Waterless Energy Efficient Flooded Multi-Evaporator Cooling & Heating System By Surendra H. Shah

ZonAll™is an innovative distributed cooling/heating system designed to eliminate the use of central chillers and boilers in large installations. It uses a stabilizer that allows multiple AHUs in one user defined zone to be cooled or heated by a DX condensing unit. It is different from other similar sounding systems  in that the zone evaporators are flooded for better efficiency and do not have any expansion valves or capillaries. The lines leading to and from the zone evaporators/heaters are at low pressure. Each evaporator can modulate its cooling/heating capacity from full to nil without destabilizing the main unit.  There are no electric heaters. Other devices such as ductable units, hi-wall and cassette units etc can also be attached to the stabilizer.

ZonAll™ system comprises:

1. Central condensing unit
2. Cooling Stabilizer
3. Heating Stabilizer
4. External evaporator
5. Multiple AHUs having heating and cooling coils
6. Piping between condensing unit & stabilizer and between stabilizer and the AHUs.
7. Controls.

ZonAll™ Operation:

1. Each AHU connected to the ZonAll™ system has a flooded cooling coil and a heating coil.
2. In the cooling mode, the air passing through the flooded coil causes some liquid to evaporate. The vapour travels to the cooling stabilizer where it condenses due to the action of the condensing unit. This liquid goes back to the coil by gravity.
3. All the vapour and liquid lines from the zone AHUs are connected to thestabilizer.
4. Heating in winter is provided through a similar circuit by the heating stabilizer that is heated by the condensing unit. An external evaporator draws the heat from cool ambient air.

ZonAll™ advantages:

1. Elimination of water chillers. This removes:
   1. Long and large sized insulated chilled water lines.
   2. Long insulated hot water/steam lines and heating boiler.
   3. Large sized condenser water lines.
   4. Large chilled and condenser water pumps.
   5. Large system inertia causing sluggish response to load changes.
   6. DM/soft water plant for boiler and cooling tower.
   7. Need for plant room and cooling tower space
2. Advantages of intrinsically stable design:
   1. Low system inertia allows rapid response to quickly match capacity to load variations.
   2. Total flexibility of operation through few sophisticated international branded controls.
   3. Ease of future expansion; no need to modify existing system.
   4. Increased efficiency due to pumpless operation.
   5. Heating energy supplied efficiently by external evaporator that allows simultaneous heating and cooling in the zone and also the same AHU if required for humidity control.
   6. Combining one group of related activities into one zone so that the entire plant can shut down if the group is not operational.
   7. Fault tolerance. Problem in one zone will not affect others.
   8. There can be no fouling of heat exchange surfaces with either dirt or scale. Thus peak performance is always maintained and there is no need for de-scaling.
3. Large saving in water through use of air cooled condensers with evaporative precoolers.

In Closing: The replacement of a central chilled water system fed by a large chiller by ZonAll™ units having their own energy efficient cooling/heating systems is similar to the replacement of line shafts powered by large motors in old factories by modern machines with their own more efficient motors and drives. Since one would always choose the modern option for the factories, the same logic should apply to the choice of the cooling system.