显热是在不引起相变的情况下传递至物质或从物质传递出的热量。 这是当我们触摸热或冷的东西时我们感受到的热量。
潜热是在相变过程中传递到物质或从物质传递出来的热量，例如从液体到气体或从气体到固体。 它是在不改变物质温度的情况下改变物质状态所需的热量。
总热量是显热和潜热的总和。 它是传递到物质或从物质传递出的热量的总量。
方程
显热：
显热是我们可以感觉到并用温度计测量的热量。 它是改变物质温度而不改变其相（例如，从固体到液体或液体到气体）所需的能量。
$$H_S = 1.08 \times CFM \times \Delta T$$潜热：
潜热是改变物质相（例如，从固体到液体或从液体到气体）所需的能量。 它不会引起温度变化。
$$H_L = 0.68 \times CFM \times \Delta W_{GR}$$总热量：
总热量是显热和潜热的总和。
$$H_T = H_S + H_L$$哪里：
- H小号 是显热 (Btu/hr)
- H大号是潜热 (Btu/hr)
- HŤ 是总热量 (Btu/hr)
- CFM是空气流量（立方英尺每分钟）
- ΔŤ是温差 (°F)
- Δw ^GR 是湿度比差（颗粒 H2O/lb. DA）
例
空调每小时可排出房间 10,000 Btu 的总热量。 空气流速为 1000 CFM，温差为 20°F。 湿度比差为 0.005 格令 H2O/磅。 DA。
显热：
$$H_S = 1.08 \times 1000 \times 20 = 21,600 Btu/hr$$潜热：
$$H_L = 0.68 \times 1000 \times 0.005 = 3.4 Btu/hr$$总热量：
$$H_T = H_S + H_L = 21,600 + 3.4 = 21,603.4 Btu/hr$$U 值和面积
材料的 U 值是其热阻的量度。 U值越低，绝缘性越好。
表面面积是其大小的度量。
方程
$$H = U \times A \times \Delta T$$哪里：
- H是传热速率 (Btu/hr)
- 你是 U 值（Btu/hr.ft².°F）
- 一个是面积 (ft²)
- ΔŤ是温差 (°F)
例
墙壁的 U 值为 0.25 Btu/hr.ft²。 °F，面积 100 平方英尺。 墙内和墙外的温差为 20°F。
传热速率：
$$H = 0.25 \times 100 \times 20 = 500 Btu/hr$$显热比 (SHR)
显热比（SHR）是显热与总热量的比值。 它衡量总热量中有多少是显热。
方程
$$SHR = \frac{H_S}{H_T} = \frac{H_S}{H_S + H_L}$$例
在前面的示例中，显热为 21,600 Btu/小时，总热量为 21,603.4 Btu/小时。 因此，SHR 为：
$$SHR = \frac{21,600}{21,603.4} = 0.999$$结论
显热、潜热和总热是 HVAC 中的重要概念。 通过了解这些概念，您可以更好地设计和操作 HVAC 系统。
FREQUENTLY ASKED QUESTIONS
The specific heat capacity of a substance determines how much heat energy is required to change its temperature by a given amount. Substances with high specific heat capacities, such as water, require more heat energy to change their temperature than substances with low specific heat capacities, such as air. Therefore, when designing HVAC systems, it’s essential to consider the specific heat capacity of the substances involved in heat transfer to ensure efficient sensible heat transfer.
A common example of latent heat transfer in an HVAC system is the dehumidification process in an air conditioning system. When moist air passes over a cooling coil, the latent heat of vaporization is transferred from the air to the coil, causing the water vapor to condense into liquid water. This process reduces the humidity of the air and removes heat from the space, making it an essential component of air conditioning systems.
Total heat is calculated by summing the sensible heat and latent heat transferred in an HVAC system. The sensible heat can be calculated using the specific heat capacity of the substance and the temperature change, while the latent heat can be calculated using the latent heat of vaporization or fusion and the mass of the substance undergoing a phase change. For example, in a cooling coil, the total heat transfer can be calculated by adding the sensible heat transfer due to the temperature change of the air and the latent heat transfer due to the condensation of water vapor.
The units of measurement for sensible, latent, and total heat are typically measured in joules (J) or British thermal units (BTU). The specific heat capacity of a substance is typically measured in joules per kilogram per kelvin (J/kg·K) or BTU per pound per degree Fahrenheit (BTU/lb·°F). The latent heat of vaporization or fusion is typically measured in joules per kilogram (J/kg) or BTU per pound (BTU/lb).
The humidity of the air has a significant impact on latent heat transfer in an HVAC system. When the air is humid, there is more moisture available to condense on the cooling coil, resulting in a greater amount of latent heat transfer. Conversely, when the air is dry, there is less moisture available to condense, resulting in less latent heat transfer. Therefore, it’s essential to consider the humidity of the air when designing HVAC systems to ensure efficient latent heat transfer.
Total heat transfer is an essential concept in various HVAC applications, including air conditioning systems, heat pumps, and refrigeration systems. It’s used to calculate the total cooling or heating capacity of a system, which is critical for selecting the appropriate equipment size and designing efficient systems. Additionally, total heat transfer is used to analyze the performance of HVAC systems and identify opportunities for energy savings and optimization.
