Air Conditioning Inspections for Buildings Condensers

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1 . Air Conditioning Inspections for Buildings Condensers PRESENTED BY NIRAJ MISTRY

2 Condensers Condensing Process Three main types: Air Cooled (using ambient air) Water Cooled (using mains, river or cooling tower water) Evaporative Condensers (using ambient air and recirculated water)

3 Condensers Condensing Process Superheated refrigerant vapour enters the condenser. Loses heat to a coolant (e.g. air/water). Refrigerant vapour is first cooled to its saturation temperature. As it condenses to a liquid at constant temperature, latent heat is released. Once condensation has finished, refrigerant temperature will drop again. This further cooling is known as subcooling occurs in the liquid line. In evaporative condensers the cooling is enhanced by allowing water to evaporate in the air blown over the tubes. This cools air to the wet bulb temperature.

4 Condensation

5 Coolant Temperature

6 Condensers Approach Temperature Difference (ATD) For heat transfer from the refrigerant to the coolant a temperature difference must exist approach temperature difference (ATD). The ATD must be large enough to provide the heat flow needed to achieve the required system capacity. For maximum efficiency ATD should be minimised, as this will reduce the temperature lift of the system. A sensible compromise required to ensure adequate capacity at reasonable cost and environmental impact.

7 Condensers Approach Temperature Difference (ATD) Inlet temperature of coolant is not usually controllable (air/water). If possible should be selected to have as low a temperature as possible. The lower the coolant temperature for a given ATD, the higher the efficiency. Coolant temperature naturally rises as it cools the refrigerant. Temperature rise is dependant upon flow rate and coolant type. For maximum efficiency this temperature rise should be kept low. In turn this means that the condensing temperature can be kept lower. Higher flow rates will need larger fans/pumps, hence more energy consumed.

8 Condensers

9 Condensers

10 Condensers Air Cooled Condensers The refrigerant condenses inside finned tubes by air, driven by fans. If used in a corrosive atmosphere (near sea or in polluted air) the fins are made of copper, or the fin block is tinned or coated with PVC. These types are susceptible to blockage by airborne debris dust, feathers, leaves, packaging, etc. Require regular cleaning else air flow reduces condensing pressure increases. If in a vulnerable location the fin block needs to be protected to prevent damage but air circulation should not be restricted.

11 Air Cooled

12 Air Cooled

13 Air Cooled

14 Air Cooled

15 Air Cooled

16 Air Cooled Dry Air Cooler Water/Glycol Mix

17 Condensers Water Cooled Condensers Shell and tube water cooled condensers: Refrigerant vapour is cooled and then condensed in the shell. By cooling water flowing in the tubes. Commonly used in conjunction with cooling towers or with free cooling water where available. Plate heat exchangers are also used as water-cooled condensers. If water is used from a borehole, sea, or river condensing pressure is lower and therefore the most efficient. Cooling towers and evaporative condensers have comparable efficiencies. Cooling water must be treated to prevent the formation of Legionella bacteria.

18 Water Cooled

19 Water Cooled

20 Water Cooled

21 Water Cooled Forced Draught Cooling Tower

22 Cooling Tower Vertical Induced Draught Cooling Tower

23 Cross Draught Cooling Tower Water Cooled

24 Centralised Systems Cooling Towers:

25 Condensers Evaporative Condensers Utilises both ambient air and evaporation of water to remove the heat from the refrigerant vapour flowing inside the coils. Ambient air is blown up over the condenser into water sprayed down from a sparge system mounted above the condenser. The water absorbs heat from the refrigerant and evaporates into steam at the prevailing wet bulb temperature. Steam is rapidly removed by the circulating air. This improves the cooling effect because the surface temperature of the pipework approaches wet bulb temperature improving efficiency. Continuous make up of water is required due to that lost by evaporation. Circulating water pump is much smaller than that in shell and tube. Evaporative condenser needs to be placed close to the compressor to avoid long runs of refrigerant pipework.

26 Condensers Evaporative condenser

27 Evaporative Condenser Low silhouette cross-flow cooling tower

28 Evaporative Condenser

29 Efficiency Condenser Efficiency Issues Each of the three types of condensers used in refrigeration all have associated levels of energy consumption which must be taken into account: Air-cooled fan power. Water-cooled - circulating pump power and cooling tower components. Evaporative fan and pump power. The larger the surface area of the condenser, the closer the condensing temperature is to the surface temperature of the cooling medium (air/water). Results in lower energy consumption.

30 Efficiency Condenser Efficiency Issues Heat transfer of all condenser types is reduced if they are dirty: Air-cooled condenser fin blocks should be: free of debris and in good condition. Water-cooled condenser tubes should not be: fouled corroded scaled-up (cooling water will usually need to be treated to avoid this).

31 Efficiency Condenser Efficiency Issues Air or other non-condensables in the system will increase the condensing temperature lowers efficiency. Can be prevented by good installation procedures evacuation. In large systems, which work with suction pressure below atmospheric pressure: Air can be drawn into the system during operation. Should be automatically removed using a refrigerated air purger. Prevents loss of refrigerant to atmosphere when air is removed.

32 Efficiency Condenser Efficiency Issues Condensing pressure should be allowed to float with ambient temperature to take advantage of the lower ambient temperatures over night and during winter. This can cause the pressure ratio to vary significantly, and can cause problems with some types of commonly used expansion valve. This can be avoided by using more sophisticated expansion devices: Electronic Balanced port types Or liquid pressure amplification should be considered.

33 Comparison Simplest and cheapest to buy and install. Large surface area/size. Higher running costs. Cooling duties up to 500kW. Condensing temperature 10-20K > ambient dry bulb air temperature.

Comparison Eliminates legionella problems closed water circuit. Least efficient as: Water can only be cooled within 5K of the ambient dry bulb temperature.

34 Comparison Eliminates legionella problems closed water circuit. Least efficient as: Water can only be cooled within 5K of the ambient dry bulb temperature. Condensing temperature will be 5 to 15K above the temperature supplied to the condenser. Heat recovery and free cooling can be used. Antifreeze may be required for closed water loop if temperatures are likely to drop below 0 C.

Comparison Water cooled condenser with open cooling tower is the most efficient method. Potential problems with legionella minimised by regular dosing/treatment.

35 Comparison Water cooled condenser with open cooling tower is the most efficient method. Potential problems with legionella minimised by regular dosing/treatment. Water can be cooled within 3-5K of the ambient wet bulb temperature. Condensing temperature is 5-15K above the temperature of condenser supply water. Condenser tubes can be fouled by contaminated air. Closed cooling tower circuit can be a better option.

36 Comparison Evaporative condensers are the most efficient. Not often used in building services applications. Refrigerant piping needs to be installed on site. Potential risks of legionella.

37 Comparison

38 Reference Material Heating, Ventilation, Air Conditioning and Refrigeration, CIBSE Guide B, Chartered Institute of Building Services Engineers, 2005 Energy Efficiency in Buildings, CIBSE Guide B, Chartered Institute of Building Services Engineers, 2005 CIBSE KS13: Refrigeration, CIBSE Knowledge Series, Chartered Institute of Building Services Engineers, 2008 BSRIA Guide AG 15/2002 Illustrated Guide to Mechanical Building Services Carbon Trust Good Practice Guide GPG280 Energy efficient refrigeration technology the Fundamentals ROGERS and MAYHEW: Engineering Thermodynamics: Work and Heat Transfer TROTT, A. R. (2000), Refrigeration and Air-Conditioning (3rd ed.) WANG, S. K.: Handbook Of Air Conditioning And Refrigeration JONES, W. P.: Air Conditioning Applications and Design BS EN 378: Specification for Refrigeration Systems and Heat Pumps; Part 1: 2000: Basic Requirements, Definitions, Classification and Selection Criteria; Part 2: 2000: Design, Construction, Testing, Marking, and Documentation; Part 3: 2000: Installation Site and Personal Protection; Part 4: 2000: Operation, Maintenance, Repair and Recovery, London: British Standard Institution, 2000

Air Conditioning Inspections for Buildings Efficiency of Air Conditioning Systems

. Air Conditioning Inspections for Buildings Efficiency of Air Conditioning Systems PRESENTED BY NIRAJ MISTRY aircon@stroma.com Cooling Load The Refrigeration Load Cooling load on refrigeration system