1 What is an AHU Describe the various components of an AHU a

1. What is an AHU? Describe the various components of an AHU, and the psychrometric processes in AHU for cooling day. (15) 2. What are the main components of a chiller? Describe the functions of the components. (15) 3. What’s the difference between primary and secondary systems? (5) 4. What types of secondary systems do you know? What are their advantages and disadvantages? (15) 5. The figure below shows the various heat exchanger loops of a complete HVAC system. Describe the working principle. (25)    6. Redraw the system in problem 5 for the case of a DX cooling coil and aircooled condenser, and describe the working principle

Solution

1. AHU is air handling unit. It is an instrument used to circulate air as air conditioning, ventilating and heating system and also for regulating the system.

The various components of an AHU are:

2. The main components of chillers and their functions are given below:

3. The primary system contains the boilers and chillers as well as the primary pumps. These primary pumps ciculate the heated or chilled air in a continuous loop between the chiller and boiler and the low loss header.

The secondary system transfers thermal energy into the rooms within the building.

4. The secondary systems include the fan coiled units, air handling units, chilled beams and under floor heating and regulators.

The secondary system will have either a variable speed pump or a constant speed pump.

The advantage of variable speed pump is that it can provide higher energy efficiency and control as they are dependent on the demand of the building occupants.

The disadvantage is that additional pumps will be required in these secondary systems to push the heating or cooling fluid around the building and also frictional losses may be significant due to the variety of pipe fittings and pipes involved.