Question

Describe and compare the following HVAC systems. How do they differ in function and what are the relative advantages and disadvantages of the systems. Graphically represent each system with a sketch.

1. All-air systems
2. All-water systems
3. Air-water systems

Answer 1

ALL AIR SYSTEMS

A single zone system has an air handling unit, a heat source and cooling source, distribution network of ducts, and appropriate delivery devices

In a multi-zone all-air system, individual supply air ducts are provided for each zone in a Construction. Cold air and return hot air are mixed at the air handling unit to achieve the thermal requirement of each zone

A terminal reheat all-air system is a multiple zone, which considers an modification of single zone system. This can be done by adding heating equipment, such as hot water coil , to the downstream side of the supply air from air handling units near each zone.

The dual duct all-air system is a terminal-controlled modification of the multi-zone. A central air handling unit provides two conditioned air streams such as a cold deck and a hot deck.

Some cooling spaces require different airflow of supply air due to the changes in thermal loads. Therefore, a variable-air-volume (VAV) all-air system is the suitable solution for achieving thermal comfort. The above types of all-air systems are constant volume systems. The VAV system consists of a central air handling unit which provides supply air to a VAV terminal control box that is located in each zone to adjust the supply air volume.

Coil Oupkicde cetRlsh fan Ayy zone A ALL A, R SINLLE 2oNE

ALL WATER SYSTEMS

In an all-water system, heated and cooled water is distributed from a central system to conditioned spaces [4, 5]. This type of system is relatively small compared to other types because the use of pipes as distribution containers and the water has higher heat capacity and density than air, which requires the lower volume to transfer heat.

SUPP Dis change Aİr o ?en' Valves Cot Fan Molur cendlen sale Rehun ALL Wakr syskns

AIR WATER SYSTEMS

Air-water systems are introduced as a hybrid system to combine both advantages of all-air and all-water systems. The volume of the combined air is reduced, and the outdoor ventilation is done to properly condition the desired zone. The water medium carries the thermal load in a building by 80–90% through heating and cooling water, while air medium conditions the remaining air.

Piar aisippu ran Hot co. Colt Cot Cola cot Fan toil unit AIR WATER SMSTEM