To understand the relationship between water vapor, air, and temperature, we will consider two conditions: a. In this course, we will only introduce the psychrometric chart and provide a very brief overview of its structure. Once you are comfortable with it, you will discover that it is a tool that can make it easier to troubleshoot air-conditioning problems in buildings. Initially, the chart can be intimidating, but as you work with it you will discover that the relationships that it illustrates are relatively easy to understand. If you are responsible for the design or maintenance of any aspect of air-conditioning in buildings, a clear and comfortable understanding of the chart will make your job easier. The psychrometric chart is an industry-standard tool that is used to visualize the interrelationships between dry air, moisture, and energy. The relationships between temperature, moisture content, and energy are most easily understood using a visual aid called the “ psychrometric chart.” Since moisture and temperature relate to the energy, or enthalpy, of the moist air we will also introduce that issue. Before we consider humidity sensors, it is important that you understand what is being measured and how the various measurements relating to moisture content and temperature interact. Eng., in Fundamentals of HVAC Control Systems, 2008 4.3 Humidity and the Psychrometric Chart The reading text for this course was originally written by. Steam can be provided by steam boilers or electric steam generators that boil water directly. This can be done with steam or other methods. In climates of low humidity, it is necessary to inject water vapor into the supply air to increase the humidity to the target level.
Then, if the air is heated to 70F without the addition of water, the humidity will change to about 60%, according to the chart. According to the psychrometric chart, if the relative humidity of the outside air is 80% and the outside air temperature is 85☏, when the air is cooled to 55☏, vapor will condense out of the air, and the relative humidity will be 100%. In a warm and humid climate, supply air can be drawn into a system and then exposed to cooling coils that drop the air temperature to 55☏.
#How to read ashrae psychrometric chart code
The Uniform Mechanical Code (Uniform Mechanical Code, 2003) calls for OR relative humidities of 50%-60%. Control of humidity is not required by most codes in all areas, but is for some in most geographic areas. This template allows a designer or operator to “work backwards” from a desired room relative humidity to the desired condition of the air as it enters the supply duct. The psychrometric chart ( Figure 108-2) is a tool for understanding the relationships between the various parameters of supply air and the relative humidity. This can be done with steam or other methods steam can be provided by steam boilers or electric steam generators that boil water.
Then, if the air is heated to 70☏ without the addition of water the humidity will change to about 60%, according to the chart. According to the psychrometric chart, if the relative humidity of the outside air is 80% and the outside air temperature is 85☏, when the air is cooled to 55☏, vapor will condense out of the air and the relative humidity will be 100%. In a warm and humid climate, the supply air can be drawn into a system and then exposed to cooling coils that drop the air temperature to 55☏. The Uniform Mechanical Code ( IAPMO, 2018) calls for OR relative humidities of 50%–60%. Control of humidity is not required by most codes in all areas but is for some in most geographic areas. 2) is a tool for understanding the relationships between the various parameters of supply air and the relative humidity.
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