Zone Control System - Air Conditioning
Air conditioning systems can be broadly classified into two. First is self contained units, in which a single air conditioning unit with refrigeration unit, blower, etc. is installed in a space which is to be conditioned. Second one is central air conditioning unit, in which refrigeration unit and blower unit is different because of their larger capacity. Here things are a bit more complicated than self contained type. Former is used for small spaces such as cabins, rooms, etc. while latter for large areas like buildings, hospitals, etc.
Zone Control System
This is a simple type of air conditioning system compared to the others. Here accommodations with different temperature requirement is divided into a number of zones. One refrigeration unit and three steam heaters are installed to create three different temperature zones, as shown in the figure below.
- Air filter
- Three zone heaters
- Insulated pipes carrying air to different zones
- Sound attenuating air terminal, with volume control
- Automatically operated steam valves
- Steam trap for each steam valves
- Cooling thermostat
- Airconditioning compressor unit
- Capacity control for compressor
- Refrigerant Condensor and Receiver
- Expansion valve
- Sea water pump for condensor
- Blower starter
- Air conditioning compressor starter
- Condensor sea water pump starter
Blower supplies both fresh and recirculated air through evaporator coils to the steam heater. This cool air passes through steam heater where air is heated to attain required temperature for each zone. Then using insulated pipe lines, air is delivered to different zones. Steam control valves measure the temperature of heater outlet as well as fresh air to determine amount of steam to be passed through the heater. A thermostat is provided at the fresh air intake side, which enables the compressor to work at required capacity in summer season. Air conditioning compressor unit is often installed in machinery spaces, while blower unit (also called Air Handling Unit or AHU) is located in accommodation area.
Even though the system is simple, it has some drawback also. In case the users of one zone reduces the volume of air delivered, pressure in other zones increases, and controllers in those zones need to be readjusted.This is normally taken care of by installing a pressure sensor and control valve for air at each air duct branches. The control valve open or close according to the signal from pressure sensor, to stabilize the air pressure for all consumers.