Any industry utility can make use of the surrounding ‘Ambient Wet Bulb’ temperature and improve its heat transfer energy efficiency in its sub systems. Irrespective of any location, in the utility house like the compressor house, DG shed, HVAC outdoor condenser etc…, the localised heat surrounding the machines is always higher than the ambient temperature and there’s low RH in any season of the year in India. The heat transfer across any HX can be improved by retrofitting this evaporative mist cooling retrofit.
Existing Utility’s Heat Exchangers’ Working Condition Now
- We can see the sankey energy flow diagrams of DG set, screw air compressor utility now. The heat rejected/exhausted by the DG set/compressor is revolving inside the DG house only making the house hotter as DG/compressor runs for more hours.
- This is why the industry is running practically, with open doors, their compressor- in-hood/DG set-in-hood and keep the area fully open ventilated on all sides. In spite of that, the engine’s hotter skin air is only reaching the skid-mounted finned radiator. So many industries have opted for remote coil cooler/water cooled heat exchanger like cooling tower etc to improve the DG set efficiency drastically and in turn better UPL.
- Why has the same industry not taken up this HX relocation from their existing compressor packages? And why is the compressor OEM not suggesting this relocation as site option for their healthy compressor workings? Any compressor house, wherein the screw compressor kept in acoustic hood and the refrigerated dryer, their hot exhaust air is short circuited to air intake suction and as suction to the finned heat exchangers and thus, reducing the compressor and dryer efficiency due to higher temperature air inlet and poor heat transfer.
- The reason for the above is that as well, the radiator/air operated heat exchangers are kept inside the hood and this condition heats up the inside-hood further and the totally the utility house.
DG radiator heating the surroundings inside… - DG house, compressor house etc. needs excess amount of air changes and positive cross ventilation – whereas it is not there now and energy experts tolerate 5°C above ambient is max allowable temperature inside as one of the better DG house-keeping practices.
- Since the above is not possible, many industries started putting Turbo vents on Compressor, DG shed roofs. This definitely improves the house inside ambient parameters.
- The HOC i.e., the Heat of Compression liberating from the air compressor element is as such, heating up the compressor element inside and outside in the compressor hood and house. The same HOC happens in DG set combustion chamber and hence the heat dissipation is more from the engine.
- For sustainable efficiency in compressor or DG set, the heat transfer across the finned HX is a critical parameter. If the heat transfer is not done effectively, the compressor / DG performance will be affected and their health will deteriorate – and de-rating too will happen earlier than their life cycle.
How to address the internal heat generation in compressor house?
The heat balance of a compressor station…
- Inside the screw compressor hood, the air operated HX/finned Radiator must not take hood-inside air as suction as compressor inlet and to cool the post-compressed air/lub oil cooling.
- The finned radiator surface needs to sit on hood side wall and to face outside ambient surrounding.
- Provide a physical barrier or insulated partition so that the hot exhausted air from top is prevented to enter back to the air intake suction side and as well not to enter the air & oil cooler Radiator fins.
- Now the air surrounding compressor has always low RH and high temp and it’s dry.
- Provide Box type Pre-filter on the HX outer face for daily scrub cleaning the same inside & outside.
- Now we can think of adiabatic mist cooling of HX so as to utilise ambient wet bulb at that location.
- Fix water supply piping along with few nozzles near the bottom of HX facing the finned outer surface.
- Make use of SS impulse piping for water and air supply from air receiver to this nozzle piping.
- Now we can provide mist using pneumajet concept i.e., water and compressed air mixed at the nozzle that can spread water mist on the finned faces and cool the fins by evaporative cooling.
- This is simple zero cost in-house implementable exercise which can be done instantly now.
- Other alternatives are costly retrofits like mist fogging on HX, adiabatic cooler retrofit outside house.
- Water supply either can be RO /DM water from outside or the air receiver drain & filtered water.
- The same water can be cooled before; using spiral SS tubing immersed in a water vessel at cooler location before misting through nozzles to achieve better heat transfer across the HX.
- This can be done on ref. dryer as well and this will reduce Freon compressor discharge pressure quickly.
How to address the internal heat generation in DG house?
- The DG shed too needs to be addressed like this adiabatic mist cooling retrofit…
- First, completely removing the hot exhausted air from the DG set and not to short circuit to inside.
- Secondly isolating radiator within the house by physical barrier from engine heat not to reach HX.
- Thirdly provision of ambient surrounding air to HX by providing barrier and ducting to fresh air.
- Fourth provision of adiabatic cooling to the Engine HX and to the Diesel Return line HX radiator cooling by air and water (Industry has understood now that Diesel input to engine when maintained at 40°C < neither at 30°C or at 50°C> gives optimum viscosity to diesel to engine and thus, in giving better UPL)
How to address the internal heat generation in coil cooler / HVAC outdoor?
- Please think of the old window AC where the OEM gives a splash ring to the condenser fan blade so as to collect and throw water on the fins to provide Ambient wet bulb cooling. The same working we are trying to put in all the utilities to utilise the Ambient Wet Bulb parameter.
- Now few utility OEMs are providing professional evaporative cooling retrofit to the coil cooler utility.
- Some industries achieved huge water savings by converting their coil cooler with this retrofit.
- Triplex plunger water pump type can be used to achieve mist fogging through nozzles, alternately.
Conclusion
The industry can run the utility efficiently by providing the breathing space in between the equipments, orientation of the equipments such that equipments’ exhaust is smoothly driven out of the utility house with minimum restrictions in between. Raise trees around the industry not only for greening purpose but also to reduce the Solar Heat on & around the sheds. Added to that, Heat reflective paint on the existing shed reduces Solar Heat gain. Ultimately, comforting the utility and improving the heat transfer efficiency of the machine’s sub systems will improve the overall efficiency and increase the healthy life of utility. We must keep in mind that the individual sub system efficiency when multiplied will reduce the overall efficiency say, the kW/CFM or UPL when calculating the efficiency of compressor or DG set.
