Friday, 17 March 2017

Efficient Commercial Cooling System !!!

HVAC chiller is a key component of many commercial and industrial cooling and refrigeration systems. A chiller is a machine that removes heat from a liquid via a vapor-compression . Industrial chillers are generally installed in a mechanical equipment room, beside an industrial process, or outside the building. Residential HVAC chillers can be installed in a storage tank next to the home. Chiller system changes the physical state of refrigerant to transfer heat from one area to another. The laws of pressure-temperature relationship state that increased pressure on a refrigerant increases its temperature while decreased pressure lowers its temperature. As the refrigerant circulates through the HVAC chiller, various components change its pressure and temperature, causing it to boil into a gas and condense into a liquid. During the change of state from liquid to gas, the refrigerant absorbs heat, and the refrigerant releases heat when it returns to its liquid state. A commercial chiller system is a form of air conditioning, mounted on the roof of an office building or similar structure. They come in two types: air cooled and water cooled. Air-cooled systems blow warm air from your building across a set of coils circulating refrigerant. Water-cooled systems send the heat from the air into water, which facilitates a heat exchange with a series of copper tubes containing refrigerant. It works more effectively than air-cooled chillers for larger offices, which naturally have higher demands on an air conditioning system.

Water Cooled Chiller vs Air Cooled Chiller in HVAC System
  • Initial cost of air cooled chillers is lower than water cooled chillers as air cooled systems don’t require cooling towers,condenser water pumps and associated HVAC components.
  • Small systems are almost always air-cooled since the extra requirements of water treatment and maintenance are capital intensive and will not be offset quickly by the lower operating costs.  Larger HVAC water chillers are almost always water cooled .HVAC engineers and technicians feel easy with maintenance free or less maintenance equipment.
  • Water cooled chillers may be preferred because of  better heat transfer properties of water as compared to air cooled chillers.The primary advantage of water is that the film coefficient is 10-100 times better with water than air.Film coefficient controls heat transfer with given constant area and temperature difference.
  • Water-cooled HVAC units make less noise and give more cooling per square foot.While air cooled chillers have comparatively less cooling per square foot and are more noisy HVAC machines.Noisy machines are annoying especially for occupants of nearest offices or zones.
  • While comparing  air and water cooled chillers, an overall system cost (both running and installed) has to be worked out. Size of HVAC unit matters when selecting the water cooled chiller or air cooled chiller.Smaller HVAC units are usually air cooled, larger are water cooled.
  • HVAC engineers have to evaluate air cooled and water cooled chillers keeping in mind various factors.Refrigeration engineer has to consider the ambient conditions (wet bulb and dry bulb), number of hours of operation, part load pattern and cost of maintenance etc.
  • HVAC experts have no single answer to when asked “water cooled chiller is better or air cooled chiller?”. The fact is that “It all depends”. Water-cooled chillers will normally condense at an average lower pressure than air-cooled chillers.  This is because the water temperature will usually be less than the air temperature.If your condenser is operating at lower pressure then it is directly reflected and translated into lower operating costs.
  • The difference between the wet-bulb temperature and the dry-bulb temperature gives the available difference between the condensing temperatures of water-cooled and air-cooled condensers respectively.  
  • Cooling towers and/or evaporative condensers have main disadvantage of maintenance and water treatment costs. This running cost is not present in air cooled chillers.
  • When comparing water cooled and air cooled chiller,scarcity of water and hence cost of water is another issue which is a point to be considered while deciding on the system.  This happens in many countries .
  • Space is also of importance in some applications. Air cooled chillers can utilize open space, such as a parking lot, roof or ground level area. Although smaller in size but Water cooled chillers require a mechanical room and cooling towers.
  • Air recirculation is very important for air cooled chillers.Any obstruction in the circulation of air near water chillers would adversely affect the performance of air cooled chillers.Air cooled chillers can have problems with recirculation if there are walls higher than the unit or too many units to close together. If there is a situation where outside walls are required for building code and the unit will not be receiving enough fresh air, then a water cooled application may be the best option.
  • Water cooled chillers have longer life,higher efficiency,large capacity and also refrigerant containment.While looking on dis-advantatges of air cooled chillers,they have lower efficiency,comparatively short life span and available in low capacity range.

Tuesday, 7 March 2017

Ensure Good Ventilation to Avoid Health Hazards !!

Ventilation Control

All occupied buildings require a supply of outdoor air. Depending on outdoor conditions, the air may need to be heated or cooled before it is distributed into the occupied space. As outdoor air is drawn into the building, indoor air is exhausted or allowed to escape (passive relief), thus removing air contaminants. The term “HVAC system” is used to refer to the equipment that can provide heating, cooling, filtered outdoor air, and humidity control to maintain comfort conditions in a building. HVAC systems range in complexity from stand-alone units that serve individual rooms to large, centrally controlled systems serving multiple zones in a building. 

Some buildings use only natural ventilation or exhaust fans to remove odors and contaminants. In these buildings, thermal discomfort and unacceptable indoor air quality are particularly likely when occupants keep the windows closed because of extreme hot or cold temperatures.
In order to exhaust air from the building, make-up air from outdoors must be brought into the HVAC system to keep the building from being run under negative pressure. This make-up air is typically drawn in at the mixed air plenum as described earlier and distributed within the building. For exhaust systems to function properly, the control air must have a clear path to the area that is being exhausted. To prevent operating the building under negative pressures (and limit the amount of unconditioned air brought into the building by infiltration), the amount of make-up air drawn in at the air handler should always be slighter greater than the total amount of relief air, exhaust air, and air exfiltration through the building shell. Excess makeup air is generally relieved at an exhaust or relief outlet in the HVAC system, especially in air economizer systems. In addition to reducing the effects of unwanted infiltration, designing and operating a building at slightly positive or neutral pressures will reduce the rate of entry of soil gases when the systems are operating. 

The selection of a specific ventilator should be based on the following factors:
  •  Job details such as the atmospheric hazard, the size of the confined space, etc
  • Airflow required
  • Airflow volume required at the end of the duct to control the hazards present; and Breeze to ensure worker comfort in the space.
  • Duct friction loss to ensure adequate air volume reaches the end of the duct.

Aims of HVAC Control Systems:

  • HVAC Control Systems are used for the following benfits:
  • Lower energy cost.
  •  Lower operations cost.
  • Increase flexibility.
  • Ensure quality building environment.

Esaplling Pvt. Ltd.
Contact no:020-65366661