**Abstract:** A comprehensive case study on the design and installation of a solar hot water system is presented.
**Keywords:** solar hot water, air source heat pump
Three years ago, we successfully designed and installed a solar thermal water supply system at a major hospital in Beijing, capable of producing 30 tons of hot water daily. The system has been well-received by users, operating efficiently throughout the year, maintaining a temperature of at least 45°C. In urban Beijing, coal boilers have long been banned, leading many institutions to switch to gas boilers. However, this transition significantly increased fuel costs, placing a heavy financial burden on businesses.
From an environmental standpoint, the shift from coal to gas is beneficial for society and public health. However, the rising operational costs for gas-fired boilers remain a challenge. This is where solar thermal systems offer a compelling alternative, combining environmental benefits with economic advantages. Our project clearly demonstrates how such systems can deliver both social and economic value, providing substantial cost savings over time.
During the initial design phase, we meticulously remapped the building according to the original blueprints. Many structures had undergone multiple modifications during construction, resulting in discrepancies between the actual dimensions and the drawings. To ensure accuracy, we updated all relevant markings, which greatly aided in the final assembly process.
The building's orientation posed some challenges. A large elevator room was located on the front side, causing partial shading from morning and afternoon sunlight. With limited space, we aimed to maximize the usable area. Traditional solar installation methods based on latitude calculations were not sufficient due to the complex geometry of the building. We had to carefully plan the layout to avoid shading issues and optimize performance.
After calculating the available area—approximately 570 square meters—we subtracted the space occupied by the elevator room, the boiler room, and more than 20 air conditioning units. This left us with less than 500 square meters for the solar collectors. At that time, the Chinese standard GB/T 18713-2002 for solar hot water systems had just been issued but wasn't widely adopted yet. We studied international practices and found that many countries used horizontal or low-angle installations, which showed promising results.
For example:
1. Fluid mechanics suggested that horizontal installation allows smoother water flow, reducing pressure loss.
2. The system’s vertical transitions are minimal, reducing the risk of vacuum tube blockages.
3. In northern regions, horizontal installation captures more sunlight throughout the day, especially during summer.
4. Using the top of the building maximizes space utilization, with even weight distribution.
Based on previous projects in southern China, we used a 0–30° angle for installation. After one year, the system performed well, and user feedback was positive. Given the constraints, we divided the irregular area into rectangles, creating two parallel loops. By combining series and parallel configurations, we achieved a total collection area of 400 square meters.
Although some areas were shaded by the elevator room, the system still maintained temperatures between 50°C and 75°C in most seasons. In winter, when solar energy was insufficient, we integrated an air-source heat pump with a 100 kW output to maintain the desired temperature.
The 30-ton storage tank was too heavy to be placed on the roof, so we opted for a basement location. This allowed us to utilize existing infrastructure, such as condensate tanks and pumping stations, which also helped in managing waste heat from the boiler room. During winter, the heat pump absorbed heat from the boiler room, while condensate was automatically drained. This ensured efficient use of both heat and dry air.
The heat pump, consuming about 27 kW of power, provided 100 kW of heat and approximately 90 kW of cooling in the summer. It served multiple departments and improved overall efficiency. The system’s coefficient of performance (COP) reached around 3.5, meaning for every unit of energy input, we got 3.5 units of heat. Combined with cooling, the effective benefit was roughly 6–6.5 times the input. This made the hospital’s solar hot water system highly efficient and economically viable.
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JIANGSU FUERMU WELDING CORPORATION , https://www.fuermuwelding.com