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1. Overview of Central AC Maintenance Demand in Nanjing
As a megacity in the Yangtze River Delta, Nanjing experiences distinctively hot and humid summers, with an air conditioning cooling season lasting up to 5 months (late May through early October) and extreme temperatures reaching above 40℃. The urban core, Jiangbei New District, and Jiangning Development Zone concentrate a large number of commercial complexes, office buildings, star-rated hotels, and high-tech manufacturing enterprises — all of which widely depend on large-scale central air conditioning systems to maintain indoor environments.
According to Nanjing Municipal Bureau of Statistics data, the tertiary sector accounted for over 65% of GDP in 2025, with AC coverage approaching 100% in commercial, financial, and technology service buildings. On the industrial side, electronics manufacturing, biomedical, and automotive parts enterprises in Jiangning and Pukou Districts extensively use chillers and constant temperature/humidity AC systems. The main challenges currently facing central AC system operation and maintenance in the Nanjing area include: scaling and biofouling deposition from long-term cooling water system operation, gradual annual decline in refrigerant system efficiency, and air quality hazards such as mold growth in ventilation ducts.
As large integrated electromechanical systems, central AC systems left uncleaned for extended periods not only increase energy consumption by 15%~30% but also cause reduced cooling capacity, shortened equipment lifespan, and even public health risks from pathogen proliferation such as Legionella. Therefore, the national "Hygienic Specification for Central Air Conditioning Ventilation Systems in Public Places" explicitly requires regular central AC system cleaning — generally 1~2 times per year for commercial buildings and quarterly maintenance for industrial cleanrooms.
2. Analysis of Common Central AC Problems in Nanjing
2.1 Cooling Water Quality and Scaling Characteristics
Surface water in the Nanjing area is primarily sourced from the Yangtze River, with medium-to-hard water quality: total hardness approximately 120~180 mg/L (as CaCO₃) and Cl⁻ content approximately 20~40 mg/L. Under open-loop circulation conditions, the central AC cooling water system continuously evaporates and concentrates, with Ca²⁺ and Mg²⁺ concentrations in the circulating water gradually rising. Upon contact with atmospheric CO₂, CaCO₃ scale layers form and adhere to the inner walls of condenser copper tubes. Each 0.6mm increase in scale thickness reduces heat exchange efficiency by approximately 20% and increases compressor energy consumption by approximately 10%.
Simultaneously, in Nanjing's hot and humid summer environment, algae and biofouling readily proliferate on cooling tower fill surfaces. These organic materials intertwine with inorganic scale to form composite fouling, making chemical cleaning significantly more difficult than for purely inorganic scale.
2.2 System Types and Common Faults
The distribution of central AC system types in Nanjing is as follows: commercial buildings predominantly use Freon chiller + cooling tower configurations, with some earlier projects employing lithium bromide absorption units; industrial plants mostly use large screw-type or centrifugal chillers; high-end office buildings and hotels often feature independent ductwork systems and terminal fan coil units. Common issues by system:
| System Component | Common Issues | Impact |
|---|---|---|
| Condenser | Water-side CaCO₃ scaling, biofouling | Increased condensing pressure, reduced cooling capacity |
| Evaporator | Chilled water-side rust deposition, oil film contamination | Lowered evaporation temperature, reduced COP |
| Cooling Tower | Fill scaling, water distributor blockage, Legionella proliferation | Reduced cooling efficiency, hygiene hazard |
| Lithium Bromide Unit | Solution crystallization, copper tube corrosion, vacuum degradation | Cooling capacity deterioration, shortened unit lifespan |
| Ductwork System | Dust accumulation, mold, bacterial growth | Indoor air quality degradation, odors |
3. Central AC Cleaning Technical Solutions
3.1 Condenser Chemical Cleaning Process
For the typical CaCO₃ + biofouling composite scale in the Nanjing area, a three-step process of "biocide stripping → acid descaling → neutralization passivation" is employed:
Step 1: Biocide Stripping. Add non-oxidizing biocide (e.g., isothiazolinone) and slime stripping agent to the cooling water system, circulate for 4~6 hours to disperse and detach biofilm from metal surfaces. This step is crucial for the algae problems prevalent in Nanjing summers — if skipped and acid cleaning is performed directly, the acid solution cannot effectively contact the underlying inorganic scale.
Step 2: Acid Descaling. Use LX-903 (sulfamic-acid-series compound cleaner) as the primary agent, supplemented with dedicated corrosion inhibitors, pH controlled at 2~3, ambient temperature circulation cleaning for 4~8 hours. LX-903 has strong CaCO₃ dissolution capability with extremely low corrosion rates on copper tubes (≤0.5 g/m²·h), making it the preferred agent for copper tube condenser cleaning. For stainless steel plate heat exchangers, switch to LX-900 series (organic-acid compound cleaner) formulation to avoid Cl⁻-induced stress corrosion cracking.
Step 3: Neutralization and Passivation. After acid cleaning, drain the acid solution, flush with clean water to pH≈6, add sodium carbonate for neutralization, then apply nitrite-series or molybdate-series passivators to form a protective film on copper tube surfaces.
3.2 Lithium Bromide Unit Cleaning and Maintenance
The cleaning focus for lithium bromide absorption units is chemical descaling of generator copper tubes and solution regeneration. Using an LX-903 (sulfamic-acid-series compound cleaner) + dedicated corrosion inhibitor formulation, check vacuum recovery after circulation cleaning. Simultaneously check solution concentration and pH, performing solution filtration for impurity removal or replacement/regeneration as needed. For some legacy units nearing design life in Nanjing, special attention must be paid to copper tube ammonia corrosion issues — copper tubes in contact with ammonia during operation form cuprammonium complex ions, and the risk of tube wall thinning cannot be ignored.
3.3 Cooling Tower and Ductwork Cleaning
Cooling towers are cleaned using high-pressure water jetting at 15~25 MPa, combined with biocide/algaecide immersion treatment. Ductwork systems are cleaned using mechanical brushing + negative pressure vacuuming, with dust accumulation and microbiological indicator testing conducted after cleaning in accordance with the "Hygienic Specification for Central Air Conditioning Ventilation Systems in Public Places."
4. Service Coverage and Response Mechanism
Danyang Blue Star Cleaning serves all 11 municipal districts of Nanjing:
| Service Area | Coverage |
|---|---|
| Urban Core Districts | Gulou, Xuanwu, Qinhuai, Jianye, Yuhuatai, Qixia |
| New Urban Districts | Jiangning, Pukou, Liuhe, Lishui, Gaochun |
Response time: Urban core districts: on-site inspection within 4 hours; new urban districts: within 8 hours. 24-hour standby for emergency repairs. Danyang is approximately 90 km from downtown Nanjing, with a 1~1.5 hour drive, enabling same-day round-trip operations.
Service process: Free on-site inspection → scale sample analysis → customized cleaning solution → service contract signing → site mobilization → quality acceptance → maintenance recommendations → regular follow-up visits.
5. Local Cleaning Case Studies
Case 1: Lithium Bromide Unit Cleaning at a Nanjing Commercial Complex
This complex is located in the Hexi CBD of Jianye District, using two 2 million kcal lithium bromide absorption units. After 11 years of operation, cooling capacity had dropped by approximately 35%. On-site testing revealed: CaCO₃ scale thickness on generator copper tube inner walls approximately 1.2mm, solution concentration deviated 15% from normal values. The LX-903 (sulfamic-acid-series compound cleaner) + dedicated corrosion inhibitor formulation was used for circulation cleaning for 6 hours, achieving >95% copper tube descaling rate; simultaneous solution filtration and regeneration treatment was performed. After cleaning, unit cooling capacity was restored to 92% of rated value, with annual natural gas savings of approximately 80,000 m³.
Case 2: Online Condenser Cleaning for a Nanjing Pharmaceutical Enterprise Chiller
This pharmaceutical plant is located in Jiangning High-Tech Zone, with 4 screw-type chillers used for cleanroom temperature and humidity control. Since production could not be interrupted, an online chemical cleaning protocol was adopted: a cleaning pump station was connected in parallel to the cooling water pipeline, injecting LX-903 (sulfamic-acid-series compound cleaner) + dedicated corrosion inhibitor, with circulation flow rate controlled at 0.5~1.0 m/s, cleaning duration 8 hours. After cleaning, the condenser approach temperature (difference between condensing temperature and cooling water outlet temperature) decreased from 6.8℃ before cleaning to 2.1℃, with unit COP improving by approximately 18%.
6. Why Choose Danyang Blue Star Cleaning?
- China Industrial Cleaning Association member, 25 years of professional experience, serving the Nanjing market for over 15 years, having provided central AC cleaning services to over 50 enterprises and institutions in the Nanjing area
- Dual technology full coverage: Chemical cleaning + high-pressure water jet cleaning, customized optimal solutions for different scale types and equipment materials
- Safety and environmental compliance: Cleaning agent formulations use biodegradable environmentally friendly acids, waste liquid is neutralized and discharged in compliance with standards; operators are certified and equipped with full PPE protective gear
- Complete central AC system cleaning capability: Covering chillers, lithium bromide units, cooling towers, ductwork systems, and terminal coils, providing one-stop cleaning and maintenance services
- Rapid response: Danyang to Nanjing in 1 hour direct access, 4-hour emergency response in urban core districts, without disrupting commercial operations or production schedules
7. Nanjing Central AC Cleaning FAQ
Q1: How often should central AC systems be cleaned?
Per China's Public Place Central AC Ventilation Hygiene Regulation, commercial buildings should be cleaned 1–2 times per year and industrial cleanrooms maintained quarterly. With Nanjing's hot, humid summers, cooling towers should be cleaned and disinfected twice a year (before and after summer). Uncleaned systems see energy consumption rise 15%–30% with reduced cooling capacity and shorter equipment life.
Q2: Will cleaning damage the condenser copper tubes?
No. Copper-tube condensers are cleaned with LX-903 (sulfamic-acid-series compound cleaner) — strong CaCO₃ dissolution with an extremely low copper corrosion rate (≤0.5 g/m²·h) plus dedicated corrosion inhibitors. Stainless steel plate heat exchangers use LX-900 series (organic-acid compound cleaner) to avoid chloride-induced stress corrosion cracking. Neutralization and passivation after cleaning form a protective film.
Q3: Does cleaning require shutdown? Can it be done online?
Yes, online is possible. For pharmaceutical plants, data centers and other continuous operations, online chemical cleaning connects a pump skid in parallel to the cooling water circuit while the chiller keeps running. Case: four screw chillers at a pharmaceutical plant cleaned online for 8 hours — condenser approach dropped from 6.8°C to 2.1°C and COP rose about 18%.
Q4: How is Legionella risk in cooling towers handled?
First, non-oxidizing biocides (e.g. isothiazolinone) and slime removers are dosed into the cooling water and circulated 4–6 hours to strip biofilms from metal surfaces; then high-pressure water jetting (15–25 MPa) flushes the fill, with biocide soaking. After cleaning, dust and microbial indicators are tested per the Public Place Central AC Ventilation Hygiene Regulation.
Q5: How fast is response in Nanjing?
On-site survey within 4 hours in the main urban districts, 8 hours in new districts, and 24-hour standby for emergency repairs. Danyang is about 90 km from Nanjing's main city (1–1.5 hours by road), enabling same-day round trips. Process: free on-site survey → scale analysis → customized plan → construction → acceptance → regular follow-up.
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The cleaning processes and acceptance criteria described here follow GB/T 25146-2010 Industrial Equipment Chemical Cleaning Quality Acceptance Standard.