www . refrigerationandaircon . co . za RACA Journal I February 2024 35
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3 . Steam heating coils
Robyn , let us have a closer look at electric heating elements .
Advantages :
• Smaller pipes required due to high latent heat of condensation being released
• Steam produced centrally
• Alternative fuels can be used
Disadvantages :
• More complex installation
• Higher capital cost / if steam generators are installed for heating purposes only
• Higher maintenance cost
• Trained personnel required
• Reticulation pipe work required – central plant-room required
• Steam heating coils are not in common use except in industrial applications .
4 . Heat pumps Like an air-conditioner , a heat pump uses refrigerant to move heat from one location to another . In fact , the two systems operate identically in the summer , extracting heat from inside your home and exhausting it outside .
Advantages :
• Versatile : Smaller units offer heating and cooling and can heat water and air
• Environmentally friendly : With no open flames or fumes , these risks don ’ t exist with an electric heat pump , making it one of the safest types of HVAC equipment . The lack of direct fossil fuel emissions also makes heat pumps more eco-friendly
• Energy efficient : Even the most advanced furnace type systems or element-based systems can never be more than 100 % efficient , whereas heat pumps boast an excess of 300 % efficiency
• Solar power : Heat pumps pair well with solar panels – if you have solar panels or are thinking of installing them , know that they are compatible with electric heat pumps
• Better humidity control and air quality
Disadvantages
• Reduced efficiency in cold weather : Effectively extracting thermal energy from outdoor air becomes increasingly difficult as the temperature drops
• The need to defrost : Sub-freezing temperatures cause ice to form on the outdoor heat pump unit . This forces the system to enter defrost mode , melting the ice so it can continue operating
• More noise : Longer run cycles also mean the fan and compressor are on more often in cold weather , which creates operating noise
• Shorter lifespan
• Higher capital and maintenance costs
Heating of air in an air-conditioning system can be achieved by means of electric heating elements because of the advantages mentioned earlier . Electric heating elements basically consist of a length of resistance wire , commonly nickel chromium , to which a voltage is supplied .
The resistance wire may be as you found , bare or encased . There has been considerable debate on the relative merits of bare and incoloy ( or sheathed ) elements .
The incoloy elements are a bit more expensive , have higher air side pressure drop and require more space . Bare coil elements are cheaper to repair if only the coil is damaged . Labour costs can decrease out this advantage . Bare coil elements are rarely used in South Africa and as such will only be dealt with briefly .
BARE COIL ELEMENTS These heating elements consist of a coil of nickel-chromium resistance wire held in place by a metal frame and porcelain spacers . When the resistance wire breaks , only the wire has to be replaced . The other advantage of the bare coil element is its low residual heat . This is an advantage when the fan is switched off while
Bare coil element . the heater is on and involves material that can melt such as plastics , or have been used for the construction of parts close to the heater bank . Examples of this are in diffuser in inducting grills .
INCOLOY ELEMENTS Robyn , Incoloy is an alloy made up primarily of nickel , iron and chromium , with smaller amounts of aluminium and titanium added in certain cases . It ’ s commonly used as a heating element due to its high melting point ( 1 350 ° C ), excellent corrosion resistance , and good thermal stability even at extreme temperatures .
Incoloy elements are the most popular heating elements in South Africa . They are mechanically stronger and if the sheath makes contact with the body or casing of the heater bank there is no danger of short circuits . Sheathed ( or incoloy elements as they are commonly called ) consist of a thin coil of resistance wire ( diameter 2 – 3mm ) which is installed centrally in an incoloy tube ( incoloy is a metal similar to stainless steel ). The space in between the coil and the incoloy sheath is filled with a
Incoloy element structure . magnesium powder which after heat treatment of the element changes into magnesium oxide .
Image supplied by Grant Laidlaw
www . refrigerationandaircon . co . za RACA Journal I February 2024 35