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Table of Contents
- Introduction to Summer Air-Conditioning Systems
- Summer Air-Conditioning for Hot and Dry Conditions
- Summer Air-Conditioning for Hot and Humid Conditions
- Single Cooling Coil and Mixing for Summer Cooling
- Summer Air-Conditioning using Direct Expansion
- Bypass Mixing for Controlled Room Temperature
- Single Cooling Coil with Absorbent Dehumidifier
- Evaporative Cooling for Cost-Effective Solutions
- Conclusion: Choosing the Right System for Your Needs
1. Introduction to Summer Air-Conditioning Systems
Summer air-conditioning systems play a pivotal role in creating comfortable indoor environments tailored to specific atmospheric conditions. These systems are designed to address the challenges posed by varying weather patterns, ensuring optimal thermal conditions for occupants. In this exploration, we delve into diverse summer air-conditioning strategies, each tailored to specific climatic conditions.
From combating the intense heat of hot and dry regions to managing the high humidity levels in tropical climates, the engineering behind these systems is a fascinating blend of technology and environmental science. Join us as we navigate through the intricacies of HVAC (Heating, Ventilation, and Air Conditioning) systems optimized for different summer conditions, exploring the equipment arrangements, psychrometric processes, and practical considerations that make these systems effective.
Whether you are an HVAC professional, a technician, or someone curious about how these systems work, this journey will provide valuable insights into the world of summer air-conditioning. Let’s embark on this exploration to understand the principles that make indoor spaces cool, comfortable, and conducive to various activities even amid the sweltering heat of summer.
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2. Summer Air-Conditioning for Hot and Dry Conditions
Summer air-conditioning systems designed for hot and dry conditions are HVAC systems specifically tailored to address atmospheric conditions characterized by high temperatures ranging from 38–42°C(100.4–107.6°F) and low relative humidity levels of about 20–25%. These systems aim to optimize indoor comfort by reducing air temperature and increasing relative humidity to meet desired conditions of 24ºC(75.2ºF) and 60% RH. The equipment arrangement and the psychrometric processes involved in achieving this are illustrated in the figures below.
The process involves the filtration of atmospheric air, passing through dampers before traversing the cooling coil. The air’s temperature undergoes reduction through sensible cooling, pinpointed at point 2 on the psychrometric process chart. Subsequently, the air leaving the cooling coil at point 2 enters an adiabatic humidifier. In this stage, water vapor is introduced, increasing humidity levels, and the conditioned air exits the humidifier at point 3.
Efficiency = [(T2 – T3) / (T2 – T5)] × 100
Total capacity of cooling coil = (V / Hf) × [(h3 – h1) / 1000] KW of refrigeration
Capacity of humidifier = (V / Vs) × [(w3 – w2) / 1000] kg/sec
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3. Summer Air-Conditioning for Hot and Humid Conditions
Summer air-conditioning systems designed for hot and humid conditions cater to atmospheric conditions characterized by temperatures ranging from 32–38°C (89.6–100.4°F) and relative humidity of about 70–75%. The equipment arrangement and psychrometric processes for achieving the desired comfort conditions of 24ºC (75.2ºF) and 60% RH are illustrated in the figures below.
The process involves air filtration and passage over the cooling coil for dehumidification. As the air moves over the cooling coil, with a temperature below the dew point of incoming air, both temperature and humidity are reduced, resulting in the air exiting at point 3.
Total capacity of cooling coil = (Hf×V) × [(h1 – h3) / 1000] KW of refrigeration
The air then enters the heating coil condition 3 and leaves at condition 5
Capacity of heating coil = Hf×V × (h5 – h3) / 1000 KW
Where:
- Hf: Density of moist air (Kg/m³)
- V: Volume of handled air (L/sec)
- (h1 – h3): Enthalpy difference across the cooling coil (kJ/kg)
- h5 – h3: Enthalpy difference across the heating coil (kJ/kg)
4. Single Cooling Coil and Mixing for Summer Cooling
A summer air conditioning system designed for hot and dry conditions operates with a single cooling coil and mixing process. Here’s how it works:
1. Outside air, along with recirculated air from the conditioned space, flows through a damper and mixes.
2. The mixed air passes through a filter to eliminate dirt, dust, and impurities.
3. Passing through a cooling coil, the air is cooled and dehumidified.
4. The cooled air moves through a perforated membrane, shedding moisture in condensed form, collected in a sump.
5. The air then passes through a heating coil, slightly raising its temperature to match the designed dry bulb temperature and relative humidity.
6. Cold and hot streams flow through separate ducts and are mixed before entering each conditioned space or zone.
The process from 1 to 2 illustrates the state of the air as it traverses the air-conditioned room, accounting for the load within the room. At the fourth stage of the process, air undergoes mixing under the conditions specified in points (2) and (3). Subsequently, at the fifth stage, we observe the state of the air as it exits the cooling coil, with the transition from 5 to 1 indicating the heating of the air due to friction as it passes through the blower. `
Maintaining indoor humidity below 60% during summer is crucial for optimal air conditioning performance. This system reduces the load on the cooling coil by mixing conditioned air, which is at a lower temperature than outdoor conditions, with fresh air.
5. Summer Air-Conditioning using Direct Expansion
This cycle repeats as needed to maintain the desired indoor temperature. The single-coil design simplifies the process, making it a cost-effective and widely used solution for cooling in hot summer conditions.
6. Bypass Mixing for Controlled Room Temperature
Bypassing with a single coil in a summer air-conditioning system for fixed temperature. Source: IDC
This system is utilized to regulate the Dry Bulb Temperature (DBT) in the air-conditioned room based on the load in the room. The system’s arrangement is illustrated in Figure 2.33. Condition 4 involves the mixing of air at conditions 2 and 3. Condition 5 represents the state of air exiting the cooling air. Condition 6 entails the mixing of air at conditions 5 and 2. Process 4–5 signifies the cooling and dehumidifying of air passing through the cooling coil. Process 6-1 represents the heat generated by the fan and motor. Process 1–2 characterizes the state of air passing through the room as it takes the load in the room. The re-heating of air passing through the blower due to friction is disregarded for plotting on the psychrometric chart.
The previous system had limitations, as the temperature in the air-conditioned room couldn’t be controlled according to the load in the room. The control of DBT is deemed more crucial than humidity control unless humidity is excessively high.
The present system is employed during partial load operation. The face dampers on the cooling coil and bypass dampers are motor-controlled to maintain a constant DBT. As the sensible heat gain of the air-conditioned space decreases, more re-circulated air is bypassed. However, with a direct expansion cooling coil, the air passing across the coil may be more thoroughly dehumidified than when the full air quantity is handled. Thus, satisfactory space humidity conditions may be maintained during some partial load conditions without the need for re-heating.
7. Single Cooling Coil with Absorbent Dehumidifier
The cooling coil, as discussed in the previous methods for air cooling, also induces some dehumidification alongside the cooling process. However, dehumidification by a refrigerant cooling coil has limitations, especially when the coil surface temperature falls below 0°C, leading to frost formation and reduced heat transfer rates. This necessitates the implementation of a defrosting system and the reheating of air before it enters the air-conditioned space. As the required air dew point temperature is lowered, this refrigeration system becomes more complex and costly to own and operate.
In contrast, the absorbent system depicted in the following figure can minimize the required surface temperature of the cooling coil, entirely avoiding the possibility of coil frosting since the necessary coil temperature remains above 0°C. Consequently, this method achieves extremely low air dew-point temperatures more reliably and economically than the refrigeration method.
As you can see in the psychrometric processes for this system condition 4 involves the mixing of airstreams at conditions 2 and 3. Process 4–5 represents the adiabatic dehumidification of air passing through the absorbent dehumidifier. Process 5–6 is the sensible cooling of air passing through the cooling coil with a surface temperature considerably above the required frosting temperature. Process 6–1 represents the heat generated by the fan and fan motor. Process 1–2 signifies the condition of air passing through the air-conditioned room, accounting for the existing load.
8. Evaporative Cooling for Cost-Effective Solutions
Considering air-conditioning systems, I’ve come across information indicating that comfort systems designed to maintain optimal thermal conditions can be quite costly. In situations where financial constraints limit the installation of a fully effective system, partially effective systems with reduced costs may be a more appealing option. In hot and dry regions, evaporative cooling systems offer significant relief in enclosed spaces.
The commonly used evaporative cooling system, as shown above involves a straightforward process. Process 3–1 represents evaporative cooling, and process 1–2 represents the room load absorbed by the air passing through the room. Although state 2 represents an acceptable space condition, it may not necessarily be the optimum one. State 3 of the outdoor air is at a much higher temperature but lower relative humidity than state 2. As the air-washer is the sole processing device in the system, the overall cost is considerably lower than systems designed for optimal comfortable conditions.
Typically, evaporative cooling systems use a much higher flow rate of air (2 to 3 times that of conventional systems). The increased air movement past an individual provides a similar degree of comfort but with higher effective temperatures compared to situations where air movement is low.
9. Conclusion: Choosing the Right System for Your Needs
As we conclude our exploration of summer air-conditioning systems, we’ve unveiled the diverse strategies and technologies employed to tackle the challenges presented by different climatic conditions. From the arid heat of hot and dry regions to the humidity-laden atmospheres of tropical climates, these HVAC systems stand as technological marvels, ensuring indoor comfort even in the harshest summer conditions.
The journey has taken us through the intricacies of cooling coils, refrigeration units, and innovative approaches like evaporative cooling and absorbent systems. Understanding the psychrometric processes and equipment arrangements has shed light on the sophisticated engineering that goes into creating optimal indoor environments.
As technology continues to advance, so does our ability to refine and optimize summer air-conditioning systems. Whether it’s achieving energy efficiency, cost-effectiveness, or sustainable solutions, the field of HVAC is ever-evolving. We hope this exploration has deepened your understanding of the principles behind summer air-conditioning and sparked an appreciation for the engineering ingenuity that makes indoor spaces comfortable, no matter the external weather conditions.
Thank you for joining us on this journey through the world of HVAC technology. Stay cool!
Related posts:
Practical Applications of Psychrometry in Various Industries and Environments
Introduction to Psychrometry: Understanding the Properties of Moist Air
Understanding Psychrometric Charts: 10 Things Every HVAC Engineer and Technician Must Know
Mastering Psychrometric Processes in HVAC: A Comprehensive Guide
