Question

 

12.  Which component of a vapor-compression refrigeration machine provides for the cooling effect in the conditioned space?

16.  Why would one choose a fire tube boiler instead of a water tube boiler?

17.  How does one de-humidify an air mass?

18.  Define an HVAC zone?

 

Answer 1

12)

The vapour compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to cooled and subsequently rejects that heat elsewhere. The main components of vapour compression refrigeration is compressor , condenser , thermal expansion valve and evaporator. The compressed fluid with high pressure is taken to condenser and temperature is reduced. This fluid is expanded in expansion valve . The expanded fluid is unstable and expanded to initial condition in evaporator by absorbing the heat from cooling space . This cycle repeats. The cooling is done by the evaporator.

16)

In fire tube boilers hot flue gases pass through tubes and water surroundes them. These are operated at low pressure up to 20 bar . The rate of steam generation and quality of steam are very low , therefore not suitable for power generation. Load fluctuations can not be handled. Overall efficiency is up to 75%. Simple design and easy to erect and low maintenance costs. Even less skill operators are sufficient for efficient operation. Used in process industry.

17)

Cool air holds less moisture than warm air . Properly installed air conditioning system removes moisture from the air by taking up warm air cooling it and circulating the cool and dry air back into the room. A humidistat can be attached to the unit to control the humidity. This how dehumidification done .

18)

A thermal zone is a space or collection of space within the building having sufficiently similar space conditioning requirements so that those conditions could be maintained with a single thermal controlling device. A HVAC zone is a physical space within the building that has its own thermostat and zonal system for maintaining thermal comfort. HVAC zones are identified on the HVAC plans . HVAC zones should not be split between thermal zones, but a thermal zone may include more than one HVAC zone. A HVAC zone may contain more than one space function.