Page 72 - GRIHA Manual Volume III - Introduction to National Rating System
P. 72
Building and system design optimization 65
Cooling capacity: 3, 5, and 7 TR (tonnes of refrigeration)
• Floor- mounted package air-conditioners: These units are typically shaped like cupboards
with all components like compressor, evaporator, blower, and so on, placed inside the
shell. These ACs are usually placed in a small enclosure adjacent to the conditioned area.
Cooling capacity: 5–16.5 TR (tonnes of refrigeration).
Features: Floor-mounted package units are available in both air-cooled and water-
cooled models. They can be easily serviced and can handle longer ducts since the fans
installed in them are more powerful. These units can handle large tonnages with lesser
units of power.
ii. Central plant
These are usually large air-conditioning plants assembled at the site and used for big
buildings.
Components: Basic components are compressors, condensers, air-handling units, water
chillers, and cooling towers.
Types of central plants
• DX (direct expansion) systems: In DX systems, the air is cooled and conditioned in the
plant room. The treated air is then pumped to various parts of the building through
ducts. Air returning from the conditioned spaces is sucked by a fan through a coil-fin
arrangement. The coil-fin arrangement acts as the heat exchanger. The refrigerant
inside the coil absorbs the heat from the return air and cools it. The cold air is then
pumped back to the air-conditioned space. In DX plants, the heat exchange takes
place in the air-handling unit (AHU).
• Chilled water systems: In a chilled water system, refrigerant and water interact to
provide the required cooling. In the heat exchanger, the refrigerant picks up the heat
from the water, which flows in the tube, thereby cooling the water. This chilled water
is then circulated to various water-air heat exchangers called fan-coil units and air-
handling units from where the cool air is sent to the conditioned spaces.
• Variable refrigerant low systems: In a variable refrigerant low (VRF) system, the
central cooling plant operates as a condensing unit, similar to the outdoor unit of a
split AC model. In non-central units, each unit is driven by a separate compressor. In
a VRF system, all indoor units are driven by a single compressor. The refrigerant flows
through smart valves to different units. The valves are automatically controlled so as
to allow only the required volume of refrigerant to flow in through each indoor unit.
This allows for lesser refrigerant to flow to rooms, which require lesser cooling at
any given point of time and greater refrigerant flow to areas that have a higher heat
load. This controlled flow ensures optimized cooling of spaces and makes the system
quite efficient.
Features: VRF systems could be as much as 30% more efficient than conventional
central plants. They are also more versatile, as indoor units in a VRF system can be
a convenient mix of high-wall mounted cassette, or any other type with capacities
down to multiples of 1TR.
Cooling capacity: 3, 5, and 7 TR (tonnes of refrigeration)
• Floor- mounted package air-conditioners: These units are typically shaped like cupboards
with all components like compressor, evaporator, blower, and so on, placed inside the
shell. These ACs are usually placed in a small enclosure adjacent to the conditioned area.
Cooling capacity: 5–16.5 TR (tonnes of refrigeration).
Features: Floor-mounted package units are available in both air-cooled and water-
cooled models. They can be easily serviced and can handle longer ducts since the fans
installed in them are more powerful. These units can handle large tonnages with lesser
units of power.
ii. Central plant
These are usually large air-conditioning plants assembled at the site and used for big
buildings.
Components: Basic components are compressors, condensers, air-handling units, water
chillers, and cooling towers.
Types of central plants
• DX (direct expansion) systems: In DX systems, the air is cooled and conditioned in the
plant room. The treated air is then pumped to various parts of the building through
ducts. Air returning from the conditioned spaces is sucked by a fan through a coil-fin
arrangement. The coil-fin arrangement acts as the heat exchanger. The refrigerant
inside the coil absorbs the heat from the return air and cools it. The cold air is then
pumped back to the air-conditioned space. In DX plants, the heat exchange takes
place in the air-handling unit (AHU).
• Chilled water systems: In a chilled water system, refrigerant and water interact to
provide the required cooling. In the heat exchanger, the refrigerant picks up the heat
from the water, which flows in the tube, thereby cooling the water. This chilled water
is then circulated to various water-air heat exchangers called fan-coil units and air-
handling units from where the cool air is sent to the conditioned spaces.
• Variable refrigerant low systems: In a variable refrigerant low (VRF) system, the
central cooling plant operates as a condensing unit, similar to the outdoor unit of a
split AC model. In non-central units, each unit is driven by a separate compressor. In
a VRF system, all indoor units are driven by a single compressor. The refrigerant flows
through smart valves to different units. The valves are automatically controlled so as
to allow only the required volume of refrigerant to flow in through each indoor unit.
This allows for lesser refrigerant to flow to rooms, which require lesser cooling at
any given point of time and greater refrigerant flow to areas that have a higher heat
load. This controlled flow ensures optimized cooling of spaces and makes the system
quite efficient.
Features: VRF systems could be as much as 30% more efficient than conventional
central plants. They are also more versatile, as indoor units in a VRF system can be
a convenient mix of high-wall mounted cassette, or any other type with capacities
down to multiples of 1TR.
