Continuous casting slabs or primary rolling slabs are used as raw materials, heated by a stepping furnace, and dephosphorized by high-pressure water, and then enter the roughing mill. The rough rolling material is cut through the head, tail, and then into the finishing mill, and computer-controlled rolling is carried out. After the final rolling, it will go through laminar cooling (computer-controlled cooling rate) and take-up by the coiler to become a straight hair coil. The head and tail of straight hair curls tend to be tongue-shaped and fish-tailed, with poor thickness and width accuracy, and often have wavy, folded, tower-shaped and other defects on the edges. The coil is heavier and the inner diameter of the steel coil is 760mm. (Generally used in the pipe-making industry.) After straightening the hair through the cutting head, tail cutting, trimming and multi-pass straightening and smoothing finishing lines, and then cutting or re-rolling, it becomes: hot rolling steel plates, flat hot rolled steel coils, slitting tapes and other products. If the hot-rolled finishing coil is pickled to remove scale and coated with oil, it will become a hot-rolled pickled coil.
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2. Heat Pump Technology for Recovering Swimming Pool Wet Air Heat
Heat pump technology, based on general heat pump water heaters, can be used for various swimming pool heating applications. Units such as "air-conditioner-hot water units" and "dehumidification-hot water units" utilize the latent and sensible heat from indoor air in swimming pools to achieve functions like "one machine dual use" or "one machine, three uses." These systems not only help maintain the temperature of the swimming pool but also improve indoor air quality by dehumidifying and cooling the space. Below are three examples of such technologies.
**2.1 United States CRISPAIR Company’s “E-Tech PHD†Indoor Heated Swimming Pool Super Energy-Saving Hot Water Air Conditioning System**
This system (see Figure 2) uses a heat pump to absorb the latent and sensible heat from the indoor air and warm pool water, transferring it back to heat the pool. It simultaneously dehumidifies and cools the indoor air, while introducing fresh air to maintain air quality and prevent condensation.
The internal components and processes of the host unit are shown in Figure 3. The system reduces cooling costs by up to 2/3, heating costs by 3/4, and dehumidification costs by 3/4. With a COP of 3, the system effectively manages both heating and dehumidification. It uses heat pipes to adjust the dew point, performing double dehumidification—once at the cold end of the heat pipe and once in the evaporator. Part of the return air is drained, and fresh air is introduced, controlled by a dew point regulator.
**2.2 France Private Indoor Swimming Pool with “Heat Pump Dehumidifier-Hot Water Unitâ€**
This unit primarily focuses on dehumidification, with some heat transferred to the heated pool. Data indicates that for private pools, the moisture generated per square meter of water area is about 0.10–0.15 kg/hm², plus 0.40–0.50 kg/h per person. Annually, this equates to approximately 1 ton of water vapor per square meter, with an equivalent heat value of around 700 kWh. The ventilation required for dehumidification is roughly 25–40 m³/m²/h.
Using a heat pump for dehumidification and heating allows the system to extract heat from the air, reduce humidity, and then reheat the air to supply the room. If the heat pump's output exceeds the heating requirement, the excess can be used to further heat the pool water.
**2.3 DRY-O-TRON Brand Indoor Swimming Pool, Jacuzzi, and Small Commercial Climate and Energy Regeneration System by DECTRON Canada**
This system recovers heat from water vapor evaporated from the pool and uses it to heat the pool water while returning the air to the system. By lowering the air temperature to the dew point, water vapor condenses, reducing humidity and recovering the evaporated water, which is then returned to the pool. This helps maintain consistent temperature and humidity levels, saves energy, and reduces makeup water usage.
**3. Heat Pump Hot Water Unit for Swimming Pools: Process and Economy**
**3.1 Process and Control**
The recommended process for a heat pump hot water unit in a swimming pool heating system is illustrated in Figure 7. The system involves circulating heated water through a reheater, mixing it with tap water, and maintaining the pool level and surface height. Unused hot water is cycled back for reheating.
**3.2 Design Calculations and Steps**
Given conditions include a pool volume of 300 m³, daily hot water demand of 6750 liters at 55°C, and average temperatures for the pool and indoor environment. The calculations consider initial filling loads, daily heat losses, and replenishment requirements.
**3.3 Program Economy**
By utilizing the heat from wet indoor air, the system significantly reduces electricity consumption. For example, using indoor air as a heat source saves approximately 19,656 kWh annually, increases the annual energy efficiency ratio (EER) by 9.1%, and provides free cooling capacity. This makes the system more efficient and cost-effective compared to traditional outdoor air sources.