{"id":16128,"date":"2023-07-31T15:53:15","date_gmt":"2023-07-31T07:53:15","guid":{"rendered":"https:\/\/aircondlounge.com\/?p=16128"},"modified":"2024-05-06T10:24:08","modified_gmt":"2024-05-06T02:24:08","slug":"what-is-the-temperature-of-cooling-coils","status":"publish","type":"post","link":"https:\/\/aircondlounge.com\/what-is-the-temperature-of-cooling-coils\/","title":{"rendered":"What is the Temperature of Cooling Coils?"},"content":{"rendered":"\n
Cooling coils have specific design and operating temperatures. They must be cold enough to dehumidify the air but not too cold to cause freezing. So, what should be the temperature of a cooling coil?<\/p>\n\n\n\n
For comfort cooling applications, the temperature of the air leaving the cooling coil or off coil temperature should be around 13\u00b0C (55\u00b0F). If the off coil temperature is too high, the room may not be sufficiently cooled and dehumidified<\/strong>.<\/p>\n\n\n\n Problems with insufficient cooling and dehumidification are often associated with the off coil temperature being too high. However, other cooling coil temperatures must also be examined.<\/p>\n\n\n\n Off coil temperature is the temperature of the air leaving the cooling coil. Off coil temperature is also known as leaving air temperature or supply air temperature.<\/p>\n\n\n\n Generally, the off coil temperature is between 12\u00b0C (53.6\u00b0C) and 14\u00b0C (57.2\u00b0F) for standard cooling and dehumidification. However, during startup, the off coil temperature can be as high as 18\u00b0C (64.4\u00b0F) or even 20\u00b0C (68\u00b0F) depending on the initial room temperature.<\/p>\n\n\n\n The off coil temperature depends on the on coil temperature which is the temperature of the air entering the cooling coil. The higher the on coil temperature, the higher the off coil temperature.<\/p>\n\n\n\n On coil temperature is the temperature of the air entering the cooling coil. On coil temperature is also known as entering air temperature or return air temperature.<\/p>\n\n\n\n Cooling coils are constructed and tested according to the AHRI standards. Based to the AHRI rated conditions, the on coil temperature is 27\u00b0C (80\u00b0F) dry bulb and 19\u00b0F (27\u00b0C) wet bulb.<\/p>\n\n\n\n The Celsius and Fahrenheit are rounded to match the respective practice.<\/em><\/p>\n\n\n\n However, in practice, the on coil dry bulb temperature is between 24\u00b0C (75\u00b0F) and 26\u00b0C (79\u00b0F) depending on the temperature setpoint.<\/p>\n\n\n\n Theoretically, the on coil temperature should be equal to the room temperature. However, some air conditioning systems have a long return duct which causes the actual on coil temperature to be 1 to 2\u00b0C higher than the room temperature.<\/p>\n\n\n\n The off coil temperature depends on the on coil temperature because most cooling coils are designed to have a specific delta T. In other words, there is a specific range of temperature differences between the on coil and off coil temperature.<\/p>\n\n\n\n The temperature difference across a cooling coil is known as delta T (\u0394T). Given that the airflow is constant, the greater the delta T, the higher the capacity of the cooling coil.<\/p>\n\n\n\n Q = mc\u0394T<\/p>\n\n\n\n From the above heat transfer equation, if the mass flow rate, which is the product of airflow and density is fixed, increasing the \u0394T will increase the Q which is the capacity of the cooling coil.<\/p>\n\n\n\n Traditional evaporator coils are designed at a delta T of between 10-12\u00b0C (18-21\u00b0F). Meaning, if the on coil temperature is 24\u00b0C (75\u00b0F), the off coil temperature should be around 12-14\u00b0C (54-57\u00b0F).<\/p>\n\n\n\n Initially, the room temperature may be around 30\u00b0C (86\u00b0F). As the air conditioner starts to operation, the on coil temperature or return air temperature is around 30\u00b0C (86\u00b0F) as well. So, the off coil temperature or supply air temperature is expected to be around 20\u00b0C (68\u00b0F).<\/p>\n\n\n\n However, some air conditioners are designed to have a higher delta T across their evaporator coil. For example, mini-split air conditioners typically have a delta T from 10\u00b0C (18\u00b0F) up to 20\u00b0C (29\u00b0F). Depending on the outdoor temperature, the off coil temperature can be as low as 10\u00b0C (50\u00b0F).<\/p>\n\n\n\n In commercial buildings, chilled water air handling units (AHUs) and fan coil units (FCUs) typically have cooling coils that are selected as follows:<\/p>\n\n\n\nOff Coil Temperature<\/h2>\n\n\n\n
On Coil Temperature<\/h2>\n\n\n\n
Cooling Coil Temperature Difference<\/h2>\n\n\n\n
Water Cooling Coil Temperature<\/h2>\n\n\n\n