Linkage Control Design of Hotel Solar Water Heating System and Auxiliary Heat Source
I am Daniel Wang, a water supply and drainage specialist. The linkage control design between the hotel solar hot water system and auxiliary heat source that you proposed is a core element of hotel energy-saving operation and hot water supply stability. In many years of engineering practice, I have seen many problems caused by improperly designed linkage control logic, including low solar system efficiency, frequent start-stop of auxiliary heat sources, and even fluctuations in hot water supply, which directly affect guest experience and hotel energy consumption. Therefore, this design must be finely planned based on system load characteristics, climate conditions, and equipment performance.
First, according to Article 6.3.8 and its explanatory notes in the Standard for Design of Building Water Supply and Drainage GB 50015-2019, a solar hot water system should be provided with an auxiliary heat source, and its start-stop should be automatically controlled based on the outlet water temperature of the collector system or the water temperature of the heat storage tank. Specifically for linkage control, I usually adopt the following strategies:
1. **Temperature-priority control logic**: Set multiple temperature sensors in the heat storage tank (such as top, middle, and bottom). When the average water temperature in the tank is below the set lower limit (such as 45℃), the auxiliary heat source (such as an air-source heat pump or gas boiler) automatically starts heating; when the water temperature reaches the upper limit (such as 55℃), auxiliary heating stops. At the same time, the solar system operates with priority: when the collector outlet temperature is more than 10℃ higher than the tank bottom temperature, the circulation pump starts; otherwise it stops to avoid heat backflow.
2. **Dual control by time and load**: During hotel peak water-use periods (such as 6-8 a.m. and 8-10 p.m.), the auxiliary heat source can be set to start in advance to ensure stable water temperature. For example, in a five-star hotel project located in the south, solar energy is abundant in summer, and the auxiliary heat source only needs to start on cloudy and rainy days or in winter. We adopted a "solar priority + auxiliary supplement" mode, using a PLC controller to monitor tank heat loss in real time. When the tank temperature is below the set value and solar energy is insufficient, the auxiliary heat source is automatically put into operation.
3. **Overheat prevention and antifreeze protection**: According to Article 6.3.10 of GB 50015, solar systems need overheat prevention and antifreeze measures. In linkage control, when the tank temperature exceeds 60℃ (or the overheat prevention temperature), the auxiliary heat source is automatically shut off and the heat dissipation circulation is started; in winter, when the collector temperature is below 5℃, the antifreeze circulation pump is started.
In an actual engineering case, I was responsible for a northern resort hotel project that adopted a combined "solar + air-source heat pump" system. In the initial stage, the linkage control was simple, which caused frequent start-stop of the heat pump, high energy consumption, and shortened service life. It was later optimized as follows: a buffer tank was added on the heat pump side (volume designed as 20% of the hotel's maximum hourly heat demand), and the control logic was changed to "temperature difference + time delay" (the heat pump starts only when the temperature difference exceeds 5℃ and lasts for 5 minutes), while also incorporating a weather forecast module (such as preheating in advance on cloudy and rainy days). After the retrofit, heat pump start-stop frequency was reduced by 70%, with annual energy savings of about 12%.
**Summary**: The core of linkage control between the hotel solar system and auxiliary heat source lies in "solar priority, auxiliary supplement, precise temperature, overheat and antifreeze prevention." It is necessary to combine GB 50015, actual load curves, and climate data to achieve intelligent regulation through a PLC or DDC system. The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific operating conditions, site conditions, and other factors.