heating air © commonwealth of australia 2010 | licensed under aesharenet share and return licence

HEATING AIRHEATING AIR

© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Hello, I would like to show Hello, I would like to show you the three most common you the three most common methods of heating air:methods of heating air:

1.1. Electric element heaters.Electric element heaters.

2.2. Reverse cycle or heat Reverse cycle or heat pump heating.pump heating.

3.3. Hot water or steam coil Hot water or steam coil heating.heating.


Electric element heating is a very simple way of Electric element heating is a very simple way of heating the air being supplied to a zone. heating the air being supplied to a zone.

In an installation of this type, the area in the duct In an installation of this type, the area in the duct surrounding the heaters would need to be constructed surrounding the heaters would need to be constructed of non-combustible materials to offer protection in the of non-combustible materials to offer protection in the case of a fire. A safety thermostat would also need to case of a fire. A safety thermostat would also need to be installed in the vicinity of the heaters so that should be installed in the vicinity of the heaters so that should an overheat situation occur, the power to the heaters an overheat situation occur, the power to the heaters is cut off thus preventing further damage.is cut off thus preventing further damage.

Electric element heating can be applied to most air Electric element heating can be applied to most air conditioning systems from the smallest to the largest.conditioning systems from the smallest to the largest.


Reverse cycle or heat pump heating is Reverse cycle or heat pump heating is mostly applied to systems at the mostly applied to systems at the smaller end of the range. This method smaller end of the range. This method utilises the refrigeration system to utilises the refrigeration system to provide the heating by installing a provide the heating by installing a reversing valve in the system.reversing valve in the system.

This allows the refrigerant to reverse its This allows the refrigerant to reverse its direction of flow in most parts of the direction of flow in most parts of the system with the result that the system with the result that the evaporator (inside coil) becomes the evaporator (inside coil) becomes the condenser, and the normal condenser condenser, and the normal condenser (outside coil) becomes the evaporator.(outside coil) becomes the evaporator.

We call the normal evaporator the We call the normal evaporator the inside coil and the normal condenser inside coil and the normal condenser the outside coil.the outside coil.


The main advantage of The main advantage of this method of heating is this method of heating is the reduction in operating the reduction in operating costs when compared to costs when compared to other heating methods. other heating methods. The unit is not producing The unit is not producing the heat directly as in the heat directly as in electric element heating, electric element heating, but is simply removing it but is simply removing it from the ambient air and from the ambient air and transferring the heat to transferring the heat to the inside air. In effect, the inside air. In effect, the unit is attempting to the unit is attempting to refrigerate the ambient refrigerate the ambient air.air.

An efficient reverse cycle heating system could be An efficient reverse cycle heating system could be expected to have operating costs about 50% of an expected to have operating costs about 50% of an electric element heater of the same capacity. electric element heater of the same capacity.


This is an example of a reversing This is an example of a reversing valve. These are sometimes valve. These are sometimes called four-way valves because called four-way valves because of the four line connections of the four line connections required for their installation. required for their installation. The valve consists of a main The valve consists of a main body, four line connections and a body, four line connections and a solenoid valve attached to the solenoid valve attached to the main body.main body.

The valve is composed of three The valve is composed of three basic components: pilot valve, basic components: pilot valve, main valve body (including valve main valve body (including valve slider) and solenoid coil.slider) and solenoid coil. The four-way valve slider is shifted by changes in The four-way valve slider is shifted by changes in

differential pressure in the valve that is actuated by differential pressure in the valve that is actuated by the pilot solenoid valve. The valve slider is specially the pilot solenoid valve. The valve slider is specially designed to prevent incomplete change-over and designed to prevent incomplete change-over and movement with minimum pressure differential. movement with minimum pressure differential.


Cooling CycleCooling Cycle

The pilot solenoid is de-energised during the The pilot solenoid is de-energised during the operating cycle.operating cycle.

Discharge vapour enters the top connection and Discharge vapour enters the top connection and pressurises the valve body. This vapour bleeds pressurises the valve body. This vapour bleeds through the two bleed ports in the slider through the two bleed ports in the slider mechanism and pressurises these two chambers to mechanism and pressurises these two chambers to discharge pressure. The right hand pilot tube is discharge pressure. The right hand pilot tube is connected to the suction line via the pilot valve, connected to the suction line via the pilot valve, which reduces the pressure in the right hand which reduces the pressure in the right hand chamber to suction pressure and the left chamber chamber to suction pressure and the left chamber is at a higher pressure.is at a higher pressure.

The resulting pressure differential causes the slide The resulting pressure differential causes the slide mechanism to move to the left of the body.mechanism to move to the left of the body.


Heating CycleHeating Cycle

The pilot solenoid is energised during this cycle. The pilot solenoid is energised during this cycle. Discharge vapour enters the top connection and Discharge vapour enters the top connection and pressurises the valve body. This vapour bleeds pressurises the valve body. This vapour bleeds through the bleed ports in the slider mechanism through the bleed ports in the slider mechanism and pressurises these two chambers to discharge and pressurises these two chambers to discharge pressure. The left hand pilot tube is connected to pressure. The left hand pilot tube is connected to the suction line via the pilot valve, which reduces the suction line via the pilot valve, which reduces the pressure in the left hand chamber to suction the pressure in the left hand chamber to suction pressure and the right hand chamber is now at a pressure and the right hand chamber is now at a higher pressure.higher pressure.

The resulting pressure differential causes the slide The resulting pressure differential causes the slide mechanism to move to the right of the body.mechanism to move to the right of the body.


ApplicationsApplications

The two main uses for reversing valves are:The two main uses for reversing valves are: reverse cycle air conditioning (valve is de-reverse cycle air conditioning (valve is de-

energised in the cooling mode)energised in the cooling mode) reverse cycle defrost of commercial refrigeration reverse cycle defrost of commercial refrigeration

(not used very often in modern systems).(not used very often in modern systems).


Some units may be equipped with a de-icing thermostat which senses the Some units may be equipped with a de-icing thermostat which senses the ice forming on the outside coil, causing it to revert back to normal cooling ice forming on the outside coil, causing it to revert back to normal cooling mode until the ice melts before resuming reverse cycle heating.mode until the ice melts before resuming reverse cycle heating.

Some systems are equipped with an Some systems are equipped with an electric heaterelectric heater and a and a low-ambient low-ambient thermostat. thermostat. If the ambient temperature becomes too cold for the heat pump If the ambient temperature becomes too cold for the heat pump to operate successfully, the low-ambient thermostat stops the refrigeration to operate successfully, the low-ambient thermostat stops the refrigeration system and supplements the heat by engaging the electric heater. system and supplements the heat by engaging the electric heater.

Reverse cycle systems Reverse cycle systems lose efficiency when the lose efficiency when the ambient temperature drops ambient temperature drops lower than about 7 °C. At lower than about 7 °C. At these temperatures the these temperatures the outside coil tends to ice-up outside coil tends to ice-up and this leads to a and this leads to a restriction of the air flow. restriction of the air flow.


Hot water or steam coil heating is sometimes used Hot water or steam coil heating is sometimes used in larger systems where it is economical to do so in larger systems where it is economical to do so such in situations and locations where hot water or such in situations and locations where hot water or steam are readily available at a reasonable cost. steam are readily available at a reasonable cost.

The coil is constructed similarly to an evaporator The coil is constructed similarly to an evaporator coil and installed in the air passage or duct. coil and installed in the air passage or duct.


heating air © commonwealth of australia 2010 | licensed under aesharenet share and return licence

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