank and its accessories. The maintenance of this system mainly includes: 

1. Regularly inspect the sealing performance and insulation layer of the water storage tank. If any damage to the sealing is detected, it should be repaired promptly. 

2. Regularly check whether the water replenishment valve, safety valve, liquid level controller and exhaust device of the water storage tank are functioning properly to prevent air from entering the system. 

3. Regularly check whether any foreign objects have entered the water storage tank to prevent the circulation pipeline from getting clogged. 

4. Regularly remove the scale from the water storage tank. In some areas, the water quality is hard and prone to forming scale. If left for a long time, it will affect the water quality and the operation of the system. Depending on the specific situation, it is recommended to clean the tank every six months to one year.